molecules Review
Room Temperature Ionic Liquids as Green Solvent Alternatives in the Metathesis of Oleochemical Feedstocks Priya A. Thomas † and Bassy B. Marvey *,† Department of Chemistry, Sefako Makgatho Health Sciences University, P. O. Box 138, Medunsa 0204, South Africa;
[email protected] * Correspondence:
[email protected]; Tel.: +27-12-521-4371; Fax: +27-12-521-5893 † These authors contributed equally to this work. Academic Editor: Jason P. Hallett Received: 30 September 2015 ; Accepted: 25 January 2016 ; Published: 6 February 2016
Abstract: One of the most important areas of green chemistry is the application of environmentally friendly solvents in catalysis and synthesis. Conventional organic solvents pose a threat to the environment due to the volatility, highly flammability, toxicity and carcinogenic properties they exhibit. The recently emerged room temperature ionic liquids (RTILs) are promising green solvent alternatives to the volatile organic solvents due to their ease of reuse, non-volatility, thermal stability and ability to dissolve a variety of organic and organometallic compounds. This review explores the use of RTILs as green solvent media in olefin metathesis for applications in the oleochemical industry. Keywords: RTILs; green solvents; olefin metathesis; oleochemical feedstocks
1. Introduction Olefin metathesis was discovered by Banks and Bailey in 1964, while looking for an effective heterogeneous catalyst to replace hydrogen fluoride for converting olefins into high-octane gasoline via olefin-isoparaffin alkylation [1]. When heated with molybdenum in the form of its metal oxide or [Mo(CO)6 ], propylene can be catalytically converted to ethylene and 2-butene. This process was subsequently commercialized as the Philips Triolefin Process. In 1967, Calderon named the reaction metathesis, while converting 2-pentene into 2-butene and 3-hexene using the catalyst system WCl6 /EtAlCl2 /EtOH [2]. Metathesis reactions are under thermodynamic control, however, metathesis of a terminal alkene or alkyne displaces the reaction towards the product. The reaction under reduced pressure helps to eliminate volatile olefin and displaces metathesis reaction. Alkene metathesis also leads to the formation of both Z and E isomers. Many metathesis reactions are also under kinetic control. Recent advances in olefin metathesis has provided new opportunities for converting oleochemical feedstocks into a variety of high value intermediates which find applications in the polymer, petrochemical, oleochemical and pharmaceutical industries [3–6]. Olefin metathesis is an alkylidene exchange reaction (Scheme 1) between two reacting alkenes, mediated by transition metal alkylidene complexes [7]. The word metathesis is derived from the Greek word µεταθεσιζ that meaning transposition. The reaction involves the exchange of ions to produce the most stable ion pairs (Scheme 1a) [8]. It follows the Chauvin mechanism in which carbon-carbon double bonds are ruptured and new bonds are formed (1b) [9]. The process involves the reaction between an olefin and a transition metal alkylidene complex in a [2+2] fashion to generate an unstable metallacyclobutane intermediate. This cyclobutane intermediate then rearranges to form a new metal carbene and an olefin (Scheme 1b) [9].
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A + D - + C+ B A + D - + C+ B -
A + B - + C+ D A + B - + C+ D 2 RCH=CHR' 2 RCH=CHR' M=CHR + R' M=CHR + R'
(a) (a)
RCH=CHR + R'CH=CHR' (R and R' = alkyl or H) RCH=CHR + R'CH=CHR' (R and R' = alkyl or H) M M R'HC R'HC
R R
R M=CHR' ' + R M=CHR +
CHR CHR CHR CHR
(b) (b)
(c) (c)
R R
Scheme 1. Olefin metathesis reaction (a) (a) IonIon exchange; (c)Chauvin Chauvinmechanism. mechanism. Scheme 1. Olefin metathesis reaction exchange;(b) (b)Olefin Olefin metathesis; metathesis; (c) Scheme 1. Olefin metathesis reaction (a) Ion exchange; (b) Olefin metathesis; (c) Chauvin mechanism.
Several types of olefin metathesis are identified [10,11] and include self-metathesis (SM), Several types types ofof olefin olefin metathesis metathesis are are identified identified [10,11] [10,11] and and include include self-metathesis self-metathesis(SM), (SM), Several cross-metathesis (CM), ring-closing metathesis, (RCM), ring-opening metathesis (ROM), ring-opening cross-metathesis (CM), ring-closing metathesis, (RCM), ring-opening metathesis (ROM), ring-opening cross-metathesis (CM), ring-closing metathesis, (RCM), ring-opening metathesis (ROM), ring-opening metathesis polymerisation (ROMP) and acyclic diene metathesis polymerisation (ADMET) (Scheme 2). metathesispolymerisation polymerisation(ROMP) (ROMP)and andacyclic acyclicdiene dienemetathesis metathesispolymerisation polymerisation(ADMET) (ADMET)(Scheme (Scheme2).2). metathesis The metathesis reactions that are most widely applied in oleochemistry are SM, CM and ADMET. Using The metathesis reactions that are most widely applied in oleochemistry are SM, CM and ADMET. The metathesis reactions that are most widely applied in oleochemistry are SM, CM and ADMET. Using these metathesis reactions, the double bonds present in vegetable oils can be altered leading to the Using these metathesis reactions, the double bonds present in vegetable oils can be altered leading these metathesis reactions, the double bonds present in vegetable oils can be altered leading to theto introduction of new functional groups. the introduction of new functional groups. introduction of new functional groups. R1 R1
R2 R2
R1 R1
R1 + R2 R1 + R2
R1 + R1 + R2 R2
R1 R1
R2 R2
+ +
(a) (a)
R2 R2
+ R1 + R1
R1 R1
+ +
R2 R2
R2 R2
(b) (b)
(c) (c)
+ +
(d) (d)
R1 R1
n n
n n
+ +
R2 R2
R3 R3
R2 R2
R1 + R3 R1 + R3
R2 R2
R1 R1
(e) (e)
(f) (f)
n n
n n
R3 R3
+ +
(g) (g)
R1,R2,R3 = heteroatom, alkyl, aryl, allyl etc. or other substituents R1,R2,R3 = heteroatom, alkyl, aryl, allyl etc. or other substituents Scheme 2. Types of olefin metathesis reaction (a) Self-metathesis; (b) cross-metathesis; (c) Ring-Closing Scheme ofofolefin metathesis (a) Self-metathesis; (b) (c) Scheme2.2.Types Types olefin metathesisreaction reaction Self-metathesis; (b)cross-metathesis; cross-metathesis; (c)Ring-Closing Ring-Closing (RCM); (d) Ring-Closing Ene-Yne(a)Metathesis (RCEYM); (e) Ene-Yne Cross-Metathesis Metathesis (RCM); (d) Ring-Closing Ene-Yne Metathesis (RCEYM); (e) Ene-Yne Cross-Metathesis Metathesis Metathesis (RCM); (d) Ring-Closing Ene-Yne Metathesis (RCEYM); (e) Ene-Yne Cross-Metathesis (EYCM); (f) Ring-Opening Metathesis Polymerisation (ROMP); (g) Acyclic Diene Metathesis (EYCM); Metathesis (EYCM); (f) (f) Ring-Opening Ring-Opening Metathesis Polymerisation Polymerisation (ROMP); (ROMP); (g) (g) Acyclic Acyclic Diene Diene Metathesis Metathesis Polymerisation (ADMET). Polymerisation (ADMET). Polymerisation (ADMET).
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2. 2. OleochemicalFeedstocks Feedstocksin inOlefin Olefin Metathesis Metathesis 2. Oleochemical Oleochemical Feedstocks in Olefin Metathesis Fats Fats and oils of animal origin, e.g., fish oils, and oils of vegetable origin, e.g., soybean, linseed, Fats and and oils oils of of animal animal origin, origin, e.g., e.g., fish fish oils, oils, and and oils oils of of vegetable vegetable origin, origin, e.g., e.g., soybean, soybean, linseed, linseed, palm and sunflower oils, well as their derivatives, have been the most important renewable palm as palm and and sunflower sunflower oils, oils, as as well well as as their their derivatives, derivatives, have have been been the the most most important important renewable renewable feedstocks feedstocks that have received growing attention from the academy and industry in recent recent years. feedstocks that that have have received received aaa growing growing attention attention from from the the academy academy and and industry industry in in recent years. years. Vegetable fats contain more unsaturation, allowing for functionalization, and hence considered Vegetable for functionalization, and hence areare considered to Vegetablefats fatscontain containmore moreunsaturation, unsaturation,allowing allowing for functionalization, and hence are considered to be more healthy than animal fats. The abundance and relatively low cost of these food components be more healthy than animal fats. The abundance and relatively low cost of these food components to be more healthy than animal fats. The abundance and relatively low cost of these food components make interesting the most make them an raw material for the chemical industry. Vegetable oils are one of make them them an an interesting interesting raw raw material material for for the the chemical chemical industry. industry. Vegetable Vegetable oils oils are are one one of of the the most most important oils are composed of acylglycerols or important sources of polymer precursors. Vegetable triglycerides important sources sources of of polymer polymer precursors. precursors. Vegetable Vegetable oils oils are are composed composed of of acylglycerols acylglycerols or or triglycerides triglycerides (Figure 1) [12], which are the esters of glycerol with three fatty acids. (Figure The double bonds, ester groups (Figure1) 1) [12], [12], which which are are the the esters esters of of glycerol glycerol with with three three fatty fatty acids. acids. The The double double bonds, bonds, ester ester groups groups and triglycerides variety and allylic positions present in the are highly reactive sites, from which of and allylic allylic positions positions present present in in the the triglycerides triglycerides are are highly highly reactive reactive sites, sites, from from which which aaa variety variety of of polymers with different structures and functionalities be fatty polymers and functionalities cancan be prepared. The The commonly used used fatty polymerswith withdifferent differentstructures structures and functionalities can be prepared. prepared. The commonly commonly used acids fatty acids the of platform chemicals are in 22 [13,14]. for thefor synthesis of renewable platform chemicals are shown in Figure 2 [13,14]. acids for the synthesis synthesis of renewable renewable platform chemicals are shown shown in Figure Figure [13,14].
Figure 1. showing tthheereactive reactive sites: double bond; == monoallylic Figure1. 1. Structure Structure of of aaa triglyceride triglyceride showing showingthe reactivesites: sites:111===double doublebond; bond;222 = monoallylic Figure Structure of triglyceride monoallylic position; bisallylic position; group. position;333===bisallylic bisallylicposition; position; = ester ester group. position; 4 4=4 =ester group. OO
(a) (a)
HO HO OO
(b) (b)
HO HO OO
(c) (c)
HO HO OO
(d) (d)
HO HO OO
(e) (e)
HO HO OO
HO HO
(f) (f)
HO HO OO
OO
(g) (g)
HO HO OO HO HO
(h) (h)
Figure Figure 2. 2. Commonly Commonly used used fatty fatty acids acids for for the the synthesis synthesis of of renewable renewable platform platform chemicals chemicals (a) (a) oleic oleic acid acid Figure 2. Commonly used fatty acids for the synthesis of renewable platform chemicals (a) oleic acid acid (e) petroselinic acid (f) ricinoleic acid (g) vernolic (b) linoleic acid (c) linolenic acid (d) erucic acid petroselinic (f) ricinoleic (g) vernolic (b) linoleic linoleicacid acid(c) (c)linolenic linolenicacid acid erucic (b) (d)(d) erucic acid (e) (e) petroselinic acidacid (f) ricinoleic acid acid (g) vernolic acid acid (h) acid (h) 10-undecenoic 10-undecenoic acid. (h) 10-undecenoic acid. acid.
3. of Catalyst Systems 3. Overview Overview 3. Overview of of Catalyst Catalyst Systems Systems Many used for the metathesis reactions. metal Many catalysts catalysts have have been been used used for for the the metathesis metathesis reactions. reactions. The The most most widely widely used used are are metal metal Many catalysts have been The most widely used are alkylidene complex of a transition metal such as molybdenum or ruthenium (Figure 3). Amongst alkylidene complex complex of of aa transition transition metal metal such such as as molybdenum molybdenum or or ruthenium ruthenium (Figure (Figure3). 3). Amongst Amongst them them alkylidene them are Grubbs first generation (5a), Grubbs second generation (5b), Hoveyda-Grubbs first generation (5c), are Grubbs first generation (5a), Grubbs second generation (5b), Hoveyda-Grubbs first generation (5c), are Grubbs first generation (5a), Grubbs second generation (5b), Hoveyda-Grubbs first generation Hoveyda-Grubbs Hoveyda-Grubbs second second generation generation (5d), (5d), Grubbs Grubbs and and Hoveyda Hoveyda type type ruthenium ruthenium alkylidene alkylidene (5e–j); (5e–j); Piers Piers second second generation generation (5k) (5k) and and Schrock Schrock molybdenum molybdenum alkylidene alkylidene catalysts catalysts (5l). (5l). The The complexes complexes of of
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4ofof16 16 second generation (5d), Grubbs and Hoveyda type ruthenium alkylidene 4(5e–j); Piers second generation (5k) and Schrock molybdenum alkylidene catalysts (5l). The complexes of othermetals metalssuch suchas astungsten, tungsten,rhenium rheniumand andosmium osmiumare arealso alsoused usedin inolefin olefinmetathesis, metathesis,however, however,these these other other metals such as tungsten, rhenium and osmium are also used in olefin metathesis, however, these exhibit lower reactivity [15]. Schrock Mo catalyst is generally more reactive than the Ru catalysts and exhibit [15]. Schrock MoMo catalyst is generally moremore reactive than the Ruthe catalysts and isis exhibitlower lowerreactivity reactivity [15]. Schrock catalyst is generally reactive than Ru catalysts prepared andhandled handled underinert inert atmosphere. Rucomplexes complexes aremore morepopular popular than Mocomplexes complexes prepared and under atmosphere. Ru are than Mo and is prepared and handled under inert atmosphere. Ru complexes are more popular than Mo due to their inertness to air and water. Sanford et al. [16] have reported the mechanism of rutheniumdue to their inertness to air and water. Sanford et al. [16] have reported the mechanism of rutheniumcomplexes due to their inertness to air and water. Sanford et al. [16] have reported the mechanism of catalyzedolefin olefinmetathesis metathesis reactions(Scheme (Scheme3) 3)[17,18]. [17,18]. In thefirst first step, anstep, 14eintermediate intermediate (B)isis catalyzed reactions the an 14e (B) ruthenium-catalyzed olefin metathesis reactions (Scheme 3)In [17,18]. In step, the first an 14e intermediate generated from ruthenium alkylidene (A) by the loss of one of the ligands. The metal carbene species generated from ruthenium alkylidene (A) by the loss of one of the ligands. The metal carbene species (B) is generated from ruthenium alkylidene (A) by the loss of one of the ligands. The metal carbene (C)reacts reacts with olefin formto anform unstable ruthenaclobutane intermediate (D).Finally, Finally, thenew new olefin (C) with olefin totoolefin form an unstable ruthenaclobutane intermediate (D). the olefin species (C) reacts with an unstable ruthenaclobutane intermediate (D). Finally, the new isformed formed bythe theshift shift inshift direction perpendicular theinitial initial olefinshift. shift. shift. isolefin by in aadirection perpendicular totothe is formed by the in a direction perpendicular to the olefin initial olefin
PCy33 PCy Cl Cl Ru Ru Cl Cl Ph Ph PCy33 PCy 5a 5a
NN NN Cl Cl Ru Ru Cl Cl Ph Ph PCy33 5b PCy 5b
NN NN Cl Cl Ru Ru Cl Cl OO
OO 5c 5c
NN NN Cl Cl Ru Ru Cl Cl NN
5e 5e
NN NN Cl Cl Ru Ru Cl Cl PCy33 PCy
Cl Cl
PCy33 PCy Cl Cl Ru Ru
NN NN Cl Cl Ru Ru Cl Cl Ph Ph PCy33 PCy 5g 5g
5f5f NN NN Cl Cl Ru Ru N N Cl Cl Ph Ph NN
Br Br
5d 5d
Cl Cl
PCy33 PCy Cl Cl Ru Ru PCy33 PCy
5h 5h
NN NN Cl Cl CF33 CF Ru Ru CF CF Cl 33 Cl PCy33 PCy BF44 BF
Br Br
5i5i
NN NN Cl Cl Ru Ru Cl Cl OO
5j5j
5k 5k
NN OO
Mo Mo OO
CF33 CF 5l5l
Ph Ph
CF33 CF
Figure Somecommercially commerciallyavailable availableRu Ruand and Mo based metathesis catalysts (Cy Figure 3.3.3.Some available Ru andMo Mobased basedmetathesis metathesiscatalysts catalysts (Cy =cyclohexyl). cyclohexyl). Figure Some commercially (Cy ==cyclohexyl).
LL XX Ru Ru XX PR33 PR
-PR33 -PR XX
LL XX Ru Ru
+olefin +olefin XX
CC
BB
AA
LL XX Ru Ru
XX
olefin olefin -olefin -olefin LL XX Ru Ru XX PR PR33
PR33 PR
LL XX Ru Ru XX
olefin olefin
LL XX Ru Ru DD
LL XX Ru Ru XX
FF EE GG Scheme3.3.Dissociative Dissociativemechanism mechanismfor forRu-catalysed Ru-catalysedolefin olefinmetathesis metathesisshowing showingRuthenium Rutheniumalkylidene alkylidene Scheme Scheme 3. Dissociative mechanism for Ru-catalysed olefin metathesis showing Ruthenium alkylidene (A,G);14e 14eintermediate intermediate(B,F); (B,F);16e 16especies species(C,E); (C,E);ruthenacyclobutane ruthenacyclobutane(D). (D). (A,G); (A,G); 14e intermediate (B,F); 16e species (C,E); ruthenacyclobutane (D).
Grubbsfirst firstgeneration generationcatalyst catalyst5a 5acontaining containingbulky bulkytrialkylphosphine trialkylphosphineligands ligandshave havelow lowthermal thermal Grubbs stability at 50 °C and low reactivity towards internal olefins. Grubbs second generation catalyst 5b stability at 50 °C and low reactivity towards internal olefins. Grubbs second generation catalyst 5b bearing an an N-heterocylic N-heterocylic carbene carbene ligand ligand such such as as 1,3-bis(2,4,6-trimethyphenyl)imidazol-2-ylidene 1,3-bis(2,4,6-trimethyphenyl)imidazol-2-ylidene bearing (IMes)isisthermally thermallymore morestable stablethan thancatalyst catalyst5a 5aand andalso alsoexhibit exhibithigher higheractivity activityfor forfunctionalized functionalizedand and (IMes)
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Grubbs first generation catalyst 5a containing bulky trialkylphosphine ligands have low thermal stability at 50 ˝ C and low reactivity towards internal olefins. Grubbs second generation catalyst 5b bearing an N-heterocylic carbene ligand such as 1,3-bis(2,4,6-trimethyphenyl)imidazol-2-ylidene (IMes) is thermally more stable than catalyst 5a and also exhibit higher activity for functionalized and internal olefins [19,20]. The new catalyst bearing a 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene and styrenyl ether ligand, was synthesized based on the accelerating effect of a variety of saturated and unsaturated imidazolin-2-ylidene carbine ligands on the activity of Ru based metathesis catalysts [21]. 4. RTILs as Green Solvent Alternatives The demand for environmentally friendly solvents has led to the development of alternative solvents and technologies. In the previous years, water has emerged as a useful reaction medium and has been successfully used in metal catalyzed reactions [22–25]. However, the low miscibility of organic substrates in water has limited its usage in organic reactions. The usage of perfluorinated solvents has been reported for many organic and catalytic reactions [26,27]. The need for specific ligands to solubilize catalyst in the perflourinated phase and the decomposition of these solvents at high temperature to toxic compounds has limited its utility. Another type of solvents used in organic and catalytic reactions is supercritical fluids. e.g., supercritical carbon dioxide [28]. Although they are described as green solvents, the critical conditions needed for their use is still a limitation. Ionic liquids (ILs) are a new class of compounds that have received wide attention as green solvent alternatives. The terms room temperature ionic liquids (RTILs), molten salt, nonaqueous ionic liquid, liquid organic salt and fused salt have all been used to describe these salts [29]. ILs have been known for a long time, but their use as solvents has recently become significant. ILs such as [EtNH3 ][NO3 ] was first described in 1914 [30]. In the early 1970s, ILs were initially developed by electrochemists, for use as battery electrolytes [31]. Recently, ILs have found applications such as electrolytes for electrochemical devices and processes, homogeneous and heterogeneous catalysis, purification of gases, enzyme catalysis, biological reaction media and removal of metal ions [31]. As alternatives to volatile organic solvents (VOCs), ILs show nonvolatility, nonflammability, as well as high thermal and chemical stability [32]. Despite the aforementioned properties which make them environmentally friendly, an assessment of their impact on the environment and health is required to establish the safe use of some of them. For example, some recent reports have suggested that the ecotoxicity of alkyl methyl imidazolium cations used in biocatalysis increases with alkyl chain length in cation [33]. ILs can be prepared with different cation and anion combinations. Consequently the physical and chemical properties of ILs can be tuned according to the cation and anion used in the preparation. The properties of ILs are determined by mutual fit of cation and anion, size, geometry and charge distribution. Properties such as acidity, basicity, water miscibility and immiscibilty, hydrophilic and hydrophobic properties all result from the composite properties of cations and anions. The cation of the IL is generally a bulk organic structure with low symmetry. The most popularly used cations are ammonium (7a) [34–36], phosphonium (7b) [37], sulphonium (7c) [38], imidazolium (7d) [39–43], pyridinium 7e) [44–46], pyrrolidinium (7f) [47], thiazolium (7g) [48], triazolium (7h) [49], oxazolium (7i) [50] and pyrazolium (7j) [51] cations (Figure 4). The most commonly used ILs are the salts based on the N,N1 -dialkylimidazolium cation (7d). The melting point of IL decreases with the increase in size and asymmetry of the cation. Also an increase in the branching on the alkyl chain increases the melting point. The anions present in the IL determine the hydrophobicity, viscocity, density and solvation of the IL system [52]. Different classifications have been used to describe IL anions, for example, as inorganic and organic anions as shown in Figure 4, or as fluorous anions such as PF6 ´ , BF4 ´ , CF3 SO3 ´ , (CF3 SO3 )2 N´ and non-fluorous anions such as Al2 Cl7 ´ , Al3 Cl10 ´ , Au2 Cl7 ´ , Fe2 Cl7 ´ . The most widely used ILs are the ones with PF6 ´ and BF4 ´ anions. However, these two anions decompose when heated in presence of the water and produce HF. Anions such as CF3 SO3 ´ and (CF3 SO3 )2 N´ give thermally stable salts [53,54]. In these anions, the fluorine of the anion is bonded to carbon atom resulting in the C-F bond which is inert to hydrolysis.
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Cations [NRxH(4 - x)]+
[PRxH(4 - x)]+
7a
[SRxH(3 - x)]+ N 7c R1
7b
N R2 7d
N R1
S R2
R4
R2
R1
N
N
R3
N
R2
R1
R2 7h
7g
R4
R5 N N
O
N
R1
R4
7f
R3 N
N R 7e
R4 7i
R3
R3
R1 R2 7j
Anions [Cl]-, [Br]-, [I]-, [Br4]-, [PF6]-, [NO3][N(CN)2]-, [C(CN)3]-, [B(CN)4]-, [AlCl4]-, [Al2Cl7][N(CN)2]-, [CF3SO3]-, [CH3SO3]-, [RSO4]-, -
inorganic
organic
-
[RCO2] , [(CF3SO2)2N]
Figure Examples of of cations cationsand andanions anionsdescribed describedin inionic ionicliquids. liquids. Figure 4. 4. Examples
Properties Properties of of RTILs RTILs RTILs liquid at at room room temperature. temperature. They RTILs are are salts salts that that are are liquid They are are also also referred referred to to as as “designer “designer solvents” solvents” since since their their solvent solvent properties properties can can be be tuned tuned for for aa specific specific application application by by varying varying the the anion anion cation combinations. They have a unique array of physico-chemical properties, which make cation combinations. They have a unique array of physico-chemical properties, which make them them superior, superior, compared compared to to the the conventional conventional organic organic solvents solvents [55–59]. [55–59]. The The main main factors factors that that influence influence the the physical physical properties properties of of RTILs RTILs are are hydrogen hydrogen bonding, bonding, charge charge distribution distribution on on the the anions, anions, polarity polarity and and dispersive dispersive interactions. interactions. Some Some of of their their basic basic properties properties are are listed listed below below [60]: [60]: •‚ •‚ •‚ •‚ •‚ • ‚ • ‚ • ‚ • ‚
Ability inorganic and and organometallic organometallic compounds. compounds. Ability to to dissolve dissolve many many organic, organic, inorganic Immiscibility solvents. Immiscibility with with many many organic organic solvents. High polarity. High polarity. Loosely ions. Loosely coordinating coordinating bulky bulky ions. Generally very low vapor pressures and low low volatility. volatility Generally very low vapor pressures and Thermal stability up to 300 °C approximately. Thermal stability up to 300 ˝ C approximately. High thermal conductivity and a large electrochemical window. High thermal conductivity and a large electrochemical window. Most have a liquid window of up to 200 ˝°C which enables wide kinetic control. Most have a liquid window of up to 200 C which enables wide kinetic control. Nonaqueous polar alternatives for phase transfer processes. Nonaqueous polar alternatives for phase transfer processes.
5. Applications of RTILs in Metathesis of Oleochemical Feedstocks 5. Applications of RTILs in Metathesis of Oleochemical Feedstocks 5.1. 5.1. Self-Metathesis Self-Metathesis The self-metathesis of of seed oil oil derived olefins waswas investigated in our The role roleof ofionic ionicliquids liquidsfor forthe the self-metathesis seed derived olefins investigated in lab [41,61] using methyl oleate and methyl ricinoleate as subtrate esters. Self-metathesis of our lab [41,61] using methyl oleate and methyl ricinoleate as subtrate esters. Self-metathesis of these these oleochemical oleochemical feedstocks feedstocks with with Grubbs Grubbs and and Hoveyda-Grubbs Hoveyda-Grubbs catalysts catalysts was was carried carried out out using using 1,1-dialkyl 1,1-dialkyl − and 1,2,3-trialkyl imidazolium type ionic liquids [bmim][X] where X = BF 4−, PF´ 6− and NTf2´ ´ and 1,2,3-trialkyl imidazolium type ionic liquids [bmim][X] where X = BF4 , PF6 and NTf2 and and − − [bdmim][X] = BF BF4 ´and PF 6 .´ The structures forforbmim and bdmim are shown ininFigure 5.5. [bdmim][X] where where X X= and PF . The structures bmim and bdmim are shown Figure 4 6 Schemes 4 and 5 show the metathesis products of methyl oleate (9a), namely, 9-octadecene (9b) and Schemes 4 and 5 show the metathesis products of methyl oleate (9a), namely, 9-octadecene (9b) and dimethyl 9-octadecenedioate (9c) and the metathesis products of methyl ricinoleate (10a), which are 9-octadecene-7,12-diol (10b) and dimethyl 9-octadecenedioate (10c).
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dimethyl 9-octadecenedioate (9c) and the metathesis products of methyl ricinoleate (10a), which are Molecules 2016, 21, 184 7 of 16 9-octadecene-7,12-diol Molecules 2016, 21, 184 (10b) and dimethyl 9-octadecenedioate (10c). 7 of 16
NNCH CH3
NN
CH3 CH 3
NN
3
CH CH 3 3
NN bmim bmim
bdmim bdmim
Figure 1-Butyl-3-methylimidazolium ion ion (bmim) (bmim) and and 1-butyl-2,3-dimethylimidazolium ion Figure 5. 5. 1-Butyl-3-methylimidazolium ion(bdmim). (bdmim). Figure 5. 1-Butyl-3-methylimidazolium ion (bmim) and 1-butyl-2,3-dimethylimidazolium 1-butyl-2,3-dimethylimidazolium ion (bdmim). O
O
OMe
OMe Ethenolysis
9d
9d + +
Ethenolysis
O
O OMe OMe
9e
9a
9e
9a Self-metathesis
Self-metathesis 9b +
O
O
9b +
MeO
O
OMe
O
9c
OMe
MeO
Scheme 4. Methyl oleate metathesis.
9c
O
Scheme metathesis. Scheme 4. 4. Methyl Methyl oleate oleate metathesis.
OMe
OMe
O
2
O
+
OMe
2
OH 10a
OH
OMe
OMe
OH
+
10b
OH
10a
O
OH
Scheme 5. Self-metathesis of methyl ricinoleate. OH
O 10c
OMe O
10b moiety does influence catalytic 10c Activity studies have shown that the anionic activity besides its influence on physical properties such as viscosity, density, hydrophobicity and solvation of ILs. Scheme of methyl methyl ricinoleate. ricinoleate. Scheme5.5. Self-metathesis Self-metathesis of The catalytic activity of Grubbs first generation catalyst (5a) for example, changes with varying anionic moiety in the following order: [bdmim][BF4] > [bdmim][PF6] > [bmim][BF4] > [bmim][NTf2] > Activity studies have shown that the anionic anionic moiety does influence influence catalytic activity besides besides [bmim][PFstudies 6]. Studies further recordthat optimum activitiesmoiety and selectivies at moderatecatalytic reaction temperatures Activity have shown the does activity its influence influence on hydrophobicity and not exceeding 60 °C. properties its on physical physical properties such such as as viscosity, viscosity, density, density, hydrophobicity and solvation solvation of of ILs. ILs. The catalytic activity of Grubbs first generation catalyst (5a) for example, changes with varying Grubbs second generation catalyst exhibits higher methyl oleate conversions with improved The catalytic activity of Grubbs first generation catalyst (5a) for example, changes with varying selectivity ionic order: liquids[bdmim][BF over conventional organic solvents (Table 1) [41]. The higher 2] > anionic moietyin in[bmim][X] the following following 4] > [bdmim][PF 6] > [bmim][BF 4] > [bmim][NTf anionic moiety in the order: [bdmim][BF 4 ] > [bdmim][PF6 ] > [bmim][BF4 ] > [bmim][NTf2 ] activity of Grubbs second generation catalyst is attributed to the stabilization of the metallacycle [bmim][PF 6]. Studies further record optimum activities and selectivies at moderate reaction temperatures > [bmim][PF 6 ]. Studies further record optimum activities and selectivies at moderate reaction intermediate the more bulky not exceeding 60 by °C. ˝ C. and basic N-heterocyclic carbene ligand. Methyl oleate also exhibit temperatures not exceeding 60 high conversions (Table 2) when the metathesis reaction carried usingconversions Hoveyda-Grubbs Grubbs second second generation generation catalyst catalyst exhibits higheris methyl methylout oleate withsecond improved Grubbs exhibits higher with improved generation catalyst (5d). In particular higher substrate conversionsoleate were conversions obtained in [bdmim][BF 4] selectivity in in [bmim][X] ionic ionic liquids liquids over over conventional conventional organic solvents (Table 1) [41]. [41]. The The higher higher selectivity organic at solvents (Table 1) compared[bmim][X] to [bmim][BF4] with excellent selectivity (>99%) observed moderate reaction temperatures activity of of Grubbs Grubbs second second generation catalyst catalyst is is attributed attributed to to the the stabilization stabilization of of the metallacycle metallacycle activity [61]. Methyl ricinoleate generation (methyl (9Z,12R)-12-hydroxyoctadec-9-enoate), whose fatty the acid moiety intermediate by the more more bulky and basic basic N-heterocyclic carbene ligand. Methyl Methyl oleate also exhibit exhibit constitutes 90% ofbulky fatty acids in castor oil, also undergoes self-metathesis in ILs oleate using Grubbsintermediate byabout the and N-heterocyclic carbene ligand. also
high conversions when thethe metathesis reaction is carried out using second high conversions(Table (Table2)2) when metathesis reaction is carried out Hoveyda-Grubbs using Hoveyda-Grubbs generation catalyst (5d). In particular higher substrate conversions were obtained in [bdmim][BF4] compared to [bmim][BF4] with excellent selectivity (>99%) observed at moderate reaction temperatures [61]. Methyl ricinoleate (methyl (9Z,12R)-12-hydroxyoctadec-9-enoate), whose fatty acid moiety constitutes about 90% of fatty acids in castor oil, also undergoes self-metathesis in ILs using Grubbs-
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second generation catalyst (5d). In particular higher substrate conversions were obtained in [bdmim][BF4 ] compared to [bmim][BF4 ] with excellent selectivity (>99%) observed at moderate reaction temperatures [61]. Methyl ricinoleate (methyl (9Z,12R)-12-hydroxyoctadec-9-enoate), whose fatty acid moiety constitutes about 90% of fatty acids in castor oil, also undergoes self-metathesis in ILs using Grubbs-type catalysts. Ricinoleate ester coversions in [bmim][PF6 ], [bmim][BF4 ] and [bmim][NTf2 ] are shown in Table 3. Consorti et al. [62] have reported the transformation of methyl (ethyl) linoleate and soya bean oil into their conjugated isomers by RuHCl(CO)(PPh3 )3 or RhCl(PPh3 )3 in ILs. The ILs used in the study were [bmim][PF6 ], [bmim][NTf2 ], [bmPy][PF6 ] and [bmPy][NTf2 ]. A conversion of 80% was obtained when methyl linoleate was catalyzed using RuHCl(CO)(PPh3 )3 in [bmim][NTf2 ] at 80 ˝ C. A complete conversion of methyl or ethyl linoleate was observed with RhCl(PPh3 )3 /SnCl2 in [bmim][NTf2 ]. Table 1. Activity and selectivity of Grubbs catalysts 5a and 5b on methyl oleate in ILs vs. selected organic solvents. Solvent/RTIL
Temperature/˝ C
DCM
20 100
DCE
Conversion/%
Selectivity/%
Substrate/Ru
49 59
100 71
102
20
51
100
102
[bmim][PF6 ]
20 60
50 59
100 99
104
[bmim][BF4 ]
20 60
54 61
100 95
104
[bmim][NTf2 ]
20 60
51 61
100 99
104
Catalyst 5a
Catalyst 5b DCM
20 120
52 81
100 27
102
DCE
20
51
100
102
[bmim][PF6 ]
20 60
53 75
100 81
104
[bmim][BF4 ]
20 60
59 78
100 87
104
[bmim][NTf2 ]
20 60
61 73
99 72
104
Abbreviations: DCM (dichloromethane), DCE (Dichloroethane); Reference [41].
Table 2. Activity and selectivity of Hoveyda-Grubbs catalysts 5c and 5d on methyl oleate in ILs. RTIL
Temperature/˝ C
[bmim][PF6 ]
40 60
[bmim][BF4 ]
40 60
Conversion/%
Selectivity/%
Substrate/Ru
57 60
99 97
102
58 60
99 97
102
Catalyst 5c
Catalyst 5d [bdmim][PF6 ]
40 60
81 90
98 95
102
[bdmim][BF4 ]
40 60
85 92
99 95
102
Reference [61].
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Table 3. Table 3. Activity Activity and and selectivity selectivity of of Hoveyda-Grubbs Hoveyda-Grubbs catalysts catalysts 5c 5c and and 5d 5d on on methyl methyl ricinoleate ricinoleate in in ILs. ILs.
RTIL RTIL
Temperature/°C Temperature/˝ C
Conversion/% Selectivity/% Selectivity/% Substrate/Ru Substrate/Ru Conversion/%
[bmim][PF6] [bmim][PF ] [bmim][BF4]6 [bmim][BF4 ] [bmim][NTf [bmim][NTf2]2 ]
60 60 60 60 60 60
99 99 99 99 99
[bdmim][PF6] [bdmim][PF6 ] [bmim][BF [bmim][BF4]4 ] [bdmim][NTf [bdmim][NTf2]2 ]
60 60 60 60 60
Catalyst 5a Catalyst 5a 45 45 41 41 3838 Catalyst 5b Catalyst 5b 58 58 5656 5555
60
99
99
99 99 99 99 99
Ref. [61]. Reference [61].
102
102
102
102
10210
2
5.2. Ethenolysis 5.2. Ethenolysis Cross-metathesis of oil derived derived olefins olefins with with ethylene ethylene provides provides an an interesting interesting route route for for the the Cross-metathesis of oil synthesis of of short-chain short-chain intermediates intermediates with with potential potential application application in in polymer, lubricant and and surfactant surfactant synthesis polymer, lubricant industries [63]. [63]. Ethenolysis Ethenolysis of methyl oleate (9a) gives gives rise rise to to 1-decene 1-decene (9d) (9d) and and methyl methyl 9-decenoate 9-decenoate industries of methyl oleate (9a) (9e) as as shown shownin inScheme Scheme4.4.1-Decene 1-Decenehas hasnumerous numerousindustrial industrial applications, example, is used as (9e) applications, forfor example, it isitused as an an intermediate in the production of epoxides, amines, oxo alcohols, synthetic lubricants, synthetic intermediate in the production of epoxides, amines, oxo alcohols, synthetic lubricants, synthetic fatty fatty acids, and alkylated aromatics and as a monomer in co-polymers. Methyl 9-decenoate is an acids, and alkylated aromatics and as a monomer in co-polymers. Methyl 9-decenoate is an intermediate intermediate in the of many products, chemical products, for example, nylon-10 well as lubricants in the synthesis ofsynthesis many chemical for example, nylon-10 as wellasas lubricants and and plasticizers Thurier al. [64] reported ethenolysis methyloleate oleateininimidazolium-type imidazolium-type ionic ionic plasticizers [63].[63]. Thurier et al.et[64] reported thethe ethenolysis ofofmethyl liquids using using Grubbs Grubbs and and Hoveyda Hoveyda type type catalysts. catalysts. When When three three imidazolium imidazolium based based ILs ILs ([bmim][OTf], ([bmim][OTf], liquids [bmim][NTf22]] and atat room temperature in in thethe presence of catalyst 5a, [bmim][NTf and[bdmim][NTf [bdmim][NTf2]2 ]were wereevaluated evaluated room temperature presence of catalyst the the highest conversion (83%) was Hoveyda-type catalysts bearing an 5a, highest conversion (83%) wasobtained obtainedinin[bdmim][NTf [bdmim][NTf2]. ]. Hoveyda-type catalysts bearing an 2 ionic tag (Figure 6) were also evaluated in the presence of [bdmim][NTf 2 ]. Catalyst 11a gave a better ionic tag (Figure 6) were also evaluated in the presence of [bdmim][NTf2 ]. Catalyst 11a gave a better catalytic activity activity (89%) (89%) compared compared to to 11b 11b although although its its recyclability recyclability was was poor. poor. catalytic
PCy3 Cl Ru
PCy3 Cl Ru Cl N
Cl O
O
N O
N PF6-
N
N PF6-
11a
PCy3 Cl Ru
PF6
N H
Cl O 11b
11c
Figure6.6.Hoveyda-type Hoveyda-type catalysts [63]. Figure catalysts bearing bearingan anionic ionictag tag [63].
5.3. Cross-Metathesis Cross-Metathesis in in Biphasic Biphasic Systems Systems 5.3. Ethenolysis of of methyl methyl oleate oleate using using Ru-imidazolium-tagged Ru-imidazolium-tagged carbene Ethenolysis carbene complexes complexes (12a,b) (12a,b) (Figure (Figure 7) 7) in biphasic systems with ILs have been reported by Aydos et al. [65]. A substrate conversion of 62% in biphasic systems with ILs have been reported by Aydos et al. [65]. A substrate conversion of accompanied withwith the best selectivity of 46% was reported forforthe in 62% accompanied the best selectivity of 46% was reported theionic ionictagged taggedcatalyst catalyst 12b 12b in [bmim][PF66]] and the viscosity viscosity [bmim][PF and toluene toluene as as the the co-solvent. co-solvent. The The addition addition of of organic organic solvents solvents to to IL IL reduces reduces the of the the mixture and gas bubbling capability of ILs. To solve the of mixture and andinfluences influencesthe thetransport transportproperties properties and gas bubbling capability of ILs. To solve problems associated with ionic the reaction performed using Silicausing Aerosil 200 the problems associated with phase ionic mass phasetransfer, mass transfer, the was reaction was performed Silica as the solid support. This modification resulted in a significant increase in catalytic activity. However, Aerosil 200 as the solid support. This modification resulted in a significant increase in catalytic activity. the solid support used did not influence selectivity ethenolysis. The supported liquid phase However, the solid support used did notthe influence thefor selectivity for ethenolysis. Theionic supported ionic (SILP) catalyst prepared with the IL 1-isopentyl-3-methylimidazole hexafluorophosphate [ipmim][PF6] and silica showed a turnover number almost twice that of biphasic systems).
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liquid phase (SILP) catalyst prepared with the IL 1-isopentyl-3-methylimidazole hexafluorophosphate 10 of 16 10 of 16 showed a turnover number almost twice that of biphasic systems).
Molecules 2016, 21, 184 Molecules 2016,6 ]21, 184 silica [ipmim][PF and
N N
N N PF PF6 -
PCy PCy33 Cl Cl Ru Ru Cl Cl O O
N N
N N
PCy PCy33 Cl Cl Ru Ru Cl Cl O O
PF PF66-
6
12a 12a
12b 12b
Figure Ru-imidazolium-tagged carbene complexes complexes [65]. [65]. Figure 7. 7. R u-imidazolium-tagged carbene Figure 7. Ru-imidazolium-tagged carbene complexes [65].
5.4. Ring Ring Closing Metathesis Metathesis 5.4. 5.4. Ring Closing Closing Metathesis Ring closing closing metathesis has has been successfully successfully employed in in the synthesis synthesis of macrocyclic Ring Ring closing metathesis metathesis has been been successfully employed employed in the the synthesis of of macrocyclic macrocyclic compounds from from olefinic fatty compounds in conventional organic solvents. For example compounds compounds from olefinic olefinic fatty fatty compounds compounds in in conventional conventional organic organic solvents. solvents. For For example example civetone, civetone, civetone, an important ingredient in musk perfume can RCM be synthesized by RCM of oleon an an important important ingredient ingredient in in musk musk perfume perfume can can be be synthesized synthesized by by RCM of of oleon oleon (9,26-pentatriacontadien(9,26-pentatriacontadien(9,26-pentatriacontadien-18-one) which is first obtained by Claisen condensation of methyl oleate [66]. 18-one) 18-one) which which is is first first obtained obtained by by Claisen Claisen condensation condensation of of methyl methyl oleate oleate [66]. [66]. Alternatively, Alternatively, civetone civetone Alternatively, civetone could be synthesized in good yields via Ti-Claisen condensation(Scheme of methyl could could be be synthesized synthesized in in good good yields yields via via Ti-Claisen Ti-Claisen condensation condensation of of methyl methyl 9-decenoate 9-decenoate (Scheme 6) 6) 9-decenoate (Schemeβ-ketoester 6) followed byusing RCM of β-ketoester 13b form using Grubbs catalyst 5a to form a followed followed by by RCM RCM of of β-ketoester 13b 13b using Grubbs Grubbs catalyst catalyst 5a 5a to to form aa 17 17 membered membered β-ketoester β-ketoester 13c 13c 17 membered β-ketoesterNaOH 13c which gets subjected to NaOH hydrolysis and acidic decarboxylation which which gets gets subjected subjected to to NaOH hydrolysis hydrolysis and and acidic acidic decarboxylation decarboxylation to to form form civetone civetone 13d 13d [67]. [67]. to form civetone 13d [67].esters However, RCM of also diallyl esters in RTILs have also been reported using However, RCM of diallyl in RTILs have been reported using catalysts 11a and 11b However, RCM of diallyl esters in RTILs have also been reported using catalysts 11a and 11b [68]. [68]. As As 11a and 11b [68]. Asdiallylmalonate a model substrate, dimethyl diallylmalonate was subjected to RCM acatalysts model substrate, dimethyl was subjected to RCM in [bmim][NTf 2] under mild a model substrate, dimethyl diallylmalonate was subjected to RCM in [bmim][NTf2] under mild in [bmim][NTf mild reaction conditions (Scheme 7).better Catalyst 11b than displayed a 11a rather better reaction (Scheme 2 ] under reactionconditions conditions (Scheme7). 7).Catalyst Catalyst11b 11bdisplayed displayedaarather rather betteractivity activity than catalyst catalyst 11aalthough although the latter maintained constant activity upon recycling. Conversely, catalyst 11b activity than catalyst an 11aalmost although the latter maintained an almost constant activity upon recycling. the latter maintained an almost constant activity upon recycling. Conversely, catalyst 11b showed showed aa Conversely, catalyst 11b showed a decrease in activity with the number of catalytic cycles. decrease decrease in in activity activity with with the the number number of of catalytic catalytic cycles. cycles.
CO CO22Me Me
TiCl TiCl44-Bu3N/ -Bu3N/
O O
o Toluene, Toluene, 0-5 0-5 oC, C, 1h 1h
CO Me CO22Me
13b 13b
13a 13a
[5a] [5a] o 110 C, 2h 2h 110 oC, O O O O
CO CO22Me Me
(i) (i) 5% 5% NaOH/THF/MeOH NaOH/THF/MeOH (ii) (ii) 10% 10% H H22SO SO44
civetone civetone 13d 13d
13c 13c
Scheme 6. 6. Synthesis of civetone via Ti-Claisen condensation and RCM. Scheme Scheme 6. Synthesis Synthesis of of civetone civetone via via Ti-Claisen Ti-Claisen condensation condensation and and RCM. RCM.
MeO2C MeO2C MeO2C MeO2C 14a 14a
[bmim][NTf2] [bmim][NTf2]
MeO2C MeO2C
[cat] 5 mol%, r.t., 1h [cat] 5 mol%, r.t., 1h
MeO2C MeO2C
+ + 14b 14b
Scheme 7. RCM of dimethyl diallylmalonate in [bmim][NTf2]. Scheme 7. RCM of dimethyl diallylmalonate in [bmim][NTf2].
civetone 13d
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Scheme 6. Synthesis of civetone via Ti-Claisen condensation and RCM.
MeO2C
[bmim][NTf2]
MeO2C
[cat] 5 mol%, r.t., 1h
MeO2C
+ MeO2C
14b
14a Molecules 2016, 21, 184 Molecules 2016, 21, 184
Scheme 7. 7. RCM RCM of of dimethyl dimethyl diallylmalonate Scheme diallylmalonate in in [bmim][NTf2]. [bmim][NTf2].
11 of 16 11 of 16
Ruthenium imidazolium imidazolium tagged tagged catalyst catalyst 11b 11b also also shows shows excellent excellent activity activity for for the the RCM RCM of of Ruthenium imidazolium tagged catalyst 11b activity N,N-diallyltosylamide (Scheme 8) in the presence of [bdmim][PF 6 ] resulting in the formation of cyclic N,N-diallyltosylamide(Scheme (Scheme8)8)inin presence of [bdmim][PF the formation of N,N-diallyltosylamide thethe presence of [bdmim][PF 6] resulting in theinformation of cyclic 6 ] resulting olefin olefin 15b [68]. [68]. However, due to todue the difficulty difficulty in reforming reforming the initial initial complex, catalytic activity drops cyclic 15bHowever, [68]. However, to the difficulty in reforming the complex, initial complex, catalytic activity olefin 15b due the in the catalytic activity drops drastically with the the number of catalytic catalytic cycles whilewhile the activity activity of 11a 11a remains almost constant up drops drastically with the number of catalytic cycles the activity of remains 11a remains almost constant drastically with number of cycles while the of almost constant up to the second cycle and drops gently with further recycling. Audic et al. [69] have also reported the upthe to the second cycle and drops gently with furtherrecycling. recycling.Audic Audicetetal. al.[69] [69]have havealso also reported reported the to second cycle and drops gently with further RCM of of N,N-diallyltosylamide N,N-diallyltosylamide in in [bmim][PF [bmim][PF666]]] using using catalyst catalyst 11c. 11c. The The above above developments developments present present using catalyst RCM interesting possibilities possibilities for for applications applications of of RTILs RTILsin inRCM RCMof ofoleochemicals. oleochemicals. interesting RTILs in RCM of oleochemicals. Ts Ts N N
mol% 2.5 mol% [cat], 2.5 [cat],
15a 15a
in [bdmim]PF [bdmim]PF6 in 6 min 45 min C, 45 60 ooC, 60
Ts Ts N N
15b 15b
Scheme in [bdmim][PF6]. Scheme 8. 8. RCM RCM of of N,N-diallyltosylamide N,N-diallyltosylamide in in [bdmim][PF [bdmim][PF6].]. Scheme 8. RCM of N,N-diallyltosylamide 6
5.5. Metathesis Metathesis Using Using Supported Supported Ionic Ionic Liquid Liquid Phase Phase 5.5. Metathesis Using Supported Ionic Liquid Phase 5.5. Supported ionic ionic liquid liquid phase phase (SILP) (SILP) catalysts catalysts are are aaa combination combination of of metal metal catalyst, catalyst, ionic ionic liquid liquid and and Supported ionic liquid phase (SILP) catalysts are combination of metal catalyst, ionic liquid and Supported a porous support. Dugue et al. [70] reported a continuous flow homogeneous olefin metathesis using a porous support. Dugue et al. [70] reported a continuous flow homogeneous olefin metathesis using a porous support. Dugue et al. [70] reported a continuous flow homogeneous olefin metathesis using aaa SILP catalyst. catalyst. A A SILP SILP catalyst catalyst (16c) (16c) immobilized immobilized on on aaa thin thin film film of of [bmim][NTf [bmim][NTf222]]] and and supported supported within within SILP A SILP catalyst (16c) immobilized on and supported within SILP catalyst. thin film of [bmim][NTf the pores of silica, was used with compressed CO 2 as the flowing medium. This system was applied the pores of silica, was used with compressed CO as the flowing medium. This system was applied the pores of silica, was used with compressed CO22 as the flowing medium. This system was applied for the the self-metathesis self-metathesisof ofmethyl methyloleate oleateleading leadingtoto toa aaconversion conversion of up to 64% and turn over number for ofof upup toto 64% and a turn over number of for the self-metathesis of methyl oleate leading conversion 64% and aa turn over number of >10,000 was obtained after 9 h. The same SILP system was used for the cross-metathesis of methyl >10,000 was obtained after 9 h. The same SILP system was used for the cross-metathesis of methyl of >10,000 was obtained after 9 h. The same SILP system was used for the cross-metathesis of methyl oleate with with dimethyl maleate (Scheme 9)9) [70]. The reaction yields an unsaturated unsaturated α,ω-diester (16a)(16a) and oleate withdimethyl dimethylmaleate maleate(Scheme (Scheme9) [70]. The reaction yields an unsaturated α,ω-diester oleate [70]. The reaction yields an α,ω-diester (16a) and an α,β-unsaturated α,β-unsaturated terminal ester (16b) which when carbonylated leads totothe the formation dimethyl and an α,β-unsaturated terminal ester (16b) which when carbonylatedleads leadsto theformation formation dimethyl dimethyl an terminal ester (16b) which when carbonylated 1,12-dodecandioate. These are all important feedstocks for applications in polymer synthesis [71–73]. 1,12-dodecandioate. These are all important feedstocks for applications in polymer synthesis [71–73]. 1,12-dodecandioate. These are all important feedstocks for applications in polymer synthesis [71–73]. O O
MeO MeO
OMe OMe + + MeO MeO
OMe OMe O O
16a 16a + +
O O OMe OMe
OMe OMe 16b 16b NMes NMes Cl RuCl Ru Cl O Cl O
O O
MesN MesN
16c 16c
11c 11c H H
N N
N PF - N PF66-
Scheme 9. Cross-metathesis of methyl with Scheme 9. 9. Cross-metathesis Cross-metathesis of of methyl methyl oleate oleate with with dimethyl dimethyl maleate maleate using using 16c. 16c. Scheme oleate dimethyl maleate using 16c.
5.6. Limitations Limitations with with RTILs RTILs 5.6. The main main limitations limitations faced faced by by RTILs RTILs are are high high cost cost and and lack lack of of physical physical property property and and toxicity toxicity data. data. The They are are comparatively comparatively more more expensive expensive than than organic organic solvents solvents and and their their cost cost depend depend on on the the composition composition They of cations and anions and the scale of production [74]. The expensive cleaning methods due to to their their of cations and anions and the scale of production [74]. The expensive cleaning methods due non-volatile nature and low melting points is another contributory factor to their high cost. Also, the
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5.6. Limitations with RTILs The main limitations faced by RTILs are high cost and lack of physical property and toxicity data. They are comparatively more expensive than organic solvents and their cost depend on the composition of cations and anions and the scale of production [74]. The expensive cleaning methods due to their non-volatile nature and low melting points is another contributory factor to their high cost. Also, the desired RTIL quality (halide, water and amine content) may affect the price. The non-availability of toxicity and biodegradability data is another challenge for the industrial scale application of RTILs [74,75]. Incomplete physico-chemical data also pose problems for the future use of RTILs. The data that is available currently is mainly on physical properties such as viscosity, density and phase transitions. Until recently, very few microscopic physical properties are available which is needed for the synthesis of new RTILs. The recycling processes of RTILs available currently involves washing with water or volatile organic compounds, and the latter pose a threat to the environment. However, the application of supercritical extraction technologies and membrane separation processes is a promising intervention in the recycling RTILs. Still, some solid impurities are found to be adsorbed on the RTILs, which need to be eliminated using new technologies. The high viscosities further pose problems for its large scale application [76,77]. The viscosities of RTILs are higher than those of conventional organic solvents and similar to that of oils. The high viscosities may lead to a decrease in the rate of many organic reactions. Increasing the temperature and changing the anion-cation combinations can lower the viscosity of RTILs. 6. Future Directions The introduction of room temperature ionic liquids to the transition metal catalysed reactions instead of conventional organic solvents has made the process more compatible to the environment and is found to be economical due to their unique physical and chemical properties such as non-volatility, excellent thermal stability, the ease of recovery and good ability to dissolve many organometallic compounds. In most of the publications reported, the use of ionic liquids in metathesis has led to significant enhancement in the reactivity, yield and reaction rate. Another advantage of using ionic liquids is the ease of recovering and reusing the catalyst and the ionic liquids without much drop in activity [78]. The ability to manipulate structure and function of ILs affords possibilities for designing a new generation of solvents with improved greener qualities and a wider industrial application [79]. Recent developments in olefin metathesis have promised a great future for the “green” metathesis in ionic liquids both in scientific research and in industrial and pharmaceutical applications. In spite of all these developments, many critical areas in catalytic olefin metathesis remain to be modified. The synthesis of more robust and active catalysts that can be easily prepared requires attention. The preparation of catalysts that can control olefin stereochemistry remains a challenge. Although many of the metathesis reactions yield the desired products, the high catalyst loadings required for an efficient and cost effective process is also under question. 7. Conclusions Olefin metathesis is a ground-breaking advance that has cleared the route to many difficult chemical syntheses and is likely to continue to do so. The major disadvantages of the Ru catalysts are their poor recyclability and the difficulty of removing the Ru waste from the products. However, by the introduction of RTILs as solvents, the task of separating Ru catalysts from the products could be overcome. High conversions can therefore be achieved, and the catalyst can be reused and recycled. To overcome the problem of leaching of the catalyst into the organic phase, charged catalyst systems have been successfully employed. These charged catalysts improve the immobilization of the catalyst by increasing catalyst affinity to the ionic liquid. Furthermore, RTILs provide less harzadous and environmentally friendly reaction media. Nonetheless, a few limitations related to their high cost,
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availability of toxicity data and high viscosities should be taken into consideration before their large scale application. Acknowledgments: National Research Foundation of South Africa (NRF) for financial support. Author Contributions: Authors’ (P.A.T. and B.B.M.) contribution to the work was equal. Conflicts of Interest: The authors declare no conflict of interest.
References 1. 2. 3. 4. 5. 6. 7. 8. 9.
10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.
22.
Banks, R.L.; Bailey, G.C. Olefin disproportionation: A new catalytic process. Ind. Eng. Chem. Prod. Res. Dev. 1964, 3, 170–173. Calderon, N.; Chen, H.Y.; Scott, K.W. Olefin metathesis—A novel reaction for skeletal transformations of unsaturated hydrocarbons. Tetrahedron Lett. 1967, 34, 3327–3329. Mol, J.C. Applications of olefin metathesis in oleochemistry: An example of green chemistry. Green Chem. 2002, 4, 5–13. [CrossRef] Mol, J.C. Catalytic metathesis of unsaturated fatty acid esters and oils: Catalytic conversion of renewables. Top. Catal. 2004, 27, 97–104. Plugge, M.F.C.; Mol, J.C. A new synthesis of civetone. Synlett 1991, 70, 507–508. [CrossRef] Ivin, K.J. Some recent applications of the olefin metathesis in organic synthesis: A review. J. Mol. Catal. A Chem. 1998, 133, 1–16. Copéret, C. Stereoselectivity of supported alkene metathesis catalysts: A goal and a tool to characterize active sites. Beilstein J. Org. Chem. 2011, 7, 13–21. [PubMed] Loupy, A.; Tchoubar, B.; Astruc, D. Salt effects resulting from exchange between two ion-pairs and their critical role on reaction pathways. Chem. Rev. 1992, 92, 1141–1165. Hérisson, J.-L.; Chauvin, Y. Catalyse de transformation des olefins par les complexes du tungsténe II. Télomérisation des olefins cycliques en presence d1 oléfines acycligues. Makromol. Chem. 1971, 141, 161–176. [CrossRef] De Espinosa, L.M.; Meier, M.A.R. Olefin metathesis of renewable platform chemicals. Top. Organomet. Chem. 2012, 39, 1–44. Fischmeister, C.; Bruneau, C. RTILS in catalytic olefin metathesis reactions. Top. Organomet. Chem. 2013, 51, 287–305. Miao, S.; Wang, P.; Su, Z.; Zhang, S. Vegetable-oil-based polymers as future polymeric biomaterials. Acta Biomater. 2014, 10, 1692–1704. [CrossRef] [PubMed] Lligadas, G.; Ronda, J.C.; Galià, M.; Cádiz, V. Renewable polymeric materials from vegetable oils: A perspective. Mater. Today 2013, 16, 337–343. Meier, M.A.R. Metathesis with oleochemicals: New approaches for the utilization of plant oils as renewable resources in polymer science. Macromol. Chem. Phys. 2009, 210, 1073–1079. Hoveyda, A.H.; Zhugralin, A.R. The remarkable metal-catalysed olefin metathesis reaction. Nature 2007, 37, 2433–2442. [CrossRef] [PubMed] Sanford, M.S.; Ulman, M.; Grubbs, R.H. New insights into the mechanism of Ruthenium-catalyzed olefin metathesis reactions. J. Am. Chem. Soc. 2001, 123, 749–750. [PubMed] Sanford, M.S.; Love, J.A.; Grubbs, R.H. Mechanism and activity of ruthenium olefin metathesis catalysts. J. Am. Chem. Soc. 2001, 123, 6543–6554. [CrossRef] [PubMed] Adlhart, C.; Chen, P. Mechanism and activity of ruthenium olefin metathesis catalysts: The role of ligands and substrates from a theoretical perspective. J. Am. Chem. Soc. 2004, 126, 3496–3510. [CrossRef] [PubMed] Scott, S.L. Catalytic transformation of seed oil derivatives via olefin metathesis. HELIA 2007, 30, 133–142. Weskamp, T.; Schattenmann, W.C.; Spiegler, M.; Hermann, W.A. A novel class of ruthenium catalysts for olefin metathesis. Angew. Chem. Int. Ed. 1998, 37, 2490–2493. Hoveyda, A.H.; Gillingham, D.G.; van Veldhuizen, J.J.; Kataoka, O.; Garber, S.B.; Kingsbury, J.B.; Harrity, J.P.A. Ru complexes bearing bidentate carbenes: From innocent curiosity to uniquely effective catalysts for olefin metathesis. Org. Biomol. Chem. 2004, 2, 8–23. [CrossRef] [PubMed] ´ Sled´ z, P.; Mauduit, M.; Grela, K. Olefin metathesis in ionic liquids. Chem. Soc. Rev. 2008, 37, 2433–2442. [PubMed]
Molecules 2016, 21, 184
23. 24. 25. 26. 27. 28. 29. 30. 31. 32.
33.
34. 35.
36. 37. 38. 39.
40.
41. 42. 43. 44. 45. 46.
14 of 16
Cornils, B.; Herrmann, W.A. Aqueous-Phase Organometallic Catalysis—Concept and Applications; Wiley/VCH: Weinheim, Germany, 1998. Joo, F.; Beck, M.T. Formation and catalytic properties of water-soluble phosphine complexes. React. Kinet. Catal. Lett. 1975, 2, 257–263. Kuntz, E. Homogeneous catalysis in water. Chemtech 1987, 17, 570–575. Horvath, I.T.; Rabai, J. Facile catalyst separation without water: Flourous biphase hydroformylation of olefins. Science 1994, 266, 72–75. [CrossRef] [PubMed] Horvath, I.T. Flourous phases. In Aqueous-phase Organometallic Catalysis-Concepts and Applications; Cornils, B., Herrmann, W.A., Eds.; Wiley/VCH: Weinheim, Germany, 1998; p. 548. Jessop, P.G.; Ikariya, T.; Noyori, R. Homogeneous catalysis in supercritical fluids. Chem. Rev. 1999, 99, 475–493. [PubMed] Welton, T. Room temperature ionic liquids: Solvents for synthesis and catalysis. Chem. Rev. 1999, 99, 2071–2084. [PubMed] Sugden, S.H.; Wilkins, H. The parachor and chemical constitution. Part X11. Fused metals and salts. J. Chem. Soc. 1929, 1291–1298. Gorman, J. Faster, better, cleaner?: New liquids take aim at old-fashioned chemistry. Sci. News 2001, 160, 156–158. [CrossRef] Tavares, A.P.M.; Rodrígues, O.; Macedo, E.A. New generations of ionic liquids applied to enzymatic biocatalysis. In Ionic Liquids—New Aspects for the Future; Kadokawa, J., Ed.; Intech: Rijeka, Croatia, 2013; pp. 537–556. Peric, B.; Martí, E.; Sierra, J.; Cruanas, ´ R.; Garau, M.A. Green chemistry: Ecotoxicity and biodegradability of ionic liquids. In Recent Advances in Pharmaceutical Sciences II; Munoz-Torrero, ´ D., Haro, D., Vallés, J., Eds.; Transworld Research Network: Kerala, India, 2012; pp. 89–113. Bond, D.R.; Jackson, G.E.; Joao, H.C.; Hofmeyr, M.N.; Modro, T.A.; Nassimbeni, L.R. Liquid clathrates. J. Chem. Soc. Chem. Commun. 1989, 24, 1910–1911. Hill, M.G.; Lamanna, W.M.; Mann, K.R. Tetrabutylammonium tetrakis[3, 5-bis(trifluoromethyl)phenyl]borate as a non-coordinating electrolyte: Reversible 1e-oxidations of ruthenocene, osmocene, and Rh2(TM4)42+. Inorg. Chem. 1991, 30, 4687–4690. Sun, J.; Forsyth, M.; Mac Farlane, D.R. Room temperature molten salts based on quartenary ammonium ion. J. Phys. Chem. B 1998, 102, 8858–8861. Olivier-Bourbigou, H.; Magna, L. Ionic liquids: Perspectives for organic and catalytic reactions. J. Mol. Catal. A Chem. 2002, 182, 419–437. Miyatake, K.; Yamamoto, K.; Endo, K.; Tsuchida, E. Superacidified reaction of sulfides and esters for the direct synthesis of sulfonium derivatives. J. Org. Chem. 1998, 63, 7522–7524. [PubMed] Wilkes, J.S.; Levisky, J.A.; Wilson, R.A.; Hussey, C.L. Dialkylimidazolium chloroaluminate melts: A new class of room temperature ionic liquids for electroscopy, spectroscopy and synthesis. Inorg. Chem. 1982, 21, 1263–1264. Fannin, A.A., Jr.; King, L.A.; Levisky, J.A.; Wilkes, J.S. Properties of 1,3-dialkylimidazolium chloride-aluminium chloride ionic liquids. 1. Ion interactions by nuclear magnetic resonance spectroscopy. J. Phys. Chem. 1984, 88, 2609–2614. [CrossRef] Thomas, P.A.; Marvey, B.B. C18:1 methyl ester metathesis in [bmim][X] type ionic liquids. Int. J. Mol. Sci. 2009, 11, 5020–5030. Bonhˆote, P.; Dias, A.P.; Papageorgiou, K.; Kalyanasundaram, K.; Grätzel, M. Hydrophobic, highly conductive ambient-temperature molten salts. Inorg. Chem. 1996, 35, 1168–1178. Hurley, F.H.; Weir, T.P. Electrodeposition of metals from fused quarternary ammonium salts. J. Electrochem. Soc. 1951, 98, 203–206. Gale, R.J.; Osteryoung, R.A. Infrared spectral investigations of room-temperature aluminium chloride-1-butylpyridinium chloride melts. Inorg. Chem. 1980, 19, 2240–2242. Tait, S.; Osteryoung, R.A. Infrared study of ambient-temperature chloroaluminates as a function of melt acidity. Inorg. Chem. 1984, 23, 4352–4360. [CrossRef] Mac Farlane, D.R.; Meakin, P.; Sun, J.; Amini, N.; Forsyth, M. Pyrrolidinium imides: A new family of molten salts and conductive plastic crystal phases. J. Phys. Chem. B. 1999, 103, 4164–4170. [CrossRef]
Molecules 2016, 21, 184
47. 48. 49. 50.
51. 52. 53. 54. 55. 56.
57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69.
70. 71.
15 of 16
Davis, J.H., Jr.; Forrester, K.J. Thiazolium-ion based organic ionic liquids. Tetrahedron Lett. 1999, 40, 1621–1622. [CrossRef] Vestergaard, B.B.; Petrushina, N.J.I.; Hjuler, H.A.; Berg, R.W.; Begtrup, M. Molten triazolium chloride systems as new aluminium battery electrolytes. J. Electrochem. Soc. 1993, 140, 3108–3113. Jorapur, Y.R.; Chi, D.Y. Ionic Liquids: An Environmentally Friendly Media for Nucleophilic Substitution Reactions. Bull. Korean Chem. Soc. 2006, 27, 345–354. Hussey, C.L. The electrochemistry of room temperature haloaluminate molten salts. In Chemistry of Nonaqueous Solutions: Current Progress; Mamantov, G., Popov, A.I., Eds.; VCH: New York, NY, USA, 1994; pp. 227–275. Brennecke, J.F.; Maginn, E.J. Ionic liquids: Innovative fluids for chemical processing. AIChE J. 2001, 47, 2384–2388. Garcia, M.T.; Gathergood, N.; Scammells, P.J. Biodegradable ionic liquids Part II. Effect of the anion and toxicology. Green Chem. 2005, 7, 9–14. [CrossRef] Tao, G.-H.; He, L.; Sun, N.; Kou, Y. New generation ionic liquids: Cations derived from amino acids. Chem. Commun. 2005, 28, 3562–3564. [CrossRef] [PubMed] Yang, Q.; Dionysiou, D.D. Photolytic degradation of chlorinated phenols in room temperature ionic liquids. J. Photochem. Photobiol. A: Chem. 2004, 165, 229–240. Seddon, K.R. Room-temperature ionic liquids-neoteric solvents for clean catalysis. Kinet. Catal. 1996, 37, 693–697. Lagrost, C.; Carrié, D.; Vaultier, M.; Hapiot, P. Reactivities of some electrogenerated organic cation radicals in room-temperature ionic liquids: Toward an alternative to volatile organic solvents? J. Phys. Chem. A 2003, 107, 745–752. [CrossRef] Shariati, A.; Peters, C.J. High-pressure phase equilibria of systems with ionic liquids. J. Supercrit. Fluids 2005, 34, 171–176. Shariati, A.; Gutkowski, K.; Peters, C.J. Comparison of the phase behavior of some selected binary systems with ionic liquids. AIChE J. 2005, 51, 1532–1540. Zhao, H.; Xia, S.; Ma, P. Use of ionic liquids as green solvents for extractions. J. Chem. Technol. Biotechnol. 2005, 80, 1089–1096. Keskin, S.; Kayrak-Talay, D.; Akman, U.; Hortaçsu, Ö. A review of ionic liquids towards supercritical fluid applications. J. Supercrit. Fluids 2007, 43, 150–180. [CrossRef] Thomas, P.A.; Marvey, B.B.; Ebenso, E.E. Metathesis of fatty acid ester derivatives in 1,1-dialkyl and 1,2,3-trialkyl imidazolium type ionic liquids. Int. J. Mol. Sci. 2011, 12, 3989–3997. [PubMed] Consorti, C.S.; Aydos, G.L.P.; Ebeling, G.; Dupont, J. Multiphase catalytic isomerization of linoleic acid by transition metal complexes in ionic liquids. Appl. Catal. A 2009, 371, 114–120. Khorasvi, E.; Snymanska-Buzar, T. Ring opening metathesis polymerization and related chemistry. Nato Sci. Ser. 2000, 56, 381. Thurier, C.; Fischmeister, C.; Bruneau, C.; Olivier-Bourbigou, H.; Dixneuf, P.H. Ethenolysis of methyl oleate in room-temperature ionic liquids. ChemSusChem. 2008, 118, 118–122. Aydos, G.L.P.; Leal, B.C.; Perez-Lopez, O.W.; Dupont, J. Ionic-tagged catalytic systems applied to the ethenolysis of methyl oleate. Catal. Commun. 2014, 53, 57–61. [CrossRef] Boelhouwer, C.; Mol, J.C. Metathesis of fatty acid esters. J. Am. Oil Chem. Soc. 1984, 61, 425–430. [CrossRef] Hamasaki, R.; Funakoshi, S.; Misaki, T.; Tanabe, Y. A highly efficient synthesis of civetone. Tetrahedron 2000, 56, 7423–7425. Thurier, C.; Fischmeister, C.; Bruneau, C.; Olivier-Bourbigou, H.; Dixneuf, P.H. Ionic imdazolium containing ruthenium complexes and olefin metathesis in ionic liquids. J. Mol. Catal. A Chem. 2007, 268, 127–133. Audic, N.; Clavier, H.; Mauduit, M.; Guillemin, J.-C. An ionic liquid-supported Ruthenium carbene complex: A robust and recyclable catalyst for ring-closing olefin metathesis in ionic liquids. J. Am. Chem. Soc. 2003, 125, 9248–9249. [PubMed] Duque, R.; Ochsner, E.; Clavier, H.; Caijo, F.; Nolan, S.P.; Mauduit, M.; Cole-Hamilton, D.J. Continuous flow homogeneous alkene metathesis with built-in catalyst separation. Green Chem. 2011, 13, 1187–1195. Patel, J.; Mujcinovic, S.; Jackson, W.R.; Robinson, A.J.; Serelisand, A.K.; Such, C. High conversion and productive catalyst turn overs in cross-metathesis reactions of natural oils with 2-butene. Green Chem. 2006, 8, 450–454.
Molecules 2016, 21, 184
72. 73.
74. 75. 76. 77. 78. 79.
16 of 16
´ Jimenez-Rodriguez, C.; Eastham, G.R.; Cole-Hamilton, D.J. Dicarboxylic acid esters from the carbonylation of unsaturated esters under mild conditions. Inorg. Chem. Commun. 2005, 10, 878–881. [CrossRef] Patel, J.; Elaridi, J.; Jackson, W.R.; Robinson, A.J.; Serelisand, A.K.; Such, C. Cross-metathesis of unsaturated natural oils with 2-butene. High conversion and productive catalyst turnovers. Chem. Commun. 2005, 44, 5546–5547. Kerton, F. Alternative Solvents for Green Chemistry:RCS Green Chemistry Book Series; The Royal Society of Chemistry: London, UK, 2009; pp. 118–142. Sowmiah, S.; Srinivasadesikan, V.; Tseng, M.-C.; Chu, Y.-H. On the chemical stabilities of Ionic liquids. Molecules 2005, 14, 3780–3813. [CrossRef] [PubMed] Andreussi, O.; Marzari, N. Transport properties of RTILs from classical molecular dynamics. J. Chem. Phys. 2012, 137, 044508. Ghandi, K. A review of ionic liquids, their limits and applications. Green Sustain. Chem. 2014, 4, 44–53. Fishmeister, C.; Bruneau, C. RTILs in catalytic olefin metathesis reactions. In Ionic Liquids (ILs) in Organometallic Catalysis; Dupont, J., Kollar, L., Eds.; Springer-Verlag: Berlin, Germany, 2015; pp. 287–306. Pagni, R.M. Ionic liquids as alternatives to traditional organic and inorganic solvents. In Green Industrial Applications of Ionic Liquids; Rogers, R.D., Seddon, R.K., Volkov, S., Eds.; Springer Science and Business Media: London, UK, 2003; pp. 105–127. © 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons by Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
