Reactions of aromatic compounds with nucleophilic reagents in liquid

Russian Journal of Organic Chemistry, Vol. 36, No. 6, 2000, pp. 801-807. Translated from Zhurnal Organicheskoi Khimii, Vol. 36, No. 6, 2000, pp, 835-841. Oi'iginal Russian Text Copyright 9 2000 by Politanskaya, Ryabitskaya, Malykhin, Steingartz.

Reactions of Aromatic Compounds with Nucleophilic Reagents in Liquid Ammonia: XVII.* Effect of Ionic Association on the Orientation in Aryloxydefluorination of 2,4-Difluoronitrobenzene L. V. Politanskaya, E.V. Ryabitskaya, E.V. Malykhin, and V.D. Steingartz Novosibirsk Institute of Organic Chemistry, Siberian Division, Russian Academy of Sciences, Novosibirsk, 630090 Russia Received August 14, 1998 Abstract--The analysis of dependence of fluorine replacement orientation in 2,4-difluoronitrobenzene effected by nucleophiles Y-C6H4OM (Y = p-OMe, p-Me, m-Me, H, p-F, p-Cl, m-F, m-Cl; M = Li, Na, K, Et4N, Bu4N) in liquid ammonia medium at --35~ on the nature of M, Y, on nucleophile concentration, on addition of crown ethers, diaminoalkanes, and dimethoxyethane indicates the occurrence of ionic association at M -- K, Na. In the environment of low and moderate polarity [2] (in benzene, dioxane [3], 2-propanol, tert-BuOH [4]) the rate constants of substitution of halogens F, C1 in the aromatic ring effected by reagents of ROM type (R =Ar, Alk; M = alkali metal) at 2080~ are significantly higher for ortho- than paraposition with respect to nitro group. For instance, in tert-BuOH the rate constants of fluorine substitution differ by two and more orders of magnitude. However in the presence of crown ethers the rate constants became of the same order of magnitude [4], as was observed also in highly polar aprotic solvents [3]. This difference in rate constants of SNAr-processes in low polar environment is attributed to chelation effect in the transition state of ortho-substitution consisting in coordination of the metal cation to the oxygens of nitro group and O-nucleophile [3, 4]. The effects of ionic association in the SNAr-processes with participation of charged nucleophiles are also manifested in the change of halogen substitution orientation in a substrate containing two reactive sites at variation in nucleophile concentration, the nature of cation, or in the presence of crown ethers [3, 5, 6]. Liquid ammonia is a medium of moderate polarity (~ 26.7 at -60~ [7]). The ionogenic compounds dissolved therein are regarded as existing in the form of contact ion pairs or more complex aggregates [8] and relatively more seldom as free ions. The latter is characteristic of lithium salts due to efficient interaction of the cation with ammonia resulting in a For communication XVI, see ll].

complex cation [Li(NH3)4] + [8]. It is revealed in no significant dependence on concentration of PhOLi of orientation in phenoxydefluorination of 2,4-difluoronitrobenzene in the liquid ammonia. This fact alongside some other observations permitted an assumption on the participation of nucleophile in the reaction as a free ion or similar in reactivity "loose" ionic associate [1, 9]. It is also known that alkoxydefluorination of ortho- and para-nitrofluorobenzenes effected by sodium alcoholates (Alk = Me, tert-Bu) in liquid ammonia [10] is 105-107 times faster than in alcohols [4, 11-13]. It is apparently due first of all to virtually aprotic solvation of anion with liquid ammonia [9], but indirectly it may indicate low degree of association of the counterions of the reagent. The latter is evidenced by insignificant influence of the cation character on the orientation of alkyl- and phenyloxydefluorination of 2,4-difluoronitrobenzene when treated respectively with AIkOM (Alk = Me, Et, i-Pr, M = Na, K) and PhOM at -70~ [5]. Resulting from the combination of these factors caused by the specific features of liquid ammonia as solvent the anionic nucleophile exhibits activity close to that of a free anion in the absence of specific solvation. Taking into account that the said features of the liquid ammonia as highly efficient solvent may provide new possibilities in the synthesis and production processes [14] based on the aromatic nucleophilic substitution in extension of investigation of factors determining the orientation in SNAr-processes with participation of charged nucleophiles (see [1,5,9.10])

1070-4280/00/3606-0801 $25.00 9 2000 MAIK "Nauka/lnterperiodica"

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of compound I did not exceed ~20-25%. Thus it may be considered that in the ratio of isomeric 2-nitro-5fluoro-3'(or 4")-Y- and 4-nitro-3-fluoro-3' (or 4")-Ydiphenyl ethers of VII and VIII type respectively the fluorine substitution orientation in compound I (o/p-ratio) was not distorted by subsequent aminoand aryloxydefluorination thereof [9]. The relative amounts of compounds of VII and VIII type in the reaction mixtures were measured by integral intensity ratio in the 19F NMR spectra (data on the chemical shifts of the signals belonging to compounds of VII and VIII type are given in [6, 9]). The integral intensity was registered from three to five times with various relaxation time. For each nucleophile the o/p ratio was determined as arithmetic mean from data of 2-4 experiments on VII/VIII ratio.

Scheme

~ F I

OM F +~

NH3 (aqueouS) Y lla-h-VIa-h

F

Y Vlla-h

NO2 + ~

NH2 F

Y Vllla-h

The data presented in Table l show that the prevalence of ortho-substitution smoothly grows with the radius of metal cation in the nucleophile: the o/p ratio changes from ~1.4 to ~3.0 on going in the phenolate series from lla to I l i a and further to IVa. In reaction with tetraalkylammonium phenolates Va, Via this ratio is of intermediate value ~1.7-1.8. The twice increased nucleophile concentration in the case of phenolate IVa somewhat enhanced the o/p ratio (to ~3.4), whereas with phenolates lla and I l i a it remained practically unchanged.

Y = H (a), p-OMe (b), p-Me (c), m-Me (d), p-F (e), p - C l (f), m-F (g), m-Cl (h); M = Li (II), Na (HI), K (IV), Et4N (V), Bu4N (VI). we revealed in this study the dependence of orientation in aryloxydefluorination of 2,4-difluoronitrobenzene (I) effected by nucleophiles of Y-C6H4OM type [Y = H (a), p-OMe (b), p-Me (e), m-Me (d), p-F (e), p-Cl (f), m-F (g), m-C1 (h), M = Li (II), Na (lllb), K (IV), Et4N (V), Bu4N (VI)] at -35~ (see Scheme) on the nature of substituents and cation in the nucleophile, on its concentration, and on additives: crown ethers, diaminoalkanes, and dimethoxyethane. The aim of the study was to establish the possibility and character of influence on the orientation of the ionic association.

Table 1. Orientation at fluorine substitution in reaction of 1-nitro-2,4-difluorobenzene (I) with phenolates Ha-Via

[Vlll/[Vllll

[lIa9 "

la],

tool l-I

The reactions were carded out for 6-20 min at reagents ratio I:Y-C6H4OM equal to 2: l, also at variation of the concentrations. The reactions were stopped by adding excess of ammonium chloride. The time of reaction was so adjusted that the conversion

~.02 0.04

lla

Hla

IVa

Va

Via

1.4+0.2 2.0 +0.1 3.0+0.1 1.7+0.2 1.36+0.02 2.1+0.1 3.4 +0.1

1.8+0.2

Table 2. Orientation at fluorine substitution in reaction of 1-nitro-2,4-difluorobenzene (I) with phenolates lla-Vla in the presence of chelating agents for cations [VIIa]/[Vllla]

Chelating agent

c, mol 1-I

m

15-crown-5 Dicyclohexyi- 18-crown-6 Tetramethylethylenediamine 1,4-Diaminobutane Dimethoxyethane

0.04 0.04 0.04 0.04 0.24

Ha

IHa

IVa

1.4+0.1 1.5+0.2 1.5+0.2 1.5+0.1

2.1 +0.1 2.0+0.2 2.0+0.2

3.4 +0.1 2.5+0.3 2.1 +0.2 3.7+0.2 3.6+0.4 3.5+0.3

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Table 3. Orientation at fluorine substitution in reaction of 1-nitro-2,4-difluorobenzene (I) with phenolates IIa-h-IVa-h, s 0.04 mol 1-~ [VIIa-h]/[Vllla-h] Compd. no.

HI

IV V II VI VH

VIH IX

~v [16]

-0.27 -0.17 -0.07 0.00 0.06 0.23 0.34 0.37

Y-C6H4OLi [9]

Y-C6H4ONa

Y-C6H4OK

1.12+0.02 1.23+0.02 1.28+0.02 1.36+0.02 1.49+0.02 1.56+0.02 1.67+0.02 1.70+0.02

2.0+0.1 2.1+0.1 2.1+0.1 2.1+0.1 2.1+0.1 2.1+0.1 2.1 +0.2 2.2+0.2

3.7 +0.1 3.5+0.1 3.4+0.2 3.4 +0.1 3.4+0.1 3.3+0.1 3.2+0.2 3.2+0.2

In general the influence of the cation nature and phenolate concentration on the orientation in the SNAr-process under study in liquid ammonia medium at -35~ should be regarded as weak compared to low polar media [3]. Also the narrow range of o/p ratio, 1.4-1.8, apparently indicates that in reaction with participation of mainly free anion of phenolate IIa and ion pairs in tetraalkylammonium phenolates Va, Via is obtained similar orientation. Thus these o/p values apparently reflect the orientation when no significant distinctions in the character of ionic association arise between the transition states of competing directions of the reaction, and the difference is due to the proper structural characteristics of the transition states [9]. From this point of view the fact that in reaction of compound I with phenolate IVa the o/p ratio is notably greater than in the reaction with phenolates IIa, IIIa, Va, Via, and tends to increase at growing nucleophile concentration (Table l) may indicate that certain difference in the character of ionic association in the competing transition states exists for potassium cation. This assumption is also supported by the following facts. We established that the o/p ratio in reaction of compound I with potassium phenolate IVe increased twice at raising nucleophile concentration 100 times: at [IVc] 0.004, 0.018, 0.03, 0.04, 0.06, 0.07 and 0.40 mol 1-l the ratio [VIIc]/[VIIIc] equals respectively to 3.0, 3.0, 3.4, 3.1, 3.5, 3.4, 3.6, 4.0, 6.0. These data show however weak, but distinct influence of changed nucleophile concentration on orientation. The same conclusion may be drawn from the experiments on the effect of crown ethers addition on the orientation in the reaction of compound I with phenolates IIa-IVa (Table 2). For instance, the addition to the reaction mixture of a quantity of

15-crown-5 or dicyclohexyl-18-crown-6 equimolar with respect to nucleophile virtually does not affect the o/p ratio in reaction with lithium and sodium phenolates (lla, Ilia), but in reaction with potassium phenolate (IVa) in the presence of dicyclohexyl-18crown-6 efficiently forming complexes with potassium cation [4] the above ratio decreases to ~2 value characteristic of the reaction with participation of phenolate I l i a in the absence of crown ether. Note (Table 2) that addition of tetramethylethylenediamine, 1,4-diaminobutane, and dimethoxyethane as agents capable to form chelate complexes with alkali metal cations [15] did not affect the o/p value in reaction of compound I with phenolate IVa. Apparently dimethoxyethane and diamines same as ammonia are less efficient in competition for association with potassium cation than negatively charged species participating in the reaction under study (nucleophile, anionic c-complexes). Thus the sum of the data presented in Tables 2 and 3 allows a conclusion that ionic association as a factor capable to affect the orientation of aryloxydefluorination of compound I in liquid ammonia at -35~ appears in increase of o/p ratio with growing ionic radius of the nucleophile cation and actually manifests itself at the use of potassium phenolates. To evaluate the relative significance of the factors affecting the orientation in the reaction under study, we compared the o/p ratios reported here for reaction between compound I and phenolates (Ilia, IVa)(lllh, IVh) at -35~ and those obtained in [9] for reaction with phenolates l l a - h (Table 3). The comparison shows that growing electron-acceptor power of meta- and para-substituents in the phenolate resulted in increase of o/p ratio for the series of lithium phenolates, the ratio tended to decrease in the


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series of potassium phenolates (1Va-h) and remained nearly constant with sodium phenolates (Ilia-h). It is possible to state in general that variation of the nature of substituents Y in phenolates at fixed counterion, and variation of the nature of the latter at fixed substituent Y approximately to an equal degree affect the orientation of aryloxydefluorination of compound I. Attention should be drawn to, firstly, general trend in increase of o/p ratio in the cation series in going from lithium to potassium, and, secondly, that the range of changes in the o/p ratio is greater for phenolates with electron-donating substituents (e.g., from 1.1 to 3.7 with Y = p-OMe) than for those with electron-withdrawing substituents (from 1.7 to 3.2 with Y = m-C1). As a result the effect of the character of substituent in the nucleophile on the orientation in reaction of compound I with potassium phenolates IVa-h is the opposite to that observed in reaction with lithium phenolates IIa-h. The sum of the data obtained suggests that in the reaction of compound I with oxygen-containing charged nucleophiles into the variation of o/p ratio on changing cations similarly contribute the differences in enthalpy and entropy of activation of the competing directions (AA*Ho/p and AA*So/p respectively [1]). This assumption i s supported also by already mentioned effect of crown ether addition on the rate of alkoxydefluorination of isomeric fluoronitro-benzenes treated with potassium alcoholates in alcoholic media [4]. Thus the presence of crown ether affects the activation parameters to such extent that their changes due to the character of ionic association (Aia) in the temperature range under study approximately compensate each other (I (AiaA*Hol 9 I TA'iaA*SoI): the rate constant increases only thrice in the system t-BuOK- t-BuOH at +25~ and decreases only by 1.3 times for the system i-PrOK-i-PrOH. Unlike that in reactions of para-fluoronitrobenzene these contributions are essentially different (1 (AiaA*Hn I # [TA'iaA*Sn[): in the two latter systems reagentsolvent on addition of crown ether the rates get greater 103 and 23 times respectively. It was established in [1] that for lithium phenolates the predominance of the ortho-substitution described by the. value AA*Ho/ decreased with reduced electrondonating power of the subsmuent m the phenolate, i.e., with reduced activity of the nucleophile. It was assumed [1, 5, 9] that this change occurred with sir str respect to the value AA Ho/p [AA~ Ho/p = AA:#Ho/p + solv # # str ~ solv 9 9 A A Ho.t p , A A So.l p = A A. So.t p + A A So.l p , activation . . parameters governing the orientation and caused P

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respectively by operation of structural (str) and solvation (solv) factors]. Taking into account the above and the other circumstances the predominance of the ortho-substitution in reactions with phenolates containing strong donor substituents was associated with the character of electron density distribution in compound I; it meant essentially the application of a model where the orientation arose due to the factors of an "early" transition state. If so, then the operation of the other factors shifting the position of the transition state along the reaction coordinate in direction of the intermediate t~-complex should result in further decrease in the predominance of the ortho-substitution in the value AA*Holp, and at temperature corresponding to the enthalpy control of the o/p ratio should occur decrease of the latter. It is reasonable to presume that association of the counterions of the reagent may be such a factor. Since the Gibbs free energy of solvation with ammonia decreases in going from Li + to K+ [8], the degree of contact in ion pairs grows for the phenolates of alkaline metals in the same series, and the activity should decrease corresponding to the approach of the transition state to t~-complex. Since the experimental dependence o/p ratio on the cation nature observed in this study is opposite to that derived from the above reasoning it should be interpreted proceeding from the other factors that override the variation of the value AA ustr caused by association of the counterions of "" olp the reagent or effect the change in the other activation parameters governing the orientation (AA*HoS)'p Iv, solv str AAr So~ p or AA~:So/~. Thus the character of ionic association may considerably affect the value ^~ ^ * t _ /~s t9ro / p in the transition state of the ortho-substitution that is electrostatically unfavorable due to repulsion of the some like charges belonging to the adjoining oxygen atoms of the phenolate moiety and the nitro group [17]. In [3] is presumed that this repulsion was to a great measure relieved at coordination of the alkali metal cation with the mentioned oxygen atoms, and it should result in a change in the parameter AA, H~,/r str in 9 favor of the ortho-substitution. In keeping with the above mentioned change in the Gibbs free energy of solvation of alkali metal cations with ammonia [8] it is presumable that transition from Li + to K+ should be accompanied with stronger contact of cation and the negative sites of the chelate complex, and conA A ~:/--/str sequently result in a change of the parameter ,_~ "o/p in favor of the ortho-substitution. Since the orthosubstitution is advantageous from the enthalpy OF

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REACTIONS OF AROMATIC COMPOUNDS WITH NUCLEOPHILIC REAGENTS viewpoint, and at temperatures corresponding to enthalpy control of the o/p ratio the increase of the latter is achieved9 In the similar way the smaller growth of the o/p ratio in the phenolate series containing electronacceptor substituents compared to those with electrondonor substituents in going from Li + to Na § and then to K§ (Table 4) may be rationalized as prevailing influence of the extent of contact between the oppositely charged fragments in the transition state of the ortho-substitution on the value AA~:/./Sir ~ "o/r~ At the fixed alkali metal cation its bond with the oxygen atoms apparently weakens as the density of the negative charge on the oxygens decreases, i.e. at greater electron-acceptor power of the substituent in the phenolate. Therefor at relatively lesser contact of counterions in the transition state the variation in cation nature should less affect the value A . . .A~/-/sir . o/1,and consequently the o/p ratio. According to this interpretation the dependence of orientation on the nature of nucleophile (Table 4) for reactions with potassium phenolates may apparently be regarded as due to a certain prevalence of the effect of changes in extent of contact between counterions over the repulsion of the negative charges localized on oxygen atoms, whereas in the reactions of sodium phenolates these effects cancel out each other. Considering the possible changes in the other activation parameters governing the orientation we should note that prevalence of para-substitution over A A#K'sIr ortho-replacement with respect to parameter ,.~ %/p may be caused [10] by hindrance to some intramolecular motions in the transition state of the orthosubstitution due to "clutch" of the nitro group between two geminal substituents. In keeping with above it should be expected that formation of the cation-containing six-membered chelate cycle would result in some additional "rigidity" of the transition state of ortho-substitution, and consequently to increased advantage of para-substitution with respect to structural entropy factor. In this connection note that in going from lithium phenolates where participation in the reaction of free anion of the nucleophile was assumed [9] to the reactions of sodium and potassium phenolates occurred increase in o/p ratio, i.e. the change was the opposite to that expected basing on the change in the quantity AA, So!p str . that was due to the formation of the chelate complex. This apparently means that the analysis of the experimental pattern should not be limited to consideration of contribution of structural factors into the activation parameters governing the orientation. RUSSIAN JOURNAL OF ORGANIC CHEMISTRY

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Similar to the conclusions in [10] the effect of cation variation in the nucleophile on the quantity AA*SoS~ Iv apparently should be ascribed first of all to .P the different decrease in the number of solvent molecules surrounding cations in going from reagents to the transition state of chelate type. It is obviously less for Na § than for K§ since the coordination number of the former is smaller [8]. However the specific free energy of cation solvation is greater with Na § [8], and due to the opposite effects of the gAA,ivenfactors respectively on the values AA*SoS)'tv ~ and H o/p s~ the change in their relative contributions into the difference of activation free energies of the competing processes at cation variation may be of complicated character. In this connection note that published data and experimental findings of this study may be qualitatively predicted by a formal model describing the dependence of the activation entropy of the competing processes AA*So/_ on the character of ionic association. The model proceeds from the already mentioned data [4] that the separation of the ion pair of the nucleophile at addition of crown ether to the reaction system sharply increases (by two and more orders of magnitude) the rate constant of fluorine substitution located in para-position to nitro group, whereas the rate constant of ortho-substitution does not change significantly. To the first approximation these data may be illustrated by the shift along the ordinate of the straight line logk P vs 1/T relative to a similar plot for ortho-substitution. This shift corresponds the change in the relative activation entropy for isomeric substrates at alteration in degree of contact of oppositely charged fragments in the transition state, AA*So and AA*S_ whereas the relative values of activation enthalpy A~*Ho and AA*Hp remains about the same. From the shift of the plot logkp follows the changed position of the projection of the intersection of the lines logkp and logko onto the abcissa axis (the reciprocal o f "isokinetic temperature"). With decrease in the contact of the ion pairs the reciprocal of isokinetic temperature grows (the isokinetic temperature gets lower) at relative entropic feasibility of para-substitution; on the contrary, this value would decrease (the isokinetic temperature would rise) at relative entropic preference of the

ortho-substitution. The relative activation parameters of methoxydefluorination of ortho- and para-fluoronitrobenzenes treated with MeONa [12, 13] evidence the entropic preference of the para-substitution; at the same time the isokinetic temperature is close to -130~ [5], and consequently at 25~ and higher kp > ko. In methanol transition from MeONa to MeOK results No. 6

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apparently in more tight contact of ion pairs, and in the framework of the model under consideration it should lead to higher isokinetic temperature. Actually, at 25~ the relation of reaction rate constants of the isomeric fluoronitrobenzenes with MeONa in going to MeOK is reversed . , (kP . > ko) [4], corresponding to transfer of the ~sokmetlc temperature into the region over 25~ The addition of crown ether apparently decreases the contact in the ion pair, and it should result in decrease of the isokinetic temperature. Actually, the experimental [4] relation of reaction rate constants for o- and p-nitrofluorobenzenes with MeOK in MeOH (kp > ko) evidences the shift of the isokinetic temperature below 25~ Similar reasoning may be applied also to the reactions of isomeric nitrofluorobenzenes in the system i-PrOK-iPrOH at 75~ [18]. The sum of the data from [5, 9] indicated that aryloxydefluorination of compound I by phenolates ( l l a - h - l V a - h ) in the liquid ammonia at -35~ and lower occurred at enthalpy control of the o/p ratio, and the ortho-substitution is preferable because of enthalpy (o/p ratio > 1). This means that the isokinetic temperature is higher than -35~ In going from Li + to Na § and then to K§ at the fixed substituent in the phenolate, i.e. at increasing extent of contact in ion pairs, the isokinetic temperature should grow, accordingly increasing the predominance of the ortho-substitution. Addition of crown ether into the reaction of compound I with potassium phenolate lVa decreases the extent of contact in the ion pairs and thus should decrease the isokinetic temperature and accordingly the o/p ratio. Analogous to this reasoning due to lesser contact in the ion pairs in going from electron-donor to electron-acceptor substituents in the phenolates should decrease the changes in the isokinetic temperature and in o/p ratio caused by cation variation. All these conclusions from the model under consideration are in agreement with the experimental data (Tables 2, 3). EXPERIMENTAL 19F NMR spectra were registered on spectrometer Bruker WP-200 SY from solution of reaction products in ethyl ether (concentration ~50 vol%), internal reference hexafluorobenzene.

Reagents and solvents. 2,4-Difluoronitrobenzene (I) was prepared by procedure [1]. m-Cresol was distilled, the boiling point was consistent with the published value [20]. m-Chlorophenol was prepared as in [21], m-fluorophenol was obtained analogously from m-fluoroaniline. Phenol, p-cresol, p-methoxy-

phenol, p-fluorophenol, and p-chlorophenol of "pure" grade were used without preliminary purification. Liquid ammonia was purified by dissolving therein of metallic sodium (3 wt%) followed by distillation into the reaction vessel cooled to -78~ just before the start of the experiment. Metallic lithium, sodium, and potassium were freed from the surface oxide film under anhydrous heptane and were weighed just before charging into the reaction vessel. Dicyclohexyl-18-crown-6 and 15-crown-5 obtained from OKhP NIOKh of Siberian Division, Russian Academy of Sciences, tetramethylethylenediamine, and 1,4-diaminobutane of "pure" grade were used without preliminary purification. Dimethoxyethane was purified by procedure [22]. Hydroxides of tetraethyl and tetrabutylammonium (50% water solutions) were used without preliminary purification.

Preparation of tetraalkylammonium phenolates Va, Via. Tetraethyl- (Va) and tetrabutylammonium (Vla) phenolates were obtained on mixing the equimolar amounts of phenol and the appropriate tetraalkylammonium hydroxides in benzene with subsequent distilling off water-benzene azeotrope, then benzene, and drying the residue in a vacuum. The resulting oily compounds showed in the JH NMR spectra the expected signals and no impurity signals. Preparation of solutions of meta- and para-Yphenolates of alkali metals IIa-g-IVa-h in liquid ammonia. To 75 ml of liquid ammonia cooled to -4~ was added while stirring 0.003 g-atom of alkali metal. To the blue solution obtained was added --0.005 g of FeCI3...6H20, and stirring was continued till arose a suspension of an amide of the corresponding metal with simultaneous decoloration of the reaction mixture. Then was charged equimolar to amide quantity of meta- or para-Y-phenol (c 0.04 mol l-l). The formation of alkali metal phenolate was revealed by disappearance of amide suspension.

Reaction of 2,4-difluoronitrobenzene (I) with alkali metal phenolates lla-g-IVa-h and tetraalkylammonium phenolates Va, Vla in liquid ammonia. To the stirred solution of phenolate of alkali metal or tetraalkylammonium at -35~ in one portion was added 1 g of 2,4-difluoronitrobenzene (c 0.08 mol l-l), and the stirring was continued for 620 min. Then the reaction mixture was poured on cooled to -50~ suspension of 2 g of ammonium chloride in 100 ml of ethyl ether, and the mixture was stirred. On completion of ammonia evaporation 50 ml of water was added to the residue, and the products were extracted into ethyl ether (2...50 ml). The combined extracts were washed with 5% water


REACTIONS OF AROMATIC COMPOUNDS WITH NUCLEOPHILIC REAGENTS solution of NaOH (2...50 ml), then with water (50 ml), and dried with MgSO 4. The ratio of compounds of VII and VIII type in the mixture of the reaction products obtained on evaporation of the solvent was determined by 19F NMR spectroscopy using the data from [1, 6] on chemical shifts of fluorine signals in the spectra of the mixtures under study: ~62 ppm for compounds of type VII, and ~50 ppm for compounds of type VIII. The data on the ratios VII/VIII obtained are given in the article and in Tables 1-3.

9.

10. 11.

REFERENCES 12. 1. Politanskaya, L.V., Malykhin, E.V., and Shteingarts, V.D., Zh. Org. Khim., 1997, vol. 33, no. 5, pp. 703-710. 2. Reichardt, Ch., Losungsmittel-Effekte in der Organischen Chemie, Verlag Chemie, 1969. Printed under the title Rastvoriteli v organicheskoi khimii, Leningrad: Khimiya, 1973, pp. 74-78. 3. Kimura, M., Sekiguchi, S., and Matsui, K., Koguo Kagaku Zasshi., 1970, vol. 73, no. 3, pp. 513-516. 4. Del Cima, F., Biggi, G., and Pietra, F., J. Chem. Soc., Perkin Trans. II, 1973, no. 1, pp. 55-58. 5. Kizner, T.A. and Shteingarts, V.D., Zh. Org. Khim., 1985, vol. 21, no. 11, pp. 2376-2382. 6. Masud, T., Kimura, M., Seino, Y., and Sawaguchi, H., Koguo Kagaku Zasshi, 1970, vol. 73, no. 3, pp. 516-518. 7. Gordon, A.J. and Ford, R.A., The Chemist's Companion, New York: Wiley-Interscience, 1972. 8. Plowman, K.R., and Lagowski, J.J., J. Phys. Chem., 1974, vol. 78, no. 2, pp. 143-148; Lemley, A.T. and Lagowski, J.J., J. Phys. Chem., 1974, vol. 78, no. 7,

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