Indian Journal of Chemistry Vol. 49B, November 2010, pp. 1556-1560
Note Solid state synthesis of ring-substituted aminobenzenesulphonic acids Inder Pal Singh Kapoor, Manisha Kapoor & Gurdip Singh* Department of Chemistry, DDU Gorakhpur University, Gorakhpur 273 009, India & Roland Fröhlich Organisch-Chemisches Institut, Universität Münster, D-48149 Münster, Germany E-mail:
[email protected] Received 23 June 2009; accepted (revised) 31 August 2010 Treatment of 2-methoxyaniline and 3,5-dichloroaniline with conc.H2SO4 in 2:1 molar ratio at RT affords the corresponding sulphate salts. These salts have been characterized by X-ray diffraction and spectral analyses. Both these salts are found to form ring substituted aminobenzenesulphonic acids in solid state, via proton transfer, under thermal and microwave irradiations. Keywords: Aminobenzenesulphonic acid, solid state synthesis, sulphonation, proton transfer
Sulphanilic acid (4-aminobenzenesulphonic acid) and ring-substituted aminobenzenesulphonic acids constitute an important class of chemically and medically significant compounds, which finds application in sulpha drugs, dyestuffs and organic synthesis1. Over the past years, a number of ring substituted phenylammonium sulphates have been prepared2-6 which on heating (under vacuum) in solid state afforded corresponding aminobenzenesulphonic acids. It is generally agreed that thermal decomposition is initiated by proton transfer (a primary and rate determining step) from +NH3 to SO4-2 ion. Recent studies of the thermal decomposition of nitrates and perchlorates7 revealed that these salts too involve proton transfer (N-H bond heterolysis) process. Nowa-days there is growing interest in microwave irradiation due to less time and high yield as compared to conventional heating. This paper reports the preparation, crystal structure, thermal and microwave studies on di-(2-methoxyanilinium)sulphate [Di-(2-MA)S] and di-(3,5dichloroanilinium) sulphate [Di-(3,5-DCA)S]. The results indicate that under solvent-free conditions,
thermal and microwave treatment transform these salts to corresponding substituted aminobenzenesulphonic acids by proton transfer reaction followed by sulphonation. Experimental Section Samples of 2-methoxyaniline and 3,5-dichloroaniline (supplied by S.d. fine) were purified by distillation. Microwave reaction was conducted in a commercial household microwave oven model (MS 1921 HE, LG electronics private Ltd). Further homemade tube furnace8 was used for under vacuum (conventional) heating purpose. Preparation and characterization of Di-(2-MA)S and Di-(3, 5-DCA)S salts The sulphate salts of 2-methoxyaniline and 3,5dichloroaniline were prepared by the reaction of corresponding amine and conc. H2SO4 in 2:1 molar ratio at room temperature without use of a solvent (Scheme I). Rapid reaction yields white crystalline solid. The resulting products di-(2-MA)S and di-(3,5DCA)S were washed with diethyl ether and ethyl acetate to remove the unreacted amine. Di-(2-MA)S and di-(3,5-DCA)S were thereafter recrystallised, under vacuum at room temperature from water (21 hr) and methanol (10 hr) to affords pure salts di-(2-MA)S (m.p. 178°C, yield 58%; Rf 0.58; mobile phase: chloroform:acetic acid:benzene; locating reagent: iodine) and di-(3,5-DCA)S (m.p. 210°C, yield 59%; Rf 0.91; mobile phase: chloroform:acetic acid:benzene locating reagent: iodine). These salts were identified by X-rays and FTIR analyses. Crystal structure determination of di-(2-MA)S and di-(3, 5-DCA)S Suitable single crystal of di-(2-MA)S and di-(3,5DCA)S were obtained by recrystallizion from aq. solution and methanol respectively, to give pink plates and white needles. The data collection on the crystals of di-(2-MA)S and di-(3,5-DCA)S was done at low temperature (223 K) using a Nonius Kappa CCD diffractometer equipped with a rotating anode
NOTES
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NH2
OCH3 OCH3
+
H2SO4
OCH3
2+ + NH3SO4H3N
RT 2:1
Di-(2-MA)S NH2
+ Cl
Cl
Cl
Cl
H2SO4
2+ + NH3SO4H3N
RT 2:1 Cl
Cl
Di-(3,5-DCA)S
Scheme І
generator Nonius FR 591 (ref. 9). The structure was solved by direct methods (program SHELXS-97) (ref. 10) and refined using SHELXL-97 (ref. 11). Hydrogen atoms were placed in geometrically calculated positions using a riding model. Images were created with the SCHAKAL program12. Refinement with anisotropic thermal parameters for non-hydrogen atoms led to R values of 0.045 and 0.038 respectively for di(2-MA)S and di-(3, 5-DCA)S. The molecular geometries of salts are shown in Figure 1. The crystal data and structure refinement are summarized in Table І.
O3 O1 O4
S1 C3
N11
C4
C2
C5
C19
O2
C12
N1
C7
O18
C13
C17
C6 O8
C14
C16 C15
C9
(a) Di-(2-Methoxyanilinium) sulphate
Thermal analysis Non-isothermal TG of sulphate salts (mass 20 mg, 100-200 mesh) were undertaken in static air at a heating rate of 10ºC/min using home made TG apparatus13 fitted with temperature-cum-controller. The accuracy of the furnace was ±1°C. A round bottom gold crucible was used as sample holder. The fractional decomposition (α) vs temperature (ºC) thermograms for salts are presented in Figure 2. Conversion of sulphate salts into corresponding substituted aminobenzene-sulphonic acids The quantities of the reactants were kept same under both sets (thermal and microwave) of reaction conditions. Conventional (thermal) process The samples of di-(2-MA)S and di-(3,5-DCA)S were heated, in a tube furnace at 250 and 240ºC for 40 and 35 min under reduced pressure. Each residue was then washed with a solvent and recrystallized from water (concentrated under vacuum) and their purity was checked by TLC. The reaction products were identified, respectively as 3-methoxy-4-aminoben-
O2 S1
O3
O1 O4 N1
N11
Cl14 C13 C2
C3
C12
C14
C17 C7
Cl4 C4 C5
C15
C16
C6 Cl6
(b) Di-(3, 5- dichloroanilinium) sulphate Figure 1 ― Crystal structures of sulphate salts
Cl16
INDIAN J. CHEM., SEC B, NOVEMBER 2010
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Table І ― Crystal data and structure refinement for di-(2-MA)S and di-(3,5-DCA)S Crystallographic data Emperical formula Formula weight Temperature Wavelength Crystal system, space group Unit cell dimensions
Di-(2-MA)S (C7H10NO)2SO4 344.38 223(2) K 0.71073 Ǻ monoclinic, P21/c a = 6.9782(2) Ǻ b = 11.1279(3) Ǻ c = 20.7394(6) Ǻ β = 95.487(1)°
Volume Calculated density Crystal size Limiting indices Refinement method
1603.09(8) Ǻ3 1.427 Mg/m3 0.40 × 0.20 × 0.15 mm -9
