Indian Journal of Chemistry Vo1.368, July 1997, pp.590 - 595 Sulfonation of arylamines : Part VII-Kinetics of thermal decomposition of tetramethyldianilinium sulfates Gurdip Singh", Inder Pal Singh KapoorzyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM & Jyotsna Singh Department of Chemistry, University of Gorakhpur, Gorakhpur 273 009, India Received 26 April 1996; revised and accepted 25 September 1996 Tetramethyldianilinium sulfates (TMDAS) have been prepared and characterised. Thermal de- composition of these salts has been studied by TG and kinetics evaluated using Prout-Tompkins equation. Activation energies of these salts are found to be linearly related to theutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLK pKa of the corre- sponding amine. It has been found that TMDAS give dimethylaminobenzenesulfonic acids (DMAB- SA) via solid state reaction induced by heat. A reaction scheme representing the thermal decompo- sition pathways of these salts has been suggested. The proton transfer (unimolecular elementary reaction) seems to be the primary step which is followed by a bimolecular step (sulfonation) for the decomposition of these salts. Extensive studies have been made on the prepar- ation, characterisation and thermal decomposition of ring monosubstituted arylammonium sulfates 1-7. It has also been found that these sulfates undergo decomposition to ring substituted aminobenzene- sulfonic acids which find applications" in organic syntheses, dyestuffs, medicines and tanneries. Re- cently, we have investigated the thermolysis of di- methylaniJinium nitrates'! and perchlorates III. Not much work has been reported on tetramethyldian- ilinium sulfates ll - 12 (TMDAS). As a part of our ongoing research programme, TMDAS have been prepared and characteriscd. The kinetics of ther- mal decomposition of these salts have also been undertaken. Materials and Methods Materials like 3, 4-, 2, 5- and 2, -l-dimcrhylani- lines (DMA) (E. Merck); sulfuric acid (AR QuaJi- gens); silica gel G TLC grade (Oualigcns) and bar- ium chloride (BDH) were used as received. Preparation and characterisation of TMDAS.-White precipitates of the sulfates of 3, 4-, 2, 5- and 2, 4-dimethylanilines were obtained immediately on reacting eonc. sulfuric acid with the corresponding amine in 2: I molar ratio at room temperature (RT), and the reaction is shown in Scheme I. The precipitates were washed thrice with ethyl acetate to remove the unreacted amine. All sul- fates were recrystallised from doubly distilled wa- ter after concentration (under vacuum), the crys- tals vacuum dried, and the purity was checked by TLC. These salts were characterised by microan- alysis and spectroscopy 13-1,. They were found to decomposes before melting, and arc nonhygro- scopic and quite stable at room temperature. 3, 4, 3', 4'-TMDAS Anal. Calcd for C1h H 2 .jN 2 SO.j: C, 56.47; H, 7.06; N, R.24. (Found: C, 56.50; H, 7.50; N, R.04°/c,; UV(H 2 0): 332.H (Jog E O'()H), 2RR.O (0.33), 26R (O.R7), 260 (1.12), 235.6 (1.61), 216.4 (3.42) nm; MS (relative inten- sity) m/z 120( 100), 121(30.7), 106(49.6), 92(15.9), 79(23.0), 77(70.0), 59(17.0), 53(62.0), 50(25.0), 43(29.0); IR(KBr): 3390-3465 br, 25RO m, 1945 m, 1600 s, 156R m, 1494 s, 1450 m, 13R2 S, 133() m, 12RR s, 1245 m, 1215 m, l1R5 rn, 1100 br, 1072 m, 103R m, R74 s. 2, 5, 2', 5'-TMDAS: Anal. Calcd for C U ,H 2 .jN 2 SO.j: C, 56.47; H, 7'()6; N, R.24. Found: C, 56.49; H, 7.35; N, R.12%; UV (H 2 0): 2R1.6 (log E 0.2R), 271.2 (0.31), 232 (0.65) and 20R.H (2.97) nm; IR(KBr): 3300-3500 br, 2R40- 3040.br, 2565 m, 1570 br, 1504 m, 1290 m, 1190 m, 1100 m, 1042 br, 985 s, 962 m, 872 m, ROO s; IH NMR (DMSOD(,): () 6.70-7.40 (6H, aromatic), 4.3 (6H, NH,); 2.3( 12H, Me). 2, 4, 2', 4'-TMDAS: Anal. Calcd for C1Il H 2 .jN 2 SO.j: C, 56.47; H, 7.06; N, R.24. Found: C, 56.52; H, 7.34; N, 8.16%; MS (relative intens- ity): rn/z 104(100) 229(24.1), 197(16.0), 180(20.0), 153(36.0), 151(20.0), 121(43.0), 120(88.0), 119(60.0), 105(60.0), 90(29.0), 77(92.0), 75(18.0), 64(15.0), 53(16.0), 52(15.0), 51(33.0), 42(15.0): IH NMR (DoO): () 2.1(12H, Me), 6.68-6.94(6H, aromatic). -