Kapoor, Inder Pal Singh

Singh, Gurdip

Singh, Jyotsna

NOPR

Indian Journal of ChemistryVo1.368, July 1997, pp.590 - 595Sulfonation of arylamines :Part VII-Kinetics of thermal decomposition oftetramethyldianilinium sulfatesGurdip Singh", Inder Pal Singh Kapoor & Jyotsna SinghDepartment of Chemistry, University of Gorakhpur, Gorakhpur 273 009, IndiaReceived 26 April 1996; revised and accepted 25 September 1996Tetramethyldianilinium sulfates (TMDAS) have been prepared and characterised. Thermal de-composition of these salts has been studied by TG and kinetics evaluated using Prout-Tompkinsequation. Activation energies of these salts are found to be linearly related to the 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 elementaryreaction) seems to be the primary step which is followed by a bimolecular step (sulfonation) for thedecomposition of these salts.Extensive studies have been made on the prepar-ation, characterisation and thermal decompositionof ring monosubstituted arylammonium sulfates 1-7.It has also been found that these sulfates undergodecomposition to ring substituted aminobenzene-sulfonic acids which find applications" in organicsyntheses, dyestuffs, medicines and tanneries. Re-cently, we have investigated the thermolysis of di-methylaniJinium nitrates'! and perchlorates III. Notmuch work has been reported on tetramethyldian-ilinium sulfatesll-12 (TMDAS). As a part of ourongoing research programme, TMDAS have beenprepared and characteriscd. The kinetics of ther-mal decomposition of these salts have also beenundertaken.Materials and MethodsMaterials 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 ofTMDAS.-White precipitates of the sulfates of 3,4-, 2, 5- and 2, 4-dimethylanilines were obtainedimmediately on reacting eonc. sulfuric acid withthe corresponding amine in 2: I molar ratio atroom temperature (RT), and the reaction isshown in Scheme I.The precipitates were washed thrice with ethylacetate 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 byTLC. These salts were characterised by microan-alysis and spectroscopy 13-1,. They were found todecomposes before melting, and arc nonhygro-scopic and quite stable at room temperature.3, 4, 3', 4'-TMDAS Anal. Calcd forC1hH2.jN2SO.j: C, 56.47; H, 7.06; N, R.24. (Found:C, 56.50; H, 7.50; N, R.04°/c,; UV(H20): 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, 25ROm, 1945 m, 1600 s, 156R m, 1494 s, 1450 m,13R2 S, 133() m, 12RR s, 1245 m, 1215 m, l1R5rn, 1100 br, 1072 m, 103R m, R74 s.2, 5, 2', 5'-TMDAS: Anal. Calcd forCU,H2.jN2SO.j: C, 56.47; H, 7'()6; N, R.24. Found:C, 56.49; H, 7.35; N, R.12%; UV (H20): 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 forC1IlH2.jN2SO.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). -SINGH et al.. SULFONA nON OF ARYLAMINES: PART VII 5911.0(0) + -2 + 0 b) + -2 + o cl + -2 + 0H'C~SO'~CH'H:3N S0l. NH3 HJN S0l.~0.8 H'C~ he H3\9 CH3•.•.•.. 0;f!. o.~ H3 H.JC'-' CH3 H3 • CH3 H3Ul •Ul0-.oJ 0.1.-s:01'(l;0.23:A A0.0~o '&fO 220 300 380 300 380 iO 1GO 21.0 320 ['00Terriperature ,DCA-S: Dl'compn.of 3,~,3',4-TMcv.sB-C: Stab. of 2-A-4,S-DMBSAC-D: Dl'compn.ot 2-A-4,S -OMBSAA-B: Dl'compn.oI2,s,z',5_TM~SB-C: Stob. of 2-A -3,5-0MBSAC- 0: Decornpn. of 2-A-3,5-DMBSAA -+8: Decornp n. of 2,4 2'~'-TMDAS, ,B--C: Stob. of 4-A-3,S-OMBSAC-O: Dl'compn.of Z-A-3,S-DMBSAFigure I-TG curves of (a) 3, 4, 3', 4'-TMDAS, (b) 2,5,2', 5'-TMDAS, (c) 2, 4,2', 4'-TMDASConversion of TMDAS to dimethylaminoben-zenesulfonic acid (DMABSA). The samples of 3,. 4, 3',4'-,2, 5, 2', 5'- and 2,4, 2',4'-TMDAS wereheated respectively at 155°, 195° and 180° ± 2°Cin a tube furnace!" for 50 min at 60 ± 2 mm Hgpressure. Each residue was washed with ethylacetate and dissolved in water which on concen-tration under vacuum gave an amorphous solid.Their purity was checked by TLC. These com-pounds were also found to decompose duringmelting and were identifed as 2-A-4, 5-DMBSA,4-A-2, 5-DMBSA, and 2-A-3, 5-DMBSA. Thestructure, physical parameters, and R, values(TLC) of TMDAS and DMABSA are given inTable I.Cross-sulfonation studies!". The samples of allthe three sulfates were heated separately in a tubefurnace with small amount of aniline at the sametemperature and pressure given above for 35 min.The products were separated by preparative TLCusing glacial acetic acid, chloroform, abs. ethanoland n-butanol (1.8:2.6:0.6:1.0) as eluent andidentified as sulfanilic acid, 2-A-4, 5-DMBSA,4-A-2, 5-DMBSA, 2-A-3, 5-DMBSA, 3, 4-DMA,2, 5-DMA, 2, 4-DMA and aniline.Thermogravimetry (TG) studies on TMDAS:(a) Dynamic TG. Analyses of these sulfates (wt 30mg, 200-400 mesh) were carried out in static airat a heatng rate of 5°C min - I using an indigene-ously fabricated apparatus I? The plots showingwt loss (01,) verses temperature (0C) are shown inFigure 1.(b) Isothermal TG. Isothermal TG analyses ofTMDAS were carried out in static air using thesame apparatus and 30 mg of the sample (200-40() mesh) at appropriate temperatures: 270°,285°, 300°, 315°C for 3, 4, 3', 4'-TMDAS; 24(t,255°, 27(t, 285°, 300°C for 2, 5, 2', 5'-TMDAS;and 2100, 220°, 230°, 240°, 250°C for 2, 4, 2', 4'-TMDAS. Wt loss (o,{») versus I (min) plots arcshown in Figure 2.Results and DiscussionWeight loss. Temperature curves (Figure 1) anddecomposition pathways reported in Scheme Isuggest that the thermal decomposition ofTMDAS salts involves more than one steps. Itseems that all salts (Scheme I) decompose in thesolid state (1) via proton transfer (N -H) bondheterolysis to form the corresponding amine andsulfuric acid molecules in condensed phase (3,step ii). However, the N - H bond heterolysis (aunimolecular elementary reaction) occurs throughan activated complex (2, step i). It is reportedl'i-"that the basicity of the anion SO~- increases withtemperature untill it reaches the base strength ofthe dimethylaniline. At this temperature, the anionbase removes a proton from the dimethylanilini-urn ion to form the correspondng dimethylanilineand sulfuric acid molecules in condensed phase(3). The proton transfer has been confirmed byadding a drop of sulfuric acid or amine to the592 INDIAN J.CHEM.SEC H. JULY 19970.5 I I2,L.,2,1.-TMOAS0.1.•0.3 o)t-210~~-220t:.-230~A-2L.0~s-2S0C0.20.18 16 21. 32 1.0 1.80.5I I2,S,2,5-TMOASoX-2L.0~0- 25SJ:4-270S;.-28S~EJ-300C12O.L.0.3olC-270 Co6-28SJ:.- 3000CGI-31S C0.1O.OL-......-l---:-I::--~---:l=---f-=-;-I::------I8 16 2{. 32 1.0 1.8Time (min)Figure 2-ls"thcrmal TC ClII'\C'of '.<1, 3,4, T. 4'-TM[);\S. (b)2.5.2'. 5'-TMDAS. (c) 2. 4. 2'. 4'-TMDASsample during TG. Lower values of a were ob-tained which suggest the shifting of equilibrium tothe left. Such N - H bond heterolysis has alsobeen reported by many workcrs+": c(J~~ for var-ious ammonium and substituted ammonium salts.The dissociation involving proton transfer seemsto be the primary step in the decomposition ofH~+ 2- +~H3yNH3 S04 H3N.~H3C TMDAS(l) CH3Condenspd phase (3)Sulfn 1 'w,+ '9'11'1 +..»,yNI12H3CDMI\AS!\ ( 4 ,Pt - Proton t r an s f o r , Sulfn - s u Lf o na t j onScheme I-e-Thcr rnul decomposition pathways of tctramcthyl-dianilinium sulphateTMDAS. Moreover. cross-sulfonation studieshave proved the formation of the correspondingdimethylanilinc and sulfuric acid molecules in thecondensed phase (3 ).Sulfur trioxide (liberated from H2SOJ seems tosulfonate dimethylanilines at higher temperaturesby bimolecular C-sulfonation in the condensedphase (3, Scheme I, step iii) and the correspond-ing DMABSA' 4 are formed.Dynamic TG curves, presented in Figure 1,clearly show that all sulfates decompose in differ-ent temperature ranges; 3, 4, 3', 4'-TMDAS deco-mpose between 75° and 270°C (Table II, Figure 1apart A -> B) to form 2-A-4, 5-DMBSA (Table 1)which is stable between 275° and 368°C (part A-> C Table II). A wt loss of 43.0% was observedSINGH et al.. SULFONATION OF ARYLAMINES: PART VII 593Table I-Structure, physical parameters and TLC data of tetramethyldianilinium sulfates and dimethylaminohenzenesulfonic acidsSulfate taken Aminobenzenesulfonic acid formedCompd Crystals R/ o«, Structure Crystals Yield Decomp. Tic(%) temp. (0C)Eluent! Spot!(~)3,4,3',4'-Tetramethyl- Light yellow 0.79 5.17 2-Amino-4,5-dime- White 51l.5 366 a:b:c Yellowdianilinium sulfate needles thylbenzenesulfonic flakes (3.5:2:1.5) (0.1l3)(3,4,3'4'-TMDAS) acid (2-A.-4,5-DMBSA)2,5,2',5'-Tetramethyl-dianilinium sulfate(2,5,2',5'-TMDAS)0,1l5 4.53 4-Amino- 2,5-dime-thyl-benzenesulfonicacid (4-A-2, 5-DMB-SA)Grayamorphous2,4,2',4' -Tetramethyl- Whitedianilinium sulfate rectangular(2,4,2',4'-TMDAS) plates0,90 4.89 2-Amino-3,5-dime-thylbenzenesulfonicacid (2-A-3,5-DMBSA)• Eluent, chloroform; locating reagent, iodine; spots, yellowish greent a = Gl.acetic acid; b = benzene; c = acetone; d = abs. ethanol! With iodine ..Dark greenamorphous51l.1 342 a:b:d(4:2:1)Brown(0.82)Yellowplates57,8 320 a:d(2:1.5)Brownishyellow(0.75)Table 11- Thermogravimetric analysis of tetramethyldianiliniumsulfatesCompd Decomposition ofTMDAS· Stability range_________ ofDMABSASdt Fdt(0C) (0C)3,4,3',4'-TMDAS 75 275 275-363°C2, 5,2', 5'-TMDAS 157 264 264-320·C2,4, 2', 4'-TMDAS 87 250 250-326°C* Sdt = starting decomposition temperature; Fdt =final decom-position temperaturewhich is comparable with the theoretical wt lossof 40.9%, The decomposition temperature rangeof 2, 5, 2', 5'-TMDAS is 157-264°C (Figure 1b,part A -+ B) and the corresponding acid (4-A-2,5-DMBSA, Table ]) does not decompose be-tween 264° and 320cC (plateau B -+ C). The ob-served wt loss is 41,0% which is quite comparablewith the theoretical value (40.9%). 2, 4, 2', 4'-TMDAS was found to decompose between 87°and 250°C (Figure l c part A -+ B) giving 2-A-3,5-DMBSA (Table I) which does not decompose,and remains stable in the temperature range 250-3260 (part B -+ C) (observed wt loss, 42.0%.Calcd, 40.9%). Thus, TG studies confirmed theformation of DMABSA from their correspondingsalts. Amines and water formed during decompo-sition escape as vapours at higher temperatures,and DMA were characterised by co-Tl.C, chemi-cal analyses, and water by Karl Fischer reagent".All TMDAS when heated in air at higher tem-peratures gave brownish black material containingDMABSA It was difficult to isolate DMABSAfrom the above material. Thus, to obtain DMAB-SA in a pure form, samples of TMDAS were594 INDIAN J.CHEM.SEC 8, JULY 1997Table Ill+Kinetic parameters for the thermal decomposition oftetramethyldianilinium sulfatesk(1O-2/min) (temp. "C)Salt Ea___________ (kcal/mol)3,4,3',4'-TMDAS2,5,2',5'-TMDAS2,4,2',4'-TMDAS9.06 11.92 25.82 31.92(270) (285) (300) (315)35.00 41.14 42.70 50.78 64.29(240) (255) (270) (285) (300)6.3 13.54 19.12 28.46 36.15(210) (220) (230) (240) (250)18.46.016.8heated in vacuum at a constant temperature in anindigenously fabricated tube furnace. The prob-able structures of DMABSA's are given in TableI. Heating 2-A-4, 5-DMBSA (Figure la, part C-+ D), 4-A-2, 5-DMBSA (Figure l b part C -+ D)and 2-A-3, 5-DMBSA (Figure Ic part C -+ D)beyond 368°, 320° and 326°C, respectively bringsabout decomposition by deamination, desulfona-tion, dealkylation, followed by ring rupture.Isothermal TG of TMDAS in static air gave ac-celeratory curves (Figure 2). The kinetics of thethermal decomposition of these salts(a=0.05 -0.30%) were evaluated using Prout andTompkins equation" (Eq. 1).log a/( 1- a) = kt+ C ... (1)The kinetic parameters are presented in Table III.The values E, (Table III) for the thermal decom-position of TMDAS were found in the order 3, 4,3', 4'-TMDAS > 2, 4, 2', 4'-TMDAS > 2, 5,2'5'-TMDAS. Linear relationship was obtainedwhen E" was plotted against acid dissociationconstant (pK/·7) (Figure 3) which clearly indicatesthat a salt having higher dissociation constant (lowpKa) has a lower value of Ea'It is reported that ortho2H-.'O and meta2:>'.24.31-:>'2methyl groups exert-/ effects and para-methyl ac-tivates the benzene ring due to + / and hypercon-jugative " effects. Thus, in 2, 4, 2', 4'- and 2, 5, 2',5 -sulfates, -/ effect together with the orthdR-30and steric strain:" effects causes weakening of theN - H bond thereby favouring N - H bond heter-olysis. The low value of E; for 2, 5' 2', 5'-TMDASseems to be due to strong -/ effect of m-CH,alongwith ortho and steric strain which causes ea-:+:sy removal of proton (low pKa 4.53) from - NH,to SO~- whereas in 2, 4, 2', 4'- and 3, 4, 3', 4'-TMDAS, the strengthening of N - H bond is dueto hyperconjugative ( + I) electron release from P:CH3•ConclusionsThe kinetic parameters for the thermal decorn--o> 2,5 -e20.02,1.-e3,4-e>.01 15.0...<l1CW§ 10.0-u« 5.0O.O~_----:--;:-_---;-I-;:--_-:f--=: __ L-...JL..L. L..~ 1..8 5.0 5.2pkaFigure 3-Plot of E; versus pKa of TMDASposition of TMDAS have been found to be relat-ed to pKa of arylamines. The N - H bond hetero-lysis seems to be the primary step for the decom-position of salts. An abnormal behaviour of elec-tron-donating group (- CH3) was also observedwithin a class of compounds.AcknowledgementThe authors thanks the Head of Chemistry De-partment for providing laboratory facilities,CDRI, Lucknow for elemental and spectral ana-lyses, and CSIR, New Delhi for financial help toone of the authors (IPSK).ReferencesI Singh G & Kapoor IPS. J Chern Sac Perkin Trans-Z1989.2155. '2 Singh G & Kapoor IPS, Indian J Chern, 298, 1990,57.3 Singh G, Kapoor IPS & Jain M, J Chern Sac PerkinTrans-2, 1993. 1521.4 Singh G, Kapoor IPS & Jain M, Indian J Chern, 358,1996,369.5 Singh G, Kapoor IPS & Jain M, J Indian Chern Soc,1996, revised version communicated.o Singh G, Kapoor IPS & Jain M, Thermochim Acta,3166.1977,1.7 Singh G, Kapoor IPS & Singh J, J Therm Ana~ 1996,revised version communicated.X Lubs H A, The chemistry of synthetic dyes and pigments,(R E Kneger Publ, Malabar, Florida 1982.9 Singh G, Kapoor IPS & Mannan S M, Thermochim Ac-ta. 262. 1995. 117.lO Singh G, Kapoor IPS & Mannan S M, J Energ Mat, 13,1995, 141.11 .Arient J & Pardubis, Czech Patent J PIS, 1973, ChernAbs. 83.1975,96735 f.12 Kanetani F & Yamaguchi H. Bull Chim Sac Iapn, 54,1981,304X.SINGH et al.: SULFONATION OF ARYLAMlNES: PART VII 59513 Dyer J R, Application of absorption spectroscopy of 0""ganic compounds, (Prentice Hall of India, Pvt Ltd, NewDelhi) 1987.14 Ault A & Ault M R, A handy and systematic catalog ofNMR spectra (Mill valley, California) 1980.15 Gunther H, NMR spectroscopy (John Wiley & Sons Ltd)1980.16 Singh G, Vasudeva S K & Kapoor IPS, Indian J Tech-nol; 29, 1991, 589.17 Singh G & Singh R R, Res Ind; 23, 1978,92.18 Erdey L, Gal S & Liptay G, Talanta, 11, 1964, 913.19 Erdey L & Gal S, Talanta, 10, 1963, 23.20 Brill T B, Brush P J & Patil D G, Combust Flame, 92,1993,178.21 Rosser W A, Inami S H & Wise J H, J Phys Chern, 69,1963,1753.22 Patil D G, Jain S R & Brill T B, Propellants ExplosivesPyrotechnics, 17, 1992,99.23 Singh G & Kapoor IPS, Combust Flame, 92, 1993,283.24 Singh G & Kapoor IPS, J Phys Chern, 96, 1992, 1215.25 Dixon J P, Modem methods in organic microanalysis (VanNostrand Londori) 1968.26 Prout E G & Tompkins F C, Trans Faraday Soc, 40,1944,488.27 Dean J C, Langes hand book of chemistry, 13th edn(McGraw Hill;New York) 1985.28 Brown H C & Cohn A, JAm chem Soc, 72, 1950,2930.29 Bennett & Masses, J Chem Soc, 1930,2367.30 Thomson, J Chem Soc, 1946, 113.31 Schlyer P V R & Woodworth G W, JAm chem Soc, 90,1963,6530.32 Lowry T H & Richardson K S, Mechanism and theory inorganic chemistry (Harper and Row, New YOlk) 1976, pp.226,229-250.

Sulfonation of arylamines : Part VII-Kinetics of thermal decomposition of tetramethyldianilinium sulfates

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Sulfonation of arylamines : Part VII-Kinetics of thermal decomposition of tetramethyldianilinium sulfates

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