Mahadevappa, D. S.

Naidu, H. M. K.

English

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INDIAN J. CHEM., VOL. 14A, OCTOBER 1976Ka1 Ka,OC.II.CONH.+OH- .= -OC8H,CONH2 .=-OC.H.COXH-+H20 .)/).,.,)1.Scheme 1line medium. The observed pH-rate profile indi-cates that the contribution to the rate through thedianionic tetrahedral addition intermediate is al-most negligible probably due to the presence ofionized phenolic group. The steady state treatmentto the reactive tetrahedral addition intermediate(D) leads to the kinetic Egn (2).k k 1(a1 [OH-121 J Kw .IKobs= (k_1+k?)(1+ ~: [OH-] + ~:1.~~[OH-]2)... (2)The Eqn (2) is further reduced to the Eqn (3)by applying the condition that1«~:[OH-] + ~:. ~: [on-J2)which is satisfactorily acceptable as Ka1is of theorder ,.....,10-8.k1kz(OH-]Kobs = (k_1+kJ( 1+~:-=-'[-O-H--]-"-)Eqn (3) is similar to the best fitted empiricalEqn (1) withB - (k1+k2) tc.; d1- kk 'K-an1 2 wAt relatively higher [OH-]1< Kat [OH-] is found toKwpronounced and henceto Eqn (4),K _ klk2obs - (k-l +k2)Ka.IKwwhich shows that the rate is independent of [OH)The authors thank Prof. "V. Rahman for provid-ing facilities, and the CSIR, New Delhi, for financialassistance to tW0 of them (KA. and M.N.K.).... (3)B _ (k_l+k~2 - klk2the conditionbe kinetically moreEqn (3) is further reduced... (4)References1/REID, E. E., Am. chem. j., 21 (1899), 284; 24 (1900),397.2. KOSHY, K. T., j. pharm. Sci., 58 (1959), 560.3. BRuI~E, T. C. & TAN:<ER, D. W., J. org . Chem., 30 (1965),166'8.4. DARKE, D., SCHOWEN, R. L. & JAYARAMAN, H., j. Am.chem. Soc., 95 (1973), 454.5. BIECHLER, S. S. & TAFT (Jr), R. "V., j. Am. chem, Soc.,79 (1957), 492ii.6. POLLACK, R. M. B: BENDER, ~1. L., j. Am. chem . Soc.,92 (1970), 71 CWo ,7. STAUFFER, C. E., J. Am. chem, Soc., 94 (1972), 1791.8. ERIKSSON, S. 0., Acta pharm. Suecica, 6 (1969), 1J9.808J,4.15.KHAN(_1. N. & KHAN, A. A., j. org. Chem., 40 (1975),179J.BUNTON, C. A., N,WAK, B. & O'CONl'!OR, C., J. org,Chem., 33 (1 '.168;, 51·2. .BENDER" lVI, L., GINGER, ~. D. & KElVIP, K c.. j. Am.cheni. Soc., 76 (1954). 3~.)0; 80 (19S8), ID44. /YAKOYAMA, F.,.f. phar ni. Soc. Japan, 63 (1943),,5.HALE, C. H., HALE, M. x. & JONES, "V. II., Anolyt,ci-.« .. 21 (1949), 15,49.LY:-1E, x. R., j. phys. cu;«, 69 (1965), 6137.BU:<To:-1, C. A., FARRER, S. J., M[LBANK, A. J. G.,O'CO:-1XOR, C. j. & 'feRNEY, J. A., J. chem, Sac, PerkinII, (1972), 1869,Kinetics of Oxidation of Cinnamyl Alcohol withChloramine- T in Hydrochloric Acid MediumD. S. l\IAHADEVAPPA & H. M. K. NAIDUDepartment of Postgraduate Studies & Research inChemistry, University of Mysore, Mysore 570006Received 15 July 1975; accepted 6 Ma'Ych 1976The kinetics of oxidation of cinnamyl alcohol bychloramine-T in the presence of hydrochloric acid(0·1-0·3M) has been studied at 0°. The reaction showsfirst order dependence on [chlorarntne-T], second orderin [H'r] and is independent of [substrate). The energyand entropy of activation of the reaction have beenfound to be 57·2 KJ mole= and -75·01 .TK-I respec-tively. The Arrhenius factor is 1·203 x 10· sec=. Ionicstrength and presence of p-toluenesulphonamide havevery little influence on the rate of reaction. The pro-posed mechanism assumes a stepwise addition of twoprotons to release the precursor chloriniwn Ion, whichon hydrolysis yields H.OCI+. The latter attacks thesubstrate in a fast step to form the reaction products,cinnamic aldehyde and p-toluenesulphonamide.thatIT was earlier! noticed that cinnamvl alcohol in50% aq, ethanol (v/v) underwent ready oxidationby chloraminc-T (CAT) in the presence of HCI(0·1 to O'3M'). The results of kinetic studies of thisreaction are reported in this note. Since the re-action is fairly rapid at room temperature (25°),the kinetic runs were made at 0°.Chloramine-T (E. Merck) was purified by themethod of Morris at al.2 and its aqueous solutionstandardized by the iodometric method. Stocksolutions of cinnamyl alcohol (Naarden, b.p. 256·6°)were prepared in 50% aq. ethanol (vJv). A concen-tratcd solation of sodium perchlorate was used tokeep the ionic strength constant. All other chemi-cals used were of analytical reagent grade. Theexperimental procedure has been described earlier'.Stoichiometry- Reaction mixtures containing ex-cess CAT over cinnamyl alcohol in the presenceof HCI (overall concentration, 0·5 to 1·0M) were keptat room temperature (25°) for 24 hr. Estimationof the unreacted CAT showed that one mole ofcinnamyl alcohol consumed one mole of CATcorresponding to a two electron change. Theproducts were identified as cinnamic aldehydeand p-toluenesulphonamide3.Kinetics of the reaction was studied at severalinitial [cinnamyl alcohol] and [CAT]. When theTABLE 1- EFFECT OF VARYING INITIAL [CINNAMYLALCOHOL] AND [CHLORAMINE-Tl ON RATE CONSTANT{Solvent: aq. ethanol (50%. v!v); [H+J=0-2M; !1-=1-0Al;temp. = O°C}hi X 10' [Clllor-sec-1 tlmine-TJo!'il[Chlor-arnine-T'[,111[Sub-strate],M[Sub-str.itc],Mhi X 10'see-I0-005 0-10 5-114 0-008 0-10 5-0480-005 0-15 5-318 0-009 0-10 5-1780-005 0-20 5-230 0-005* 0-10 5-1140-005 0-30 5-157 O-OOst 0-10 5-1410-005 0-40 5-160 O-OOSt 0-10 5-1810-006 0-10 5-290 0-005** 0-10 5-8730-007 0-10 5-124 O-OOs§ 0-10 4-984* In presence of excess p-toluenesulphon:l1nide_[ Ionic strength 0-5M_tIonic strength l-SM_··Solvent: ethanol-water (60% v[v],§Solvent: ethanol-water (40% vIv)-TABLE 2 - EFFECT OF VARYING [H+] ON THE REACTlO:-1RATE{[Chloramine-TJo = 0-005.11; [Substratc'[, = 0-1M;!I. = I-OM; temp. = O°C}[H+lM 10'k, 102hd [H+].vT 10'k, 102k,!sec-t [H+}2 sect- [l-P)'0-1000-1250-1500-1751-2371-9962-8063-8231-2371-2771-2481-2480-2000-2250-2500-3005-1146-4667-80911-1501-2781-2771-2491-239TABLE 3 - EFFECT OF VARYING TEMPERATURE 0:-1REACTION RATE([Chloramine-T]o = 0-005M; (Substrate) = 0-lM; [H+) =0-2111; !I. = I-OM}Temp. hi X10' Temp.(OK) sec-' (O,q273-0 5-114 282-4278-1 8-482 285-5280-3 10-710 288-012-1215-6820-66alcohol is in large excess, a plot of log (a/a-x)versus time is found to be linear. The pseudo-firstorder rate constants (k1) in CAT are recorded inTable 1. It is found that the reaction is first orderwith respect to [CAT] and is independent of [sub-strate]. The reaction rate increases with an increasein [HCl] (0·1 to 0·3M) and the ratio k1/[H+J2 isconstant (Table 2). Further, a plot of log kl versuslog [H+] is linear with slope 2_ Hence the rate ofreaction is proportional to [H+]2.The thermodynamic parameters were calculatedby carrying out the reaction at different tempera-tures (Table 3)_ The values are E" = 57·2 K]mole:", Arrhenius factor A = 1·203 + 0·044 X 109sec+; ASt =-75·01 ± 0·08 f K:', -On varying the ionic strength of the medium from0·5 to 1·5M, the rate constant was unchanged(Table 1). Further, the rate was unaffected bythe addition of excess of p-toluenesulphonamide(Table 1). The dielectric constant effect on thereaction was followed at different ratios of ethanol-water mixtures and the rate constant increasedslightly with the increase in ethanol content (Table 1)_Chloramine-T is a strong electrolyte which dis-NOTESsociates in aqueous solution asRNCINa ~ RNCI- + Na"where R = P-CH3CaHtS02·The active chlorine in the compound is assumed tobe positive chlorinium ion (Cl") which is fo~edby a stepwise addition of two protons to the amonRNC1- as follows:k,RNCl- + H+ ~ RNHCI ... (1)»:k,RNHCl + H+ -s- RNH2 + cr- ._.(2)The Cl" ion is only a precursor for the protonatedH20Cl+ which could be the oxidizing species inchloramine-T oxidations.k,Cl" + H~O --+ H~OCl+ ... (3)Ias tfastH,OCl+ +C6H4CH = CHCH20H --+- C6Hr;CH = CHCHO + HCI + H30+ ... (4)Reaction (2) is assumed to be slowest and ratedetermining, which also accounts for the absenc~ ofany significant effect .of RNH2 on the reaction,The chlorinium ion (Cl"] produced in step (2) under-goes hydrolysis by a rapid step to give H2~Cl+.This provides an alternate path to the hydrolysis ofRNHCI giving rise to HOCI which is subsequentIy pro-tonated in acid medium as shown in Eqs, (5) and (6).RNHCl + H20 ~ RNHJ + HOCI (5)HOCI + Cl+ ;;=: H20Cl+ (6)It is probable that the bypassing of reactions (5)and (6) by (2) and (3) is to be expected in chlor-aminometric oxidations at higher acid concentra-tions. Reaction (4) is also a fast step in the oxida-t ion. H20Cl+ can form a chloronium complex ofthe type CeH5CH = CHCH20HCIOH~ with thesubstrate by a fast step. The complex undergoes aproton abstraction reaction promoted by the re-elec-tron cloud in the substrate leading to the formationof cinnamic aldehyde. Applying steady-state con-ditions for RNHCI in steps (1) and (2) we getd[CAT] k1k2[CAT] [H+] 2----= +dt k_l + k2 [H ]By a consideration of the initial rates of the re-action, the termolecular rate constant k = kIk2/k_lis found to be 0·05 litre- mole-2secI_ From thisvalue, k2 is calculated as 8·5 X 10-5 mirr '. Since klis fairly high, k., ~ k2 [H+] would be a reasonableapproximation. With this assumption, the ratelaw becomes_ d[CAT] = k[CAT][H+Pdtwhich is in agreement with the experimental results,The rate of disappearance of CAT is independent oft he ionic strength of the medium suggesting aninteraction between an ion and a neutral molecule.This is further supported by the small increase in kwith the decrease in dielectric constant of themedium and the observed stoichiometry cif thereaction.One of the authors (D_S_M.) is grateful to theUGC, New Delhi, for financial assistance.809INDIAN J. CHEM., VOL. 14A, OCTOBER 1976References1. l\IAHADEVAPPA, D. S. & NAIDU, H. M. E., A1!.~t.J. Chem.,27 (1974), 1203; 28 (1975), 899.2. MORRIS, J. C., SALAZAR, J. A. & WINEnIAN, M. A., J. Am.chem. Soc., 70 (1948), 2036.3. NAIDU, H. M. K. & MAHADEVAPPA, D. S., Indian ]: Chem.,13 (1975), 976.Diamagnetic Susceptibilities ofSome Cyclic DialkylsilylamidoximesA. B. GOEL"Chemistry Department, Rajasthan UniversityJ aipur 302004Received 14 January 1976; accepted 6 March 1976The diamagnetic susceptibilities of some newly syn-thesized dialkylsilylamidoximes derived from dialkyl-dichlorosilanes and amidoximes have been determinedand found to be in good agreement with calculatedvalues obtained by the method of Baudot. The XS!and XCH,values have also been reported and the lowervalues of XS! have been explained on the basis of'back- bonding"./DIAMAGNETIC studies have been proved helpfulin the interpretation of structural chemistry ofsilicon". The values of XSi and XCH• calculated for aseries of silicon compounds containing Si-O bondshave thrown light on the nature of Si-O bonding.However, very little attention was paid to thecompounds containing Si-N bond". Very recentlydiamagnetic studies of trialkylsilylamidoximes" anddialkylsilyl derivatives of amidoximes- have beenreported. In this note experimental and the calcu-lated values of diamagnetic susceptibility of cyclicdialkylsilylamidoximes (containing both Si-O andSi-N bonds) and the values of XSi and XCH, for theseseries are being reported and discussed.Precautions were taken to exclude moisturethroughout the experimental manipulations.Freshly prepared and purified samples of dialkyl-silylamidoximes- (I) were used for the diamagneticsusceptibility measurements. Benzene was usedas a reference liquid having specific susceptibility-0·702 X 10-6 cgs units and all the measurementswere carried out at room temperature (38°) byGouy method. For the theoretical value of mole-cular susceptibility, a wave mechanical methodusing the concept of bond susceptibility has beenemployed+".R(HN)C = NOSiR~I II a, R' = CH.b, R' = C,H.The experimentally determined and the theoreti-cal values for diamagnetic susceptibility are sum-marized in Table 1 and exhibit fairly goodagreement.The XM values for. the compounds Ia and Ib(n = 1, 2, 3) reported in Table 1 have been treatedgraphically by plotting molar susceptibility against·Present address: School of Chemistry, Georgia Instituteof Technology, Atlanta, Georgia 30332.810TABLE 1- DIAMAGNETIC SUSCEPTIBILITY DATA FORDIALKYLSILYLAMIDOXIMES (Ia and b)!{ H.' J.M* Dif!. (%)(obs.) betweenobs. and calc.COMPOUNDS OF TI-IE TYPE IaMe Me 81·8 -5·2Et Me 93·0 -4·8Pr Me 105·0 -4·0Ph Me 125·4 -1-6COM' OUNDS OF THE TYPE It>Me Et 105·0 -4·0Et Et: 116·0 -3-6Pr Et 127·5 -32Ph Et 148·2 -1-3+Numencal values ure -10-& cgs units.TABLE 2 - DIAMAGNETIC SVSCEPTIBILITY OF THEMETHYLENE GROUPS AND THE CENTRAL l\IETAL ATOM INIa AND IbJ.CH, AxialinterceptGradientof plct ofX.w vs nCO:\-II'OUNDS OF THE TYPE Ia11·22 11·22 70·47 17·77COMPOUNDS OF TIlE TYPE Ib11·26 11·26 93·22 17-80the length of the alkyl chains in the homologouscompounds. Both the plots were linear and theaxial intercepts of both give the values of molarsusceptibility for the compounds Ia and Ib whenn = O. XSi and XCH, (Table 2) have been obtainedwith the help of these plots using the standardvalues 6.9, ~O.The lower values of XSi (17·77 and 17·80) incomparison to XSi for Si-C system (reported to be21·00 for tetra-compounds) is explainable by • back-bonding' to the silicon atom from oxygen andnitrogen lone-pairs forming (p -+ d) re-bonding.These results are consistent with earlier findingsfor dialkylsilyl derivatives of amidoximes' (systemscontaining two Si-O bonds). The relatively lowervalues can be attributed to the lower electronegati-vity of nitrogen (in comparison to oxygen) permit-ting relatively stronger re-bonding. Further, theseXSi values are consistent with that for monomericdialkylsilyl derivatives of amidoximes ; supportsproposed symmetrical structure (II) for dimericdialkylsilylamidoximes''.'-./N-O-Si-NH-C-RII nR-C-HN-Si-O-NAIIThe author wishes to thank the CSIR, New Delhi,for financial support.References1. MITAL, R. L. & GUPTA, R. R., Tnorg, Chim. Acta Reus.,4 (1970), 97.2. ABEL, E. \\T., BUSH, R. P., JENKINS, C. R. & ZOBEL, T.,Trans. Faraday Soc., 60 (1964), 1214.3. GOEL, A. B. & GUPTA, V. D., Indian]. Chem., 13 (1975),. 181.

Kinetics of Oxidation of Cinnamyl Alcohol with Chloramine- T in Hydrochloric Acid Medium

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Kinetics of Oxidation of Cinnamyl Alcohol with Chloramine- T in Hydrochloric Acid Medium

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