COMMUNICA TlONS

Kinetics & Mechanism of HalogenativeOligomerization of Mesityl Oxide by

Chloramine-T: Evidence for a Novel Pathwayin Aqueous Sulphuric Acid*

TABLE 1- STABILITY CONSTANTS OF MIXED LIGANDCOMPLEXES

[Temp. = 25°; !1. = 0·1 (NaCIO.); pH = 4'0]

System Stability constant Ref.

~Ni(en)~+~4Ni(cN)1-

KfJi)~n.K,K2k3K.' s,K,K2K,K2K121

~112

2'40 X 10132·54 X 1030

1·50 X 10'2·39 X 109

1'08 X 10-7

1'37 X 107

1·05 X 103

1'42 X 1010

1·37 X 107

4·29 X 1015

789

This workdodododododo

Formation rate of tetracyanonickelate(II) - The rateof reaction was measured by monitoring the forma-tion of [Ni(CN)i-] with time spectrophotometricallyat 267 nm (e = 1·16x 104M-I em-I) and 285 nm(e = 4-63 X 103M-I cnr+). Kinetic runs were carriedout in the presence of large excess of cyanide underconditions described above.

Excellent pseudo-first order: plots were obtained onplottion log (A -At) vs time (Fig. 1). A variable depen-dence of rate o~ [cyanide] was observed as in the caseof aminocarboxylatesv". The slopes of these plotsgave first order rate constant k3 and second orderrate constant K2k3. Third order dependence wasnot seen in this case though the same has been re-ported for some aminocarboxylates--".

Dissociation rate of tetracyanonickelate(II) inpresence of excess ethylenediamine - The rate ofreverse reaction was measured by observing thedisappearance of Ni(CN)~- at 267 nm or 285 nm.The reverse reaction was forced in the presence oflarge excess of ethylenediamine. The reverse re-notion is first order in [Ni(CN)~-], first orderIn [ethylenediamine] and inverse first order in[cyanide]. The value of reverse rate constant k;(= K4Ik_3) was calculated from inverse first orderplots (not shown).

Evaluation of stability constants of mixed inter-mediate complexes - The values of forward andreverse rate constants as determined above madeit possible to evaluate the stability constants ofintermediates of steps (1) and (2) as defined inEqs. (6) and (8). These values and also the valuesof other constants that have been used in thesecalculations are given in Table 1.References1. KUMAR, K. & NIGAM, P. C., Paper presented at Annual

Convention of Chemists (India), 1977.2. KL:MAR, K., NIGAM, P. C. & PANDEY, G. S., J. phys. cu»;

(in press).3. COO~!BS, L. C., MARGERUM, D. "V. & NIGAM, P. C., Tnorg,

Chem., 9 (1970), 2081.4. COOMBS, L. C. & MARGERUM, D. W., Inorg. Chem., 9 (1970),

1711.5. MARGERUM, D. "V., BYDALEK, T. J. & DISHOP, J. J., J.

Am. chem. Soc., 83 (1961), 1791.6. PAGENKOPF, G. K., J. coord. Chem., 2 (1972), 129.7. DAVIES, T., SINGER, S. S. & STAVELEY, L. A. K., J. chem,

Soc. (Lond.), (1954), 2304.8. CROUSE, "V. C. & MARGERUM, D. W., Inorg, cu-«, 7

(1968), 2239.9. CAULLET, c.. Bull. Soc. cu«, s-: (1963), 688.

S. VIVEKANANDAN, K. VENKATARAO & M. SANTAPPA

Department of Physical Chemistry, University of MadrasGuindy Campus, Madras 600025

and

SP. SHANMUGANATHAN

Department of Chemistry, Pachaiyappa's CollegeMadras 600030

Received 26 April 1978; accepted 23 May 1978

The kinetics of the reaction between mesityl oxideand chloramine-T (CAT) in aqueous sulphuric acidin the presence of KHSO. has been studied. Theresults indicate a radical chain mechanism to beoperative which is quite novel in CAT kinetics.

CHLORAMINE-T (CAT) has estab!ished itselfas an efficient and dependable OXidant and a

versatile chlorinating agent in chemical analysis--'and in reaction kinetics=". Only simple productsha ve been noticed so far in its reaction withsubstratess", We report in this communi~ation .ourkinetic evidence for a novel halogena tive oligo-merization of mesityl oxide (MO) by chloramir.e-Tin aqueous (O'375M) sulphuric acid.. .

In the presence of KHS04, the r~actIO!l manifestsa typical fractional order behaVIOur, i.e. a clean1·5 order in [CAT] and a 0·5 order at low [MO]«O·OI5M) which changes to zero. order . ~md~rpseudo conditions (1 :.15).. Thi~ is. qurte f"!luhar l,nfree radical polymerization kinetics. Beslde~ th:sMichaelis-Menten type of behavic:~r, .the rea.ctIOn ISassociated with very fast equilibria dunng theinitial stages. This kinetic evidence fo~ co.mplexformation is supported by the large shifts m theA values for the reaction mixture when com-p~~~d to those of the reactants. A ne&ligible salteffect (fL: 0·477M to 0'777M; k at 40 : 0·219 to0.2671\,1-0•5 sec+) and a marginal increase in ratewith increasing [H30+] (0·113M to 0'375M; ~ at40°: 0·244 to O·320M-0.5 sec+) have been noticed.This beha viour indicates that the ionic mechanismpostulated in reactions involvir,g. CA16 may r.ot.beoperative under our kinetic conditions. The reactionis considerably faster in the absence of. addedmineral acids suggesting <in altogether differentmechanism. Initially added CI. has a markedinfluence on the rate which could be explained byits oxidation to Cl" that helps fz ster prop, gat ionof the chains. The overall activation energy is64·7 kJ mol! (35-50°; k: 0·254 to O·958M-0.5 see-I).Mass law effect is not observed. Ir.stead, the rateincreases slightly with increasing initially cddedp-toluenesulphonamide (PTS) which is one of the

*Presented as a preliminary report at the All I.ndiaseminar on Oxidation-reduction reactions held at the Univer-sity of Madras, January 1978 and with further resultspresented as a paper at the Chemistry symposium heldat the lIT. Madras, March 1978.

519

INDIAN J. CHEM., VOL. 16A, JUNE 1978

Na CH. H 0

/ '" I "{P-H.C.C,H•.S02}·N : CAT; C=C-C-CH •. MO

. R '" Cl CH: 4 3 2 1 .CHa H 0

"'.. I "C-C-C-CH#: M"

/ ICH, Cl

Rrim: C";

Scheme 1

reaction products (2'5x 10-4M to 1X 10-3M; k at40°: 0·267 to 0·309M-o.5 sec-I). This <gain isin contrast to the rate suppression encountered inreactions wherein ionic mechanism is operatives.

Chlorinated oligomeric material Were found to bethe other reaction product. Further, the reactionshows variable stoichiometry clearly ir.dicatir g thatthe nature of the reaction products markedlydepends on reactant concentratiors, kinetic condi-tions and reaction time? Separate kinetic studiesusing dichloramine-T rule out its involvement in thekinetic scheme under our experimental conditions.Further, induced polymerize tion of acrylonitrileshows the involvement of free radicals in thesystem .. All these experimental facts lead us to aradical chain mechanism (Scheme 1) which is quitenovel in CAT kinetics.CAT+H+ ~ CH+Na+MO(keto)~ MO(enol)

KMO(enol)+CH ~ CM

1<.CM-+C'+M"

•.. (1)•.. (2)

•. .(3)

•.. (4)

•.. (5)

••. (6)

• .. (7)

k,M"+M-+M2

k,.C·+M -+ M'+PTS

fl.M'+M-+M2

•.. (8)

520

k,M~+CH -+ Oligomeric material +C'

k,

... (11)

where[CM]

K = [CATJt[M]t ... (12)

[M], ~ [M], (t = total: f = free)Since the major CAT consuming step is only (9),the first term on the right hand side of (1l) willnot be signifier nt which is in agreement with theobserved order for the reaction.

The present work indicates for the first timethe potentiality of CAT as an initia tor in freeradical polymerization. Further investigations (i) onsuch polymeriz ..tior s, (ii) with other a~-ursa tura tedsystems, and (iii) in different solvent enviror mar.tsare in progress.

One of the authors (S.V.) is grateful to the UGC,New Delhi for a teacher research fellowship.

References1. JENNINGS, V. ]., CRC Crit. Rev. Anal. Chem., 3 (1974),

407.2. SHANMUGANATHAN, SP. & VIVEKANANDAN, S., Indian J .

Chem., 15A (1977), 428.3. MAHADEVAPPA, D. S. & NAIDu, H. M. K., Indian J.

Chem., 14A (1976), 808.4. RADHAKRISHNAMURTHI. P. S. & SAHU, B., Indian J.

Chem., 15A (1977), 700.5. MUSHRAN, S. P., SANEHI, R. & AGRAWAL, M. C., Z.

Naturforsch, 27B (1972), 1161.6. NATARAJAN, M. M. & THIAGARAJAN, V., J. chem. Soc.

Perkin II, (1975), 1590.7. A complete and detailed discussion of the product

analysis and identification under our kinetic and otherdifferent conditions by TLC, GLC and elemental ana-lysis and UV, IR, NMR and mass spectral studiesappears elsewhere.