INDIAN J. CHEM., VOL. 20A, APRIL 1981

Kinetics & Mechanism of the Oxidation of AliphaticAlcohols by Sodium N-ChlorQbenzenesulphonamide in

Acid Medium

JOGESHWARMUKHERJEE& KALYANK. BANERJI*Department of Chemistry, University of Jodhpur,

Jodhpur 342 001

Received 1 May 1980; revised 23 July 1980; acepted29 August 1980

The title reaction is first order each with respect to the oxidant,alcohol and hydrogen ions. The primary kinetic isotope effect(kH/kD), in the oxidation of ethanol, has a value of 4.79±0.05at 298K. The solvent isotope effect. k(H.O)/k(D.O) is 0.420at 298K. The reaction exhibits a reaction constant p* = -2.20at 298K. The probable oxidizing species is PhSO.NHCI. Amechanism involving transfer of a hydride ion to the oxidantis suggested.

REPORTS are available in the literature about .the mechanism of oxidation by CAT and

NBSl,2. However, no information is available aboutthe mode of reaction of sodium N-chlorobenzene-sulphonamide (chloramine-B or CAB). In thisnote we report the kinetics of oxidation of nineprimary alcohols (RCH20H; R = H, methyl, ethyl,n-propyl, i-propyl, n-butyl, s-butyl, MeOCH2 andCICH0·

Most of the alcohols used were of AR quality. Pre-paration and specifications of others have been des-cribed earlier", The isotopic purity of IX,IX-dideuterio-ethanol (CHaCDPH), as ascertained by its PMRspectrum was 92 ± S%. Perchloric acid was usedas a source of hydrogen ions.

The reactions were arranged to be under pseudo-first-order conditions i.e. [alcohol] > > [CAB] .Thereactions were carried out at constant temperatureand were followed iodometrically. The pseudo-first order rate constant, k-; was computed from theplot of log [oxidant] against time. The solvent wasalways 1:1 (vjv) acetic acid-water unless men-tioned otherwise. . '

T~e o;x:idation ?f ethanol by CAB in 1:1 (v/v)acetic ac~d-water, III t~e presence of perchloric acid,resulted I? the formation of acetaldehyde, which wascharacterised and estimated as its 24-DNP deri-vative. The reaction exhibited al :1 'stoichiometryin accordance with Eq. (1)

PhSOzNCI- + MeCHzOH -----+PhSOzNH2 + MeCHO + Cl" .. (1)

The reaction is found to be first order each withrespect to oxidant, alcohol and acidity and is notaffected by added radical scavengers like allyl acetate(up to 0.02M). The oxidation of ethanol under Nat:n:osphere fai~e~ to induce polymerisati~n of acry:lonitrile. Addition of benzenesulphonamide (upO.OSM) did not affect the rate.

The oxidation of IX,IX-dideuterioethanol showed aprimary kinetic isotope effect, kH/kD of 4.79 ± O.OS

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at 298 K. The rate constants for the oxidation inH20 and D2.0 (overall Dp = 9S%) at 298 K are105 k = 2.94 and 7.00 litre" mol ? see"? respectively •The solvent isotope effect, k(H20)/k(D2.0), is 0.42.In this set of experiments no acetic acid was addedto the reaction mixture......The rates of. oxidation of nine different primaryalcohols were determined at different temperatures(Table 1) and activation parameters evaluated(Table 2).

~ot much i~form.at.ion is available about the equili-bria present III acidified CAB solution. Assumingthat CAT and CAB behave similarly, the possibleoxidising species in acidified CAB solution arePhS02,NHCl, PhSOzNCI2. and HOC!. Dichlora-mine-B can be ruled out as the active oxidisingspecies in view of the strict first order dependence onCAB. Further, nil effect of added benzenesulphona-mide precludes both HOCI and PhSONClz as theoxidising species. This leaves PhSOoNHCI as themost probable oxidising species. -

The large primary kinetic isotope effect confirmsthat the rate-determining step involves cleavage ofhydrogen from carbon bearing hydroxyl group.

The activation enthalpies and entropies are linearlyrelated (r = 0.9998). The correlation has beentested and found genuine by applying Exner's cri-teriorr'. Isokinetic temperature computed from theplot is 40S.7K.

The oxidation rates of the nine primary alcoholscorrelate well with Taft's 0'* values". The reaction

TABLE 1 - RATE CONSTANTSFOR THEOXIDATIONOF PRIMARYALCOHOLS(RCH.OH) BY CAB

Substituent 10' k (litre" mol=" see-I)(R)

298 303 308 313K

H 66.0 120 212 380Me 796 1240 1900 2860Et 1320 2000 2920 4370n-Pr 1420 2140 3140 4720i-Pr 2120 3030 4420 6400n-Bu 1550 2300 3390 4920s-Bu 2290 3300 4900 6920MeOCHj 57.7 105 188 330CICH2 3.90 8.53 17.8 37.3

TABLE 2 - ACTIVATIONPARAMETERSFORTHEOXIDATIONOFALCOHOLS (RCH20H) BY CAB

Substituent £:,.Ht 6S:j: £:,.G:j:(R) (kJ mor-') (J mol-l K-I) (kJ morl)

H 90.0 -44.4 103Me 66.0 -104 97.0Et 61.4 -116 96.0n-Pr 61.2 -115 95.5i-Pr 58.2 -123 94.8n-Bu 59.5 -121 95.6s-Bu 57.5 -125 94.5MeOCH2 90.3 -44.6 104CICH2 116 19.6 110

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constants at 298K and 313K are -2.20 (r = 0.9993)and ~ 1.80 (r=0.9999) respectively. The largenegative reaction constant and substantial kineticisotope effect indicate a considerable carbonium ioncharacter in the transition state. The above resultspoint to a hydride ion transfer in the rate-determin-ing step.

The following mechanism may then be proposed.K

PhS02NCI - + HaO+ ~ PhS02NHCI + H20 .. (2)HI F'.i. n.. k2

R~C-H +CI-NHS02Ph -+ RCHOH +I -NHS02Ph+HCl .. (3)

OH+ fast

RCHOH ~--+ RCHO + H+ -- .. (4)fast

PhS02,NH- + HCI ~----+ PhS02,NHa + CI- (5)

Thanks are due to the UGC, New Delhi forfinancial assistance.

l,References1. CAMPBELL,M. M. & JOHNSON,S., Chern. Rev.,78 (1978),

65.2. VENKATASUBRAMANIAN,N. & THIAGARAJAN, V., Can.

J. Chern., 47 (1969), 694.3. BANERJI,K. K., Bull. chem. Soc. Japan, 46 (1973), 3623.4. EXNER, 0., Colln Czech. Chern. Commun., 29 (1964),

1094.5. WELL, P. R., Linear free energy relationships (Academic

Press, London), 1968,35.

Kinetics of Oxidative Deamination & Decarboxylationof Some Amino Acids by Diperiodatocuprate(III)

in Alkaline Medium

K. BAL REDDY, B. SETHURAM& T. NAVANEETHRAo*Department of Chemistry, Osmania University,

Hyderabad 500 007

Received 30 July 1980; accepted 18 August 1980

The kinetics of oxidation of glycine, alanine, phenylalanine,valine, leucine and serine by diperiodatocuprate(III) in alkalinemedium has been studied. The order in [amino acid] and[Cu(III)] is one each. The rate decreases with increase in [OH-]and [periodate], The products of oxidation are CO2, NHa andthe corresponding aldehydes. A probable mechanism consistentwith the observed results is discussed.

DIPERIODATOCUPRATE(III) (DPC) hasbeen used in the estimation of amino acids-,

Cu(III) is also shown to be an intermediate in theCu(II)·catalysed oxidation of amino acids by per-oxodisulphate". Therefore it Was worthwhile tostudy the kinetics of oxidation of amino acids bydiperiodatocuprate(III) in alkaline medium.

All the chemicals used were of AR(BDH) grade.Amino acids were either Fluka or BDH products.DPC was prepared by a method given earlier". The

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course of the reaction was followed by measuringthe absorbance of unreacted DPC at 413 nm atregular time intervals, using Carl Zeiss spectrophoto-meter. The reactions were usually followed upto50 to 60 % completion. The molar absorption co-efficient ofCu(IIl) under our experimental conditionswas 1.0 x 104 litre mo)-l cm". Blank reactions werecarried out and necessary corrections made for anyself-decomposition of DPC during the reaction.

Under the conditions employed the products of thereaction were identified 4 as ammonia, carbon dioxideand the corresponding aldehydes. Stoichiometricstudies, carried out by adding dropwise DPC ofknown concentration to 0.1 M glycine until no furtherdecolourisation occurred, revealed that one mol ofamino acid required 2 mol of DPC.

Under the conditions [AA] » [DPC] the plot oflog [absorbance] versus time was linear showing thatthe reaction is first order in lDPC] (Fig. lA). Thiswas also confirmed by varying [DPC], which didnot show any change in pseudo-first order rate con-stants (k'). The reactions also exhibited a first orderdependence in [AA] (Fig. IB). At constant [DPC],[AA] and temperature the rate decreased withincreasing [OH-] and also [periodate] (Table 1).

The diperiodatocuprate(III), [Cu(I06hF- has beendemonstrated to exist as an aquo or hydroxyhydro-periodatocuprateflfl)" which we prefer to expressas Cu(HL)2 in our discussion. The effect of perio-date on the rate of oxidation is similar to that ob-served in our earlier work" suggesting monoperio-datocuprate(III) to be the active species of DPC inthe oxidation of amino acids.

Contrary to the earlier observation in the oxidationof alcohols by DPC3 the rate decreased with thejncreasing [OH-] at constant [DPC], [AA] and[IO~]. This could be due to the existence of theequilibrium (1) in alkaline medium.

According to equilibrium (1) the rate should decreasewith the increasing [OH-] if the dipolar form of theamino acid is the reactive species. This was foundto be true, indicating that dipolar form of the aminoacid is the reactive species even in alkaline medium.

TABLE 1- EFFECT OF VARYING[KOH] AND [KIO.] ON RATEOF OXIDATIONOFGLYCINE

[Cu(III)] = 5.10 x 10-5M; [Glycine] = 2.00 x 10-3M;temp = 300K

[KOH] [KIO.] k'x 10" [KOH] [KIO.] k' x 10'X 10' X 10· (mirr") x 10' x to- (mirr=)(M) (M) (M) (M)

1.0 6.8 5.40 4.0 6.8 2.402.0 6.8 3.70 1.0 3.4 7.102.5 6.8 3.20 1.0 10.2 4.03

. 3.0 6.8 2.80 1.0 20.4 2.80

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