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

Kinetics of Carboxylic Acid Catalysed Hydrolysis ofFormamide : Evidence for Specific Hydronium Ion

Catalysis

(Mrs.) S. MITrAL, K. S. GUPTA & Y. K. GUPTA·Department of Chemistry, University of Rajasthan.

Jaipur 302 004

Received 18 June 1981 j accepted 26 September 1981

The kinetics of the hydrolysis of formamide at 65° catalysedby acetic, propanoic, glycollic, formic, mono-, di- and trichloro-,and trifluoroacetic acids obey the rate law:

d[N~;+] = k2 [H+] [HCONH2].

where [H+] is the concentration of hydrogen ions formed due toequilibrium dissociation of above mentioned acids. An analysisof kinetic results shows that the hydrolysis is specific hydroniumion catalysed and there is no detectable contribution from thegeneral acid-catalysis.

A LTHOUGH the acid and alkaline hydrolysesof aliphatic ami des have been the subject of

several studies, it is not yet clear whether theseare subject to general acid-base catalysis. Onlyrecently the alkaline hydrolysis- of acetamideand its N-substituted derivatives has been shown tobe general base catalysed. For the same amide thecatalysis by acetic acid by prototropic mechanism,i.e. general acid catalysis has been reported- at220°C. For other ami des such studies do not appearto have been carried out. The acid hydrolyses ofamides are, in general, slow and more so in thepresence of weak acids, requiring higher tempera-tures, (e.g. 220°C for acetamide) to get meaningfuland measureable rates. The acid hydrolysis of for-mamide is comparatively faster and has a measurablerate in the presence of carboxylic acids at 65°. We,therefore, decided to examine the effect of severalcarboxylic acids on the rate of its hydrolysis to seeif the reaction proceeds by general acid or specifichydronium ion catalysis.

The chemicals used in this study were: formamide(Koch-Light, AR), acetic and monochloroaceticacid (BI?H, ~R or AR), formic acid (BDH, LR),propanoic acid (Narden), glycolic acid (ReidelDehan, A. G.) dichloroacetic acid (Reidel LR)trichloroacetic acid (E. Merck) and trifiuor~aceti~acid (Reidel Prosynth). The kinetics were followed byestimating ammonia by forrnol titration methods-",The results w~re reproducible within ± 5 %.

Concentration of formic acid was varied from0.1 to O.4M at 65° keeping [HCONH2] = O.IM.As noted in the hydrochloric acid catalysed hydro-lysis", the kinetics were overall first order. Theeffect of some eight other carboxy lie acids wasalso examined by determining the first order rateconstants (koh.) in the presence of added acids(O.IM) at the same temperature. The values of kobsare given in Table 1.. In the acid hydrolysis of amides, the first stage isthe transfer of a proton to the substrate, RCONH2(ref. 6): In specific hydronium ion catalysis, onlyH30+ IS able to transfer proton to amide moleculeand the rate law, in this case, would be

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TABLE 1 - VALUESOF FIRST ORDER RATE CoNSTANT (kobo)IN PRESENCEOF DiFFERENTCARBOXYLICACIDS AT 65° AND-

[HCONHsJ = O.1M

Acid [Acid] K~[Ml

103[H+1 10" kobo(M) (sec-')

Acetic 0.1Propanoic 0.1Glycollic 0.1Formic 0.1Formic 0.2Formic 0.3Formic 0.4Chloroacetic 0.1Dichloroacetic 0.1Trichloroacetic 0.1Trifiuoroacetic 0.1

1.754 X 10-' 1.3161.754 x 10-' 1.3161.48 x io= 3.7741.77 x 10-4 4.1031.77 x 10-' 5.831.77 x ro> 7.171.77 x 10-0 8.291.349 x 10-' 10.965.623 x 10-' 51.962.19 x 10-174.605.89 x 10-1 87.11

6.16.1

22.217.324.031.942.048.0

211.0403.0432.0

Av.=

4.64.65.94.34.14.45.04.44.15.45.04.7±0.5

(a) Taken from reference (5). K« values were obtained at25° except for CI.CHCOOH (18°) and C1.CCOOH (20°).

d[N:t ] = k2[H+] [RCONH2] ••• (1)

or kobs = k2 [H+] ... (2}

Ho.wever, if the hydrolysis is susceptible to cata-lysis b?, proton tr~nsfe~ fron: acids other than (andlll~ludlllg) ~ydrollJum ion, It is a case of generalacid catalysis and the experimental rate law in thepresent case, where only one Bronsted acid other thanH30+ is present, would be given by Eq. (3)

kobl = k2 [H+] + k'2 [RCOOH] ... (3}If H30+ is the only effective catalyst present in

the system th~. rate 'Yill depend on the [H:t]because the ability of different carboxylic acids to-catalyse. the ~ydrolysis of. HCONH2 will not dependon the identity of the acid per se but on its abilityto create H30+ ion in solution. In this situationthe values of kObs/[H+] in accordance with the ratelaw (2) would be constant. To test this hypothesisthe equilibrium [H+] resulting by the dissociation ofdifferent carboxylic acids was calculated using theirtabulated dissociation constants", Kd (Table 1). Thevalues of kOb,/[H+] so computed are reasonablyconstant. The agreement in kobs/[H-"] values shouldbe considered satisfactory although Kd and koblrefer to different temperatures. '

The plot of.kob' and [H+] is shown in Fig. 1. Inaccordance. with rate law (2) it is linear passingt~rough origin. These observations are compatibleWIth the rate law (3) if k' 2 [RCOOH]~O under ourexper!me~tal conditions, i.e. there is no significantcontribution from general acid catalysis.

From the slope of the line in Fig. 1 the value ofk2 is found to be 4.8 ± 0.3 x 10-3 litre mol-1 sec+!which is in good agreement with the value of 5.7 +0.3 x 10-3 litre mol-l secl determined usinghydrochloric acid as catalyst", This also shows thatin the present reaction there is no significant con-·rtibution from general acid catalysis.

4!lO

400

350

300

·U 250.,'"~

'".00 O.

"" 200J:>!2

150

100

15 9030 45 60

103 [H+]. fA

Fig. 1 -- Plot of kObo and [H+] for the hydrolysis ofHCONH.catalysed by weak acids at 65°.

References1. YAMANA, T., MIZUKAMJ, Y., TSUJI, A., YASUDA,.Y. &

MASUDA, K., Chem. pharm. Bull., 20 (1972), 881.2. WYNESS., K. G., J. chem. Soc .. (1958), 2934.3. HAWK, P. B., Practical physiological chemistry (P.

Blackiston, Philadelphia), 1920, 525.4. MITrAL, S., GUPTA, K. S. & GUPTA, Y. K., Indian J.

Chem. 15A (1977), 827.5. ALBERT, A. & SERGEANT, E. P., Ionisation constants,

(John Wiley, New York), 1962.,6. BENDER,M. L. & BRUBACHER,L. J., Catalysis and enzyme

action (McGraw Hill, New York, 1973, 48.7. MITrAL, S., Kinetics and mechanism of the hydrolysis of

some amides, Ph. D. Thesis, University of Rajasthan,Jaipur, 1978.

Kinetics of Ag(l) Catalysed Oxidation of AlicyclicAlcohols by Peroxydisulphate

S. P. SRIVASTAVA-& V. K. GUPTADepartment of Chemistry, University of Roorkee,

Roorkee 247 672and

R. G. SHARMA& B. P. SINGH-N. A. S. College, Meerut and D. P. College, Anupshahr

Received 26 August 1980; revised 12 November 1980; re-revised27 April 1981; accepted 14 May 1981

The AgO) catalysed oxidation of cyclopentanol, cyclohexanol.and cycloheptanol by peroxydisulphate in aqueous medium is'first order in K2S20. and AgO) and zero order in alcohol. Thesalt effect is negative and of primary exponential type. Eachreaction is suppressed by the addition of allyl acetate. A radicalmechanism is proposed and 'the corresponding rate expression·derived.

NOT ES

THE kinetics of oxidation of both aliphatic=sand aromatic alcohols'< have been reported

in the literature, but the kinetics of Ag(I) catalysedoxidation of alicyclic alcohols by peroxydisulphatehas not been studied so far. However, Thiagrajanand Venkatsubramaniant and Mushran and co-workers? have studied the kinetics of oxidation ofthese alcohols by bromine and chloramine-T respec-tively. In this communcation, we report thekinetics of Ag(I) catalysed peroxydisulphate oxida-tion of cyclopentanol, cyclohexanol and cyc1ohep-tano!.

K2S20S' AgN03, substrates and other reagentswere either of E. Merck (GR) or BDH (Analar)grade. K2S20S was used after recrystallisation fromdoubly distilled water. The progress of the reactionwas followed by estimating unreacted peroxydisul-phate iodometrically=v.

The stoichiometry of the reaction was evaluatedby the graphical method-s. Under the condition[S20~-] > > [substrate] at fixed catalyst concentra-tion it was found that one mol of K2S20S reactedwith one mol of alcohol in accordance with Eq. (1),where (CH2)4 CHOH represents cyclopentanol

(CH2)4 CHOH + S20~- ----*(CH2)4 CO + 2HSO~ ... (1)

The main product of the reaction was the corres-ponding ketone, identified by spot tests and furtherconfirmed by TLC and IR spectral studies of the2,4-DNP derivative.

As the self-decomposition of peroxydisulphate isappreciable under the present experimental condi-tions and is known to follow first order behaviour,the rate of oxidation of substrate has been determinedby subtracting the rate of self-decomposition of theoxidant from the observed rate.

The order of reaction is found to be one in [S20~-]and zero in [substrate] which is a general feature ofperoxydisulphate oxidations=v. However, thefirst order specific rate decreases with the increasein [K2S20S] at constant ionic strength (Table 1).We believe that the behaviour is due to the presenceof trace impurities even in AR sample of K2S20S'This type of behaviour has also been observed inthe case of Ag(I) catalysed oxidation of aromaticalcohols by peroxydisulphate ion-.

The first order rate constant remains almost un-affected even by an eight-fold increase in [substrate]

TABLE1 - EFFECTOF VARYING[K2S.O.] AT CoNSTANT IONICSTRENGTH

([Substrate] = O.OIM;

[K.S20.] [K.SO.]X W(M) x W(M)

[AgN03] = O.OOIM; temp.=35°q

k x; 103(min-1)

Cyclopenta- Cyclohexa- Cyclohep-nol nol tanol

2.5 17.5 9.4 7.9 4.25.0 15.0 8.' 7.4 3.87.5 12.5 8.2 6.9 3.6

10.0 10.0 7.8 6.6 3.212.5 7.5 7.5 6.2 2.815.0 5.0 7.1 .5.8 2.6

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