4504
A. R.AMELL,C. G. HOULEAND WILLIAM A. CILLEP [CONTRIBUTION FROM THE
Vol. 81
DEPARTMENT OF CFiEMISTRY OF THE UNIVERSITY OF NEWHAMPSHIRE]
The Exchange of C1*between Urea and Cyanate and between Cyanate and Carbonate B Y ALEXANDER R. AMELL,CONRAD G, HOULEAND W'ILLIAIII A. CILLEY RECEIVED FEBRUARY 12, 1959 The exchange of C14 between labeled urea and cyanate ion has been studied a t 80". The experimentally determined rate equation has the form R = kl(urea) k2(urea)(OCN-). At 80°,kl is 2.5 X 10-6 sec.-l and k, is 1.2 X 10-6 M-l sec.-l. Two possible mechanisms are given. Both mechanisms lead t o a rate equation of the form found. The two mechanisms are discussed. No exchange occurs between urea and cyanate at room temperature. No exchange of C14 occurs between labeled carbonate and cyanate a t temperatures u p to 80'.
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Introduction The hydrolysis of urea,' the formation of urea from ammonium cyanateZ and the hydrolysis of cyanate, a all have been widely studied in aqueous solution. It is generally accepted that in the nonenzymatic hydrolysis of urea, ammonium cyanate is an intermediate. The hydrolysis of cyanate probably is through an intermediate of carbamic acid, and thus the complete hydrolysis of the urea would be through cyanate and carbamic acid. In the enzymatic hydrolysis of urea, the mechanism most consistent with experimental data appears to be the so-called carbamic acid mechanism' in which the urea goes to carbamic acid, which then reacts to form carbon dioxide and ammonia. A study of the rates of exchange of carbon-14 between the various binary systems of urea, cyanate, carbonate and carbamate, combined with the present knowledge of the rates of decomposition and formation of these interdependent compounds, might help elucidate the mechanisms. In this paper the results of the exchange between urea and cyanate and between cyanate and carbonate are reported. The results of exchanges in the other systems will be reported later. Experimental Reagents.-C.P. potassium cyanate was recrystallized accorcliiig to the procedure in "Inorganic Syntheses."6 Tests for carbonate and ammonia on the recrystallized p r o d y t were negative. Analysis for cyanate was made as previously described,aa and showed a minimum of 96% cyanate. CWabeled urea was purchased from Tracerlab with a specific activity of 1.46 millicuries per millimole. For these experiments the urea was diluted with C.P. urea which had been recrystallized from alcohol. The active urea was dissolved in ethyl alcohol, the inactive urea added, the total urea dissolved and then precipitated by evaporation of the alcohol a t room temperature and reduced pressure. Melting point of the urea was 132". This urea was used in all exchange reactions involving urea. The specific activity of this urea was determined by diluting a small weighed sample with a weighed sample of inactive urea and hydrolyzing this mixture t o carbon dioxide. The carbon dioxide was frozen out in a trap immersed in liquid nitrogen and counted according t o the procedures of Christman.' 7 7 . $729 (1) W. M. R . Shaw and J. J. Bordeaux, THISJOTJRNAI,. (1956). (2) A. A. Frost and R. G. Pearson, "Kinetics and Mechanism." John Wiley and Sons, Inc., New York. N. Y.,1953, p. 257. 78, 6234 (195G); (b) I. A. Kemp (3) (a) A. R . Amell, TAISJOURNAL, and G. Kohnstam, J. Chetn. Soc., 900 (19.56); (c) M , W.Lister, Can.J . Chcm., 33, 420 (1955). (4) J. H.Wang and D. A. Tarr, Tnxs JOURNAL. 77, 6205 (1955). (5) "Inorganic Syntheses," Vol. 11, McCraw-Hill Book Co., Inc., New York, N. Y., 1940, p. 86. (6) D.R. Christman, N, E. Day, P. I
