KINETICS OF CARBAMATE FORMATION AND BREAKDOWN

The rate law for reaction of amines with carbon dioxide is rate = kamine(R2NH)(CO2) + kamine ‘(R2NH) (OH)(CO2), where the first and second terms are for uncatalyzed and hydroxide-catalyzed pathways. The latter reaction, which involves proton abstraction in the rate-determining step, is not observed with all amines. Values for kamine at 10° follow the Brpnsted relationship log kamine (M-1 sec-1) = mpK + Y, with values of m and Y equal to 0.43 and ---1.50 for reactions of primary and secondary amines, and 0.48 and ---0.20 for the reactions of hydrazine and hydroxylamine derivatives. Second-order rate constants for hydrogen ion catalyzed decarboxylation of carbamates formed from amines of pK --- 1.05 to approximately 5 may be fitted to a Brpnsted relationship log ks * (M-1 sec-1) = 0.77pK + 3.6 at 10°. Rates for carbamates formed from moee basic amines are virtually independent of basicity and are approximately 108 M-1 sec-1. The rate-limiting step in carbamate formation and breakdown with weakly basic amines involves carbon-nitrogen bond formation and cleavage. It is suggested that proton transfer may be rate limiting in the synthesis and breakdown of carbamates formed from basic amines. © 1968, American Chemical Society. All rights reserved.