THE MECHANISM OF THERMAL ELIMINATION OF UREA AND THIOUREA DERIVATIVES.1. RATE DATA FOR PYROLYSIS OF N-ACETYLUREA, N-ACETYLTHIOUREA, N,N'-DIACETYLTHIOUREA, AND N-ACETYLTHIOBENZAMIDE

Rates of thermal decomposition of N-acetylurea (1), N-acetylthiourea ( 2), N,N'-diacetylthiourea (3), and N-acetylthiobenzamide (4) have been measured over a 45 K range for each compound. The molecules were foun d to undergo unimolecular first-ordev elimination reactions for which log A = 11.9, 11.6, 11.8, and 13.4 s(-1), and E(a) = 181.2, 135.9, 128 .3, and 130.3 kJ mol(-1), respectively. The reactivities of these comp ounds have been compared with those of amide derivatives and with each other. Product analysis together with the kinetic data were used to o utline feasible pathways for the elimination reactions of the compound s under study. (C) 1996 John Wiley & Sons, Inc.