The mechanism of thermal elimination of urea and thiourea derivatives. Part 2. Rate data for pyrolysis of N-acetyl-N′-phenylthiourea and N-benzoyl-N′-arylthioureas

The first-order rate constants of N-acetyl-N′-phenylthiourea (1), N-benzoyl-N′-phenyl-(2a), N-benzoyl-N′-(4-nitrophenyl)-(2b), N-benzoyl-N′-(3-chlorophenyl) (2c), N-benzoyl-N′-(4-chlorophenyl) (2d), and N-benzoyl-N′-(4-methylphenyl)thiourea (2e) were measured between 423 and 500 K. The reactions were homogeneous and unimolecular with log A (s⁻¹) = 12.0, 13.2, 13.8, 10.9, 11.8, and 12.7 and E_a kJ mol⁻¹ = 130.3, 141.4, 134.6, 114.9, 124.1, and 141.1, respectively. The rate data gave good Hammett correlation with σ^o values, and ρ is 1.99 at 450 K. © 1997 John Wiley & Sons, Inc.