Kinetics and mechanisms of the gas-phase elimination of arylethyl N,N-dimethylcarbamates and ω-phenylalkyl N,N-dimethylcarbamates

• Published in: Journal of physical organic chemistry 2003-01, Vol.16 (1), p.40-46
• Main Authors: Chuchani, Gabriel, Dominguez, Rosa M., Rotinov, Alexandra, Herize, Armando
• Format: Article
• Language: English
• Subjects: arylethyl N; arylethyl N,N‐dimethylcarbamates; gas-phase elimination; kinetics; mechanism; N-dimethylcarbamates; ω-phenylalkyl N; ω‐phenylalkyl N,N‐dimethylcarbamates
• ISSN: 0894-3230; 1099-1395
• DOI: 10.1002/poc.567

The gas‐phase elimination kinetics of several arylethyl N,N‐dimethylcarbamates and ω‐phenylalkyl N,N‐dimethylcarbamates were determined in the temperature range 299.6–399.9 °C and pressure range 18–95 Torr. The reactions in a static system, seasoned with allyl bromide, and in the presence of a free radical suppressor are homogeneous and unimolecular and follow a first‐order rate law. The rate coefficients are given by the Arrhenius equations: for 4‐phenethyl N,N‐dimethylcarbamate, log[k1 (s−1)] = (11.32 ± 0.22) −(166.9 ± 2.5) kJ mol−1 (2.303RT)−1; for methylphenethyl N,N‐dimethylcarbamate, log[k1 (s−1)] = (12.07 ± 0.36) −(178.6 ± 4.3) kJ mol−1 (2.303RT)−1; for 4‐methoxyphenethyl N,N‐dimethylcarbamate, log[k1 (s−1)] = (11.03 ± 0.60) −(167.3 ± 7.1)­kJ mol−1 (2.303RT)−1; for 4‐nitrophenethyl N,N‐dimethylcarbamate, log[k1 (s−1)] = (11.31 ± 0.54) −(163.7 ±­6.1) kJ mol−1 (2.303RT)−1; for 3‐(4‐methoxyphenyl)propyl N,N‐dimethylcarbamate, log[k1 (s−1)] =­(13.52 ± 0.54) −(208.4 ± 6.8) kJ mol−1 (2.303 RT)−1; for 4‐phenyl‐1‐butyl N,N‐dimethylcarbamate, log[k1 (s−1)] = (12.00 ± 0.34) −(185.2 ± 4.2) kJ mol−1 (2.303 RT)−1; and for 5‐phenyl‐1‐pentyl N,N‐dimethyl carbamate, log[k1 (s−1)] = (11.79 ± 0.31) −(182.2 ± 3.9) kJ mol−1 (2.303RT)−1. The results imply the absence of anchimeric assistance of the phenyl group, while the acidity of the benzylic β‐hydrogen appears to be responsible for a small but significant rate augmentation in these eliminations. Copyright © 2002 John Wiley & Sons, Ltd.