The mechanisms of the homogeneus, unimolecular elimination kinetics of ethyl 4-chlorobutyrate and 4-chlorobutyric acid in the gas phase

✍ Scribed by Gabriel Chuchani; Alexandra Rotinov

• Publisher: John Wiley and Sons
• Year: 1987
• Tongue: English
• Weight: 375 KB
• Volume: 19
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550190902

✦ Synopsis

Ethyl 4-chlorobutyrate, which is reexamined, pyrolyzes a t 350-410°C to ethylene, butyrolactone, a n d HC1. Under t h e reaction conditions, t h e primary product 4-chlorobutyric acid is responsible for the formation of y-butyrolactone and HCl. In seasoned vessels, and in the presence of a free-radical inhibitor, the ester elimination is homogeneous, unimolecular, and follows a first-order rate law. For initial pressures from 69-147 Torr, t h e rate i s given by t h e following A r r h e n i u s expression: log k , ( s -' ) = (12.21 ? 0.26) -(197.6 2 3.3) k J mol-' (2.303RT)Y'. The rates and product formation differ from the previous work on the chloroester pyrolysis.

4-Chlorobutyric acid, a n intermediate product of the above substrate, was also pyrolyzed a t 279-330°C with initial pressure within the range of 78-187 Torr. This reaction.

which yields y-butyrolactone and HCl, is also homogeneous, unimolecular, and obeys a first-order rate law. The rate coefficient, is given by the following Arrhenius equation: logk,(s '1 = (12.28 2 0.41) -(172.0 2 4.6) kJ mo1-l (2.303RT)-'. The pyrolysisofethyl chlorobutyrate proceeds by the normal mechanism of ester elimination. However, the intermediate 4-chlorobutyric acid was found to yield butyrolactone through anchimeric assistance of the COOH group and by an intimate ion pair-type of mechanism. Additional evidence of cyclic product and neighboring group participation is described and presented.