The kinetics and mechanisms of the gas-phase unimolecular eliminations of halogeno esters. Participation of the carbomethoxy group

✍ Scribed by Gabriel Chuchani; Alexandra Rotinov; Rosa M. Dominguez

• Book ID: 102926624
• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 691 KB
• Volume: 14
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550140406

✦ Synopsis

The kinetics of the gas-phase elimination of several chloroesters were determined in a static svstem over the temperature range of 410-490OC and the pressure range of 47-236 torr. T h e reactions in seasoned vessels, and in the presence of a free-radical inhibitor, are homogeneous, unimolecular, and follow a first-order law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for methyl R-chloropropionate, log k l ( s -l ) = (13.22 f 0.07) -(231.5 f 1.0) kJ/mo1/2.30:3RT; for methyl 4-chlorohutyrate, log k l ( s -l ) = (13.31 f 0.25) -(221.5 f 3.4) kJlmo1/2.:303RT; and for methyl 5-chlorovalerate. log h l ( s -' ) = (13.12 f 0.25) -(221.7 f 3.2) ktJ/mo1/2.303RT. Kate enhancements and lactone formation reveal the participation of carbonyl oxygen of the carhornethoxy group. The order COOCH:1-5 > COOCH:!-6 > COOCH:1-4 in assistance is similar to the sequence of' group participation in solvolysis reactions. T h e partial rates for the parallel eliminations to normal dehydrohalogenation products and lactones have been estimated and reported. T h e present results lead us to consider that an intimate ion-pair mechanism through participation of the carhomethoxy group may well be operating in some of these reactions.