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Kinetics of the gas-phase elimination of isopropyl α-halo acetates and the taft correlation

✍ Scribed by Gabriel Chuchani; Jose A. Hernandez; Magdalia Yepez; Miguel E. Alonso

Publisher
John Wiley and Sons
Year
1977
Tongue
English
Weight
336 KB
Volume
9
Category
Article
ISSN
0538-8066

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✦ Synopsis

Abstract

The gas‐phase pyrolysis of three secondary acetates in the temperature range of 290‐350°C and the pressure range of 40‐236 mm Hg reveals a homogeneous first‐order law and unimolecular elimination. The rate constants are given by the following Arrhenius equations: isopropyl fluoroacetate:
isopropyl chloroacetate:
isopropyl iodoacetate:

The differences in rates I > Br > Cl > F apparently question previous assumptions where the pyrolyses of esters follow the same sequence as acid strength. The experimental data give a good correlation with σ* values, where ρ* = ‐1.85 at 330°C. Some kind of discrete bond polarization at the C~α~O bond of the acetate in the cyclic transition state seems to be involved in this type of reactions.

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