Dehydrochlorination of 2-chloroethanol, 2-chloro-1-propanol, 1- chloro-2-propanol, 2-chloro-2-methyl-1-propanol and 1-chloro-2-methyl-2-propanol
Kalevi Pihlaja*, Marja-Leena Kiuru, and Anne Sippola
Department of Chemistry, University of Turku, FI-20014 Turku, Finland
E-mail:
[email protected]
Dedicated to Professor Ferenc Fülöp on the occasion of his 60th birthday
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Abstract
The reactions between a few 1,2-chlorohydrins and sodium hydroxide have been studied and shown to involve a two-step nucleophilic elimination of hydrogen chloride. The data are given for the slow rate-determining step of 2-chloroethanol 1, 2-chloro-1-propanol 2, 1-chloro-2- propanol 3, 2-chloro-2-methyl-1-propanol 4 and 1-chloro-2-methyl-2-propanol 5. Compounds 4 and 5 gave 2-methyl-1,2-propanediol as the final product instead of oxiranes given by compounds 1. 3. In contrast to some earlier reports the mere water reaction was shown to be almost negligible. In constant ionic strength the base concentration had no effect on the rates whereas at different base concentrations (0.050. 0.250 mol dm . 3) alone the rate of alkaline dehydrochlorination of 1 clearly decreased (103k2, dm3 mol . 1 s . 1: 10.0. 8.7, respectively). The rate of 2 at constant base concentration (0.010 mol dm . 3) and at different ionic strengths (dm3 mol . 1: 0.010. 0.500) decreased also (103k2, dm3 mol . 1 s . 1: 76. 65, respectively) indicating that the decrease is mainly due to the change in the ionic strength also in the former case.
Keywords: 1,2-Chlorohydrins, reactions in alkali, kinetics, mechanisms
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Introduction
Alkaline dehydrochlorination of 1,3-chlorohydrins is relatively well documented1 whereas much less information is available on that of 1,2-chlorohydrins.2. 6 Most of the reports deal with the preparation of hydrogen chloride7 or different oxiranes.8,9 The best report is that of Ballinger and Long10 on the dehydrochlorination of 2-chloroethanol 1 which also summarizes some early studies. They proved that the reaction between 1 and sodium hydroxide is a specific hydroxide ion catalysis via a two-step mechanism including the prior equilibrium and the slow rate- determining step:
