Kinetic studies on the effect of acidity and temperature on the loss of optical activity of some butanediols

In aqueous perchloric acid, butane-1,2-diol (1) and butane-2,3-diol (2) give carbonyls and butane-1,3-diol (3) gives alkenols. The rate of loss of optical activity has been determined for these diols and butan-2-ol (4) over a range of temperatures and acidities. In 1 M acid at 100�C, the rates for (1), (2), (3) and (4) are in the ratio of 1 : 2.3 : 3.7 : 45 respectively. The activation parameters are similar for all the alcohols. Hammett acidity plots give slopes of c. 0.8 for the diols and of 1 for butan-2-ol. These variations in these kinetic parameters are discussed in terms of whether hydroxyl group substitution in butan-2-ol affects the mechanism of its reaction in these circumstances.