Kinetics of the Reaction between Lactic Acid and Bromine

Department of Chemistry, Jodhpur University, Jodhpur

Manuscript received 7 August 1972 ; revised 26 August 1974; accepted 17 October 1974

It has been found possible to estimate lactic acid quantitatively by bromine at 35° within a time limit of 4 boors at pH$\sim$ 8 using, at least, 50% excess of the oxidant. The reaction has been shown to be of second order. The temperature coefficient was found to be of the order of 1.26 for temperatures 30°- 35° and 1.23 for temperatures 35°- 40" and the energy of activation, free energy and entropy of activation was 8.9 kilo cal per mole, 11.4 kilocal/mole-7.9 e. u. respectively at pH$\sim$7.60. The reaction rate was found to be maximum at pH$\sim$7.60 and decreases on both sides of this value. The inverse dependence of the rate on the concentration of the added bromide shows that the pH effect may be due to hypobromous acid being a faster oxidising agent than molecular bromine as shown by the comparatively fast reaction in bromine free hypobromous acid solution. The reactive species appear to be a combination of hypobromous acid and molecular bromine with k_HOBr > >k_Br (Tribromide ion being kinetically inactive). The reaction involves a hydride ion  transfer and proceeds through the intermediate formation of acetaldehyde.