In Cannizzaro reaction given below
the slowest step is (a) the ** of :OH– at the carboxyl group (b) the transfer of hydride to the carbonyl group (c) the abstraction of proton from the carboxylic group (d) the deprotonation of PhCH2OH
(b) : Rate determining step is always the slowest step. In case of Cannizzaro reaction, H-transfer to the carbonyl group is the rate determining step and hence the slowest. Mechanism :
