R-Cl is hydrolysed to R-OH slowly but the reaction is rapid in presence of KI as catalyst. Explain.

Explanation

KI supplies `I^(-)` ion which is strong nucleophile and hence reacts rapidly with R-Cl to form R-I. `I^(-)` is also a better leaving group than `Cl^(-)`. Hence R-I is hydrolysed rapidly to form R-OH and I. I ion is again used in converting R-Cl to R-I.
` R-Cl+H_2 O overset("slow")to R-OH +Cl`
` R-Cl +I^(-) underset(-Cl)overset("fast")to R-I underset("Fast") overset(+H_2 O) to R-OH`