Kinetics of base hydrolysis of chloropenta-ammines of the type cis-[Co en2RNH2Cl]2+ in aqueous solution at 25°

Abstract

Rate constants are reported for the base hydrolysis of seven chloropenta-ammines of cobalt(III), cis-[Co en₂RNH₂Cl]²⁺+ OH^–→[Co en₂RNH₂OH]²⁺+ Cl^– at 25° and I 0·1 M. Measurements were made over the range of pH 9·0–10·2 using a pH-stat. In contrast to previous work, it is found that within experimental error, the straight-chain amine derivatives (R = Me, Et, Prⁿ, or Buⁿ) hydrolyse at the same rate with k₂=(7·65 ± 0·2)× 10²M^–1 min.^–1. The simple ammine (R = H) hydrolyses at a somewhat slower rate (k₂= 4·85 ± 0·2 × 10²M^–1 min.^–1). The branched chain derivative (R = Prⁱ) hydrolyses ca. four times faster than the straight chain derivative (R = Prⁿ) probably due to steric acceleration of the reaction.