Oxidation of clindamycin phosphate by cerium(IV) in perchloric acid medium – A kinetic and mechanistic approach

Methyl 7-chloro-6,7,8-trideoxy-6-[(2S,4R)-1-methyl-4-propylpyrrolidine-2-carboxamido]-1-thio-1-threo-D-galactooctapyranoside monohydrochloride, commonly called clindamycin phosphate(CYN-P) used largely as an antibiotic for the treatment of serious infections caused by susceptible Gram-positive bacteria and an-aerobic bacteria was oxidized by using Ceric ammonium sulphate (Ce(IV)) in perchloric acid medium. Progress of the reaction was followed by measuring the decrease in absorbance of ceric ammonium sulphate at 360 nm. The reaction was found to be first order each in [CYN-P] and [Ce(IV)]. Order in [HClO4] was calculated as 0.8. The reactive species of Ce(IV) appears to be H3Ce(SO4)4−. Stoichiometry of the reaction was found to be 2:1 of [Ce(IV)]:[CYN-P]. Initially added product did not alter the rate of reaction. A free radical mechanism was proposed, and rate law was derived and verified. The activation parameters, ΔH≠, ΔS≠, ΔG≠ and log A were found to be 54.7 kJ mol−1, −117 J K−1 mol−1, 103 kJ mol−1 and 7, respectively