Kinetics of an Associative Ligand-Exchange Process: Alcohol Exchange with Arsenate(V) Triesters

Article abstract of DOI:10.1021/ja00538a016

The rate of alcohol exchange with trialkyl arsenates has been studied by three techniques.Exchange of the straight-chain alcohols (ethyl, n-propyl, n-butyl, and n-pentyl) was studied in acetonitrile solution by using proton NMR line broadening.Activation enthalpies and entropies were found in the ranges 1 to 6kJ mol^-1 and -204 and -226 J mol^-1 K^-1, respectively.The reactions are subject to acid catalysis for which slightly higher ΔH^<*> and less negative ΔS^<*> values were found.Methyl exchange, studied by the same technique, is about one powere of ten faster.Isopropyl exchange, about three powers of ten slower, was studied in acetonitrile and dichloromethane solutions by deuterium labeling, using proton NMR.The interchange reaction of benzyl alcohol with triisopropyl arsenate in acetonitrile or dichloromethane was followed by spectrophotometry.Hydrogen bonding between alcohol and ester (which complicates order determination) was observed when reactants were at concentrations greater than about 10^-2 M.The strongly associative mechanism is discussed.