Alcoholysis Equilibria of Dialkoxydimethylsilanes Catalyzed by Iodine or Iodine Monobromide

1987

In order to appreciate the excellent catalytic effect of iodine on the alcoholyses of alkoxysilanes more precisely, the rates of the reaction, Et3SiOBun + BusOH ⇌ Et3SiOBus + BunOH, were determined at various iodine concentrations. Both forward and reverse reactions are first order with respect to butoxysilane and to butanol, and pseudo first‐order rate constants were measured at 40°, 30°, and 20°C on reaction mixtures containing both butanols in excess by means of gas‐liquid chromatography. The observed rate constants as a function of iodine concentration gave linear relationships, and from these data the catalytic coefficients of iodine were evaluated: The enthalpies and the entropies of activation were estimated to be 53.2 kJ mol−1, −103 J K−1 mol−1 (forward, 30°C) and 51.8 kJ mol−1, minus;100 J K−1 mol−1 (reverse, 30°C).

Kinetic study of the iodine‐catalyzed alcoholysis of Butoxytriethylsilane: n‐butoxy group—s‐butoxy group exchange reaction

1987

Kinetic study of the iodine monobromide‐or iodine monochloride‐catalyzed alcoholysis of butoxytriethylsilane: n‐butoxy group — s‐butoxy group exchange reaction

1989

Self Cite

The catalytic activity of iodine monobromide and iodine monochloride were investigated in the reaction, Et3SiOBun + BusOH ⇌ Et3SiOBus + BunOH. Pseudo first‐order rate constants were measured by gas chromatography, at 10°, 20°, 30°, and 40°C for iodine monobromide and at 10°, 20°, and 30°C for iodine monochloride, on reaction mixtures containing both butanols in excess. The catalytic coefficients of both catalysts were evaluated from the observed rate constants as follows: The activation paramaters were estimated from these data, and were compared with the values for iodine catalysis. These results are consistent with the mechanism previously proposed.

Kinetic study of the bromine‐catalyzed alcoholysis of butoxytriethylsilane: n‐Butoxy group–s‐butoxy group exchange reaction

1990

In order to compare the catalytic activity of bromine with those of iodine and iodine monohalides, kinetic studies on the reaction, Et3SiOBun + BusOH ⇌ Et3SiOBus + BunOH, were undertaken. Pseudo first‐order rate constants were determined at 0°, 10°, 15°, 20°, and 30°C by means of gas chromatography on the reaction mixtures containing both butanols in excess. From the observed rate constants, the catalytic coefficients of bromine were evaluated as follows: The enthalpies and entropies of activation were estimated to be (42.0 – 42.2) kJ/mol, −(103 – 104) J/K (forward reaction), and (40.4 − 40.7) kJ/mol, − (101 − 102) J/K (reverse reactions). These data suggest that bromine is much more active than iodine and iodine monohalides, and its high activity was interpreted on the basis of the structure of the reaction intermediate.