作者:Olga A. Kurnysheva、Nina P. Gritsan、Yuri P. Tsentalovich
DOI:10.1039/b103422g
日期:——
The
rate constant kCO of decarbonylation of phenylacetyl and 2-hydroxy-2-methylpropanoyl radicals, generated
by photolysis of dibenzyl ketone and 2,4-dihydroxy-2,4-dimethyl-3-pentanone, was measured in a number of
solvents over a wide temperature range. The pre-exponential factors A and activation energies Ea were found
for all solvents. The rate constant of phenylacetyl decarbonylation decreases with the increase of the solvent
relative permittivity ε, but increases in protic solvents. The results of quantum chemistry calculations
confirm the mutual cancellation of the contributions of specific and nonspecific solvations to the activation
energy of the decarbonylation reaction in alcohols. For the 2-hydroxy-2-methylpropanoyl
radical,
the solvent effect
on the decarbonylation rate constant is very small.
在多种溶剂中测量了二苄基酮和 2,4- 二羟基-2,4-二甲基-3-戊酮光解产生的苯乙酰基和 2- 羟基-2-甲基丙酰基脱羰基的速率常数 kCO,其温度范围很宽。发现了所有溶剂的前指数 A 和活化能 Ea。苯乙酰基脱羰基化的速率常数随溶剂相对介电常数ε的增加而降低,但在质子溶剂中则增加。量子化学计算的结果证实,特异性溶解和非特异性溶解对醇中脱羰基反应活化能的贡献相互抵消。对于 2-羟基-2-甲基丙酰基,溶剂对脱羰基反应速率常数的影响非常小。