特殊盐效应对水解反应催化常数测定的影响

SPECIFIC SALT EFFECTS ON THE DETERMINATION OF CATALYTIC CONSTANTS OF HYDROLYSIS

以苯甲醛缩二叔丁醇(BDTB)、原苯甲酸三乙酯(TEDB)和N-(p-甲氧基亚苄基)吡咯烷鎓离子(MOBP)为底物,研究了在各种条件下,用不同盐维持离子强度对水解反应的酸碱催化常数测定的影响。结果表明:当离子强度低,溶剂为水或以水为主要组份的混合溶剂时,判断特殊和普通酸碱催化及测定普通催化常数的标准方法可不受特殊盐效应的干扰。

In order to investigate the influences of specific salt effect of added electrolyte on the classic buffer experiments for distinguishing general and specific acid or base catalysis, the rate constants of the hydrolysis of benzaldehyde di-ter-butyl acetal, triethyl orthobenzoate and N-p-methoxybenzyli-denepyrrolidinium ion in acetate buffers were measured under various conditions. It is found that, for a given reaction, the presence or absence of specific effect of an added salt depends mainly on the ionic stregth and solvent of the buffer solution. In buffers of low ionic strength, e.g. 0.1mol.L^(-1), using water or mixed solvents containing a small fraction of organic constituent, specific salt effect can be eliminated or considerably reduced and the classic diagnostic buffer experiments can be satisfactory.