摘要
在固定溴化十六烷基三甲基铵(CTAB)浓度远远大于临界胶团浓度(cmc)下,测定了加入八烷基硫酸钠(SOS)对于丙酸对硝基苯酯和乙酸对硝基苯酯碱水解反应速度的影响。发现:(1)在CTAB浓度固定的情况下,随SOS加入量的增加,丙酸和乙酸的对硝基苯酯的碱水解速度均下降,而且丙酸酯水解速度的下降比乙酸酯快。这说明此体系中胶团对反应速度的影响,主要是由于反应物和胶团之间静电的和疏水的相互作用引起的。(2)SOS的加入量在远远小于本身cmc(～1/100)时,即可明显降低由CTAB催化的上述酯的水解速度。说明SOS参加了CTAB的胶团形成,而且由于它的参加,改变了原来单一表面活性剂胶团的性质。这充分显示出这种混合表面活性剂在胶团催化中的特殊作用。
The rate constants for basic hydrolysis of p-nitrophenyl acetate and p-nitrophenyl propionate were determined in the aqueous solution containing cetyltrimethylammonium bromide (CTAB) and sodium octylsulfate (SOS). It was found that ( 1 ) At a constant concentration of CTAB, which was much higher than the critical micelle concentration(cmc), the rate constant for both esters decreased with the increase of the concentration of SOS, and the decreasing rate for p-nitrophenyl propionate was faster than that for p-nitrophenyl acetate;this result indicated that the rate effect in this system could be attributed to the electrostatic and the hydrophobic interaction between the reactants and micelle. ( 2 ) At a low SOS concentration, which was much lower than the cmc of SOS, the micellar catalysis of CTAB could be inhibited; this proved that SOS had participated in the formation of a miscible micelle with CTAB, the existence of SOS in the micelle could reduce the surface electric charge of micelle, leading to the decrease of the rate constant of the basic hydrolysis of ester.
