阳离子表面活性剂混合胶团对2,4-二硝基氯苯水解反应的 催化作用

研究了阳离子表面活性剂混合胶团对2,4-二硝基氯苯(DNCB)碱性水解反应的催化作用。结果表明：(1)在十六烷基三甲基溴化铵(CTAB)和十六烷基溴化吡啶(CPB)混合溶液中DNCB水解一级速率常数k1与混合胶团中CTAB或CPB的摩尔分数有直线关系，表面活性剂形成理想的混合胶团。(2)辛基三甲基省化铵(OTAB)与CTAB,CPB的cmc值相差很大，在它们的混合胶团中OTAB含量极少，DNCB水解k1与CPB/OTAB混合胶团中CPB摩尔分数的关系与直线呈负偏差。(3)在CTAB(或CPB)与OTAB混合体系中OTAB起溴盐作用，使催化活性降低。用假相离子交换(PIE)模型对所得结果给出了定量的处理和解释。

Hydrolysis of 2,4-dinitrochlorobenzene catalized by mixed cationic micelles

The hydrolysis of 2,4-dinitrochlorobenzene (DNCB) by mixed cationic micelles has been studied. The linear relation of k1 with mole fractions of surfactants in the mixed cationic micelles was obtained, where k1 is the first-order rate constant for the hydrolysis reaction of DNCB catalyzed by the mixed micellar solutions of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB). Because the cmc value of octyltrimethylammonium bromide (OTAB) was too large and the mole fraction of OTAB in CTAB/OTAB and CPB/OTAB mixed micelles was too small, the catalytic activity for hydrolysis of DNCB in these mixed micelles depended mainly on the concentration of CTAB or CPB. However, a negative deviation from the straight line in the plot of k1 vs. the mole fraction was observed. The added OTAB acted as a neutral inorganic bromide (like NaBr) in the CTAB/OTAB or CPB/OTAB mixed systems. The k1 increased with increasing the concentration of OTAB and NaBr. The above-mentioned results can be explained quantitatively with the pseudophase ion exchange (PIE) model.