RATES OF IONIZATION OF PSEUDO ACIDS .4. RELATION BETWEEN RATES AND EQUILIBRIA
RATES OF IONIZATION OF PSEUDO ACIDS .4. RELATION BETWEEN RATES AND EQUILIBRIA
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DOI：
10.1021/ja01106a048
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发表时间：
1953-01-01
影响因子：
15
通讯作者：
DILLON, RL
中科院分区：
文献类型：
--
作者：
PEARSON, RG;DILLON, RL
方法。通过使用前述电导法测量溴化速率来确定电离速率。1使用开颈电导池，以便在池中进行试剂混合。使用过量的溴，电导数据按一级反应作图。缓慢反应的l-氯硝基乙烷也被视为零级反应，使用低浓度的溴。平衡电阻有时直接在反应混合物上测定，有时从对应于最终浓度的氢溴酸的合成混合物中测定。两种方法所得结果相同。在l-氯硝基乙烷的情况下，通过直接滴定未反应的溴来检查电导法。对于硝基乙酸乙酯，先加入烯丙醇，再加入碘化钾，使溴的反应量可用标准硫代硫酸盐测定，硝基乙酸乙酯、氰基乙酸乙酯、硝基丙酮、二硝基甲烷和丙二腈每摩尔假酸消耗2摩尔溴。由于在80%的反应中得到了良好的一级动力学，因此可以认为溴化反应的第二阶段比第一阶段快得多。在氰基乙酸乙酯和丙二腈的情况下，通过制备单溴化衍生物并测量其溴化速率来检查这一点（参见表III）。上述假设并不总是正确的，
Methods.—The rates of ionization were determined by measuring the rates of bromination using the conductometric method previously described. 1 An open neck conductance cell was used so that mixingof reagents could be done in the cell. An excess of bromine was used andthe conductance data plotted as for a first-order reaction. The slowly re-acting l-chloronitroethane was also treated as a zero-order reaction using low concentrations of bromine. The equilibrium resistance was determined sometimes directly on the reaction mixture and sometimes from synthetic mixtures of hydrobromic acid corresponding to thefinal concentration. The same results were obtained by the two methods. The conductance method was checked by direct titration of unreacted bromine in the case of l-chloronitroethane. For ethyl nitroacetate a check was made by adding allyl alcohol followed by potassium iodide so that the amount of bromine reacted could be determined with standard thio-sulfate.Ethyl nitroacetate, ethyl cyanoacetate, nitroaceton, dinitromethane and malononitrile used up two moles ofebromine per mole of pseudo acid. Since good first-order ki-netics were obtained up to 80% reaction, it was assumed that the second stage ofbromination was much faster than the first. This was checked in the case of ethyl cyanoacetate and malononitrile by making the monobrominated derivative and measuring its rate of bromination (see Table III). That the above assumption isnot always true has been