Kinetic Studies of Solvolysis. XVI. Phenolysis of<i>cis</i>- and<i>trans</i>-4-<i>t</i>-Butylcyclohexy<i>p</i>-Toluenesulfonates. Rates and Product Distribution
作者:Kunio Okamoto、Seiki Saitô、Haruo Shingu
DOI:10.1246/bcsj.42.3288
日期:1969.11
The rates of the phenolysis of cis- and trans-4-t-butylcyclohexyl p-toluenesulfonates have been measured in the presence of equimolar amounts of triethylamine in phenol, phenol-benzene (3 : 1 by wt), and phenol-benzene (1 : 1 by wt) solvents. At 75°C, the axial isomer, i.e., the cis tosylate, phenolyzes more rapidly in the phenol-benzene mixture (1 : 1 by wt) than the equatorial isomer, i.e., the trans tosylate, by a factor of 3.08; this factor is not far from the axial-equatorial rate ratios observed in other hydroxylic solvents, indicating that phenol is a typical solvolytic solvent. Under the same reaction conditions as the rate measurements, the equatorial tosylate yields t-butylcyclo-hexene (72.5%), t-butylcyclohexyl phenyl ether (9.4%), predominantly inverted (cis-4-t-butylcyclo-hexyl) phenyl ether, and t-butylcyclohexylphenol (4.4%), whereas the axial tosylate yields t-butyl-cyclohexene (87%) and the phenyl ether (8.7%), largely inverted (trans-4-t-butylcyclohexyl) phenyl ether, but containing increasing amounts of retained (cis-4-t-butylcyclohexyl) and and rearranged (trans-3-t-butylcyclohexyl) ethers; the rest is a mixture of t-butylcyclohexylphenols (1.6%). The composition percentages of the retained phenyl ether obtained from the two tosylates, i.e., 20.4% for the cis tosylate and 12.9% for the trans tosylate, indicate the highest extents of retention for phenol among those known for any other hydroxylic solvents. The initially added t-butylcyclohexenes exert no influence on the olefin or on the phenyl ether composition, whereas triethylammonium and diethylammonium p-toluenesulfonates, when added initially, enhance the phenolysis rate and exert a small but definite influence on the composition of the phenyl ether. The hypothesis of the hydrogen-bridged cation, proposed in order to explain the enhanced rate of the cis isomer and in order to elucidate the retained solvolysis product, has been questioned by a consideration of the mechanism on the basis of the results of this phenolysis.
在
苯酚、苯-
苯酚(重量比3:1)和苯-
苯酚(重量比1:1)溶剂中,测量了对
苯磺酸酯的顺式和反式4-t-丁基环己基对
苯磺酸酯的
酚解速率。在75°C时,轴向异构体,即顺式
磺酸酯,在苯-
苯酚混合物(重量比1:1)中的
酚解速率比赤道异构体,即反式
磺酸酯快3.08倍;这一因子与在其他羟基溶剂中观察到的轴向-赤道速率比相差不远,表明
苯酚是一种典型的溶剂。在与速率测量相同的反应条件下,赤道
磺酸酯产生72.5%的t-丁基
环己烯、9.4%的t-丁基
环己基苯醚(主要是反转的顺式4-t-丁基
环己基苯醚)和4.4%的t-丁基环己基
酚,而轴向
磺酸酯产生87%的t-丁基
环己烯和8.7%的苯醚,主要是反转的反式4-t-丁基
环己基苯醚,但含有越来越多的保留的(顺式4-t-丁基环己基)和重排的(反式3-t-丁基环己基)苯醚,其余是1.6%的t-丁基环己基
酚混合物。从两个
磺酸酯得到的保留苯醚的组成百分比,即顺式
磺酸酯为20.4%,反式
磺酸酯为12.9%,表明
苯酚在已知的任何其他羟基溶剂中具有最高的保留程度。最初添加的t-丁基
环己烯对烯烃或苯醚的组成没有影响,而初始添加的三乙
铵盐和二乙
铵盐对
苯酚解速率的增强和对苯醚组成的轻微但明确的影响则显著。为了解释顺式异构体速率的提高和阐明保留的溶解产物,提出了氢桥阳离子的假说,但通过对这一
酚解反应结果的机制进行考虑,对该假说提出了质疑。