Studies on organic reactions in which supercritical alcohols participate as reaction partners

在这项研究中，我们发现了一些新的反应，其中超临界醇作为反应伙伴参与。带共轭芳环的烯烃和炔与超临界醇反应生成羟基烷基化衍生物和氢化衍生物。烯烃的羟基烷基化反应速率依次为：Ph_2CH = CH_2 > -PhCH = CEPh, PhCH = CH_2 > PhCH_2CH = CH_2, (CH_3)_2CHOH > CH_3CH_2OH > CH_3OH。可以认为，超临界醇中α-C-H键的断裂是烯烃羟基烷基化反应的速率决定步骤。羧酸与超临界伯醇反应生成酯。以2-丙醇为原料，酯化率小于10%。苯甲酸和2,4,6-三甲基苯甲酸用超临界甲醇酯化。通过气相色谱/质谱分析，认为反应机制受羧酸位阻的影响。在羧基周围没有位阻的羧酸中，羧基上的羰基-氧键裂解形成酯。另一方面，具有空间位阻的羧酸在超临界醇中通过碳氧键的裂解进行酯化反应。利用巨芽孢杆菌PYR 2910细胞在超临界二氧化碳条件下将吡咯转化为吡咯-2-羧酸盐，超临界二氧化碳条件下羧化反应的产率是常压条件下的12倍。

In this study, we found some novel reactions, in which supercritical alcohols participate as the reaction partners.1. Alkenes and alkynes with conjugated aromatic rings reacted with supercritical alcohols to afford hydroxyalkylated derivatives and hydrogenated derivatives. Reaction rates of the hydroxyalkylation of alkenes decreased as follows: Ph_2CH = CH_2 > trans-PhCH = CEPh, PhCH = CH_2 > PhCH_2CH = CH_2, and (CH_3)_2CHOH > CH_3CH_2OH > CH_3OH. It can be posturated that the cleavage of the α-C-H bonds in supercritical alcohols is the rate determining step in the hydroxyalkylation of alkenes.2. Carboxylic acids reacted with supercritical primary alcohols to afford esters. The esterification yields 41 were less than 10 % in the reactions using 2-propanol. Benzoic and 2,4,6-trimethylbenzoic acids were esterified using supercritical ^<18>O-methanol. Based on the results of GC/MS of the resulting esters, the reaction mechanism was suggested to be susceptible to steric hindrance of the carboxylic acids. In the cases of carboxylic acids with no steric hindrance around the carboxylic groups, the esters will be formed via the carbonyl-oxygen bond cleavage in the carboxylic group. On the other hand, the esterification of carboxylic acids with steric hindrance will proceed via the carbon-oxygen bond cleavage in the supercritical alcohol.3. Pyrrole was converted to pyrrole-2-carboxylate in supercritical carbon dioxide using cells of Bacillus megaterium PYR 2910, and the yield of the carboxylation reaction in supercritical carbon dioxide was 12 times than under atmospheric pressure.