摘要/Abstract

在温和条件下选择性活化与转化甲烷具有可观的经济效益, 但同时也是难点. 报道在环境温度条件下, 无水三氯化铁(FeCl₃)与甲烷在环境温度下的光化学反应, 这是一种有效的选择性活化甲烷生成一氯甲烷的方法. 在300 W的高压汞灯或者太阳光的照射下, 由甲烷转化的产物为单一的一氯甲烷, 而没有其它多氯代物, 最大初始生成效率为43 g_MeCl?(kg_Fe?h)^–1. 氯化铁既作为氯自由基源, 也作为氧化剂, 并在反应中被还原为氯化亚铁. 高压汞灯功率增加以及氯化铁浓度增加都会加快初始反应速率. 而反应温度以及甲烷的压力对反应的初始速率影响很小. 氯甲烷可以被水解为甲醇, 亚铁在空气以及盐酸存在下也可以被重新氧化为三价铁, 从而完成铁和氯的循环.
关键词: C—H活化, 甲烷活化与转化, 金属催化合成反应, 光催化
Selective activation of methane under mild conditions to produce functionalized products is highly lucrative but remains challenging. The photochemical reaction of anhydrous ferric chloride (FeCl₃) with methane at ambient temperature is an efficient process to selectively chlorinate methane to methyl chloride. An exclusive formation of methyl chloride instead of other multi-chlorinated products is observed, and a maximum initial productivity of 43 g_MeCl?(kg_Fe?h)^–1 was obtained under irradiation with a 300-watt high-pressure mercury lamp or solar light. Ferric chloride functions both as the source of reactive chlorine radicals and as the oxidant, and it was concomitantly reduced to ferrous chloride. The reaction rate increases with the power of the lamp and the concentration of ferric chloride. Interestingly, the reaction temperature from 25 to 75 ℃ and the methane pressure in the range of 1~4 MPa had little influence on the reaction rate. Methyl chloride was hydrolyzed to methanol with elimination of hydrogen chloride, and the ferrous product was re-oxidized to the ferric analog by oxygen in the air in the presence of hydrogen chloride, thus completing the loop of both iron and chlorine.
Key words: C—H activation, methane activation and functionalization, metal-catalyzed synthetic reaction, photocatalysis


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