摘要
通过室温下高硫煤的Ｓ甲基化反应，可使煤结构中的一种碳硫键选择性断裂。煤样先经Ｏ甲基化反应，使酚羟基转变为甲基醚，然后再经由碘甲烷和四氟硼酸银组成的Ｓ甲基化试剂进行Ｓ甲基化反应。断裂后硫以四氟硼酸三甲基锍的形式用１３ＣＮＭＲ进行检测。以模型化合物４，４二甲氧基二苄基硫醚进行Ｓ甲基化反应，亦可高产率地生成四氟硼酸三甲基锍。提出一个由苄基碳正离子和硫醚组成的离子偶极集合物作为反应中间体的反应机理。最后，１３ＣＮＭＲ定量分析结果表明，烟煤中含有约２％的４，４二甲氧基二苄基型硫醚或４，４二羟基二苄基型硫醚。
We report an S-methylation reaction on high sulfur coal at ambient temperature that appears to selectively cleave one type of carbon-sulfur bond in the coal structure. The coal is first O-methylated to render the phenolic hydroxyl groups unreactive in the subsequent S-methylation procedure. The Smethylating agent is methyl iodide in the presence of silver tetrafluoroborate.The cleaved sulfur is detected and quantified in the form trimethylsulfonium tetrafluoroborae with 13 C-NMR spectroscopy. The same product is detected from the S-methylation of a THF extract of the coal, which rules out mineral matter-as the source of sulfur. Reaction of the model compound 4, 4′-dimethoxydibenzylsulfide also yields this ion in high yield in contrast to dibenzylsulfide which yieds only the monomethylated sulfonium ion. The results of model compound point to dibenzylsulfide type structure in coal, activated by electron-donating methoxy substituents, which undergo bond cleavage. A mechanism based on formation of a benzyl carbocation-sulfide assemblage followed by s-methylation of the intermediate sulfde is proposed. Finally, quantitative 13 C-NMR analysis showed that only 2% of the total organic sulfur in biuminous coal was assigned to the structure of 4,4′-dimethoxydibenzylsulfide or 4,4′-dihydroxyldibenzylsulfide type.
出处
《燃料化学学报》
EI
CAS
CSCD
北大核心
1999年第1期68-73,共6页
Journal of Fuel Chemistry and Technology
基金
煤炭系统回国留学人员科技基金
关键词
煤化学
碳硫键
断裂
选择性
high sulfur coal, selectivity, cleavage of carbon-sulfur bond
