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انجمن علمی شیمی دانشگاه زنجان - سنتز سیکلوهگزان
سه شنبه 21 آبان 1392

سنتز سیکلوهگزان

   نوشته شده توسط: انجمن علمی شیمی دانشگاه زنجان    نوع مطلب :شیمی آلی ،

Unlike compounds like benzene, cyclohexane cannot easily be obtained from natural resources such as coal. Toward the end of the nineteenth century early chemical investigators had to depend on organic synthesis. It took them 30 years to flesh out the details.[4] In 1867 Marcellin Berthelot reduced benzene with hydroiodic acid at elevated temperatures. He incorrectly identified the reaction product as n-hexane not only because of the convenient match in boiling point (69 °C) but also because he did not believe benzene was a cyclic molecule (like his contemporary August Kekulé) but rather some sort of association of acetylene. In 1870 one of his sceptics Adolf von Baeyer repeated the reaction and pronounced the same reaction product hexahydrobenzene and in 1890 Vladimir Markovnikovbelieved he was able to distill the same compound from Caucasus petroleum calling his concoction hexanaphtene.

In 1894 Baeyer synthesized cyclohexane starting with a Dieckmann condensation of pimelic acid followed by multiple reductions:


and in the same year E. Haworth and W.H. Perkin Jr. (1860–1929) did the same in a Wurtz reaction of 1,6-dibromohexane.

Surprisingly their cyclohexanes boiled higher by 10°C than either hexahydrobenzene or hexanaphtene but this riddle was solved in 1895 by Markovnikov, N.M. Kishner and Nikolay Zelinsky when they re-diagnosed hexahydrobenzene and hexanaphtene asmethylcyclopentane, the result of an unexpected rearrangement reaction.

Today, cyclohexane can be synthesized from benzene through more advanced reduction reactions


 
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