题目

傅-克反应卤代烃酰卤活性问题!
邢大本说：傅-克反应烷基化卤代烃活性F>Cl>Br>I,酰基化酰卤活性I>Br>Cl>F,活性为什么是相反的?
大虾们分不是问题
是因为机理不同吗 但是烷基化也可以由c正离子历程啊

提问时间：2021-04-09

答案

March上面有介绍酰基化酰卤活性I>Br>Cl>F并不是绝对的,原因可能是在形成Wheland中间体后,进一步形成产物时,I的离去能力更强,C-I键能也最小,所以I活性更高,至于烷基化,可能是由于F的体积较小,配合M的能力较强,导致更易形成R+,所以F活性更高
LZ可参考以下文献
1、Challoway.N.O,JACS,59,1474(1937)
2、Brown and Jungk,JACS,77,5584(1955)
3、Yamase,Bull,Chem,Soc,Jpn,34,480（1961）
4、Corrio,Bull,Soc,Chim,Fr,821（1965）
文献1中的描述
We have found that for the acyl halides the order of activity for the halogens is as might be expected, I > Br > C1> F. The extreme sensitiveness of acetyl iodide to aluminum chloride caused a marked decomposition but did not materially interfere with the determination. For the alkyl halides the surprising order found was F>CI>Br>I. In fact, the iodine was so inert that n-butyl iodide did not react with benzene in eighteen hours in the presence of aluminum chloride at 29°C, though the other halides reacted at rapid rates at lower temperatures. It is also of interest to note that the n-butyl iodide was stable in the reaction and was recovered unchanged.