I believe everyone is familiar with Grignard reagent. The first reaction I know of Grignard reagent is probably its coupling reaction with halogenated hydrocarbons. According to its strong alkalinity, we can directly infer that it reacts well with primary halogenated hydrocarbons, while tertiary halogenated hydrocarbons will be mainly eliminated. But I'm afraid careful children must have seen such a passage in the fourth edition of basic organic chemistry:

Children, do you have many question marks?

So what is the reaction between Grignard reagent and halogenated hydrocarbon? Let Bian Xiao take you to understand it.

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Grignard reagent, which is actually an organic magnesium reagent, is very common in textbooks. In actual reaction, its coupling reaction with halogenated hydrocarbons is often not practical. Only active halogenated hydrocarbons such as benzyl and allyl can be coupled, and the yield of tertiary halogenated hydrocarbons is often low. Generally speaking, in the preparation of Grignard reagent, coupling with common halogenated hydrocarbons can only occur in a small amount. In practical synthesis, catalysts such as Cu and Pd must be added to couple primary and secondary halogenated hydrocarbons. Although some students write these impossible reactions into the synthesis route every day, Bian Xiao is not very surprised that this is the case.

Negishi once summarized the mechanism of this kind of coupling reaction in organometallic compounds in organic synthesis, and proposed that this kind of coupling reaction is mainly based on SN2 mechanism, but on the other hand, the reaction can also occur through free radical mechanism.

In 1988, Shoji Eguchi et al. found that Grignard reagent could replace tertiary haloJingang Dai in dichloromethane solvent, and Lewis acid could not promote the reaction, thus denying the SNi mechanism. At the same time, the Grignard reagent produced by 6- bromo-1- hexene has a closed loop phenomenon in the reaction, which indicates that the reaction is a free radical process.

Under this free radical mechanism, an interesting selectivity is produced, which is incredible from the point of view of SN2 mechanism.

This is about Grignard reagent and halogenated hydrocarbon. what do you think? Welcome to tell Bian Xiao in * * District. Anyway, Bian Xiao won't discuss it with you! There are more strange processes about allyl Grignard reagent, welcome to know more →

Confusion behavior of allyl magnesium reagent (1)

"Confusion Behavior" of Allyl Magnesium Reagent (2)