A kind of preparation method of benzyl bromide

Abstract

The invention provides a preparation method of benzyl bromide: in an organic solvent, the bromine released by the oxidation-reduction reaction of bromate and bromide anion under the action of an acid is used as a bromine source; The toluene compounds shown in I carry out the benzyl radical substitution reaction to prepare the corresponding benzyl bromides shown in the formula II: in the formula II, m represents the number of Br, m=1 or 2; m=1 When m=2, the formula II is a benzyl bromide compound, and when m=2, the formula II is a benzyl dibromide compound. The reaction of the present invention is carried out in an organic solvent, and an initiator is used in combination, the choice of free radical substitution reaction is better, and the scope of substrate application is wider. The substituent of substituted toluene can be either an electron withdrawing group or an electron donating group. The group can also give a high yield for a strong electron-donating group (such as: methoxy group); secondly, the present invention is also applicable to the preparation of benzyl dibromo compounds, and the yield of the product is high.

Description

Technical field: [0001] The invention relates to the field of organic chemistry, and relates to a preparation method of benzyl bromide. Background technique: [0002] Benzyl bromide is an important intermediate in organic synthesis. Therefore, the bromination reaction of the benzylic position of arenes is an important unit reaction in organic synthesis, and it is also one of the key steps in drug synthesis. The most classic benzylic bromination reaction is a free radical bromination reaction between bromine and toluene (or substituted toluene) under the initiator or photoinitiation, but due to the volatile, highly toxic, strong corrosion, high density, etc. characteristics, resulting in dangerous operation of the process, high environmental pollution, and because hydrogen bromide will be released during the reaction process, the utilization rate of bromine resources will not exceed 50% at most, and the production cost is relatively high. N-bromoamide reagents (such as: N-b...

AI Technical Summary

Problems solved by technology

Chinese patent CN1265639A has reported a kind of using azonitrile or azocarboxylate compound as an initiator, using hydrogen peroxide, bromate and other oxidizing agents to oxidize bromide anions as a bromine source, and the organic phase and the aqueous phase coexist in two The method of bromination in the phase medium, the patent clearly pointed out that the applicable substrate of this method is limited, and it is required that the aromatic ring of toluene must have electron-withdrawing substituents.

Chinese patent CN104744303A reports the preparation method of 2-R-4'-bromomethylbiphenyl, which is also carried out in a two-phase system of aqueous phase and organic phase, and the R substituent on the benzene ring is cyano, carboxyl or halogen Electron-withdrawing substituents such as atoms, applicable substrates are limited

When the aromatic ring of toluene has a strong electron-donating substituent, due to the strong activation of the electron-donating group, the positive monovalent bromine is prone to electrophilic substitution reaction with the aromatic ring to form a brominated product on the aromatic ring, reducing the The concentration of positive monovalent bromine, and then promote the balance to move to positive monovalent bromine, thereby inhibiting the formation of bromine free radicals; secondly, in these existing studies, the two-phase medium of organic phase and aqueous phase is used. The oxidation-reduction reaction is carried out in an aqueous solution, and there is a large amount of water in the reaction medium, which greatly enhances the polarity of the solvent, increases the rate of the electrophilic substitution reaction, inhibits the free radical substitution reaction, and makes it difficult to obtain the corresponding benzyl bromide In addition, due to the existence of a large amount of water, when the method is used to prepare benzyl dibromide compounds, the hydrolysis of benzyl dibromide compounds easily occurs to form corresponding aldehydes and oxidation product carboxylic acids thereof, and it is difficult to obtain pure benzyl dibromide compounds. Dibromo compounds or aldehydes

Therefore, the existing technology of preparing benzyl bromide by oxidizing bromine anion is not suitable for preparing benzyl bromide with strong electron-donating group on the aromatic ring, nor is it suitable for preparing benzyl dibromide compounds. Narrow scope of application

Images