Alkyl halides PBr3 + alcohols

Alcohols can also be converted to alkyl halides by phosphorus halides such as PCI PBr3, and PI via an 5 2 mechanism resulting in poor yields with tertiary alcohols. Another reagent for producing alkyl halides from alcohols is thionvl chloride, OCl2, resulting in sulfur dioxide and hydrochloric acid. 

Alcohols undergo many reactions and can be converted into many other functional groups. They can be dehydrated to give alkenes by treatment with POCI3 and can be transformed into alkyl halides by treatment with PBr3 or SOCU- Furthermore, alcohols are weakly acidic (p/C, — 16-18) and react with strong bases and with alkali metals to form alkoxide anions, which are used frequently in organic synthesis. 

Alkyl Halides From the Reaction of Alcohols with PBr3 or SOCl2... 

Other halides that are useful in converting alcohols to alkyl halides are PC15, PC13, PBr3, and Pl3, which are acid halides of phosphorus oxyacids. As with thionyl chloride, a weak base often is used to facilitate the reaction. The base acts to neutralize the acid formed, and also to generate bromide ion for SN reactions ... 

Alcohols can be converted to alkyl halides by reaction with thionyl chloride, SOCI phosphorous trichloride, PCI phosphorous pen-tachloride, PCI or phosphorous tribromide, PBr3. For example, ethyl chloride or ethyl bromide can be prepared from ethyl alcohol via reactions with sulfur and phosphorous halides. 

Since alkyl halides are made from alcohols by treatment with reagents such as PBr3 or HC1 and a Lewis acid, it may make sense in designing the synthesis of ethers to write the two alcohols as starting materials and decide later which to convert into an electrophile. For ether 24 the two alcohols would be 27 and 26. 

Primary and secondary alkyl halides can be formed by treatment of the corresponding alcohols with SOCI2 or PBr3. 

PBr3 and SOCI2 are used for converting secondary and primary alcohols to alkyl halides. 

Primary and secondary alcohols are best converted into alkyl halides by treatment with either thionyl chloride (SOCI2) or phosphorus tribromide (PBr3). These reactions, which normally take place readily under mild conditions, are less acidic and less likely to cause acid-catalyzed rearrangements than the HX method. 

Another C-0 bond reaction of alcohols is their conversion into alkyl halides (Section 10.7). Tertiary alcohols are readily converted into alkyl halides by treatment with either HC1 or HBr at 0°C. Primary and secondary alcohols are much more resistant to acid, however, and are best converted into halides by treatment with either SOCl2 or PBr3. 

PROBLEM 7.17 Write balanced equations for the preparation of the following alkyl halides from the corresponding alcohol and SOCI2, PCI3, or PBr3. 

Conversion of Alcohols to Alkyl Halides with SOCI2 and PBr3... 

We have just seen that an alcohol can be converted into an alkyl halide by treating it with a hydrogen halide. Better yields of the alkyl halide are obtained and carbocation rearrangements can be avoided if a phosphorus trihalide (PCI3 or PBr3) or thionyl chloride (SOCI2) is used instead. 

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