Alkyl Halides from Alcohols
If you need an alkyl halide for a reaction, it is possible to make it from a free radical halogenation. But, there are other ways to obtain alkyl halides other than this. If I was in the lab and needed an alkyl halide for a reaction, I usually open a chemical catalog and order it. It shows up in a day or two in the mail. But, if I cannot order it, I might make the alkyl halide from an alcohol. The common method to make them is from an alcohol.
Which reagent we use to make an alkyl halide from an alcohol depends on two things, the type of halogen we desire and the type of alcohol we start with.
Tertiary alcohols react with HCl, HBr, or HI to make the appropriate alkyl halide. Secondary alcohols work slower this way. Primary and methyl alcohols do not work well with this method.
Sometimes a reagent called the Lucas reagent is used to turn a secondary or tertiary alcohol into a chloride. For the Lucas reagent, zinc chloride, ZnCl2, is used with HCl. This combination of ZnCl2 and HCl works better than HCl alone.
If we try to turn a primary or secondary alcohol into a halide, we need to use different reagents. We use thionyl chloride (SOCl2) to make chlorides, phosphorus tribromide (PBr3) to make bromides, and a combination of phosphorus and iodine (P/I2) to make iodides.
Conversion of hydroxyl groups to halides
Best Reagents to Transform Alcohols to Halides
6. Fill in the appropriate reagent or product.
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b)
c)
d)
e)
f)
Answers
6. Fill in the appropriate reagent or product.
a)
b)
c)
d)
e)
f)
