Primary and secondary alcohols can be converted to haloalkanes with reagents such as: phosphorus tribromide, phosphorus trichloride, thionyl chloride, and phosphorus pentachloride.
![preparation-haloalkanes-from-alcohols preparacion-haloalcanos-a-partir-alcoholes](/images/stories/organica-i/alcoholes/haloalcanos-a-partir-alcoholes/preparacion-haloalcanos-a-partir-alcoholes-01.png)
The mechanism of these reactions is of the SN2 type and only primary and secondary alcohols react. Let's look at the mechanism of the first reaction.
![preparation-haloalkanes-from-alcohols preparacion-haloalcanos-a-partir-alcoholes](/images/stories/organica-i/alcoholes/haloalcanos-a-partir-alcoholes/preparacion-haloalcanos-a-partir-alcoholes-02.png)
Stage 1 . Alcohol attack on phosphorus tribromide
![preparation-haloalkanes-from-alcohols preparacion-haloalcanos-a-partir-alcoholes](/images/stories/organica-i/alcoholes/haloalcanos-a-partir-alcoholes/preparacion-haloalcanos-a-partir-alcoholes-03.png)
Stage 2. Bimolecular nucleophilic substitution, with bromide acting as nucleophile
![preparation-haloalkanes-from-alcohols preparacion-haloalcanos-a-partir-alcoholes](/images/stories/organica-i/alcoholes/haloalcanos-a-partir-alcoholes/preparacion-haloalcanos-a-partir-alcoholes-04.png)
All the bromines of PBr3 are reactive and the mechanism is repeated two more times.