SolutionsSubstitution of Alcohols
1. Products with HBr
Give the main product of the reaction with HBr of:
- 2-Methyl-2-propanol
- 1-Butanol
- 3,3-Dimethyl-2-butanol
- 2-Bromo-2-methylpropane (SN1, tertiary carbocation).
- 1-Bromobutane (SN2 on the protonated alcohol).
- 2-Bromo-2,3-dimethylbutane: the secondary carbocation rearranges to the tertiary one by a methyl shift.
2. Without rearrangement
How would you obtain 2-bromo-3-methylbutane from 3-methyl-2-butanol without rearrangement?
With PBr3 (or by turning the alcohol into a tosylate and treating it with bromide): the substitution is SN2 and does not go through carbocations.
3. Thionyl chloride
Which by-products are formed in the reaction of an alcohol with SOCl2 in pyridine? Why is this reagent convenient?
SO2 and pyridinium chloride. SO2 is a gas and escapes, so the alkyl chloride is easy to isolate.