Alcohols donot react with NaBr but when ...

Alcohols donot react with NaBr but when H.SO, is added they form alkyl bromides. Explain.

Text Solution

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Although `Br^(-)` is a strong nucleophile yet `OH^(-)` being a strong base is a bad leaving group. Therefore, `Br^(-)` cannot displace `OH^(-)` from ROH to form R-Br. In other words, NaBr does not react with alcohols. however, when `H_(2)SO_(4)` is added, protonation of alcohol occurs, i.e., -OH is converted into `-overset(+)(O)H_(2)`. since `H_(2)O` is a very weak base, therefore, it is a good leaving group. in otehr words, `Br^(-)` cann displace `H_(2)O` from protonated alcohol to form RBr.

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Mg reacts with alkyl bromide best in

`C_6H_5OCH_3`

`C_6H_5N(CH_3)_2`

`C_2H_5OC_2H_5`

equally in all three solvents.

Alcohol (ROH) does not react with NaBr to form alkyl bromide because

NaBr is in soluble in alcohol

`Br^(-)` is strong base than `OH^(-)`

NaBr is an ionic compound

`OH^(-)` is a strong base than `Br^(-)`

Alcohols are converted to alkyl bromides by

PBr_3`

LAH

`Br_2`

None of these