Boiling point ( ) K Butane CH -CH -CH -CH . Propanal CH -CH -CHO Methoxyethane CH -O-CH -CH . Prapan – - ol CH -CH -CH -OH . Propan – - ol CH -CH(OH)-CH .
Chemical properties of alcohols Nucleophilic substitution reactions of alcohols Alcohol has a strong basic leaving group (OH – ). So, –OH group is first converted into OH group by adding an acid. The − OH group in the protonated alcohol can be easily displaced by a nucleophile such as Br - to give alkyl halides. Example : Alcohols undergo nucleophilic substitution reaction with hydro halic acids to form alkyl halides.
In case of tertiary alcohols heating is required. HBr - H O Br Ethanol Bromoethane Alkyl halide formation from primary alcohols follow S N mechanism Example H - Br -Br - Br + H O Br ethanol bromoethane Nucleophilic attack of Br − and leaving of H O takes place simultaneously. XII U11-Hydroxy XII U11-Hydroxy - - - - Alkyl halide formation of tertiary alcohols follow S N mechanism. Example O ..
.. Br H C CH Br H C Br H C HBr Addition reaction (elimination) -Br - -methyl- -propanol -methylprop- -ene -bromo- -methylpropane Slow Fast –H + Here, the carbocation formed can undergo elimination to give an alkene. However the alkene can again undergo addition reaction with HBr to give the substituted product. Conversion of alcohol into alkyl halides: Other methods Alcohols can also be converted into an alkyl halides using PCl PBr , .
CH CH OH PCl pyridine CH CH Cl ethanol chloroethane Mechanism : S N reaction on phosphorous tri chloride CH O .. H + P Cl Cl Cl -Cl PCl PCl Cl CH CH Cl .. .. PCl N ..
chloroethane The conversion of an alcohol to alkyl halide