Removing acid impurities: Why use sodium hydrogen carbonate instead of sodium hydroxide?
Bicarbonate is a weak base when compared to carbonate, it has already been protonated once and is non nucleophilic whereas hydroxide ion is very nucleophilic and the product from your reaction is an electrophile which can react with hydroxide in solution particularly if the temperature is raised as is the case when quenching acids with bases. So to get the best yield of alkylhalide it is best to use a base which will not react with it – sodium bicarbonate.
