During reaction of 1-butanol and HBr, some unreacted amount of HBr might present in reaction mixture. Hence cold NaOH is used to neutralize unreacted HBr.
Washing with [tex]H_{2}O[/tex] is done to remove the salt produced during neutralization i.e. NaBr from organic layer of 1-bromobutane.
NaCl is added to remove water from organic layer. Because NaCl is more soluble in water than organic layer.
