Place 30 cm3 of water, 35 g of powdered sodium bromide and 25 cm3 of butan-1ol in a 250 cm3 round bottomed flask. Fit a tap funnel to the flask via a stillhead. Place 25 cm3 of concentrated sulphuric acid in the tap funnel, and then allow the acid to fall drop by drop into the flask, keeping the contents well shaken and cooled occasionally in an ice-water bath.
Why is the sulphuric acid added slowly, and why is cooling and shaking needed? Sulphuric acid when diluted with water gives out a great deal of heat, enough sometimes to raise steam which would cause dangerous splashing. Also, hot 50% sulphuric acid (which is what is produced in the flask) will cause significant oxidation of the sodium bromide to bromine, which is useless in this experiment. The yield of 1bromobutane could therefore be affected adversely. Why is a sand-bath used for heating? The sand spreads the heating uniformly over the base of the flask. This reduces the likelihood of cracking, and of unwanted side reactions occurring (e.g. excessive oxidation either of bromide ions to bromine or of the alcohol to carbon) owing to hot-spots. Why is the mixture heated for 45 minutes? Most organic reactions are slow because of the need to break strong covalent bonds. Why is the mixture distilled at this stage? The liquid 1-bromobutane is removed from the involatile sodium salts (mostly sodium hydrogen sulphate at the end of the reaction) and the much less volatile sulphuric acid. The 1-bromobutane will be contaminated with water, unchanged butan-1-ol, and some sulphuric acid carried over as tiny droplets during the distillation.
When the addition is complete, replace the tap funnel and stillhead with a reflux water condenser and gently boil the mixture over a sand-bath for about 45 minutes, shaking the flask gently from time to time.
Remove the reflux condenser and rearrange the apparatus for distillation. Distil off the crude 1-bromobutane (about 30...