iso-Propyl Bromide from iso-Propyl Alcohol

Measure 25 ml of iso-propyl alcohol into a 250 ml round-bottom flask, followed by 150 ml of 48% aqueous hydrobromic acid. (Conduct the experiment in a fume-cupboard.) Distill slowly until half the mixture has passed over. Isolate the organic layer of the distillate, then distill the aqueous layer to recover any dissolved iso-propyl bromide. Combine the products and wash with 1) a portion of concentrated hydrochloric acid, 2) a portion of water, 3) a portion of 5% sodium bicarbonate, and 4) a portion of water. Dry the crude iso-propyl bromide, filter and distill at 59�C. About 80% yield.

Note: Hydrobromic acid is prepared from bromine and sulphur dioxide. When the product is distilled at about 126�C the distillate is a 48% aqueous solution. So this is sometimes known as the constant boiling point hydrobromic acid.

tert-Butyl Chloride from tert-Butyl Alcohol

Measure 30 ml of tert-butyl alcohol into a 250 ml flask. Add 80 ml of conc. HCl acid and stir for about half an hour. (Conduct the experiment in a fume-cupboard.) Isolate the organic layer. Wash with 1) a portion of 5% sodium bicarbonate, and 2) a portion of water. Dry the product and distilled at 50�C. About 90% yield.

Isobutyl Bromide from Isobutyl Alcohol

Isobutyl alcohol is maintained at 0˚C with PBr₃ for 4 hours. The product is washed, dried, and distilled. Yield = 60%.

Cyclohexene from Cyclohexanol

100g of cyclohexanol is heated with 20 g of 85% phosphoric acid at 170˚C for 5 hours, and then at 200˚C for a further half an hour. The organic portion is dried and distilled for cyclohexene at 81 - 83˚C. Yield = 80%.