SYNTHESIS OF BUT-2-EN-1-0L (Crotyl alcohol)

• Prepare a solution of aluminium isopropoxide from 23.5 g (0.83 mol) of aluminium, 0.5 g of mercury(H) chloride and 250 ml of dry isopropyl alcohol; add 105 g (1.5 mol) of redistilled crotonaldehyde, b.p. 102-103 °C, and 500 ml of dry isopropyl alcohol. 

• Attach an efficient fractionating column to the flask and arrange for distillation from an oil bath so that the acetone distils as it is formed. 

• Maintain the temperat­ure of the bath at about 110 °C and the temperature at the top of the column at 60-70 °C. 

• When the distillate no longer gives a test for acetone (8-9 hours) (1), reflux for a further 10 minutes and then distil off most of the remaining isopropyl alcohol, preferably under reduced pressure. 

• Cool the residue to 40 °C and add 450 ml of cold 3 M sulphuric acid (from 72.5 ml of concentrated sulphuric acid and 395 ml of water); cooling is necessary. 

• Separate the upper oily layer, wash it once with water and distil at 60-70 °C while lowering the pressure slowly from about 275 mm to 60 mm; then continue the distillation to 110 °C and 20 mm. 

• In this way the crotyl alcohol (A) is separated from the higher boiling polymerisation products. 

• Combine the aqueous layers and dis­til until the distillate no longer gives a test for unsaturation with a dilute solu­tion of bromine in carbon tetrachloride. 

• Saturate the aqueous distillate with potassium carbonate, separate the oily layer and add it to (A). 

• Dry with 5 g of anhydrous potassium carbonate, decant the oil and distil through an efficient fractionating column. 

• Collect the crotyl alcohol at 119-121 °C. The yield is 55 g (50%). 

• Record the p.m.r. (CDC1₃) and compare the spectrum with that of (Z)-but-2-en-1-ol. Assign the "C-n.m.r. absorptions which occur at 617.6, 63.0, 127.1 and 130.7.