SYNTHESIS OF t-BUTYL ACETATE

Method A:

• Fit a 1-litre three-necked flask with a sealed stirrer, a reflux condenser and a dropping funnel. 

• Place 57 g (73.5 ml, 0.77 mol) of dry 2-methyl-propan-2-ol (t-butyl alcohol) (1), 101 g (106ml, 0.84mol) of pure dimethylaniline and 100 ml of anhydrous ether in the flask, set the stirrer in motion and heat the mixture to gentle refluxing on a water bath. 

• Run in 62 g (56.5 ml, 0.79 mol) of redistilled acetyl chloride at such a rate that moderate refluxing continues after the source of heat is removed. 

• When about two-thirds of the acetyl chloride has been introduced, the dimethylaniline hydrochloride commences to crystallise and the mixture refluxes very vigorously. 

• Cool immediately in an ice bath, and, after refluxing ceases, add the remainder of the acetyl chloride; then heat the mixture on a water bath for 1 hour. 

• Cool to room temperature, add about 100 ml of water and continue the stirring until all the precipitated solid has dissolved. 

• Separate the ether layer and extract with 25-ml portions of cold 10 per cent sulphuric acid until the acid extract does not become cloudy when rendered alkaline with sodium hydroxide solution. 

• Finally, wash with 15 ml of saturated sodium hydrogen carbonate solution and dry the ethereal solution with 5 g of anhydrous sodium sulphate overnight. 

• Remove the ether by distillation through an efficient fractionating column and distil the residue through the same column. 

• Collect the t-butyl acetate at 96-98 °C (mainly 97-98 °C). The yield is 55g (62%).

 Notes to keep in mind:

1. The t-butyl alcohol should be dried over calcium oxide or anhydrous calcium sulphate and distilled.

 Cognate Preparation: t-Butyl propanoate

• Use 85.5 g (110.5 ml, 1.15 mol) of t-butyl alcohol, 151.5 g (159ml, 1.26 mol) of pure dimethylaniline and 110g (103 ml, 1.19 mol) of propanoyl chloride and reflux for 3 hours (b.p. 117.5-1 18.5 °C). Yield: 92 g (62%).

Method B:

• Fit a 500-ml round-bottomed flask with a reflux condenser carrying a calcium chloride guard-tube. 

• Place 100 ml (108 g, 1.06 mol) of redistilled acetic anhydride, 100 ml (1.07 mol) of dry t-butyl alcohol (see Note in Method A) and 0.3 g of anhydrous zinc chloride in the flask and shake. 

• Heat the mixture gradually to the reflux temperature, maintain at gentle refluxing for 2 hours and then cool. 

• Replace the reflux condenser by an efficient fractionating column and distil until the temperature reaches 1 10 °C. 

• Wash the crude distillate, weighing 100-125 g, with two 25 ml portions of water, then with 25 ml portions of 10 per cent potassium carbonate solution until the ester layer is neutral to litmus, and finally dry with 10 g of anhydrous potassium carbonate. 

• Filter off the desiccant, and distil through an efficient fractionating column (e.g. Widmer column) and collect the pure t-butyl acetate at 96-98 °C. The yield is 70 g (57%).