Appendix X A. Acetyl Value

The acetyl value of a substance is the number of mg of potassium hydroxide required to neutralise the acetic acid liberated by the hydrolysis of 1 g of the acetylated substance.

Determine the saponification value, Appendix X G.

Acetylate by the following method. To 10 g in a 200-mL Kjeldahl flask add 20 mL of acetic anhydride. Support the flask on a sheet of heat resistant material in which a hole about 4 cm in diameter has been cut and heat with a small, naked flame, not more than 25 mm in height and which does not impinge on the bottom of the flask. Boil gently under a reflux air condenser for 2 hours, allow to cool, pour into 600 mL of water contained in a large beaker, add 0.2 g of pumice powder and boil for 30 minutes. Cool, transfer to a separating funnel and discard the lower layer. Wash the acetylated product with three or more 50-mL quantities of a warm, saturated solution of sodium chloride until the washings are no longer acidic to litmus paper. Finally shake with 20 mL of warm water and remove the aqueous layer as completely as possible. Pour the acetylated substance into a small dish, add 1 g of powdered anhydrous sodium sulfate, stir thoroughly and filter through a dry, pleated filter paper. Determine the saponification value of the acetylated substance.

Calculate the acetyl value from the expression 1335(b–a)/(1335–a) where a is the saponification value of the substance and b is the saponification value of the acetylated substance.