Appendix X G. Saponification Value

The saponification value is the number of mg of potassium hydroxide required to neutralise the free acids and to saponify the esters in 1 g of the substance.

Use Method I unless otherwise specified in the monograph.

Method I

Dissolve 35 to 40 g of potassium hydroxide in 20 mL of water and add sufficient ethanol (96%) to produce 1000 mL. Allow to stand overnight and pour off the clear liquid.

Weigh 2 g of the substance into a 200-mL flask, add 25.0 mL of the ethanolic solution of potassium hydroxide and boil under a reflux condenser for 1 hour, rotating the contents frequently. While the solution is still hot, titrate the excess of alkali with 0.5m hydrochloric acid VS using 1 mL of phenolphthalein solution R1 as indicator. Repeat the operation without the substance being examined.

Calculate the saponification value from the expression 28.05 v/w where v is the difference, in mL, between the titrations and w is the weight, in g, of substance taken.

Method II

The saponification value I_S is the number that expresses in milligrams the quantity of potassium hydroxide required to neutralise the free acids and to saponify the esters present in 1 g of the substance.

Unless otherwise prescribed, use the quantities indicated in Table 2.5.6.-1 for the determination.

Introduce the prescribed quantity of the substance to be examined (m g) into a 250 mL borosilicate glass flask fitted with a reflux condenser. Add 25.0 mL of 0.5 M alcoholic potassium hydroxide and a few glass beads. Attach the condenser and heat under reflux for 30 min, unless otherwise prescribed. Add 1 mL of phenolphthalein solution R1 and titrate immediately (while still hot) with 0.5 M hydrochloric acid (n₁ mL of 0.5 M hydrochloric acid). Carry out a blank test under the same conditions (n₂ mL of 0.5 M hydrochloric acid).