Burette—50 mL, class A, graduated i

Burette—50 mL, class A, graduated in 0.1 mL divisions.
4. Reflux condensers—ground-glass joints.
5. Steam bath—standard openings.
REAGENTS
1. Pyridine—reagent grade, distilling at 114–115°C (see Notes, Caution).
2. Acetic anhydride—reagent grade, fresh (see Notes, Caution).
3. Pyridine-acetic anhydride reagent—freshly prepared before using by mixing 3 volumes of pyridine with 1 volume of acetic
anhydride.
4. Normal butyl alcohol—reagent grade, neutralized with 0.5 M ethanolic KOH to a faint pink phenolphthalein end point.
5. Ethanolic potassium hydroxide (KOH) solution—0.5 M, accurately standardized according to AOCS Specification H 15-52
(see Notes, 1).
6. Phenolphthalein indicator solution—1% in ethanol.
PROCEDURE
1. Weigh to the nearest 0.1 mg into an Erlenmeyer flask the indicated amount of test sample for acetylation:
Hydroxyl value Mass of test portion, g
0–20 10 ± 0.1 g
20–50 5 g
50–100 3 g
100–200 2 g
2. Weigh 9.0–11.0 g of the test portion into another flask for determination of the acidity (see Notes, 2). For fatty acids, such
as hydroxystearic acid, the weight should be 0.9–1.1 g.
3. Pipet 5.0 mL of the pyridine-acetic anhydride reagent into the flask containing the test portion for acetylation. (For test
portions having a 0–20 hydroxyl value, add an additional 5 mL of pyridine to the flask.) Thoroughly mix the contents by
gentle swirling.
4. Pipet 5.0 mL of pyridine-acetic anhydride reagent into an empty flask for the reagent blank. (If 10.0 mL was used for the
acetylation, use 10.0 mL for the blank.)
5. Add 10 mL of pyridine (neutralized to phenolphthalein) to the test portion for which the acidity is to be determined
(Procedure, 2). Thoroughly mix the contents by gentle swirling, add 1 mL of phenolphthalein indicator solution and titrate
to a faint pink end point with 0.5 M alcoholic KOH.
6. Place the flask on a steam bath, under a reflux condenser and heat for 1 hr (see Notes, 3).
7. Add 10 mL of water through the condenser to the flask and heat on the steam bath for an additional 10 min with the reflux
condenser attached (see Notes, 3).
8. Allow the flask to cool to room temperature with condenser attached.
9. Using a total of about 25 mL of butyl alcohol (neutralized to phenolphthalein), wash the condenser with about 12 mL,
remove the condenser and use the remaining butyl alcohol to wash the sides of the flask.
10. Add 1 mL of phenolphthalein indicator solution. Titrate to a faint pink end point with 0.5 M alcoholic KOH solution