1. Erlenmeyer flasks—250 mL, with T

1. Erlenmeyer flasks—250 mL, with TS 24/40 glass stopper.
2. Pipet—5 mL, volumetric.
3. Burette—50 mL, graduated in 0.1 mL divisions.
REAGENTS
1. Pyridine—C.P. or reagent grade distilled at 114–115°C (see Notes, Caution).
2. Acetic anhydride—ACS grade, fresh (see Notes, Caution).
3. Pyridine-acetic anhydride reagent—freshly prepared before use by mixing 3 volumes of pyridine with 1 volume of acetic
anhydride.
4. n-butyl alcohol—C.P. or reagent grade neutralized with 0.5 M ethanolic KOH to faint pink phenolphthalein end point.
5. Ethanolic potassium hydroxide solution, 0.5 M or 1.0 M—standardized, using AOCS Specification H 15-52 (see
Notes, 1–3).
6. Phenolphthalein indicator solution—1% in ethanol.
PROCEDURE
1. Weigh to the nearest 0.1 mg into the Erlenmeyer flask the indicated amount of the test sample for acetylation—
Expected Hydroxyl Value Test Sample Mass
0–25 10 g ± 0.1 g
25–50 5 g ± 0.1 g
50–100 2.5 g ± 0.1 g
100–200 1.25 g ± 0.1 g
2. Pipet 5.0 mL of the pyridine-acetic anhydride reagent into the flask containing the test sample for acetylation. For test
samples having a 0–25 hydroxyl value, add an additional 5 mL of pyridine (not neutralized) to the flask. Thoroughly mix
the contents by swirling. Stopper flask using a small amount of stop-cock grease for seal. Let stand at 25°C for 24 hr.
Note—If 1.0 M alcoholic KOH is available for titrating, then use 10 mL of pyridine-acetic anhydride reagent.
3. Pipet 5.0 mL of pyridine-acetic anhydride reagent into an empty flask for the reagent blank (add the same volume of any
extra pyridine, not neutralized, that was added to test sample). Stopper the same as the test sample and let stand at 25 ± 5°C
for 24 hr.
4. Determine the Acid Value by AOCS Method Te 2a-64.
5. After the test sample and blank flasks have stood for 24 hr add 10 mL of water. Use water to wash stoppers and sides of flasks.
Add 10 mL of pyridine (not neutralized), again washing stoppers and sides of flasks. Stopper and mix thoroughly by swirling.
Let flasks stand for 30 min after mixing with occasional swirling of the flask before proceeding to next step.
6. Add 25 mL of n-butyl alcohol (neutralized to phenolphthalein end point) to both test sample and blank, again rinsing off
stoppers and sides of the flask.
7. Add 1 mL of phenolphthalein indicator solution to both test sample and blank. Titrate to a faint pink end point with 0.5 M
alcoholic KOH solution.
CALCULATIONS
1. Uncorrected Hydroxyl Value = (B – S) M 56.1
W
× ×
2. Corrected Hydroxyl Value = Uncorrected Hydroxyl Value + Acid Value
3. % OH = hydroxyl value
32.98
Page 2 of 2
INDUSTRIAL OILS AND DERIVATIVES
Tx 1a-66 • Hydroxyl Value of Epoxidized Oils
Copyright © 2009 by the AOCS
Where—
B = volume, mL KOH solution required for the reagent blank, Procedure, 7
S = volume, mL KOH solution required for the ± 0.1 titration of the acetylated test portion, Procedure, 7
W = mass of test portion used for acetylation, Procedure, 1 Acid Value determined by AOCS Method Te 2a-64
PRECISION
The method precision was determined in accordance with AOCS Method M 1-59 (surplus method, 1989), using five laboratories
and three types of epoxidized products. Precision at the 95% confidence level for each product type is:
Epoxy Epoxy Epoxy
Type of Epoxidized Oil Soybean Tallate Castor
Average hydroxyl value: 7.57 29.6 180.5
Agreement Within a Laboratory -
Two single determinations
performed within a laboratory
should not differ by more than: 1.90 2.20 6.68
Agreement Among Laboratories -
Single determinations performed
in two different laboratories
should not differ by more than: 2.31 4.50 8.53
NOTES
Caution
Pyridine is flammable and a dangerous fire risk. The explosive limits in air are 1.8–12.4%. It is toxic by ingestion and inhalation.
The TLV is 5 ppm in air. The danger from crude pyridine is greater than from pure pyridine, the associated homologs and
impurities being even more toxic than pyridine itself.
Acetic anhydride is a strong irritant and corrosive. It can cause burns and eye damage. Eyes and hands should be protected
when working with this compound. Work should be carried out in a properly operating fume hood.
NUMBERED NOTES
1. The caustic strength should not be less than 0.5 M (or 1.0 M if 10 mL of acetic anhydride reagent is used) in order that the
blank titration will not require more than 50 mL. Refilling of the burette during any single titration is to be avoided.
2. Ethanolic KOH should be prepared from Formula 30 ethanol (denatured with methanol).
3. Methanolic KOH may be substituted for ethanolic KOH.