ASTM E222 Determination of Hydroxyl Groups

Scope:

ASTM E222 covers procedures to analyze aliphatic and alicyclic compounds and phenols for hydroxyl groups. The hydroxyl groups attached to the primary and secondary carbon atoms can be determined using any one of the three test methods mentioned in this standard. Test Method A is recommended for general use. Test Method B describes the most widely used procedure whereas Test Method C is applied when the results are required in a short time span or where the ambient temperature for the reaction is desired. Test methods A and C show consistent precision over a wide range of hydroxyl content (tested over hydroxyl number range of 250 to 1600). Method B on the other hand is more precise for lower hydroxyl content levels.

Test procedure:

ASTM E222 describes three test procedures for the determination of hydroxyl groups:

Test Method A (Pressure Bottle Method)- The sample is acetylated with a solution of acetic anhydride in pyridine in a pressure bottle at 98°C. The excess reagent is hydrolyzed with water. 

Test Method B (Reflux Method)- The sample is acetylated with a solution of acetic anhydride in pyridine at the reflux temperature. The excess reagent is hydrolyzed with water. 

Test Method C (Perchloric Acid Catalysed Method)- The sample is acetylated at room temperature with a solution of acetic anhydride and perchloric acid in 1,2-dichloroethane. The excess reagent is hydrolyzed with aqueous dimethylformamide-pyridine. 

The acetic acid formed in the above-mentioned methods described in ASTM E222 is titrated with a standard sodium hydroxide solution. The hydroxyl content is calculated from the difference in the titration of the blank and sample solutions.

Video 01: Determination of hydroxyl value through titrimetric method

Specimen size:

For ASTM E222, the sample should not exceed 10 g. The sample weight is determined using one of the following equations,

where:

MW = molecular weight of the hydroxyl-containing compound, and

n = number of hydroxyl groups present in the molecule.

Data:

In ASTM E222, the hydroxyl content is calculated in terms of the hydroxyl number or percentage of the hydroxyl-containing compound as follows,

where:

A = NaOH solution, mL, required for titration of the blank,

B = NaOH solution, mL, required for titration of the sample,

N_t = meq/mL of the solution at the temperature during analysis,

n = number of hydroxyl groups in the compound,

MW = molecular weight of the hydroxyl-containing compound, and

W = sample used, g.

Conclusion:

ASTM E222 covers procedures to analyze aliphatic and alicyclic compounds and phenols for hydroxyl groups.