Determination of hydroxyl value

The hydroxyl value of a fatty alcohol or ethoxylate is defined as the number of milligrams of potassium hydroxide required to neutralise the acid required to esterify the hydroxyl groups in one gram of sample, i.e. the number of milligrams of potassium hydroxide that contains the same number of hydroxide ions as there are hydroxyl groups in one gram of sample. 

Two methods are in general use, in which acetic anhydride and phthalic anhydride are used as the respective esterifying agents. ISO 4326 [3] and ASTM Method D 4252-89 [4] describe the acetic anhydride and phthalic anhydride methods respectively, and the reader is advised to refer to the appropriate standard method. 

Both methods are applicable to ethylene oxide adducts of primary fatty alcohols, alkylphenols and fatty acids. They are also applicable to primary fatty alcohols, although this is not mentioned in either Standard. 

According to ISO 4326, the acetic anhydride method is subject to interference from a large number of materials, including amines, amides, thiols, epoxides and some fatty acids and esters, and is not applicable to propylene oxide adducts. The phthalic anhydride method may be subject to the same constraints, but the ASTM method does not say so. 

Esterification of the terminal hydroxyl groups with acetic or phthalic anhydride  

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Reaction with acetic anhydride is used in pharmacopoeial assays of benzyl alcohol and dienestrol and determination of hydroxyl values of castor oil, cetosteryl alcohol and cetomacrogol. 

SFS-ISO 1875 Plastics. Plasticized cellulose acetate. Determination of matter extractable by diethyl ether SFS-EN ISO 2554 Plastics. Unsaturated polyester resins. Determination of hydroxyl value (ISO 2554 1997)... 

Additionally, polyesters and polyethers may contain several impurities derived from their methods of manufacture and being polymeric materials may vary in molecular weight and type of end-group. For routine analysis of raw materials, a determination of hydroxyl value, acid value and water content is usually sufficient. The reactivity of polyesters of the same chemical type can vary widely and for this reason it is sensible that an activity test be performed similar to that for diisocyanates using a diisocyanate of standardized activity. 

ISO 4326 1980 Nonionic surface active agents— Polyethoxylated derivatives— Determination of hydroxyl value— Acetic anhydride method. International Organization for Standardization, Geneva. 

The percentage of each ester can then be calculated. The basis of this calculation is that the monoester has one terminal hydroxyl group and one saponifiable ester group. The net volume of alkali used to saponify the monoester is therefore equal to the net volume used in the determination of hydroxyl value. 

Fleming J. Rapid method for the determination of hydroxyl values. J Cosmet Sci 1966 17 625-630. 

Campbell, W., The Use of Near Infrared Spectroscopy for the Determination of Hydroxyl Value in AUcoxylates, in NIRS Int. Symposium, Technicon Industrial Systems. 1986. Scheveningen, Holland. 

R. 0. Crisler and A. M. Burrill, Determination of Hydroxyl Value of Alcohols by Near-Infrared Spectroscopy, Anal, Chem, 31, 2055,1959. 

International Organization for Standardization, Nonionic surface active agents— polyalkoxy-lated derivatives—determination of hydroxyl value—phthalic anhydride method, ISO 4327 1979. Geneva, Switzerland. 

Avramenko6 specified the value of the hydroxyl absorption molecular coefficient in a form convenient for use in the determination of hydroxyl concentrations under flame conditions. 

Direct injection enthalpimetry has great potential for determining the hydroxyl values of polyethers and polyesters. 

Direct injection enthaipimetry has great potential as a method for determining the hydroxyl values of polyethers and polyesters. The method is rapid, the temperature rises for two samples and a standard being recorded in duplicate in about 10 minutes. 

It is explained in note 1 that the analysis is carried out using a toluene solution of the polyol which is exactly decimolar with respect to total primary and secondary hydroxyl groups in the sample. First determine the hydroxyl value (FI, mg KOFI/g) of the polyol sample by a modified catalysed acetylation procedure. Calculate... 

Hie extent of depolymerization of PET as a result of glycolysis requires the determination of die hydroxyl value of die glycolyzed PET ... 

Results for the hydroxyl value determination were inconclusive the precision of the method and the normal range of results for receipts of EO were not significantly different. Combined with the finding of zero for the peroxide value, the oxidation hypothesis seems less likely. Moisture content and pH results were more interesting. Normally, pH readings on the ethoxylate were above 10. The moisture values were somewhat above typical values. These two results do not really support or refute the hypothesis of EO oxidation, but when solving a problem, any unusual or unexpected results are noteworthy. 

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