Submicro methods for the analysis of organic compounds : The determination of hydroxyl groups

Various procedures were examined for the determination of organic hydroxyl groups. Conventional acetylation methods could not be used on the submicro scale, but the spectrophotometric method based on esterification with 3,5-dinitrobenzoyl chloride followed by extraction of the ester and colour development with alkaline acetone proved reasonably satisfactory for aliphatic alcohols. Acidic hydroxyl groups e.g. in phenolic compounds, were titrated accurately with 0.01 M tetrabutylammonium hydroxide in benzene-methanol solution in a pyridine medium ; visual end-points or potentiometricend-points with glass-silver or glass-in-stream platinum electrode pairs were used depending on the strength of the acidic group. Some differentiating titrations were possible. A general submicro bromination method for phenols was not feasible.