Modification of a procedure for analytical hydrogenation of edible oils

Unsaturation, an important parameter in edible oils, can be determined by analytical hydrogenation. Recently Brown et al. (3-9) have proposed an "automatic" direct titration method for hydrogenation of various unsaturated organic compounds. Sodium borohydride, introduced through a pressure-actuated mercury valve, was utilized as hydrogen producing reagent, and both the hydrogen and the platinum catalyst were generated in situ. Application of the above method to determination of unsaturation in various edible oils was the subject of the present study. Several shortcomings inherent in the original procedure and apparatus have been overcome by introducing suitable changes. Isopropanol was used as a solvent for the borohydride; the buret was used at the operational stage in the near horizontal position; the end point manometer was filled with Brodie's solution; and the system was preliminarily flushed with hydrogen from an external source and was operated at a slight overpressure. As a result of those changes, the determined hydrogen iodine values were closer to the expected ones and the standard deviations were appreciably lowered. Gravimetric determinations have confirmed Brown's observation that the precipitated powder produced by reduction of chloroplatinic acid consists only of pure platinum. Microscopic examinations revealed that a finer structure and better dispersion is obtained when platinum was precipitated on activated carbon as support. This can be conceived with the observed higher over-all reaction rates achieved with the supported catalyst.