Improved procedure for titrating cyclopropene esters with hydrogen bromide [Cottonseed and other oils]

The titration of cyclopropenes in cottonseed and other oils with hydrogen bromide was improved by changes in the preparation of the sample and the titration. Methanolysis of the oil under selected conditions with a large excess of alkaline catalyst (sodium methoxide or tetramethylammonium hydroxide) yielded methyl esters free of oxidation products and partial glycerides and eliminated the need for treatment with a large amount of activated alumina, which disproportionates methyl esters. The color indicator, 4‐phenylazodi‐phenylamine, exhibited great sensitivity in toluene at 25 C. The best procedure consisted of titrating methyl esters with hydrogen bromide at 60–65 C to just past the end‐point, cooling to about 25 C, and back‐titrating with aniline in toluene. With 10‐ to 2‐g samples containing less than 1% cyclopropenes, reproducibility usually was within ±0.003% of the average value.