Epoxidized soy oil is a vegetable oil that has been reacted with an epoxidizing agent to form a resin-like substance with an epoxy group. The hydroxyl number of a substance is a measure of the amount of hydroxyl (OH) groups present in the molecule, which can react with other molecules such as acids or anhydrides.

Epoxidized soy oil can show a hydroxyl number during titration because the epoxy group in the molecule can undergo hydrolysis in the presence of a strong acid, such as perchloric acid or sulfuric acid, to form a diol. This diol contains two hydroxyl groups, which can be titrated to determine the hydroxyl number of the substance.

The hydroxyl number of epoxidized soy oil can be important in various applications, such as in the production of coatings, adhesives, and sealants. The hydroxyl number can help to determine the reactivity and functionality of the material, which can affect its performance in these applications.