I'm trying to determine the hydroxyl value of the fatty acid of castor oil in my product mixture. Ricinoleic acid has a secondary hydroxyl group in its chain. So then, if I do this test, will the carboxyl group be included? I honestly rather hope that it does not and I don;t think so, but while you are answering this question, how reliable do you think methods like acid value and hydroxyl value in accurately determining the amount of my unreacted ricinoleic acid after a reaction?
Ricinoleic acid (1 -OH and 1 -COOH) + epoxy --> Ricinoleic acid (unreacted) + RA-Epoxy (2 -OH) + other minor byproducts.
My guess is, Acid Value will tell me how much Ricinoleic acid is left and the hydroxyl value will tell me the total hydroxyl value. I can then take this total hydroxyl value and minus the acid value to exclude those hydroxyls from the unreacted ricinoleic acid.
I know it's a bit overly complicated but my attempts at silica column separation has failed miserably and our uplc system is not suitable for the separation of these compounds.
Question to your reaction: You want to produce ricinoleic acid epoxide? Or you react an epoxide with the acid to form what? Please give some details.
Be careful with this: if you use a method with acetic anh. at the end of valoration you have to use NaOH standar solution, so it neutralize not only free acetic acid but also free COOH from ricinoleic.
@ Klaus Belsner
It's a reaction with glycidyl methacrylate (epoxide with a methacrylate). Using a Phase transfer catalyst, it is an epoxide ring opening reaction. Imidazoles work too.
Usually, I would have gone the easier way of using iodine value to test for double bond addition, but apparently, the iodine value tests do not work on methacrylates, which I have no idea why. I can therefore only resort to determining how much hydroxyls there are. But then, I'm unsure if that test will affect the hydroxyls in the COOH.
@ Alberto Molina
I believe the ASTM procedure calls for a correction for free acids present in the sample. It says to add the correction if NaOH is needed to neutralize, subtract if HCl is needed to neutralize. Can I assume then that acetic anhydride will not acetylate the COOH?
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