[xyz133]

I am trying to convert benzimidazole derivate (base) to citrate. The benzimidazole is practically insoluble in water however I noticed the formation of salt when I macerate the mixture of citric acid and benzimidazole. The mixture I used was 1:1 mass ratio which resulted in final product that was part salt and part citric acid. What would be the correct procedure to obtain benzimidazol citrate (no excess base or acid)? I guess I should use molar ratio instead. But then again – citric acid contains 3 COOH groups, is the salt formation possible on all three of them? How important are steric effects here? Thanks for all the answers.

[wildfyr]

What about doing it in organic solvent ? Wikipedia says citric acid is actually soluble in a bunch of organic solvents (alcohols, ethyl acetate, ETHER?!). How about dissolving it 1:1 in ethyl acetate or ether and the salt you want may crash right out.

[sjb]

To clarify, probably a 1:1 ratio by moles rather than by mass might be better.

[wildfyr]

Good catch sjb. Yes, clearly do it by molar ratio, mass is a useless way to do a ratio when talking about any chemical reaction.

PS: I noticed also that citric acid has decent solubility in dioxane (34g/100 mL, so that is an option, and indicates THF probably works too.