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I am wondering what is the simplest tricarboxylic acid that can be isolated in a pure form. Would it be methanetricarboxylic acid or ethane-1,1,2-tricarboxylic acid or maybe even longer chain is required to make the compound stable?

pajacol
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1 Answers1

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Ethane-1,1,2-tricarboxylic acid, $\ce{C5H6O6}$, is sold by Sigma-Aldrich and has experimentally determined properties including a boiling point of 278.5°C.

Honorable mention goes to aconitic acid (propene-1,2,3-tricarboxylic acid), $\ce{C6H6O6}$, which appears as a conjugate base in the biologically important citric acid cycle. Citric acid, $\ce{C6H8O7}$ (actually its conjugate base and conjugate bases of the acids to follow), is dehydrated to give aconitic acid and then rehydrated to give isocitric acid ($\ce{C6H8O7}$, but with the alcoholic hydroxyl group on a different carbon atom), which is oxidized and decarboxylated to continue the cycle.

Oscar Lanzi
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    I have heard esters and salts of methanetricarboxylic acid but I don't think the compound itself actually exists [citation needed?]. – Nilay Ghosh Aug 12 '23 at 03:08
  • Looking up "methane tricarboxylate" on Google -> the triethyl ester turns up. Maybe placing theee carboxyl groups around one carbon atom is possible only if none is specifically COOH, which would decarboxylate. – Oscar Lanzi Aug 12 '23 at 08:17
  • This report mentions they detected methanetricarboxylic acid and that it's not available commercially. I guess it indeed decarboxylates if you'd try to make it pure, but is quite possible. Even methanetetracarboxylic salts exist, but I guess the thing breaks down very fast in low pH. – Mithoron Aug 13 '23 at 17:02
  • @Mithoron yes, I see this. As you mentioned, whether the acid can be purified (as the C5H6O6 compound is in the product quoted by Sigma-Aldruch) remains a question. – Oscar Lanzi Aug 13 '23 at 17:42