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I'm wondering if

  1. it is at all possible to vacuum distill citric acid without the slightest decomposition;
  2. it is something that can easily be done in a small lab with widely available equipment.

I've looked on internet and found the following data:

  • ~154 °C melting point (anhydrous citric acid)
  • ~175 °C starts decomposing
  • ~310 °C boiling point
  • ~$10^{-8}$ mmHg vapor pressure at 25 °C
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    $\begingroup$ If you have enough to do a real distillation (not say Kugelrohr), you should have enough for a recrystallization, and I suspect you'll get better results. $\endgroup$
    – Zhe
    Nov 4 '20 at 16:57
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    $\begingroup$ Itaconic acid is formed by the distillation of citric acid. en.wikipedia.org/wiki/Itaconic_acid $\endgroup$
    – user55119
    Nov 4 '20 at 17:28
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    $\begingroup$ Given that the citric acid has an appreciable vapor pressure at 25 °C, I'd look into purification using vacuum sublimation. $\endgroup$
    – MaxW
    Nov 4 '20 at 20:10
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    $\begingroup$ @MaxW Good point, but I don't trust that number. 10mmHg vapour pressure should give a well notiveabele acidic smell, which citric acid doesn't have. $\endgroup$
    – Karl
    Nov 4 '20 at 20:16
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    $\begingroup$ The thermal conversion of citric acid is a decarboxylative dehydration to form the double bond of itaconic acid. $\endgroup$
    – user55119
    Nov 4 '20 at 20:44

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