The solubility of folic acid is just 1.6 mg/L (25 °C).

Why is it so insoluble in water while it is one of B vitamins which are called water-soluble vitamins beside Vitamin C?

  • $\begingroup$ You don't need much of it - 400 micrograms could still be dissolved in a glass of water. $\endgroup$
    – Mithoron
    Aug 18, 2023 at 19:55
  • $\begingroup$ But when we say a compound is water-soluble we are saying it has a significance solubility in water. $\endgroup$ Aug 18, 2023 at 20:11
  • 1
    $\begingroup$ What's the solubility of the so-called water-insoluble vitamins ? $\endgroup$
    – Maurice
    Aug 18, 2023 at 20:14
  • $\begingroup$ The structure with two acid groups and at least one amine suggests that the solubility is pH dependent. Water soluble or fat soluble is determined by the ability of the body to store vitamins in fat cells or possibly the liver and to transport them from the intestines. The concentration of folate in the blood is much lower than the solubility limit. It is hard to make definitive conclusions on one data snippet. $\endgroup$
    – jimchmst
    Aug 18, 2023 at 20:22
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    $\begingroup$ Consider that sodium folate is more soluble that folic acid. similar as sodium palmitate (soap) is more soluble than palmitic acid. $\endgroup$
    – Poutnik
    Aug 19, 2023 at 3:37


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