How does the the nitrogen of thiazole in thiamine acquire a positive charge without being stabilized by another negative charge or by being a salt of an anion?

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    $\begingroup$ Even if it's not always reported, the thiamine you can buy or isolate is a salt: the thiamine molecule is a cation, and a counterion is present (typically Cl- or NO3-) $\endgroup$ – The_Vinz Dec 27 '19 at 17:34
  • $\begingroup$ But this molecule doesn't enter my mind as being simply a cation, was the nitrogen atom neutral first then the hydrogen of methylene group attached to nitrogen was striped off by a strong alkali pushing the nitrogen to form a pi bond with the deprotonated group and acquiring a positive charge? $\endgroup$ – mohamed Dec 27 '19 at 18:37

Thiamine (Vitamin B1) has a positive charge on the nitrogen of thiazole ring, because that nitrogen is tetravalent. Thus, it should be neutralized by a counter ion. Usually, the counter ion is chloride ($\ce{Cl-}$) ion. Over-the-counter Vitamin B1 usually supplies as hydrochloride salt of thiamine chloride (simply called thiamine hydrochloride), which is very soluble in water.

According to Wikipedia:

The salt thiamine mononitrate, rather than thiamine hydrochloride, is used for food fortification, as the mononitrate is more stable, and does not absorb water from natural humidity (is non-hygroscopic), whereas thiamine hydrochloride is hygroscopic. When thiamine mononitrate dissolves in water, it releases nitrate (about 19% of its weight) and is thereafter absorbed as the thiamine cation.

The structures of two compounds are depicted in following diagram:

thiamine hydrochloride and nitrate

  • $\begingroup$ But how would nitrogen acquire this charge did a base deprotonate the methylene group attached to the nitrogen causing the nitrogen atom to form a double bond and acquire a positive charge? $\endgroup$ – mohamed Dec 27 '19 at 19:01
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    $\begingroup$ In the biosynthesis, the neutral thiazole portion has a lone pair on the N that is perpendicular to the ring (ie not involved in aromaticity). It makes a nucleophilic attack on an electrophilic carbon, knocking off a negatively charged group and acquiring a positive charge because it now has four bonds. See ncbi.nlm.nih.gov/pmc/articles/PMC6039189 $\endgroup$ – Andrew Dec 27 '19 at 19:16
  • $\begingroup$ It is not uncommon in biosystems with tetravalent nitrogen (with a positive charge), e.g., nicotinamide adenine dinucleotide (NAD+). Andrew has given an excellent answer for OP. Thanks Andrew. $\endgroup$ – Mathew Mahindaratne Dec 27 '19 at 19:29

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