Thiamine
Properties
| State | Solid (white crystalline powder with slight yeast-like odor) |
| Color | White |
| Solubility | Freely soluble in water; slightly soluble in ethanol; insoluble in ether |
| Melting Point | 248-250°C (decomposes, hydrochloride salt) |
| Boiling Point | Decomposes before boiling |
About Thiamine
Thiamine, vitamin B1, was the first vitamin to be isolated and structurally characterized — Casimir Funk coined the word 'vitamine' in 1912 working on the substance in rice-bran extracts that cured beriberi, and Robert R. Williams determined the structure and synthesized it in 1936. The molecule is two heterocycles bolted together by a methylene bridge: an aminopyrimidine on one side and a thiazolium on the other. The thiazolium ring is the catalytically active piece. Its C-2 proton has an unusually low pKa (around 18), so deprotonation gives a stabilized ylide carbanion that can attack the carbonyl carbon of pyruvate or alpha-ketoglutarate. That carbanion chemistry is what pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, transketolase, and the branched-chain ketoacid dehydrogenase all exploit, working with thiamine pyrophosphate (TPP) as cofactor. Knock out thiamine and pyruvate piles up at the gate of the citric-acid cycle, lactate floods the blood, and the brainstem nuclei that depend most heavily on aerobic glucose metabolism are the first tissues to fail — which is exactly the picture of Wernicke encephalopathy. The cation form shown by C12H17N4OS+ is what circulates as the chloride hydrochloride salt sold in the pharmacy.
Where you'll encounter it
If you've ever watched an emergency department give a banana bag to an alcoholic patient before any glucose, you've seen thiamine treated with the urgency it deserves — IV glucose without thiamine in a deficient patient can precipitate Wernicke encephalopathy within hours. The classic teaching case is the chronic-alcohol patient with confusion, ataxia, and ophthalmoplegia who gets 500 mg IV thiamine before anything else. Outside the hospital, thiamine fortification of wheat flour and white rice is one of public-health chemistry's quietest wins: the United States started enrichment in 1942, and clinical beriberi essentially vanished from the general population within a decade. In the lab, thiamine pyrophosphate is also the textbook example used to teach umpolung chemistry — the cofactor reverses the normal electrophilic character of an aldehyde carbon.
Common Uses
- TPP cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase
- Mandatory fortification of wheat flour and white rice in the US, UK, Canada, and ~80 other countries
- IV thiamine (500 mg) as first-line treatment for suspected Wernicke encephalopathy in ED patients
- Component of total parenteral nutrition formulations for hospitalized patients on long-term IV feeding
- Teaching example of umpolung carbanion chemistry in undergraduate biochemistry courses
- Veterinary supplementation in ruminants on high-grain diets to prevent polioencephalomalacia
- Treatment of maple syrup urine disease responsive to high-dose thiamine (branched-chain ketoacid dehydrogenase variants)
- Pet-food additive, particularly in fish-based diets where thiaminase activity destroys dietary thiamine
Safety Information
GHS: Not classified as hazardous; FDA GRAS designation. Acute oral toxicity is very low — LD50 in rats exceeds 8 g/kg for the hydrochloride salt — because thiamine is water-soluble and excess is cleared in urine within hours. The clinically relevant safety issue is anaphylaxis to IV thiamine, reported at roughly 1 case per 100,000 doses, which is why hospital protocols dilute the dose in 100 mL saline and infuse over 30 minutes rather than IV push. The US recommended dietary allowance is 1.2 mg/day for adult men and 1.1 mg/day for women; tolerable upper intake is not established because no toxicity has been documented even at gram-per-day oral doses. No OSHA PEL is set.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.