Oligomerization Products from Thiamin in Methanol

Nishida, Clinton
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University of Hawaii at Manoa
In 1974, Shimahara, et al. [1 ] discovered that thiamin (vitamin B1 ) monochloride decomposes in alcohol solution, a reaction which cannot be accounted for solely on the basis of the known instability of thiamin in alkaline solution [2]. Of methanol, ethanol, and propanol, reaction in methanol led to the fastest decomposition rate. Reaction temperature, pH of the solution, and thiamin concentration affected the rate of reaction. For all alcohols, one of the products was determined by IR and NMR spectroscopy to be 5-(2-hydroxyethyl)-4-methyl-thiazole, the thiazole moiety of thiamin. The other product was a crystalline compound designated compound (X), or compound (X') if converted to the nitrate using silver nitrate. Initially believed to be the pentamer nitrate, penta-methi(1 ,4-dihydro-4-imino- 2-methyl-pyrimidinylen-1 ,5-amer nitrate (Fig. 1 a), based on NMR and mass spectral data, compound (X') has since been determined, via single crystal x-ray diffraction, to be the cyclic hexamer (Fig. 1 b, 2) by the Cramer group [4]. The cyclic tetramer has since been isolated and characterized as well (Fig. 1b) [5].
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