Niacin Chemistry
Nicotinic acid and nicotinamide are colourless crystalline
substances; each is insoluble or only sparingly soluble in organic solvents.
Nicotinic acid is slightly soluble in water and ethanol; nicotinamide is very
soluble in water and moderately soluble in ethanol. The two compounds have
similar absorption spectra in water, with absorption maxima at 262 nm.
Nicotinic acid is zwitterionic in nature; at high pH it is
negatively charged at the carboxylic function, while at low pH it is positively
charged at the pyridinyl nitrogen. Thus it is considered an amphoteric molecule
because it forms salts with acids as well as bases.
Both nicotinic acid and nicotinamide are very stable in dry
form; in solution nicotinamide is hydrolysed by acids and bases to yield
nicotinic acid.
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