February 6, 2008

Also appeared in print Feb. 11, 2008, p. 15

Green Chemistry

Clean Catalysis

Environmentally friendly synthesis of niacin generates less inorganic waste

Sarah Everts

Making niacin, also known as vitamin B-3, just got a lot greener. In addition to its use as a vitamin and as a supplement in foods, niacin is used as a building block for a host of commercial compounds, including cancer drugs, antibacterials, pesticides, and charge control agents in copier toners. An estimated 10,000 tons of niacin are produced annually worldwide.

Currently, corrosive oxidizing agents such as chromic acid are used in niacin's several-step industrial synthesis. In addition, almost 3 tons of inorganic waste is produced for every ton of niacin generated from the starting material, 3-picoline, notes Robert Raja, a chemist at the University of Southampton, in England. Raja and his colleagues are now reporting a new one-step reaction that generates 29% less waste.

The reaction uses a heterogeneous solid catalyst composed of manganese-substituted aluminophosphates to produce niacin from 3-picoline (Chem. Eur. J., DOI: 10.1002/chem.200701679). It also employs a solid source of active oxygen called acetyl peroxyborate, which is not a corrosive oxidant. In addition, the reaction does not produce greenhouse gases such as N₂O.

The catalyst and oxidant selectively attack 3-picoline's methyl group to make niacin while mostly sidestepping the reaction of 3-picoline's nitrogen group. In the current industrial process, this unwanted reaction generates nitrogen oxide waste products.

The physical constraints within the porous crystalline catalyst seem to provide the selectivity, Raja explains. "One might envisage the substrate approaching the active site within the crystalline framework in a particular orientation that facilitates oxidation at the methyl group."

"The selectivity is impressive," comments Alan Levy, a senior principal scientist at Honeywell Resins & Chemicals.

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