Alcohols are widely used in the fragrance industry as odour ingredients and as starting materials for the synthesis of other scented compounds.

The majority of these alcohols are created via synthetic pathways and reduction reactions involving carbonyl compounds are a common method.

Scientists led by Carla Villa from Italy have developed a method to reduce a number of carbonyl compounds to their respective alcohols, which uses no solvent and are therefore better for the environment.

New reaction is greener and faster

The scientists used the reducing agent sodium borohydride (NaBH

) which is widely employed as it is relatively safe, inexpensive and easy to handle.

Conventional reactions use this same reducing agent however large amounts of solvent are often needed and reaction times can be long.

The new method developed by Villa and the team does not use a solvent.

Instead the method involves a dispersion of NaBH

in neutral Al

O

that has previously been treated with water. The water is important as when the team attempted the same reaction with dry Al

O

the reduction rate was significantly slower.

The carbonyl compound is then mixed with the NaBH

/Al

O

which is then mechanically stirred at room temperature until the carbonyl compound has been totally converted.

The alcohol product is then recovered and purified using bulb-to-bulb distillation in a vacuum, explained the scientists.

Eight fragrance alcohols had good yields

Villa and the team tested the new method to produce eight alcohols commonly used in the fragrance industry.

For six of these the method yields more than 90 per cent of pure products - purity obviously being particularly important for the fragrance industry as impurities can easily affect the odour of a compound.

The scientists conclude that: "the methodology leads to increased safety, cost reduction and respect for the environment together with …high yields, pure products and short reaction times."

They add that the new methodology may be considered as an attractive valid alternative to classical procedures and should be of particular interest to the fragrance industry.

Source: International Journal of Cosmetic Science

2008, issue 30, pages 139-144

"Green procedure for the preparation of scented alcohols from carbonyl compounds"

Authors: Carla Villa, Beatrice Trucchi, Raffaella Gambaro and Sara Baldassari