Angewandte Chemie International Edition

Cover image for Vol. 56 Issue 32

Editor: Peter Gölitz, Deputy Editors: Neville Compton, Haymo Ross

Online ISSN: 1521-3773

Associated Title(s): Angewandte Chemie, Chemistry - A European Journal, Chemistry – An Asian Journal, ChemistryOpen, ChemPhotoChem, ChemPlusChem, Zeitschrift für Chemie

For full article and contact information, see Angew. Chem. Int. Ed. 1998, 37 (16), 2217

Bleach made from Schnapps

A new compound - modelled on a fungal enzyme -
converts alcohols into chemical raw materials

A new catalyst, developed by chemists Phalguni Chaudhuri, Martina Hess, and Karl Wieghardt at the Max Planck Institute for Radiochemistry in Mülheim, could turn out to be a kind of "Swiss Army knife" for the chemical industry. The compound, based on a fungal enzyme called galactose oxidase, converts alcohols into molecules known as aldehydes and links special molecules together to form larger units. An extremely useful by-product of the enzyme's function is hydrogen peroxide, which distinguishes itself as an environmentally friendly bleaching agent in many applications. Aldehydes themselves are desirable intermediates in the chemical industry, where they are produced in millions of tonnes each year - currently by far more difficult methods.

In order to make the required aldehydes out of alcohols - such as the familiar intoxicating ethanol - the new catalyst uses oxygen from the atmosphere. "In principle the reaction is a kind of combustion," says Karl Wieghardt. "The problem we have always had is how to stop that combustion at the right time." Because if oxygen is allowed to react with alcohol without any form of control, the aldehyde products themselves are rapidly burned to give only useless carbon dioxide and water - as in a spirit stove.

It was the fungus Dactylium dendroides which ultimately showed the chemists how to do this: it uses an enzyme called galactose oxidase to produce a particular aldehyde vital for its metabolism. The central 'workbench' of this protein - the place in the fungus where aldehydes are formed from alcohols - provided the model for Chaudhuri and Wieghardt's work.

The key to the function of their compound, as in the natural example, is the presence of copper ions, which attach themselves both to oxygen from the air and to the alcohol; this binding allows a rearrangement of atoms and electrons between the molecules to occur, giving an aldehyde and hydrogen peroxide as the final products. The unique thing about the Mülheim catalyst is really the formation of the bleach by-product: "You can actually see the glass of the reaction vessel becoming heavier as hydrogen peroxide is formed out of the air," reports Wieghardt. The catalyst therefore kills two chemical birds with one stone, and industry, unsurprisingly, has not been slow to take a commercial interest in the Mülheim process.