Atom utilisation

Sheldon, R.A. (2000) Atom Utilisation, E Factors and the Catalytic Solution. Comptes Rendus de VAcademic des Sciences Paris, Serie lie, Chimie, 3, 541-551. 

A further metric, suggested by Sheldon4 for individual reactions, is Atom Utilisation which is defined as ... 

These atom efficiencies are very useful in predicting the likelihood of a commercially attractive synthesis being produced. The very low figure for route C rules it out straight away, the low atom utilisation and the nature of the by-products indicate a serious effluent problem which will add significantly to the process costs. 

Similarly, route is by far the most attractive in terms of atom utilisation and is one of the shortest routes also, hence probably has lower process costs. 

Route A is shorter than route D but has a poorer atom utilisation. Route D requires handling acetylene which is not an attractive proposition on large scale. 

Sheldon has used the concepts of atom utilisation and environmental acceptability to assess environmental impact for a given process [13]. Environmental constraints are rendering the use of classical stoichiometric methods prohibitive, and there is a general trend towards cleaner catalytic processes, which are particularly in evidence in chemical and biological asymmetric synthesis. 

Sheldon defines atom utilisation as the ratio of the molecular weight of the desired product to the sum of all the material used (excluding solvents). 

A target for current and future industrial processes which has gained recognition is that of 100% atom utilisation [3], such that the starting materials combine to yield the product with nothing left over, either as stoichiometric co-products or as by-products arising from incomplete selectivity. 

In contrast to the previous group, this category refers mainly to chemistry developed relatively recently, and particularly to catalytic activation of hydrogen peroxide. Within it lie many oxidation systems destined for widespread use in future, since they satisfy the atom utilisation principle and enable use of simple processes without serious effluent problems. 

This route produces both organic and inorganic effluent and measures up poorly against the atom utilisation principle. 

Aromatic aldehydes can also be oxidised conveniently on small to medium scale using sodium perborate in acetic acid [120]. This system, which is not believed to work entirely through peracetic acid as an intermediate [121], leads to a precipitate of sodium borate, which does assist workup, but is not ideal from an atom utilisation viewpoint. Environmentally, however, it is better than the stoichiometric use of manganese dioxide etc., which has been widely practised for this transformation. 

The reaction or the synthesis is considered to be green if there is maximum incorporation of the starting materials and reagents in the final product. We should take into account the percentage atom utilisation, which is determined by the equation... 

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