Toxic reactants

Hazardous chemicals or mixtures may be replaceable by safer materials. These may be less toxic per se, or less easily dispersed (e.g. less volatile or dusty). Substitution is also applicable to synthesis routes to avoid the use of toxic reactants/solvents or the production, either intentionally or accidentally, of toxic intermediates, by-products or wastes. 

ACH (acetone Acetone, HCN, H2SO4 Toxic reactant Several companies... 

Specifically, the process makes use of HCN, a very toxic reactant. Difficulties in its acquisition, though, can be met in fact, HCN is a by-product of propylene ammoxidation. Integration of acrylonitrile and MM A products requires the balance... 

In addition to the main products (nitrogen, carbon dioxide and water), different subproducts can be formed as a result of partial oxidation or reduction processes. Such subproducts can be more harmful than the initial toxic reactants and as such, their formation is undesirable. Following the pioneering work by Iwamoto and co-workers as well as that of Held and co-workers, which showed the activity of Cu/ZSM-5 for the process,100,101 many systems have been tested for this reaction. Figure 8.5 gives a brief illustrative summary of different systems that have shown some success in the mentioned process. Following the approach by Iwamoto, a classification... 

A succession of books and articles have dealt with the effects of toxic chemicals on people and the environment, a hazard that accompanies industrialization. If there is any doubt that these compounds can be lethal, the horror that descended upon Bhopal, India, during the early morning hours of December 3, 1984, should be recalled. (It confirms that a large quantity of any toxic material should never be stored as such. The presumably nontoxic or less toxic reactants should instead be stored apart, to be mixed and reacted only as needed. Or better yet, manufacture the stuff from scratch only as needed.) Regarding the hypertoxic nerve gases from which organo/phosphorus/sulfur pesticides are derived, there is the unpublicized fact that a person only has about one minute to wash a drop from his skin before death intervenes. 

The current industrial production of methylmethacrylate by the acetone-cyanohydrin process suffers from a number of drawbacks, which make it environmentally unfriendly. In particular, it makes use of a very toxic reactant (HCN) and intermediate (acetone cyanohydrin), and coproduces large amounts of impure ammonium sulphate, contaminated with organic compounds. Among the several alternative synthetic routes which have been proposed, particularly interesting from both the practical and scientific points of view is the single-step oxidation of isobutane to methacrylic acid, intermediate in the synthesis of methylmethacrylate. Several industrial companies have studied this reaction (and the selective oxidation of propane to acrylic acid, as well), and it has been established that the most active and selective catalysts are those which are based on Keggin-type polyoxometalates (POM s), containing phosphorus and molybdenum as the main components [1-18]. 

The possibility of using conducting polymer films as precoats in the metallization of insulators [186-188] minimizes problems associated with the actual technologies in the field, such as the high cost of noble metal catalysts or the use of toxic reactants. In this case, the coating is obtained by direct polymerization of pyrrole on the plastic substrate, which was previously impregnated with the oxidant. 

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