4,4 -Diphenylmethane diisocyanate from aniline

The production of aniline is a major international business, carried on in the US, Europe and Asia, mainly for the conversion, by reaction with formaldehyde under acid-catalyzed conditions, into diaminodiphenylmethanes 9a, 9b and 9c, and then into isocyanates, mainly 4,4/-methylenebis(phenylisocyanate) (MDI, also known as 4,4 -methylene-di-paraphenylene isocyanate, 4,4 -diphenylmethane diisocyanate, methylene diphenylene diisocyanate and diisocyanato diphenyl methane) (9d), from which polyurethanes are produced. This accounts for well over 60% of total demand (Figure 1). Aniline is also used in bulk for the production of antioxidants and vulcanization accelerators for rubber. Some 15.5 million lbs. of cyclohexylamine are made each year mainly by catalytic hydrogenation of aniline. Half the demand is for use as a boiler water additive. Other major uses include in the manufacture of herbicides, plasticizers, emulsifying agents, dyes, dry-cleaning soaps, acid gas absorbents and, in Asia, cyclamate sweeteners. Apart from India, the use of aniline for dyestuff manufacture represents about 10% of demand. 

In the last few years, however, 4,4 -diphenylmethane diisocyanate (methane diphenyldi isocyanate, MDI), whose precursor 4,4 -diaminodiphenylmethane is obtained from the condensation of aniline with formaldehyde, has overtaken TDI. In 1990, capacities in Western Europe, the United States, and Japan for MDI were 600,000, 530,000, and 190,000, tons, respectively for TDI, they were 400,000, 360,000, and 110,000 tons [91]. 

Diphenylmethane diisocyanate (MDI) is derived from aniline the principal... 

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