Aniline isocyanate precursors

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]. 

NASA-Langley provided a further improvement in processibility by replacing the methylenedianiline with a commercial aromatic diamine mixture that afforded even better handling characteristics (17). This type of product is formed by the reaction of formaldehyde with aniline as a precursor in isocyanate manufacture. Fluorine-containing thermoplastic polyimides and polyimides end capped with acetylene groups for cross-linking are also available as potential commercial high-temperature resins. 

Carbamates are produced by the oxidative carbonylation of amines in alcohol, and active research on the commercial production of alkyl carbamate as a precursor of isocyanates based on this reaction has been carried out. As an example, ethyl phenylcarbamate (472) was produced in a high yield (95 %) with a selectivity higher than 97% by the reaction of aniline with CO in EtOH at 150 °C... 

Curtius rearrangement of these azides leads to ketones via loss of an isocyanic acid (HN=C=0) equivalent, which can be trapped in situ as shown for 49 where benzophenone resulted and addition of aniline to the isocyanic acid gave urea 50. or-Alkoxy- and or-amino acyl azides, meanwhile, are precursors to hemiaminals and hisaminals, respectively. Examples in complex natural product synthesis are shown for 81 and 66 in the Variations and Improvements Section. 

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