|Appearance Pale brown, crystalline solid|
4,4'-Methylenedianiline (MDA) is a suspected carcinogen. It is included in the "substances of very high concern" list of the European Chemicals Agency (ECHA). The compound was involved in an accidental mass poisoning in the vicinity of Epping, Essex, United Kingdom during 1965 during which 84 individuals were poisoned through accidental contamination of flour used to make bread.
In the industrial production, MDA is synthesised by reaction of formaldehyde and aniline in the presence of hydrochloric acid.
MDA is used primarily for making polyurethane foams in which case it is first reacted with phosgene to create 4,4 ́-methylene diphenyl diisocyanate (MDI) prior to polymerization with a polyol. Lower quantities are used as hardeners in epoxy resins and adhesives, as well as in the production of high-performance polymers.
MDA is considered a potential occupational carcinogen by the US National Institute for Occupational Safety and Health. The Occupational Safety and Health Administration has set a permissible exposure limit at 0.01 ppm over an eight-hour time-weighted average, and a short-term exposure limit at 0.10 ppm.