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The quality of methylene diphenyl diisocyanate (MDI)products,which are valuable feedstocks in the industrial manufacture of polyurethanes,can be compromised by the presence of color, presumed to arise fromtrace impurities. One undesired branch in the synthesis chain originateswith phosgenation of diaryl ureas, formed from reactions between arylisocyanates and polyamine precursors. Subsequent key steps include,(i) breakdown of the primary compounds, substituted chloroformamidine-N-carbonyl chlorides (CCC), to give aryl isocyanide dichlorides,ArNCCl2, (ii) an apparent equilibrium connecting CCC witharyl carbodiimides, and (iii) the thermolysis of ArNCCl2in the presence of MDI. Color formation is associated directly withthe last process; it involves several events, including HCl eliminationfrom reaction of ArNCCl2and MDI, formation of carbon-centeredradicals, and a contribution from oxidation at the methylene bridge. [ABSTRACT FROM AUTHOR]

Phenyl and 4-methylphenyl isocyanide dichlorides aremodels forbyproduct that may be formed in the later stages of certain polyurethaneproduction chains. Photochemical electron paramagnetic resonance (EPR)studies (λ > 310 nm), using the spin trap, N-tert-butyl-α-phenylnitrone, confirm a previouslymade suggestion that ArNCCl2can behave as a chlorineradical source. EPR spectra recorded during and after irradiationand supported by simulations evolve over time and indicate formationof the short-lived spin trap–Cl•adduct anda longer lived benzoyl-N-tert-butylnitroxideradical. Photolysis of C6H5NCCl2, either alone or mixed with methylene diaryl isocyanate species,in o-C6H4Cl2, apolyurethane process solvent, led to the formation of mixtures containingdichloro- and trichlorobiphenyl isomers. [ABSTRACT FROM AUTHOR]