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EC number: 701-029-8
CAS number: -
The test substance reacts with water to form predominantly solid, inert
polyurea. Yakabe et al (1994) found that for loadings of 400 - 10,000
mg/L, and under heterogeneous conditions, a structural analogue had a
half-life of ca. 20h at 25°C.
The test substance is covered by the category approach of
methylenediphenyl diisocyanates (MDI). Hence, data of the category
substances can be used to cover this endpoint. Yakabe et al (1994) found
that for loadings of 400 - 10,000 mg/L, and under heterogeneous
conditions, oligomeric MDI had a half-life of ca. 20h at 25°C when the
disappearance rate was fitted to a zero-order kinetic model. However the
rate constant increased approximately linearly with the nominal
concentration of oligomeric MDI for all constituents. For the two-ring
constituents the rate constant was found to be 0.5h-1 for a
loading of 1000 mg/L oligomeric MDI.
The findings in the Yakabe et al (1994) study concur with the generally
accepted chemistry of hydrolysis of an isocyanate whereby the initially
produced carbamate decarboxylates to amine which then reacts very
readily with more isocyanate to produce a urea. For a diisocyanate of
low solubility such as MDI, the reaction system is usually heterogenous
and these reactions, leading to insoluble polyureas, occur in both
organic and aqueous phases and at the interface, where in each case
differing concentrations of reagents and intermediates lead to different
product distributions. Under conditions typical of many types of
environmental contact, i.e. with relatively poor dispersion of the
denser isocyanate, the interfacial reaction leads to the formation of a
solid crust encasing partially or unreacted material. This crust
restricts ingress of water and egress of amine, and hence slows and
modifies hydrolysis. An important consequence of general significance to
all aquatic tests of MDI, is that, in reality, it is the breakdown
products that are being studied and the technique used for introduction
or dispersal of the substance can affect the physical form and
composition of the product (although under all tested conditions the
predominant products are solid, insoluble polyureas).
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