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Environmental fate & pathways

Hydrolysis

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Description of key information

In a read-across approach based on tests performed with MDI, the hydrolysis half time is ca. 20h at 25°C. The reaction with water followed zero order kinetics. Conversions to MDA were generally low  to very low.

Key value for chemical safety assessment

Half-life for hydrolysis:
20 h
at the temperature of:
25 °C

Additional information

These findings are in accordance 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 and MDI MT, 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 MT, 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).