m-tolylidene diisocyanate

Water solubility

Description of key information

TDI is hydrolytically unstable. It can have only a transient existence in aqueous media. A water solubility value of 124 mg/l has been estimated (West et al, 2008) using a broadly accepted program, though a water solubility value for TDI is only a notional concept.

Key value for chemical safety assessment

Water solubility:

124 mg/L

at the temperature of:

25 °C

Additional information

TDI is rapidly hydrolysed in aqueous solution, with a half-life of under one minute (Yakabe et al., 1999). The product of hydrolysis of the isocyanate group is an amine, which itself reacts with another isocyanate group to yield a urea. This reaction of an amine with isocyanate is considerably faster than the reaction of water with the isocyanate (Yakabe et al, 1999). With TDI, a diisocyanate, this reaction leads to polyureas, which are inert, insoluble solids.

However TDI is hydrophobic and poorly soluble in water (West et al., 2008), and such fast reaction is only achieved by vigorous agitation of the mixture. When the denser diisocyanate is less well dispersed into water, the reaction is heterogeneous (at the interface) and is slower. The reaction leads to the formation of a solid crust of polyureas encasing unreacted material. This crust restricts ingress of water and egress of amine, and thereby slows hydrolysis even further and enhances the amine reaction with isocyanate, leading to an even higher yield of polyureas.