Hexane, 1,6-diisocyanato-2,2,4(or 2,4,4)-trimethyl-

Endpoint summary

Additional information

Summary for the substance

According to a Mackay Level I model calculation the main target compartments for 2,2,4(or 2,4,4)-trimethylhexane-1,6-diisocyanate will be sediment (30 %) and soil (30 %) followed by the atmosphere (28 %) and the hydrosphere (12 %). The calculated Henry’s Law constant of 6.51 Pa m³/mol at 20 °C indicates moderate volatility of 2,2,4(or 2,4,4)-trimethylhexane-1,6-diisocyanate from surface waters. With a calculated Koc of 22570 l/kg, the sorption potential of 2,2,4(or 2,4,4)-trimethylhexane-1,6-diisocyanate to soil or sediment organic matter is expected to be very high (Blume scale). However, environmental transport and distribution considerations for 2,2,4(or 2,4,4)-trimethylhexane-1,6-diisocyanate are of little relevance because the reaction with water is expected to eliminate the substance from the environment rapidly. 

The QSAR calculated rate constant for the OH sensitized photodegradation of 2,2,4(or 2,4,4)-trimethylhexane-1,6-diisocyanate is approximately 8.5606E-12 cm³/(molecule * s). At 500,000 OH radicals / cm³ (approximate 24-hour mean in central) this corresponds to a half-life of 1.9 days or 45 hours. In aqueous systems, rapid hydrolysis is expected with a half-life of approximately 5 minutes at pH 7 and 20 °C. Ready biodegradation was not observed in a "CO2 Evolution test" according to EU-Method C.5. Biodegradation of the substance itself is irrelevant as primary degradation step because hydrolysis is much faster.

Bioaccumulation can be excluded because of the rapid hydrolysis and a low tendency for bioaccumulation of the main hydrolysis product 2,2,4(2,4,4)-trimethylhexane-1,6-diamine (see below).

 

Summary for the unpolymerized hydrolysis product

 

According to a Mackay Level I model calculation, the main target compartment for 2,2,4(2,4,4)-trimethylhexane-1,6-diamine will be the hydrosphere (99.97 %), followed by the atmosphere (0.02 %). The calculated Henry’s law constant of 0.00063 Pa m3/mol indicates very low volatility of 2,2,4(or 2,4,4)-trimethylhexane-1,6-diamine from surface waters. The adsorption coefficient of 2,2,4(or 2,4,4)-trimethylhexane-1,6-diamine corrected for dissociation was calculated with a QSAR published by Franco and Trapp (2008). The result was Koc = 25, log Koc = 1.40 (pH 7), corresponding to a very low potential for geoaccumulation (Blume scale).

 

The QSAR calculated rate constant for the OH sensitized photodegradation of 2,2,4(or 2,4,4)-trimethylhexane-1,6-diamine is approximately 6.96E-11 cm3/(molecule * s). At 500,000 OH radicals / cm3 (approximate 24-hour mean in central Europe), this corresponds to a half-life of 5.5 hours. Screening tests on biodegradation in water showed that the substance is neither readily nor inherently degradable. In spite of these findings biodegradation and OH sensitized photodegradation are expected to be the predominant ways of removal from the environment while hydrolytical degradation in surface waters is expected to be of minor importance. The partition coefficient 1-octanol/water is log Kow = -0.3 at 25 °C, indicating negligible potential for bioaccumulation.