Registration Dossier
Registration Dossier
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EC number: 212-485-8 | CAS number: 822-06-0
Endpoint summary
Administrative data
Description of key information
Additional information
Summary
Stability (hydrolysis):
The half-life of hexamethylene diisocyanate (HDI) in the the acetonitrile/water solution is approx. 0.23 hour at room temperature (23 °C). The concentration of the test substance in the acetonitrile solution without addition of water was stable over the measurement time (Bayer AG, 1999).
In a test on the stability of hexamethylene diisocyanate (HDI) in drinking water initial concentrations of 2 and 200 mg/l were tested at 20 °C. The reduction of the substance was 90 % after a reaction period of 50 min and 30 min., respectively. The half life in dependence of the initial concentration varied between 5 and 10 min. (Sopac, 1974).
Hydrolysis products have not been elucidated. However similar substances containing several isocyanate groups like MDI are known to react rapidly with water forming insoluble oligomeric and polymeric ureas.
In addition to the findings for the decrease of NCO groups (Bayer 1999), Sopac & Boltromejuk (1974) have reported in detail, that three main findings determine the results:
1. HDI is not soluble in the low mg/l range in water without another solvent. It forms oily droplets in water.
2. The diisocyanate ends of HDI react with water forming the amine and CO2.
3. The diisocyanate ends of HDI can also react with an amine end of an already hydrolysed (former HDI-) molecule, forming oligo-and polyureas. Depending on the use of a solvent or not, the size of the drops when direct weight is used, and the speed of a magnetic stirrer or of ultrasonic if used, determine the quantitative proportion of the hydroxylation products HDAand polyurea.
Phototransformation in air:
The calculated half-life (t1/2) of hexamethylene diisocyanate (HDI) in air due to indirect photodegradation is approx. 48 h (Currenta, 2009). As HDI hydrolyses rapidly, also the hydrolysis product hexamethylene diamine (HDA) (CAS-No. 124-09-4) was estimated with AOPWIN v. 1.92. The atmosperic half live of approx 6 hrs was calculated (Currenta, 2009).
Biodegradation:
Hexamethylene diisocyanate (HDI) is not readily biodegradable. After 28 days only 42 % of the test substance had been degraded in a manometric respiratory test (Directive 92/69/EEC, C.4-D) (Bayer AG, 2000).
Because of its expected reactivity with water in moist soil to form amine or polyurea derivatives, monomeric hexamethylene diisocyanate (HDI) is not likely to be found in soil in significant concentrations except near sources of release. Small amounts of HDI that have become encapsulated in water-insoluble polyurea agglomerates may persist in soils and sediments.
Bioaccumulation:
The direct and indirect exposure of the aquatic compartment is unlikely because hexamethylene diisocyanate (HDI) hydrolysis completely in water within far less than 1 hour at environmental relevant concentrations. For this reason, an experimental study is not useful, andcalculated values can be used. Bioconcentration factors (BCF) of 58 and 3 for hexamethylene diisocyanate (HDI) and its hydrolysis product hexamethylene diamine (HDA) (CAS 124-09-4) were obtained. Also the hydrolysis product with a bioconcentration factor of 3 does not have high bioaccumulation potential.
Adsorption:
Hexamethylene diisocyanate (HDI) is characterized by a KOC of 5861 being calculated with PCKOCWIN v. 1.66 (Currenta, 2009). According to the method of Gerstl (1990) the KOC of 1665 accounts for hexamethylene diisocyanate (HDI) (Currenta, 2009e).
As hexamethylene diisocyanate (HDI) hydrolyses rapidly, the BCF of the hydrolysis product was calculated, too. The hydrolysis product of hexamethylene diisocyanate (HDI) is characterized by a KOC of 286 being calculated with PCKOCWIN v. 1.66 (Currenta, 2009e). According to the method of Gerstl (1990) the KOC of 5 accounts for HDA (CAS 124-09-4) (Currenta, 2009f).
However, while hexamethylene diisocyanate shows moderate sorption to soil and sediment, slow migration potential to groundwater its hydrolysis product has only a negligible sorption potential to soil and sediment.
Distribution modelling:
Because of the relatively rapid reaction of hexamethylene diisocyanate (HDI) with hydroxyl radicals in the atmosphere and the rapid hydrolysis in other media , significant concentrations would not be expected to occur in air, water, or sediment and soil, except near potential emission sources of this substance (e.g., industrial waste streams, hazardous waste sites, occupational settings, environmental spills). Small amounts of unreacted hexamethylene diisocyanate (HDI) may persist in water, or sediment and soil, if encapsulated in water-insoluble polyurea crusts formed during hydrolysis.
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