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EC number: 218-485-4
CAS number: 2162-73-4
is little data available on physico-chemical properties of
2,4,6,-triisopropyl-m-phenylene diisocyanate. With the aid of the EPIWIN
software some physical-chemical properties were calculated.
substance is at room temperature a light yellowish liquid with a slight
odour. The substance is insoluble in water (< 0.05 mg/L at 20°C) and has
a logPow of 7.56. It has a low vapour pressure (0.19 Pa at 20°C). No
exact value of melting point could be determined experimentally for
2,4,6-triisopropyl-m-phenylene-diisocyanate between -90°C and 50°C
(Kintrup, 2012). Glass transition temperature (amorphous components) in
the first heating run was determined to be -56°C. The calculated melting
point was 82.9°C. The boiling point of 305.8°C was measured for
2,4,6-triisopropyl-m-phenylene-diisocyanate (Svobodova, 2012).
as a function of pH has not been determined, but comparison to its
structural analogue toluene diisocyanate revelaed a high likelihood for
hydrolysis. The substance is not toxic when administered orally to ratsc
(LD50 > 2000 mg/kg bw). However, it has been determined to be toxic
after inhalation (LC50 < 110mg/m³). It is not an eye, but a skin
irritant, and skin sensitising properties have been predicted.
Additionally, the substance was shown to be not mutagenic in studies
according to OECD471, 473 and 476.
It is also important to consider the
potential for a substance to accumulate or to be retained within the
body. Lipophilic substances have the potential to accumulate within the
body (mainly in the adipose tissue) if the dosing interval is shorter
than 4 times the whole body half-life. Although there is no direct
correlation between the lipophilicity of a substance and its biological
half-life, substances with high log P values tend to have longer
half-lives. On this basis, there is the potential for highly lipophilic
substances (Log P >4) to accumulate in individuals that are frequently
exposed. Highly lipophilic substances (Log P between 4 and 6) that come
into contact with the skin can readily penetrate the lipid rich stratum
corneum but are not well absorbed systemically. Although they may
persist in the stratum corneum, they will eventually be cleared as the
stratum corneum is sloughed off. A turnover time of 12 days has been
quoted for skin epithelial cells
Following oral exposure little TDI is
retained in the body (4 %) and following exposure via inhalation a
larger amount of TDI (34%) is retained in the carcass, indicating a slow
release of protein-bound material (Timchalk et al., 1994). However, to
our knowledge the accumulation of TDI in the stratum corneum has not
Route specific toxicity may result from
several phenomena, such as hydrolysis within the gastrointestinal or
respiratory tracts, also metabolism by gastrointestinal flora or within
the gastrointestinal tract epithelia (mainly in the small intestine),
respiratory tract epithelia (sites include the nasal cavity,
tracheo-bronchial mucosa (Clara cells) and alveoli (type 2 cells) and
It has been shown, that after oral exposure
TDI, which is hydrolysed to TDA in the gastrointestinal tract and
subsequently absorbed, can be excreted in the urine either unchanged or
as acid-labile conjugates. TDA, as a metabolite can be N-acetylated
forming mono- and diacetylated TDA metabolites which are readily
excreted in the urine (Timchalk, et al. 1994). After inhalatory
exposure, very little 2,4-TDA is formed. In addition, 90% of the
quantitated metabolites in the urine specimens following inhalation
exposure to 2,4-TDI existed as acid-labile conjugates of TDI/TDA while
only 10% existed as acetylated TDA. This indicated that following
inhalation exposure, a larger percentage of the 2,4-TDI was excreted in
the urine preferentially in a conjugated form (to proteins) and not as
oligoureas or free or acetylated TDA (Timchalk et al., 1994).
There is no data on metabolism of
2,4,6-triisopropyl-m-phenylene-diisocyanate. Similar to TDI, the
substance is expected to form conjugates with glutathione (and other
peptides) because the carbon atoms in the isocyanate group represent an
electrophile centre susceptible to nucleophile attack by such strong
nucleophiles as lysine, cysteine and histidine (Smith and Hotchkiss,
2001). The isopropyl groups on aromatic ring can however affect the
reactivity of electrophile carbon due probably to sterical hindrance. If
2,4,6-triisopropyl-m-phenylene-diisocyanate hydrolises to its
corresponding amine, the latter can be N-acetylated and then excreted in
the urine. Aromatic and aliphatic hydroxylation can also occur leading
to a hydrophyle which is easily to be excreted.
and TDI are aromatic diisocyanates with different alkyl rests
attached to benzene ring (three isopropyl groups in
2,4,6-triisopropyl-m-phenylene-diisocyanate and one methyl group in
TDI). As a result of the structural differences, such
physic-chemical properties as melting point, LogPow and water
solubility differ significantly from each other.
is expected to be absorbed to a lesser extent than TDI into the
organism after oral exposure. Absorption via oral route is assumed
to be low. Absorption after inhalation is considered to be rather
fast. Dermal absorption, however will be limited by its molecular
weight, its high lipophilicity and its high logPow. Due to high
logPow, 2,4,6-triisopropyl-m-phenylene-diisocyanate is not expected
to penetrate easily through the skin but tends to migrate towards
fat tissues but certain reactivity of isocyanate groups with
peptides and proteins might hinder accumulation. Inhalation and
dermal routes can represent sensitising and irritating hazard for
respiratory system. Nucleophilic substitution by SN2 mechanism with
electron rich nucleophile amino acids of peptides and proteins is
considered to be primary detoxifying mechanism of
2,4,6-triisopropyl-m-phenylene-diisocyanate. Excretion of
2,4,6-triisopropyl-m-phenylene-diisocyanate is expected via urine.
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