Aromatic isocyanates toxicity

No specific information on the pharmacokinetic mechanisms, mechanisms of toxicity, or animal-to-human extrapolations of these parameters for HDI were located in the available literature. In general, both aliphatic and aromatic isocyanates are considered to be pulmonary, oral, and dermal irritants. Several studies discussed earlier have reported respiratory irritation, which included burning and irritation to the nasal tract, throat, and the chest after inhalation exposure (Baur et al. 1984 Cockcroft and Mink 1979 ... 

The toxic route is primarily inhalation. The vapor pressure of this compound at ambient temperature is very low, 0.00014 torr at 25°C. However, when heated to about 75°C, the acute health hazard is greatly enhanced (Hadengue and Philbert 1983). The acute toxic symptoms were found to be similar to those of toluene-2,4-diisocyanate and other aromatic isocyanates. Inhalation of its vapors or particulates can cause bronchitis, coughing, fever, and an asthma-like syndrome. Other symptoms were nausea, shortness of breath, chest pain, insomnia, and irritation of the eyes, nose, and throat. The immunologic response, however, varied among humans. Exposure to 0.1-0.2 ppm for 30 minutes is likely to manifest the acute toxic effects in humans. 

Highly poisonous when vapors or particulates inhaled in humans, toxic symptoms characteristic of aromatic isocyanates seen at 1-min exposure to 1 mg/m (0.16 ppm) LClo (mice) 40 mg/m low oral toxicity skin and eye contact can produce severe irritation no exposure limit is set, a TLV-TWA of 0.005 ppm (0.031 mg/m ) is recommended... 

In the Part B of this text several new entries have been inducted. Many compounds are entered in the tables under miscellaneous substances in several chapters. Molybdenum has been added as a subchapter into Metals, Toxic. A number of chapters of the last edition have been fully revised in this edition. Notable among them are, Nerve Gases Dioxin and Related Compounds Metals, Toxic Pesticides, Organochlorine-, Organophosphorus-, Carbamates-, and Chlo-rophenoxy Acids- Amines, Aromatic Isocyanates, Organic Halogenated Hydrocarbons Hydrocarbons, Aromatics Asbestos Nitriles and Nitrosoamines and a number of individual compounds such as Napalm. Practically all the entries of the previous edition have been retained in this edition. All revisions have been updated wherever possible to the year 2006. 

Hydrogen cyanide adds to aliphatic and even better to aromatic isocyanates, in the presence of triethylamine, to give the expected insertion product 240. Instead of the highly toxic hydrogen cyanide, aqueous potassium cyanide can be used in the reaction with phenyl isocyanate... 

With aromatic isocyanate resins, the formation of the urethane linkage can he promoted hy a number of metals in the form of organometallics and/or salts of organic acids. Tin compounds such as dihutyl tin dilaurate and tin (II) octoate are particularly effective, having superseded the more toxic lead equivalent components. 

Some of the reaction products of polymerisation and cure can be toxic, for example, aromatic amines from hydrolysis of isocyanates and bisphenol A from... 

Aromatic amines are used in the manufacture of rubber chemicals, drugs, dyes, isocyanates, and many other miscellaneous chemical products. The toxicity of aromatic amines has been known and studied for many yearsfH They all penetrate the skin and all produce methemoglobinemia. .) Recently, the Occupational Safety and Health Administration (OSHA) established exposure limits for 14 human carcinogens, several of which are aromatic amines(3)... 

An offering by Cytec Specialty Chemicals, the meta isomer of tetramethyl xylene diisocyanate (TMXDI) is interesting because it contains an aromatic ring, but the NCO groups themselves are aliphatic isocyanates and have reaction characteristics typical of aliphatic diisocyanates. It reacts even more sluggishly than the more standard aliphatic isocyanates because of steric interactions, making the reactions easier to control. Compounds such as dimethyl tin dilaurate, lead octoate, or tetrabutyl diacetyl distannox-ane have been shown to be effective catalysts for the isocyanate-hydroxyl reaction. The manufacturer claims that it is less toxic than many other isocyanates. 

Wood stains and varnishes used indoors contain aliphatic and aromatic hydrocarbons, isocyanates, ketones, and esters. Though these have limited use compared with paint, newly finished building interiors often contain toxic levels of these. Toluene diisocyanate, used as a catalyst in polyurethane wood finishes, is a powerful respiratory irritant and sensitizer. 13 ... 

DMC is classified as a non-toxic and environmentally compatible chemical [69]. In addition, the photochemical ozone creation potential of DMC is the lowest among common VOCs (2.5 ethylene = 100). The areas in which DMC acts, or can act, as a potential phosgene substitute correspond to the main areas of phosgene industrial exploitation, that is, production of aromatic polycarbonates and isocyanates, leading the production of these important chemicals out of the chlorine cycle. 

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