Tolylene-2,4-diisocyanate

Description

Toluene diisocyanate (TDI), (OCN)2C6H3CH3, is a water-white to pale-yellow liquid with a sharp, pungent odor. It reacts with water to release carbon dioxide. The specific gravity is 1.22, which is heavier than water. TDI is toxic by inhalation and ingestion, and is a strong irritant to skin and other tissue, particularly the eyes. The TLV is 0.005 ppm in air, and the IDLH is 10 ppm. The target organs are the respiratory system and the skin. The four-digit UN identification number is 2078. The NFPA 704 designation is health 3, flammability 1, and reactivity 3. The white section at the bottom of the diamond has a W with a slash through it, indicating water reactivity. The primary uses of TDI are in the manufacture of polyurethane foams, elastomers, and coatings.

Chemical properties

colourless to light yellow liquid

Chemical properties

Toluene diisocyanate exists in two isomeric forms (2,4-toluene diisocyanate and 2,6-toluene diisocyanate), which have similar properties and effects. Toluene diisocyanate is produced commercially as an 80:20 (2,4-toluene diisocyanate:2,6-toluene diisocyanate) mixture of the two isomers. At room temperature, the mixture is a clear, pale yellow liquid with a sharp, pungent odor. It should be stored under refrigeration, away from light and moisture in a tightly closed container in an inert atmosphere. Toluene diisocyanate is insoluble in water and miscible with most common organic solvents. Toluene diisocyanate is made by reacting toluene diamine with carbonyl chloride (phosgene). Toluene diisocyanate is commonly used as a chemical intermediate in the production of polyurethane foams, elastomers, and coatings, paints, varnishes, wire enamels, sealants, adhesives, and binders. It is also used as a cross-linking agent in the manufacture of nylon polymers. 2,4-Toluene diisocyanate is used as a chemical intermediate in the production of polyurethane products, such as foams, coatings, and elastomers.

Physical properties

Clear, colorless to light yellow liquid with a pungent, fruity odor. Odor threshold concentration in air is 2.14 ppm_v (Leonardos et al., 1969).

The Uses of Tolylene-2,4-diisocyanate

Occupational asthma is the principal cause of work-related respiratory disease in the industrial world. Toluene-2,4-diisocyanate (TDI) is one of the most common respiratory sensitizers leading to occupational asthma.

The Uses of Tolylene-2,4-diisocyanate

TDI (toluene diisocyanate) is an important basic raw materials of polyurethane. TDI is a mixture of 2,4-TDI and 2,6-TDI two kinds of isomers, including 3 kinds of commonly used grades: TDI-80/20, TDI-100 and TDI-65/35. Mainly used in the production of flexible polyurethane foam and polyurethane elastomer coatings, adhesives, etc..

The Uses of Tolylene-2,4-diisocyanate

In the manufacture of polyurethane foams and other elastomers.

The Uses of Tolylene-2,4-diisocyanate

Toluene-2,4-diisocyanate is one of the mostextensively used isocyanates. It is usedin the production of rigid and flexibleurethane foams, elastomers, and coatings. Inaddition to its use as a pure compound, itis commercially available as a mixture of2,4- and 2,6-isomers (80 : 20% and 65 : 35%ratios, respectively).

Definition

ChEBI: A toluene meta-diisocyanate in which the isocyanato groups are at positions 2 and 4 relative to the methyl group on the benzene ring.

General Description

2,4-TDI is an environmental contaminant belonging to the class of diisocyanates. It is commercially used as a starting material for varnishes, paints, elastomers, polyurethane foams, wire enamels, etc.

Air & Water Reactions

Reacts with water with the evolution of carbon dioxide and formation of insoluble polyureas that are relatively nontoxic and inert [Merck 11th ed. 1989)].

Reactivity Profile

Tolylene-2,4-diisocyanate is explosive in the form of vapor when exposed to heat, flame or sparks. Undergoes potentially violent polymerization reaction with strong bases or acyl chlorides. Reacts with water to liberate carbon dioxide. Potential explosion if stored in polyethylene containers due to absorption of water through the plastic. Emits very toxic fumes of oxides of nitrogen when heated to decomposition [Lewis, 3rd ed., 1993, p. 1251].

Hazard

Toxic by ingestion and inhalation; strong irritant to skin and tissue, especially to eyes. Respiratory sensitization.

Health Hazard

Can cause death. Contact with skin may cause allergic eczema. Substance is very corrosive to eyes. Chronic exposure may cause chronic lung disease. As a vapor TDI is a powerful irritant to the respiratory tract. Chronic loss of respiratory function may occur. Acute asthmatic bronchitis or frank asthma may occur. A splash in the eyes of workmen has caused keratitis and conjunctivitis. Tolylene-2,4-diisocyanate causes inflammation of the skin, also chemical pneumonitis and pulmonary edema.

Health Hazard

Exposures to toluene diisocyanate cause severely irritating effects especially to the mucous membranes and tissues. Inhalation of toluene diisocyanate produces euphoria, ataxia, mental aberrations, vomiting, abdominal pain, respiratory sensitization, bronchitis, emphysema, and asthma. The mechanism by which toluene diisocyanate produces toxic symptoms is not known, but the compound is highly reactive and may inactivate tissue biomolecules by covalent binding. Acute and chronic exposures to toluene diisocyanate produce health disorders of the skin, the respiratory system, the CNS, and the gastrointestinal tract. A number of occupational studies have reported that chronic exposures to toluene diisocyanate reduce lung function among workers associated with the production Exposures to toluene diisocyanate cause severely irritating effects especially to the mucous membranes and tissues. Inhalation of toluene diisocyanate produces euphoria, ataxia, mental aberrations, vomiting, abdominal pain, respiratory sensitization, bronchitis, emphysema, and asthma. The mechanism by which toluene diisocyanate produces toxic symptoms is not known, but the compound is highly reactive and may inactivate tissue biomolecules by covalent binding. Acute and chronic exposures to toluene diisocyanate produce health disorders of the skin, the respiratory system, the CNS, and the gastrointestinal tract. A number of occupational studies have reported that chronic exposures to toluene diisocyanate reduce lung function among workers associated with the production of polyurethane foam Exposure to toluene diisocyanate produces severe respiratory problems and individuals with pre-existing breathing diffi culties may be more susceptible to its effects. It causes irritation of the respiratory tract. Concentration-dependent effects occur, often after a delay of 4–8 h and may persist for 3–7 days. Exposures to high-concentration inhalation of toluene diisocyanate cause symptoms of toxicity, such as chest tightness, cough, breathlessness, infl ammation of the bronchi with sputum production and wheezing with possible accumulation of fl uid in the lungs. Previously exposed occupational workers and users have been reported to develop symptoms of infl ammation of the lungs on re-exposure to even extremely low levels of toluene diisocyanate. Flu-like symptoms, such as fever, malaise, shortness of breath, and cough, can develop 4–6 h after exposure and persist for 12 h or longer. In sensitized workers/individuals, asthmatic attacks occur after exposure to extremely low toluene diisocyanate air concentrations (0.0001 ppm). The asthmatic reactions occur immediately and/or delayed (4–8 h). Exposure to toluene diisocyanate leads to reactive airway dysfunction syndrome (RADS), a chemically or irritant-induced type of asthma. Children may be more vulnerable because of relatively increased minute ventilation per kilogram and failure to evacuate an area promptly when exposed.

Health Hazard

The acute toxicity of toluene diisocyanate by inhalation is high. Exposure to TDI can cause lung damage and decreased breathing capacity. Symptoms of exposure may include coughing, tightness of the chest, chest pain, nausea, vomiting, abdominal pain, headache, and insomnia. TDI irritates the skin, and eye contact can cause irritation with permanent damage if untreated. The oral acute toxicity of this substance is low. The odor of TDI does not provide an adequate warning to avoid overexposure.
Toluene diisocyanate has caused sensitization of the respiratory tract, manifested by acute asthmatic reaction upon return to work after a period of time away from exposure. Initial symptoms include coughing during the night, with difficult or labored breathing. Skin sensitization can also occur. Toluene diisocyanate is listed in IARC Group 2B ("possible human carcinogen"), is listed by NTP as "reasonably anticipated to be a carcinogen," and is classified as a "select carcinogen'' under the criteria of the OSHA Laboratory Standard.

Health Hazard

Toluene-2,4-diisocyanate is a highly toxiccompound by inhalation, a skin and eye irritant, and a carcinogenic substance. Exposureto its vapors can cause tracheobronchitis, pulmonary edema, hemorrhage, and death. Thetarget organs are the respiratory system andskin. The toxic effects were also noted in theliver, kidney, and gastrointestinal tract.
In humans, exposure to low concentrations, 0.1–0.2 ppm, can result in irritationof the eyes, nose, and mucous membranes.Acute exposure to higher concentrationscan cause bronchitis, pneumonitis, headache,sleeplessness, pulmonary edema, and sometimes an asthma-like syndrome. Chronicexposure can result in wheezing, coughing,shortness of breath, and chest congestion.Such effects may be manifested from inhalation of 0.02–0.05 ppm of the diisocyanateover a period of time.
Acute oral toxicity of this compound,however, is low. Symptoms may be coughing, vomiting, and gastrointestinal pain.Absorption through skin can produce toxiceffects similar to those of inhalation toxicity:bronchitis, pulmonary edema, and asthma. Inaddition, the acute toxic symptoms can benausea, vomiting, abdominal pain, dermatitis, and skin sensitization. Contact with eyescan cause burning, lacrimation, prickling type sensation, and injury to vision.
LC50 value, (rats): 14 ppm/4 hr
LD50 value, oral (rats): 5800 mg/kg
LD50 value, intravenous (mice): 56 mg/kg
Toluene-2,4-diisocyanate caused tumor inthe liver and pancreas in test animals. Thereis sufficient evidence of its carcinogenicityin animals. Its cancer-causing activity inhumans has not been established.

Fire Hazard

When heated to decomposition Tolylene-2,4-diisocyanate emits very toxic fumes of cyanide and nitrogen oxides. Reacts violently with amines, alcohol, bases and warm water causing fire and explosion hazards. Avoid strong oxidizers, water, acids, bases, amines, etc., cause foam and splatter. Avoid heating. Hazardous polymerization may occur. Concentrated alkaline compound such as sodium hydroxide or tertiary amines may cause run-away polymerization. Slow, not hazardous polymerization may occur above 235F.

Fire Hazard

TDI is a combustible liquid (NFPA rating = 1). Explosive limits in air are 0.9 to 9.5% by volume. Carbon dioxide or dry chemical extinguishers should be used for TDI fires.

Flammability and Explosibility

TDI is a combustible liquid (NFPA rating = 1). Explosive limits in air are 0.9 to 9.5% by volume. Carbon dioxide or dry chemical extinguishers should be used for TDI fires.

Chemical Reactivity

Reactivity with Water: A non violent reaction occurs forming carbon dioxide gas and an organic base; Reactivity with Common Materials: No reactions; Stability During Transport: Stable; Neutralizing Agents for Acids and Caustics: Not pertinent; Polymerization: Slow polymerization occurs at temperatures above 113°F. The reaction is not hazardous; Inhibitor of Polymerization: Not pertinent.

Safety Profile

Confirmed carcinogen. Poison by ingestion, inhalation, and intravenous routes. Human systemic effects by inhalation: unspecified changes to the eyes and sense of smell, respiratory obstruction, cough, sputum, and other pulmonary and gastrointestinal changes. Mutation data reported. A severe skin and eye irritant. Capable of producing severe dermatitis and bronchial spasm. A common air contaminant. Combustible when exposed to heat or flame. Explosive in the form of vapor when exposed to heat or flame. To fight fire, use dry chemical, CO2. Potentially violent polymerization reaction with bases or acyl chlorides. Reaction with water releases carbon dioxide. Storage in polyethylene containers is hazardous due to absorption of water through the plastic. When heated to decomposition it emits highly toxic fumes of NOx. See also ISOCYANATES.

Carcinogenicity

Acute toxicity. Industrial experience has demonstrated that acute exposure to TDI vapors can produce severe irritant effects on mucous membranes, the respiratory tract, and the eyes. An acute attack of an asthma-like syndrome may occur. Exposure to high concentrations may lead to chemical bronchitis with severe bronchospasm, chemical pneumonitis, pulmonary edema, headache, and insomnia.With sufficient exposure, all persons would appear to experience these effects even on their first exposure.
Chronic and subchronic toxicity. Repeated exposures at lower concentrations of TDI may produce a chronic-like syndrome in many people. Symptoms may include coughing, wheezing, tightness or congestion in the chest, and shortness of breath and appear to be related to hypersensitization. Interstitial pulmonary fibrosis does not occur from moderately elevated exposures to TDI (mean 0.07, peak 0.2 ppm).
Exposure to TDI may lead to immunological sensitization. Some individuals become sensitized on first exposure; others may develop symptoms after exposure over days, months, or years. Other workers have experienced only minimal or no respiratory symptoms for several months of low level exposure, then suddenly develop acute asthmatic reactions to the same level. The nature of the sensitization process is unknown, and many authors have referred to it as an “allergy;” the respiratory response in sensitized people is referred to as true asthma, comparable to asthma excited by pollens and other exoallergens. Some TDI-sensitized people, however, have no history of prior allergic disease.

Environmental Fate

Chemical/Physical. Slowly reacts with water forming carbon dioxide and polyureas (NIOSH, 1997; Windholz et al., 1983).

storage

work with TDI should be conducted in a fume hood to prevent exposure by inhalation, and splash goggles and impermeable gloves should be worn at all times to prevent eye and skin contact.

Purification Methods

It is purified by fractionation in a vacuum and should be stored in a dry atmosphere. It is soluble in organic solvents but reacts with H2O, alcohols (slowly) and amines, all of which could cause explosive polymerisation. It darkens on exposure to light. It has a sharp pungent odour, is TOXIC and is IRRITATING TO THE EYES. [Siefken Justus Liebigs Ann Chem 562 75, 96, 127 1949, Bayer Angew Chem 59 257 1947.] It is a reagent for covalent crosslinking of proteins [Wold Methods Enzymol 25 623 1972.] [Beilstein 13 IV 243.]

Incompatibilities

Contact with strong oxidizers may cause fires and explosions. Contact with water, acids, bases, and amines can lead to reactions that liberate heat and CO2 and cause violent foaming and spattering. TDI will attack some forms of plastic, rubber, and coatings.

Waste Disposal

Excess TDI and waste material containing this substance should be placed in an appropriate container, clearly labeled, and handled according to your institution's waste disposal guidelines.

Precautions

Occupational workers should be careful during use and waste disposal of toluene diisocyanate. Use and storage of toluene diisocyanate requires precautions. It polymerizes under the infl uence of bases, tertiary amines, and acyl chlorides with fi re or explosion hazard. On combustion, it forms toxic vapors and gases, including nitrogen oxides and isocyanates. Toluene diisocyanate reacts readily with water, acids, and alcohols, and causes explosion hazard. The development of any unusual signs or symptoms, such as headache, increased pain or a discharge from the eyes, increased redness or pain or a pus-like discharge in the area of a skin burn within 24 h after exposure to toluene diisocyanate, requires immediate medical support to the exposed worker.