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CHEMINFO Record Number: 138
CCOHS Chemical Name: Bitoluene diisocyanate

4,4'-Biorthotolylene diisocyanate
3,3'-Dimethyl-4,4'-biphenylene diisocyanate
Isocyanic acid, 3,3'-dimethyl-4,4'-biphenylene ester
Tolidine diisocyanate

CAS Registry Number: 91-97-4
RTECS Number(s): DV3960000
Chemical Family: Isocyanic acid ester / isocyanate / aromatic isocyanate / diisocyanate / aromatic diisocyanate
Molecular Formula: C16-H12-N2-O2
Structural Formula: (O=C=N)(CH3)C6H3-C6H3(CH3)(N=C=O)


Appearance and Odour:
White or pale yellow flakes (1)

Odour Threshold:
No information available

Warning Properties:
No information available for evaluation

May contain small amounts of other bitoluene diisocyanate isomers.

Uses and Occurrences:
May be used to produce high strength elastomers, coatings and rigid plastics.


White or pale yellow flakes. Can probably burn if strongly heated. Can decompose at high temperatures forming toxic gases, such as nitrogen oxides and hydrogen cyanide. May polymerize if heated. Reacts vigorously with water at high temperatures. Closed containers may develop pressure and rupture on prolonged exposure to heat or if contaminated with water. Irritating to respiratory tract. May cause lung injury--effects may be delayed. RESPIRATORY SENSITIZER. Can cause severe allergic respiratory reaction in some people. May cause allergic skin reaction.


Effects of Short-Term (Acute) Exposure

Bitoluene diisocyanate is a solid with a very low vapour pressure. Therefore, airborne exposures are unlikely to occur unless it is heated or dust is generated. Short-term inhalation exposure to isocyanates, such as bitoluene diisocyanate can cause respiratory and mucous membrane irritation. Typical symptoms may include eye and nose irritation, dry or sore throat, runny nose, shortness of breath, difficulty in breathing, wheezing and laryngitis. Coughing with chest pain or tightness may also occur, frequently at night. These symptoms may occur during exposure or may be delayed several hours.
Inhalation of very high concentrations of isocyanates can cause inflammation of the lung tissue (chemical pneumonitis), chemical bronchitis with severe asthma-like wheezing, severe coughing spasms and accumulation of fluid in the lungs (pulmonary edema), which could prove fatal. Symptoms of pulmonary edema may not appear until several hours after exposure and are aggravated by physical exertion.
Some people may become sensitized to bitoluene diisocyanate--see Effects of Long-term (Chronic) Exposure for more information.

Skin Contact:
There have been no reports of harmful skin effects among people who work with bitoluene diisocyanate. It caused no irritation when applied to rabbit skin.(1) Isocyanates, in general, can cause skin discolouration (staining) and hardening of the skin after repeated exposures.

Eye Contact:
No human information but bitoluene diisocyanate can probably cause slight eye irritation. It caused slight eye irritation in rabbits.(1)

There have been no reports of people ingesting bitoluene diisocyanate and ingestion is unlikely to occur in the workplace. Animal studies indicate that it has low oral toxicity. Ingestion would probably cause irritation of the mouth, throat and digestive tract.

Effects of Long-Term (Chronic) Exposure

Lungs/Respiratory System:
Exposure to isocyanates is likely to aggravate individuals with existing respiratory disease, such as chronic bronchitis and emphysema.

Respiratory Sensitization:
In general, isocyanates are well known to cause respiratory sensitization. There is a strong body of evidence that isocyanates cause occupational asthma in a significant proportion of exposed workers.(13)
Isocyanate respiratory sensitization is usually caused by a very large exposure, or by multiple exposures.(2) Although varying periods of exposure (1 day to years) may elapse before sensitization occurs, it develops more often during the first few months of exposure. Sensitized individuals react to very low levels of isocyanates that have no effect on unsensitized people.(2) At first, the symptoms may appear to be a cold or mild hay fever. However, severe asthmatic symptoms can develop and include wheezing, chest tightness, shortness of breath, difficulty breathing and/or coughing. Fever, chills, general feelings of discomfort, headache, and fatigue can also occur. Symptoms may occur immediately upon exposure (within an hour), several hours after exposure or both, and/or at night.(2,3) Typically, the asthma improves with removal from exposure (e.g. weekends or vacations) and returns, in some cases, in the form of an "acute attack", on renewed exposure.(3) Sensitized people who continue to work with isocyanates may develop symptoms sooner after each exposure. The number and severity of symptoms may increase.
Long-term exposure to low levels of some isocyanates may cause impaired lung function, such as diminished respiratory capacity. Following removal from isocyanate exposure, some sensitized workers may continue to experience persistent respiratory problems such as asthmatic symptoms, bronchial problems and impaired lung function for months or years.(2,3) Others may recover fully and may gradually lose their sensitivity within several years.(2)
Cross-sensitization between different isocyanates may occur.

Skin Sensitization:
In some cases, repeated skin contact with isocyanates has caused skin sensitization. However, there is no evidence that bitoluene diisocyanate causes skin sensitization.


There is no human or animal information available.

The International Agency for Research on Cancer (IARC) has not evaluated the carcinogenicity of this chemical.

The American Conference of Governmental Industrial Hygienists (ACGIH) has no listing for this chemical.

The US National Toxicology Program (NTP) has not listed this chemical in its report on carcinogens.

Teratogenicity and Embryotoxicity:
No human or animal information is available.

Reproductive Toxicity:
No human or animal information is available.

No human or animal in vivo studies have been reported.

Toxicologically Synergistic Materials:
No information is available.

Potential for Accumulation:
Information about the absorption, metabolism and excretion of bitoluene diisocyanate is limited. Like other isocyanates, it probably does not accumulate.


Take proper precautions to ensure your own safety before attempting rescue (e.g. wear appropriate protective equipment, use the "buddy" system). Remove source of contamination or move victim to fresh air. If breathing is difficult, trained personnel should administer emergency oxygen. DO NOT allow victim to move about unnecessarily. Symptoms of pulmonary edema can be delayed up to 48 hours after exposure. Immediately obtain medical attention.

Skin Contact:
Avoid direct contact. Wear chemical protective clothing, if necessary. As quickly as possible, remove contaminated clothing, shoes, and leather goods (e.g. watchbands, belts). Quickly and gently blot or brush away excess chemical. Wash gently and thoroughly with water and non-abrasive soap for 5 minutes. Obtain medical attention immediately. Double bag, seal, label and leave contaminated clothing, shoes and leather goods at the scene for safe disposal.

Eye Contact:
Avoid direct contact. Wear chemical protective gloves, if necessary. Quickly and gently blot or brush away excess chemical. Immediately flush the contaminated eye(s) with lukewarm, gently flowing water for 5 minutes, while holding the eyelid(s) open. If a contact lens is present, DO NOT delay irrigation or attempt to remove the lens until flushing is done. Obtain medical advice immediately.

NEVER give anything by mouth if victim is rapidly losing consciousness, is unconscious or convulsing. Have victim rinse mouth thoroughly with water. DO NOT INDUCE VOMITING. If vomiting occurs naturally, have victim rinse mouth with water again. Obtain medical attention immediately.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest).
Consult a doctor and/or the nearest Poison Control Centre for all exposures except minor instances of inhalation or skin contact.
Some first aid procedures recommended above require advanced first aid training. Protocols for undertaking advanced procedures must be developed in consultation with a doctor and routinely reviewed.
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its condition of use in the workplace.


Flash Point:
214 deg C (417 deg F) (open cup) (5)

Lower Flammable (Explosive) Limit (LFL/LEL):
Not available

Upper Flammable (Explosive) Limit (UFL/UEL):
Not available

Autoignition (Ignition) Temperature:
Not available

Sensitivity to Mechanical Impact:
Information not available. Probably not sensitive. Stable material.

Sensitivity to Static Charge:
Information not available. Probably not sensitive since it has a very high flash point.

Combustion and Thermal Decomposition Products:
Nitrogen oxides, hydrogen cyanide.

Fire Hazard Summary:
This material can probably burn if stronly heated. During a fire, irritating/toxic nitrogen oxides and hydrogen cyanide may be generated. May react vigorously with water at high temperatures. Closed containers may rupture violently when heated.

Extinguishing Media:
Chemical foam, carbon dioxide, dry chemical, water spray

Fire Fighting Instructions:
Evacuate area and fight fire from a safe distance or a protected location. Approach fire from upwind to avoid hazardous vapours and toxic decomposition products.
Water, if used in very large quantities, may be effective for fighting fires involving bitoluene diisocyanate. However, proper care must be taken since the reaction between water and hot bitoluene diisocyanate can be vigorous.(4)
Isolate materials not yet involved in the fire and protect personnel. Move containers from fire area if this can be done without risk. Water spray or fog can be used to absorb heat and protect exposed material of structures. Keep fire-exposed tanks or containers cool by spraying with water to minimize the risk of rupture. If a leak or spill has not ignited, use water spray in large quantities to disperse the vapours and to protect personnel attempting to stop a leak.
After the fire has been extinguished, the area should not be considered safe until a thorough inspection for residual isocyanate has been carried out by properly protected personnel.(4) The decomposition products of bitoluene diisocyanate, for example hydrogen cyanide and nitrogen oxides, are extremely hazardous to health. Do not enter any fire area without specialized protective equipment suitable for the occasion. Firefighter's normal protective equipment (Bunker Gear) will not provide adequate protection. Chemical resistant clothing (e.g. chemical splash suit) and positive pressure self-contained breathing apparatus (MSHA/NIOSH approved or equivalent) may be necessary.


NFPA - Comments:
NFPA has no listing for this chemical in Codes 49 or 325.


Molecular Weight: 264.28

Conversion Factor:
1 ppm = 10.79 mg/m3; 1 mg/m3 = 0.093 ppm (calculated)

Physical State: Solid
Melting Point: 70 deg C (158 deg F) (1,5)
Boiling Point: 314 deg C (597 deg F) at 101.3 kPa (760 mm Hg); 160-170 deg C (320-338 deg F) at 0.5 kPa (3.8 mm Hg) (5)
Relative Density (Specific Gravity): 1.156 at 80 deg C (water = 1) (5)
Solubility in Water: Probably insoluble. Reacts slowly with water.
Solubility in Other Liquids: No information available
Coefficient of Oil/Water Distribution (Partition Coefficient): Not applicable (reacts with water)
pH Value: Not applicable (reacts with water)
Vapour Density: 9.1 (air = 1)
Vapour Pressure: 0.0013 kPa (0.01 mm Hg) at 93 deg C
Saturation Vapour Concentration: 13 ppm at 93 deg C (calculated)
Evaporation Rate: Not available. Probably low.


Normally stable

Hazardous Polymerization:
May occur on contact with incompatible materials or exposure to excessive heat. The resulting heat and pressure build-up can rupture closed containers.

Incompatibility - Materials to Avoid:

NOTE: Chemical reactions that could result in a hazardous situation (e.g. generation of flammable or toxic chemicals, fire or detonation) are listed here. Many of these reactions can be done safely if specific control measures (e.g. cooling of the reaction) are in place. Although not intended to be complete, an overview of important reactions involving common chemicals is provided to assist in the development of safe work practices.

WATER - Reacts slowly, forming carbon dioxide and non-toxic, insoluble polyureas which can rupture closed containers. At higher temperatures, the reaction may become progressively more vigorous.(4,5)
ALCOHOLS, ACIDS, BASES, AMINES - May react vigorously with the generation of heat.(4)
AMIDES, PHENOLS, MERCAPTANS, URETHANES, UREAS AND SURFACE ACTIVE MATERIALS (surfactants, non-ionic detergents) - May react vigorously or violently with generation of heat.(5)
METAL COMPOUNDS (e.g. organotin catalysts) - May polymerize with generation of heat and pressure.(5)

Hazardous Decomposition Products:
None reported.

Conditions to Avoid:
Moisture, heat.

Corrosivity to Metals:
Information not available.

Stability and Reactivity Comments:
Isocyanates are very reactive compounds and are especially highly reactive toward a large number of compounds with active hydrogens, particularly at high temperatures and in the presence of catalysts, such as acids, bases, tertiary amines and organotin compounds.(5) See reference 5 for some of the reactions of isocyanates. Isocyanates will attack and make brittle many plastic and rubber materials.(4)


LD50 (oral, rat): Greater than 4640 mg/kg (1)

Eye Irritation:

Bitoluene diisocyanate caused slight eye irritation in rabbits (no further details available).(1)

Skin Irritation:

Bitoluene diisocyanate caused no skin irritation in rabbits (no further details available).(1)

Effects of Short-Term (Acute) Exposure:

The dust or vapour caused minimal toxic effects and slight cellular (histologic) changes in animals. There were no deaths.(1)

Administration of up to 4640 mg/kg may have caused dilation of the pupils in rats at doses of 1,000 mg/kg and above. No other toxic effects were observed.(1)


Selected Bibliography:
(1) Woolrich, P.F. Monoisocyanates, diisocyanates and polyisocyanates: engineering, medical control and toxicologic considerations. Technical bulletin 106. Upjohn Company, 1973.
(2) Karol, M.H. Respiratory effects of inhaled isocyanates. CRC Critical Reviews in Toxicology. Vol. 16, no. 4 (1986). p. 349-379
(3) Musk, A.W., et al. Isocyanates and respiratory disease: current status. American Journal of Industrial Medicine. Vol. 13 (1988). p. 331-349
(4) Recommendations for the handling of aromatic isocyanates. International Isocyanate Institute, Inc, Jan. 1976
(5) Kirk-Othmer encyclopedia of chemical technology. 3rd ed. Vol. 13. John Wiley and Sons, 1981. p. 789-818
(6) Robertson, S.M. Determination of total isocyanate concentrations in air by headspace gas chromatography. Health and Safety Executive, 1986
(7) Brown, R.H., et al New methods for the determination of airborne isocyanates. Health and Safety Executive, (n.d.)
(8) Criteria for a recommended standard: occupational exposure to diisocyanates. National Institute for Occupational Safety and Health, 1978
(9) NIOSH pocket guide to chemical hazards. NIOSH, June 1994. p. 208-209
(10) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 4th ed. Van Nostrand Reinhold, 2002
(11) Key-Schwartz, R.J. Analytical problems encountered with NIOSH method 5521 for total isocyanates. AIHA Journal. Vol. 56 (1995). p. 474-479
(12) Streicher, R.P., et al. Investigation of the ability of MDHS method 25 to determine urethane-bound isocyanate groups. AIHA Journal. Vol. 56 (1995). p. 437-442
(13) Asthmagen? Critical assessments of the evidence for agents implicated in occupational asthma. Health and Safety Executive (HSE), 1997 with 1998 and 2001 supplements

Information on chemicals reviewed in the CHEMINFO database is drawn from a number of publicly available sources. A list of general references used to compile CHEMINFO records is available in the database Help.

Review/Preparation Date: 1996-03-06

Revision Indicators:
Resistance of materials for PPE 2004-04-02
Emergency overview 2006-06-14
WHMIS detailed classification 2006-06-14
WHMIS proposed classification 2006-06-14
WHMIS disclosure list 2006-06-14
WHMIS health effects 2006-06-14
OSHA hazcom 2006-06-14
Long-term exposure 2006-06-14
Bibliography 2006-06-14
Handling 2006-06-27
Engineering controls 2006-06-27

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