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CHEMINFO Record Number: 222
CCOHS Chemical Name: n-Butyl isocyanate

Butyl isocyanate
Isocyanic acid, butyl ester

Chemical Name French: Isocyanate de n-butyle
CAS Registry Number: 111-36-4
UN/NA Number(s): 2485
RTECS Number(s): NQ8250000
EU EINECS/ELINCS Number: 203-862-8
Chemical Family: Isocyanic acid ester / isocyanate / aliphatic isocyanate / monoisocyanate / aliphatic monoisocyanate
Molecular Formula: C5-H9-N-O
Structural Formula: CH3-CH2-CH2-CH2-N=C=O


Appearance and Odour:
Colourless liquid; lachrymator (vapour irritates the eyes and causes tears).(11)

Odour Threshold:
No information available

Warning Properties:
Information not available for evaluation

Uses and Occurrences:
Monoisocyanates are used as chemical intermediates in the production of drugs, pesticides, amines, ureas and other carbamoyl compounds.


Colourless liquid. Lachrymator. FLAMMABLE LIQUID AND VAPOUR. Vapour is heavier than air and may spread long distances. Distant ignition and flashback is possible. Can decompose at high temperatures forming toxic gases, such as nitrogen oxides and hydrogen cyanide. Closed containers may develop pressure and rupture on prolonged exposure to heat. Reacts violently with water. May polymerize if heated or in contact with water. VERY TOXIC. May be fatal if inhaled or swallowed. Vapour is extremely irritating to the eyes and respiratory tract. May cause lung injury--effects may be delayed. Liquid causes skin and eye irritation.


Effects of Short-Term (Acute) Exposure

n-Butyl isocyanate is a very strong irritant and initial injury is probably confined to areas of direct contact such as the nose, mouth and respiratory tract. Very serious and persistent respiratory system and lung damage may occur which can result in death. The inhalation toxicity of n-butyl isocyanate is similar to that of methyl isocyanate.(1)
Typical symptoms include breathlessness, dry cough, throat irritation or choking, chest pain/tightness, difficulty in breathing and possibly coughing up blood. Other common symptoms include lethargy, loss of appetite, convulsions and coma.(2) Symptoms may appear immediately or may be delayed several hours after exposure, depending upon the concentration, and may continue for 3 to 7 days or longer. Permanent lung damage may result.
Inhalation of very high levels might cause chemical bronchitis with asthma-like wheezing and can be fatal due to severe respiratory tract and lung damage (pulmonary edema).
There is one case report of 18 people exposed to n-butyl isocyanate vapour (concentration not known) with subsequent exposure to n-butylamine developing acute respiratory symptoms and temporary electrocardiographic (ECG) changes. It is not known which of these 2 irritants was responsible for the ECG effects.(13)

Skin Contact:
The liquid can cause severe skin irritation, with swelling and redness, based on animal information. There is no human information available.
Like other isocyanates, n-butyl isocyanate may cause skin sensitization, although there are no reports of this happening.

Eye Contact:
The liquid can cause very severe eye injury and severe permanent eye damage (tissue death). There are no human reports but it caused severe permanent eye injury in laboratory animals.
Exposure to the vapour can cause irritation with tearing. Exposure to very high concentrations can result in severe eye injury, including intense burning of the eyes, and corneal ulcerations. In most cases, these effects are expected to be temporary.

There have been no reports of people ingesting n-butyl isocyanate and ingestion is unlikely to occur in the workplace. Ingestion would probably cause irritation of the mouth, throat and digestive tract. n-Butyl isocyanate was moderately toxic in an animal study.

Effects of Long-Term (Chronic) Exposure

Lungs/Respiratory System:
Animal evidence suggests that long-term, low level exposure could result in significant damage to the respiratory system.

Exposure to isocyanates is likely to aggravate individuals with existing respiratory disease, such as chronic bronchitis, and emphysema.

Respiratory Sensitization:
Some isocyanates are well known to cause respiratory sensitization. However, there are no reports of n-butyl isocyanate or other similar monoisocyanates causing respiratory sensitization.
Isocyanate respiratory sensitization is usually caused by a very large exposure, or by multiple exposures. 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 airborne isocyanates that have no effect on unsensitized people.(3)
Cross-sensitization between different isocyanates may occur.(4)

Skin Sensitization:
There have been no reports of n-butyl isocyanate causing skin sensitization in humans. Other isocyanates are skin sensitizers.


There is no human or animal information.

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:
There is no human or animal information.

Reproductive Toxicity:
There is no human or animal information.

No human or animal in vivo studies are available.

Toxicologically Synergistic Materials:
Insufficient information

Potential for Accumulation:
Probably does not accumulate. Reacts with water and tissues to form n- butylamine.


This product is flammable. Take proper precautions (e.g. remove any sources of ignition). 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, oxygen may be beneficial if administered by trained personnel, preferably on a doctor's advice. DO NOT allow victim to move about unnecessarily. Symptoms of pulmonary edema can be delayed up to 48 hours after exposure. Immediately transport victim to an emergency care facility.

Skin Contact:
Avoid direct contact. Wear chemical protective clothing, if necessary. Quickly and gently blot or brush away excess chemical. Wash gently and thoroughly with water and non-abrasive soap for 20 minutes or until chemical is removed. Under running water, remove contaminated clothing, shoes and leather goods (e.g. watchbands, belts). Obtain medical attention immediately. Discard contaminated clothing, shoes and leather goods.

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 20 minutes, or until the chemical is removed while holding the eyelid(s) open. Take care not to rinse contaminated water into non-affected eye. Obtain medical attention immediately.

NEVER give anything by mouth if victim is rapidly losing consciousness, or is unconscious or convulsing. Have victim rinse mouth thoroughly with water. DO NOT INDUCE VOMITING. Have victim drink 240 to 300 mL (8 to 10 oz.) of water to dilute material in stomach. 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 under minor instances of inhalation or skin contact. Some recommendations in the above sections may be considered medical acts in some jurisdictions. These recommendations should be reviewed with a doctor and appropriate delegation of authority obtained, as required.
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its conditions of use in the workplace.


Flash Point:
19 deg C (66 deg F) (closed cup) (9); 17 deg C (64 deg F) (closed cup) (10)

Lower Flammable (Explosive) Limit (LFL/LEL):
Information not available

Upper Flammable (Explosive) Limit (UFL/UEL):
Information not available

Autoignition (Ignition) Temperature:
Information not available

Sensitivity to Mechanical Impact:
Insufficient information. Probably not sensitive, since it is a stable material.

Sensitivity to Static Charge:
No specific information. n-Butyl isocyanate vapours in the flammable range may be ignited by a static discharge.

Combustion and Thermal Decomposition Products:
Nitrogen oxides, hydrogen cyanide.(11)

Fire Hazard Summary:
Flammable liquid. Can release vapours that form explosive mixtures with air at, or above, 17 deg C. Vapour is heavier than air and may travel a considerable distance to a source of ignition and flash back to a leak or open container. During a fire, irritating/toxic nitrogen oxides and hydrogen cyanide may be generated. Vapour can cause death if it penetrates the firefighter's normal protective gear. Reacts violently with water. Can accumulate in confined spaces, resulting in an explosion and toxicity hazard. Closed containers may rupture violently when heated.

Extinguishing Media:
Dry chemical powder, carbon dioxide, proteinic foam, alcohol foam(9) Water spray or fog may be used for cooling. Water-based extinguishers and foams should not be used on n-butyl isocyanate since the reaction is violent.

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.
Stop leak before attempting to stop the fire. If the leak cannot be stopped, and if there is no risk to the surrounding area, let the fire burn itself out. If the flames are extinguished without stopping the leak, vapours could form explosive mixtures with air and reignite.
If possible, isolate materials not yet involved in the fire. Closed containers or tanks may explode in the heat of the fire. Move containers from fire area if this can be done without risk. Otherwise, keep fire-exposed tanks or containers cool by application of hose streams. Application of cooling streams should begin as soon as possible. If this is not possible, set up unmanned monitor nozzles and evacuate the area. Take care not to get water inside containers.
n-Butyl isocyanate (n-BIC) can react violently with water and water-based fire extinguishers. For small fires, use dry chemical powder, carbon dioxide or proteinic foam.
Water can be used as a spray or fog to absorb heat and protect exposed material of structures. 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. However, proper care must be taken because of the violent reaction between water and n-BIC.
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.
n-BIC and its decomposition products, such as hydrogen cyanide and nitrogen oxides, are extremely hazardous to health. Do not enter without specialized protective equipment suitable for the situation. Firefighter's normal protective clothing (Bunker Gear) will not provide adequate protection. A full-body encapsulating chemical resistant suit with positive pressure self- contained breathing apparatus (MSHA/NIOSH approved or equivalent) may be necessary.


NFPA - Health: 3 - Short exposure could cause serious temporary or residual injury.
NFPA - Flammability: 3 - Liquids and solids that can be ignited under almost all ambient temperature conditions.
NFPA - Instability: 2 - Undergoes violent chemical change at elevated temperatures and pressures, or reacts violently with water, or may form explosive mixtures with water.
NFPA - Specific Hazards: Water-reactive.


Molecular Weight: 99.15

Conversion Factor:
1 ppm = 4.0 mg/m3; 1 mg/m3 = 0.247 ppm at 25 deg C (calculated)

Physical State: Liquid
Melting Point: Not available
Boiling Point: 115 deg C (239 deg F) (10,11); 117 deg C (243 deg F) (2)
Relative Density (Specific Gravity): 0.88 at 20 deg C (water = 1) (11)
Solubility in Water: Slightly soluble (reacts with water)
Solubility in Other Liquids: Not available
Coefficient of Oil/Water Distribution (Partition Coefficient): Not applicable (reacts with water)
pH Value: Not applicable (reacts with water)
Vapour Density: 3.00 (air = 1)
Vapour Pressure: 1.41 kPa (10.6 mm Hg) at 20 deg C (11); 2.27 kPa (17 mm Hg) at 24 deg C (2)
Saturation Vapour Concentration: Approx. 14,000 ppm (approx. 1.4%) @ 20 deg C; approx. 22,400 ppm (approx. 2.24%) @ 24 deg C (calc)
Evaporation Rate: Not available


Normally stable. It self-reacts at elevated temperatures to form trimers and polymers giving off carbon dioxide and heat.(12)

Hazardous Polymerization:
n-BIC may undergo uncontrolled exothermic trimerization and polymerization upon contact with incompatible materials, such as trialkyl phosphines, triphenylarsenic oxide, potassium acetate and many metal compounds soluble in organic media, such as organotin compounds, or if heated.(12) The heat and products generated from this reaction can result in a pressure build-up in closed containers that is sometimes sufficient to rupture the container.

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 vigorously or violently, forming carbon dioxide gas and di-n-butylurea. The reaction may become progressively more vigorous at higher temperatures.(12) Closed containers can rupture explosively when contaminated with water.
STRONG OXIDIZING AGENTS - May react violently with the risk of fire and explosion.(11)
ALCOHOLS, ACIDS, BASES, AMINES - May react vigorously or violently with the risk of fire and explosion.(11)
CERTAIN CATALYSTS (e.g. triphenylarsenic oxide and tributyl tin oxide) - may cause a violent reaction.(12)

Hazardous Decomposition Products:
n-Butylamine (formed by reaction of n-BIC with water)

Conditions to Avoid:
Sparks, open flames, electrostatic discharge, heat, other ignition sources, moisture.

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.(12) See references 12 for some of the reactions of isocyanates.


LC50 (male rat): 15 ppm (60 mg/m3) (4-hour exposure) (14)
LC50 (female rat): 14 ppm (55 mg/m3) (4-hour exposure) (14)

LD50 (oral, rat): 600 mg/kg (5, unconfirmed)
LD50 (oral, mouse): 150 mg/kg (5, unconfirmed)
LD50 (oral, guinea pig): 250 mg/kg (5, unconfirmed)

Eye Irritation:

n-Butyl isocyanate is a very severe eye irritant, capable of producing permanent loss of vision.

Application of 0.1 mL of n-butyl isocyanate caused very severe, permanent eye injury, including corneal damage, in rabbits in a Draize test. A numerical score measured the degree of irritation, but the results are reported in common terms for simplification.(2) Application of 0.1 mL of undiluted n-butyl isocyanate produced corrosive eye injury in rabbits. In unwashed eyes, the score was 66/110. At 48-hours, there was complete loss of sight with a score of 110/110. When the eyes were washed at 5 or 10 seconds, the maximum average scores were 36/110 (5 seconds) and 48/110 (10 seconds) at 24 hours. Complete healing was observed in 5 days for the 5-second exposure and a score of 4/110 was obtained at 5 days for the 10-second exposure.(18)

Skin Irritation:

n-Butyl isocyanate is a severe skin irritant.

Application of 0.5 mL of undiluted n-butyl isocyanate for 24 hours caused moderate skin irritation in rabbits in a test conducted according to the Draize procedure. A description of moderate irritation indicates well-defined erythema with edema persisting for 48-72 hours. A numerical score measured the degree of irritation, but the results are reported in common terms for simplification.(2) Application of 0.1 mL of undiluted n-butyl isocyanate, with the procedure repeated in 1 hour, produced moderate skin irritation in rabbits. The effects were described as well-defined erythema, with slight edema with a maximum average score of 2.6/8 at 2 hours.(18) In an LD50 study, application of 0.5-1.0 cc/kg undiluted n-butyl isocyanate, under a cuff, probably for 24 hours, produced moderate edema, with bleeding or necrosis and numerous blisters in the patch area in 2 guinea pigs. At 1 week, there was scabbing over all of the patch area, surrounded by erythema. At 2 weeks, scabs or light scarring covered the patch area. The overall assessment was that n-butyl isocyanate was a moderate skin irritant.(17)

Effects of Short-Term (Acute) Exposure:

Rats exposed to 2 and 6 ppm for 4 hours experienced mild, temporary effects while severe respiratory distress was observed at 13.5 ppm. Inflammation of the airways, emphysema, pneumonia, bleeding in the lungs and edema were observed in surviving rats after 4 weeks.(7) No significant effects were observed in male rats exposed to 0.25 and 1.25 ppm for 5 days; laboured breathing and increased nasal discharge were seen at 3.7 ppm. Severe respiratory distress, lethargy, nasal discharge, cyanosis and a substantial decrease in pulmonary function were observed at 6 ppm. Twelve of 20 rats exposed to 6 ppm died 10 and 15 days after exposure. Damage to the respiratory tract and lungs were found.(1) Inhalation of 200 ppm for 10-15 minutes killed all 6 rats.(2) The majority of deaths occurred 8-22 days after exposure in rats exposed to 13.5-27 ppm for 4 hours, while deaths at 70 and 210 ppm were observed through day 2.(7)

Skin Contact:
In rabbits, the single lethal dose of a mixture of 75% n-butyl isocyanate in corn oil was 6.0-8.0 mg/kg.(6)

n-Butyl isocyanate inhibited the growth of Ehrlich ascites tumours in Swiss mice.(8)


Selected Bibliography:
(1) Pauluhn, J., et al. Altered lung function in rats after subacute exposure to n-butyl isocyanate. Archives of Toxicology. Vol. 66, no. 2 (1992). p. 118-125
(2) Woolrich, P.F. Monoisocyanates, diisocyanates and polyisocyanates: engineering, medical control and toxicologic considerations. Technical bulletin 106. The Upjohn Company, 1973
(3) Karol, M.H. Respiratory effects of inhaled isocyanates. CRC Critical Reviews in Toxicology. Vol. 16, issue 4 (1986). p. 349-379
(4) Musk, A.W., et al. Isocyanates and respiratory disease: current status. American Journal of Industrial Medicine. Vol. 13, no. 3 (1988). p. 331-349
(5) RTECS record for isocyanic acid, butyl ester. Date of last update: 9404
(6) Toxicity and safe handling of isocyanates: a review of the literature (TDI) and results of toxicity screening studies on additional compounds. Mobay Chemical Corporation, [n.d.]
(7) Pauluhn, J., et al. Functional, biochemical, and histopathological evidence of airway obstruction in rats following a four-hour acute inhalation exposure to n-butyl isocyanate. Experimental Pathology. Vol. 40 (1990). p. 197-202
(8) Moos, G.E., et al. Inhibition of growth of Ehrlich ascites tumors in ICR/Ha Swiss mice by isocyanates. Cancer Research. Vol. 31, no. 7 (July, 1971). p. 937-941
(9) Fire protection guide to hazardous materials. 13th ed. Edited by A.B. Spencer, et al. National Fire Protection Association, 2002. NFPA 325
(10) Aldrich catalog handbook of fine chemicals, 1994-1995. Aldrich Chemical Company, 1994. p. 265
(11) The Sigma-Aldrich library of chemical safety data. Edition II. Volume 1. Sigma-Aldrich Corporation, 1988. p. 634A
(12) Kirk-Othmer encyclopedia of chemical technology. 3rd. edition. Vol. 13. John Wiley and Sons, 1981. p. 789-818
(13) Engelhard, H. ECG changes in cases of acute n-butylisocyanate poisoning. Zeitschrift fur die Gesamte Hygiene. Vol. 22, no. 4 (1976). p. 235-238 (English translation: NIOSHTIC Control Number: 00102266)
(14) Pauluhn, J. A mechanistic approach to assess the inhalation toxicity and hazard of methylisocyanate and related aliphatic monoisocyanates. In: Assessment of inhalation hazards. Edited by U. Mohr. Springer-Verlag, 1989. p. 119-128
(16) Emergency response planning guidelines. AIHA Journal. Vol. 56, no. 2, 1995. p. 202
(17) Eastman Kodak Co. Letter from Eastman Kodak company to USEPA submitting enclosed health and safety study on n-butyl isocyanate with attachments Eastman Kodak Co. Date produced: Oct. 1990. EPA/OTS 86-910000053. NTIS/OTS0528347.
(18) Younger Laboratories. Toxicological investigation of n-butyl isocyanate with cover letter dated 121090. Mobay Corp. Date produced: Dec. 1990. Mobay Corp. EPA/OTS 86-910000209. NTIS/OTS0528441.

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: 1995-03-07

Revision Indicators:
Sensitivity to static charge 1995-05-01
Fire fighting instructions 1995-05-01
Extinguishing media 1995-05-01
EU class 1995-11-01
ERPG 1995-11-01
Sampling 1996-01-01
TLV comments 1996-09-01
WHMIS (proposed class) 1997-07-01
US transport 1998-03-01
Resistance of materials 1998-06-01
TDG 2002-05-27
WHMIS detailed classification 2002-06-10
WHMIS health effects 2002-06-10
NFPA (flammability) 2003-04-14
Bibliography 2003-09-19
Toxicological info 2003-09-19
Short-term skin contact 2003-09-19
WHMIS classification comments 2003-09-19
PEL-TWA transitional 2003-11-06

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