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CHEMINFO Record Number: 346
CCOHS Chemical Name: Isobutyric acid

Dimethylacetic acid
Isobutanoic acid
Isopropylformic acid
2-Methylpropanoic acid
2-Methylpropionic acid
Alpha-methylpropionic acid
2-Propanecarboxylic acid
Propane-2-carboxylic acid
Butyric acid (non-specific name)
Acide isobutyrique
Acide methyl-2 propanoique

CAS Registry Number: 79-31-2
UN/NA Number(s): 2529
RTECS Number(s): NQ4375000
EU EINECS/ELINCS Number: 201-195-7
Chemical Family: Aliphatic carboxylic acid / saturated aliphatic monocarboxylic acid / alkanoic acid / butyric acid
Molecular Formula: C4-H8-O2
Structural Formula: CH3-CH(CH3)-C(=O)-OH


Appearance and Odour:
Clear, colourless liquid with an unpleasant, pungent, butter-fat odour.(4,5)

Odour Threshold:
8 ppm (29.16 mg/m3) (low odour threshold).(6)

Warning Properties:
GOOD - detectable by odour at low concentrations which are unlikely to be harmful.

Uses and Occurrences:
Isobutyric acid is used as an antifungal agent in food and animal feed; in varnishes, disinfectants, and for deliming leather and tanning hides; as a polar solvent and in the manufacture of esters (used as solvents and in perfumes and flavourings) and salts (used as textile chemicals, tanning compounds, stabilizers, catalysts and preservatives).(1,4,5)
Isobutyric acid is a naturally occurring component of food (cheese, milk protein, vinegar and beer) and feedstuffs, and is found naturally in the body, as a product of metabolism. It has been detected in human blood and saliva.(1)


Clear, colourless liquid with an unpleasant, pungent, butter-fat odour. COMBUSTIBLE LIQUID AND VAPOUR. TOXIC. May be harmful following skin contact or if swallowed. CORROSIVE to the eyes and skin. Can cause permanent eye damage, including blindness, or permanent scarring of the skin.


Effects of Short-Term (Acute) Exposure

Inhalation of vapours or mists will likely result in mild to severe irritation of the nose, throat and lungs, depending on the airborne concentration. Symptoms would include nasal irritation, sore throat, coughing, hoarseness and, in extreme exposures, difficulty breathing. Isobutyric acid is acidic and similar effects have been observed in animal studies for n-butyric acid, a closely related carboxylic acid. There is no human information available.

Skin Contact:
Isobutyric acid can likely cause moderate to severe skin irritation depending upon the concentration of chemical and the duration of contact. Direct contact can probably cause irritation, redness and pain. Prolonged exposures to concentrated solutions may cause burns, blistering, and tissue destruction (corrosive effects). This evaluation is based on animal information for isobutyric acid and on human information for closely related carboxylic acids (propionic and n-butyric acids).
Based on animal information, isobutyric acid may be absorbed through the skin and may cause harmful effects by this route.

Eye Contact:
Contact with vapour, mist or splashes of dilute (less than 5%) solutions can probably cause redness and pain. Contact with concentrated solutions can cause corneal burns, based on animal information. Permanent eye damage, including blindness, may occur. There is no human information available.

Isobutyric acid is a naturally occurring component of food (cheese, butter, vinegar and beer) and feedstuffs, and is used as a synthetic flavouring agent. Animal information indicates that it is toxic following ingestion of large amounts. It is a corrosive liquid and ingestion of concentrated solutions can cause severe irritation or corrosive injury to the mouth, throat and stomach. Permanent injury and death could result.
There is no human information available. Ingestion is not a typical route of occupational exposure.

Effects of Long-Term (Chronic) Exposure

There is no human or animal information available. Repeated or prolonged skin contact may cause dermatitis (redness, dryness and itching of the skin).


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:
There is no human or animal information available.

Reproductive Toxicity:
There is no human or animal information available.

There is no information available.

Toxicologically Synergistic Materials:
There is no information available.

Potential for Accumulation:
Isobutyric acid does not accumulate in the body. It is metabolized to propionic acid, which is ultimately converted to glucose and glycogen (used by the body), and to carbon dioxide, which is exhaled.(1) Rats orally administered isobutyric acid rapidly eliminated 67-75% of the dose as carbon dioxide in the expired air within 4 hours, and 85-90% at 48 hours. Approximately 3 to 4% of the dose was excreted in the urine as urea (formed from carbon dioxide). Less than 1% was excreted in the feces.(2)


If symptoms are experienced, remove source of contamination or have victim move to fresh air. Obtain medical advice immediately.

Skin Contact:
Avoid direct contact with this chemical. Wear chemical protective gloves, if necessary. As quickly as possible, flush contaminated area with lukewarm, gently flowing water for 20-30 minutes, by the clock. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Under running water, remove contaminated clothing, shoes, and leather goods (e.g., watchbands, belts). If irritation persists, repeat flushing. Transport victim to an emergency care facility immediately. Completely decontaminate clothing, shoes and leather goods before re-use or discard.

Eye Contact:
Avoid direct contact with this chemical. Immediately flush the contaminated eye(s) with lukewarm, gently flowing water for 20-30 minutes, by the clock, while holding the eyelid(s) open. Neutral saline solution may be used as soon as it is available. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Take care not to rinse contaminated water into the non-affected eye or onto the face. Quickly transport victim to an emergency care facility.

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. If milk is available, it may be administered AFTER the water has been given. If vomiting occurs naturally, have victim rinse mouth and repeat administration of water. Quickly transport victim to an emergency care facility.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest).
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:
55.5 deg C (132 deg F) (closed cup) (7,8)

Lower Flammable (Explosive) Limit (LFL/LEL):
2% (7)

Upper Flammable (Explosive) Limit (UFL/UEL):
9.2% (7)

Autoignition (Ignition) Temperature:
420 deg C (788 deg F) (4); 481 deg C (900 deg F) (7)

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

Sensitivity to Static Charge:
Specific information not available. Probably does not accumulate static charge, since generally carboxylic acids have high electrical conductivities.

Combustion and Thermal Decomposition Products:
Carbon monoxide and carbon dioxide.(8) Incomplete combustion may also produce irritating fumes and acrid smoke.

Fire Hazard Summary:
Combustible liquid. Can form explosive mixtures with air at, or above, 55.5 deg C. During a fire irritating/toxic gases may be formed. Closed containers may rupture violently when exposed to fire or excessive heat for sufficient time.

Extinguishing Media:
Carbon dioxide, dry chemical powder, alcohol foam, polymer foam, water spray or fog.(8)

Fire Fighting Instructions:
Evacuate area and fight fire from a safe distance or protected location. Approach fire from upwind to avoid hazardous vapours and toxic decomposition products.
Closed containers may rupture violently when exposed to heat of fire. If possible, isolate materials not yet involved in the fire, and move containers from fire area if this can be done without risk, and protect personnel. Otherwise, fire-exposed containers or tanks should be cooled by application of hose streams. Application should begin as soon as possible and should concentrate on any unwetted portions of the container. If this is not possible, use unmanned monitor nozzles and immediately evacuate the area.
If a leak or spill has not ignited, use water spray in large quantities to disperse the vapours, protect personnel attempting to stop a leak and to dilute the spill to a nonflammable mixture. Water spray may be used to flush spills away from ignition sources. Solid streams of water may be ineffective and spread material.
For a massive fire in a large area, use unmanned hose holder or monitor nozzles. If this is not possible, withdraw from fire area and allow fire to burn. Stay away from ends of tanks. Withdraw immediately in case of rising sound from venting safety device or any discolouration of tank due to fire.
The decomposition products of isobutyric acid may be hazardous to health. Do not enter without wearing specialized protective equipment suitable for the situation. Firefighter's normal protective clothing (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 - Health: 3 - Short exposure could cause serious temporary or residual injury.
NFPA - Flammability: 2 - Must be moderately heated or exposed to relatively high ambient temperatures before ignition can occur.
NFPA - Instability: 0 - Normally stable, even under fire conditions, and not reactive with water.


Molecular Weight: 88.11

Conversion Factor:
1 ppm = 3.60 mg/m3; 1 mg/m3 = 0.278 ppm at 25 deg C (calculated)

Physical State: Liquid
Melting Point: -47 deg C (-52.6 deg F) (1,8,10)
Boiling Point: 153-155 deg C (307.4-311 deg F) (4,10,11)
Relative Density (Specific Gravity): 0.949 at 20 deg C (water = 1) (1,10)
Solubility in Water: Soluble (20 g/100 mL) at 20 deg C (10); soluble in all proportions above 26 deg C (4)
Solubility in Other Liquids: Soluble in all proportions in ethanol, diethyl ether and chloroform (1)
Coefficient of Oil/Water Distribution (Partition Coefficient): Log P(oct) = 0.50; 1.13 (calculated) (12); 0.88 (measured) (10)
pH Value: 2.9 (0.1 M solution) (calculated)
Vapour Density: 3.04 (air = 1) (10)
Vapour Pressure: 0.133 kPa (1 mm Hg) at 14.7 deg C (11)
Saturation Vapour Concentration: 1316 ppm (0.13%) at 14.7 deg C (calculated)
Evaporation Rate: Not available
Critical Temperature: 336 deg C (637 deg F) (13)

Other Physical Properties:
ACIDITY: Weak acid; pKa = 4.84 (Ka = 1.44 X 10(-5)) at 18 deg C (11)
VISCOSITY-DYNAMIC: 1.44 mPa.s (1.44 centipoises) at 18 deg C; 1.13 mPa.s (1.13 centipoises) at 30 deg C (11)
VISCOSITY-KINEMATIC: 1.517 mm2/s (1.517 centistokes) at 18 deg C (calculated)
SURFACE TENSION: 25.2 mN/m (25.2 dynes/cm) (air or vapour) at 20 deg C (11)
CRITICAL PRESSURE: 4053.33 kPa (40 atm) (13)


Normally stable

Hazardous Polymerization:
Does not occur

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.

OXIDIZING AGENTS (e.g. chromium trioxide, nitric acid, peroxides, permanganates) - may react violently or explosively. Increased risk of fire.(8)
BASES (including alkalis, such as sodium hydroxide) - vigorous or violent reaction may occur, yielding heat and pressure.(8)
REACTIVE METALS (e.g. powdered aluminum, zinc) - may produce flammable hydrogen gas.(13)
REDUCING AGENTS (e.g. hydrides such as lithium aluminum hydride) - reaction may be vigorous or violent.(8)
PHOSPHORUS TRICHLORIDE - may form spontaneously flammable phosphine and explode.(14)
POTASSIUM t-BUTOXIDE (solid) - may ignite.(14)

Hazardous Decomposition Products:
None reported

Conditions to Avoid:
Temperatures above 55.5 deg C, open flames

Corrosivity to Metals:
Based on information for the closely related acid, n-butyric acid, isobutyric is probably corrosive to metals such as steel, cast iron, and lead.(15) Aluminum is resistant at room temperature, but may be attacked at elevated temperatures. Isobutyric acid is not corrosive to copper, bronze and brass, and can be used for handling, provided acid solutions are free of oxidants. As with n-butyric acid, type 304 and 316 stainless steels are probably resistant to isobutyric acid at room temperature.(16)


LD50 (oral, rat): 270 mg/kg (3)

LD50 (dermal, rabbit): 480 mg/kg (3)

Eye Irritation:

Application of in excess of a 5% solution of isobutyric acid caused severe injury in rabbits (graded 9/10; scored over 5 where 5 is severe injury).(3)

Skin Irritation:

Application of 0.01 mL of undiluted isobutyric acid produced tissue death (necrosis) in rabbits (graded 6/10).(3)

Effects of Short-Term (Acute) Exposure:

No deaths were observed in rats following exposure to a saturated vapour concentration of isobutyric acid for 8 hours.(3)


Selected Bibliography:
(1) Katz, G.V., et al. Aliphatic carboxylic acids. In: Patty's industrial hygiene and toxicology. 4th edition. Edited by G.D. Clayton et al. Volume II. Toxicology. Part E. John Wiley and Sons, 1994. p. 3528, 3536-3538
(2) DiVincenzo, G.D., et al. Metabolic fate of (1-14C)isobutyric acid in the rat. Toxicology and Applied Pharmacology. Vol. 47 (1979). p. 609- 612
(3) Smyth, Jr., H. F., et al. Range-finding toxicity data: list VI. American Industrial Hygiene Association Journal. Vol. 23, no. 1 (1962). p. 95-107
(4) Riemenschneider, W. Carboxylic acid, aliphatic. In: Ullmann's encyclopedia of industrial chemistry. 5th completely revised edition. Vol. A 5. VCH Verlagsgesellschaft, 1985. p. 235-245
(5) HSDB record for 2-methylpropanoic acid. Last revision date: 96/01/28
(6) Ruth, J.H. Odor thresholds and irritation levels of several chemical substances: a review. American Industrial Hygiene Association Journal. Vol. 47 (March, 1986). p. A-142 to A-151
(7) Fire protection guide to hazardous materials. 13th ed. Edited by A.B. Spencer, et al. National Fire Protection Association, 2002. NFPA 325
(8) The Sigma-Aldrich library of chemical safety data. Edition II. Volume 1. Sigma-Aldrich Corporation, 1988. p. 2021C
(9) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 3rd edition. Van Nostrand Reinhold, 1997
(10) Verschueren, K. Handbook of environmental data on organic chemicals. 3rd edition. Van Nostrand Reinhold, 1996. p. 30, 396-399
(11) Weast, R.C., ed. Handbook of chemistry and physics. 66th edition. CRC Press, 1985-1986. p. C-453, D-161, D-199, F-34, F-40
(12) Leo, A., et al. Partition coefficients and their uses. Chemical Reviews. Vol. 71, no. 6 (December, 1971). p. 564
(13) Weiss, G., ed. Hazardous chemicals data book. 2nd edition. Noyes Data Corporation, 1986. p. 591
(14) Urben, P.G., ed. Bretherick's handbook of reactive chemical hazards. 5th edition. Volume 1. Butterworth-Heinemann Ltd., 1995. p. 567, 1350
(15) Corrosion data survey: metals section. 6th edition. National Association of Corrosion Engineers, 1985. p. 145-6
(16) Elder, G.B. Corrosion by organic acid. In: Process industries corrosion. National Association of Corrosion Engineers, 1975. p. 247-254
(17) European Economic Community. Commission Directive 93/72/EEC. September 1, 1993

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: 1997-04-29

Revision Indicators:
US transport 1998-03-01
Resistance of materials 1998-04-01
Bibliography 1998-04-01
Emergency overview 2000-08-01
Acute exposure (ingestion) 2000-08-01
First aid (ingestion) 2000-08-01
TDG 2002-05-29
WHMIS detailed classification 2002-06-10
WHMIS health effects 2002-06-10
Bibliography 2003-04-16
NFPA (health) 2003-04-16

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