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CHEMINFO Record Number: 472
CCOHS Chemical Name: Phthalic acid

Benzene-1,2-dicarboxylic acid
1,2-Benzenedicarboxylic acid
o-Benzenedicarboxylic acid
o-Phthalic acid
1,2-Phthalic acid

Chemical Name French: Acide phtalique
Chemical Name Spanish: Acido ftalico
CAS Registry Number: 88-99-3
RTECS Number(s): TH9625000
EU EINECS/ELINCS Number: 201-873-2
Chemical Family: Aromatic carboxylic acid / aromatic dicarboxylic acid / benzenecarboxylic acid / benzenedicarboxylic acid / phthalic acid isomer
Molecular Formula: C8-H6-O4
Structural Formula: HO-C(=O)-C6H4-C(=O)-OH


Appearance and Odour:
Colourless or white crystalline material or powder.(6,7)

Odour Threshold:
No information was located

Warning Properties:
Information not available for evaluation.

Phthalic acid is one of three chemical forms (isomers) of benzenedicarboxylic acid (1,2-benzenecarboxylic acid). 1,3-Benzenecarboxylic acid is commonly known as isophthalic acid and 1,4-benzenecarboxylic acid as terephthalic acid. For information on these related acids, refer to the relevant CHEMINFO reviews. Phthalic acid may contain traces of 2- or 3- formylbenzoic acid, o-toluic acid, benzoic acid and residual metals.

Uses and Occurrences:
Phthalic acid is seldom used commercially, since the anhydride is easier to use.(6,8,9) It is used as a laboratory reagent and in the synthesis of dyes, medicinals, synthetic perfumes, phenolphthalein, phthalimide, anthranilic acid.(9)


Colourless or white crystalline material or powder. Can burn if strongly heated. COMBUSTIBLE DUST. Can form explosive dust-air mixtures. EYE IRRITANT. Causes moderate eye irritation.


Effects of Short-Term (Acute) Exposure

Dusts and mists formed from solutions are probably irritating to the nose, throat and lungs, because phthalic acid is acidic (low pH). High concentrations of dust may cause coughing and mild, temporary irritation. There is no specific human or animal information available for phthalic acid.

Skin Contact:
Dusts and solutions may be irritating, based on the acidity of phthalic acid. One unusual case report describes a severe skin reaction which resulted after contact with tributyltin phthalate and hot water. The authors concluded that the reaction was due to phthalic acid, a hydrolysis product.(1) No conclusions can be drawn based on this one report. There is no other human or animal information available for phthalic acid.
No information is available regarding absorption through skin of phthalic acid, but a closely related acid, terephthalic acid, is not absorbed through skin.

Eye Contact:
Contact with solutions or the dust can probably cause moderate irritation, based on the acidity of phthalic acid and comparison to benzoic acid, a closely related acid.
In general, dusts are irritating as "foreign objects". Some tearing, blinking and mild temporary pain may occur as the solid material is rinsed from the eye by tears.
There is no human or animal information is available for phthalic acid.

Phthalic acid is low in oral toxicity based on animal studies. There is no human information available. Ingestion is not a typical route of occupational exposure.

Effects of Long-Term (Chronic) Exposure

There is no specific information available for phthalic acid.

Kidneys/Urinary System:
Bladder and kidney stones have been observed in animal studies following ingestion of very high concentrations of related acids (terephthalic acid and isophthalic acid). However, the dietary levels at which these effects were observed are very high and are not relevant to occupational exposures.


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 information available. Phthalic acid was not harmful to the male reproduction in one animal study.

A negative result was obtained in a test using cultured mammalian cells. There is no human or animal information available.

Toxicologically Synergistic Materials:
There is no information available.

Potential for Accumulation:
Phthalic acid is not expected to accumulate in the body, based on information for a related acid (terephthalic). In one study on the metabolism of di(2-ethylhexyl) phthalate, a phthalic acid ester, phthalic acid was not metabolised by rats and was excreted unchanged in the urine.(2)


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

Skin Contact:
Quickly blot or brush away excess chemical. Wash gently and thoroughly with water and non-abrasive soap for 5 minutes or until the chemical is removed. Under running water, remove contaminated clothing, shoes and leather goods (e.g. watchbands, belts). If irritation persists, obtain medical advice immediately. Completely decontaminate clothing, shoes and leather goods before re-use or discard.

Eye Contact:
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 the unaffected eye or onto the face. Obtain medical attention immediately.

If irritation or discomfort occur, obtain medical advice immediately.

First Aid Comments:
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:
168 deg C (334 deg F) (closed cup) (10)

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:
Not sensitive. Stable material.

Combustion and Thermal Decomposition Products:
Incomplete combustion may also produce acrid smoke and irritating fumes.

Flammable Properties:

Specific Hazards Arising from the Chemical:
During a fire, irritating/toxic gases and fumes may be generated.

Extinguishing Media:
Carbon dioxide, dry chemical powder, alcohol foam, polymer foam, water spray or fog.(7)

Fire Fighting Instructions:
Evacuate area and fight fire from a safe distance or a protected location. Approach fire from upwind to avoid toxic decomposition products.
Water or foam may cause frothing. The frothing may be violent and could endanger personnel close to the fire. However, a water spray or fog that is carefully applied to the surface of the burning material, preferably with a fine spray or fog nozzle, will cause frothing that will blanket and extinguish the fire. In addition, water spray or fog can be used to prevent dust formation, absorb heat, keep containers cool and protect exposed material. Water spray may be used to flush spills away from ignition sources. Solid streams of water may be ineffective and spread material.
The decomposition products of phthalic acid may be hazardous to health. Firefighters may enter the area if positive pressure self-contained breathing apparatus (MSHA/NIOSH approved or equivalent) and full Bunker Gear is worn.


NFPA - Health: 1 - Exposure would cause significant irritation, but only minor residual injury.
NFPA - Flammability: 1 - Must be preheated before ignition can occur.
NFPA - Instability: 0 - Normally stable, even under fire conditions, and not reactive with water.


Molecular Weight: 166.14

Conversion Factor:
Not applicable

Physical State: Solid
Melting Point: 210-211 deg C (410-412 deg F) (decomposes) (6-8,13); 230 deg C (446 deg F) when heated rapidly.(9)
Boiling Point: Decomposes (13)
Relative Density (Specific Gravity): 1.59 at 15 deg C (water = 1) (6)
Solubility in Water: Slightly soluble in water (700 mg/100 g at 25 deg C) (8)
Solubility in Other Liquids: Soluble in ethanol and methanol; slightly soluble in diethyl ether; practically insoluble in chloroform.(8,9)
Coefficient of Oil/Water Distribution (Partition Coefficient): Log P(oct) = 0.10-0.70 (calculated) (14). Also reported as log P(oct) = 0.73.(9)
pH Value: 2.2 (saturated solution (0.7% in water)) (calculated)
Acidity: Moderately strong acid; pKa1 = 2.95; pKa2 = 5.41 at 25 deg C.(8)
Vapour Density: Not applicable
Vapour Pressure: Very low at 25 deg C; 0.78 kPa (5.86 mm Hg) at 191 deg C.(9)
Saturation Vapour Concentration: Very low at 25 deg C.
Evaporation Rate: Probably very low at normal temperatures.
Critical Temperature: 527 deg C (980.6 deg F) (reported as 800 deg K) (9)
Critical Pressure: 3950 kPa (39 atm) (9)


Normally stable. Decomposes at 210-211 deg C forming phthalic anhydride with the elimination of water.(6)

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.

STRONG OXIDIZING AGENTS (e.g. perchlorates, peroxides, chlorine) - react violently or explosively. Increased risk of fire and explosion.(7,15)
FUMING NITRIC ACID/SULFURIC ACID MIXTURE - may form explosive phthaloyl nitrates or nitrites, or nitro derivatives.(10)
SODIUM NITRITE - explodes violently on heating, with risk of fire.(15,16)
ACTIVE METALS (e.g. aluminum or zinc) - may evolve flammable and potentially explosive hydrogen gas.(17)
STRONG BASES (including alkalis such as sodium hydroxide) - react vigorously.

Hazardous Decomposition Products:
None reported

Conditions to Avoid:
Generation of dust, heat, flames, sparks, build-up of static electricity and other ignition sources.

Corrosivity to Metals:
Saturated solutions are corrosive to cast iron and steel.(18) Organic acids are generally not corrosive to types 304 and 316 stainless steels, and aluminum is generally resistant to organic acids at room temperature.(19)

Stability and Reactivity Comments:
Probably attacks some forms of plastics, rubber and coatings.(17)


LD50 (oral, mouse): 2530 mg/kg (3)

Reproductive Toxicity:
No harmful effects on the testes (concentration of testosterone, dihydrotestosterone, or zinc) were observed in rats fed high levels (2% phthalic acid) for 1 week.(4)


Selected Bibliography:
(1) Hamanaka, S., et al. Phthalic acid dermatitis caused by an organostannic compound, tributyl tin phthalate. Dermatology. Vol. 184, no. 3 (1992). p. 210-212
(2) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 3rd ed. Van Nostrand Reinhold, 1997
(3) Lin, G.H.Y., et al. Acute oral toxicity (LD50) study in mice with phthalic acid. Journal of the American College of Toxicology. Part B. Vol. 1 (1992). p. 711
(4) Oishi, S., et al. Testicular atrophy induced by phthalic acid esters: effect on testosterone and zinc concentrations. Toxicology and Applied Pharmacology. Vol. 53, no. 1 (1980). p. 35-41
(5) Phillips, B.J., et al. Genotoxicity studies of di(2-ethylhexyl)phthalate and its metabolites in CHO cells. Mutation Research. Vol. 102, no. 3 (Oct. 1982). p. 297-304
(6) Towae, F.K., et al. Phthalic acid and derivatives. In: Ullmann's encyclopedia of industrial chemistry. 5th completely revised ed. Vol. A 20. VCH Verlagsgesellschaft, 1992. p. 181-211
(7) The Sigma-Aldrich library of chemical safety data. Ed. II. Vol. 2. Sigma-Aldrich Corporation, 1988. p. 2827D
(8) Park, C-H, et al. Phthalic acids and other benzenepolycarboxylic acids. In: Kirk-Othmer encyclopedia of chemical technology. 4th ed. Vol. 18. John Wiley and Sons, 1996. p. 991--1043
(9) HSDB record for phthalic acid. Last revision date: 96-10-15
(10) Fire protection guide to hazardous materials. 13th ed. Edited by A.B. Spencer, et al. National Fire Protection Association, 2002. NFPA 325; NFPA 491
(11) Grossel, S.S. Safety considerations in conveying of bulk solids and powders. Journal of Loss Prevention in the Process Industries. Vol. 1 (Apr. 1988). p. 62-74
(12) Schwab, R.F. Dusts. In: Fire protection handbook. Edited by A.E Cote. 18th ed. National Fire Protection Association, 1991. p. 4-174 to 4-181
(13) Weast, R.C., ed. Handbook of chemistry and physics. 66th ed. CRC Press, 1985-1986. p. C-429, D-162
(14) Leo, A., et al. Partition coefficients and their uses. Chemical Reviews. Vol. 71, no. 6 (Dec. 1971). p. 581
(15) Chemical safely sheets: working safely with hazardous chemicals. Kluwer Academic Publishers, 1991. p. 714
(16) Urben, P.G., ed. Bretherick's handbook of reactive chemical hazards. 5th ed. Vol. 1. Butterworth-Heinemann Ltd., 1995. p. 944-945, 1672
(17) Emergency action guide for terephthalic acid. Association of American Railroads, Sept. 1992
(18) Corrosion data survey: metals section. 6th ed. National Association of Corrosion Engineers, 1985. p. 96-16 to 97-16
(19) Elder, G.B. Materials of construction for organic acids. In: Process industries corrosion: the theory and practice. Edited by B.J. Moniz, et al. National Association of Corrosion Engineers, 1986. p. 287-296

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: 1997-12-24

Revision Indicators:
Resistance of materials 1998-02-01
NFPA (health) 2003-04-17
NFPA (reactivity) 2003-04-17
Toxicological info 2003-12-05
Bibliography 2003-12-05
Short-term inhalation 2004-01-06
Short-term skin contact 2004-01-06
Short-term eye contact 2004-01-06
WHMIS detailed classification 2004-01-06
WHMIS proposed classification 2004-01-06
WHMIS disclosure list 2004-01-06
WHMIS health effects 2004-01-06
OSHA hazcom 2004-01-06
Emergency overview 2004-01-06
First aid eye 2004-01-06
Handling 2004-01-10
Skin protection 2004-01-10
Conversion factor 2006-10-05
Vapour density 2006-10-05
Sensitivity to static charge 2006-10-05
UFL/UEL 2006-10-05
LFL/LEL 2006-10-05

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