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Propionic acid

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Propionic acid Basic information

Product Name:
Propionic acid
Mol File:

Propionic acid Chemical Properties

Melting point:
−24-−23 °C(lit.)
Boiling point:
141 °C(lit.)
0.993 g/mL at 25 °C(lit.)
vapor density 
2.55 (vs air)
vapor pressure 
2.4 mm Hg ( 20 °C)
refractive index 
n20/D 1.386(lit.)
Flash point:
125 °F
storage temp. 
organic solvents: soluble(lit.)
4.86(at 25℃)
≤10, APHA:
Specific Gravity
0.996 (20/4℃)
2.5 (100g/l, H2O, 20℃)
Odor Threshold
explosive limit
Water Solubility 
37 g/100 mL
JECFA Number
Exposure limits
TLV-TWA 10 ppm (~30 mg/m3) (ACGIH).
Stable. Incompatible with strong oxidizing agents. Flammable.
CAS DataBase Reference
79-09-4(CAS DataBase Reference)
NIST Chemistry Reference
Propanoic acid(79-09-4)
EPA Substance Registry System
Propionic acid (79-09-4)

Safety Information

Hazard Codes 
Risk Statements 
Safety Statements 
UN 3463 8/PG 2
WGK Germany 
Autoignition Temperature
955 °F
HS Code 
Hazardous Substances Data
79-09-4(Hazardous Substances Data)
LD50 orally in rats: 4.29 g/kg (Smyth)



Propionic acid Usage And Synthesis

Chemical Properties

Propionic acid, CH3CH2COOH, also known as propanoic acid and methylacetic acid, is a clear, colorless liquid that boils at 140°C (284 OF). It is flammable. It has a pungent odor and is soluble in water and alcohol. The Odor Threshold is 0.16 ppm. Propionic acid is an aliphatic monocarboxylic acid. Propionic acid is used in nickel electroplating solutions,perfumes, artificial flavors, pharmaceuticals, and manufacturing propionates.


Reported found in apple, apple juice, banana, currants, pineapple, raspberry, papaya, onion, sauerkraut, tomato, vinegar, beef, beef broth, beer, blackberry juice, bread, cheese, cherry juice, butter, yogurt, milk, cream, lean and fatty fish, cured pork, cooked beef and mutton, chicken fat, cognac, rum, whiskies, cider, sherry, roasted cocoa bean, cocoa powder, coffee, black currant juice, white currant juice, grape juice, grape musts and port wine, grapefruit juice, grape syrup, orange juice, Valencia orange oil, orange essence, roasted peanuts, pecans, potato chips, honey, soybean, Arctic bramble, coconut meat, cloudberry, mushroom, sesame seed, cardamom, rice, jackfruit, sake, buckwheat, laurel, peated malt, cassava, Bourbon vanilla, oyster, mussels, scallop, Chinese quince and maté.


Propionic acid is used in the productionof propionates used as mold inhibitors andpreservatives for grains and wood chips, inthe manufacture of fruit flavors and perfumebases, and as an esterifying agent.


Propionic acid is used as a mold inhibitor in bread and cheese products; in fungicides and herbicides; preservative for grains and wood chips; in emulsifying agents; in solutions for electroplating nickel, perfume esters, artificial fruit flavors, pharmaceuticals, and cellulose propionate plastics.


Propionic Acid is the acid source of the propionates. propionic acid in the liquid form has a strong odor and is corrosive, so it is used as the sodium, calcium, and potassium salts as a preservative. these yield the free acid in the ph range of the food in which they are used. it functions principally against mold. see calcium propionate; sodium propionate.

Production Methods

Propionic acid can be obtained from wood pulp waste liquor by fermentation. It can also be prepared from ethylene, carbon monoxide and steam; from ethanol and carbon monoxide using boron trifluoride catalyst; from natural gas; or as a by-product in the pyrolysis of wood. Very pure propionic acid can be obtained from propionitrile. Propionic acid can be found in dairy products in small amounts.


ChEBI: A short-chain saturated fatty acid comprising ethane attached to the carbon of a carboxy group.


A colorless liquid carboxylic acid.

Biotechnological Production

Generally, propionic acid is produced via petrochemical routes. However, fermentative processes are interesting for food-grade production, although the price of biotechnologically produced propionic acid may be twice that of petrochemistry- based propionic acid. The microbial production of propionic acid is done with propionibacteria (e.g. Propionibacterim freudenreichii) . Several fermentation methods have been studied. For example, an extractive fermentation is suggested to avoid low productivity and yields caused by product inhibition . With this technique, a product concentration of 75 g.L-1 propionic acid, a yield of 0.66 g propionic acid per gram lactose, and a productivity of approximately 1 g.L-1.h-1 are reached .
Different substrates, such as glycerol , wheat flour , or mixtures of glycerol and glucose , have been analyzed to reduce costs. Also, techniques of cell immobilization show promising results . Fibrous-bed reactor systems show the highest product concentrations: up to 106 g.L-1 propionic acid and a yield of 0.56 g propionic acid per gram glycerol. In recent years, metabolic engineering has been used to improve the acid tolerance and to reduce byproduct formation . 104 H. Quitmann et al.
For example, the acetate kinase gene has been inactivated by mutation of Propionibacterium acidipropionici . Additionally, an adaptive evolution has been carried out. As result, the productivity was enhanced by approximately 50 %, up to 0.25 g.L-1.h-1 and a yield of 0.59 g propionic acid per gram glycerol, using immobilized cells adapted to high acid concentration.

Taste threshold values

Taste characteristics at 60 ppm: acidic, dairy with a pronounced fruity lift.

General Description

A clear oily aqueous liquid with a pungent rancid odor. Burns skin and the vapors irritate mucous membranes. Corrosive to most metals and tissue. Density 8.3 lb / gal.

Air & Water Reactions

Dilution with water causes release of heat.

Reactivity Profile

Propionic acid reacts as an acid to neutralize bases in exothermic reactions. Burns when exposed to heat, flame or oxidizers. When heated to decomposition emits acrid smoke and irritating fumes [Lewis, 3rd ed., 1993, p. 1090].


Moderate fire risk. Strong eye, skin and upper respiratory tract irritant.

Health Hazard

Propionic acid is a toxic and corrosive liquid. Contact with the eyes can result ineye injury. Skin contact may cause burns.Acute exposures to its vapors can causeeye redness, mild to moderate skin burns,and mild coughing (ACGIH 1986). Ingestionof high amounts of this acid may producecorrosion of the mouth and gastrointestinaltract in humans. Other symptoms includevomiting, diarrhea, ulceration, and convulsions. Oral LD50 value in rats is about3500–4300 mg/kg. The LD50 value by skinabsorption in rabbits is 500 mg/kg..

Fire Hazard

Flammable/combustible material. May be ignited by heat, sparks or flames. Vapors may form explosive mixtures with air. Vapors may travel to source of ignition and flash back. Most vapors are heavier than air. They will spread along ground and collect in low or confined areas (sewers, basements, tanks). Vapor explosion hazard indoors, outdoors or in sewers. Runoff to sewer may create fire or explosion hazard. Containers may explode when heated. Many liquids are lighter than water.

Pharmaceutical Applications

Propionic acid is primarily used as an antioxidant and antimicrobial preservative in foods, and in oral and topical pharmaceutical applications. It is also used as an esterifying agent.

Clinical Use

Propionic acid is an antifungal agent that is nonirritatingand nontoxic. After application, it is present in perspiration in low concentration ( 0.01%). Salt forms with sodium,potassium, calcium, and ammonium are also fungicidal.Propionic acid is a clear, corrosive liquid with a characteristicodor. It is soluble in water and alcohol. Thesalts are usually used because they are nonvolatile andodorless.

Safety Profile

Poison by intraperitoneal route. Moderately toxic by ingestion, skin contact, and intravenous routes. A corrosive irritant to eyes, skin, and mucous membranes. Flammable liquid. Highly flammable when exposed to heat, flame, or oxidizers. To fight fire, use alcohol foam. When heated to decomposition it emits acrid smoke and irritating fumes.


Propionic acid is generally regarded as a nontoxic and nonirritant material when used in low levels as an excipient. Up to 1% may be used in food applications (up to 0.3% in flour and cheese products). Propionic acid is readily metabolized.
The pure form of propionic acid is corrosive and will cause burns to any area of contact. Both liquid and vapor forms are flammable. Concentrated propionic acid is harmful if swallowed, inhaled or absorbed through the skin. See also Sodium Propionate.
(mouse, IV): 0.63 g/kg
(rabbit, skin): 0.5 g/kg
(rat, oral): 2.6 g/kg

Chemical Synthesis

Commercial processes produce propionic acid by chemical synthesis and in small quantities by bacterial fermentation

Potential Exposure

Propionic acid is used in the manufac- ture of inorganic propionates and propionate esters which are used as mold inhibitors, electroplating additives; emul- sifying agents; flavors and perfumes. It is an intermediate in pesticide manufacture, pharmaceutic manufacture; and in the production of cellulose propionate plastics. Also used as grain preservative.


Rats fed high levels of propionic acid (4%) in a powdered diet developed forestomach neoplasia, which was believed to have arisen from sustained high levels of cellular proliferation. When administered at 4% in the diet as a pellet rather than as a powder, cellular hyperplasia and the associated severe inflammatory response were absent. In another study whereWistar ratswere fed 75%bread containing5%of the salt, sodiumpropionate rather than the acid for 1 year, no histopathology of the forestomach was reported. This suggests that the form of chemical (salt versus free acid), as well as the type of diet, is also an important factor in eliciting this effect. Harrison notes that a variety of chemicals, chemical and mechanical irritants, parasites, and dietary deficiencies cause forestomach tumors in rats. The predictive value of this finding in humans is, therefore, problematic because humans have no forestomach and food transit times are much faster. Interestingly, propionic acid inhibited the growth of the human adenocarcinoma cell line HT29 derived from similar epithelial tissue of human colon cancer patients, whereas other short-chain fatty acids, such as acetate, enhance transformation.


Although stable, propionic acid is flammable. It should be stored in an airtight container away from heat and flames.


UN1848 Propionic acid, Hazard class: 8; Labels: 8-Corrosive material. UN3463 Propionic acid, with not <90% acid by mass, Hazard Class 8; Labels: 8-Corrosive material, 3-Flammable liquid.

Purification Methods

Dry the acid with Na2SO4 or by fractional distillation, then redistil after refluxing with a few crystals of KMnO4. An alternative purification uses conversion to the ethyl ester, fractional distillation and hydrolysis. [Bradbury J Am Chem Soc 74 2709 1952.] Propionic acid can also be heated for 0.5hour with an amount of benzoic anhydride equivalent to the amount of water present (in the presence of CrO3 as catalyst), followed by fractional distillation. [Cham & Israel J Chem Soc 196 1960, Beilstein 2 IV 695.]


Propionic acid is a medium strong acid. Incompatible with sulfuric acid, strong bases; ammonia, isocyanates, alkylene oxides; epichlorohydrin. Reacts with bases; strong oxidizers; and amines, causing fire and explo- sion hazard. Attacks many metals forming flammable/ explosive hydrogen gas. It can be salted out of aqueous solutions by the addition of calcium chloride or other salts.

Waste Disposal

Incineration in admixture with flammable solvent.

Regulatory Status

GRAS listed. Accepted for use in Europe as a food additive. In Japan, propionic acid is restricted to use as a flavoring agent.


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