Description
First described by Johann Gottlieb in 1844, propanoic acid has
become one of the most widely used additives in processed
foods for human consumption and animal feedstocks. Originally,
Gottlieb found the compound among the degradation
products of certain sugars. The term – propionic acid – itself has
the unique distinction of once being the designation for all
fatty acids due to the writings of Jean-Baptiste Dumas, who, in
1847, postulated that all fatty acids were in reality just one
compound. While larger chain fatty acids are important
components of all living things, propionic acid is the shortest
fatty acid that exhibits the classic behaviors of similar
compounds.
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.
Occurrence
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.
Uses
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.
Uses
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.
Definition
ChEBI: Propionic acid is a short-chain saturated fatty acid comprising ethane attached to the carbon of a carboxy group. It has a role as an antifungal drug. It is a short-chain fatty acid and a saturated fatty acid. It is a conjugate acid of a 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.
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
Propionic acid is 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].
Hazard
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.
Flammability and Explosibility
Flammable
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.
Safety
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
Synthesis
Commercial processes produce propionic acid by chemical synthesis and in small quantities by bacterial fermentation. Industrially Propionic acid is produced by hydrocarboxylation of ethylene in presence nickel carbonyl as a catalyst.
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.
Carcinogenicity
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.
Environmental Fate
The widespread use of propionic acid has led to its detection in
waste streams and groundwater. It is a degradation product of
longer chain fatty acids, and has been detected in waste streams
following olive oil production and other processes. Additionally,
propionic acid has been qualitatively detected as a volatile
component of cooked potatoes and meats as well as in other
foods and beverages, including dairy products. Propionic acid
is a major component of the gas phase of the smoke of unfiltered
cigarettes, with quantities estimated at 100–300 mg per
cigarette.
In a direct fashion, propionic acid is released to the environment
through effluents from the manufacture, use, and
disposal of coal-derived and shale oil liquid fuels as well as
through wood-preserving chemical waste byproducts. Textile
mills and sewage treatment facilities may also be sources of
propionic acid-containing waste. Landfills and hazardous
waste sites can leach propionic acid to groundwater supplies.
Propionic acid can exist as a vapor in the ambient atmosphere
with a vapor pressure of 3.53 mmHg at 25 °C, and can
be degraded in the atmosphere by reaction with photochemically
produced hydroxyl radicals; the half-life for this reaction
in air is estimated to be 11 days. Photolysis of propionic acid is
not expected to be important, and wet deposition of propionic
acid is expected to occur readily as an atmospheric removal
process.
Biodegradation is likely to be the most important removal
mechanism of propionic acid from both soil and water. In
terrestrial environments, propionic acid will exist as a ratio of the
free acid and its conjugate base due to its pKa of 4.87. With an
estimated HenryK’s law constant of 4.15 ×10
-7 atmm3 mol
-1,
it is not expected to volatilize from soil. Its mobility in soil is
expected to be high, with an estimated Koc of 36. The high water
solubility of propionic acid and its existence as a charged species
result in low absorption by particulate and organic matter in
aquatic environments.
storage
Although stable, propionic acid is flammable. It should be stored in
an airtight container away from heat and flames.
Shipping
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.]
Toxicity evaluation
The behavior of propionic acid is largely pH dependent, and it
can alter the local pH in areas where it is applied or ingested.
It can behave as a moderately strong acid when concentrated,
and can be corrosive under such conditions. There has been
some evidence that propionic acid inhibits CO2 production
from palmitate in fibroblast cells and ureagenesis in rat liver
slices. This is perhaps related to fatty degeneration of the liver
and hyperammonemia in propionic and methylmalonic
acidemia – an autosomal disorder that results from a defect of
propionyl coenzyme A carboxylase. In the latter case, symptoms
can include vomiting, lethargy, hypotonia, and metabolic
ketoacidosis.
Incompatibilities
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.
