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Propionic acid
Propionic acid
Propionic acid
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Propionic acid
Simplified skeletal formula
Simplified skeletal formula
Full structural formula
Full structural formula
Ball-and-stick model
Ball-and-stick model
Space-filling model
Space-filling model
Names
Preferred IUPAC name
Propanoic acid
Other names
Carboxyethane
Ethanecarboxylic acid
Ethylformic acid
Metacetonic acid
Methylacetic acid
C3:0 (Lipid numbers)
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.001.070 Edit this at Wikidata
EC Number
  • Propionic acid: 201-176-3
E number E280 (preservatives)
  • Propionic acid: 1062
RTECS number
  • Propionic acid: UE5950000
UNII
  • InChI=1S/C3H6O2/c1-2-3(4)5/h2H2,1H3,(H,4,5) checkY
    Key: XBDQKXXYIPTUBI-UHFFFAOYSA-N checkY
  • Propionic acid: CCC(=O)O
  • Propionate: CCC(=O)[O-]
Properties
C3H6O2
Molar mass 74.079 g·mol−1
Appearance Colorless, oily liquid[1]
Odor Pungent, rancid, unpleasant[1]
Density 0.98797 g/cm3[2]
Melting point −20.5 °C (−4.9 °F; 252.7 K)[8]
Boiling point 141.15 °C (286.07 °F; 414.30 K)[8]
Sublimes at −48 °C
ΔsublHo = 74 kJ/mol[3]
8.19 g/g (−28.3 °C)
34.97 g/g (−23.9 °C)
Miscible (≥ −19.3 °C)[4]
Solubility Miscible in EtOH, ether, CHCl
3[5]
log P 0.33[6]
Vapor pressure 0.32 kPa (20 °C)[7]
0.47 kPa (25 °C)[6]
9.62 kPa (100 °C)[3]
4.45·10−4 L·atm/mol[6]
Acidity (pKa) 4.88[6]
−43.50·10−6 cm3/mol
1.3843[2]
Viscosity 1.175 cP (15 °C)[2]
1.02 cP (25 °C)
0.668 cP (60 °C)
0.495 cP (90 °C)[6]
Structure
Monoclinic (−95 °C)[9]
P21/c[9]
a = 4.04 Å, b = 9.06 Å, c = 11 Å[9]
α = 90°, β = 91.25°, γ = 90°
0.63 D (22 °C)[2]
Thermochemistry
152.8 J/mol·K[5][3]
191 J/mol·K[3]
−510.8 kJ/mol[3]
1527.3 kJ/mol[2][3]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Corrosive
GHS labelling:[7]
GHS02: FlammableGHS05: CorrosiveGHS07: Exclamation mark
Danger
H314[7]
P280, P305+P351+P338, P310[7]
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
3
2
0
Flash point 54 °C (129 °F; 327 K)[7]
512 °C (954 °F; 785 K)
Lethal dose or concentration (LD, LC):
1370 mg/kg (mouse, oral)[5]
NIOSH (US health exposure limits):
PEL (Permissible)
 none[1]
REL (Recommended)
 TWA 10 ppm (30 mg/m3) ST 15 ppm (45 mg/m3)[1]
IDLH (Immediate danger)
 N.D.[1]
Related compounds
Acetic acid
Lactic acid
3-Hydroxypropionic acid
Tartronic acid
Acrylic acid
Butyric acid
Related compounds
 1-Propanol
Propionaldehyde
Sodium propionate
Propionic anhydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Propionic acid (/proʊpiˈɒnɪk/, from the Greek words πρῶτος : prōtos, meaning "first", and πίων : píōn, meaning "fat"; also known as propanoic acid) is a naturally occurring carboxylic acid with chemical formula CH
3CH
2CO
2H. It is a liquid with a pungent and unpleasant smell somewhat resembling body odor. The anion CH
3CH
2CO−
2 as well as the salts and esters of propionic acid are known as propionates or propanoates.

About half of the world production of propionic acid is consumed as a preservative for both animal feed and food for human consumption. It is also useful as an intermediate in the production of other chemicals, especially polymers.

History

[edit]

Propionic acid was first described in 1844 by Johann Gottlieb, who found it among the degradation products of sugar.[10] Over the next few years, other chemists produced propionic acid by different means, none of them realizing they were producing the same substance. In 1847, French chemist Jean-Baptiste Dumas established all the acids to be the same compound, which he called propionic acid, from the Greek words πρῶτος (prōtos), meaning first, and πίων (piōn), meaning fat, because it is the smallest H(CH
2)
nCOOH acid that exhibits the properties of the other fatty acids, such as producing an oily layer when salted out of water and having a soapy potassium salt.[11]

Properties

[edit]

Propionic acid has physical properties intermediate between those of the smaller carboxylic acids, formic and acetic acids, and the larger fatty acids. It is miscible with water, but can be removed from water by adding salt. As with acetic and formic acids, it consists of hydrogen bonded pairs of molecules in both the liquid and the vapor.

Propionic acid displays the general properties of carboxylic acids: it can form amide, ester, anhydride, and chloride derivatives. It undergoes the Hell–Volhard–Zelinsky reaction that involves α-halogenation of a carboxylic acid with bromine, catalysed by phosphorus tribromide, in this case to form 2-bromopropanoic acid, CH
3CHBrCOOH.[12] This product has been used to prepare a racemic mixture of alanine by ammonolysis.[13][14]

Manufacture

[edit]

Chemical

[edit]

In industry, propionic acid is mainly produced by the hydrocarboxylation of ethylene using nickel carbonyl as the catalyst:[15]

Hydrocarboxylation of ethene with carbon monoxide and water to form propionic acid in the presence of nickel tetracarbonyl as catalyst

It is also produced by the aerobic oxidation of propionaldehyde. In the presence of cobalt or manganese salts (manganese propionate is most commonly used), this reaction proceeds rapidly at temperatures as mild as 40–50 °C:

Liquid-phase oxidation of propionaldehyde with atmospheric oxygen to form propionic acid in the presence of manganese(II)-propionate as catalyst

Large amounts of propionic acid were once produced as a byproduct of acetic acid manufacture. At the current time, the world's largest producer of propionic acid is BASF, with approximately 150 kt/a production capacity.

Biotechnological

[edit]

Biotechnological production of propionic acid mainly uses Propionibacterium strains.[16] However, large scale production of propionic acid by Propionibacteria faces challenges such as severe inhibition of end-products during cell growth and the formation of by-products (acetic acid and succinic acid).[17] One approach to improve productivity and yield during fermentation is through the use of cell immobilization techniques, which also promotes easy recovery, reuse of the cell biomass and enhances microorganisms' stress tolerance.[18] In 2018, 3D printing technology was used for the first time to create a matrix for cell immobilization in fermentation. Propionic acid production by Propionibacterium acidipropionici immobilized on 3D-printed nylon beads was chosen as a model study. It was shown that those 3D-printed beads were able to promote high density cell attachment and propionic acid production, which could be adapted to other fermentation bioprocesses.[19] Other cell immobilization matrices have been tested, such as recycled-glass Poraver and fibrous-bed bioreactor.[20][21]

Alternative methods of production have been trialled, by genetically engineering strains of Escherichia coli to incorporate the necessary pathway, the Wood-Werkman cycle.[22]

Industrial uses

[edit]

Propionic acid inhibits the growth of mold and some bacteria at levels between 0.1 and 1% by weight. As a result, some propionic acid produced is consumed as a preservative for both animal feed and food for human consumption. For animal feed, it is used either directly or as its ammonium salt. This application accounts for about half of the world production of propionic acid. The antibiotic monensin is added to cattle feed to favor propionibacteria over acetic acid producers in the rumen; this produces less carbon dioxide and feed conversion is better. Another major application is as a preservative in baked goods, which use the sodium and calcium salts.[15] As a food additive, it is approved for use in the EU,[23] US,[24] Australia and New Zealand.[25]

Propionic acid is also useful as an intermediate in the production of other chemicals, especially polymers. Cellulose-acetate-propionate is a useful thermoplastic. Vinyl propionate is also used. In more specialized applications, it is also used to make pesticides and pharmaceuticals. The esters of propionic acid have fruit-like odors and are sometimes used as solvents or artificial flavorings.[15]

In biogas plants, propionic acid is a common intermediate product, which is formed by fermentation with propionic acid bacteria. Its degradation in anaerobic environments (e.g. biogas plants) requires the activity of complex microbial communities.[26]

In production of the Jarlsberg cheese, a propionic acid bacterium is used to give both taste and holes.[27]

Biology

[edit]

Propionic acid is produced biologically as its coenzyme A ester, propionyl-CoA, from the metabolic breakdown of fatty acids containing odd numbers of carbon atoms, and also from the breakdown of some amino acids. Bacteria of the genus Propionibacterium produce propionic acid as the end-product of their anaerobic metabolism. This class of bacteria is commonly found in the stomachs of ruminants and the sweat glands of humans, and their activity is partially responsible for the odor of Emmental cheese, American "Swiss cheese" and sweat.

The metabolism of propionic acid begins with its conversion to propionyl coenzyme A, the usual first step in the metabolism of carboxylic acids. Since propionic acid has three carbons, propionyl-CoA cannot directly enter either beta oxidation or the citric acid cycles. In most vertebrates, propionyl-CoA is carboxylated to D-methylmalonyl-CoA, which is isomerised to L-methylmalonyl-CoA. A vitamin B12-dependent enzyme catalyzes rearrangement of L-methylmalonyl-CoA to succinyl-CoA, which is an intermediate of the citric acid cycle and can be readily incorporated there.[28]

Propionic acid serves as a substrate for hepatic gluconeogenesis via conversion to succinyl-CoA.[29][30] Additionally, exogenous propionic acid administration results in more endogenous glucose production than can be accounted for by gluconeogenic conversion alone.[31] Exogenous propionic acid may upregulate endogenous glucose production via increases in norepinephrine and glucagon, suggesting that chronic ingestion of propionic acid may have adverse metabolic consequences.[32]

In propionic acidemia, a rare inherited genetic disorder, propionate acts as a metabolic toxin in liver cells by accumulating in mitochondria as propionyl-CoA and its derivative, methylcitrate, two tricarboxylic acid cycle inhibitors. Propanoate is metabolized oxidatively by glia, which suggests astrocytic vulnerability in propionic acidemia when intramitochondrial propionyl-CoA may accumulate. Propionic acidemia may alter both neuronal and glial gene expression by affecting histone acetylation.[33][34] When propionic acid is infused directly into rodents' brains, it produces reversible behavior (e.g., hyperactivity, dystonia, social impairment, perseveration) and brain changes (e.g., innate neuroinflammation, glutathione depletion) that may be used as a means to model autism in rats.[33]

Human occurrence

[edit]

The human skin is host of several species of Propionibacteria. The most notable one is the Cutibacterium acnes (formerly known as Propionibacterium acnes), which lives mainly in the sebaceous glands of the skin and is one of the principal causes of acne.[35] Propionate is observed to be among the most common short-chain fatty acids produced in the large intestine of humans by gut microbiota in response to indigestible carbohydrates (dietary fiber) in the diet.[36][37] The role of the gut microbiota and their metabolites, including propionate, in mediating brain function has been reviewed.[38]

A study in mice suggests that propionate is produced by the bacteria of the genus Bacteroides in the gut, and that it offers some protection against Salmonella there.[39] Another study finds that fatty acid propionate can calm the immune cells that drive up blood pressure, thereby protecting the body from damaging effects of high blood pressure.[40]

Bacteriology

[edit]

The Bacteria species Coprothermobacter platensis produces propionate when fermenting gelatin.[41] Prevotella brevis and Prevotella ruminicola also generate propionate when fermenting glucose.[42]

Propionate salts and esters

[edit]

The propionate /ˈproʊpiəneɪt/, or propanoate, ion is C
2H
5COO−
, the conjugate base of propionic acid. It is the form found in biological systems at physiological pH. A propionic, or propanoic, compound is a carboxylate salt or ester of propionic acid. In these compounds, propionate is often written in shorthand, as CH
3CH
2CO
2 or simply EtCO
2.

Propionates should not be confused with propenoates (commonly known as acrylates), the ions/salts/esters of propenoic acid (also known as 2-propenoic acid or acrylic acid).

Examples

[edit]

Salts

[edit]

Esters

[edit]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Propionic acid

View on Grokipedia
from Grokipedia
Propionic acid, also known as propanoic acid, is a straight-chain saturated with the molecular formula CH₃CH₂COOH and a molecular weight of 74.08 g/mol. It appears as a colorless to pale yellow oily liquid at , characterized by a sharp, pungent odor reminiscent of rancid . As one of the simplest , it plays a key role in and is naturally produced during the of carbohydrates in the gastrointestinal tracts of ruminants and humans. Propionic acid is primarily produced industrially through processes, such as the of (Reppe process) or the oxidation of derived from . Alternatively, it can be synthesized via microbial using like Propionibacterium freudenreichii, which converts lactate or sugars into the acid, offering a sustainable alternative especially from renewable feedstocks like . This biotechnological route has gained interest due to its potential for cost-effective production and reduced environmental impact compared to . In applications, propionic acid serves as a versatile chemical intermediate in the manufacture of esters, salts, and polymers, including cellulose propionate plastics and herbicides like 2,4-dichlorophenoxypropionic acid. It is widely used as a food preservative (E280) to inhibit mold and bacterial growth in baked goods, cheeses, and animal feeds, leveraging its antimicrobial properties at concentrations typically below 0.3%. Medically, its calcium or sodium salts act as antifungal agents in topical treatments and veterinary products. Regarding safety, propionic acid is classified as corrosive to , eyes, and respiratory tissues, with potential to cause severe burns upon direct contact or of vapors. It is flammable, with a of 52°C and explosive limits of 2.9–14.8% in air, necessitating proper ventilation and protective equipment in handling. Acute oral toxicity is moderate (LD50 in rats: 2,600 mg/kg), and it is (GRAS) by the FDA for use at approved levels, though excessive exposure may lead to gastrointestinal irritation or metabolic disturbances. No evidence of carcinogenicity has been established.

History

Discovery

Propionic acid was first identified in 1844 by German chemist Johann Gottlieb during his investigations into the degradation products of sugar treated with potassium hydroxide. In 1847, French chemist Jean-Baptiste Dumas demonstrated that all previously reported forms of the compound were identical, establishing its chemical unity. Dumas coined the name "acide propionique" (propionic acid in English), derived from the Greek terms prōtos (first) and pion (fat), highlighting its position as the shortest-chain fatty acid following acetic acid. This naming reflected the emerging systematic understanding of organic acids in early organic chemistry. In 1878, Albert Fitz demonstrated bacterial synthesis of propionic acid, establishing the Fitz equation to describe its production by fermentation.

Commercial Development

Propionic acid transitioned from a laboratory compound, first described in 1844, to commercial production in the early 20th century through chemical synthesis methods, driven by increasing demand for effective preservatives in the food industry. By the 1930s, its antifungal properties were recognized for preventing spoilage in baked goods, leading to initial industrial applications as calcium or sodium propionate salts. This marked the beginning of its role as a commodity chemical, with early production focused on meeting needs for mold inhibition in grains and dairy products. Following , production scaled significantly with advancements in processes, exemplified by 's ethylene-based synthesis. In 1941, chemist Walter Reppe developed a method to produce propionic acid from ethylene and , followed by a in 1951 and commercial launch in 1952 at a capacity of 1,200 tons per year. By 1960, expanded to a large-scale facility in , , reaching 149,000 metric tons annually as of recent years, which facilitated broader industrial adoption in preservatives and intermediates. This post-war expansion aligned with rising availability, propelling propionic acid from niche use to a key bulk chemical. As of , global production is approximately 560,000 metric tons annually, fueled by demand in and manufacturing for applications like herbicides and propionate. The market was valued at approximately $1.11 billion in 2023, projected to grow at a (CAGR) of 3.4% from 2024 through 2030.

Properties

Physical Properties

Propionic acid has the molecular formula C₃H₆O₂ and the CH₃CH₂COOH. Its molecular weight is 74.08 g/mol. At standard conditions, propionic acid appears as a colorless, oily with a pungent and rancid . This characteristic arises from its volatile nature and contributes to its role as a in various applications. The compound has a of -20.7 °C, remaining at typical room temperatures, and a of 141.1 °C at 760 mmHg. Its density is 0.993 g/cm³ at 20 °C, slightly less than that of . Propionic acid exhibits high solubility, being miscible with , , and , which reflects its polar functionality. The vapor pressure is 2.9 mmHg at 20 °C, indicating low to moderate volatility under ambient conditions. Additionally, its refractive index is 1.3869 at 20 °C, a value typical for short-chain s.

Chemical Properties

Propionic acid behaves as a weak in aqueous solutions, partially dissociating to form the propionate ion and hydronium ion. Its is Ka=1.34×10−5K_a = 1.34 \times 10^{-5} at 25 °C, corresponding to a pKa value of 4.87, which indicates moderate acidity compared to stronger acids but sufficient for applications requiring adjustment. Like other carboxylic acids, propionic acid exhibits characteristic reactivity at the carboxyl group. It neutralizes bases to form water-soluble salts, such as sodium or calcium propionates, through proton transfer. With alcohols under acidic , it undergoes Fischer esterification to produce esters, while reactions with amines yield amides, often requiring activation or heating for efficient conversion. These reactions highlight its versatility in forming derivatives central to . Under high temperatures with (a mixture of and ), propionic acid or its sodium salt undergoes , losing the carboxyl group as to produce . The compound remains stable in air at ambient conditions, showing no significant or . However, its acidity makes it corrosive to many metals, including iron and , where it reacts to generate gas and metal propionates./Carboxylic_Acids/Reactivity_of_Carboxylic_Acids/The_Decarboxylation_of_Carboxylic_Acids_and_Their_Salts)

Production

Chemical Synthesis

The primary industrial chemical synthesis of propionic acid involves the process, a hydrocarboxylation reaction of using catalysts. This method, originally developed by Walter Reppe and colleagues at in the early 1950s, proceeds under high pressure (100–300 bar) and temperature (250–320 °C) with (Ni(CO)4) as the catalyst, often promoted by additives like to enhance selectivity and prevent catalyst precipitation. The key reaction is the of with and : C2H4+CO+H2O→CH3CH2COOH\mathrm{C_2H_4 + CO + H_2O \rightarrow CH_3CH_2COOH} This direct route yields propionic acid in a single step, with the crude product purified by and the catalyst recycled; byproducts such as off-gases are managed through with heat recovery. A variant of the Reppe process emphasizes -based for improved efficiency, making it a dominant route due to its cost-effectiveness from readily available feedstocks like derived from or . Alternative chemical routes include the oxidation of propanal, typically produced via of followed by air oxidation under mild conditions (40–50 °C) with optional manganese salts as catalysts, achieving yields over 90%. Similarly, n-propanol can be oxidized to propionic acid using oxygen or air in the presence of catalysts like or silver, though this is less common industrially due to higher costs. Another pathway is the of ethyl alcohol with , catalyzed by metals such as or , but this method is largely obsolete owing to economic disadvantages compared to ethylene-based processes. These routes collectively enable large-scale production from sources, emphasizing efficiency and integration with existing processing infrastructure.

Biotechnological Methods

Biotechnological production of propionic acid primarily relies on anaerobic fermentation processes mediated by bacteria from the genus Propionibacterium, such as P. acidipropionici, which convert various carbon sources into propionate through the Wood-Werkman cycle. In this pathway, lactate serves as a key substrate, undergoing fermentation according to the Fitz equation: three molecules of lactate yield two molecules of propionate, one molecule of acetate, one molecule of CO₂, and energy in the form of ATP. This process is obligately anaerobic and leverages the bacteria's ability to oxidize lactate to support reductive steps, producing propionic acid as the primary end product while generating acetate and CO₂ as byproducts. A range of renewable substrates can be utilized by species to enhance sustainability, including derived from , from , and whey lactose from dairy processing. , in particular, supports high propionate yields due to its compatibility with the bacteria's metabolic pathways, often outperforming traditional sugars in co-fermentation setups. Similarly, whey permeate provides an economical waste-based feedstock, enabling efficient conversion without significant inhibition. conditions are optimized for maximal productivity, typically at a of 6-7 to maintain activity and prevent stress, and temperatures of 30-35°C to balance growth and product formation rates. Under these parameters, yields can reach up to 0.6 g of propionic acid per gram of substrate consumed, demonstrating the process's efficiency with low-cost inputs. Recent advancements as of have focused on integrating these fermentations into bio-refineries that utilize waste streams, such as agroindustrial effluents and food byproducts, to produce propionic acid at scale while minimizing environmental impact. These integrated systems, exemplified by processes from companies like and , incorporate waste-derived feedstocks like and biomass sugars, achieving reductions of 20-30% compared to conventional methods reliant on . Such developments underscore the shift toward models, where propionibacteria fermentation not only valorizes wastes but also aligns with broader goals of renewable chemical production, though chemical synthesis still dominates global production (over 95%). Propionibacteria naturally contribute to processes like Swiss cheese ripening through similar fermentative pathways.

Applications

Industrial Applications

Propionic acid plays a significant role as a chemical intermediate in various non-food industrial sectors, comprising approximately 48% of global production as of 2024. It is employed in the synthesis of herbicides, such as the propionic acid derivative , which is used for broadleaf weed control in . Additionally, propionic acid serves as a for producing perfumes and fragrances, contributing to their through esterification processes, and for rubber accelerators and stabilizers that enhance in and manufacturing. In the , propionic acid and its anhydride are key components in the production of propionate, a versatile applied in coatings, printing inks, and specialty films due to its optical clarity and durability. The acid also functions as an in , aiding in the dissolution and of resins and emulsions for adhesives and coatings. As of 2025, industry trends emphasize the integration of propionates into sustainable polymers, with growing demand for bio-based derivatives to meet regulations on eco-friendly materials and reduce reliance on petroleum-derived alternatives. Its preservative properties further enable applications in industrial formulations requiring microbial stability.

Food and Feed Applications

Propionic acid is recognized as (GRAS) by the U.S. () for use as a direct , specifically under 21 CFR 184.1081, and is designated as E280 in the . This status enables its application as an that inhibits the growth of molds and certain bacteria, thereby extending shelf life in various edible products. Its effectiveness stems from lowering and disrupting microbial metabolism, making it suitable for incorporation at controlled concentrations. In food applications, propionic acid or its salts, such as calcium propionate, are commonly added to baked goods like and tortillas to prevent mold contamination, typically at levels of 0.1-0.3% by weight. Similarly, it is used in cheeses to control fungal growth during storage and ripening, maintaining product quality without altering sensory attributes significantly at these dosages. In animal feed preservation, particularly , propionic acid enhances aerobic stability by reducing heating and microbial spoilage when applied at 0.1-0.3%, allowing for better nutrient retention in ensiled forages. A key role in feed applications involves preventing mycotoxin formation by inhibiting toxin-producing fungi such as species, which can contaminate grains and forages during storage. Approximately 40% of global propionic acid production is directed toward and preservation, underscoring its importance in livestock to mitigate risks from s. As of 2025, the market for propionic acid in natural preservative formulations is experiencing growth, driven by consumer preferences for clean-label products and biotechnological production methods that emphasize bio-based sources over synthetic alternatives. This trend supports reduced reliance on purely chemical additives while leveraging propionic acid's naturally occurring origins from microbial .

Biological Role

Human Physiology

Propionic acid is produced in the human colon through the of dietary fibers by , serving as a key short-chain (SCFA). This process involves anaerobic bacteria breaking down indigestible carbohydrates, yielding propionic acid alongside and butyrate. As an SCFA, propionic acid contributes to colonic energy metabolism, where SCFAs collectively provide approximately 10% of the host's daily caloric needs through beta-oxidation in colonocytes, supporting epithelial cell function and barrier integrity. Absorbed propionic acid is transported via the to the liver, where it undergoes to propionyl-CoA, subsequently converted to for entry into the tricarboxylic acid cycle; this pathway enables its utilization in , contributing to glucose . In healthy individuals, this hepatic processing maintains balanced levels, but disruptions occur in , a rare autosomal recessive caused by deficiency in propionyl-CoA carboxylase. Elevated propionic acid accumulation in this condition leads to , , and neurological symptoms, including developmental delays, seizures, and autism-like behavioral traits such as social withdrawal and repetitive actions. Humans typically obtain 100–500 mg of propionic acid daily through dietary sources, including fermented foods and additives like calcium propionate used as preservatives in baked goods. Recent 2025 highlights propionic acid's potential effects on gut , with studies showing that propionate-producing supplementation reduces obesity-related via G-protein coupled receptor 41 signaling, modulating immune responses and improving metabolic outcomes in high-fat diet models.

Microbiology

Propionibacterium freudenreichii, a Gram-positive, anaerobic bacterium, plays a central role in the production of propionic acid during the ripening of . Under anaerobic conditions in the cheese matrix, this bacterium ferments lactate to generate propionic acid as the primary end product, along with acetic acid and , which contributes to the formation of characteristic eyes (holes) in the cheese. The propionic acid imparts a nutty flavor to the cheese through the involvement of propionyl-CoA in metabolic pathways. In rumen fermentation, propionic acid is a key volatile fatty acid produced by ruminal such as elsdenii and species from the breakdown of carbohydrates in feed, serving as an energy source for the host animal and helping to regulate rumen . Propionic acid also functions as a natural preservative in , where it is generated during or applied exogenously to lower and inhibit the growth of pathogens like typhimurium by disrupting their cellular and invasion mechanisms. Ecologically, propionic acid contributes to cycling in microbiomes, where like and species produce it during the of residues, facilitating solubilization and . In systems, propionic acid such as Propionibacterium acidipropionici generate propionic acid as an intermediate in of organic waste, supporting the conversion of complex substrates into precursors and aiding in the overall cycling of .

Derivatives

Salts

Propionate salts are formed through the neutralization reaction of propionic acid with a metal hydroxide or carbonate, as exemplified by the general equation: CH3CH2COOH+MOH→CH3CH2COOM+H2O\mathrm{CH_3CH_2COOH + MOH \rightarrow CH_3CH_2COOM + H_2O} where M represents a metal cation. These salts exhibit high water solubility, with sodium propionate dissolving at approximately 1 g per ml in water, and are generally less volatile than the parent acid due to their ionic nature, which reduces vapor pressure and odor intensity compared to the rancid-smelling propionic acid. Key examples include calcium propionate (E282), widely used as an agent in and other baked goods to inhibit mold growth and extend . Sodium propionate (E281) serves primarily as a feed additive in animal , acting as an to preserve and prevent spoilage. Zinc propionate is employed in , particularly in foot care products, for its properties against molds, fungi, and . In the propionic acid derivatives market, salts such as calcium and accounted for approximately 30% of the in 2023.

Esters

Propionate esters are organic compounds derived from propionic acid through esterification, a reaction in which propionic acid reacts with an alcohol in the presence of an acid catalyst, typically , to form the ester and water. The general reaction is represented as: CH3CH2COOH+ROH→H2SO4CH3CH2COOR+H2O\mathrm{CH_3CH_2COOH + ROH \xrightarrow{H_2SO_4} CH_3CH_2COOR + H_2O}
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