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Sorbic acid, or 2,4-hexadienoic acid, is a natural
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
used as a food
preservative A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or b ...
. It has the
chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
and the
structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such a ...
. It is a colourless solid that is slightly
soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...
in water and sublimes readily. It was first isolated from the unripe berries of the ''Sorbus aucuparia'' (
rowan The rowans ( or ) or mountain-ashes are shrubs or trees in the genus ''Sorbus'' of the rose family, Rosaceae. They are native throughout the cool temperate regions of the Northern Hemisphere, with the highest species diversity in the Himalaya ...
tree), hence its name.


Production

The traditional route to sorbic acid involves condensation of
malonic acid Malonic acid (IUPAC systematic name: propanedioic acid) is a dicarboxylic acid with structure CH2(COOH)2. The ionized form of malonic acid, as well as its esters and salts, are known as malonates. For example, diethyl malonate is malonic acid' ...
and crotonaldehyde. It can also be prepared from isomeric hexadienoic acids, which are available via a nickel-catalyzed reaction of allyl chloride,
acetylene Acetylene ( systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...
, and
carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
. The route used commercially, however, is from crotonaldehyde and
ketene In organic chemistry, a ketene is an organic compound of the form , where R and R' are two arbitrary monovalent chemical groups (or two separate substitution sites in the same molecule). The name may also refer to the specific compound ethen ...
. An estimated 30,000 tons are produced annually.


History

Sorbic acid was isolated in 1859 by
distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...
of
rowan The rowans ( or ) or mountain-ashes are shrubs or trees in the genus ''Sorbus'' of the rose family, Rosaceae. They are native throughout the cool temperate regions of the Northern Hemisphere, with the highest species diversity in the Himalaya ...
berry oil by A. W. von Hofmann. This affords
parasorbic acid Parasorbic acid is the cyclic lactone of sorbic acid. Thermal treatment or hydrolysis converts the lactone to sorbic acid. Toxicity Parasorbic acid is toxic and causes indigestion and nausea, however cooking and exposure to moisture convert i ...
, the lactone of sorbic acid, which he converted to sorbic acid by hydrolysis. Its antimicrobial activities were discovered in the late 1930s and 1940s, and it became commercially available in the late 1940s and 1950s. Beginning in the 1980s, sorbic acid and its salts were used as inhibitors of ''
Clostridium botulinum ''Clostridium botulinum'' is a Gram-positive, rod-shaped, anaerobic, spore-forming, motile bacterium with the ability to produce the neurotoxin botulinum. The botulinum toxin can cause botulism, a severe flaccid paralytic disease in humans ...
'' in meat products to replace the use of nitrites, which can produce carcinogenic nitrosamines.


Properties and uses

With a p''K''a of 4.76, sorbic acid is about as acidic as acetic acid. Sorbic acid and its salts, especially potassium sorbate and
calcium sorbate Calcium sorbate is the calcium salt of sorbic acid. Calcium sorbate is a polyunsaturated fatty acid salt. It is a commonly used food preservative; its E number E numbers ("E" stands for "Europe") are codes for substances used as food addi ...
, are antimicrobial agents often used as preservatives in food and drinks to prevent the growth of
mold A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not ...
,
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...
, and
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...
. In general the salts are preferred over the acid form because they are more soluble in water, but the active form is the acid. The optimal pH for the antimicrobial activity is below pH 6.5. Sorbates are generally used at concentrations of 0.025% to 0.10%. Adding sorbate salts to food will, however, raise the pH of the food slightly so the pH may need to be adjusted to assure safety. It is found in foods such as various kinds of cheese, bread, muffins, donuts, pies, cookies, protein bars, syrups, lemonades, fruit juices, dried meats, sausages, nuggets, burgers, sandwiches, tacos, pizzas, smoked fish, margarine, sauces, soups, and more. The E numbers are: * E200 Sorbic acid * E201
Sodium sorbate Sodium sorbate is the sodium salt of sorbic acid. It is an unstable white solid. Unlike other sorbic acid salts such as potassium sorbate (E202) and calcium sorbate (E203), the use of sodium sorbate as a food additive is not allowed in the EU du ...
* E202 Potassium sorbate * E203
Calcium sorbate Calcium sorbate is the calcium salt of sorbic acid. Calcium sorbate is a polyunsaturated fatty acid salt. It is a commonly used food preservative; its E number E numbers ("E" stands for "Europe") are codes for substances used as food addi ...
Some molds (notably some ''
Trichoderma ''Trichoderma'' is a genus of fungi in the family Hypocreaceae that is present in all soils, where they are the most prevalent culturable fungi. Many species in this genus can be characterized as opportunistic avirulent plant symbionts. This ref ...
'' and ''
Penicillium ''Penicillium'' () is a genus of ascomycetous fungi that is part of the mycobiome of many species and is of major importance in the natural environment, in food spoilage, and in food and drug production. Some members of the genus produce pe ...
'' strains) and
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...
s are able to detoxify sorbates by
decarboxylation Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is ...
, producing ''trans''-1,3-pentadiene. The pentadiene manifests as a typical odor of
kerosene Kerosene, paraffin, or lamp oil is a combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in aviation as well as households. Its name derives from el, κηρός (''keros'') meaning " wax", and was re ...
or
petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
. Other detoxification reactions include reduction to 4- hexenol and 4-hexenoic acid. Sorbic acid can also be used as an additive for cold rubber, and as an intermediate in the manufacture of some plasticizers and
lubricants A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, t ...
.


Safety

Sorbic acid and sorbate salts have a very low mammalian toxicity and carcinogenicity. Its is estimated to be between 7.4 and 10 g/kg.


See also

*
Sorbitol Sorbitol (), less commonly known as glucitol (), is a sugar alcohol with a sweet taste which the human body metabolizes slowly. It can be obtained by reduction of glucose, which changes the converted aldehyde group (−CHO) to a primary alcoho ...
* Polysorbate *
Acids in wine The acids in wine are an important component in both winemaking and the finished product of wine. They are present in both grapes and wine, having direct influences on the color, balance and taste of the wine as well as the growth and vitality of ...
*
Parasorbic acid Parasorbic acid is the cyclic lactone of sorbic acid. Thermal treatment or hydrolysis converts the lactone to sorbic acid. Toxicity Parasorbic acid is toxic and causes indigestion and nausea, however cooking and exposure to moisture convert i ...


References


External links


Sorbic inchem.org
{{Authority control Enoic acids Preservatives E-number additives Conjugated dienes