Dibasic acid, also called Dicarboxylic Acid or Diprotic Acid, has two dissociation constants.

Synonyms: Dicarboxylic acids, DCAs, DCA

Dibasic acids are organic compounds that contain two functional carboxylic acid (–COOH) groups. 

Dibasic Acid produces two H+ ions. Dibasic Acid dissociates in two steps, so its basicity is 2.

Dibasic acid's molecular formula can be written as HO2C−R−CO2H, where R can be aliphatic or aromatic. 

The molecular formula for dibasic acids is HOOC (CH2)n COOH, where n is 0 for oxalic acid, 1 for malonic acid, 2 for succinic acid, 3 for glutaric acid, 4 for adipic acid, 5 for Pimelic acid, 6 for Suberic Acid, 7 for Azelaic Acid, 8 for Sebacic Acid, 9 for undecanedioic acid, 10 for dodecanedioic acid etc. 

The carbon chain lengths range from C2 to the longer carbon chains of C24, which rarely exist naturally.

Dibasic acids are essential in producing polyester, polyols, polyamides, and nylon and as a precursor to active pharmaceutical ingredients and additives. 

Dibasic acids are important water-soluble components of atmospheric aerosols. 

Dicarboxylic acid can yield two kinds of salts or esters, as its molecules contain two carboxyl groups. 

Dibasic acids generally show similar chemical behavior and reactivity to monocarboxylic acids.

Dibasic acids are used to prepare copolymers such as polyamides and polyesters. 

The industry's most widely used dibasic acid is adipic, a precursor in the production of nylon. 

Other examples of dibasic acids include aspartic acid and glutamic acid, two amino acids in the human body. 

The name can be abbreviated to diacid.

Dibasic acids are crystalline solids. 

Dicarboxylic acids are solids at room temperature and they have melting points that are higher than those of monocarboxylic acids containing the same number of carbon atoms, since stronger associations between molecules exist, mainly as a result of hydrogen bond formation.

Solubility in water and melting point of the α,ω- compounds progress in a series as the carbon chains become more extended, alternating between odd and even numbers of carbon atoms so that for even numbers of carbon atoms, the melting point is higher than for the next in the series with an odd number.

These compounds are weak dibasic acids, with pKa tending towards ca. 4.5 and 5.5 values as the separation between the two carboxylate groups increases. 

Thus, in an aqueous solution at pH about 7, typical of biological systems, the Henderson–Hasselbalch equation indicates they exist predominantly as dicarboxylate anions.

The Dibasic acids, especially the small and linear ones, can be used as crosslinking reagents.

Dibasic acids, where the carboxylic groups are separated by none or one carbon atom, decompose when heated to release carbon dioxide and leave behind a monocarboxylic acid.

Blanc's Rule says that heating a barium salt of a Dibasic acid or dehydrating it with acetic anhydride will yield a cyclic acid anhydride if the carbon atoms bearing acid groups are in position 1 and (4 or 5). 

So, succinic acid will produce succinic anhydride. 

For acids with carboxylic groups at positions 1 and 6, this dehydration causes carbon dioxide and water loss to form a cyclic ketone; for example, adipic acid will form cyclopentanone.

Dicarboxylic acids can generate monoamides in which only one COOH group is replaced by CONH2, diamides where both carboxyl groups are transformed into primary amides, and imides, which are cyclic secondary amides formed by the replacement of two OH groups from the carboxyls with one bidentate NH group.

Linear and cyclic saturated dibasic acids:

0 Oxalic acid ethanedioic acid

1 Malonic acid propanedioic acid

2 Succinic acid butanedioic acid

3 Glutaric acid pentanedioic acid

4 Adipic acid hexanedioic acid

5 Pimelic acid heptanedioic acid

6 Suberic acid octanedioic acid

6 1,4-Cyclohexanedicarboxylic acid

7 Azelaic acid nonanedioic acid

8 Sebacic acid decanedioic acid

9 undecanedioic acid

10 dodecanedioic acid

13 Brassylic acid tridecanedioic acid

14 Thapsic acid hexadecanedioic acid

19 Japanic acid heneicosanedioic acid

20 Phellogenic acid docosanedioic acid

28 Equisetolic acid triacontanedioic acid

Dicarboxylic acids have a wide range of industrial applications, directly or indirectly. 

The specific use depends on the particular dicarboxylic acid.

Succinic acid is used as an acidity regulator in the food and beverage industry.

Adipic acid, despite its name (in Latin, adipis means fat), is not a normal constituent of natural lipids but is a product of oxidative rancidity. 

Adipic acid was first obtained by oxidation of castor oil (ricinoleic acid) with nitric acid. 

Adipic acid is now produced industrially by oxidation of cyclohexanol or cyclohexane, mainly for making Nylon 6-6. 

Adipic acid has several other industrial uses in the production of adhesives, plasticizers, gelatinizing agents, hydraulic fluids, lubricants, emollients, polyurethane foams, leather tanning, urethane, and also as an acidulant in foods.

Pimelic acid, also called heptanedioic acid, was first isolated from oxidized oil. 

Derivatives of pimelic acid are involved in the biosynthesis of lysine.

Suberic acid was first produced by nitric acid oxidation of cork (Latin suber). 

This acid is also created when castor oil is oxidized. 

Suberic acid manufactures alkyd resins and synthesizes polyamides (nylon variants).

Azelaic acid's name stems from the action of nitric acid (azote, nitrogen, or azotic, nitric) oxidation of oleic acid or elaidic acid. 

It was detected among products of rancid fats. 

Its origin explains its presence in poorly preserved samples of linseed oil and in specimens of ointment removed from Egyptian tombs 5000 years old. 

Azelaic acid was prepared by oxidation of oleic acid with potassium permanganate, but now by oxidative cleavage of oleic acid with chromic acid or by ozonolysis. 

Azelaic acid is used as simple esters or branched-chain esters) in the manufacture of plasticizers (for vinyl chloride resins, rubber), lubricants, and greases. 

Azelaic acid is now used in cosmetics (treatment of acne). 

It displays bacteriostatic and bactericidal properties against various aerobic and anaerobic micro-organisms on acne-bearing skin. 

Azelaic acid was identified as a molecule that accumulated at elevated levels in some parts of plants and was shown to enhance plants' resistance to infections.

Sebacic acid is named from sebum (fat). 

Thenard isolated this compound from distillation products of beef fat in 1802. 

It is produced industrially by alkali fission of castor oil.

Sebacic acid and its derivatives have a variety of industrial uses, such as plasticizers, lubricants, diffusion pump oils, cosmetics, candles, etc. 

It is also used to synthesize polyamide, nylon, and alkyd resins. 

An isomer, isosebacic acid, has several applications in manufacturing vinyl resin plasticizers, extrusion plastics, adhesives, ester lubricants, polyesters, polyurethane resins, and synthetic rubber.

Brassylic acid can be produced from erucic acid by ozonolysis and by microorganisms (Candida sp.) from tridecane. 

This diacid is produced on a small commercial scale in Japan to manufacture fragrances.

Dodecanedioic acid produces nylon (nylon-6,12), polyamides, coatings, adhesives, greases, polyesters, dyestuffs, detergents, flame retardants, and fragrances. 

It is now produced by fermentation of long-chain alkanes with a specific strain of Candida tropicalis.

Traumatic acid is its monounsaturated counterpart.

Thapsic acid was isolated from the dried roots of the Mediterranean "deadly carrot," Thapsia garganica (Apiaceae).

Japan wax contains triglycerides of C21, C22, and C23 Dibasic acids obtained from the sumac tree (Rhus sp.).

An extensive survey of the Dibasic acids present in Mediterranean nuts revealed unusual components.

A total of 26 minor acids (from 2 in pecan to 8% in peanut) were determined: 8 species derived from succinic acid, likely about photosynthesis, and 18 species with a chain from 5 to 22 carbon atoms. 

Higher weight acids (>C20) are found in suberin present at vegetal surfaces (outer bark, root epidermis). C16 to C26 a, ω-dioic acids are considered diagnostic for suberin. With C18:1 and C18:2, their content amount from 24 to 45% of the whole suberin. 

They are present at low levels (< 5%) in plant cutin, except in Arabidopsis thaliana where their content can be higher than 50%.

It was shown that hyperthermophilic microorganisms contained a large variety of Dibasic acids.

This is probably the most crucial difference between these microorganisms and other marine bacteria. 

Dioic fatty acids from C16 to C22 were found in a hyperthermophilic archaeon, Pyrococcus furiosus. 

Short and medium-chain (up to 11 carbon atoms) dioic acids have been discovered in Cyanobacteria genus Aphanizomenon.

Dibasic acids may be produced by ω-oxidation of fatty acids during their catabolism. 

Long-chain Dibasic acids are important derivatives of fatty acids and act as precursors for the synthesis of various industrial products such as perfumes, polymers, plastics, lubricants, adhesives, etc. 

Usually, Long-chain Dibasic acids are chemically synthesized from petroleum-based products, but due to environmental concerns, biotransformation using hydrophobic substrates like fatty acids hydrocarbons has attracted significant interest

Branched-chain Dibasic acids

Long-chain Dibasic acids containing vicinal dimethyl branching near the center of the carbon chain have been discovered in the genus Butyrivibrio. 

These bacteria participate in the digestion of cellulose in the rumen.

These fatty acids, named diabolic acids, have a chain length depending on the fatty acid used in the culture medium. 

The most abundant diabolic acid in Butyrivibrio had a 32-carbon chain length. 

Diabolic acids were also detected in the core lipids of the genus Thermotoga of the order Thermotogales, bacteria living in Solfatara springs, deep-sea marine hydrothermal systems, and high-temperature marine and continental oil fields.

About 10% of their lipid fraction was shown to be symmetrical C30 to C34 diabolic acids. 

The C30 (13,14-dimethyloctacosanedioic acid) and C32 (15,16-dimethyltriacontanedioic acid) diabolic acids have been described in Thermotoga maritima.

Some parent C29 to C32 diacids but with methyl groups on the carbons C-13 and C-16 have been isolated and characterized from the lipids of thermophilic anaerobic bacterium Thermoanaerobacter ethanolicus.

The most abundant diacid was the C30 a,ω-13,16-dimethyloctacosanedioic acid.

Biphytanic diacids are present in geological sediments and are considered tracers of past anaerobic methane oxidation.

Cenozoic seep limestones have detected several forms without or with one or two pentacyclic rings. 

These lipids may be unrecognized metabolites from Archaea.

Crocetin

Crocetin is the core compound of crocins (crocetin glycosides), which are the primary red pigments of the stigmas of saffron (Crocus sativus) and the fruits of gardenia (Gardenia jasminoides). 

Crocetin is a 20-carbon chain Dibasic acid, a diterpenenoid considered a carotenoid. 

It was the first plant carotenoid to be recognized as early as 1818, while the history of saffron cultivation spans more than 3,000 years. 

The major active ingredient of saffron is the yellow pigment crocin 2 (three other derivatives with different glycosylations are known), containing a gentiobiose (disaccharide) group at each end of the molecule. 

A simple and specific HPLC-UV method has been developed to quantify the five primary biologically active ingredients of saffron: the four crocins and crocetin.

Unsaturated dicarboxylic acids: 

Maleic acid (Z)-Butenedioic acid cis

Fumaric acid (E)-Butenedioic acid trans

Acetylenedicarboxylic acid But-2-ynedioic acid

Glutaconic acid (Z)-Pent-2-enedioic acid cis

(E)-Pent-2-enedioic acid trans

2-Decenedioic acid trans

Traumatic acid Dodec-2-enedioic acid trans

Diunsaturated Muconic acid (2E,4E)-Hexa-2,4-dienedioic acid trans,trans

(2Z,4E)-Hexa-2,4-dienedioic acid cis,trans

(2Z,4Z)-Hexa-2,4-dienedioic acid cis,cis

Glutinic acid

(Allene-1,3-dicarboxylic acid) (RS)-Penta-2,3-dienedioic acid HO2CCH=C=CHCO2H

Branched Citraconic acid (2Z)-2-Methylbut-2-enedioic acid cis HO2CCH=C(CH3)CO2H

Mesaconic acid (2E)-2-Methyl-2-butenedioic acid trans HO2CCH=C(CH3)CO2H

Itaconic acid 2-Methylidenebutanedioic acid –

Traumatic acid was among the first biologically active molecules isolated from plant tissues. 

This dibasic acid was shown to be a potent wound-healing agent in plants that stimulates cell division near a wound site; it derives from 18:2 or 18:3 fatty acid hydroperoxides after conversion into oxo-fatty acids.

trans,trans-Muconic acid is a metabolite of benzene in humans. 

The determination of its concentration in urine is therefore used as a biomarker of occupational or environmental exposure to benzene.

Glutinic acid, a substituted allene, was isolated from Alnus glutinosa (Betulaceae).

While polyunsaturated fatty acids are unusual in plant cuticles, a unsaturated dicarboxylic acid has been reported as a component of some plant species' surface waxes or polyesters. 

Thus, octadeca-c6,c9-diene-1,18-dioate, a derivative of linoleic acid, is present in Arabidopsis and Brassica napus cuticle.