DICARBOXYLIC ACID

A dicarboxylic acid is an organic compound containing two carboxyl functional groups (−COOH). 
The general molecular formula for dicarboxylic acids can be written as HO2C−R−CO2H, where R can be aliphatic or aromatic. 
In general, dicarboxylic acids show similar chemical behavior and reactivity to monocarboxylic acids. 
Dicarboxylic acids are also used in the preparation of copolymers such as polyamides and polyesters. 
The most widely used dicarboxylic acid in the industry is adipic acid, which is a precursor used in the production of nylon. 
Other examples of dicarboxylic acids include aspartic acid and glutamic acid, two amino acids in the human body. 
The name can be abbreviated to diacid.

Dicarboxylic acid are acids in which there are two carboxyl groups separated by a chain of more than five carbon atoms  (n>5)  for the most part have unexceptional properties, and the carboxyl groups behave more or less independently of one another.

Dicarboxylic acids are organic compounds containing two carboxylic acid functional groups. Dicarboxylic acids generally show the same chemical behavior and reactivity as monocarboxylic acids. The ionization of the second carboxyl group occurs less readily than the first one, because more energy is required to separate a positive hydrogen ion from the anion than from the neutral molecule.

Dicarboxylic acids are important metabolic products, for example, as Krebs cycle intermediates (e.g., α-ketoglutaric acid, HOOC(CH2)2COCOOH) and the products of fatty acid oxidation. 
The simplest dicarboxylic acid is oxalic acid (HOOCCOOH), others important in biochemistry include malonic (HOOCCH2COOH), succinic (HOOC(CH2)2COOH), and glutaric (HOOC(CH2)3COOH) acids. 
The protein amino acids, aspartic (HOOCCH2CH(NH2)COOH)) and glutamic (HOOC(CH2)2CH(NH2)COOH)) acids, are also dicarboxylic acids.


Dicarboxylic Acids contain two acid moieties and have the generic structural formula of HOOC-(CH2)n-COOH. 
Long Chain Dicarboxylic Acids are all diacids whose total amount or carbon atoms is greater than nine (>9). 
Due to their physical characteristics dicarboxylic acids are especially useful for the production of high-performance polymers (polyester, polyamides), anti-corrosives, lubricants, adhesives, various coatings and many more.


Dicarboxylic acids have the capability to 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

Dicarboxylic acids are organic compounds that contain two functional carboxylic acid (–COOH) groups. 
Industrially, they are important in production of polyester, polyols, polyamides, and nylon and as a precursor to active pharmaceutical ingredients and additives. 
Dicarboxylic acids are important water-soluble components of atmospheric aerosols. 
Succinic, adipic, and glutaric acid may be harmful if inhaled, swallowed, or absorbed through skin. 
All these acids alone or in combination do not show any mutagenic effect. 
Some of the dicarboxylic acids (sebacic acid) have been advocated to have anti-hyperglycemic effect, whereas analysis of serum free fatty acids from patients with Reye's syndrome (acute encephalopathy with visceral steatosis syndrome) had revealed the presence of dicarboxylic acids in over half of the patients' total free fatty acids; both medium-chain (6–12 carbon lengths) and long-chain (14–18 carbon lengths) dicarboxylic acids were identified in such studies. 
Malathion, a well-known organophosphate pesticide, was previously marketed as Malathion dicarboxylic acid, is fetotoxic and toxic to infants and children.


Aliphatic and aromatic acids containing two carboxyl (−COOH) groups are referred to as dicarboxylic acids. 
Most of them are known by their common names, since they are naturally highly abundant as salts and are easily separated from the other substances with which they are found.

4.1 Physical Properties
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.

Dicarboxylic acids have the capability to 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 (imides pyrolysis is discussed in the next subsection).

Typical thermal decomposition of monoamides of dicarboxylic acids occurs in a manner analogous to the decomposition of dicarboxylic acids.
 When the formation of a stable cycle is possible, the pyrolysis usually generates either imides or anhydrides, depending on the molecule structure


Dicarboxylic acids that also contain an OH group in the molecule can form lactones involving one of the COOH groups


Dicarboxylic acids synthesized by the direct carboxylation of unsaturated fatty acids are important intermediates in the preparation of various polymers, plasticizers, lubricants, and other functional fluids.
The long-chain dibasic acids impart inherent high organic solvent solubility and moisture resistance, making them highly desirable in certain polymers.
Condensation polymers, such as polyamides (PAs), polyesters, and alkyd resins, have been synthesized.
The reaction of diacids with various amines produces various spinnable PAs200 and transparent PAs.
PA coatings for leather are known to provide good resistance to rubbing, scuffing, and perspiration, and also form glossy, smooth, and elastic coatings.
Diimidazolines formed by reaction with 1,2-diamines can serve as coreactants in epoxy resins.
Poly(amine–amides) from carboxystearic acid produce clear, hard, tough, abrasion-, and solvent-resistant castings and coatings.
Diacids have also been used as components in unsaturated polyester resins (UPRs), resulting in flexible and moisture-resistant materials for electrical purposes and coatings.
Varnishes, castings, laminated resins, adhesives, curing agents, and PAs that impart high gloss, excellent hardness, and flexibility to epoxy resins have been synthesized, useful in transparent films, textile fibers, or paper, and as protective coatings for metal objects.
Diesters synthesized from diacids are particularly useful as lubricants and are highly efficient low-temperature plasticizers.

Adipate Esters.
Aliphatic dicarboxylic acid esters are prepared by the esterification of diacids such as adipic or azelaic acid with C6 to C10 monohydric alcohols. 
This class of plasticizer is used to extend the useful temperature range of plasticized PVC products, by providing increased flexibility at lower temperatures. 
Di-2-ethylhexyl adipate (DOA), which is prepared by the esterification of one mole of adipic acid with two moles of 2-ethyl hexanol, is the most important plasticizer in this class. 
Another important adipate is diisononyl adipate which offers greater permanence over DOA. 
Di-2-ethylhexyl azelate (DOZ), di-2-ethylhexyl sebacate (DOS), and diisodecyl adipate are used for extremely demanding low temperature applications or low temperature applications requiring lower plastisol volatility over that of DOA. 

The adipate and azelate esters may be used as primary or as secondary plasticizers.


lthough the dicarboxylic acids do not occur in appreciable amounts as components of animal or vegetal lipids, they are in general important metabolic products of fatty acids since they originate from them by oxidation. 
Dicarboxylic acids are suitable substrates for preparation of organic acids for the pharmaceutical and food industries. 
Furthermore, they are useful materials for the preparation of fragrances, polyamides, adhesives, lubricants, and polyesters. 

 

They have the general type formula:

 

HOOC-(CH2)n-COOH

 

In vegetal, a great variety of molecular forms of dicarboxylic acids are found : 

1- simple forms with a straight carbon chain or a branched chain

2- complex forms with a dicarboxylic acid and an alkyl side chain : alkylitaconates

Dicarboxylic Acid
M.S. Parmar, in Encyclopedia of Toxicology (Third Edition), 2014

Abstract
Dicarboxylic acids are organic compounds that contain two functional carboxylic acid (–COOH) groups. Industrially, they are important in production of polyester, polyols, polyamides, and nylon and as a precursor to active pharmaceutical ingredients and additives. Dicarboxylic acids are important water-soluble components of atmospheric aerosols. Succinic, adipic, and glutaric acid may be harmful if inhaled, swallowed, or absorbed through skin. All these acids alone or in combination do not show any mutagenic effect. Some of the dicarboxylic acids (sebacic acid) have been advocated to have anti-hyperglycemic effect, whereas analysis of serum free fatty acids from patients with Reye's syndrome (acute encephalopathy with visceral steatosis syndrome) had revealed the presence of dicarboxylic acids in over half of the patients' total free fatty acids; both medium-chain (6–12 carbon lengths) and long-chain (14–18 carbon lengths) dicarboxylic acids were identified in such studies. Malathion, a well-known organophosphate pesticide, was previously marketed as Malathion dicarboxylic acid, is fetotoxic and toxic to infants and children.

Organic Geochemistry
M.A. Sephton, in Treatise on Geochemistry (Second Edition), 2014

12.1.5.4 Dicarboxylic Acids
Aliphatic dicarboxylic acids were first identified in acidified hot water extracts of Murchison (CM2), and most of the possible branched- and straight-chained isomers were detected (Lawless et al., 1974). Seventeen dicarboxylic acids were present, including 15 saturated and two unsaturated aliphatic compounds (fumaric and/or maleic acid) and, overall, they were one or two orders of magnitude higher in abundance than amino acids in the same meteorite. The chiral methyl succinic acid was present as a racemic mixture. The number of dicarboxylic acids identified in Murchison (CM2) was extended to at least 40 with compounds through C9 (Cronin et al., 1993). The calcium salt of oxalic acid was detected in Murchison (CM2) (Lawless et al., 1974), and it is possible that the dicarboxylic acids were present in the meteorite as carboxylate dianions (Cronin and Pizzarello, 1993).

The most varied components in water extracts of the Tagish Lake (C2) meteorite were the aliphatic dicarboxylic acids, including both saturated and unsaturated compounds up to C10 (Pizzarello et al., 2001), and a total of 44 of these compounds were detected (Pizzarello and Huang, 2002). Linear, saturated acids dominated and decreased in amount with increasing chain length. The more abundant species occurred as dicarboximides. A simultaneous extraction of Murchison (CM2) produced dicarboxylic acids of similar abundance and distribution, albeit with a slightly lower ratio of linear to branched acids (Pizzarello and Huang, 2002). Saturated or partially unsaturated nitriles and dinitriles were proposed as precursors as their hydrolysis upon exposure to water, could produce the dicarboxylic acids and other carboxylated species found in Tagish Lake (Pizzarello and Huang, 2002).

Dicarboxylic acids were abundant in hot water extracts of Ivuna (CI1) and Bells (CM2); these meteorites contained linear dicarboxylic acids between C4 and C14, a number of branched species up to C8, and unsaturated species between C4 and C6. The distribution of dicarboxylic acids in Ivuna (CI1) and Bells (CM2) was similar to that observed previously for Murchison (Pizzarello and Huang, 2002). Tricarboxylic acids (Cooper et al., 2011) were searched for but not found (Monroe and Pizzarello, 2011).

Carboxylic Acids
In Enological Chemistry, 2012

4 Dicarboxylic Acids
Aliphatic and aromatic acids containing two carboxyl (−COOH) groups are referred to as dicarboxylic acids. Most of them are known by their common names, since they are naturally highly abundant as salts and are easily separated from the other substances with which they are found.

4.1 Physical Properties
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.

4.2 Chemical Properties
Dicarboxylic acids are dibasic or diprotic acids and therefore have two dissociation constants, Ka1 and Ka2:

Each carboxyl group can ionize independently but, as shown in Table 8.4, the first carboxyl group is generally much more acidic than the second (lower pKa, dissociates more easily), especially when the two are in close proximity. This is explained by the inductive electron-acceptor effect of the second carboxyl group that increases the stability of the ionized group and therefore also the acidity.

TABLE 8.4. Structure and Properties of Dicarboxylic Acids

Structure    Common Name    IUPAC Name    Melting Point (°C)    Ka1    Ka2
HO-CO-OH    Carbonic            3.02 × 10−7    6.31 × 10−11
HOOC-COOH    Oxalic acid    Ethanedioic    189    3.5 × 10−2    4.0 × 10−5
HOOC-CH2-COOH    Malonic acid    Propanedioic    136    1.4 × 10−3    2.2 × 10−6
HOOC-(CH2)2-COOH    Succinic acid    Butanedioic    185    6.4 × 10−5    2.5 × 10−6
HOOC-(CH2)3-COOH    Glutaric acid    Pentanedioic    98    4.5 × 10−5    3.8 × 10−6
HOOC-(CH2)4-COOH    Adipic acid    Hexanedioic    151    3.7 × 10−5    2.4 × 10−6
Maleic    cis-2-butenedioic acid    130    1.2 × 10−2    3 × 10−7
Fumaric    trans-2-butenedioic acid    302    9.3 × 10−4    2.9 × 10−5
Phthalic acid    o-benzenedicarboxylic acid    231    1.2 × 10−3    3 × 10−6
Isophthalic acid    m-benzenedicarboxylic acid    348    2.9 × 10−4    2.7 × 10−5
Terphthalic acid    p-benzenedicarboxylic acid    300 (sublimation)    1.5 × 10−4    –
The dipolar structure of the C=O double bond in the carboxylate ion stabilizes the negative charge that is produced by ionization of the carboxyl group; however, Ka2 is lower than K1 because the presence of a carboxylate ion reduces the acidity of the second carboxyl group due to the electrostatic repulsion between the two negative charges on the dicarboxylate ion. This effect will be lessened as the length of the chain separating the carboxyl groups increases. Accordingly, the difference between Ka1 and Ka2 will reduce with increasing chain length.

Among other chemical properties of biological interest, all dicarboxylic acids are stable in the presence of oxidizing agents, with the exception of oxalic acid, which can be oxidized to CO2, and hence functions as a reducing agent.

The effect of heat on these acids depends upon the position of the carboxyl groups in the chain. Thus, acids in which the second carboxyl group is in an α or β position are decarboxylated by heat:

Acids with a second carboxyl group at positions γ or δ generate cyclic anhydrides:


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Synthetic biodegradable medical polymer
R. Ghadi, ... X. Zhang, in Science and Principles of Biodegradable and Bioresorbable Medical Polymers, 2017

5.4.3 Dehydrative coupling
Dicarboxylic acid monomer can be converted into a polyanhydride using a dehydrative coupling agent under ambient conditions. The dehydrative coupling agent, N'N bis [2-oxo-3-oxazolidinyl] phosphonic chloride, was the most effective in forming polyanhydrides. A Dp around 20 was achieved (Leong et al., 1987). It is essential that the catalyst be ground into fine particles before use and should be freshly prepared. A disadvantage of this method is that the final product contains polymerisation by-products that have to be removed by washing with protic solvents such as methanol or cold dilute hydrochloric acid. The washing by protic solvents may evoke some hydrolysis of the polymer. Coupling agents such as phosgene and diphosgene in the presence of a base, tertiary amines or carbonate salt, can also be used for the polyanhydride formation (Domb et al., 1988).

Pyrolysis of Various Derivatives of Carboxylic Acids
Serban C. Moldoveanu, in Pyrolysis of Organic Molecules (Second Edition), 2019

Amides of Dicarboxylic Acids
Dicarboxylic acids have the capability to 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 (imides pyrolysis is discussed in the next subsection).

Typical thermal decomposition of monoamides of dicarboxylic acids occurs in a manner analogous to the decomposition of dicarboxylic acids. When the formation of a stable cycle is possible (see Subchapter 12.2), the pyrolysis usually generates either imides or anhydrides, depending on the molecule structure [6]. Two different examples are shown below:

(14.6.8)
Phthalic acid monoamide as well as substituted phthalic acid monoamide generate the corresponding imide by thermal decomposition.

When a cycle formation is not feasible due to steric constraints, the decomposition takes place by different paths, usually with the elimination of CO2 from the carboxyl group. As an example, a monoamide of a derivative of malonic acid decomposes around 165°C, as shown below [5]:

(14.6.9)
The same trend as for the decomposition of dicarboxylic acids is seen for the decomposition of diamides. In the case of diamides, where the formation of a stable cycle is not possible, the decomposition leads to a mixture of products. Oxalic acid diamide, for example, decomposes with the formation of NH3, CO, HCN, urea, and NH4OCN (ammonium cyanate). On the other hand, the diamide of succinic acid (succinamide) generates by thermal decomposition around 200°C mainly succinimide, as shown in the following reaction:

(14.6.10)
Similarly, phthalic acid diamide (phthalamide) changes easily into phthalimide by the elimination of NH3, and maleic acid diamide changes into maleimide. The formation of stable five-atom cyclic imides explains the reactions in the case of the diamides of succinic, maleic, and phthalic acids.

A diamide also can be generated from adipic acid (adipamide). This compound would produce by pyrolysis a seven-atom cycle, when it follows a reaction similar to (14.6.10). However, the stability of a seven-atom cycle is not as high as that of five- or six-atom cycles, and adipic acid diamide generates more than one major pyrolysis product. An experiment was performed on adipic acid diamide starting with a 1.0 mg sample at Teq = 900°C, β = 10°C/ms, THt = 10 s, and housing temperature Thou = 280°C. The analysis of the pyrolyzate was performed under conditions given in Table 1.4.1. The pyrogram for adipic acid diamide is shown in Fig. 14.6.1. The compound identifications and their relative molar content in 100 moles of pyrolyzate are given in Table 14.6.1.

Fig. 14.6.1
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Fig. 14.6.1. Pyrogram obtained at 900°C for adipamide (MW = 144).

Table 14.6.1. Peak Identification as a Function of Retention Time for the Pyrogram of Adipamide Shown in Fig. 14.6.1

No.    Compound    Retention Time (Min)    MW    CAS#    Moles %
1    Carbon dioxide    4.30    44    124-38-9    3.37
2    Cyclopentanone    27.39    84    120-92-3    6.80
3    6-Methyl-3-pyridinol    45.84    109    1121-78-4    0.82
4    Hexanedinitrile    48.61    108    111-69-3    36.03
5    Azaperhydroepine-2,7-dione    49.01    127    N/A    9.94
6    2-Imino-cyclopentanecarbonitrile    49.37    108    2321-76-8    0.85
7    5-Cyanopentanoic acid    50.17    127    5264-33-5    30.55
8    5-Cyanopentanamide    56.05    126    N/A    11.64
H2, H2O, HCN, CO, NH3, CH4, and N2 were not included due to the MS settings.

Note: Bold numbers indicate major component in the pyrolyzate.


The identification in the pyrolyzate of the expected adipimide (azaperhydroepine-2,7-dione) was done tentatively based on the mass spectrum shown in Fig. 14.6.2.

Fig. 14.6.2
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Fig. 14.6.2. Mass spectrum of (tentatively) azaperhydroepine-2,7-dione.

As shown in Table 14.6.1, the adipimide (azaperhydroepine-2,7-dione) is not the main pyrolysis product of adipic acid diamide, but it is present at relatively high levels. This compound is generated by the following reaction:

(14.6.11)
The identification of azaperhydroepine-2,7-dione was done only tentatively because its mass spectrum is not available in common mass spectral libraries (see Fig. 14.6.2).

The main pyrolysis product of adipic acid diamide is hexandinitrile, which is generated in a reaction as shown below:

(14.6.12)
Partial dehydration with the elimination of only one water molecule generated 5-cyanopentanamide, also present in the pyrogram at a relatively high level.

Another major component of pyrolysis of adipic acid diamide is 5-cyanoadipic acid (5-cyanopentanoic acid). This compound has one amide group hydrolyzed to acid and the other group changed into a nitrile by water elimination. The formation of 5-cyanoadipic acid may take place by various paths. One possibility is the hydrolysis of one amide group from the initial adipic acid diamide into an acid and the elimination of water from the remaining amide group. Another alternative is the formation of a dinitrile that is further hydrolyzed at one nitrile group to acid. Other paths are also possible such as formation of the (cyclic) adipimide (azaperhydroepine-2,7-dione), followed by a rearrangement.

Pyrolysis of Carboxylic Acids
Serban C. Moldoveanu, in Pyrolysis of Organic Molecules (Second Edition), 2019

Lactonic Acids
Dicarboxylic acids that also contain an OH group in the molecule can form lactones involving one of the COOH groups. For example, a β-lactone can be formed from malic acid (hydroxybutanedioic acid) by pyrolysis at lower temperatures (at higher temperatures maleic anhydride is formed by the elimination of a water molecule). This compound decomposes as shown in the following reaction:

(12.4.17)
The four-atom cycle tension and the stability of the tetrahydrofurandione cycle easily explain this reaction path. Thermal decomposition of γ-valerolactone carboxylic acid simply generates CO2 and forms γ-valerolactone, which is also a stable compound. The reaction is shown below:

(12.4.18)
These reactions show that the decarboxylation takes place much more easily in comparison with the decomposition of the trihydrofuranone cycle. Other acids with the COOH group attached in 3-position in the furanone cycle also decompose with decarboxylation [5].

Some lactonic acids eliminate CO2, but the reaction takes place with the opening of the lactone ring and the formation of an unsaturated acid, as shown below for β,γ-dimethyl-paraconic acid (2,3-dimethyl-5-oxo-2,3,4-trihydrofuran-3-carboxylic acid):

(12.4.19)
However α-ethyl-γ-methylparaconic acid generates both diethylmaleic anhydride and α-ethyl-γ-methylpentenoic acid.

Polymers for a Sustainable Environment and Green Energy
T.W. Abraham, R. Höfer, in Polymer Science: A Comprehensive Reference, 2012

10.03.3.4.1(iv) Applications
Dicarboxylic acids synthesized by the direct carboxylation of unsaturated fatty acids are important intermediates in the preparation of various polymers, plasticizers, lubricants, and other functional fluids. 
The long-chain dibasic acids impart inherent high organic solvent solubility and moisture resistance, making them highly desirable in certain polymers.
Condensation polymers, such as polyamides (PAs), polyesters, and alkyd resins, have been synthesized.
The reaction of diacids with various amines produces various spinnable PAs200 and transparent PAs.
PA coatings for leather are known to provide good resistance to rubbing, scuffing, and perspiration, and also form glossy, smooth, and elastic coatings.
Diimidazolines formed by reaction with 1,2-diamines can serve as coreactants in epoxy resins.
Poly(amine–amides) from carboxystearic acid produce clear, hard, tough, abrasion-, and solvent-resistant castings and coatings.
Diacids have also been used as components in unsaturated polyester resins (UPRs), resulting in flexible and moisture-resistant materials for electrical purposes and coatings.
Varnishes, castings, laminated resins, adhesives, curing agents, and PAs that impart high gloss, excellent hardness, and flexibility to epoxy resins have been synthesized, useful in transparent films, textile fibers, or paper, and as protective coatings for metal objects.
Diesters synthesized from diacids are particularly useful as lubricants and are highly efficient low-temperature plasticizers.

1,2,5-Oxadiazoles and their Benzo Derivatives
R.M. Paton, in Comprehensive Heterocyclic Chemistry, 1984

Furazan- and furoxan-carboxylic acids and their derivatives
The dicarboxylic acid compounds are apt to undergo ring cleavage reactions, particularly in the presence of alkali; boiling water converts furazandicarboxylic acid to cyanooximinoacetic acid, presumably via initial decarboxylation to the monoacid.

Acid derivatives including esters, amides, halides and nitriles are readily accessible. 
Dicyanofuroxan shows in its reactions some similarities to phthalonitrile 〈75LA1029〉; it also provides a source of fused pyridazino- and oxazino-furoxans and via addition with hydrazine and hydroxylamine, respectively 〈82H(19)1063〉. 
The tetronic acid compound yields a hydroxyamide on aminolysis 〈79S977〉.

Arylfurazancarboxamides on treatment with alkaline hypochlorite undergo Hofmann degradation to the amines; likewise carbamates result from Curtius rearrangement of furazanylacyl azides in the presence of alcohols.

PLASTICIZERS
ALLEN D. GODWIN, in Applied Polymer Science: 21st Century, 2000

Adipate Esters.
Aliphatic dicarboxylic acid esters are prepared by the esterification of diacids such as adipic or azelaic acid with C6 to C10 monohydric alcohols. 
This class of plasticizer is used to extend the useful temperature range of plasticized PVC products, by providing increased flexibility at lower temperatures. Di-2-ethylhexyl adipate (DOA), which is prepared by the esterification of one mole of adipic acid with two moles of 2-ethyl hexanol, is the most important plasticizer in this class. Another important adipate is diisononyl adipate which offers greater permanence over DOA. Di-2-ethylhexyl azelate (DOZ), di-2-ethylhexyl sebacate (DOS), and diisodecyl adipate are used for extremely demanding low temperature applications or low temperature applications requiring lower plastisol volatility over that of DOA. The adipate and azelate esters may be used as primary or as secondary plasticizers.

Plasticizers
Allen D. Godwin, in Applied Plastics Engineering Handbook, 2011

Dibasic Acid Esters
Aliphatic dicarboxylic acid esters are prepared by the esterification of diacids such as adipic or azelaic acid with C6 to C10 monohydric alcohols. 
This class of plasticizer is usually used to help extend the useful temperature range of plasticized PVC products, by providing increased flexibility at lower temperatures. DEHA, which is prepared by the esterification of one mole of adipic acid with two moles of 2-ethyl hexanol, is the most important plasticizer in this class. 
Another important adipate is diisononyl adipate (DINA) which offers greater permanence over DEHA. 
Di-2-ethylhexyl azelate (DEHZ), di-2-ethylhexyl sebacate (DEHS), and diisodecyl adipate (DIDA) are used for extremely demanding low-temperature applications or low-temperature applications requiring lower volatility over that of DEHA. 
The adipate and azelate esters may be used as primary or as secondary plasticizers.


Dicarboxylic acid is a compound containing two carboxylic acid, -COOH, groups. 
Straight chain examples are shown in table. 
The general formula is HOOC(CH2)nCOOH, where oxalic acid's n is 0, n=1 for malonic acid, n=2 for succinic acid, n=3 for glutaric acid, and etc. 

In substitutive nomenclature, their names are formed by adding -dioic' as a suffix to the name of the parent compound. 
They can yield two kinds of salts, as they contain two carboxyl groups in its molecules. 
The range of carbon chain lengths is from 2, but the longer than C 24 is very rare. 
The term long chain refers to C 12 up to C 24 commonly. 
Carboxylic acids have industrial application directly or indirectly through acid halides, esters, salts, and anhydride forms, polymerization, and etc. 
Dicarboxylic acids can yield two kinds of salts or esters, as they contain two carboxyl groups in one molecule. 
It is useful in a variety of industrial applications include;
Plasticizer for polymers
Biodegradable solvents and lubricants
Engineering plastics
Epoxy curing agent
Adhesive and powder coating
Corrosion inhibitor
Perfumery and pharmaceutical
Electrolyte
There are almost infinite esters obtained from carboxylic acids. 
Esters are formed by removal of water from an acid and an alcohol. 
Carboxylic acid esters are used as in a variety of direct and indirect applications. 
Lower chain esters are used as flavouring base materials, plasticizers, solvent carriers and coupling agents. Higher chain compounds are used as components in metalworking fluids, surfactants, lubricants, detergents, oiling agents, emulsifiers, wetting agents textile treatments and emollients.
They are also used as intermediates for the manufacture of a variety of target compounds. 
The almost infinite esters provide a wide range of viscosity, specific gravity, vapor pressure, boiling point, and other physical and chemical properties for the proper application selections.

C length (Straight)
Product
CAS #
Melting Point
Boiling Point

C 2
Oxalic Acid
(Ethanedioic Acid)    
144-62-7    
189 - 191 C

Sublimes

C 3
Malonic Acid
(Propanedioic Acid)
141-82-2    
131 - 135 C    
Decomposes

C 4
Succinic Acid
(Butanedioic Acid)
110-15-6    
185 - 190 C
235 C

C 5
Glutaric Acid
(Pentanedioic Acid)
110-94-1    
95 - 99 C
302 C

C 6
Adipic Acid
(Hexanedioic Acid)
124-04-9    
151 - 153 C
265 C at 100 mmHg

C 7
Pimelic Acid
(Heptanedioic Acid)
111-16-0    
105 - 106 C
212 C at 10 mmHg

C 8
Suberic Acid
(Octanedioic Acid)
505-48-6    
143 - 144 C
230 C at 15 mmHg

C 9
Azelaic Acid
(Nonanedioic Acid)
123-99-9    
100 - 103 C
237 C at 15 mmHg

C 10
Sebacic Acid
(Decanedioic Acid)
111-20-6    
131 - 134 C
294 at 100 mmHg

C 11
Undecanedioic acid    
1852-04-6    
109 - 110 C

 

C 12
Dodecanedioic acid    
693-23-2    
128 - 129 C
245 C at 10 mmHg

C 13
Brassylic acid
(Tridecanedioic acid)    
505-52-2    
112 - 114 C

 

C 14
Tetradecanedioic acid    
821-38-5    
126 - 128 C

 

C 15
Pentadecanedioic acid    
1460-18-0    
 

C 16
Thapsic acid
(Hexadecanedioic acid)    
505-54-4    
124 - 126 C

 
C 18
Octadecanedioic acid
871-70-5    
 

 

Common name    Systematic IUPAC name
Oxalic acid    ethanedioic acid
Malonic acid    propanedioic acid
Succinic acid    butanedioic acid
Glutaric acid    pentanedioic acid
Adipic acid    hexanedioic acid
Pimelic acid    heptanedioic acid
Suberic acid    octanedioic acid
Azelaic acid    nonanedioic acid
Sebacic acid    decanedioic acid
    undecanedioic acid
    dodecanedioic acid
Brassylic acid    tridecanedioic acid
Thapsic acid    hexadecanedioic acid
Japanic acid    heneicosadioic acid
Phellogenic acid    docosanedioic acid
Equisetolic acid    triacontanedioic acid

Occurrence
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. 
It was first obtained by oxidation of castor oil (ricinoleic acid) with nitric acid. 
It is now produced industrially by oxidation of cyclohexanol or cyclohexane, mainly for the production of Nylon 6-6. 
It 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 (Greek pimelh, fat) was also 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 produced when castor oil is oxidised. 

Suberic acid is used in the manufacture of alkyd resins and in the synthesis of 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 for 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 a variety of aerobic and anaerobic micro-organisms present 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 be able to enhance the resistance of plants to infections.

Sebacic acid, named from sebum (tallow). 
Thenard isolated this compound from distillation products of beef tallow in 1802. 
It is produced industrially by alkali fission of castor oil.
Sebacic acid and its derivatives have a variety of industrial uses as plasticizers, lubricants, diffusion pump oils, cosmetics, candles, etc. 
It is also used in the synthesis of polyamide, as nylon, and of alkyd resins. 
An isomer, isosebacic acid, has several applications in the manufacture of vinyl resin plasticizers, extrusion plastics, adhesives, ester lubricants, polyesters, polyurethane resins and synthetic rubber.

Brassylic acid can be produced from erucic acid by ozonolysis but also by microorganisms (Candida sp.) from tridecane. 
This diacid is produced on a small commercial scale in Japan for the manufacture of fragrances.

Dodecanedioic acid is used in the production of 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 is a mixture containing triglycerides of C21, C22 and C23 dicarboxylic acids obtained from the sumac tree (Rhus sp.).

A large survey of the dicarboxylic 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 in relation with 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 as diagnostic for suberin. 
With C18:1 and C18:2, their content amount from 24 to 45% of 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 specifically contained a large variety of dicarboxylic acids.
This is probably the most important difference between these microorganisms and other marine bacteria. 
Dioic fatty acids from C16 to C22 were found in an hyperthermophilic archaeon, Pyrococcus furiosus. 
Short and medium chain (up to 11 carbon atoms) dioic acids have been discovered in Cyanobacteria of the genus Aphanizomenon.[8]

Dicarboxylic acids may be produced by ω-oxidation of fatty acids during their catabolism. 
It was discovered that these compounds appeared in urine after administration of tricaprin and triundecylin. 
Although the significance of their biosynthesis remains poorly understood, it was demonstrated that ω-oxidation occurs in rat liver but at a low rate, needs oxygen, NADPH and cytochrome P450. 
It was later shown that this reaction is more important in starving or diabetic animals where 15% of palmitic acid is subjected to ω-oxidation and then tob-oxidation, this generates malonyl-coA which is further used in saturated fatty acid synthesis.
The determination of the dicarboxylic acids generated by permanganate-periodate oxidation of monoenoic fatty acids was useful to study the position of the double bond in the carbon chain


Branched-chain dicarboxylic acids
Long-chain dicarboxylic acids containing vicinal dimethyl branching near the centre of the carbon chain have been discovered in the genus Butyrivibrio, bacteria which 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.
It was shown that about 10% of their lipid fraction were 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 eubacterium Themanaerobacter ethanolicus.
The most abundant diacid was the C30 a,ω-13,16-dimethyloctacosanedioic acid.

Biphytanic diacids are present in geological sediments and are considered as tracers of past anaerobic oxidation of methane.
Several forms without or with one or two pentacyclic rings have been detected in Cenozoic seep limestones. 
These lipids may be unrecognized metabolites from Archaea.


Crocetin
Crocetin is the core compound of crocins (crocetin glycosides) which are the main red pigments of the stigmas of saffron (Crocus sativus) and the fruits of gardenia (Gardenia jasminoides). 
Crocetin is a 20-carbon chain dicarboxylic acid which is a diterpenenoid and can be considered as a carotenoid. 
It was the first plant carotenoid to be recognized as early as 1818 while the history of saffron cultivation reaches back 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 major biologically active ingredients of saffron, namely the four crocins and crocetin

Maleic acid    (Z)-Butenedioic acid
Fumaric acid    (E)-Butenedioic acid
Acetylenedicarboxylic acid    But-2-ynedioic acid
Glutaconic acid    (Z)-Pent-2-enedioic acid
    (E)-Pent-2-enedioic acid
    2-Decenedioic acid
Traumatic acid    Dodec-2-enedioic acid
Diunsaturated    Muconic acid
    Glutinic acid
    (Allene-1,3-dicarboxylic acid)
Branched    Citraconic acid
    Mesaconic acid
    Itaconic acid


Traumatic acid, was among the first biologically active molecules isolated from plant tissues. 
This dicarboxylic acid was shown to be a potent wound healing agent in plant 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 diunsaturated dicarboxylic acid has been reported as a component of the surface waxes or polyesters of some plant species. 
Thus, octadeca-c6,c9-diene-1,18-dioate, a derivative of linoleic acid, is present in Arabidopsis and Brassica napus cuticle.

Alkylitaconates

Itaconic acid

Several dicarboxylic acids having an alkyl side chain and an itaconate core have been isolated from lichens and fungi, itaconic acid (methylenesuccinic acid) being a metabolite produced by filamentous fungi. 
Among these compounds, several analogues, called chaetomellic acids with different chain lengths and degrees of unsaturation have been isolated from various species of the lichen Chaetomella. 
These molecules were shown to be valuable as basis for the development of anticancer drugs due to their strong farnesyltransferase inhibitory effects.

A series of alkyl- and alkenyl-itaconates, known as ceriporic acids (Pub Chem 52921868), were found in cultures of a selective lignin-degrading fungus (white rot fungus), Ceriporiopsis subvermispora.
The absolute configuration of ceriporic acids, their stereoselective biosynthetic pathway and the diversity of their metabolites have been discussed in detail.[25]


Tartronic acid    2-Hydroxypropanedioic acid
Mesoxalic acid    Oxopropanedioic acid
Malic acid    Hydroxybutanedioic acid
Tartaric acid    2,3-Dihydroxybutanedioic acid
Oxaloacetic acid    Oxobutanedioic acid
Aspartic acid    2-Aminobutanedioic acid
dioxosuccinic acid    dioxobutanedioic acid
α-hydroxyGlutaric acid    2-hydroxypentanedioic acid
Arabinaric acid    2,3,4-Trihydroxypentanedioic acid
Acetonedicarboxylic acid    3-Oxopentanedioic acid
α-Ketoglutaric acid    2-Oxopentanedioic acid
Glutamic acid    2-Aminopentanedioic acid
Diaminopimelic acid    (2R,6S)-2,6-Diaminoheptanedioic acid
Saccharic acid    (2S,3S,4S,5R)-2,3,4,5-Tetrahydroxyhexanedioic acid

Aromatic dicarboxylic acids


Phthalic acid    Benzene-1,2-dicarboxylic acid
o-phthalic acid    
Isophthalic acid    Benzene-1,3-dicarboxylic acid
    
    
m-phthalic acid    
Terephthalic acid    Benzene-1,4-dicarboxylic acid
    
    
p-phthalic acid    
Diphenic acid    2-(2-Carboxyphenyl)benzoic acid
    
Biphenyl-2,2′-dicarboxylic acid    
2,6-Naphthalenedicarboxylic acid    2,6-Naphthalenedicarboxylic acid

Properties
Dicarboxylic acids are crystalline solids. 
Solubility in water and melting point of the α,ω- compounds progress in a series as the carbon chains become longer with 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 values of ca. 4.5 and 5.5 as the separation between the two carboxylate groups increases. 
Thus, in aqueous solution at pH about 7, typical of biological systems, the Henderson–Hasselbalch equation indicates they exist predominantly as dicarboxylate anions.

The dicarboxylic acids, especially the small and linear ones, can be used as crosslinking reagents.
Dicarboxylic acids where the carboxylic groups are separated by none or one carbon atom decompose when they are heated to give off carbon dioxide and leave behind a monocarboxylic acid.

Blanc's Rule says that heating a barium salt of a dicarboxylic 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 (3,4 or 5). 
So succinic acid will yield succinic anhydride. 
For acids with carboxylic groups at position 1 and 6 this dehydration causes loss of carbon dioxide and water to form a cyclic ketone, for example adipic acid will form cyclopentanone.

Derivatives
As for monofunctional carboxylic acids, derivatives of the same types exist. 
However, there is the added complication that either one or two of the carboxylic groups could be altered. 
If only one is changed then the derivative is termed "acid", and if both ends are altered it is called "normal". 
These derivatives include salts, chlorides, esters, amides, and anhydrides. 
In the case of anhydrides or amides, two of the carboxyl groups can come together to form a cyclic compound, for example succinimide

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