BROWSE BY STRUCTURE
Properties, Types, Comparisons, Uses & Suppliers
A dicarboxylic acid contains two carboxyl groups. The two carboxyl protons dissociate in separate steps, so a single pKa does not describe the whole acid–base system. Chain length, a double bond and additional groups distinguish the examples below.
Oxalic has no methylene spacer; malonic has one; succinic has two. Fumaric adds an E/trans double bond. Malic and tartaric also belong to the hydroxy-acid family.
Sources: OpenStax · Structure and properties of carboxylic acids (opens new tab) · OpenStax · Substituent effects on acidity (opens new tab)
Membership and structural distinctions are grounded in the linked identity records in the comparison below. The categories overlap intentionally.
| Acid / formula | Carbons / COOH | Profile form | pKa reference | Structural distinction / specification |
|---|---|---|---|---|
| Adipic AcidC₆H₁₀O₄ · CAS 124-04-9 | 6 carbons 2 COOH | Solid | See compound referenceNo number repeated here. | Four methylene groups between two carboxyl groups.Specify process-specific impurity limits and the six-carbon diacid identity.Identity source (opens new tab) · Technical reference |
| Azelaic AcidC₉H₁₆O₄ · CAS 123-99-9 | 9 carbons 2 COOH | Free acid | See compound referenceNo number repeated here. | Seven CH₂ groups separate its two carboxyl groups. There is no alkene or stereocenter in the neutral free-acid identity.TCI’s verified Austria-facing prices are EUR; Sigma and Wako listings are US dollar catalogs. Wako Practical Grade 95% titration is not equivalent to a 98% reagent or a pharmaceutical specification. No currency conversion or supplier-price ranking is supplied.Identity source (opens new tab) · Technical reference |
| Fumaric AcidC₄H₄O₄ · CAS 110-17-8 | 4 carbons 2 COOH | Solid | 3.03 / 4.54 (25 °C)Reference & conditions (opens new tab) | An E/trans double bond between the carboxyl-bearing carbons.Confirm fumaric E/trans identity rather than maleic cis form or a fumarate salt.Identity source (opens new tab) · Technical reference |
| Glutaric AcidC₅H₈O₄ · CAS 110-94-1 | 5 carbons 2 COOH | Free acid | See compound referenceNo number repeated here. | Two terminal COOH groups flank a three-carbon methylene spacer. There is no additional hydroxyl group, carbon–carbon double bond or stereocenter in this free-acid identity.The displayed products are neat solids. TCI G0245 is a different commercial form with 50–55% w/w concentration by titration; that is not 50–55% chemical purity and it is excluded from the neat-product table. Merck acidimetric assay and TCI GC are distinct measurements.Identity source (opens new tab) · Technical reference |
| Isophthalic AcidC₈H₆O₄ · CAS 121-91-5 | 8 carbons 2 COOH | Free acid | See compound referenceNo number repeated here. | One ring carbon lies between the two COOH-bearing carbons along the shorter ring path. This positional arrangement differs from both neighboring ortho groups and opposite para groups; the neutral identity is achiral.Wako’s 95% capillary-GC 1st Grade is not equivalent to the 99% TCI or Sigma products. Neutralization titration does not itself prove positional identity. A clear solution in NaOH is not the solubility of neutral acid in water.Identity source (opens new tab) · Technical reference |
| Maleic AcidC₄H₄O₄ · CAS 110-16-7 | 4 carbons 2 COOH | Z / cis free acid | See compound referenceNo number repeated here. | Two carboxyl groups lie on the same side of the carbon–carbon double bond. Fumaric acid places them on opposite sides. The same formula and molecular weight do not establish interchangeable identity.TCI M0006 specifies minimum 99% titration but minimum 98% GC. Merck 800380 specifies HPLC area and acidimetric assays separately. All displayed entries are free-acid solids; Wako’s discontinued 0.1 mol/L item is excluded.Identity source (opens new tab) · Technical reference |
| Malic AcidC₄H₆O₅ · CAS 6915-15-7 | 4 carbons 2 COOH | Solid · DL identity | See compound referenceNo number repeated here. | A hydroxy diacid with one stereocenter; this profile uses DL identity.Specify DL, L, or D form and require stereochemical evidence when relevant.Identity source (opens new tab) · Technical reference |
| Malonic AcidC₃H₄O₄ · CAS 141-82-2 | 3 carbons 2 COOH | Solid | See compound referenceNo number repeated here. | One methylene group between two carboxyl groups.Match the free-acid identity, grade, assay method and lot documentation.Identity source (opens new tab) · Technical reference |
| Oxalic AcidC₂H₂O₄ · CAS 144-62-7 | 2 carbons 2 COOH | Solid · anhydrous identity | 1.27 / 4.266 (25 °C, water, zero ionic strength)Reference & conditions (opens new tab) | Two carboxyl carbons directly joined, without a methylene spacer.Specify anhydrous or dihydrate; for a solution, state normality, temperature, and method.Identity source (opens new tab) · Technical reference |
| Phthalic AcidC₈H₆O₄ · CAS 88-99-3 | 8 carbons 2 COOH | Free acid | See compound referenceNo number repeated here. | Two neighboring ring carbons carry COOH groups. Their adjacent arrangement is positional isomerism, not a cis/trans alkene designation. The neutral acid is achiral.TCI uses GC and titration, Wako uses capillary GC and Sigma’s ACS reagent assay method is unstated. Positional identity, water and anhydride impurity need their own controls. ACS or JP test-reagent terminology does not establish pharmaceutical-ingredient suitability.Identity source (opens new tab) · Technical reference |
| Pimelic AcidC₇H₁₂O₄ · CAS 111-16-0 | 7 carbons 2 COOH | Free acid | See compound referenceNo number repeated here. | Two carboxyl groups terminate a chain containing five CH₂ groups. The neutral free acid is achiral and has no carbon–carbon double bond.TCI lists GC and neutralization titration independently. Wako states 99% titration without a named grade. Sigma’s 98% assay method is unstated, and its 25 g page shows both a list price and a web promotion; no lowest-price ranking is supplied.Identity source (opens new tab) · Technical reference |
| Sebacic AcidC₁₀H₁₈O₄ · CAS 111-20-6 | 10 carbons 2 COOH | Free acid | See compound referenceNo number repeated here. | Eight methylene groups connect its two terminal carboxyl groups. Decanedioic acid is distinct from decanoic acid, which has only one carboxyl group.TCI lists minimum 98% GC and titration; Wako 1st Grade specifies 97% titration; Sigma states 99% without a retrieved assay method. Sigma’s 250 g list and promotional prices are labeled separately. Mass packages do not establish identical impurity or processing specifications.Identity source (opens new tab) · Technical reference |
| Suberic AcidC₈H₁₄O₄ · CAS 505-48-6 | 8 carbons 2 COOH | Free acid | See compound referenceNo number repeated here. | Six methylene groups connect two terminal carboxyl groups. Octanedioic acid is the free acid; disuccinimidyl suberate is a chemically activated ester derivative.TCI’s 99% GC and titration thresholds, Wako’s 98% titration and Sigma’s method-unspecified 98% are separate specifications. An analytical-standard grade from Supelco 75462 is not transferred to Sigma S5200 or another reagent.Identity source (opens new tab) · Technical reference |
| Succinic AcidC₄H₆O₄ · CAS 110-15-6 | 4 carbons 2 COOH | Solid | See compound referenceNo number repeated here. | A saturated four-carbon chain with two carboxyl groups.Specify free acid versus succinate salt and the four-carbon backbone.Identity source (opens new tab) · Technical reference |
| Tartaric AcidC₄H₆O₆ · CAS 87-69-4 | 4 carbons 2 COOH | Solid · L-(+) identity | 3.036 / 4.366 (25 °C, water, zero ionic strength; L-(+) form)Reference & conditions (opens new tab) | A hydroxy diacid with two stereocenters; this profile uses L-(+).Require L-(+) identity, stereochemical specification, and separate chemical and optical assay.Identity source (opens new tab) · Technical reference |
| Terephthalic AcidC₈H₆O₄ · CAS 100-21-0 | 8 carbons 2 COOH | Neutral free acid; water and derivatives specified separately | See compound referenceNo number repeated here. | The 1,4, or para, arrangement is a molecular-connectivity identity. It is distinct from 1,2 phthalic acid and 1,3 isophthalic acid despite sharing their formula and molecular weight.Laboratory GC, titration and method-unspecified products are not automatically purified terephthalic acid qualified for an industrial polymer line. Wako 95% capillary GC differs from the 98–99% entries. Confirm para identity and process-specific impurities.Identity source (opens new tab) · Technical reference |
Four methylene groups between two carboxyl groups.
Specify process-specific impurity limits and the six-carbon diacid identity.
Seven CH₂ groups separate its two carboxyl groups. There is no alkene or stereocenter in the neutral free-acid identity.
TCI’s verified Austria-facing prices are EUR; Sigma and Wako listings are US dollar catalogs. Wako Practical Grade 95% titration is not equivalent to a 98% reagent or a pharmaceutical specification. No currency conversion or supplier-price ranking is supplied.
An E/trans double bond between the carboxyl-bearing carbons.
Confirm fumaric E/trans identity rather than maleic cis form or a fumarate salt.
Two terminal COOH groups flank a three-carbon methylene spacer. There is no additional hydroxyl group, carbon–carbon double bond or stereocenter in this free-acid identity.
The displayed products are neat solids. TCI G0245 is a different commercial form with 50–55% w/w concentration by titration; that is not 50–55% chemical purity and it is excluded from the neat-product table. Merck acidimetric assay and TCI GC are distinct measurements.
One ring carbon lies between the two COOH-bearing carbons along the shorter ring path. This positional arrangement differs from both neighboring ortho groups and opposite para groups; the neutral identity is achiral.
Wako’s 95% capillary-GC 1st Grade is not equivalent to the 99% TCI or Sigma products. Neutralization titration does not itself prove positional identity. A clear solution in NaOH is not the solubility of neutral acid in water.
Two carboxyl groups lie on the same side of the carbon–carbon double bond. Fumaric acid places them on opposite sides. The same formula and molecular weight do not establish interchangeable identity.
TCI M0006 specifies minimum 99% titration but minimum 98% GC. Merck 800380 specifies HPLC area and acidimetric assays separately. All displayed entries are free-acid solids; Wako’s discontinued 0.1 mol/L item is excluded.
A hydroxy diacid with one stereocenter; this profile uses DL identity.
Specify DL, L, or D form and require stereochemical evidence when relevant.
One methylene group between two carboxyl groups.
Match the free-acid identity, grade, assay method and lot documentation.
Two carboxyl carbons directly joined, without a methylene spacer.
Specify anhydrous or dihydrate; for a solution, state normality, temperature, and method.
Two neighboring ring carbons carry COOH groups. Their adjacent arrangement is positional isomerism, not a cis/trans alkene designation. The neutral acid is achiral.
TCI uses GC and titration, Wako uses capillary GC and Sigma’s ACS reagent assay method is unstated. Positional identity, water and anhydride impurity need their own controls. ACS or JP test-reagent terminology does not establish pharmaceutical-ingredient suitability.
Two carboxyl groups terminate a chain containing five CH₂ groups. The neutral free acid is achiral and has no carbon–carbon double bond.
TCI lists GC and neutralization titration independently. Wako states 99% titration without a named grade. Sigma’s 98% assay method is unstated, and its 25 g page shows both a list price and a web promotion; no lowest-price ranking is supplied.
Eight methylene groups connect its two terminal carboxyl groups. Decanedioic acid is distinct from decanoic acid, which has only one carboxyl group.
TCI lists minimum 98% GC and titration; Wako 1st Grade specifies 97% titration; Sigma states 99% without a retrieved assay method. Sigma’s 250 g list and promotional prices are labeled separately. Mass packages do not establish identical impurity or processing specifications.
Six methylene groups connect two terminal carboxyl groups. Octanedioic acid is the free acid; disuccinimidyl suberate is a chemically activated ester derivative.
TCI’s 99% GC and titration thresholds, Wako’s 98% titration and Sigma’s method-unspecified 98% are separate specifications. An analytical-standard grade from Supelco 75462 is not transferred to Sigma S5200 or another reagent.
A saturated four-carbon chain with two carboxyl groups.
Specify free acid versus succinate salt and the four-carbon backbone.
A hydroxy diacid with two stereocenters; this profile uses L-(+).
Require L-(+) identity, stereochemical specification, and separate chemical and optical assay.
The 1,4, or para, arrangement is a molecular-connectivity identity. It is distinct from 1,2 phthalic acid and 1,3 isophthalic acid despite sharing their formula and molecular weight.
Laboratory GC, titration and method-unspecified products are not automatically purified terephthalic acid qualified for an industrial polymer line. Wako 95% capillary GC differs from the 98–99% entries. Confirm para identity and process-specific impurities.
Numerical pKa values are repeated here only for the six independently reviewed profiles, with their reference conditions. Other values remain in the individual technical references. Compare matched identities and conditions; no acidity ratio or solubility ranking is inferred.
Directly joined carboxyl carbons versus a methylene spacer.
Compare these acids →A methylene spacer changes the carbon framework while both retain two carboxyl groups.
Compare these acids →Contrast an E/trans double bond with a saturated four-carbon chain.
Compare these acids →A longer saturated diacid framework changes the structural comparison.
Compare these acids →Two versus one hydroxyl-bearing stereocenters, with different profile stereochemical identities.
Compare these acids →Define chemical assay and method, hydrate state, stereochemical form, physical form and package size. Oxalic solids and standardized solutions require different specifications. Confirm bulk terms directly with the supplier.