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Glutaric Acid (HOOC-(CH2)3-COOH) is the organic compound Pentanedioic acid - its preferred IUPAC name. It is a 5 carbon, linear, dicarboxylic acid (defined as per the classification here) with the formula C3H6(COOH)2. Of all the linear dicarboxylic acids related to it (which are only soluble in water up to a few per cent), Glutaric Acid is soluble up to 50% w/w. Glutaric acid is present in all living organisms - ranging from various kinds of bacteria to humans. It is produced by the human body during the metabolism of amino acids; namely tryptophan and lysine. It acts as an acetogen and a metabotoxin when present in sufficiently high quantities.
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Key Terms: Dicarboxylic acid, acid anhydrides, acidity, acid strength
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Structure of Glutaric Acid
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Glutaric acid (C3H6(COOH)2) is an alpha,omega-dicarboxylic acid; and a lipid. It comprises a conjugate acid of a glutarate(1-) and a glutarate. The following are its various views of its chemical structures in different forms:
Two-Dimensional Depiction
Two-dimensional Structure of Glutaric Acid
Three-Dimensional Conformer
Three-Dimensional Conformer
With reference to the above structures: The linear carbon structure is seen as described previously. The two -COOH groups on the acid, present at the two extremities of the carbon chain, combine with the loss of a water molecule to yield the glutaric anhydride.
Chemical Properties of Glutaric Acid
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| Chemical formula | C5H8O4 |
| Molecular Weight | 132.11g/mol |
| Formal Charge | 0 |
| Bronsted acid | The acid is capable of donating a hydron to an acceptor |
Physical Properties of Glutaric Acid
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- Glutaric acid is a colorless, odorless compound.
- It appears as colourless crystals or white solid.
- The Melting Point of the acid is 97 - 98°C.
- The Boiling Point of the acid is 303°C.
- Solubility: As discussed earlier, the ‘linear’ dicarboxylic acids, like adipic and succinic acids, are soluble in water only to a few per cent at room temperature. However, unlike them, glutaric acid’s solubility in
- Water: soluble 5 mg/mL, clear to slightly hazy, colourless to faintly yellow
- Alcohol: soluble
- Chloroform: soluble
The solution of the acid in water makes for a medium strong acid.
- The density for glutaric acid is 1.4 g/cm3.
Nomenclature and Naming Glutaric Acid
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According to the IUPAC naming convention, the compound is named pentanedioic acid.
Additionally, its synonyms are:
- Glutaric acid (most commonly used name)
- 1,3-Propanedicarboxylic acid
- 1,5-pentanedioic acid
Also refer to: IUPAC nomenclature for alcohols, phenols and ethers for additional practice.
Means of Production Glutaric Acid
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Various means of mass production for glutaric acid are:
- One of the means of production of glutaric acid is by the ring-opening of butyrolactone with potassium cyanide to give the mixed potassium carboxylate-nitrile that is hydrolyzed to the diacid.
- Another means of production is making use of hydrolysis followed by oxidation of dihydropyran which gives glutaric acid.
- The acid can also be prepared from reacting 1,3-dibromopropane with sodium or potassium cyanide to obtain the dinitrile which is then going to be followed by hydrolysis.
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Uses of Glutaric Acid
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- Utilized in the complexation with DL-lysine.
- Synthesis of complexes with L-arginine and L-histidine.
- Used in the process of preparation of glycine-glutaric acid co-crystals.
- Through the hydrogenation of glutaric acid, we can produce 1,5-Pentanediol- which is a common plasticizer.
- Glutaric acid itself has been used in the production of polymers such as polyester polyols, polyamides. The odd number of carbon atoms (i.e. 5 in the case of glutaric acid) is useful in decreasing polymer elasticity.
- By the action of ammonia on glutaric acid, we can obtain uvitonic acid.
- The glutaric diester can be used for the production of pyrogallol.
Safety and Possible Hazards
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Glutaric acid is irritating to the eyes, skin and respiratory tract. The hazards also include the fact that the compound may be harmful through ingestion, inhalation or skin absorption.
The safety measures that are to be taken when handling the compound are:
- You are advised to make use of a local exhaust or breathing protection.
- Skin and eye protection measures involve making sure that gloves and eye protection are worn at all times while handling the acid.
- It is imperative that there be no open flames near the acid.
- When working with the neat compound, it is important to wear a half face respirator which has been equipped with an organic vapour or an acid gas cartridge that is specific for organic compounds and strong acids; to be accompanied with a dust filter in order to avoid inhalation of particles of the acid.
Things to Remember
- Glutaric acid is a linear chained dicarboxylic acid.
- The increased number of hydrogen bonding and greater molecular weights of the glutaric acid contribute to it having a higher melting point than pentanoic acid (monocarboxylic acid).
- Distinguishing between glutaric acid and pentanoic acid/ pentanol is done on the basis of chemical reactions to reach a definite conclusion.
- Although the uses of glutaric acid are many, the safety measures detailed above should be practiced for self-preservation.
- The role of glutaric acid within the human body is that of great importance (any imbalance in levels can cause serious ailments).
Sample Questions
Question 1: Glutaric acid is:
(A) Butane-1,4-dioic acid
(B) Ethane- 1,2-dioic acid
(C) Propane- 1,3-dioic acid
(D) Pentane-1 ,5-dioic acid (1 Mark)
Ans. D. Pentane-1 ,5-dioic acid
Explanation: According to the IUPAC convention of nomenclature, the compound HOOC-(CH2)3-COOH, with reference to the structure, will be named as Pentane-1 ,5-dioic acid.
Question 2: The following question is of the assertion and reasoning type. Choose the correct reasons that support the assertion being made in the statement.
Assertion: Trihydroxy glutaric acid (HCOO-CHOH-CHOH-CHOH-COOH) exists in four stereoisomeric forms, two of which are optically active while the other two are meso forms.
Reason: It contains two asymmetric and one pseudo-asymmetric carbon atoms.
(A) Both assertion and reason are correct and the reason is the correct explanation for the assertion.
(B) Assertion is correct but the reason is incorrect
(C) Both assertion and reason are correct but the reason is not the correct explanation for the assertion.
(D) Both assertion and reason are incorrect. (3 Marks)
Ans. A. Both assertion and reason are correct and the reason is the correct explanation for the assertion.
Explanation: While observing the structure of trihydroxy glutaric acid, we see that there are 3 chiral carbons, but amongst those 3, there is one which is pseudo- asymmetric carbon. Hence, we can then say that there are two asymmetric carbon and one pseudo-asymmetric carbon which is present in the Trihydroxy glutaric acid.
The number of optical isomers and respective meso forms of Trihydroxy glutaric acid can be found as follows:
The total number of optical isomers present = 22 − 21
= 4−2 = 2
The total number of meso forms present = 2*(3−1)/2
= 2
Hence, the total number of stereoisomers present within the Trihydroxy glutaric acid is given as = 2 + 2
= 4
Question 3: In glutaric acid, the pKa1 Is 4.35 while the pKa2 is 5.42. Why is the second carboxylic acid less acidic? (4 Marks)
Ans. Carboxylic acids where there are two carboxyl groups present which are separated by a chain of more than five carbon atoms (n>5), as is the case with glutaric acid, for the most part, have unexceptional properties. The carboxyl groups attached to the carbon chain behave more or less independently of one another.
We know that the smaller the pKa value, the stronger the acid. In glutaric acid, the first carboxyl group is generally much more acidic than the second (i.e. has a lower pKa and dissociates more easily). We understand that the inductive electron-acceptor effect of the second carboxyl group increases the stability of the ionized group which also has an effect on the acidity.
Generally, in dicarboxylic acids, the Ka2 being lower than K1 reduces the acidity of the second carboxyl which is aided by the presence of a carboxylate ion group; due to the electrostatic repulsion between the two -ve charges present on the dicarboxylate ion. This effect reduces the strength as the length of the chain separating the carboxyl groups increases as is the case with Glutaric Acid which has a 5 carbon chain.
Question 4: Why is the acid generally referred to as glutaric acid? (1 Mark)
Ans. The 5 carbon, linear, dicarboxylic acid (C3H6(COOH)2) is an alpha,omega-dicarboxylic acid which comprises a conjugate acid of a glutarate (1-) and a glutarate. Its common name i.e. “glutaric acid” is derived from the conjugate acids of glutarate and glutarate (1-).
Question 5: Which of the following common names does not represent a dicarboxylic acid?
(A) lactic acid
(B) succinic acid
(C) phthalic acid
(D) glutaric acid (1 Mark)
Ans. A. Lactic Acid
Lactic acid’s is a mono carboxylic acid. The other acids are dicarboxylic acids
Question 6: Consider the following acids:
I glutaric acid HOOCCH2CH2CH2COOH
II malonic acid CH2(CO2H)2
III oxalic acid (CO2H)2
IV succinic acid HO2C(CH2)2CO2H
What is the order of increasing acid strength? (weaker < stronger)
(A) IV < III < II < I
(B) I < II < III < IV
(C) I < IV < II < III
(D) II < I < IV < III (2 Marks)
Ans. C. I < IV < II < III
In dicarboxylic acids, the acidity of the second carboxyl is lower than that of the first. This is aided by the presence of a carboxylate ion group; due to the electrostatic repulsion between the two -ve charges present on the dicarboxylate ion.
This effect reduces the strength as the length of the chain separating the carboxyl groups increases as is the case with Glutaric Acid which has a 5 carbon chain.
Question 7: Draw the structure of pentanedioic acid. (1 Mark)
Ans.
Question 8: How will you distinguish between pentanol and pentanedioic acid? (2 Marks)
Ans. When pentanedioic acid is made to react with NaHCO3, CO2 gas is evolved as a result of the reaction. The equation for this reaction is:
H2C5H6O4 + 2 NaHCO3 -------------> 2 CO2 + 2 H2O + Na2C5H6O4
Pentanol, on the other hand, does not react with NaHCO3.
Question 9: What happens when you heat glutaric acid? (1 Mark)
Ans. Upon heating glutaric acid, the glutaric anhydride is obtained (following dehydration due to heat).
Question 10: Why do dicarboxylic acids have higher melting points when compared to their monocarboxylic acid counterparts? (2 Marks)
Ans. The molecular weight of the dicarboxylic acid compound is higher than that of its monocarboxylic acid counterpart which directly leads to an increase in the melting point. The most important ability of dicarboxylic acids is their ability to form a greater number of hydrogen bonds which in turn, need higher energy to be broken in order to allow the melting of the acid.
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