Acidic nature of Carboxylic Acids

Carboxylic acid is an organic compound having a carboxyl group (COOH) affixed to an alkyl or aryl group. They react with metals and alkalis to produce carboxylate ions. These reactions of carboxylic acids proves their acid nature. The acidity of carboxylic acids is more as compared to simple phenols, as they, in reaction with weak bases like carbonates and bicarbonates, liberate carbon dioxide gas. when a substance gives a proton, the Carboxylic Acid naming occurs; generally, hydrogen to other things. Because hydrogen belongs in the -COOH group, the carboxylic acids are acidic in nature.

Acidity of carboxylic acids and derivatives

Carboxylic acids disintegrate in water to form the hydronium ion and carboxylate ion. The carboxylate ion which is formed, is stabilised through the process of resonance by effective delocalisation of the negative charge.

Carboxylic acids are the strongest among the organic compounds but weaker than mineral acids. The acidity of a carboxylic acid is higher than phenols and even alcohols. As discussed above, carboxylate ion,( the conjugate base of a carboxylic acid) is stabilised by 2 identical resonance structures in which the negative charge is efficiently delocalised between 2 more electronegative O atoms.

On the other hand in case of phenols, negative charge is less efficiently delocalised over one O atom and less electronegative C atoms in phenoxide ion. Therefore, the carboxylate ion displays higher stability in association to phenoxide ion. Hence, the carboxylic acids are more acidic than phenols. Carboxylic acids on reaction with metals and alkalis form carboxylate ions, which can only be stabilised due to resonance. The simplest way to acknowledge carboxyl groups is simply by understanding that taking out electrons leads to the rise in acidity of carboxyl groups, whereas giving away an electron usually leads to the fall of acidity in carboxyl groups.

Uses of Carboxylic Acids

• Fatty acids that are important to human beings constitute carboxylic acids. Examples given omega-6 and omega-3 fatty acids.

• In the manufacture of soaps, higher fatty acids are also used.

• Many carboxylic acids are used in the production of soft drinks and many other food products.

• The manufacture of rubber includes the use of acetic acid (coagulant).

• In the manufacture of nylon-6,6 hexanedioic acid is used.

• Carboxylic acids are very useful in the rubber, textile, and leather industries.

• Ethylenediaminetetraacetic acid is a widely used chelating agent.

• The manufacturing of many drugs involves the use of the said compounds. Therefore, carboxylic acids are very essential in pharmaceuticals.

• The manufacturing of many polymers includes the use of compounds in which a carboxyl functional group is present.

Carboxylic Acid Structure

The formula of a carboxylic acid is, generally represented by the formula R-COOH, where COOH means to the carboxyl group, and R means to the remaining of the molecule to which this group is bonded to. In this carboxyl group, there is a C which shares a double bond with an O atom and a single bond with a -OH group.

The first four carboxylic acids obtained from alkanes are methanoic acid (HCOOH), ethanoic acid (CH3COOH), propanoic acid (C2H5COOH) and butanoic acid (C3H7COOH).

It can be observed that a carboxylic acid contains a hydroxyl group attached to a carbonyl carbon. Due to the electronegativity of the O atom, this functional group can easily undergo ionization and release a proton.

The carboxylate ion, formed from the removal of a proton from the carboxyl group, is stabilized by the presence of two O atoms. Some examples of carboxylic acids are acetic acid  and Formic acid.

Nomenclature of Carboxylic Acids

Generally, these organic compounds are denoted by their trivial names, which contain the suffix “-ic acid”. An example of a trivial name which is for a carboxylic acid is acetic acid (CH3COOH).  According to IUPAC nomenclature of these compounds, the suffix “-oic acid” is assigned.

The guidelines that must be followed in the IUPAC nomenclature of carboxylic acids are listed below.

• The suffix “e” in the name of the given alkane should be replaced with “oic acid”.

• When the aliphatic chain has only one carboxyl group, the carboxylic carbon is always prioritized as one. For example, the compound CH3COOH is named as ethanoic acid.

• When the aliphatic chain has more than one carboxyl group, the total number of C atoms is counted and the number of carboxyl groups is shown by Greek numeral prefixes such as “di-”, “tri-“, etc.

• Then this carboxylic acid is named by joining these prefixes and suffixes to the parent alkyl chain. Arabic numerals are used for indicating the positions of the carboxyl group.

• The name “carboxylic acid” or “carboxy” can also be assigned for a carboxyl substituent on a carbon chain. An example of such nomenclature is the name 2-carboxyfuran for the compound 2-Furoic acid.

Conclusion: –

The acidity of carboxylic acids additionally depends on the nature of substituent aryl or alkyl group affixed to the carboxyl group. An electron-taking group ensures efficient delocalization of negative charge through resonance or inductive effect. Thus, electron-taking groups increase the stability of the conjugate base results and therefore the acidity of carboxylic acids. On the other side, electron-giving groups destabilise the conjugate base formed and therefore result in falling of the acidity of carboxylic acids. A general tendency can be seen as: –

NC-CH2COOH  < NO2CH2COOH < CHCl2COOH  < CCl3COOH  < CF3COOH