Methods of Preparation of Carboxylic Acids

Carboxylic Acids are one of the imperative organic compounds found in a wide variety of living things. The Carboxylic Acid is part of the amino acids and amino acids are the building block of proteins. We all have heard about vinegar. Do you know that acetic acid, one of the type carboxylic acids, is responsible for the formation of vinegar?

Browse more Topics under Aldehydes Ketones And Carboxylic Acids

• Chemical Reactions and Uses of Carboxylic Acids
• Nomenclature and Structure of Carbonyl Group
• Nomenclature and Structure of Carboxyl Group
• Nucleophilic Addition Reaction
• Oxidation
• Physical properties of Aldehydes, Ketones and Carboxylic Acids
• Preparation of Aldehydes
• Preparation of Aldehydes and Ketones
• Preparation of Ketones
• Reactions due to Alpha-Hydrogen
• Reduction
• Uses of Aldehydes and Ketones

Thus, carboxylic acid occurs in metabolism. Few examples which contain carboxylic acid include coconut oil, butter, peanut oil, citrus fruits, etc. Now, how this group of organic compounds is prepared? Let us study the preparation method of carboxylic acid in detail in this topic.

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Carboxylic Acids

It is a group of an organic compound containing a carboxylic group (C(=O)OH). Carboxylic acid contains a carbonyl group to which the hydroxyl is attached. The general formula of the group is R-COOH. In the formula, R denotes the rest of the group attached to the functional group. The structure of carboxylic acid is

Methods of Preparation of Carboxylic Acids

The primary preparation technique involves oxidation of different types of functional groups. Let us go through the important preparation technique.

Preparation from Primary Alcohols

Primary alcohols, as well as aldehydes, can undergo oxidation reaction to form corresponding carboxylic acids with the help of oxidizing agents such as potassium permanganate (KMnO₄ for neutral or acidic or alkaline media), chromium trioxide (CrO₃^– H₂SO₄^– Jones reagent), and potassium dichromate (K₂Cr₂O₇^– acidic media).

Primary alcohol undergoes oxidation to produce carboxylic acid on the addition of the oxidizing agents. Therefore, the oxidation of primary alcohols produces aldehydes which further repeat the oxidation to produce carboxylic acids. The strong oxidizing agents including potassium dichromate, potassium permanganate, and chromium trioxide can readily oxidize the aldehyde to form carboxylic acids.

However, mild oxidizing agents can only undergo one step and convert the primary alcohols into aldehydes. Example of mild oxidizing agents includes manganese dioxide (MnO₂) and Tollen’s reagent [Ag(NH₃)₂⁺ OH⁻]. Hence, they are not strong enough to undergo oxidation twice. Therefore, the mild oxidizing agents are used for converting aldehydes into carboxylic acids.

It is important to remember that acidified oxidizing agents like potassium dichromate and Jones reagent lead to the formation of esters in a small amount. Therefore, it is preferable to use neutral or alkaline agents such as potassium permanganate for this preparation method.

Preparation from Aldehydes

As discussed in the above topic, Preparation of carboxylic acid is possible from the usual strong oxidizing agents. Carboxylic acids formation is possible with mild oxidizing agents such as Tollen’s reagents [Ag(NH ₃) ₂ ⁺OH ⁻] and manganese dioxide (MnO₂).

Preparation from Alkylbenzenes

Aromatic carboxylic acid preparation is possible through the oxidation of alkylbenzenes. Vigorous oxidation of alkyl benzene compound with acidic or alkaline potassium permanganate or chromic acid can lead to the formation of aromatic carboxylic acid compounds. The oxidation of complete side chain of the carboxyl group takes place regardless of the side chain length.

The resulting side products of the reaction vary depending on the primary or secondary alkyl groups. However, the tertiary alkyl group is not affected. Moreover, properly substituted alkenes can also undergo oxidation process to form carboxylic acids with the help of these oxidizing agents. Refer to the example below for the reactions under this preparation technique.

Preparation from Nitriles

Nitriles undergo hydrolysis to form amides. The amides further undergo reaction in the presence of a catalyst which then to form carboxylic acids. The catalyst for this reaction is H⁺ or OH^–. Furthermore, application of mild reaction condition helps in ceasing the reaction in the amide stage

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Preparation from Amides

Amide undergoes hydrolysis in the presence of catalyst H⁺ or OH^– to form carboxylic acids.

Preparation from Grignard Reagents

The carboxylic acid formation is possible by Grignard reagents reaction. The reaction of Grignard reagents with crushed dry ice or solid carbon dioxide leads to the formation of salts of carboxylic acids. Further, the acidification of the salts of a carboxylic acid with mineral acids leads to the formation of corresponding carboxylic acids.

Thus, preparation of Grignard reagents and nitriles is possible from alkyl halides. The preparation techniques help in the conversion of alkyl halides into the respective carboxylic acids. The resultant carboxylic acid will always have one carbon atom more than the corresponding alkyl halides.f

Preparation from Acyl Halides and Anhydrides

Hydrolysis of acid chlorides with water produces carboxylic acids. Additionally, acid chlorides can easily undergo hydrolysis with aqueous base to produce carboxylate ions which undergo further acidification to provide respective carboxylic acids. On the other hand, anhydrides undergo hydrolysis with water to produce respective acid. Thus, we can summarize

• Hydrolysis of acid chlorides with water to produce carboxylic acids
• Acid chlorides undergo reaction with a base and further acidification leads to carboxylic acid
• Hydrolysis of acid anhydrides leads to carboxylic acids.

Carboxylic Acids from Esters

Acidic hydrolysis of esters leads to the formation of carboxylic acids. However, hydrolysis of the base produces carboxylates followed by acidification leads to the formation of corresponding carboxylic acids. Furthermore, hydrolysis of esters is carried out with mineral acids or alkali in order to produce a carboxylic acid.

Solved Example for You

Question: Explain Koch Reaction and its application.

Solution: Koch Reaction is used for the production of fatty acids. In this process, heating of olefin takes place with CO and steam at the temperature of 300-400 ° C and under pressure. The reaction occurs in the presence of phosphoric acid that behaves as a catalyst during the production of fatty acid. The reaction for this process is

CH₂ = CH₂ + CO + H₂O → CH₃ – CH₂ – COOH