Preparation of Carboxylic Acid

Before jumping to the preparation of carboxylic acid, it is important to know what carboxylic acid is and the nature of carboxylic acid. Carboxylic acid is an organic compound in which a carbon atom is doubly bonded to an oxygen atom and with a hydrogen atom with a single bond. The carboxyl group (COOH) gets its name because of the carbonyl group (C=O) and a hydroxyl group. Carboxylic acids are much more acidic in nature than other compounds containing a hydroxyl group. The general formula for carboxylic acid can be denoted as CnH2n+1COOH. Generally, carboxylic acids contain one carboxyl group, but sometimes two or more groups are also attached. These acids are further called as dicarboxylic acids, tricarboxylic acids, and so on. It is a very useful product and used in many different industries.

Structure of Carboxylic Acid

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Methods Of Preparation Of Carboxylic Acids

The preparation of carboxylic acids can be done using various methods. Some of them are listed below-

  1. Preparation of Carboxylic Acid from the Grignard Reagent

The preparation of carboxylic acid can be done using Grignard reagents chemical reaction. It can be simply done by first reacting to Grignard reagent with dry ice (crushed) or solid CO2. In this step, salts of carboxylic acids are formed, after that, acidification of these salts with mineral acids gives corresponding carboxylic acids.

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  1. Preparation of Carboxylic Acid from Alcohol

It is very easy to prepare carboxylic acids from alcohol. Alcohols easily undergo oxidation reaction using oxidizing agents such as potassium permanganate (KMnO4), chromium trioxide (CrO3H2SO4), and potassium dichromate (K2Cr2O7). These strong oxidizing agents make alcohols undergo oxidation reaction twice and convert alcohol into carboxylic acids directly.

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  1. Preparation of Carboxylic Acid from Aldehyde

The preparation of carboxylic acids can also be done using mild oxidizing agents also. Alcohols, when oxidized using a mild oxidizing agent such as Tollen’s reagents [Ag(NH3)2+OH] and manganese dioxide (MnO2), undergo oxidation reaction only once and form corresponding aldehydes. When these aldehydes further undergo oxidation reaction using mild oxidizing agents only, gives carboxylic acid.

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  1. Preparation of Carboxylic Acid from Ester

When ester undergoes acidic hydrolysis, it leads to the formation of carboxylic acids. In the first step of basic hydrolysis of ester, it produces carboxylates. On further acidification, it gives corresponding carboxylic acids. Also, it is necessary to carry out hydrolysis of esters with mineral acids or alkali to produce a carboxylic acid.

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  1. Preparation Of Carboxylic Acid From Acyl Halides and Anhydrides

When acid chlorides undergo hydrolysis with water, it gives carboxylic acids. Another way to produce carboxylic acid from acid chlorides is by making it undergo hydrolysis with aqueous base. This reaction produces carboxylate ions, on further acidification of which will give corresponding carboxylic acids.

Anhydrides, on the other side, simply undergo hydrolysis with water and give corresponding carboxylic acid.

  1. Preparation from Nitriles and Amides

On the hydrolysis of nitriles, it forms amides. These amides chemically react in the presence of catalysts such as H+ or OH- to give carboxylic acids. In a similar way, amides can directly react to produce carboxylic acid in the presence of H+ or OH- catalyst.

  1. Preparation from Alkylbenzenes

Alkylbenzenes undergo oxidation reactions to form aromatic carboxylic acids. When the alkyl benzene compound goes under oxidation with acidic or alkaline potassium permanganate or chromic acid it gives carboxylic acid, which is aromatic in nature.

In this process, the side products of oxidation reaction depend upon the alkyl groups, whether it is primary or secondary. The tertiary alkyl group remains unaffected in this reaction.

Conversion Of Carboxylic Acid To Alcohol

Conversion of carboxylic acid to alcohol is a very simple process. It is done by reduction of carboxylic acid using reagents such as Lithium tetrahydridoaluminate or dry ether (LiAlH4).

The -COOH group in carboxylic acid turns into -CH2OH which is a primary alcoholic group.

Uses of Carboxylic Acids

Carboxylic acids are very useful in our daily lives. They act as an important ingredient in the manufacturing of many common goods. Some of the common uses are stated below-

  • Manufacturing of soaps

  • It is very useful in the food industry. It is used in the production of soft drinks also.

  • Used in the production of vinegar.

  • It is very useful in the pharmaceutical industry also. It is an important ingredient used in the production of drugs such as aspirin etc.

  • It is also used in the rubber industry.

  • These acids are used in the production of dye, perfumes, etc.

FAQ (Frequently Asked Questions)

1. What is a Koch Reaction? Write its Applications.

It is a reaction used for the production of carboxylic acids or fatty acids. In this reaction, olefin is heated with CO and steam. This is done at a really high temperature around 300-400 degrees C. Koch Reaction takes place in the presence of phosphoric acid. It acts as a catalyst in this reaction.

Koch reaction can be represented as-

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

2. Write Some Chemical and Physical Properties of Carboxylic Acids.

Chemical Properties of Carboxylic Acid Include 

  • Soluble in water

  • Capable of forming hydrogen bonds with water

  • They are polar in nature

  • They are highly acidic in nature

   Physical Properties of Carboxylic Acid Include

  • Carboxylic acids have higher boiling points.

  • They are usually odourless.

  • Their solubility is inversely proportional to the number of carbon atoms.

  • Their melting point has no particular trend.