Cinnamic acid: Synthesis, Occurrence, Properties, Uses

Cinnamic acid is a naturally occurring chemical and exists in two main forms. It is white crystalline compound that is slightly soluble in water. It is classified as an unsaturated carboxylic acid. It’s mostly used as a flavouring agent or in the perfume industry, but it's also used to make various pharmaceuticals. It is prepared by cinnamaldehyde, condensation of benzyl chloride and Perkin reaction which is the oldest commercial route.

Key Takeaways- Carboxylic acid, Cinnamic acid, Cinnamaldehyde, Benzal chloride, Perkin reaction

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Synthesis of Cinnamic

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Perkins condensation

Aromatic aldehydes react with aliphatic acid anhydride in the presence of salt of corresponding acid anhydride and give α, β unsaturated acid is known as perkins condensation. Aromatic aldehyde should not possess any alpha hydrogen and aliphatic acid should posses alpha hydrogen

Reaction

Cinnamaldehyde

Cinnamic acid can be prepared by oxidation of cinnamic acid. Cinnamaldehyde is an organic compound with C6H5CH=CHCHO. Molar mass is 132.16 g/mol and yellow in colour. It is slightly soluble in water and soluble in ether chloroform. It is insoluble in petroleum ether. 

Cinnamaldehyde                                                              Cinnamic acid

It is less toxic in nature and that is why it is used in agriculture. It is used as an insecticide. It is effective against mosquito larva. It is used as a corrosion inhibitor for steel. It is a skin irritant.

Benzal chloride (C₆H₅-CHCl₂)

Condensation of benzal chloride gives cinnamic acid by following the method of acid hydrolysis . The main industrial use of benzyl chloride is as precursor to benzaldehyde. 

Knoevenagel condensation

There is another way to make cinnamic acid i.e. Knoevenagel condensation reaction. It is a modification of aldol condensation. The reactants are benzaldehyde and malonic acid in the presence of weak base and followed by acid catalysed decarboxylation.

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Occurrence of Cinnamic

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Cinnamic acid is obtained from oil of cinnamon. It is found in shea butter also. It has a honey-like odour. Its more volatile ethyl ester are flavour components in the essential oil of cinnamon in which cinnamaldehyde is the major constituent. 

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Properties of Cinnamic

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Following are the Properties of cinnamic acid:

• Cinnamic acid is colourless and crystalline solid 
• Slightly soluble in water 
• Chemical formula is C₉H₈O₂ 
• Molar mass is 148.161 g/mol

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Uses of Cinnamic

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Following are the Uses of cinnamic acid:

• It is used in flavourings, synthetic indigo
• It is used in certain pharmaceuticals 
• The major use in perfume industry
• It is precursor to the sweetener aspartame
• It can be dimerized in non-polar solvents resulting in different linear free energy relationships. 

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Points to Remember

Following are the important points:

• The unsaturated carboxylic acids are cinnamic acid and crotonic acid
• In cinnamic acid, major constituent is cinnamaldehyde
• Perkins condensation, oxidation of cinnamaldehyde, condensation of benzal chloride and knoevenagel condensation reaction these are the methods of synthesis of cinnamic acid
• Oil of cinnamon is natural resource of cinnamic acid
• The Pharmaceutical and perfume industry are two major applications for cinnamic acid.

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