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The delectable strawberries that some of us indeed love, could contain as much as 29mg/kg of benzoic acid. In fact why only strawberries! Even prunes, cranberries, yogurt and spices like cloves, salvia, thyme and nutmeg contain this famous aromatic carboxylic acid called benzoic acid.
It is also an antiseptic and fungistatic agent to prevent the growth of bacteria and fungi and cure skin diseases.
It indeed finds great utility in the food, medicine, and personal care industries. Hence, it is essential to understand the chemistry of this acid.
TABLE OF CONTENTS
Benzoic acid is a white or colourless solid-state organic chemical compound with the formula
It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin, which was for a long time its only source. The gum benzoin is a balsamic resin obtained from the bark of several species of trees in the genus Styrax.
Benzoic acid occurs naturally in many plants and serves as an intermediate in the biosynthesis of many secondary metabolites. It consists of a carboxyl group attached to a benzene ring. Therefore, benzoic acid is also called aromatic carboxylic acid. This compound is attained as a crystalline, colourless solid under normal conditions.
The empirical formula denoting benzoic acid is and the molecular formula is denoted by
. It is also called benzene carboxylic acid.
It has seven carbon atoms, six hydrogen atoms, and two oxygen atoms. It is a ring of six carbons attached with alternate bonds with a group attached to it in one of the vertices. The
group makes it benzoic acid.
Benzoic Acid |
|
Molar Mass |
122.12 |
Density |
1.27 g cm-3 at 5oC |
Boiling Point |
523 K |
Melting Point |
395 K |
The commercial production of benzoic acid is done via the partial oxidation of toluene with oxygen, catalyzed by manganese or cobalt naphthenates.
Another industrial method of preparing benzoic acid is by reacting tri-chlorotoluene with calcium hydroxide in the presence of water, and the treatment of the calcium benzoate product with hydrochloric acid.
Generally, carboxylic Acids are prepared in the ways stated below. Let’s check some specific methods of preparing benzoic acid which is the simplest aromatic carboxylic acid.
Benzonitrile undergoes acidic or basic hydrolysis to produce benzoic acid.
Benzoic acid undergoes several reactions involving cleavage of -C-bond. These reactions are stated below.
Acyl halides when hydrolysed give carboxylic acids. Acyl halides are more readily hydrolysed with an aqueous base to give carboxylate ions. Carboxylate ions on acidification produce corresponding carboxylic acids.
Q.1. The major product formed in the following reaction is:
Solution: Since benzoic acid is the meta directing and deactivating group, thus meta Bromo-benzoic acid is formed.
Q.2. Which is the best method for carrying out the following reaction?
A)
B) ,
,
C) ,
,
D) ,
,
Solution:
Hence option B is correct.
Q.3. Why does the potassium salt of benzoic acid doesn't undergo Kolbe’s electrolysis reaction to give biphenyl?
Answer: The reason is the intermediate phenyl radical formed is highly unstable. This is the reason why it doesn't undergo Kolbe’s reaction.
Q.4. Benzoic acid is treated with sodium borohydride. The compound obtained is:
Answer: Benzoic acid doesnot get reduced by sodium borohydride (NaBH4). Hence answer would be Option D. Benzoic acid on reaction with lithium aluminium hydride undergoes reduction gives benzyl alcohol.
Q.5. What is the product of the following reaction?
Answer: Acyl derivative of benzoic acid is obtained.
Question 1. What happens when Benzoic acid is heated?
Answer. When benzoic acid is heated in the presence of a dehydrating agent like P2O5 it forms benzoic anhydride.
Question 2. What is the negative impact of benzoic acid on skin?
Answer. If someone is exposed to Benzoic Acid in larger concentrations, it may generate rashes or hives due to skin allergy.
Question 3. Is benzoic acid polar?
Answer. Only the carboxylic acid group (- COOH) is polar present in the benzoic acid molecule is polar, the bulk of the benzoic acid molecule is no-polar i.e., the benzene ring part. It is only the carboxylic group that is polar. This is the reason why benzoic acid dissolves only slightly in cold water.
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Structure, physical properties, chemical properties and uses of carboxylic acid |
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Acid derivatives - Structure and chemical properties |