Some biphenyl ( C6H5----C6C5) is produced as a by-product in the synthesis of benzoic acid . Where does this come from?
Biphenyl (C12H10), which has the molecular formula C6H5-C6H5, is produced as a by-product during the synthesis of benzoic acid. This biphenyl by-product is formed through the reaction between two molecules of benzene (C6H6).
To understand where the biphenyl comes from during the synthesis of benzoic acid, we need to look at the reaction involved in the process. The commonly used method for synthesizing benzoic acid is the oxidation of toluene (C6H5CH3) using a strong oxidizing agent, such as potassium permanganate (KMnO4) or chromic acid (H2CrO4).
The reaction can be represented as follows:
C6H5CH3 + 2O2 → C6H5COOH + H2O
During this oxidation reaction, one of the methyl groups of toluene (C6H5CH3) is transformed into a carboxylic acid group (-COOH) to form benzoic acid (C6H5COOH). However, because this reaction involves the oxidation of the aromatic ring, there are side reactions occurring simultaneously, leading to the formation of biphenyl.
The side reaction involving the formation of biphenyl during benzoic acid synthesis is known as the oxidative coupling of aromatic compounds. It occurs when two benzene molecules undergo a coupling reaction, facilitated by the oxidation conditions used in the synthesis. This reaction can be represented as follows:
2C6H6 → C6H5-C6H5 + H2
So, in summary, as a by-product of the oxidation of toluene to form benzoic acid, the unwanted reaction between two benzene molecules occurs, resulting in the production of biphenyl (C6H5-C6H5).