INTRODUCTION
Aromatic compounds are regarded as the class of organic compounds which resemble benzene in their chemical characteristics. Many of the aromatic compounds posses fragment odour 'aroma' . In fact the term aromatic is somehow associated with chemical stability. The stable character of aromatic compound is attributed to the presence of a ring structure specific of benzene. All aromatic compounds generally contain one or more benzene rings in their molecules. As naphthalene, anthracene, etc. are also aromatic compounds, those are often called arenes and benzene and its derivatives are called Benzenoids . There are a number of cyclic compounds which do not contain a benzene ring but are still aromatic in nature. Such compounds are called non-benzenoids. Like the aliphatic compounds, aromatic compounds also include hydrocarbons, hydroxy compounds, aldehydes, ketones, acids etc.
Nomenclature of Aromatic compounds -: here 👇👇
METHODS OF PREPARATION OF BENZENE -:
(A) On Industrial Scale . 1. From Coal tar. Coal tar is a dark brown sticky liquid. By the fractional distillation of coal tar, a light oil fraction is obtained at 353K - 443K. It is called light oil, as it is lighter than water. In addition to neutral substances like benzene, toluene and xylene, it also contains traces of acidic substances like phenols and cresols and basic substances like pyridine and thiophene. Light oil is washed with conc. H2SO4 to remove the basic substances. The oil is then treated with sodium hydroxide to remove the acidic substances. It is then washed with water and again subjected to fractional distillation. The first fraction (90% Benzol) obtained upto 110⁰C contains 70% Benzene, 25% toluene and rest is xylene. 90% Benzol is put to fractional distillation and at 353K, pure Benzene is collected. Pure toluene is collected at 110⁰C.
Next other preparations of Benzene . Click here 👇👇
ELECTROPHILIC AROMATIC SUBSTITUTION
General Mechanism of electrophilic substitution -:
Get here these notes 👇👇
Side chain Oxidation of Alkyl Benzenes -:
It is known that benzene and alkanes are quite stable towards oxidising agents. The presence of benzene ring makes the side chain susceptible to oxidation. The alkyl benzene can be easily oxidised to benzoic acid with hot alkaline potassium permanganate. Due to oxidation, only the side chain (irrespective of its length) is oxidised to carboxylic acid and the ring remains intact.
The position of the -COOH group after oxidation, indicates the position of the alkyl group.
Other structures are get here 👇👇
Oxidation of Side chain with chromyl chloride (Etard's reaction).
See here 👇👇
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