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When ortho substitution occurs in benzoic acid, steric hindrance causes the carboxyl group to twist out of the plane of the benzene ring. The twisting inhibits the resonance of the carboxyl group with the phenyl ring, leading to increased acidity of the carboxyl group.
Via the Hock rearrangement, cyclohexylbenzene hydroperoxide cleaves to give phenol and cyclohexanone. Cyclohexanone is an important precursor to some nylons. [8] Starting with the alkylation of benzene with mixture of 1 and 2-butenes, the cumene process produces phenol and butanones. [5]
Benzoic acid is cheap and readily available, so the laboratory synthesis of benzoic acid is mainly practiced for its pedagogical value. It is a common undergraduate preparation. Benzoic acid can be purified by recrystallization from water because of its high solubility in hot water and poor solubility in cold water. The avoidance of organic ...
It oxidizes rapidly in healthy individuals to benzoic acid, conjugated with glycine in the liver, and excreted as hippuric acid. Very high concentrations can result in toxic effects including respiratory failure, vasodilation, hypotension, convulsions, and paralysis. Benzyl alcohol is toxic to neonates and is associated with the gasping syndrome.
Acetophenone is formed as a byproduct of the cumene process, the industrial route for the synthesis of phenol and acetone.In the Hock rearrangement of isopropylbenzene hydroperoxide, migration of a methyl group rather than the phenyl group gives acetophenone and methanol as a result of an alternate rearrangement of the intermediate:
The reaction constant, or sensitivity constant, ρ, describes the susceptibility of the reaction to substituents, compared to the ionization of benzoic acid. It is equivalent to the slope of the Hammett plot. Information on the reaction and the associated mechanism can be obtained based on the value obtained for ρ. If the value of:
One method involves its conversion to the Grignard reagent, phenylmagnesium bromide. This reagent can be used, e.g. in the reaction with carbon dioxide to prepare benzoic acid. [4] Other methods involve palladium-catalyzed coupling reactions, such as the Suzuki reaction. Bromobenzene is used as a precursor in the manufacture of phencyclidine.
Although of no commercial significance, many other routes to benzene exist. Phenol and halobenzenes can be reduced with metals. Benzoic acid and its salts undergo decarboxylation to benzene. The reaction of the diazonium compound derived from aniline with hypophosphorus acid gives benzene. Alkyne trimerisation of acetylene gives benzene.