Alkyl benzenes reduction

Note that the Wolff-Kishner reduction accomplishes the same overall trans-fonnation as the catalytic hydrogenation of an acylbenzene to yield an alkyl-benzene (Section 16.10). The Wolff-Kishner reduction is more general and more useful than catalytic hydrogenation, however, because it works well with both alkyl and atyl ketones. 

Methods of synthesis for carboxylic acids include (1) oxidation of alkyl-benzenes, (2) oxidative cleavage of alkenes, (3) oxidation of primary alcohols or aldehydes, (4) hydrolysis of nitriles, and (5) reaction of Grignard reagents with CO2 (carboxylation). General reactions of carboxylic acids include (1) loss of the acidic proton, (2) nucleophilic acyl substitution at the carbonyl group, (3) substitution on the a carbon, and (4) reduction. 

It has become clear that benzoate occupies a central position in the anaerobic degradation of both phenols and alkylated arenes such as toluene and xylenes, and that carboxylation, hydroxylation, and reductive dehydroxylation are important reactions for phenols that are discussed in Part 4 of this chapter. The simplest examples include alkylated benzenes, products from the carboxylation of napthalene and phenanthrene (Zhang and Young 1997), the decarboxylation of o-, m-, and p-phthalate under denitrifying conditions (Nozawa and Maruyama 1988), and the metabolism of phenols and anilines by carboxylation. Further illustrative examples include the following ... 

Because polyacylation does not occur (cf. p.145), it is often preferable to prepare alkyl-benzenes by acylation, followed by Clemmensen or other reduction, rather than by direct alkylation ... 

MBR [Mobil benzene reduction] A catalytic process for reducing the benzene content of gasoline. It combines features of three earlier processes benzene alkylation with tight olefins, olefin equilibration with aromatization, and selective paraffin cracking. The olefins are obtained from FCC offgas. The catalyst is a modified ZSM-5 zeolite. Developed by Mobil Research Development Corporation in 1993. 

Oxidation of an alkylated benzene (making an aryl carboxylic acid) is a method of converting an ortho-para activator into a meta director. The reduction of a nitro group to make an aryl amine is a way of changing a meta director into an ortho-para activator. 

This method is used for the reduction of acyl benzenes to alkyl benzenes, but it also reduces aldehydes and ketones to alkanes. 

In benzene, Mowah observed some differences between symmetrical amides RCONR2 and unsymmetrical amide RCON(CII3)R. The influence of the dose on >u(vu was stronger for. V-mcthyl-A -alkyl amides (reduction of factor 4 compared to factor 1.7—1.8 for RCONR() (192), related to the extractant s lower stability. 

Nitration puts in a substituent para to the alkyl group, which, after reduction, becomes a powerful ortho director so that the bromine is directed meta to the original alkyl group (Chapter 22). Removal of the amino group by reduction allows the preparation of meta bromo alkyl benzenes that cannot be made directly. 

The need for benzene reduction is one of the determining factors in the way refiners will have to modify their process portfolio to meet future specifications. Apart from lowering the reformer severity, pre-fractionation and post-fractionation provide viable tools to reduce benzene in the gasoline pool. Pre-fractionation and subsequent hydrogenation of benzene is a typical solution. However, the products (cyclohexane and alkyl-cyclohexanes) are low in octane. Therefore, this option is only feasible if the refinery is not short in octane. The octane loss can be compensated for by the addition of oxygenates or preferably by the addition of alkylates. If more octane is needed, post-fractionation is one of the solutions. 

Somehow related to Uris Lewis acid assisied reduction of CO is the work by Olive, who describes the reaction of CO.II3 in the presence of benzene with W(CO) /AlCl3 (78). The gas phase contains small amounts of Ci and Cj hydrocarbons. As main products, alkylated benzenes are obtained w hich follow a Schulz—Flory distribution. By using CO. Vollhardi could demonstrate that the alkyl groups of the alkylated benzenes do not originate from CO/H2 but stem from the benzene used [79]. 

Oemmensen reduction (Section 18.14B) A method to reduce aryl ketones to alkyl benzenes using Zn(Hg) in the presence of a strong acid. 

Aryl amine intermediates for azo and triphenylmethane dyes, as well as a number of vat dye (anthraquinone) intermediates, are made from compounds such as benzene, alkyl benzenes (toluene and higher homologues), phenol and naphthalene. A limited number of reactions are used to produce the most important dye intermediates, including nitration, reduction, halogenation, sulfonation, /V-alkylation, /V-acylation and alkali fusion33,34. 

Lithium chloride serves as an electrolyte in the electrolytic reduction of alkyl-benzenes in methylamine in a cell which can be operated either with or without an asbestos divider for separation of the anode and cathode compartments. Without the divider, excellent conversions into 1,4-dihydro products result. When the same hydrocarbon is reduced with the divider in place, equally excellent conversions into tetrahydro products are obtained. 

Hydrogenation of carbocyclic aromatic compounds requires only mild conditions over Rh catalysts. Rhodium is an outstandingly active catalyst for reduction of benzene. Catalyst efficiency is influenced by trace materials that act as inhibitors or promoters. Hydrogen halides are strong inhibitor for reductions in MeOH over Rh-on-carbon or on alumina. Small amounts of acetic acid promote reduction of aromatics over Rh-on-alumina. In a clean medium, 5% Rh-on-carbon or Rh-on-alumina in MeOH reduces alkyl benzenes at room temperature, under 500 kPa . Reaction is facilitated at higher T or by adding glacial acetic acid. 

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