Benzene, alkylation nitration

The reactivity of Ce, C7, Cg aromatics is mainly associated with the benzene ring. Aromatic compounds in general are liable for electrophilic substitution. Most of the chemicals produced directly from benzene are obtained from its reactions with electrophilic reagents. Benzene could be alkylated, nitrated, or chlorinated to important chemicals that are precursors for many commercial products. 

Similar to the alkylation and the chlorination of benzene, the nitration reaction is an electrophilic substitution of a benzene hydrogen (a proton) with a nitronium ion (NO ). The liquid-phase reaction occurs in presence of both concentrated nitric and sulfuric acids at approximately 50°C. Concentrated sulfuric acid has two functions it reacts with nitric acid to form the nitronium ion, and it absorbs the water formed during the reaction, which shifts the equilibrium to the formation of nitrobenzene ... 

Bats, 54 Batteries, 54 Benzene isomers, 55 Benzyl compounds, 55 Bis(arenediazo) oxides, 56 Bis(arenediazo) sulfides, 56 Bis(difluoroamino)alkyl nitrates, 56 Bis(fluorooxy)perhaloafkanes, 57 Bis(sulfur)diimides, 57 Bitumen, 57 Bleaching powder, 57 Bleve, 58... 

In all of these reactions, benzene is nitrated and the nitro group is ultimately reduced, but the timing of the reduction step is important in arriving at the correct product. In (a), nitrobenzene is immediately reduced and alkylated. In (c), chlorination occurs before reduction so that chlorine can be introduced in the /n-position. In (b) and (d), nitrobenzene is reduced and then acetylated in order to overcome amine basicity and to control reactivity. In both cases, the acetyl group is removed in the last step. 

Like CH3, other alkyl groups release electrons, and like —CH3 they activate the ring. For example, Icrt-butylbenzene is 16 times as reactive as benzene toward nitration. Electron release by —NH2 and —OH, and by their derivatives -- OCH3 and —NHCOCH3, is due not to their inductive effect but to resonance, and is discussed later (Sec. 11.20). 

R = alkyl, aryl R = 1° or 2 alkyl, allyl, benzyl, activated aryl, acyl X - Cl, Br, I, OTs electrophile epoxide, dialkyl sulfate, alkyl sulfonate, alkyl nitrate base = NaOR NaH base = KOf-Bu, cone. NaOEt, NaH solvent = R OH, f-BuOH, benzene, ether, DMF... 

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. 

Alkyl acetone Alkyl alcohol Alkyl benzene Alkyl chloride Alkyl sulfide Aluminum acetate Aluminum bromide Aluminum chlorate Aluminum chloride Aluminum ethylate Aluminum fluoride Aluminum fluorosilicate Aluminum formate Aluminum hydroxide Aluminum nitrate Aluminum oxalate Aluminum phosphate Aluminum sulfate Alum... 

Quantitative eomparisons of aromatic reactivities were made by using the competitive method with solutions of nitronium tetrafluoroborate in sulpholan, and a concentration of aromatic compounds 10 times that of the salt. To achieve this condition considerable proportions of the aromatic compoimds were added to the medium, thus depriving the sulpholan of its role as true solvent thus, in the nitration of the alkyl- and halogeno-benzenes, the description of the experimental method shows that about 50-60 cm of mixed aromatic compounds were dissolved in a total of 130 cm of sulpholan. 

Nitration in sulphuric acid is a reaction for which the nature and concentrations of the electrophile, the nitronium ion, are well established. In these solutions compounds reacting one or two orders of magnitude faster than benzene do so at the rate of encounter of the aromatic molecules and the nitronium ion ( 2.5). If there were a connection between selectivity and reactivity in electrophilic aromatic substitutions, then electrophiles such as those operating in mercuration and Friedel-Crafts alkylation should be subject to control by encounter at a lower threshold of substrate reactivity than in nitration this does not appear to occur. 

The importance of a primary steric effect in the nitration of alkyl-benzenes has been mentioned ( 9.1.1). The idea was first introduced by Le Fevre to account for the fact that -alkyltoluenes (alkyl = Et, -Pr,68a t-Bu ) are nitrated mainly adjacent to the methyl group. Without the rate data reported for the alkylbenzenes the effect might equally well have been accounted for by hyperconjugation. 

Hammett s equation, and substituent effects, 137-43 heteromolecules, 130 Holleman s product rule, 3 hyperconjugation, in nitration of alkyl-benzenes, 165-7 in nitration of positive poles, 169... 

More quantitative results are available for the nitration of alkyl-thiazoles Dou et al. (373) determined the reactivity, relative to benzene, of the nitration site of various mono- and dialkylthiazole by competition experiments (Table 1-53). 

TABLE 1-53. ORIENTATION AND REACTTV-ITY RELATIVE TO BENZENE m THE NITRATION OF ALKYL-THIA20LES AT 70°C BY SUL-FONITRIC AQD (373)... 

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