Alkyl nitrates, aromatic nitration with

Poly(phenylene oxide)s undergo many substitution reactions (25). Reactions involving the aromatic rings and the methyl groups of DMPPO include bromination (26), displacement of the resultant bromine with phosphoms or amines (27), lithiation (28), and maleic anhydride grafting (29). Additional reactions at the open 3-position on the ring include nitration, alkylation (30), and amidation with isocyanates (31). 

Like other aromatic compounds, aromatic ethers can undergo substitution in the aromatic ring with electrophilic reagents, eg, nitration, halogenation, and sulfonation. They also undergo Eriedel-Crafts (qv) alkylation and acylation. 

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. 

Many variations of the reaction can be carried out, including halogenation, nitration, and sulfonation. Friedel-Crafts alkylation and acylation reactions, which involve reaction of an aromatic ling with carbocation electrophiles, are particularly useful. They are limited, however, by the fact that the aromatic ring must be at least as reactive as a halobenzene. In addition, polyalkylation and carbocation rearrangements often occur in Friedel-Crafts alkylation. 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

From the recent advances the heteroatom-carbon bond formation should be mentioned. As for the other reactions in Chapter 13 the amount of literature produced in less than a decade is overwhelming. Widespread attention has been paid to the formation of carbon-to-nitrogen bonds, carbon-to-oxygen bonds, and carbon-to-sulfur bonds [29], The thermodynamic driving force is smaller in this instance, but excellent conversions have been achieved. Classically, the introduction of amines in aromatics involves nitration, reduction, and alkylation. Nitration can be dangerous and is not environmentally friendly. Phenols are produced via sulfonation and reaction of the sulfonates with alkali hydroxide, or via oxidation of cumene, with acetone as the byproduct. 

Several metal oxides could be used as acid catalysts, although zeolites and zeo-types are mainly preferred as an alternative to liquid acids (Figure 13.1). This is a consequence of the possibility of tuning the acidity of microporous materials as well as the shape selectivity observed with zeolites that have favored their use in new catalytic processes. However, a solid with similar or higher acid strength than 100% sulfuric acid (the so-called superacid materials) could be preferred in some processes. From these solid catalysts, nation, heteropolyoxometalates, or sulfated metal oxides have been extensively studied in the last ten years (Figure 13.2). Their so-called superacid character has favored their use in a large number of acid reactions alkane isomerization, alkylation of isobutene, or aromatic hydrocarbons with olefins, acylation, nitrations, and so forth. 

Both nitric acid and nitrogen dioxide, in the liquid and vapour phase, have been used for the nitration of the alkyl side chains of various alkyl-substituted aromatics without affecting the aromatic nucleus.Thus, treatment of ethylbenzene with nitric acid of 12.5 % concentration in a sealed tube at 105-108 °C is reported to generate a 44 % yield of phenylnitroethane. The nitration of toluene with nitrogen dioxide at a temperature between 20-95 °C yields a mixture of phenylnitromethane and phenyldinitromethane with the proportion of the latter increasing with reaction temperature. ... 

Many compounds have been tested as ignition quality improvers—additives which shorten the ignition delay to a desirable duration. An extensive review in 1944 (6, 43) listed 303 references, 92 dealing with alkyl nitrates and nitrites 61 with aldehydes, ketones, esters, and ethers 49 with peroxides 42 with aromatic nitro compounds 29, with metal derivatives 28 with oxidation and oxidation products 22 with polysulfides 16 with aromatic hydrocarbons nine with nitration and four with oximes and nitroso compounds. In 1950, tests at the U. S. Naval Engineering Experiment Station (48) showed that a concentration of 1.5% of certain peroxides, alkyl nitrates, nitroaikanes, and nitrocarbamates increased cetane number 20 or more units. 

Nitration of an aromatic ring138 to give ArNOa is most often carried out with nitric acid in sulfuric acid however, concentrated nitric acid, aqueous nitric acid, and nitric acid in polar organic solvents are also commonly used, as is preliminary nitrosation followed by oxidation of the aromatic nitroso compound (ArNO). Alkyl nitrates (R0N02) are also nitrating agents in the presence of some Bronsted and Lewis acids.139... 

Traditionally, nitration has been performed with a mixture of nitric and sulfuric acids (mixed acid method). However, the method is highly unselective for nitration of substituted aromatic compounds and disposal of the spent acid reagents presents a serious environmental issue. In order to address these problems several alternative methods for aromatic nitration have been developed recently. For example, lanthanide triflates catalyse nitration with nitric acid, which avoids the use of large volumes of sulfuric acid but provides no enhancement of selectivity.6 Selectivity of nitrations with alkyl nitrates,7 acyl nitrates,8 or even nitric acid itself9,10 can, however, be enhanced by zeolites. 

Liquid/liquid reactions of industrial importance are fairly numerous. A list of 26 classes of reactions with 61 references has been compiled by Doraiswamy and Sharma Heterogeneous Reactions, Wiley, 1984). They also indicate the kind of reactor normally used in each case. The reactions range from such prosaic examples as making soap with alkali, nitration of aromatics to make explosives, and alkylation of Csulfuric acid to make improved gasoline, to some much less familiar operations. 

Alkyl nitrates in sulphuric acid have already been used as nitrating agents (Vol. I, p. 122). Poly(phosphoric) acid [73] and Lewis acid halides [74—76] were also used with alkyl nitrates. Olah and Lin [77] nitrated a number of aromatic compounds with methyl nitrate and BF3 in nitromethane solution. Only mononitration took place. 

Alkaline hydrolysis of a variety of organic compounds nitration of chlorobenzene alkylation of benzene with straight-chain olefins reduction of aromatic nitro compounds to corresponding aromatic amines with aqueous NajS or Na2Sj. 

Hafnium triflate has also been used for acylation and alkylation of aromatic compounds.64 It has also been used in aromatic nitration in a process (6.18) that eliminates the usual waste acid from such reactions.65 The products are intermediates in the synthesis of toluene diisocyanates used in making polyurethanes. The catalyst could be reused with... 

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