Toluene nitrosation

Snia Viscosa. Catalytic air oxidation of toluene gives benzoic acid (qv) in ca 90% yield. The benzoic acid is hydrogenated over a palladium catalyst to cyclohexanecarboxyhc acid [98-89-5]. This is converted directiy to cmde caprolactam by nitrosation with nitrosylsulfuric acid, which is produced by conventional absorption of NO in oleum. Normally, the reaction mass is neutralized with ammonia to form 4 kg ammonium sulfate per kilogram of caprolactam (16). In a no-sulfate version of the process, the reaction mass is diluted with water and is extracted with an alkylphenol solvent. The aqueous phase is decomposed by thermal means for recovery of sulfur dioxide, which is recycled (17). The basic process chemistry is as follows ... 

Scheme 11.11 gives some representative preparative reactions based on these methods. Entry 1 is an example of the classical procedure. Entry 2 uses crown-ether catalysis. These reactions were conducted in the aromatic reactant as the solvent. In the study cited for Entry 2, it was found that substituted aromatic reactants such as toluene, anisole, and benzonitrile tended to give more ortho substitution product than expected on a statistical basis.180 The nature of this directive effect does not seem to have been studied extensively. Entries 3 and 4 involve in situ decomposition of A-nitrosoamides. Entry 5 is a case of in situ nitrosation. 

Typical primary amines which undergo such nitrosation are m-toluidine, p-xylidine, m-anisidine, 2-amino-4-methoxytoluene, 3-amino-4-methoxy-toluene, m-aminophenol, a-naphthylamine, l-naphthylamine-2-, -6-, -7-, and -8-monosulfonic acids, and l-naphthylamine-4-monosulfonic acid (which reacts with displacement of the sulfonic acid group). The secondary amines derived from these primary amines also can be nitrosated directly (i.e., without the intermediate formation of an JV-nitroso compound which needs to be subjected to the Fischer-Hepp rearrangement). The entering nitroso group appears to substitute exclusively in the para position. 

SNAICO Engineering SpA Caprolactam Toluene Process yields high-purity product via hydrogenation and nitrosation 4 1994... 

Most aromatic compounds, whether of high or low reactivity, can be nitrated, because a wide variety of nitrating agents is available. For benzene, the simple alkylbenzenes, and less reactive compounds, the most common reagent is a mixture of concentrated nitric and sulfuric acids,but for active substrates, the reaction can be carried out with nitric acid alone, or in water, acetic acid, acetic anhydride, or chloroform.Nitric acid in acetic anhydride/trifluoroacetic anhydride on zeolite H-(3 was used to convert toluene to 2,4-dinitrotoluene, and AcONOi on clay converted ethylbenzene to ortho-para nitro ethylbenzene. " In fact, these milder conditions are necessary for active compounds, such as amines, phenols, and pyrroles, since reaction with mixed nitric and sulfuric acids would oxidize these substrates. With active substrates, such as amines and phenols, nitration can be accomplished by nitrosation under oxidizing conditions with a mixture of dilute nitrous and nitric acids.A mixture of N02/02/Fe(acac)3 can be used for active compounds, as can NaN02 with trichloroisocyanuric acid on wet silica gel, or N2O4 and silica acetate. Trimethoxybenzenes were nitrated easily with ceric ammonium nitrate on silica gel, and mesitylene was nitrated in an... 

Bridge s classical procedure287 may be cited as an example of nitrosation of a phenol Phenol (60 g), sodium hydroxide (27 g), and sodium nitrite (54 g) are dissolved in water (1500 ml) and treated gradually with a mixture of concentrated sulfuric acid (150 g) and water (400ml) at 7-8° with cooling. After 2 h the precipitated nitrosophenol is filtered off, washed with ice-water, taken up in ether, and shaken with animal charcoal at room temperature. Evaporation of the ether affords an 80% yield of p-nitrosophenol as yellow needles that melt at 125° with decomposition. For purification it may be recrystallized from benzene or toluene. 

The nitrito-onium salts act as nitrating agents for aromatics that do not undergo nitrosation. Their nitrating ability is, however, considerably less compared to that of the corresponding nitro-onium salts (e.g., toluene is nitrated only at g60 C whereas the nitro-onium salts nitrate at s25°C). 

Toluene is oxidized in liquid phase to benzoic acid, which is subsequently hydrogenated to cyclohexane carboxylic acid. Reaction of this acid with nitrosylsulfuric acid in oleum then results directly in the formation of caprolactam sulfate by a mechanism that entails simultaneous nitrosation, decarboxylation, and rearrangement of the formed oxime. 

Methods of Synthesis. C-Nitrosierungen Qber Silyl-derivate [nitrosation of (trimethyl-silyl)benzene, p-(trimethylsilyl)toluene, and 4-(trimethylsilyl)pyrazole with alkyl nitrite-CFj-COaH or NaNOa-CFj COaH gives nitrosobenzene, p-nitrosotoluene, and 4-nitrosopyrazole, respectively]. Dimethyl Sulphoxide Oxidations A New Method for the Conversion of C = S and C=Se Groups into a Carbonyl Group [CFj-COaH catalyses the conversion of thio- or seleno-carbonyl groups into C=0 via reaction... 

---