Anisoles nitration

In order to examine the effect of the nitrating agent, anisole can be also treated with Me02CPyN02, PyN02 and MeOPyN02. Control experiments carried out simultaneously in the dark establish the absence of any electrophilic (thermal) component to anisole nitrations under all charge-transfer conditions (Kim et al., 1993 ). The photochemical nitrations of... 

Why is anisole nitrated more rapidly than thioanisole under the same conditions ... 

The nitration of anisole in 40% aq. nitric acid in the presence of some nitrous acid yielded 2,4-dinitrophenol as the main product. In more concentrated solutions of nitric acid 0- and />-nitroanisoles were the main products, less than o-1 % of the weta-isomer being formed. " The isomeric ratios for nitration imder a variety of conditions are given later ( 5.3.4). 

The kinetics of nitration of anisole in solutions of nitric acid in acetic acid were complicated, for both autocatalysis and autoretardation could be observed under suitable conditions. However, it was concluded from these results that two mechanisms of nitration were operating, namely the general mechanism involving the nitronium ion and the reaction catalysed by nitrous acid. It was not possible to isolate these mechanisms completely, although by varying the conditions either could be made dominant. 

It was shown that in preparative experiments sulphuric acid markedly catalysed, and acetate ions markedly anticatalysed the nitration of anisole. ... 

The authors of this work were concerned chiefly with additions to alkenes, and evidence about the mechanism of aromatic nitration arises by analogy. Certain aspects of their work have been repeated to investigate whether the nitration of aromatic compounds shows the same phenomena ( 5-3-6). It was shown that solutions of acetyl nitrate in acetic anhydride were more powerful nitrating media for anisole and biphenyl than the corresponding solutions of nitric acid in which acetyl nitrate had not been formed furthermore, it appeared that the formation of acetyl nitrate was faster when 95-98% nitric acid was used than when 70 % nitric acid was used. 

Zeroth-order nitrations. The rates of nitration at 25 °C in solutions of acetyl nitrate (6xio —0-22 mol 1 ) in acetic anhydride of 0- and jw-xylene, and anisole and mesitylene were independent of the concentration and nature of the aromatic compound provided that... 

Acetoxylation and nitration. It has already been mentioned that 0- and m-xylene are acetoxylated as well as nitrated by solutions of acetyl nitrate in acetic anhydride. This occurs with some other homologues of benzene, and with methyl phenethyl ether,ii but not with anisole, mesitylene or naphthalene. Results are given in table 5.4. 

Anisole] = 0 4 mol 1 zeroth-order reactions, except for that with added nitrate, which was of the first order with respect to the concentration of anisole. 

Without further studies little weight can be given to these ideas. In particular there is the possibility that with acetanilide, as with anisole, nitrosation is of some importance, and further with nitrations in sulphuric acid the effect of protonation of the substrate needs quantitative evaluation. The possibility that the latter factor may be important has been recognised, and it may account for the difference between nitration in sulphuric acid and nitration with nitronium tetrafluoroborate. 

Other substituents which belong with this group have already been discussed. These include phenol, anisole and compounds related to it ( 5.3.4 the only kinetic data for anisole are for nitration at the encounter rate in sulphuric acid, and with acetyl nitrate in acetic anhydride see 2.5 and 5.3.3, respectively), and acetanilide ( 5.3.4). The cations PhSMe2+, PhSeMe2+, and PhaO+ have also been discussed ( 9.1.2). Amino groups are prevented from showing their character ( — 7 +717) in nitration because conditions enforce reaction through the protonated forms ( 9.1.2). 

The nitration of 6-methoxyquinoxaline in concentrated sulfuric acid at 0°C gives 6-methoxy-5-nitroquinoxaline. The position of the nitro group is confirmed by reduction of the product to 5-amino-6-methoxy-quinoxaline identical with a sample prepared from 2,3,4-triamino-anisole and glyoxal ... 

Dinitro Methyl Anisole (4-Nitro-2-nitromethyl anisole, 3-Nitro-6-methoxynitromethyI toluol. or Methyl-[5-nitro-2-nitromethylphenyl] -ether). CH3.0.(N02)C6H3.CH2N02, mw 212.18, N 13.21%, OB to C02 —113.11%, cryst, mp 93—94°. Prepd from 4-nitro-2(lodomethyl) anisole in ether-ben2ene soln by treatment for 3 days at RT with Ag nitrate. The sodium salt explodes violently on heating Refs 1) Beil, not found 2) G. Bendy,... 

Kinetic studies have been made on the nitration of anisole, 4-chloroanisole, 4-nitrophenol and mesitylene105. For anisole the kinetics are complicated by demethylation for 4-chloroanisole, nitration by 4-10 M nitric acid in glacial... 

The charge-transfer nitrations of the aromatic donors are generally carried out to rather low actinic conversions to avoid complications from light absorption by the nitroarene products, and in duplicate sets (with a dark control) to monitor simultaneously any competition from thermal processes. For example, the yellow solution of anisole and Me2PyN02 in acetonitrile at — 40°C is irradiated with the aid of the cut-off filter that effectively removes all excitation light with Aexc<400nm. After reasonable photochemical conversions are attained, the H NMR spectrum is found to be virtually identical to that of the reaction mixture obtained by electrophilic (thermal) nitration (60). 

The observation of second-order kinetics (ku) for the spectral decay of the anisole cation radical in Fig. 15 points to the disappearance of AN + - after its separation from the initially formed triad in (63). Owing to the high yields of nitroanisoles obtained, such a process can be formulated as in Scheme 11 as the bimolecular (homolytic) reaction in (64) that produces the critical Wheland intermediate in aromatic nitration according to Perrin (1977) and Ridd (1991). 

The ambiphilic reactivity of aromatic cation radicals, as described in Schemes 12 and 13, is particularly subtle in the charge-transfer nitration of toluene and anisole, which afford uniformly high (>95%) yields of only isomeric nitrotoluenes and nitroanisoles, respectively, without the admixture of other types of aromatic byproducts. Accordingly, let us consider how the variations in the isomeric (ortho meta para) product distributions with... 

Anisole. The simultaneous (homolytic and nucleophilic) annihilations of AN+ as described by the time-resolved spectroscopic results lead to the distinctive mixtures of o- and p-nitroanisoles, in which the isomeric composition is strongly dependent on the nitrating reagent in the following way. 

Isomeric product distributions. Isomeric product distributions obtained from toluene and anisole have been the subject of considerable mechanistic discussion in electrophilic aromatic nitration (Schofield, 1980 Olah et al., 1989). As applied to nitrations with iV-nitropyridinium ion, the yellow colour of the EDA complex immediately attendant upon the mixing of toluene and PyN02 in acetonitrile persists for about a day (in the dark), whereas the charge-transfer colour of toluene and Me2PyNOj is discharged within 10 min at 25°C. Both bleached solutions afford an identical product mixture (81), consisting of o- (62%), m- (4%) and p-nitrotoluenes (34%)... 

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