1.4- Dimethoxybenzene, nitration

It has been considered that nitric acid was responsible for the oxidation of the nitroso compoimd, but there is recent evidence from the catalysed nitration of p-dimethoxybenzene in carbon tetrachloride that dinitrogen tetroxide is involved ... 

With the oxides which are nitrated as the cations the difficulties are much less serious for the use of an acidity function is not involved. Comparison of 2,6-dimethoxy- and 3,5-dimethoxy-pyridine i-oxide with wt-dimethoxybenzene (which is nitrated at the encounter rate)... 

Nitration versus oxidative dealkylation with nitrogen dioxides. The reaction of various substituted hydroquinone ethers with nitrogen oxides leads to either oxidation (i.e. 1,4-benzoquinones) or nitration (i.e. nitro-p-dimethoxybenzenes) depending on the reaction conditions239 (equation 84). 

An attempt to combine electrochemical and micellar-catalytic methods is interesting from the point of view of the mechanism of anode nitration of 1,4-dimethoxybenzene with sodinm nitrite (Laurent et al. 1984). The reaction was performed in a mixture of water in the presence of 2% surface-active compounds of cationic, anionic, or neutral nature. It was established that 1,4-dimethoxy-2-nitrobenzene (the product) was formed only in the region of potentials corresponding to simultaneous electrooxidation of the substrate to the cation-radical and the nitrite ion to the nitrogen dioxide radical (1.5 V versus saturated calomel electrode). At potentials of oxidation of the sole nitrite ion (0.8 V), no nitration was observed. Consequently, radical substitution in the neutral substrate does not take place. Two feasible mechanisms remain for addition to the cation-radical form, as follows ... 

The tri-nitration of 1,3-dimethoxybenzene with mixed acid, followed by amination, is a patented route to DATB. A similar route to TATB employing 1,3,5-trimethoxybenzene and dinitrogen pentoxide only results in moderate yields. ... 

A series of azophenol acerands 4 was prepared by condensation of crowned benzoquinones 10 with 2,4-dinitrophenylhydrazine in ethanol [7b], The quinone was derived from p-methoxyphenol (6) as shown in Scheme 1 [8]. By bis(hy-droxymethylation) (67% yield of 6, followed by methylation (92%) of the phenol group and Williamson-type reaction with ditosylates of oligoethyleneglycol in the presence of sodium hydride, crowned 1,4-dimethoxybenzene 9 was obtained in reasonable yields. Oxidative demethylation of 9 with ceric ammonium nitrate (CAN) in aqueous acetonitrile at 50 °C gave the desired crowned benzoquinones 10 in good yields. 

TrmitTO-l, 2-dimethoxybenzene or 3,4.5 Trm 7.royerfliro/e-, crysts (from benz or acet acid), mp 144—45° sol in hot ale, eth, toluene or butanol si sol in w, heptane methanol prepd by nitration of veratrole with coned HNOg H2SO4 at 100°(Ref 5)... 

Trinitro-1,3-dimethoxybenzene, col crysts (from ale), mp 193° obtd by nitrating 5-nitroresorcinol-dimethylethet or 4,5 dinitroresorcinol-dimethylether with HNO3 coned H2SO4 (Ref 8)... 

Quinones can be prepared by the oxidation of phenols, dihydroxy-benzenes, dimethoxybenzenes and anilines. For example, 1,4-dihydroxy-benzene (hydroquinone) can be oxidized in good yield using sodium chlorate in dilute sulfuric acid in the presence of vanadium pentoxide and also by manganese dioxide and sulfuric acid and by chromic acid. Other reagents which convert hydroquinones to quinones include Fremy s salt [potassium nitrosodisulfonate, (KS03)2NO] and cerium(IV) ammonium nitrate [CAN, Ce(NH4)2(N03)J. 

The regioselectivity observed with many nucleophilic arenes is moderate to excellent, and generally follows the pattern expected for aromatic electrophilic substitution (e.g., nitration, bromination, etc.) of the arenes. 3-Methoxythiophene reacts first at the 2-position but double arylation at the 2- and 5-positions is achieved in the absence of DME additive. 2-Ethylthiophene, 2,3-dimethylfuran, and 2,2 -bithiophene react at the expected 5-position and, similarly, thiophene reacts at the 2-position. 1,3-Dimethoxybenzene reacts exclusively at the 4-position while... 

The conversion of naphthalene to 2-naphthoic acids by irradiation with carbon dioxide and electron donors (e.g. amines or dimethoxybenzene) has been further investigated and the quantum yields of the reaction measured for different solvents and donors. Electron transfer also occurs in the photochemical phosphonation of naphthalene and phenanthrene achieved by irradiation with trialkyl-phosphites and electron acceptors such as 1,3-dicyanobenzene. The photonitration of phenol in aqueous solutions of nitrate ion has been reported and phenols have been prepared by irradiation of substituted benzenes with the aromatic N-oxide (132). ... 

N-CIDNP was used to investigate photoinduced nitrations of aromatic compoimds ArH with tetranitromethane. The polarizations invariably arise from radical pairs ArH NO, but the experiments reveal different pathways of formation of these pairs. With a substrate such as 1,2-dimethoxybenzene, the precursor multiplicity is triplet and the pairs are produced by a dissociative electron transfer from the aromatic compound to tetranitromethane, which then cleaves into an NO2 radical and C(N02)3. In contrast, the very similar substrate anisole (methoxybenzene) exhibits polarizations indicating a singlet precursor, and the radical pair is thought to be formed by decomposition of a preceding unstable diamagnetic intermediate, most probably a nitro-trinitromethyl adduct. ... 

The dimethoxybenzene nucleus of brucine (159), its methosulfate (82), dihydrobrucine (159), the brucinesulfonic acids (60, 93), pseudobrucine and its dihydro derivative (162, 165), iV-methyl-sec-pseudobrucine (168) as well as that of a number of transformation products of brucine (brucinonic acid (126), brucinolic acid (126), dihydrobrucinonic acid (126), bromo-dihydrodesoxybrucine (32), and dihydrodesoxybrucine (32)) is attacked by nitric acid (chromic acid in a few instances) at 0-5° with the formation of the respective o-quinones, which in turn may be reduced (SO2) to the respective colorless hydroquinones (or isomerized by HCl to colored isomers). More vigorous conditions (temperature and concentration of the oxidant) effect a simultaneous nitration of the quinone nucleus and a hydrolysis of the lactam grouping. 

One might imagine that these comprehensive data on anisole would enable us to predict the intramolecular selectivity of nitration of veratrole (1,2-dimethoxybenzene) with some success. Veratrole is nitrated at the limiting rate (Figure 5). (19) The... 

Enantiomer selective coloration of optically active amines, our important project, was realized by chiral azophenol crown 4 incorporated with two units of optically active hydrobenzoin. The synthetic route is shown in Scheme 2. Reaction of 2,6-bis(bromomethyl)-l,4-dimethoxybenzene 22, which is derived from hy-droquinone monomethylether 19 by a three-step procedure, with the dibutyltin derivative 26 of optically active dihydrobenzoin gives optically active podand 23 in 63% yield. Cyclization of 23 with the ditosylate of polyethylene glycol, followed by oxidation with ceric ammonium nitrate (CAN) and treatment with dinitrophenylhy-drazine, affords the desired chiral azophenol crowns 4n. 

Note Reagents for TM 2.15a and 2.15b are available aromatic compounds, products of the petrochemical industry. Para-nitrobenzoic acid is produced by nitration of toluene to para-isomer as the prevailing product, followed by oxidation of methyl to the carboxylic group. Orf/m-dimethoxybenzene is produced from ort/to-diphenol, which in turn is available by oxidation of phenol. One technological process uses hydrogen peroxide as oxidant [25], and annual production of ort/io-diphenol reaches 20,000 tons/year, mainly intended for the production of pesticides and perfumes. 

Cyclotriveratrylene in acetic acid added to a soln. of acetyl nitrate prepared by stirring a mixture of acetic anhydride and cupric nitrate trihydrate at room temp., then stirred 0.5 hr. at 50 4-(4,5-dimethoxy-2-nitrobenzyl)-5-(2-acetoxy-methyl-4,5-dimethoxybenzyl)-l,2-dimethoxybenzene. Y 76.5%. F. e. s. T. Sato, T. Akima, and K. Uno, Soc. Perkin I 1973, 891. 

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