Benzenes Dimethoxybenzenes

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. 

Dimethoxybenzene [150-78-7] M 137.2, m 57.2-57.8 . Steam distd. Crystd from hexane or benzene, and from MeOH or EtOH but these are wasteful due to high solubilities. Dried under vacuum. Also sublimes under vacuum. 

Anions of CH-acidic compounds (dimethyl malonate and nitromethane) can he linked to aromatics (benzene, toluene, naphthalene, and 1,4-dimethoxybenzene) when they are coelectrolyzed in methanol-sodium methoxide [167]. 

Figure 45. Cyclic voltammetry of (a) 4-halo-1,2-dimethoxy-benzenes (Reproduced with permission from ref 432 (Figure 8). Copyright 1999 The Electrochemical Society.) and (b) 1,3-dimethoxybenzenes in LiPFe/PC/DMC on Pt (Reproduced with permission from ref 432 (Figure 9). Copyright 1999 The Electrochemical Society.)...

The three dimethoxybenzenes as well as the three trimethoxy-benzenes undergo smooth photocyanation, yielding in all cases the products to be expected from ortho-para orientation (Figure 9) (den Heyer, 1973). 

Radical-cations generated in this way are characterised by their uv spectra (Table 6.2) and their esr spectra. The oxygen lone-pairs in meftoxybenzene radical-cations participate in delocalization of the positive charge so that, on the esr time-scale, phenomena due to hindered rotation about the benzene-oxygen bond appear. The two ortAo-hydrogens in anisole radical-cation have different esr coupling constants. 1,4-Dimethoxybenzene radical-cation is found as a mixture of cis- and fra j-isomers due to this hindered rotation [22],... 

All the 3-diazoindazoles 2, irradiated in an aromatic solvent (benzene, p-chlorotoluene, benzonitrile, 1,2-dimethoxybenzene), gave by ring substitution the corresponding 3-arylindazoles in variable yields (66LA17). 3-Diazoindazole 2b, irradiated in pyridine and in thiophene, gave the 6-chloro-3-(2-pyridyl)-indazole and the 6-chloro-3-(2- or 3-thiophenyl)-indazole (66LA17). 

Dimethoxybenzene and derivs 5 D1302-D1303 dinitrodimethoxy benzene 5 D1302 mononitrodimethoxybenzene 5 D1302 trinitrodimethoxybenzenes 5 D1302... 

To a stirred solution of 19.8 g of 2-(n)-propylthio-l,3-dimethoxybenzene in 200 mL CH,C12 there was added 15.4 g elemental bromine dissolved in 100 mL CH2C1,. The reaction was not exothermic, and it was allowed to stir for 1 h. The reaction mixture was washed with H,0 containing sodium hydrosulfite (which rendered it nearly colorless) and finally washed with saturated brine. The solvent was removed under vacuum leaving 3 3.5 g of apale yellow liquid. This was distilled at 112-120 °C at 0.3 mm/Hg to yield 4-bromo-2-(n)-propylthio-l,3-dimethoxy-benzene as a pale yellow oil. Anal. (CnH 5Br02S) C,H. 

Triflic acid is also efficient in the alkylation of electron-rich aromatics (anisole, 1,3-dimethoxybenzene, 2-methylfurane, pyrrole, benzofurane, indole) with secondary benzylic alcohols and 3-phenylallyl alcohols (50°C, 1-9 h, 66-95% yield).201 Benzene, toluene, and halobenzenes are also alkylated with hydroxy-biindantetraone 53 in triflic acid within 1-2h202 [Eq. (5.78)]. Suprisingly, however, the primary products (with the exception of the 4-methylphenyl-substituted compound) undergo rearrangement upon prolonged treatment to yield alkenes... 

Efficient synthesis of 6,7-dimethoxybenzopentathiepin 102 and 6-(2-aminoethyl)benzopentathiepin 103 (Figure 29), which are sectional structures of varacin, were proposed from 1,2-dimethoxybenzene and 1,2-benzene-dithiol, respectively <1995H(41)893>. 

Similar para-quinone derivatives can be obtained by oxidative demethyla-tions of phenol ethers which can be performed in water. Either [bis(trifluo-roacetoxy)iodo]benzene 4 or the polymer-supported reagent 19 can be used for the generation of para-quinones 38 from 1,4-dimethoxybenzene derivatives of type 39, Scheme 19 [93]. 

Similar results were obtained [139] with the three dimethoxybenzenes and acrylonitrile, methacrylonitrile, and crotonitrile. The amounts of substitution products decrease in the order acrylonitrile (49%) > methacrylonitrile (45%) > crotonitrile (6%), which agrees with the electron affinities of these compounds. Simultaneously, the amount of addition product increases acrylonitrile, 0% methacrylonitrile, 38% crotonitrile, 67%. In the series of anisole and the dimethoxybenzenes with crotonitrile, the amount of substitution products decrease in the order ortho- and para-dim ethoxy benzene > meta-dimethoxyben-zene > anisole, which is just the reverse of the order of their oxidation potentials. Ohashi et al. [139] have attempted to relate the photochemical behavior of these systems to the free enthalpy of electron transfer in the excited state as calculated with the Rehm-Weller equation, AG = E(D/D+) - E(A /A) - el/eR - AE00. 

Analytical Properties Separation of dimethylbenzene isomers, dihalobenzene isomers (Cl, Br), haloketone benzene isomers, dimethoxybenzene isomers Reference 14... 

When 1,3-dimethoxybenzene is heated in benzene with la-acetyl-l-phthalamido-la,6b-dihydro-benzofuro[2,3-fo]az.irine as a source of phthalimidonitrene, 2,4-dimethoxy-7-phthalimido-3//-azepine is isolated in modest yield <95JCS(PI )809>. If the reaction is carried out over a shorter time period (5h instead of 18h), it is the 2//-azepine which is isolated in 18% yield. A number of other analogues have been prepared and the X-ray structure of 5,7-dimethoxy-3-methyl-2-phthalimido-27/-azepine has been determined. 

In the years since 1998, some papers have reported the benzoylation of substituted benzene derivatives, such as toluene, [9-11] ethyl benzene,[11] xylene,19 11 121 anisole/9 131 dimethoxybenzene,[14] biphenyl/151 phenol[16] and chlorobenzene1171 in the presence of zeolites and, in most cases, particularly H-BEA zeolite. 

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