1.3- Dimethoxy-5- benzen

The authors repeated the experiment with two, more strongly retained, solutes m-dimethoxy benzene and benzyl acetate. These solutes were found to elute at (k ) values of 10.5 and 27.0 respectively on a silica column operated with the same mobile phase. The results obtained are shown as similar curves in Figure 13. The m dimethoxy benzene, which eluted at a (k ) of 10.5, also failed to displace any ethyl acetate from the silica gel even when more than 0.5 g of solute resided on the silica surface. Consequently, the m-dimethoxy benzene must have also interacted with the surface by a sorption process. 

Katsuya et al. [5 published the oxidative coupling (agent copper(II) chloride/ aluminum chloride) of electron-rich benzene derivatives such as 2,5-dimethoxy-benzene to poly(2,5-dimethoxy-1,4-phenylene) (2). The resulting polymer is only soluble in concentrated sulfuric acid, and is fusible at 320r C. Ueda et al. 16] described the coupling of the same monomer with iron(III) chloride/aluminum chloride. The polymers obtained by the authors were not thoroughly para-linked. 

Phenol ethers show some, admittedly low, reactivity towards diazonium ions and also undissociated phenols (see Sec. 12.7). An instructive example of the reactivity of phenol ethers was reported by Ronaldson (1981). He found that 1,2-dimethoxy-benzene (veratrole) does not react with the 4-nitrobenzenediazonium ion, but the azo coupling product is formed when the more electrophilic 2,4-dinitrobenzenediazo-nium ion is used. 

Tetramethyl-1,4-dimethoxy-benzene Polycyclic aromatic hydrocarbons 1-46 (g) 8.06 (0... 

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.)...

A second example from the same group is the synthesis of an elaborate diethynyltriphenylene derivative (Scheme 7 Table 8,entries 12,13) [58].Zn/Pd-promoted homocoupling of a 4-iodo-l,2-dialkoxybenzene furnishes the desired tetraalkoxybiphenyl, an electron-rich aromatic system. Iron trichloride-catalyzed Friedel-Crafts arylation of the biphenyl derivative with dimethoxy-benzene furnishes an unsymmetrical triphenylene derivative. Deprotection, oxidation, and subsequent Diels-Alder reaction with cyclohexadiene is followed by catalytic hydrogenation and reoxidation. TMS-CC-Li attack on the quinone delivers the alkyne modules, treatment with SnCl2 aromatizes the six-mem-bered ring, while KOH in MeOH removes the TMS groups cleanly to give the elaborate monomer. 

Particularly striking is the reaction of 5-nitro-l,3-dimethoxy-benzene (Wiegerink, 1973). Equation (18) demonstrates that the ortAo-j ara-orientation by the two methoxy-groups may successfully compete with the mete-activation by the nitro-substituent. 

Anisyl Alcohol (/imoles) 1,4-dimethoxy Benzene (/imoles) % Yield of Anisaldehyde % TDCSPPFeCl Left After Reaction... 

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. 

It has been demonstrated9 that photo-protonation of 2-diphenylmethyl-l,3-dimethoxy-benzene (4) to the cyclohexadienyl cation (5) not only results in dissociative cleavage of the diphenylmethyl cation (the reverse of the step in a Friedel-Crafts alkylation that produces the cyclohexadienyl cation), but is accompanied by a surprising rearrangement to the isomeric 2,4-dimethoxybenzenium ion (6). This (see Scheme 3) represents the first example of a system where rearrangement involving two isomeric... 

As for the anode process at comparable conditions, the yield of 2,5-dimethoxy nitro benzene depends distinctly on the electrical nature of the micelle. Namely, the yields are equal to 30% for the positively charged micelle, 40% for the negatively charged micelle, and 70% for the neutral charged micelle. The observed micellar effect corroborates the mechanism, including the dimethoxy benzene cation radical and the nitrogen dioxide radical as reacting species. 

For Hammett correlations for rate constants of substituted benzenes reacting with hydroxyl radicals under experimental conditions of pH 9, the elementary hydroxyl radical rate constants (l/m sec 108) containing toluene, dimethoxy-benzene, benzene, and nitrobenzene correlate with aresonance as follows ... 

Stoddart representation "blue box" with included p-dimethoxy benzene in red... 

Table 12.4 summarizes the voltammetric oxidation potentials and peak currents for l,4-(MeO)2Ph and other alkoxy-substituted benzenes, phenols, and benzyl alcohols. Only the 1,4-(MeO)2PhX members of the series exhibit an initial irreversible anodic cyclic voltammogram via the sequence of Eq. (12.37). These plus the l,2-(MeO)2Ph isomer yield a metastable product from the second oxidation [species A, Eq. (12.37)] that undergoes a reversible reduction. Thus, the two-electron oxidation of dimethoxy benzenes yields the corresponding quinone. 

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