2.4- dimethoxybenzene-, sodium

Halophenols without 2,6-disubstitution do not polymerize under oxidative displacement conditions. Oxidative side reactions at the ortho position may consume the initiator or intermpt the propagation step of the chain process. To prepare poly(phenylene oxide)s from unsubstituted 4-halophenols, it is necessary to employ the more drastic conditions of the Ullmaim ether synthesis. A cuprous chloride—pyridine complex in 1,4-dimethoxybenzene at 200°C converts the sodium salt of 4-bromophenol to poly(phenylene oxide) (1) ... 

Derbyshire and Waters202 carried out the first kinetic study, and showed that the chlorination of sodium toluene-m-sulphonate by hypochlorous acid at 21.5 °C was catalysed more strongly by sulphuric acid than by perchloric acid and that the rate was increased by addition of chloride ion. A more extensive examination by de la Mare et al.203 of the rate of chlorination of the more reactive compounds, anisole, phenol, and />-dimethoxybenzene by hypochlorous acid catalysed by perchloric acid, and with added silver perchlorate to suppress the formation of Cl2 and C120 (which would occur in the presence of Cl" and CIO-, respectively),... 

Sulfonamides are very difficult to hydrolyze. However, a photoactivated reductive method for desulfonylation has been developed.240 Sodium borohydride is used in conjunction with 1,2- or 1,4-dimethoxybenzene or 1,5-dimethoxynaphthalene. The photoexcited aromatic serves as an electron donor toward the sulfonyl group, which then fragments to give the deprotected amine. The NaBH4 reduces the radical cation and the sulfonyl radical. 

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]. 

I. 4-methoxyacetophenone (30 //moles) was added as an internal standard. The reaction was stopped after 2 hours by partitioning the mixture between methylene chloride and saturated sodium bicarbonate solution. The aqueous layer was twice extracted with methylene chloride and the extracts combined. The products were analyzed by GC after acetylation with excess 1 1 acetic anhydride/pyridine for 24 hours at room temperature. The oxidations of anisyl alcohol, in the presence of veratryl alcohol or 1,4-dimethoxybenzene, were performed as indicated in Table III and IV in 6 ml of phosphate buffer (pH 3.0). Other conditions were the same as for the oxidation of veratryl alcohol described above. TDCSPPFeCl remaining after the reaction was estimated from its Soret band absorption before and after the reaction. For the decolorization of Poly B-411 (IV) by TDCSPPFeCl and mCPBA, 25 //moles of mCPBA were added to 25 ml 0.05% Poly B-411 containing 0.01 //moles TDCSPPFeCl, 25 //moles of manganese sulfate and 1.5 mmoles of lactic acid buffered at pH 4.5. The decolorization of Poly B-411 was followed by the decrease in absorption at 596 nm. For the electrochemical decolorization of Poly B-411 in the presence of veratryl alcohol, a two-compartment cell was used. A glassy carbon plate was used as the anode, a platinum plate as the auxiliary electrode, and a silver wire as the reference electrode. The potential was controlled at 0.900 V. Poly B-411 (50 ml, 0.005%) in pH 3 buffer was added to the anode compartment and pH 3 buffer was added to the cathode compartment to the same level. The decolorization of Poly B-411 was followed by the change in absorbance at 596 nm and the simultaneous oxidation of veratryl alcohol was followed at 310 nm. The same electrochemical apparatus was used for the decolorization of Poly B-411 adsorbed onto filter paper. Tetrabutylammonium perchlorate (TBAP) was used as supporting electrolyte when methylene chloride was the solvent. 

The following chemicals were obtained from Aldrich Chemical Company, Inc. and used without further purification 1,3-dimethoxybenzene (99%) butyl lithium (1.6 M in hexanes) 1-formylpiperdine (99%) boron trifiuoride-diethyl ether (purified, redistilled) 2,3-dichloro-5,6-dicyano-l,4-benzo-quinone (98%), and pyridine hydrochloride (98%). All solvents were reagent grade and were obtained from Fisher Scientific and used without further purification except where noted. Silica gel (230-400 mesh) was obtained from EM Scientific. Chloroform was stored over activated, 4-A molecular sieves for at least 24 h prior to use. Tetrahydrofuran (optima grade) was distilled from sodium benzophenone. Pyrrole (99%) was obtained from Aldrich Chemical Company, Inc. and distilled from calcium hydride. 

The solubility of the components in the solvent must be sufficient. To improve the solubility, cosolvents can be used. Another possibility is the application of a two-phase system or an emulsion in the presence of phase-transfer catalysts. A two-phase system also has advantages in product isolation and continuous electrolysis procedures. A typical example is the synthesis of p-methoxy benzonitrile by anodic substitution of one methoxy group in 1,4-dimethoxybenzene by the cyanide ion (Eq. 22.21). The homogeneous cyanation system (acetonitrile, tetraethylammonium cyanide) [24] can be efficiently replaced by a phase-transfer system (dichloro-methane, water, sodium cyanide, tetrabutylammonium hydrogen sulfate) [71]. 

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. 

Nucleophilic bis-O-demethylation of dimethoxybenzenes in one flask is often difficult. It can, however, be achieved by use of sodium TMS thiolate in l,3-dimethyl-2-imidazolidinone (DMEU) at high temperature in a sealed tube101. The same reagent system converts nitriles into primary thioamides at or slightly above room temperature in varying yields102. 

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 sodium nitrite (Laurent et al. 1984). The reaction was performed in a mixture of water with in 2% surface-active compounds of cationic, anionic, or neutral nature. It was established that 2,5-dimethoxy-l-nitrobenzene—the product—was formed only in the region of potentials corresponding to simultaneous electro-oxidation of the substrate to the cation radical and of the nitrite ion to the nitrogen dioxide radical (1.5 V versus saturated calomel electrode). 

Demethoxylationl-Alkyl-3,4,5-trimethoxybenzenes are converted into 1-alkyl-3,5-dimethoxybenzenes on treatment with potassium sand in THF. Either sodium or potassium can be used to convert 1,2,3-trimethoxybenzene into 1,3-dimethoxybenzene (85% yield). 

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. 

Sodium hydride (0.8 g) was added to 50 ml THE and diethylmalonate added over 5 minutes. l-Bromo-2,4-dimethoxybenzene (1.08 g) was then added in one portion and the reaction flask cooled to — 20°C. A few crystals of 1,10-phenanthroline were added as an indicator and the flask further cooled to —60°C. A few drops of n-BuLi were added until the brown color of the indicator persisted. Thereafter n-BuLi (3.05 mmol) and 0.91ml diisopropylamine was added to form lithium diisopropyl-amide. In order to observe a product conversion of 97%, a total of 2.5 ml EDA added drop wise via cannula in 24 minutes at —20°C to —24°C. The solution was acidified using 1.0 M HCl and the organic portion isolated, washed with brine and isolated in 93.2% purity as a yellow oil. H-NMR data supplied. 

Hwu and co-workers reported selective cleavage of a benzyl (Bn) ether with lithium di-isopropylamide (LDA) in the presence of a methoxy group however, by using sodium bis(trimethylsilyl)amide [NaN(SiMe3)2], the dimethoxybenzene undergoes selectively mono-O-demethylation (Scheme 1.21). 

A solution containing 15.4 g. of l-hydroxy-2,6-dimethoxybenzene and 14.4 g. of 1,1-dimethyl-1-hydroxyheptane in 20 mL. of methane-sulfonic acid was heated at 50° C. and stirred for three and one-half hours. The reaction mixture next was poured over 50 g. of ice, and the resulting aqueous solution was extracted several times with dichloromethane. The organic extracts were combined, washed with water and with saturated aqueous sodium bicarbonate solution, and dried. Removal of the solvent by evaporation under reduced pressure provided 27.4 g. of l-hydroxy-2,6-dimethoxy-4-(l,1-dimethyl-heptyl)benzene as an oil. Source Dominianni 1978... 

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. 

A suspension of KCl (59 mmol), 18-crown-6(264mg) (1 mmol) and the phenol ether in dichloromethane (35 ml) cooled to OC and with stirring treated with 3-chlorobenzoic acid (2.59g 12mmol). Reaction stirred 15 mnn. and workred up with sodium bisulphite to give 4-chloro-1,3-dimethoxybenzene. 

Irradiation of N-tosylamines in aqueous ethanol in the presence of an aromatic electron donor such as 1,4-dimethoxybenzene, and a reductant such as sodium borohydride induced detosylation and liberation of the corresponding primary or secondary amine 70 selective deprotection of some Ne- tosyl-lysine peptides was successful. 

A common intermediate in the synthesis of benzo[c]phenanthridines is the 2-aryl-l-tetralone, which provides rings A, B, and D of the alkaloid nucleus. In 1973, two independent research groups reported the synthesis of nitidine via the 3,4-dihydro-2-(3,4-dimethoxyphenyl)-6,7-methylenedioxy-(2/7)-naphthalone 29 (Scheme 2). The synthesis of this intermediate was arrived at by two different routes. Kametani ei al. (73JHC31) reduced 3-(3,4-methylenedioxyphenyl)proprionate 21 to the corresponding alcohol 22 with lithium aluminium hydride, which was then converted to the chloride 23 with thionyl chloride. After production of the nitrile 24 by reaction with sodium cyanide and subsequent hydrolysis to the carboxylic acid 25, Friedel-Crafts cyclization of the acid chloride 26 afforded the tetralone intermediate 27. Reaction with l-bromo-3,4-dimethoxybenzene 28 in the presence of sodium amide yielded the tetralone intermediate 29 in an overall yield of 4%. 

To a stirred solution of 60 g of 2-ethylthio-1,3-dimethoxybenzene in 300 mL CH2CI2 there was added 49 g elemental bromine dissolved in 100 mL CH2CI2. The reaction was not exothermic, and it was allowed to stir for 2 h. The reaction mixture was washed with H20, then with aqueous NaOH, and finally with H20 that contained sodium hydrosulfite. 

Captan Copper oxide (ous) 1,4-Dichloro-2,5-dimethoxybenzene Drazoxolon Mancozeb Metam-sodium Methoxyethylmercury acetate Paraformaldehyde Prochloraz Propamocarb hydrochloride... 

---