1,4-dimethoxybenzene, 1,4-addition

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),... 

In the oxidation of aromatic substances at the anode, radical cations or dications are formed as intermediates and subsequently react with the solvent or with anions of the base electrolyte. For example, depending on the conditions, 1,4-dimethoxybenzene is cyanized after the substitution of one methoxy group, methoxylated after addition of two methoxy groups or acetoxylated after substitution of one hydrogen on the aromatic ring, as shown in Fig. 5.55, where the solvent is indicated over the arrow and the base electrolyte and electrode under the arrow for each reaction HAc denotes acetic acid. 

Overcharge tests were carried out in LiCo02 cathode half-cells that contained these additives, and a redox shuttle effect was observed between 4.20 and 4.30 V, close to the redox potentials of these additives. The same shuttling effect was observed even after 2 months of storage for these cells, indicating the stability and redox reversibility of these additives. A closer examination of the capacity retention revealed that 4-bromo-l,2-dimethoxybenzene seemed to have the best shuttle-voltage performance for the 4.0 V lithium cell used." The stability of these additives against reductive decomposition was also tested by the authors on metallic lithium as well as on carbonaceous anodes, and no deterioration was detected. 

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 ... 

SYNTHESIS A well stirred suspension of 140 g anhydrous A1C13 in400 mL CH,C.l, was treated with 102 g butyryl chloride. This mixture was added in small portions, over the course of 20 min, to a well-stirred solution of 110.4gp-dimethoxybenzene in 300 mL CH2C12. After an additional 1 h stirring, the mixture was poured into 1... 

SYNTHESIS To a solution of 165 g 1,4-dimethoxybenzene in 1 L of CH,C12, in a well ventilated place and well stirred, there was cautiously added 300 mL chlorosulfonic acid. With about half the acid chloride added, there was a vigorous evolution of HC1 gas and the generation of a lot of solids. As the addition was continued, these redissolved to form a clear, dark green solution. Towards the end of the addition, some solids were again formed. When everything was stable, there was added 2 L H20, a few mL at a time, commensurate with the vigorofthereaction. 

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. 

In the NMR spectrum integrated signals are exactly proportional to the number of contributing nuclei. The Comite Consultatif pour la Quantite de Matiere (CCQM) has started international comparison of quantitative NMR experiments. In the first round the possible reproducibility should be established. The composition of a mixture of organic compounds has been determined by integration of the NMR signals. Already the first experiments (Fig. 9) have shown the problems arising by isomerization (ethyl-4-toluene sulphonate), decomposition (1,3-dimethoxybenzene), purity of standard compound and superimposition of isotopic satellites. Additional experiments with a new composition are necessary. 

In fact, the addition of 1,4-dimethoxybenzene (DMB) and/or several similar compounds, at concentrations as low as 10 4 M, to a mixture of aryl-olefins and DCA almost completely inhibits the reactions. Concentration dependence and flash photolysis studies confirm that the primary electron-transfer process occurs between the singlet excited sensitizer and DMB (E01 = 1.34 V vs SCE) with the generation of the corresponding radical ion pair. As a consequence, quantum yields lower than 1, even at infinite substrate concentration, are measured [95]. In this regard, valuable confirmations came from the cyanoaromatic photoinduced electron-transfer oxygenation of alkynes [99], Farid and Mattes reported that the photooxygenation of diphenylacetylene DPA (E° = 1.85 V vs SCE) 25, leading to a mixture of benzil 26 and benzoic acid 27, was efficiently sensitized by DCA ( = 0.15), but poorly by TCA ( > < 0.001) [Eq. (12)] [99]. 

In fact, the addition of 1,4-dimethoxybenzene (DMB) (0.13 equiv.), easier to oxidize than 21, appreciably quenches the reaction. The laser flash photolysis with a nitrogen-pulsed laser (337 nm) of a TPP+BF4 (1.6 x 10-4 M) dichloromethane solution, in the presence of 21 (6.2 x 10 2 M), conditions in which nearly 80% of the singlet excited sensitizer (Ered = 0.29 V vs SCE) is quenched by 21, gives a transient absorption (A 550 nm) assigned to a pyranil radical TPF. 

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