Dimethoxy hydroquinone

The most simple artificial system consists of cofacial bis-quinone cyclo-phanes in which the two quinones have different redox potentials. Extreme differences in relative orientations have been realized with the ortho and geminal isomers in which a tetracyanoquinomethane oxidant and dimethoxy hydroquinone reduc-tants are connected by two propylene bridges (Fig. 7.2.4). A strong broad charge transfer band (600-1000 nm) was observed for the geminal isomer (e = 35(X)) and a weaker one for the ortho isomer (e = 120), indicating the importance of the relative orientation of electron donors and acceptors (Staab and BCnaus, 1979). 

Preparation by reaction of acetic acid on 2,5-dimethoxy-hydroquinone diacetate with boron trifluoride etherate at 75° [2998,3139], (55%) [3139],... 

Preparation by Fries rearrangement of 2,6-dimethoxy-hydroquinone diacetate with aluminium chloride at 120-125° (80%) [3146]. 

COCH2 —( y Obtained (by-piodnct) by condensation of 2,6-dimethoxy-hydroquinone with the com-CH3O y OCH3 pjgjj phenylacetic acid and boron trifluoride... 

Thallium trinitrate oxidi2es naphthols and hydroquinone monoethers, respectively, to quinones and 4,4-diaIkoxycyclohexa-2,5-dienones, eg, 4,4-dimethoxy-2-methyl-2,5-cyclohexadienone [57197-11 -2] (108) (111,112). The yield of (108) is 89%. Because the monoacetal is easily converted to the quinone, the yield of 5-hydroxy-l,4-naphthoquinone [481-39-0] is 64%. 

Ceric ammonium nitrate converts a 1,4-dimethoxy aromatic compound to the quinone, which is reduced with sodium dithionite to give a depro-tected hydroquinone. ... 

The monomers studied, 2-hydroxyethyl methacrylate (HEMA) and diethylene glycol dimethacrylate (DEGDMA), were obtained from Aldrich (Milwaukee, WI) and Polysciences, Inc. (Warrington, PA), respectively, and were used after dehibition to remove the hydroquinone inhibitor. 2,2-Dimethoxy-2-phenyl acetophenone (DMPA), the conventional initiator used in this study, was obtained from Ciba-Geigy (Hawthorne, NY) and the tetraethylthiuram disufide (TED) was obtained from Aldrich. 

Anodic addition converts enolacetates into a-acetoxyketones or enones, depending on the reaction conditions [135], conjugated dienes into 1,2- or 1,4-dimethoxy alkenes [65], and hydroquinone dimethyl ethers into quinone bisketals [136, 137]. Anodic addition also affords products, some of which are of industrial interest, such as propylene oxide [138a] or 1,4-dimethoxydihydrofuran [138b]. To... 

The preparation of coenzyme Q usually involves either 2,3-dimethoxy-5-methylbenzoquinone or hydroquinone as the starting material. Treatment of the hydroquinone with geranyl bromide followed by oxidation affords (61, n = 2) (214). A facile and efficient preparation of ubiquinone-10 (61, n = 10) has been developed (215). 

The last of the butyl isomers, the tert-butyl compound, was made from a much more obvious starting material. This is the commercially available tert-butyl hydroquinone. It was methylated in sodium hydroxide with methyl iodide, and then carried through the above sequence (benzaldehyde. mp 124 °C from cyclohexane, nitrostyrene, yellow crystals from methanol, mp 95-96.5 °C, and lithium aluminum hydride reduction) to give 2,5-dimethoxy-4-(l,l-dimethylethyl)amphetamine hydrochloride (DOTB, mp 168 °C). Rats trained in a process called the Sidman Avoidance Schedule gave behavior that suggested that DOTB had no activity at all, and in human trials, doses of up to 25 milligrams were totally without effect. 

There are many examples in the literature on applications of 1,4-hydroquinones as polymer stabilizers and as antioxidants. The natural ubiquinols are 2,3-dimethoxy dialkyl derivatives of these hydroquinones and these natural compounds are now known to be of great importance in biological systems. We select a few examples of 1,4-hydroquinones as antioxidants to illustrate the effect of structure (e.g. substituents) on their reactivity, but especially to emphasize the role that hydrogen bonding plays in the reactivity of catechols, 1,4-hydroquinones and methoxy derivatives. 

The antioxidant properties of the ubiquinols have been reviewed recently and this material will not be discussed here. Nevertheless, we emphasize the importance of intramolecular hydrogen bonding again here. The 2,3-dimethoxy-l,4-hydroquinones are strongly hydrogen bonded at both sites as shown in structure 37. Transition state... 

Hydroquinones — quinones [1, 533-534, at end]. The most convenient synthesis of 4,5-dimethoxy-o-benzoquinone (8) involves oxidation of catchol (7) with lead dioxide (Riedel-deHaen) in the presence of sodium methoxide.7a... 

H.42) Benzene, 1,4-dimethoxy-, 1,4-dimethoxybenzene, hydroquinone dimethyl ether, quinol dimethyl ether, p-methoxyanisole [150-78-7] FEMA 2386... 

Synonyms Anisole, p-methoxy- Benzene, 1,4-dimethoxy- 1,4-Dimethoxybenzene Dimethyl ether hydroquinone Dimethyl hydroquinone Dimethylhydroquinone ether DMB DMHQ HQDME Hydroquinone dimethyl ether p-Methoxyanisole Quinol dimethyl ether Classification Aromatic ether Definition Obtained by methylation of hydroquinone using dimethyl sulfate and alkali Empirical CsHio02 Formula C6H4(OCH3)2... 

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