Hydroquinone ether

The BFT, PFg" and SbCl salts of cation radicals are readily prepared by oxidation of organic donors with the corresponding NO+ salts in a relatively nonpolar solvent such as dichloromethane. For example, a solution of the hydroquinone ether MA in anhydrous (deaerated) dichloromethane turns purple upon the addition of crystalline NO+BFT at low temperature ( 50°C).173 The coloration is due to formation of the donor/acceptor complex [MA, NO+] (equation 34). 

The strongly oxidizing SbCl5 is an effective oxidant for the preparation of cation-radical salts of hexachloroantimonate (SbCl ) from a variety of organic donors, such as para-substituted triarylamines, fully-substituted hydroquinone ethers, tetraarylethylenes, etc.176 For example, the treatment of the hydroquinone ether EA (2 mmol) with SbCl5 (3 mmol) in anhydrous dichloromethane at — 78°C immediately results in an orange-red solution from which the crystalline cation radical salt readily precipitates in quantitative yield upon the slow addition of anhydrous diethyl ether (or hexane)173 (equation 36). 

Nitration versus oxidative dealkylation with nitrogen dioxides. The reaction of various substituted hydroquinone ethers with nitrogen oxides leads to either oxidation (i.e. 1,4-benzoquinones) or nitration (i.e. nitro-p-dimethoxybenzenes) depending on the reaction conditions239 (equation 84). 

Electron-transfer activation. The observation of intense coloration upon mixing the solutions of hydroquinone ether MA and nitrogen dioxide at low temperature derives from the transient formation of MA+ cation radical, as confirmed by the spectral comparison with the authentic sample. The oxidation of MA to the corresponding cation radical is effected by the nitrosonium oxidant, which is spontaneously generated during the arene-induced disproportionation of nitrogen dioxide,239 i.e.,... 

The thermal electron-transfer (ET) via the charge-transfer (CT) equilibrium depicted in equation (86) is established by temperature dependent (UV-vis) spectral studies. For example, an equimolar mixture of hydroquinone ether MA and NO + salt at low temperatures (—78°C) immediately forms the purple [MA, NO+] charge-transfer complex (lmax = 360 nm). However, upon warming the solution an orange-red color of the MA+ cation radical (Amax = 518 nm) develops, and the intensity increases with increasing temperature. Moreover, the identity of liberated NO is confirmed by the quantitative analysis of the head gas with a diagnostic N—O stretching band at 1876 cm -1 in the infrared... 

Fig. 19 Temperature-dependent interconversion of the hydroquinone ether (MA) cation radical (Amax = 518nm) and its EDA complex with nitrosonium cation (imax = 360 nm) according to equation (86) in the temperature range from +40°C to -78°C (incrementally).

Quinone dyes, 9 503 Quinone ketals, anodic oxidation of hydroquinone ethers to, 21 264 Quinone methides, 2 209-211 Quinone Michael addition chemistry, 21 248-249, 250, 252 Quinone monoacetals, 21 251 Quinone monoimine (QMI), 19 246 Quinone oximes, formation of,... 

The anodic oxidation of hydroquinone ethers to quinone ketals yields synthetically useful intermediates that can be hydrolyzed to quinones at the desired stage of a sequence. 

The compound C12H10O3 is soluble in alcohol, melts at 75°, and is isomeric with the hydroquinone ether obtained by Etard from chlorchromic acid and phenol. It has tne composition... 

Cerium(IV) ammonium nitrate in aqueous acetonitrile will also cleave a p-methoxyp/zeny/ ether (presumably to benzoquinone).335 The reaction was used in a synthesis of Stigmastellin A [Scheme 4.183] to release a primary alcohol in the presence of a benzyl ether.339 In an extension of the method, a bidirectional strategy for the synthesis of 2,3 5-trisubstitute d tetrahydrofuran components of annonaceous acetogenins benefited from the simultaneous protection of two primary hydroxyls as their Cj-symmetric hydroquinone ether [Scheme 4.184].340... 

When the hydroquinone ether 11 is cyclized with palladium(II) acetate and copper(II) chloride in methanol under a carbon monoxide atmosphere, a 60 40 (cisitrans) diastereomeric mixture is obtained in 75% yield. The products are characterized on the basis of spectra] data8 . 

Oxidative cleavage of hydroquinone ethers.2 The reagent oxidatively cleaves p-hydroquinone dimethyl ethers to p-quinones in good yield. A mineral add (nitric or perchloric adds are most efficient) is required and the oxidant must be present in excess for high conversions. o-Quinones can be obtained in moderate yields. 

CHEMICAL PROPERTIES Will polymerize to plastic when in contact with oxidizers, chlorosLilfonic acid, nitric acid or oleum flammable liquid often contains polymerization inhibitors such as hydroquinone ethers incompatible with oxidizing agents, peroxides, aluminum, copper, sunlight, heat and air FP (-15°C) LFL (6.5%) UFL (15.5%) AT (519°C). 

Rathore R, Bosch E, Kochi JK (1994) Selective nitration vctsus oxidative dealkylation of hydroquinone ethers with nitrogen-dioxide. Tetrahedrrai 50 6727... 

Bis (P-hydroxyethyl) hydroquinone ether. See Hydroquinone bis (2-hydroxyethyl) ether Bis-(2-hydroxyethyl) isodecyloxypropylamine CAS 34360-00-4... 

Treatment of the hydroquinone ethers with NO in dichloromethane at room temperature readily leads to the corresponding 1,4-quinones and alkylnitrite [17]. The trivial work-up procedure for the ready isolation of pure quinones in essentially quantitative yields, establish this to be the method of choice for the oxidative dealkylation of fully substituted hydroquinone ethers. The formation of radical cations of hydroquinone ethers (R Q ) as intermediates provides the key to understand how the alkoxy bonds are cleaved in these compounds. The activation for this oxidative process depends on the ability of the aromatic ether to undergo one-electron transfer to the nitrosonium ion [15] ... 

The electron-donating properties of the hydroquinone ethers decrease from = 1.12 V) to ( = 1.57 V). 

In both reactions it is evident that AgOH+ is a more reactive species toward the substrates than Ag + however, both species may be reacting via direct electron transfer. Pathways in which Ag might be considered a reactive species are excluded since a second-order dependence on [Ag ] and an inverse first-order dependence on [Ag ] would be predicted in this situation. The use of silver(n) as a reagent for oxidative cleavage of hydroquinone ethers has been reported. In the apparently homogeneous reaction between Ag and chloro-amines, in the presence of base, the rate is probably promoted by a trace of silver metal and is sensitive to oxygen. 

Could hydroquinones be generated thermally from a precursor that was incorporated in the HABI/leucodye-recipe Dr. Philip Manos, a chemist working on another project volunteered his services and prepared a number of hydroquinone ethers. Filter paper containing the leucodye, HABI and such ethers could be imaged, and thermally fixed by converting the ether to a hydroquinone. 

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