Dibenzyl ether, oxidation

It is evident that dibenzyl ether oxidation proceeds with remarkable speed only in the presence of the solvents with high pK. All our research on dibenzyl ether oxidation kinetics was carried out in the presence of sulpholane. 

Oxidation product analysis by GLC shows that the only dibenzyl ether oxidation product is benzaldehyde At the same time during the oxidation process small amounts of benzyl alcohol are detected in the reaction media Benzyl alcohol oxidation rate is five times higher than that for dibenzyl ether. The form of kinetic curves for benzyl alcohol oxidation is typical for intermediate products in consecutive processes. It must be emphasized that the benzyl alcohol formation is not a result of hydrolysis. Furthermore it was established that in early stages of oxidation both products benzaldehyde and dibenzyl ether are formed simultaneously. All these data obtained proved consecutive dibenzyl ether oxidation followed ... 

Kinetic investigations of dibenzyl ether oxidation shows that like benzyl alcohol oxidation, there are the same two areas of process parameters with different reaction kinetics area A with "low" acidity ([HC104]=5.0-5.8 M) and high oxygen partial pressure (( 0.5-1.0)x lO Pa), and area B with "high" acidities [HC104]= 5.8-6 6 M) and low oxygen pressures ((0.05-0.5)x 10 Pa). The main kinetic features of oxidation, that is rate dependence on concentrations and temperatures, both for dibenzyl ether and benzaldehyde are one and the same. The mechanism of dibenzyl ether oxidation appears as follows ... 

Benzyl alcohol formed in reaction (XI) oxidises into benzaldehyde according to the mechanism mentioned above (reactions (II) - (VI)). Kinetic aspects of dibenzyl ether oxidation into benzaldehyde are described in more details in [8],... 

V.Nehoroshkov, G.Kamalov at al. Dibenzyl ether oxidation method, USSR Patent No. 1154261 (1985). 

Peroxides. These are formed by aerial oxidation or by autoxidation of a wide range of organic compounds, including diethyl ether, allyl ethyl ether, allyl phenyl ether, dibenzyl ether, benzyl butyl ether, n-butyl ether, iso-butyl ether, r-butyl ether, dioxane, tetrahydrofuran, olefins, and aromatic and saturated aliphatic hydrocarbons. They accumulate during distillation and can detonate violently on evaporation or distillation when their concentration becomes high. If peroxides are likely to be present materials should be tested for peroxides before distillation (for tests see entry under "Ethers", in Chapter 2). Also, distillation should be discontinued when at least one quarter of the residue is left in the distilling flask. 

The main oxidation product from dibenzyl ether is benzaldehyde (up to 80% yield) with smaller amounts of benzyl alcohol and benzoic acid. The rates of oxidation are only slightly affected by major stereochemical changes, and it is considered that an outer-sphere oxidation of the ether is followed by radical breakdown, viz. 

Allyl and aryl ethers produce carboxylic esters in good yields (60-80%) upon oxidation by benzyltriethylammonium permanganate in dichloromethane [33], e.g. dibenzyl ether gives benzyl benzoate (80%). 

A number of substrates having a benzylic ether moiety were reacted with 51 to afford the corresponding benzylic esters in good yields (equation 84). For evaluating the effects of p-substiments on the oxidation of a series of benzylic ethers, a competitive oxidation of p-substimted benzylic propyl ethers with 51 was carried out. The Hammett correlation plot for the oxidation reaction gave a better correlation of the relative ratio factors with the a rather than with the a+ substituent constants and afforded a reaction constant p+ = —0.57 (r = 0.99). This p+ value shows that 51 is an electrophilic species and appears to be comparable to the p+ value of —0.65 for benzylic hydrogen abstraction from dibenzyl ethers by the benzoyloxy radicaP . 

Let us compare the competition of intermolecular and intramolecular chain propagations in oxidized dibenzyl ether. The rate constant A p(R02 + RH) = 95 L mol-1s-1 (T = 303 K, Table... 

X = CH2, 31h-k) and sulfones (Y = S02. X = CH2, 311,m) participated effectively in the oxidative coupling reaction. Dibenzyl ethers (Y = O, X = CH2, 31n-r) were also coupled in fair to good yields. Cleavage of the temporary tether subsequently delivers the acyclic biaryls 33a-r. 

Debiais, Niclause, Horstmann, and Letort to represent the oxidation (photochemical or induced) of dibenzyl ether in liquid phase ... 

It has to be noted that 97 and 98 could not be obtained, by a biomimetic way, i.e. oxidative cyclization of the corresponding open chain phenols 137 and 138 respectively. In contrast the bromo compound 157 prepared from 154 could be induced to undergo photocyclization yielding a mixture of myricanone and its mono and dibenzyl ethers. 

Preparatively benzaldehyde synthesis according this method may be realised as follows [7], Into a thermostated two space reactor with the volume 75 ml in one part of reactor, are placed 10.0 ml 10.4 M H2SO4 and 0.792 g dibezyl ether but into another - 0.20 ml 2.00 M NaN02 solution. Oxidation by oxygen proceeds in 10 min. The reaction mixture is diluted by water three times and extracted by benzene. According to GLC data, the benzene solution contains app. 99% benzaldehyde and traces of benzoic acid. Dibenzyl ether transformed completely. 

Partial oxidation of benzyl alcohol has been studied in detail. Benzyl alcohol undergoes dehydration to dibenzyl ether and water, disproportionation to benzaldehyde and toluene over alumina and other acid catalysts [2] whereas it undergoes dehydrogenation on metal oxides to yield benzaldehyde and toluene as major products and benzylbenzoate, benzene and methanol in small amounts depending upon the reaction conditions [10]. The various products formed as a result of catalytic decomposition may be represented as... 

In the second synthesis, D and L-myo-inositol-2,4-dibenzyl ethers were both phosphicylated with (BnO)2PNPr 2 t6trazole subsequent oxidation with MCPBA and hydrogenolysis afforded the desired tetraphosphate (61). ... 

DIBENZYL ETHER (103-50-4) Combustible liquid (flash point 275°F/135°C). Capable of spontaneous explosion. Forms unstable peroxides. Violent reaction with oxidizers. Flow or agitation of substance may generate electrostatic charges due to low conductivity. 

Fig. 1. Oxidation of mixtures of cumene and aralkyl hydrocarbons at 90°C, 0.02 M f-butyl perbenzoate. A, Dibenzyl ether B, indan C, diphenylmethane D, ethylbenzene E, theoretical for an inert diluent. Reprinted with permission from ref. 139. Copyright by the American Chemical Society.

Dibenzyl ether is oxidized to hydroperoxide which decomposes under mild conditions to benzaldehyde and benzyl alcohol [186—188,294], viz. 

In both the systems, it was found that the capsule membrane technique was exclusively selective, in that the hydrolysis reaction led to the formation of only benzyl alcohol and the oxidation reaction to only benzaldehyde. Furthermore, the rates of reaction were substantially enhanced. For a liquid-liquid PTC hydrolysis, there is a substantial formation of the byproduct dibenzyl ether. The oxidation of benzyl chloride with chromate under L-L PTC also results into byproduct formation, including benzyl... 

Decomposition of Cured Resoles and Novolaks. Above 250°C, cured phenolic resins begin to decompose. For example, dibenzyl ethers such as 9 disproportionate to aldehydes (salicylaldehyde) and cresols (o-cresol). The aldehyde group is rapidly oxidized to the corresponding carboxylic acid. In an analogous reaction in hexa-cured novolaks, tribenzylamines decompose into cresols and azome-thines, which cause yellowing. 

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