Dibenzyl ethers

Dibenzyl ether is a clear, almost colorless liquid. It is miscible with alcohols and ethers, but insoluble in water, benzyl ether is used as special solvent and delustering agent for textiles. 

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Another process employs a pH maintained at 4—7 and a catalyst that combines a divalent metal cation and an acid. Water is removed continuously by azeotropic distillation and xylene is recycled. The low water content increases the reaction rate. The dibenzyl ether groups are decomposed by the acid the yield of 2,2 -methylene can be as high as 97% (34). 

Resoles. The advancement and cure of resole resins foUow reaction steps similar to those used for resin preparation the pH is 9 or higher and reaction temperature should not exceed 180°C. Methylol groups condense with other methylols to give dibenzyl ethers and react at the ortho and para positions on the phenol to give diphenyknethylenes. In addition, dibenzyl ethers eliminate formaldehyde to give diphenyknethanes. 

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. 

Comparison of Table 5.4 and 5.7 allows the prediction that aromatic oils will be plasticisers for natural rubber, that dibutyl phthalate will plasticise poly(methyl methacrylate), that tritolyl phosphate will plasticise nitrile rubbers, that dibenzyl ether will plasticise poly(vinylidene chloride) and that dimethyl phthalate will plasticise cellulose diacetate. These predictions are found to be correct. What is not predictable is that camphor should be an effective plasticiser for cellulose nitrate. It would seem that this crystalline material, which has to be dispersed into the polymer with the aid of liquids such as ethyl alcohol, is only compatible with the polymer because of some specific interaction between the carbonyl group present in the camphor with some group in the cellulose nitrate. 

Sprung and Gladstone were the first to show the formation of dibenzyl ether linkages during the condensation of hydroxymethyl phenols, as depicted in Scheme 4c [152], These results have been corroborated by a number of researchers since [128,144,147,148], This condensation was reportedly second-order and takes place at pH conditions near neutral and at temperatures less than 130°C [128,147,153], At temperatures of 160°C the dibenzyl ethers are converted to something else, most likely to methylene linkages and formaldehyde [132],... 

In addition to the normal methylene linkage formation involved in polymerization with both resoles and novolaes, other, usually less desirable, eondensation by-products are also seen in novolac synthesis. Among these are benzodioxanes and dibenzyl ethers. The reaction pH has significant effect on the relative amounts produced. Fig. 15 shows typical structures for these by-products. When such byproducts are present, the meaning of the molar ratio changes and variability with respect to molecular weight development, glass transition point, and solubility may be seen. They also lead to poor raw material utilization. 

The mixture was kept at 40-50 C for 3 h and then overnight at room temperature Dibenzyl ether (25%) was isolated Nitrobenzyl fluorides are obtained by adding the alcohol to an excess of the fluonnating agent When hexafluoropropyldiethylamine is added to the alcohol, dibenzyl ethers are formed exclusively ... 

Phenol-formaldehyde reactions catalyzed by zinc acetate as opposed to strong acids have been investigated, but this results in lower yields and requires longer reaction times. The reported ortho-ortho content yield was as high as 97%. Several divalent metal species such as Ca, Ba, Sr, Mg, Zn, Co, and Pb combined with an organic acid (such as sulfonic and/or fluoroboric acid) improved the reaction efficiencies.14 The importance of an acid catalyst was attributed to facilitated decomposition of any dibenzyl ether groups formed in the process. It was also found that reaction rates could be accelerated with continuous azeotropic removal of water. 

The formation of ethers such as 1806 by EtsSiH 84b can also be catalyzed by trityl perchlorate to convert, e.g., benzaldehyde in 84% yield into dibenzyl ether 1817 [48]. The combination of methyl phenethyl ketone 1813 with O-silylated 3-phenyl-n-pro-panol 1818, in the presence of trityl perchlorate, leads to the mixed ether 1819 in 68% yield [48] (Scheme 12.15). Instead of trityl perchlorate, the combination of trityl chloride with MesSiH 84a or EtsSiH 84b and sodium tetrakis[3,5-bis-(trifluoro-methyl)phenyl]borane as catalyst reduces carbonyl groups to ethers or olefins [49]. Employing TMSOTf 20 as catalyst gives very high yields of ethers. Thus benzaldehyde reacts with O-silylated allyl alcohol or O-silylated cyclohexanol to give the... 

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. 

Kim Y-H, K-H Engesser (2004) Degradation of alkyl ethers, aralkyl ethers, and dibenzyl ether by Rhodo-coccus sp. strain DEE 5151, isolated from diethyl ether-containing enrichment cultures. Appl Environ Microbiol 70 4398-4401. 

Ether peroxidation was responsible for the detonation that occurred when dibenzyl ether was treated by the etherate of dichloroaluminium hydride. Note that in this case as well as for diallyl ether there will be easy peroxidation since both sites are of allyl and benzyl nature respectively. 

With the sodium derivative of benzyl alcohol, dibenzyl ether was obtained in 63% yield, accompanied by 24% of A-benzylimidazole. Formation of the latter compound results from the reaction of the benzyl sulfonate with imidazol sodium in competition with the second step of the ether synthesis (b). 

Dibenzyl ether was entirely converted to toluene and benzaldehyde. The formation of products can be explained by the following reaction shceme. 

It was found that the addition of coal ash remarkably accelerates the rate of decomposition of dibenzyl ether and also drastically changes the distribution of reaction products, that is, benzyl tetralin becomes the main reaction product instead of a mixture of toluene and benzaldehyde, as shown in Table V. 

When reactions with oxygen-containing acceptors were performed [3] in the 300-400°C region, the formation of adducts occurred with both Tetralin and mesitylene. This reaction was observed when benzyl radicals were generated from dibenzyl ether, dibenzyl sulfide, benzyl alcohol, and benzaldehyde. 

Dibenzyl ether reacted with Mg after five days of reflux in THF to give phenylacetic acid in 42% yield after carbonation. Maercker(99) was able to obtain a 15% yield of 3-butenoic acid from allyl methyl ether after 56 h of reflux. 

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