Dimethylether

G in the presence of a catalytic amount of a Lewis base such as dimethylether, (GH2)20. In addition to the gas-phase pyrolysis of diborane, can be prepared by a solution-phase process developed at Union Garbide Gorp. Decaborane is a key intermediate in the preparation of many carboranes and metaHa derivatives. As of this writing, this important compound is not manufactured on a large scale in the western world and is in short supply. Prices for decaborane in 1991 were up to 10,000/kg. 

Example 30 Estimate thermal conductivity of a mixture of 0.23 mole fraction dimethylether (1) and 0.77 mole fraction methyl chloride (2) at... 

A mixture of 2.9 grams of 5-chloro-2,4-disulfamvl-aniline in 20 ml of anhydrous diethylene-glycol dimethylether, 0.44 gram of propionaldehyde and 0.5 ml of a solution of hydrogen chloride in ethyl acetate (109.5 grams hydrogen chloride per 1,000 ml) Is heated to 80° to 90°C and maintained at that temperature for 1 hour. The reaction mixture is concentrated under reduced pressure on addition of water, the product separates and is then recrystal-lized from ethanol or aqueous ethanol to yield the desired 6-chloro-3-ethvl-7-sulfamyl-3,4-dihydro-1,2,4-benzothiadiazine-1,1-dioxide, MP 269° to 270°C. 

Delocalization, 1, 49 Dewar benzene, 260 Diazirine, 49, 135 reactivity, 40 Diazomethane, 126 Diborane, 86 Diimide, 85 Dimethylether, 167... 

Quinone methides are the key intermediates in both resole resin syntheses and crosslinking reactions. They form by the dehydration of hydroxymethylphenols or dimethylether linkages (Fig. 7.24). Resonance forms for quinone methides include both quinoid and benzoid structures (Fig. 7.25). The oligomerization or crosslinking reaction proceeds by nucleophilic attack on the quinone methide carbon. 

In addition to methylene and dimethylether linkages, cured networks contain ethane and ethene linkages (Fig. 7.31). These side products are proposed to form through quinone methide intermediates. 

The results in Table 3 show that H-mordenite has a high selectivity and activity for dehydration of methanol to dimethylether. At 150°C, 1.66 mol/kg catal/hr or 95% of the methanol had been converted to dimethylether. This rate is consistent with that foimd by Bandiera and Naccache [10] for dehydration of methanol only over H-mordenite, 1.4 mol/kg catal/hr, when extrt lat to 150°C. At the same time, only 0.076 mol/kg catal/hr or 4% of the isobutanol present has been converted. In contrast, over the HZSM-5 zeolite, both methanol and isobutanol are converted. In fact, at 175 X, isobutanol conversion was higher than methanol conversion over HZSM-5. This presents a seemingly paradoxical case of shape selectivity. H-Mordenite, the zeolite with the larger channels, selectively dehydrates the smaller alcohol in the 1/1 methanol/ isobutanol mixture. HZSM-5, with smaller diameter pores, shows no such selectivity. In the absence of methanol, under the same conditions at 15(fC, isobutanol reacted over H-mordenite at the rate of 0.13 mol/kg catal/hr, higher than in the presence of methanol, but still far less than over H M-5 or other catalysts in this study. 

The strategy of manipulation of the macro-environment can be utilized for biotransformations. Thus, Zelinski and Kula (1997) have enzymatically reduced lipophillic ketones like 2-acetylnaphthalene using dimethylether of P-cyclodextrin in the organic phase. The use of cyclodextrin increases the solubility of the ketone by a factor of 147 resulting in high yields with excellent enantioseiectivity. 

The mono- and dinuclear ethylzinc complexes 137 and 138, respectively, were obtained when a 1,3-dimethylether /j-BT-calixMarene was treated with one and two equivalents of diethylzinc (Scheme 87).198 Excess [ZnEt2(tmeda)], in turn, reacted with this calixarene to furnish a pentanuclear dicalixarene. The syntheses and structures of related diorganozinc calixarenes, featuring both identical and non-identical organozinc moieties, were reported recently.199 The solid-state structure of the bis(ethylzinc)-l,3-dibenzylether-/)-But-calix[4]arene 139, which bears a close resemblance to 138, is shown in Figure 64. 

A conmercial catalyst frcm Harshaw was used, a 3 1 mixture of molybdenum trioxide and ferric molybdate, as well as the two separate phases. Kinetic experiments were done previously in a differential reactor with external recycle using these same catalysts as well as several other preparations of molybdenun trioxide, including supported samples. Hie steady state kinetic experiments were done in the temperature range 180-300 C, and besides formaldehyde, the following products were observed, dimethylether, dimethoxymethane, methyl formate, and carbon-monoxide. Usually very little carbon dioxide was obtained, and under certain conditions, hydrogen and methane can be produced. 

The conclusions on the rate limiting step are again supported by the differences in product selectivity if completely deuterated methanol is used the selectivity to dimethylether relative to formaldehyde is much larger. This is shown for the three catalysts in Figures 10-12, in which the ratio of the amounts of dimethylether and formaldehyde formed is plotted as a function of temperature. In the case of CH,0D, the water observed is a mixture of H20, HDO, and D20, most of it being HDO. 

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