Dimethyl ether decomposition

After Lindemann and Christiansen put forward their mechanism, experimental work was carried out to verify if the unimolecular reactions did become second order at sufficiently low pressures. Figure 8.1 illustrates the order of dimethyl ether decomposition in the vapour phase as a function of the addition of a foreign gas. In qualitative terms, the mechanism of Lindemann-Christiansen gives a good account of the experimental observations,... 

SuIfona.tlon, Sulfonation is a common reaction with dialkyl sulfates, either by slow decomposition on heating with the release of SO or by attack at the sulfur end of the O—S bond (63). Reaction products are usually the dimethyl ether, methanol, sulfonic acid, and methyl sulfonates, corresponding to both routes. Reactive aromatics are commonly those with higher reactivity to electrophilic substitution at temperatures > 100° C. Tn phenylamine, diphenylmethylamine, anisole, and diphenyl ether exhibit ring sulfonation at 150—160°C, 140°C, 155—160°C, and 180—190°C, respectively, but diphenyl ketone and benzyl methyl ether do not react up to 190°C. Diphenyl amine methylates and then sulfonates. Catalysis of sulfonation of anthraquinone by dimethyl sulfate occurs with thaHium(III) oxide or mercury(II) oxide at 170°C. Alkyl interchange also gives sulfation. 

The reaction mixture is evaporated to a small volume, whereupon the d-tubocurarine dimethyl ether iodide precipitates. The precipitate is filtered off and dissolved in boiling water. The hot solution is treated with a small amount of decolorizing carbon, the carbon filtered off and the filtrate cooled to about 0°C. The dimethyl ether of d-tubocurarine iodide crystallizes in white crystals which melt at about 267°-270°C with decomposition. 

The decomposition of dimethyl ether (CH3OCH3) to methane, carbon monoxide, and hydrogen gases is found to be first-order At 500°C, a 150.0-mg sample of dimethyl ether is reduced to 43.2 mg after three quarters of an hour. Calculate... 

DMC and EG were main products of the transesterification reaction. No by-product such as dimethyl ether and glycol monoethyl ether was observed in the resulting products. Only small peaks of ethylene oxide from the decomposition of EC could be detected at longer reaction time and at high temperature. 

Hinshelwood and Askey (6) have investigated the gas phase decomposition of dimethyl ether according to the following reaction. 

For the irreversible, gas-phase decomposition of dimethyl ether (CH3OCH3) to CH4, H2, and... 

Show that, for the bimolecular reaction A + B - products, kscr is given by equation 6.4-17. 6-4 Some of the results obtained by Hinshelwood and Askey (1927) for the decomposition of dimethyl ether, (CH3)20 (A), to CH4, CO and H2 at 777.2 K in a series of experiments in a constant-volume batch reactor are as follows ... 

Suppose the mechanism for the thermal decomposition of dimethyl ether to methane and formaldehyde... 

These include the variations of sacrificial anode, sonication, and alternating polarity cell mentioned above, different solvent/co-solvent and electrolyte systems, monomer concentration, total current passed, and temperature. Best results appear to be obtained with THF and dimethyl ether (DME) as solvent and a perchlorate supporting electrolyte in some systems using fluorides, electrolyte decomposition occurred releasing fluoride anion which formed unreactive fluorosilanes.125... 

Dimethyl ether, 31 41, 244 formation in zeolites, 42 95-98 Dimethylethylbenzenes, 20 281 Dimethylindan, cyclization, 28 298, 299 Dimethylindene, cyclization, 28 298, 299 Dimethyl methyl phosphonate, catalytic decomposition, 35 159-160 Dimethylnaphthalenes, hydrogenation of, 18 64-102... 

The kinetic and activation parameters for the decomposition of dimethylphenylsilyl hydrotrioxide involve large negative activation entropies, a significant substituent effect on the decomposition in ethyl acetate, dependence of the decomposition rate on the solvent polarity (acetone-rfe > methyl acetate > dimethyl ether) and no measurable effect of the radical inhibitor on the rate of decomposition. These features indicate the importance of polar decomposition pathways. Some of the mechanistic possibilities involving solvated dimeric 71 and/or polymeric hydrogen-bonded forms of the hydrotrioxide are shown in Scheme 18. 

Methanol can be converted to hydrocarbons over acidic catalysts. However, with the exception of some zeolites, most catalysts deactivate rapidly. The first observation of hydrocarbon formation from methanol in molten ZnCl2 was reported in 1880, when decomposition of methanol was described to yield hexamethylbenzene and methane.414 Significant amounts of light hydrocarbons, mostly isobutane, were formed when methanol or dimethyl ether reacted over ZnCl2 under superatmo-spheric pressure.415 More recently, bulk zinc bromide and zinc iodide were found to convert methanol to gasoline range (C4-C13) fraction (mainly 2,2,3-trimethyl-butane) at 200°C with excellent yield (>99%).416... 

If the level of the cooling bath is too high, or if the bath temperature is less than —40°, unnecessary condensation of dimethyl ether occurs. If the level of the bath is too low, a brownish ring of decomposition product forms in the flask. Since the brown material is soluble in dimethyl ether and ethyl acetate, it does not contaminate the trimethyloxonium salt. 

Methylnitramine decomposes explosively in contact with concentrated sulfuric acid. If the substance is dissolved in water, and if concentrated sulfuric acid is added little by little until a considerable concentration is built up, then the decomposition proceeds more moderately, nitrous oxide is given off, and dimethyl ether (from the methyl alcohol first formed) remains dissolved in the sulfuric acid. The same production of nitrous oxide occurs even in the nitrometer in the presence of mercury. If methylnitramine and a small amount of phenol are dissolved together in water, and if concentrated sulfuric acid is then added little by little, a distinct yellow color shows that a trace of nitric acid has been formed. The fact that methylnitramine gives a blue color with the diphenylamine reagent shows the same thing. 

Fig. 31. Catalytic activities of acidic Na or Cs salts of HjPW 204o as a function of Na or Cs content, (a) M = Na (O) dehydration of 2-propanol, (A) decomposition of formic acid, ( ) conversion of methanol, ( ) conversion of dimethyl ether, (b) M = Cs (O) dehydration of 2-propanol, ( ) conversion of dimethyl ether, (A) alkylation of 1,3,5-trimethylbenzene with cyclohexene. (From Refs. 46 and 128.)...

A study concerning the yields of fluorination by acid decomposition of piperidinotriazenes from several anilines with hydrogen fluoride (anhyd HF, coned aq HF, or HF, pyridine) in various solvents, such as tetrahydrofuran, benzene, dichloromethane, and acetic acid, was carried out in order to establish the best reaction conditions for the [ F]fluorine labeling of estrogens. Hence, 2 -fluorohexcstrol dimethyl ether (4) can be obtained from triazene 3 using 49% aqueous hydrogen fluoride. ... 

---