Dimethyl carbonate, hydrogenation

Leek and Baagander [311] determined reduced sulfide compounds in seawater by gas chromatography using a flame ionisation detector. Substances determined include methyl mercaptan, dimethyl sulfide, hydrogen sulfide and carbon disulfide. Detection limits range from 0.2ng/l (carbon disulfide) to 0.6 ng/1 (methyl mercapton). 

In contrast with the reactions involving sulphide or hydrogen sulphide anions, aryl alkyl thioethers and unsymmetrical dialkyl thioethers (Table 4.3) are obtained conveniently by the analogous nucleophilic substitution reactions between haloalkanes and aryl or alkylthiols under mildly basic conditions in the presence of a quaternary ammonium salt [9-15] or polymer-supported quaternary ammonium salt [16]. Dimethyl carbonate is a very effective agent in the formation of methyl thioethers (4.1.4.B) [17]. 

Copper, silver, and gold colloids have been prepared by Chemical Liquid Deposition (CLD) with dimethoxymethane, 2-methoxyethyl ether, and ethylene glycol dimethyl ether. The metals are evaporated to yield atoms which are solvated at low temperatures and during the warm-up process colloidal sols with metal clusters are obtained. Evaporation of the solvent was carried out under vacuum-generating metal films. These films are showing very low carbon/hydrogen content and were characterized by elemental analyses and infrared spectroscopy (Cardenas et al., 1994). 

However, the methyl cation (in itself a very energetic, unprobable species in the condensed state) is not expected to attack a carbon-hydrogen bond in dimethyl ether (or methanol) in preference to the oxygen atom. The more probable attack on oxygen would lead to the trimethyloxonium ion, which was observed experimentally447,463 On the action of a basic site the trimethyloxonium ion can then be deprotonated to form dimethyloxonium methylide ... 

In the case of experiments performed under the conditions of run 6, but in the presence of 1 ml of methanol, 1.6 equivalent of dimethyl carbonate was obtained according to GC analysis. No dimethyl carbonate was observed in the absence of hydrogen chloride. Therefore, in the early stage of the carbonylation of 3, Pd/C is partly oxidized to palladium chloride (eqn. 2). This compound reacts in turn with CO and MeOH to give, according to one of the routes described in Scheme 2, dimethyl carbonate and a zerovalent palladium complex (noted [Pd]). 

Draw a schematic diagram of a carbon-hydrogen combustion analyzer. Write a few sentences to describe each stage of the analysis as dimethyl ether, C2H60, passes through the apparatus. 

The dimethyl carbonate decomposition has been shown to proceed heterogeneously at relatively high temperatures on a quartz surface - By contrast, alkyl and aryl carbonates with j8-carbon hydrogens, decompose smoothly homogeneously and unimolecularly in surface conditioned reactors at appreciably lower temperatures T > 600 °K) to give olefin, alcohol, and carbon dioxide. Gas phase kinetic results for some 1-arylethyl methyl carbonates S for methyl ethyl carbonate, and for diethyl carbonate are shown in Table 14. Some gas phase relative rate results for substituted 1- and 2-arylethyl carbonates have also been determined (Table 15). 

In Stork s synthesis (148), 5 - methyl - 6 - methoxy - 1 - tetralone (CLXXXIV) was converted into the tricyclic intermediate CLXX XVII in several steps involving condensation with dimethyl carbonate, addition of methyl isopropenylketone, and cyclization to the a, -unsaturated ketone CLXXXVI, followed by catalytic hydrogenation, replacement of the hydroxyl group in the resulting dihydro alcohol by a chlorine atom on treatment with phosphorus oxychloride in pyridine solution, and elimination of hydrogen chloride by methanolic sodium methoxide. 

Kiaas, M. R., Warwei, S. Chemoenzymatic Epoxidation of Aikenes by Dimethyl Carbonate and Hydrogen Peroxide. Org. Lett. 1999,1, 1025-1026. 

Most mechanistic interest attaches to the formation of olefins. Even the formation of ethylene from one dimethyl ether molecule involves breakage of two carbon-oxygen and two carbon-hydrogen bonds and formation of a carbon-carbon double bond. The stoichiometric simplicity obviously masks relatively complex reaction mechanisms. 

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