Methoxy decomposition

TPRS experiments for this reaction step. The two hydrogens released in the methanol adsorption and the surface methoxy decomposition steps are eventually converted to water. Spectroscopic details about the formation of water are presently not available, but the formation of water most likely proceeds via the condensation of two surface hydroxyl groups. The reduced surface vanadia site is readily reoxidized back to vanadium (+5) by gas phase oxygen as shown by in situ Raman measurements.42... 

Surface-bound methoxy, CH3O, is an intermediate in a variety of surface processes in catalysis and electrocatalysis involving methanol. The chemistry of methoxy on Pt(lll) and the Sn-alloys had been elusive because of the difficulty of cleanly preparing adsorbed layers of methoxy. One approach is to use the thermal dissociation of an adsorbed precursor, methyl nitrite (CH O-NO), to produce methoxy species on such surfaces at temperatures lower than required for methoxy formation from methanol [58, 59]. The methoxy intermediate is strongly stabilized (to 300 K) against thermal decomposition on both Sn/Pt(lll) alloys, whereas on Pt(lll), dissociation occurs below 140 K. There is a high selectivity to formaldehyde, CHjO, on both alloys, i.e., methoxy disproportionates to make equal amounts of formaldehyde and methanol. The two Sn/Pt(lll) alloys do not form CO and products characteristic of methoxy decomposition on Pt(l 11). 

Figure 11.8 Redox TOP of bulk metal oxides toward methanol selective oxidation as a function of the temperature of surface methoxy decomposition (From Badlani, M. and Wachs, I.E. CatalLett. 2001, 75,137-149. With permission.)...

Alkoxyall l Hydroperoxides. These compounds (1, X = OR , R = H) have been prepared by the ozonization of certain unsaturated compounds in alcohol solvents (10,125,126). 2-Methoxy-2-hydroperoxypropane [10027-74 ] (1, X = OR , R" = methyl), has been generated in methanol solution and spectral data obtained (127). A rapid exothermic decomposition upon concentration of this peroxide in a methylene chloride—methanol solution at 0°C has been reported (128). 2-Bromo-l-methoxy-l-methylethylhydroperoxide [98821-14-8]has been distilled (bp 60°C (bath temp.), 0.013 kPa) (129). Two cycHc alkoxyaLkyl hydroperoxides from cyclodecanone have been reported (1, where X = OR R, R = 5-oxo-l, 9-nonanediyl) with mp 94—95°C (R" = methyl) and mp 66—68°C (R" = ethyl) (130). Like other hydroperoxides, alkoxyaLkyl hydroperoxides can be acylated or alkylated (130,131). 

When the reaction was followed by proton magnetic resonance, it was found that the yield reached a maximum after 18 hours longer refluxing resulted in decomposition and lower yields. At this time, also, the maximum proportion of the 1-methoxy isomer was produced this isomer is converted into the dienone complex. 

While this work was in progress Spath and Bretschneider showed that strychnine, on oxidation with permanganate in alkaline solution, furnished W-oxalylanthranilic acid (VII), brucine yielding oxalyl-4 5-dimethoxy-anthranilic acid, the latter observation providing confirmation of the evidence previously adduced that the two methoxy-groups in brucine are in the oj Ao-position relative to each other as indicated by Lions, Perkin and Robinson. The results so far considered indicate the presence in brucine and strychnine of the complex (VIII), which can be extended to (IX) if account is taken of the readiness with which carbazole can be obtained from strychnine and brucine and certain of their derivatives by decomposition with alkali at temperatures ranging from 200° to 400°, Knowledge of the structure of the rest of the molecule is mainly due to the results of the exhaustive study by Leuchs and his pupils of the oxidation... 

In 10 ml of ethanol was dissolved with heating 200 mg of 2-methyl-6-(1-methoxy-2-carba-moyloxyethyl)-1,4-benzoquinone and the resulting solution was cooled. To the cooled solution was added 0.5 ml of aziridine and then the resulting mixture was allowed to stand In a refrigerator at 5°C to 8°C for 4 days. Thereafter, the crystalline substance which precipitated in situ was recovered by filtration and washed with ethanol to give 50 mg of the desired product as red crystals melting at 200°C (with decomposition). 

To a solution of 7 (d-p-hydroxyphenyl-0i-carboxyacetamido-7(l-methoxy-3-(1-methyl-tetrazol-5-vl)thiomethyl-1-oxadethia-3-cephem4-carboxylic acid (359 mg) in methanol (7 ml) is added a solution of sodium 2-ethylhexanoate in methanol (2 mols/liter 1.73 ml) at room temperature. After stirring for 10 minutes, the reaction mixture is diluted with ethyl acetate, stirred for 5 minutes, and filtered to collect separated solid, which is washed with ethyl acetate, and dried to give disodium salt of 7 (a-p-hydroxyphenyl-a-carboxyacetamido)-7Q -methoxy-3-(1-methyl-tetrazol-5-vl)thiomethyl-1-oxadethia-3-cephem4-carboxylic acid (342 mg). Yield 885%. Colorless powder. MP decomposition from 170°C. 

At high alkali coverages (near monolayer coverage), when the adsorbed alkali overlayer shows a metal-like character, alkali-methoxy species are formed. As shown by TPD experiments in the system K/Ru(001) these alkali-methoxy species are more stable than the methoxy species on clean Ru(001) and adsorbed methanol on 0.1K/Ru(001). On metal surfaces inactive for methanol decomposition, e.g. Cu(lll), these alkali-methoxy species are formed even at low alkali coverages, due to the weaker interaction of the alkali atoms with the metal surface. The formation of these species stabilizes the methoxy species on the metal surface and enhances the activity of the metal surface for methanol decomposition. 

More functionalized 5,6-dihydro-2H-pyran-derivatives 71 and 72 have been prepared [26] by cycloaddition of 1 -methoxy-3-trialkylsilyloxy-1,3-butadienes 69 with t-butylglyoxylate (70) (Scheme 5.6). Whereas thermal reactions did not occur in good yields because of the decomposition of the cycloadducts, application of pressure (10 kbar) allowed milder conditions to be used, which markedly improved the reaction yields. The use of high pressure also gives preferentially en Jo-adduct allowing a stereocontrolled synthesis of a variety of substituted 5,6-dihydro-2H-pyran-derivatives, which are difficult to prepare by other procedures. 

The methoxy group of methyl acetate formed during the thermal decomposition of acetyl peroxide appears as an emission, whereas methyl chloride shows enhanced absorption. Consider the reaction sequence in equation (40). 

Figure 5. Cartoon models of the reaction of methanol with oxygen on Cu(llO). 1 A methanol molecule arrives from the gas phase onto the surface with islands of p(2xl) CuO (the open circles represent oxygen, cross-hatched are Cu). 2,3 Methanol diffuses on the surface in a weakly bound molecular state and reacts with a terminal oxygen atom, which deprotonates the molecule in 4 to form a terminal hydroxy group and a methoxy group. Another molecule can react with this to produce water, which desorbs (5-7). Panel 8 shows decomposition of the methoxy to produce a hydrogen atom (small filled circle) and formaldehyde (large filled circle), which desorbs in panel 9. The active site lost in panel 6 is proposed to be regenerated by the diffusion of the terminal Cu atom away from the island in panel 7.

Presence of carbon dioxide in solutions of the hydride in dimethyl or bis(2-methoxy-ethyl) ether can cause a violent decomposition on warming the residue from evaporation. Presence of aluminium chloride tends to increase the vigour of decomposition to explosion. Lithium tetrahydroaluminate may behave similarly, but is generally more stable. 

The hydroxyl group was usually protected, because cyanohydrins have tendency to racemization or even decomposition. Vinyl ethers or acetal and acid catalysts furnish acetals [62]. Trialkylsilyl chlorides and imidazole are used to give silyl ethers [63]. Commonly used protective groups are silyl ether, ester, methoxy isopropyl (MIP) ether, and tetrahydro-pyranyl ether. ( -Protected cyanohydrins are tolerant to a wider range of cyanide/nitrile transformations and are utilized widely in the synthesis of compounds of synthetic relevance in organic chemistry. 

Rh2(OAc)4-catalyzed decomposition of m-methoxy-substituted diazoketones 244 furnishes 6-methoxy-2-tetralones rather than the expected bicyclo[5.3.0]decatrienones. This demonstrates that the direction of ring opening in the norcaradienone intermediate 245 may well be influenced by the nature and position of a substituent. 

Interaction of a carbonyl group with an electrophilic metal carbene would be expected to lead to a carbonyl ylide. In fact, such compounds have been isolated in recent years 14) the strategy comprises intramolecular generation of a carbonyl ylide whose substituent pattern guarantees efficient stabilization of the dipolar electronic structure. The highly reactive 1,3-dipolar species are usually characterized by [3 + 2] cycloaddition to alkynes and activated alkenes. Furthermore, cycloaddition to ketones and aldehydes has been reported for l-methoxy-2-benzopyrylium-4-olate 286, which was generated by Cu(acac)2-catalyzed decomposition of o-methoxycarbonyl-m-diazoacetophenone 285 2681... 

The question of rearrangement in acyloxy radicals is still unsettled. In the case of the decomposition of -methoxy- -nitrobenzoyl peroxide rearrangement is observed, but the other circumstances indicate a polar mechanism for the reaction.118... 

Although benzoyl peroxide will initiate the polymerization (by a radical chain reaction) of either styrene or acrylonitrile, -methoxy- -nitrobenzoyl peroxide will not initiate polymerization efficiently in the latter monomer because it is too rapidly destroyed by the polar decomposition. Acrylonitrile, but not styrene, causes the polar decomposition to predominate, and the intermediates of the polar decomposition are not catalysts for the polymerization of acrylonitrile. 

There is considerable overlap in the effective range of the initiators, but this is less troublesome than it might seem since the various mechanisms can be expected to differ in their response to inhibitors. And if the alternatives are free radical and ion-pair with one of the possible ions not very reactive, decision is easy. For example, the polar decomposition of >-methoxy-/> -nitro benzoyl peroxide in acrylonitrile initiates... 

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