Oxidation products methanol yield dependence

The yield of the liquid oxidation products increases with pressure, but differently for different components for example, the yields of the aldehydes are virtually identical at 10 and 15 atm, whereas the methanol 3d eld continues to increase within this pressure interval (Fig. 10.19, Table 10.10). The absolute yield of the liquid oxidation products only slightly depended on the temperature within the range covered, but the carbon selectivity of formation of the products decreased with increasing temperature. The maximum yield of the products was achieved within 4—8 s and then, up to 12 s, decreased insignificantly, probably because of their deeper oxidation to CO and CO2. 

These conclusions were supported by the results obtained in a study of the reactions of various types of acetylenes with TTN (94). Hydration of the C=C bond was found to occur to a very minor extent, if at all, with almost all of the compounds studied, and the nature of the products formed was dependent on the structure of the acetylene and the solvent employed. Oxidation of diarylacetylenes with two equivalents of TTN in either aqueous acidic glyme or methanol as solvent resulted in smooth high yield conversion into the corresponding benzils (Scheme 23). The mechanism of this oxidation in aqueous medium most probably involves oxythallation of the acetylene, ketonization of the initially formed adduct (XXXV) to give the monoalkylthallium(III) derivative (XXXVI), and conversion of this intermediate into a benzoin (XXXVII) by a Type 1 process. Oxidation of (XXXVII) to the benzil (XXXVIII) by the second equivalent of reagent would then proceed in exactly the same manner as described for the oxidation of chalcones, deoxybenzoins, and benzoins to benzils by TTN. The mechanism of oxidation in methanol solution is somewhat more complex and has not yet been fully elucidated. 

Electrochemical oxidation of thiophene derivatives in methanol at a Pt anode leads to different types of reactions depending upon the electrolytes used. With sodium meth-oxide, 2,5-dimethyl- and tetramethylthiophene [207] afforded 2,5-dimethoxy adducts as a mixture of cisitrcms isomers together with side-chain oxidation products. However, in the presence of sodium acetate, the latter become the main products. In methanol/sulfuric acid solutions, at a carbon anode, thiophene and derivatives [208] oxidations resulted in a ringopening reaction with loss of the sulfur atom, yielding y-dicarbonyl compounds and their... 

Various kinds of metal catalysts are reported to be active for methanol synthesis from H2/CO2. Activity of metal catalyst for methanol yield increased with following order, Cu Co=Pd=Re>Ni>Fe Ru=Pt>Os>Ir=Ag=Rh>Au.[8] Needless to say, catalytic activity is much dependent on metal dispersion, additives and type of support. It is apparent, however, Copper is the most active metal species for methanol production. Effect of metal oxide support to 5wt%Cu catalyst was studied. [9]... 

With TS-1 as the catalyst, the oxidation products of phenol are hydro-quinone and catechol (para- and ort/to-hydroxyphenol), with minor yields of water and tar formed as by-products. Numerous early papers are concerned with this reaction (218), and patents (219) have been iiled. In the reaction catalyzed by TS-1, the conversion of phenol and the selectivity to dihydroxy products are significandy higher than achievable by either radical-initiated oxidation or acidic catalysts. The catechol/hydroquinone molar ratio is within the range of 0.5—1.3 and depends on the solvent. When the reaction occurs in aqueous acetone, the ratio is close to 1.3. It is believed that the product ratio is the result of restricted transition-state selectivity as well as mass transport shape selectivity associated with the different diffusivities of the ortho and para products. Hydroxylation at the para-position of phenol should be less hindered relative to that at the ortho-position, and hydroqui-none has a smaller kinetic diameter than catechol, facilitating diffusion. Tuel and Taarit (220) proposed that catechol is mainly produced at the external surface of TS-1 crystals. Thus, the different catechol/hydroquinone ratios obtained when methanol or acetone is used as a solvent could be explained by either rapid or very slow poisoning of external sites by organic deposits, respectively. Accordingly, the authors were able to show that tars were easily dissolved by acetone (i.e., external sites for catechol formation remained available in this solvent) while they were insoluble in methanol. 

The oxidative aromatization of tetrahydro-5(l/f)-quinolinones and tetrahydropyrido [2,3-fif]pyrimidin-4(//)-one withpara-benzaldehydes as oxidants in NaOEt/EtOH results in the formation of the corresponding quinolone and aryl methanol because of the hydride transfer from tetrahydroquinoline to arylaldehydes during the oxidation process. The yield of the products basically depends on the substituents with -l-M effect attached to the para position of benzene rings connected to the 2- and 4-positions of the hydro-quinolinone moiety and substituents with -I effect attached to the aryl aldehydes. 

In the electrochemical oxidation of methanol, carbon dioxide gas is the chief reaction product. The yields of other potential products of the oxidation reaction, such as formaldehyde, formic acid, and the like, are a few percent at most. Arico et al. (1998) concluded from a chromatographic analysis of the reaction products that the chief product of electrochemical oxidation of ethanol (with a yield of about 98%) is CO2, just as for methanol. This conclusion is inconsistent with the results obtained by other workers. Wang et al. (1995) studied the reaction products of ethanol and propanol oxidation by differential electrochemical mass spectrometry. They found that during the reaction, only 20 to 40% of the theoretical yield of CO2 is produced, whereas acetaldehyde is formed to 60 to 80% (even traces of acetic acid are formed). Rousseau et al. (2006) used a high-performance liquid chromatograph for analysis of the products of ethanol oxidation. According to their data, about 50% aldehyde, 30% acetic acid, and only about 20% CO2 are formed at a temperature of 90°C at a platinum catalyst. With Pt-Sn or Pt-Sn-Ru catalysts, somewhat different numbers were obtained 15% aldehyde, 75% acid, and 10% CO2. It follows from these data that the composition of the reaction products depends heavily on the catalyst used for the... 

Wang and Willey (260) report the oxidation of methanol in SCCO2 over pure and mixed oxide (Fe, Si, and Mo) aerogel catalysts. Selective oxidation products of dimethyl ether, methyl formate, and formaldehyde were found from 200°C to 300°C, and the selectivity depended on the catalyst used. Pure iron oxide favored dimethyl ether (80% yield), low levels of iron oxide on silica favored... 

A one-pot annulation reaction of aniline and its ring-substituted derivatives with l,l,2-trichloro-2-nitroethene (TCNiE) was developed delivering exclusively 3-chloroquinoxalin-2(l//)-one 4-oxides in good yields (Meyer et al. 2008). If one equivalent of aniline or a derivative 286 and two equivalents of a tertiary amine such as ttiethylamine (TEA) or l,4-diazabicyclo[2.2.2]octane (DABCO) were added to a solution of 287 in a solvent such as methanol, tetrahydrofitran, or toluene, the new quinoxalin-2(lfl)-one 4-oxide 288 precipitated completely (Scheme 2.49) (Meyer et al. 2008). The yield of the product depended on the reaction temperature, the addition rate of the aniline to the reaction mixture, the solvent, and the substitution pattern of the aniline. 

How the total yield of the main liquid oxidation products and their individual concentrations depend on e oxygen concentration was examined in detail in [91]. The maximum concentration of methanol in the liquid products formed in a stainless steel, 42%, was reached at an initial oxygen concentration of 3.5% (Fig. 3.40). The maximum yield of methanol, 20 g/m of passed gas, was observed at a somewhat higher initial oxygen concentration ( 4.5%), due to the liquid product s yield increasing with the conversion. In a quartz reactor, the maximum yield of methanol was about the same, but it was reached at a higher initial oxygen... 

A well-pronounced dependence of the yield of DMTM products on the reactor surface material (quartz vs. stainless steel) at a short residence time ( 2s), especially strong at lower pressures, was observed in [91] (Fig. 3.14). Only at high pressures, close to 80 atm, the difference becomes insignificant. At this pressure, both materials provided nearly the same maximum yield of methanol, which was achieved, however, at different oxygen concentrations 3.5% O2 for the stainless steel reactor and 6—8% O2 for the quartz reactor (Fig. 3. 40). Such a sharp distinction can be explained not only by different rates of the heterogeneous activation of methane and decomposition of the products on these surfaces, but also by different rates of the heterogeneous oxidation of methane to deep-oxidation products, CO2 and H2O. 

The temperature dependences of the concentrations of the main oxidation products are shown in Fig. 10.6. In this case, too, the experimental and calculation results on the yields of methanol and ethylene are in qualitative agreement, while the formation of carbon oxides is not adequately described. The model gives an overestimated yield of CO and greatly underestimated the yield of CO2. Most likely, this is because the model ignores the heterogeneous transformation of CO to CO2. 

Oxidation of chalcones with TTN has been studied in detail (95, 96), and it has been shown that the products obtained depend on the amount of reagent and the solvent employed. Oxidation with 1 equivalent of TTN in methanol, methanol-chloroform, or methanol-boron trifluoride leads to acetals of the type (XXXIV) (see also Scheme 21) in yields of 20-80%. When 3 equivalents of TTN are employed, however, and aqueous glyme containing a little perchloric acid used as solvent, the products are benzils. This remarkable transformation, which proceeds in yields varying from moderate to good (40-80%), involves three distinct oxidations by TTN, and these are outlined in Scheme 22. Each individual step in this reaction sequence has been investigated in detail, with the result that useful procedures have been developed for the oxidation of both deoxybenzoins and benzoins to benzils with TTN (96). 

Both inter- and intramolecular [5 + 2] cycloaddition modes have been utilized in the synthesis of natural products. Successful intermolecular cycloaddition depends on making an appropriate selection of solvent, supporting electrolyte, oxidation potential, and current density. This is nicely illustrated in Schemes 23 to 25. For example, in methanol the controlled potential oxidation of phenol (101) affords a high yield (87%) of (102), the adduct wherein methanol has intercepted the reactive intermediate [51]. In contrast, a constant current electrolysis conducted in acetonitrile rather than methanol, led to an 83% yield of quinone (103). 

Where there is direct overlap with the valence band edge, the electron transfer process may be so facile as to give rise to the Hofer-Moest reaction (.2), in which the intermediate alkyl radical is itself oxidized (while it is still adsorbed to the electrode surface) to give a carbonium ion. The reaction of this carbonium ion with the aqueous electrolyte would then yield water-soluble products such as methanol, in keeping with our observation that anodic gas evolution is suppressed under these conditions. In acidic solutions, where the Kolbe reaction is energetically allowed, its kinetic competition with the other reactions on SrTiC>3 thus depends on the absence of defect surface states which are present in some electrode crystals and not in others. 

Figure 4.10 Temperature dependencies of reaction product yields and selectivity at methane oxidation molar ratio CH4 25% H202 = 1 1, t= 1.2s (1 methanol 2 CO + C02 3 formaldehyde 4 selectivity by formaldehyde and 5 total methane conversion).

Figure 4.13 Temperature dependence of reaction product yields and selectivity at methanol oxidation molar ratio CH3OH 25% aqueous H20, vCH3oH = 1.44ml/h, vH2q2 = 2.32ml/h (1 CO 2 C02 3 formaldehyde 4 selectivity and 5 total methanol conversion).

Olefins undergo a two-step oxidative process, with the first step leading to an epoxide that, in the presence of excess oxidant, subsequently is cleaved to afford aldehydes or ketones, dependent on the position of the olefinic bond. Oxidative reactions by peroxovanadates tend to be retarded by protic solvents such as water or methanol. For instance, oxidation of norbomene by picolinatooxomonoperoxo-vanadate in acetonitrile affords 22% of the product epoxide in 9 min. After 120 min in methanol solvent, only 1.8% yield was obtained. In dichloromethane, even cyclohexane is oxidized faster than this, giving 4% cyclohexanol and 9% cyclohexanone in 120 min, whereas benzene in acetonitrile yields 56% of phenol [23],... 

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