Schmidt reactions pathways

Concerning the reaction pathway, two routes have been proposed the sequence of total oxidation of methane, followed by reforming of the unconverted methane with CO2 and H2O (designated as indirect scheme), and the direct partial oxidation of methane to synthesis gas without the experience of CO2 and H2O as reaction intermediates. The results obtained by Schmidt and his co-workers [4, 5] indicate that the direct reaction scheme may be followed in a monolith reactor when an extremely short contact time is employed at temperatures in the neighborhood of 1000°C. However, the majority of previous studies over numerous types of catalysts show that the partial oxidation of methane follows the indirect reaction scheme, which is supported by the observation that a sharp temperature spike occurs near the entrance of the catalyst bed, and that essentially zero CO and H2 selectivity is obtained at low methane conversions (<25%) where oxygen is not fully consumed [2, 3]. A major problem encountered... 

Schmidt et al. reported similar reactions of 3-butynols with Cr(CO)5(L) and Mo(CO)5(L) [18]. In most cases, a similar tendency to that reported by McDonald was observed, that is, five-membered cyclic carbene complexes were obtained when Cr(CO)5(OEt2) was employed, while dihydrofurans were obtained when Mo(CO)5 (NEt3) was employed, however, in one specific case, a unique difference of the reaction pathway was observed. Thus, when hemiacetal 44 was treated with Cr (CO)5(OEt2), the corresponding carbene complex 45 was obtained, which was further converted to dihydrofuran by treatment with DM AP. On the other hand, when 44 was... 

About 15 years ago, Aube et al. reported that alkyl azides undergo Lewis acid-mediated reactions with ketones 76 to give the corresponding lactams 78 via 77 (Azido-Schmidt reaction Scheme 14A) [44-48]. However, this reaction pathway does not proceed when a,/3-unsaturated ketones are used. It was recently shown that Lewis acid-activated enones like 79 undergo a [3-P2] cycloaddition with alkylazides, likely via an 1,2,3-triazoline intermediate 80, to give the corresponding enaminone 80 (Scheme 14B) [49]. 

Katori T, Itoh S, Sato M, Yamataka H (2010) Reaction pathways and possible path bifurcation for the Schmidt reaction. J Am Chem Soc 132(10) 3413-3422. doi 10.1021/ja908899u... 

Vogler EA, Hayes JM (1979) Carbon isotopic fractionation in the Schmidt decarboxylation evidence for two pathways to products. J Org Chem 44 21) 3682—3686 Richard JP, Amyes TL, Lee Y-G, Jagannadham V (1994) Demonstration of the chemical competence of an iminodiazonium ion to serve as the reactive intermediate of a Schmidt reaction. J Am Chem Soc 116(23) 10833-10834... 

A crude scheme of the electron pathway for the primary bluelight reaction was recently suggested by Hemmerich and Schmidt (87 cf. 4.1) ... 

It is assumed that the majority of carbon monoxide is removed from the atmosphere by these reactions. Seiler (1974) hypothesizes that the yearly CO loss in the troposphere due to [3.5] and [3.7], is (1940-5000) x 1061 yr-1 The corresponding figure for the stratosphere is estimated to be 110 x 106 t yr-1 (see Table 7). In contrast, Warneck (1974) speculates that the global atmospheric strength of this sink is much smaller than the Seiler s figure. Finally, according to the calculations of Ehhalt and Schmidt (1978) about (1500-2900) x 1061C02 is produced yearly from CH4 by reaction steps [3.4], [3.2], [3.5] and [3.7]. On the basis of these data for the schematic representation of the atmospheric pathways of carbon a value of 2800 x 106 t yr 1 expressed in C02 will be accepted (see Fig. 8, p. 46) for this sink term. 

As mentioned earlier, the increase in the in HTW and SCW produces equivalent quantities of and OH and therefore the increase in the observed rate of reaction could also arise from base catalysis. Eckert et al. observed base catalysis in HTW in the Claisen-Schmidt condensation of benzaldehyde and 2-butanone. The product outcome of this reaction under normal aqueous conditions depends upon whether the reaction is acid or base catalysed in acid catalysis a monosubstituted enone is formed whereas the base-catalysed route yields a disubstituted enone as the favoured product (Scheme 3.6). The disubstituted enone was found to be the dominant product for the Claisen-Schmidt condensation in HTW indicating base catalysis as the dominant pathway in HTW. 

Scheme 4.S Schmidt versus Mannich pathways in intermolecular reactions.

The synthetic pathways developed to access the target pyridazinone arrays are based on the assembly of the exocyclic a,P-unsaturated framework through either Knoevenagel (chemotype A) or Claisen-Schmidt (chemotypes B and C) condensations (Scheme 1.11) with silica-supported aluminum chloride anployed as a catalyst. In comparison with conventional aluminum chloride, the silica-supported equivalent offers several advantages over the free catalyst (milder acidity, superior shelf Ufe, and the ability to condnct nonaqueous workups) and the polystyrene-supported version (no swelling and ability to carry out reaction in polar solvents). 

A part of the OH-added radical isomerizes as in pathway (c), and forms vinoxy radical (CH2CHO) (Schmidt et al., 1985), but its succeeding reactions are not well known yet. 

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