Methane intermediates

The effect of crystal size of these zeolites on the resulted toluene conversion can be ruled out as the crystal sizes are rather comparable, which is particularly valid for ZSM-5 vs. SSZ-35 and Beta vs. SSZ-33. The concentrations of aluminum in the framework of ZSM-5 and SSZ-35 are comparable, Si/Al = 37.5 and 39, respectively. However, the differences in toluene conversion after 15 min of time-on-stream (T-O-S) are considerable being 25 and 48.5 %, respectively. On the other hand, SSZ-35 exhibits a substantially higher concentration of strong Lewis acid sites, which can promote a higher rate of the disproportionation reaction. Two mechanisms of xylene isomerization were proposed on the literature [8] and especially the bimolecular one involving the formation of biphenyl methane intermediate was considered to operate in ZSM-5 zeolites. Molecular modeling provided the evidence that the bimolecular transition state of toluene disproportionation reaction fits in the channel intersections of ZSM-5. With respect to that formation of this transition state should be severely limited in one-dimensional (1-D) channel system of medium pore zeolites. This is in contrast to the results obtained as SSZ-35 with 1-D channels system exhibits a substantially higher... 

Thomas, M. Behar, E. Modelling of structure H hydrate equilibria for methane, intermediate hydrocarbon molecules and water systems. Proceedings of the 75th GPA Annual Convention, March 11-13, 1996 Denver Colorado. 

Direct irradiation of dibenzobarrelene (106a) in solution yields the di-T-methane product (107) and the cyclooctatetraene (108). Acetone-sensitized irradiation affords compound (107) only. In the crystalline phase, however, a new product (109) is obtained as well as (107) and (108). A reinvestigation of this has suggested that the biradical (110) is involved in the formation of both the ester (109) and the cyclooctatetraene (108). The formation of the biradical could involve a tri-m-methane intermediate such as (111). Other examples (106b, c) have been studied and while the solid state irradiation does not yield the appropriate diester corresponding to (109) the cyclooctatetraene obtained does have the correct substitution pattern in confirmation of the involvement of a biradical analogous to (110) rather than the (2+2)-cycloaddition reaction path which has been favoured in the past. A further study of the asymmetric induction in the di-n-methane rearrangement has examined the... 

The undoubted highlight of the year in triterpenoid synthesis is the paper by Kametani and his colleagues which describes the full details (see Vol. 8, p. 174) of a stereoselective synthesis of the pentacyclic intermediates (132) and (133), used by Ireland in his syntheses of alnusenone and friedelin. This paper also includes a short non-stereoselective synthesis of (132) and (133) (see the Scheme). The key step is an intramolecular cycloaddition of the o-quinodi-methane intermediate (130). 

Figure 1 Typical SSITKA transients with area between CH4 and Ar determining t, surface residence time of methane intermediates...

As was shown above, the time dependence of semi-logarithmic decay of C in the product reveals information about the reaction mechanism. The downward convexity observed for both Co/Ti02 (Figure 51.9B) and Co sponge (not shown see figure 6.35 in Reference [21]) catalysts at different H2/CO ratios characterizes the presence of at least two pools of methane intermediates on the catalyst surface (C and Cp), that in turn, is heterogeneous toward methane formation. Thus, Ti02 does not seriously influence the formation mechanism of hydrocarbon reaction products, and the methane formation route via CFI Oads species on the support has an inappreciable contribution. 

The catalyst surface is heterogeneous with respect to the methane intermediate. Two methane intermediates are defined Ca,ads and C 3,ads. 

Both methane intermediates are O-free surface species. 

Numerical Modeling of Transient Isotope Responses On the first step, the authors analyzed in detail five possible heterogeneous methanation models based on two gas phase (CO, CH4) and three surface components (COads, Ca,ads, and Cp,ads) that follow from qualitative analysis of CO labeling data [19,21]. These models contained either a buffer step or parallel routes of methane formation. The homogeneous model having one type of methane intermediate was also considered. A methanation reaction was modeled separately from the entire set of reactions included in the Fischer-Tropsch ... 

There are several studies related to the formation of intermediate species. Calculations of the binding energies of species and surfaces can help verifying the possible formation of species during the chemical reaction. In particular, Van Santen et al. [4] showed in this way the dissociation of methane (intermediates CH. where x = A nH) on ruthenium surface (1120) by applying the density functional theory (DFT) [4]. 

As shown in Schane 10.35a, this distinct synthesis began with the scalable preparation of benzocyclobntenol silyl ether 178 from 6-bromopiperonal (177) throngh epoxida-tion, cyclization, and silylation procedure [69]. The subsequent thermal cycloaddition of 179, via an o-quinodi-methane intermediate 180, with fumarate-derived amide 181 afforded C—H functionalization precursor 182 albeit in moderate yield and diastereoselectivity. As expected, when this amide is subjected to stoichiometric Pd(OAc)j in hot CHjCN, the Pd" complex 183 was formed in 53% yield. However, upon the exposure of this intermediate with C7 —H activation to excess of 3,4,5-trimethoxyiodobenzene (163) under the usual arylation condition, p-lactam 184 was obtained exclusively in 75% yield, instead of the expected... 

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