Indirect conversion, synthesis

Indirect conversion of oximes to nitro compounds viact-halo nitro compounds has provided a useful method for synthesis of nitro compounds, as shown m Scheme 2 1... 

In the 1930s, Standard Oil of New Jersey (7) was the first company to employ on a commercial scale the indirect conversion of methane, the main component of natural gas, via steam reforming to give synthesis gas, which is a mixture of H2 and CO, with the H2/CO ratio depending on the reactant composition. C02 is also formed in synthesis gas production, and sulfur compounds are present as impurities. Synthesis gas can be used as a feedstock for numerous chemicals and fuels and as a source of pure hydrogen or carbon monoxide. 

The indirect conversion of an aromatic aldehyde into the corresponding nitrile by dehydration of an oxime is illustrated by the synthesis of veratronitrile (Expt 6.170). The dehydrating agent is acetic anhydride which probably effects an initial acetylation of the oximino group followed by the elimination of acetic acid. 

Catalytic hydrogenation of CO2 to hydrocarbons is classified into two categories. The one is direct hydrogenation fix)m H2/CO2 to hydrocarbons. The other is indirect process which includes methanol sjmthesis fix>m H2/CO2, followed by in situ methanol conversion to hydrocarbons using sohd acid catalyst in H2/CO2 feed. Study on indirect hydrocarbon synthesis is now popular. 

Introduction. Indirect natural gas conversion consists of two major steps in series, i.e., natural gas conversion to synthesis gas and synthesis gas conversion to liquid fuels. The dominant commercial practices of the two steps are Steam Reforming and methanol synthesis, respectively. Consequently, the Natural Gas to Methanol via Steam Reforming (SRM) is adopted as the standard indirect conversion technology for comparison. 

A typical process scheme for this indirect conversion technology consists of the following steps in series steam reformer, cooling and separation, CH3OH synthesis, and cooling and... 

There are a number of current R D activities in indirect conversion. However, none of their potential benefits are included in this studies. Of course, a large number of indirect conversion technologies is possible simply by combining the various natural gas to synthesis technologies and synthesis gas conversion technologies. Readers are referred to a brief review by Kuo (1992) in reaching the above choice. 

Figure 4 A part of carbon phase diagram 1, a triple point 2, melting of graphite 3, diamond graphite transformation 4, Liepunski s prediction for indirect conversion (Fe—C) 5, Bundy s minimum for diamond formation from Fe—C 6, synthesis of diamond from glassy carbon (12) 7, the same according to Ref. 13.

Indirect Hquefaction of coal and conversion of natural gas to synthetic Hquid fuels is defined by technology that involves an intermediate step to generate synthesis gas, CO +. The main reactions involved in the generation of synthesis gas are the coal gasification m2LC ions Combustion... 

Gasification. Gasification of coal is used to provide gaseous fuels by surface and underground appHcations, Hquid fuels by indirect Hquefaction, ie, catalytic conversion of synthesis gas, and chemicals from conversion of synthesis gas. There are also appHcations in steelmaking (see Coal conversion PROCESSES, gasification). 

Status of Indirect Liquefaction Technology The only commercial indirect coal liquefaction plants for the production of transportation fuels are operated by SASOL in South Africa. Construction of the original plant was begun in 1950, and operations began in 1955. This plant employs both fixed-bed (Arge) and entrained-bed (Synthol) reactors. Two additional plants were later constructed with start-ups in 1980 and 1983. These latter plants employ dry-ash Lurgi Mark IV coal gasifiers and entrained-bed (Synthol) reactors for synthesis gas conversion. These plants currently produce 45 percent of South Africa s transportation fuel requirements, and, in addition, they produce more than 120 other products from coal. 

The direct conversion of 3-methylcyclohex-2-enone into 2-allyl-3-methylcyclohexanone provides an interesting example of the utility of the reduction-alkylation procedure. Synthesis of this compound from 3-methy I cyclohexanone would be difficult because the latter is converted mainly into 2-alkyl-5-methylcyelohexanones either by direct base-catalyzed alkylation11 or by indirect methods such as alkylation of its enamine (see Note 13) or alkylation of the magnesium salt derived from its cyclohexylimine.12... 

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... 

In mammals and in the majority of bacteria, cobalamin regulates DNA synthesis indirectly through its effect on a step in folate metabolism, catalyzing the synthesis of methionine from homocysteine and 5-methyltetrahydrofolate via two methyl transfer reactions. This cytoplasmic reaction is catalyzed by methionine synthase (5-methyltetrahydrofolate-homocysteine methyl-transferase), which requires methyl cobalamin (MeCbl) (253), one of the two known coenzyme forms of the complex, as its cofactor. 5 -Deoxyadenosyl cobalamin (AdoCbl) (254), the other coenzyme form of cobalamin, occurs within mitochondria. This compound is a cofactor for the enzyme methylmalonyl-CoA mutase, which is responsible for the conversion of T-methylmalonyl CoA to succinyl CoA. This reaction is involved in the metabolism of odd chain fatty acids via propionic acid, as well as amino acids isoleucine, methionine, threonine, and valine. 

Scheme 6. Synthesis of dendrimer 22 a and its TMSI mediated conversion (dedendronization) to 22b. 22b is needed to indirectly determine the molecular weight of 22a...

Substituted furan formation by an indirect cyclization of 1,4-dicarbonyl derivatives has also been adopted as a key step in the synthesis of 3-oxa-guaianolides. Although 1,4-dicarbonyl compounds have been traditionally considered as the direct precursors for furans, treatment of 1,4-dicarbonyl compounds having a tertiary acetoxy group with p-toluenesulfonic acid leads to only 11% yield of an alkenylfurans as derived from a cyclization/acetoxy-elimination route. The following scheme shows an alternative multi-step conversion of the 1,4-dicarbonyl that leads to a more acceptable yield of the acetoxyfuran . 

Consequently, in the early 1990s, interest in the direct processes decreased markedly, and the emphasis in research on CH4 conversion returned to the indirect processes giving synthesis gas (13). In 1990, Ashcroft et al. (13) reported some effective noble metal catalysts for the reaction about 90% conversion of methane and more than 90% selectivity to CO and H2 were achieved with a lanthanide ruthenium oxide catalyst (L2Ru207, where L = Pr, Eu, Gd, Dy, Yb or Lu) at a temperature of about 1048 K, atmospheric pressure, and a GHSV of 4 X 104 mL (mL catalyst)-1 h-1. This space velocity is much higher than that employed by Prettre et al. (3). Schmidt et al. (14-16) and Choudhary et al. (17) used even higher space velocities (with reactor residence times close to 10-3 s). 

We chose to study the generation of alkoxycarbenium ion 26 from thioacetal 28. The electrochemically generated ArS(ArSSAr)+, 37 which was well characterized by CSI-MS, was found to be quite effective for the generation of alkoxycarbenium ions, presumably because of its high thiophilicity (Scheme 17). The conversion of 28 to 26 requires 5 min at -78 °C. The alkoxycarbenium ion pool 26 thus obtained exhibited similar stability and reactivity to that obtained with the direct electrochemical method. The indirect cation pool method serves a powerful tool not only for mechanistic studies on highly reactive cations but also for rapid parallel synthesis. 

The answer is E. Methotrexate is an analog of folic acid that binds with very high affinity to the substrate-binding site of dihydrofolate reductase, the enzyme that catalyzes conversion of DHF to THE, which is used in various forms by enzymes of both the purine and pyrimidine de novo synthetic pathways. Thus, synthesis of dTMP from dUMP catalyzed by thymidylate synthetase and several steps in purine synthesis catalyzed by formyltransferase are indirectly blocked by the action of methotrexate because both those enzymes require THE coenzymes. 

In the kidney, PTH stimulates the conversion of 25-(0H)D3 into 1,25-(0H)2D3. Intrarenal l,25-(OH)2D3 causes an amplification of the PTH-induced calcium reabsorption and phosphate diuresis. l,25-(OH)2D3 enhances PTH action in bone also. Once again, PTH does not directly affect intestinal calcium absorption, but it does so indirectly through induction of l,25-(OH)2D3 synthesis and enhanced enterocyte absorption. 

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