Preformed methane

Carbon in gas, %C in coal Carbon in CH4, % C in coal Preformed methane, %... 

Over the entire range of experimental conditions covered by these experiments—i.e., pressure, 60-350 atm. temperature, 730-770°C.( reaction time, 2-120 min.—methane is the main product on a heating value basis. It constitutes more than 90% of the total B.t.u. in the gas at the 10% conversion level, and it still is more than 70% of the total B.t.u. in the gas formed even at 60% conversion level. All the data from batch autoclave tests are compared in Figure 10 on the basis of conversion of coal to gas and formation of preformed methane. 

Figure 10. Yields of gas and preformed methane in batch autoclave...

Figure II. Correlation of total gas yield and preformed methane in continuous flow reactor tests...

In this model, the intermediacy of a monomeric zinc species is postulated. To support this assumption, an examination of the effect of stoichiometry and solvent in cyclopropanation involving the 2,4-pentanediol auxiliary was preformed [59]. In the initial reaction protocol, a large excess of both diethylzinc and diiodo-methane is employed. Such excessive conditions are justified on account of the instability of the zinc carbenoid under the reaction conditions. To minimize the un-... 

Scheme 2.12 shows some representative Mannich reactions. Entries 1 and 2 show the preparation of typical Mannich bases from a ketone, formaldehyde, and a dialkylamine following the classical procedure. Alternatively, formaldehyde equivalents may be used, such as l>is-(di methyl ami no)methane in Entry 3. On treatment with trifluoroacetic acid, this aminal generates the iminium trifluoroacetate as a reactive electrophile. lV,A-(Dimethyl)methylene ammonium iodide is commercially available and is known as Eschenmoser s salt.192 This compound is sufficiently electrophilic to react directly with silyl enol ethers in neutral solution.183 The reagent can be added to a solution of an enolate or enolate precursor, which permits the reaction to be carried out under nonacidic conditions. Entries 4 and 5 illustrate the preparation of Mannich bases using Eschenmoser s salt in reactions with preformed enolates. 

Methane high-temperature, in-situ cracking to carbon and easily disposed of gaseous by products is practiced in the carbon/graphite composites industry where additional layerings of amorphous or microstructured carbon deposits are fabricated on preformed scaffolds. These are utilized primarily in the aerospace industry. Thin diamond coatings are also fabricated by the low-vacuum, in-situ chemical vapor deposition from methane decomposition. 

In recent years reactions have been carried out in aprotic solvents with preformed iminium salts. Another recent modification is the use of bis(dialkylamino)methanes (aminais) and aikoxydialkylamino-methanes (aminol ethers) in aprotic solvents in the presence of nonprotic acids. A number of aromatic substrates that do not give Mannich bases under the classical aqueous reaction conditions do react under these aprotic conditions. 

Preformed imines of te-C2V-diarylimines react to give primary amines (60-80% yield), accompanied by small amounts of aryl-h/s-(indol-3-yl)methanes, in the presence of Dy(OTf)3 or other lanthanide salts [304]. 

---