Reductive quenching

REDUCTION WITH LITHIUM ALUMINUM HYDRIDE Acidic Quenching. Reduction of Aldehydes and Ketones [ 5]... 

The possibilities of the two kinds of back electron transfer can be diminished to one by selecting the reaction components. When the excited state of P is quenched oxidatively by T, the only possible back electron transfer is from (T,)red, to (P)M. On the contrary, when P is quenched reductively by T2, the back electron transfer to be considered is only from (P)rcd to (T2)ox. In either case, the back electron transfer can be prevented by a molecular design based on reaction dynamics. For the... 

An attractive flexibility in using anomeric phenyl sulfones is that a stereodivergent synthesis of C-glycosides is available by alkylation before the reductive desulfonylation event. Thus, a one-pot four-step sequence of sulfone deprotonation-electrophile quenching-reductive lithiation-methanol quenching on sulfone 14 provides stereoselectively P-C-glycosides 19 as shown with aldehyde 16 (Fig. 

In these devices no other known redox couple works nearly as well. Although in solution I is capable of quenching reductively the excited state of many dyes (Eq. (25)), on a semiconductor surface such as Sn02 and Ti02, the iodide quenching is not able to compete kinetically with the ultrafast charge injection [89]. 

Triton X-100 and y-cyclodextrin, and subsequent charge separation via reductive quenching Chem. Phys. Lett. 223 511-16... 

The economics of the arc-coal process is sensitive to the electric power consumed to produce a kilogram of acetylene. Early plant economic assessments indicated that the arc power consumption (SER = kwh/kgC2H2) must be below 13.2. The coal feedcoal quench experiments yielded a 9.0 SER with data that indicated a further reduction to below 6.0 with certain process improvements. In the propane quench experiment, ethylene as well as acetylene is produced. The combined process SER was 6.2 with a C2H2/C2H4 production ratio of 3 to 2. Economic analysis was completed uti1i2ing the achieved acetylene yields, and an acetylene price approximately 35% lower than the price of ethylene was projected. 

At atmospheric pressure, the conversion to trichlorosilane is limited to about 16%. The conversion of SiCl to HSiCl was found to be at equiUbrium. If contact time was greater than 45 s and the mole ratio of hydrogen to siUcon tetrachloride 1 1, then at 14 kPa (2 psi) and 550°C, the HSiCl mole fraction reached 0.7 but substantial formation of H2SiCl2 occurred (62). Enhancements in yield have been reported through preactivating the siUcon mass by removal of oxides (73) and the rapid thermal quench of the effluent gas stream (74). The reduction of siUcon tetrachloride in a plasma has also been reported (75). 

After the molten glass has become a homogeneous Hquid, it is poured in a thin stream into water or between closely spaced, water-cooled rotating metal rollers. This quenched glass, termed frit, is a friable material easily reduced to small-sized particles by a ball-milling operation. Ball-milling the glass frit into small-sized particles can be carried out whether the frit is to be used wet or dry (see Size reduction). 

Toluene is a useful co-solvent in metal-ammonia reductions as first reported by Chapman and his colleagues. The author has found that a toluene-tetrahydrofuran-ammonia mixture (1 1 2) is a particularly useful medium for various metal-ammonia reductions. Procedure 8a (section V) describes the reduction of 17-ethyl-19-nortestosterone in such a system. Ethylene dibromide is used to quench excess lithium. Trituration of the total crude reduction product with methanol affords an 85% yield of 4,5a-dihydro-17-ethyl-19-nortestosterone, mp 207-213° (after sintering at 198°), reported mp 212-213°. For the same reduction using Procedure 5 (section V), Bowers et al obtained a 60% yield of crude product, mp, 196-199°, after column chromatography of the total reduction product. A similar reduction of 17-ethynyl-19-nortestosterone is described in Procedure 8b (section V). The steroid concentration in the toluene-tetrahydrofuran-ammonia system is 0.05 M whereas in the ether-dioxane-ammonia system it is 0.029 M. 

Samples were deformed by rolling at room temperature after disordering and quenching (40% and 80% reduction in thickness) and after ordering by a 19h annealing at 300°C (30% reduction). Completely recrystallized samples were prepared by annealing 48h at 600°C. Resistivity measurement was done by the potentiometric method in liquid N2 relative to a dummy specimen (accuracy 3x10" ). 

Figure 7. Resistivity change during isochronal anneaUng of Ni76Al24+0.19at%B ( pure ordering ) after separating non-ordering effects of defect recovery from as-measured curves (broken line) For more details see . S1(G) 8% reduction, S2(0) 14% reduction, S3(i) slow-cooling, S4( ) quenched from 973K.

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