Heterogeneous reagents

Molar ratio LAH 90 ketone = 1.0 2.30 0.64. Reaction at -65°C with heterogeneous reagent used immediately on preparation. Analysis based on NMR of MTPA esters in presence of Eu(fod)3 shift reagent. 

Review. Use of C8K as a heterogeneous reagent in organic synthesis has been reviewed, particularly as a reducing agent for C=C and C—N bonds, and for reductive cleavage of the C—S bond of a,p-unsaturated sulfones. C8K has been used to obtain active metals dispersed on graphite by reduction of metal halides. 

The dehydration of diethylcarbinol in 1932 was the first example of synthetic chemistry attempted in flow mode using a heterogeneous reagent [67] although no experimental details were given, it was reported that the use of acidic silica gel at high temperature promoted the dehydration of the compound to various alkenes. 

The second question is more difficult to answer. Indeed, since the electrical perturbation extends only over a few angstroms from the electrode surface, the medium in which the electrogenerated intermediates react is identical to the bulk of the solution, which favors a positive answer. On the other hand, they react under essentially nonisotropic conditions because of the existence of concentration profiles, that is, of concentration changes with distance of the electrode (see Fig. 15). Yet this is a situation identical to that encountered when heterogeneous reagents or polyphasic conditions are used in usual homogeneous chemistry. A more serious difference is related to the nature of the media... 

From an electrochemical point of view it is easily inferred that the solution in a cell near an electrode is separable into two parts a stagnant layer adjacent to the electrode in which no convective motions occur, and the remainder of the solution, which is homogeneous (bulk solution). Yet this is not a particularity of electrochemical methods since the same phenomena occur at any solid/liquid interface, as when metal particles (reductions by Zn or Na, for example) or any heterogeneous reagent is used in organic homogeneous chemistry, as well as in phase-transfer catalysis or related methods. 

Reviews on the use of DMSO in synthesis,1 functionalized polymers as heterogeneous reagents,2 methods of fluorination,3 and the application of the torsion angle notation in 5-, 6-, and 7-membered rings4 all contain steroidal examples. 

Among other commonly used oxidants, Mn02 and Pb02 have been traditionally applied as heterogeneous reagents in the oxidative phenolic couplings affording a wide variety of alkaloid structures, almost always in very low yields [33,34]. 

Iranpoor, N. Firouzabadi, H. Heydari, R. Silica-acetate complex of N2O4 a heterogeneous reagent for the selective nitration of phenols and nitrosation of thiols. Synth. Commun. 2003,33, 703-710. 

Rosenfeld A., Avnir D., Blum J. Sol- el encapsulated transition metal quaternary ammonium ion pairs as highly efficient recyclable catalysts. J. Chem. Soc., Chem. Commun. 1993 583 584 Rosenfeld A., Blum J., Avnir D. Disproportionation of dihydroarenes by soL el entrapped RhCls-quaternary ammonium ion pair catalysts. J. Catal 1996 164 363-368 Sarussi L., Blum J., Avnir D. Doped sol gel materials as heterogeneous reagents for organic synthesis. J. Sol-Gel Sci. Tech. 2000 19 17-22... 

TaKing into account that C.B. are heterogeneous reagents constituted of some remaining solid sodamide, a white suspension and a limpid liquid we interpreted the phenomena as follows (Scheme 2) ... 

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