Solvent effect nitriles

In 1996, a new type of thioglycoside donor, the A, lV-diacetyl sialyl donor, was devised by Boons and co-workers. This is the beginning of the third period. The iV,iV-diacetyl sialyl donor was followed by other analogous C5-modified sialyl donors. Very recently, Tanaka and his coworkers have developed the 5-iV-4-0-oxazolidinone sialyl donor, which can provide a-sialo-side without assistance of the nitrile solvent effect despite the absence of an auxiliary at the C3 or Cl positions. 

An unusual solvent effect was observed in cycloadditions of aromatic nitrile N-oxides with alkyl-substituted p-benzoquinones in ethanol-water (60 40) the reaction rates were 14-fold greater than those in chloroform (148). The use of ion pairs to control nitrile oxide cycloadditions was demonstrated. A chiral auxiliary bearing an ionic group and an associated counterion provides enhanced selectivity in the cycloaddition the intramolecular salt effect controls the orientation of the... 

Polymerization of acrylonitrile in polar solvents. Polar solvents are expected to interfere with the association of nitrile groups in pairs and to replace the nitrile-nitrile association complex by a nitrile-solvent association. Under such conditions structures such as IV should no longer arise and the "matrix effect" should disappear. 

Utilizing MeCN there is the possibility of a special solvent effect, directing to this converse selectivity, named nitrile effect.28,29 30... 

Another noticeable characteristic of captodative olefins is the influence of the reaction medium. The stabilizing effect of solvent on the persistency of a captodatively radical has been reported experimentally for the bond homolysis of bis(3,5,5-trimethyl-2-oxomorpholin-3-yl) [111], but was not found for the 2,3-diphenyl-2,3-dimethoxysuccinonitrile homolysis [112]. Theoretically the solvent-assisted stabilization las been predicted for the captodative substituted nitriles in solvent with large dielectric constants [113-114], Table 16 illustrates the solvent effect on the spontaneous thermal polymerizations [115]. The polymer yields are... 

The oxidized dimer, [Fe2(TPA)20(0Ac)]3+, 41, was shown to be an efficient catalyst for cyclohexane oxidation using tert-BuOOH as a source of oxygen (69). This catalyst reacts in CH3CN to yield cyclohexanol (9 equiv), cyclohexanone (11 equiv), and (tert-butylperoxy)cyclohexane (16 equiv) in 0.25 h at ambient temperatures and pressures under an inert atmosphere. The catalyst is not degraded during the catalytic reaction as determined by spectroscopic measurements and the fact that it can maintain its turnover efficiency with subsequent additions of oxidant. Solvent effects on product distribution were significant benzo-nitrile favored the hydroxylated products at the expense of (tert-butyl-peroxy)cyclohexane, whereas pyridine had the opposite effect. Addition of the two-electron oxidant trap, dimethyl sulfide, to the catalytic system completely suppressed the formation of cyclohexanol and cyclohexanone, but had no effect on the production of (tert-butylper-oxy)cyclohexane. These and other studies suggested that cyclohexanol and cyclohexanone must arise from an oxidant different from that responsible for the formation of (tert-butylperoxy)cyclohexane. Thus, two modes of tert-BuOOH decomposition were postulated a heterolytic... 

The piperidinium benzoyltrifluoroacetone derivative shows even more interesting behavior. In the alcohol mixture, it is completely dissociated. Adding dimethylformamide decreases the degree of dissociation to 47 %, while a solution of this compound in nitrile solvents (in which the benzoylactonate is found to be completely dissociated) even at room temperature, is less than 10% dissociated. The high inherent quantum efficiency of this and closely related fluorinated chelates (J5), and the specific beneficial effect of nitrile solvents has permitted laser action to occur at room temperature with, for example, piperidinium (BTFA)4Eu in acetonitrile 28). 

In either dimethyl-formamide or dimethyl sulfoxide, the reaction rates became too fast to measure even in the absence of a catalyst. It thus appears that while the ionizing power of the solvent as indicated by the dielectric constant is an important factor for the solvent effect, it is not the only one. The slow reaction in the case of acetonitrile may have been caused by the nitrile competing with the isocyanate for the electrons of the base catalyst and thereby neutralizing the catalyst by complexing. 

---