Reactions performed in situ during

Reactions Performed in situ During Dess-Martin Oxidation... 

Propanol oxidation under mild conditions takes place with high selectivity. No products other than acetone were observed in the ATR spectra recorded in situ. The situation is more complex for the oxidation of primary alcohols such as ethanol. The first oxidation step produces acetaldehyde, which is prone to further reactions, as is apparent in the ATR spectra. Figure 20, left, shows ATR spectra recorded in situ during ethanol oxidation. Figure 20, right, shows some signals as a function of time. The experiment was performed in a manner similar to that of the one... 

It has been noted elsewhere that the order of addition of reagents is the most important single variable to influence product distribution. A procedure which is convenient and normally reliable is based on the addition of small pieces of metal to a mixture of substrate, ammonia, solvent and (if appropriate) alcohol at less than -70 °C until the blue colour persists for a reasonable period (approximately 10 min). For less reactive substrates, lithium should be used and the addition of the alcohol delayed so that a higher concentration of metal is maintained during the reduction process. Quenching is best effected by 1,3-penta-diene (or similar substance), followed either by ammonium chloride or another electrophile. In reactions where in situ alkylations are performed these are best carried out on lithium derivatives, so in cases where other metals have been used for reduction carefully dried lithium bromide is added before the electrophile. 

The Heck reaction performed in ILs has various advantages compared with all previously described molecular solvents, such as catalytic efficiency for the vinylation of chloroarenes, improved thermal catalyst stability and lifetime during the reaction. In the reactions performed in 1,3-dialkylimidazolium ILs, jV-heterocyclic carbene complexes of palladium can be formed in situ. These palladium-carbene complexes are formed from the deprotonation of the imidazolium cation in the presence of the catalyst precursor. ... 

Particular attention has been devoted to the catalytic activity of palladium (Pd /Pd ) salts, mostly because of their high reactivity in mild conditions. The reaction can be driven toward the formation of oxalate or carbonate (9-1J). The reoxidation of Pd° salts with oxygen can be easily performed in-situ if a suitable co-catalyst is used. Copper has been the most widely proposed. Unfortunately, the formation of water during the reoxidation process heavily interferes with the catalytic cycle. Therefore, non-conventional oxidants like peroxides (J2) or processes involving a separate reoxidation step have been proposed. A vapor phase two-step process based on palladium catalyzed carbonylation of methyl nitrite has been developed on an industrial scale in Japan (13). 

Cu(II) state mostly existed on the catalyst surface. However, after the reaction, the relative areal intensity ratio between Cu(l) and Cu(ll) states remaikably increases up to more than 1 1. Note that the Cu(ll) state after the chemical reaction might be formed by air oxidation during the sample preparation of the XPS measurement. Consequently, it is believed that the present cycloaddition reactions were proceeded by the Cu(l) species formed in situ during the reaction. The excess amount of phenylacetylene could behave as a reductant to convert Cu(l) from the activated Cu(ll) surface, via the formation of Cu(II)-acetylide. Apparently, such a well-defined hybrid system with bifunctional components provides a new way to design high-performance catalysts with high activity and reusability for gas- and solution-phase reactions. 

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