Catalytic turnover number

MeOH was studied. Using Mel as co-catalyst, catalytic turnover numbers of 1,800 were obtained within 14 h.71... 

The substituents on the alkyne and the cyano components can be widely varied so that we have been able to develop the basic reaction of Eq.(l) into a general synthetic method for preparing pyridines (see Section III). We have concentrated on the development of highly reactive organoco-balt(I) complexes and have tested a number of catalyst complexes under standard conditions. Both the influence of the controlling ligand Y and the neutral ligand L on the catalytic turnover number (TON) have been determined. The final step involves the optimization of the reaction conditions. 

The rate constant, ko was found to be 1.0 0.2 x 105 M-2 min-1 and the apparent order of catalytic activity was CoTSP > NiTSP > CuTSP over a wide range of pH. The catalytic turnover numbers for the reactions were generally found to be greater than 100,000 (23). 

Yet another example of catalysis by cluster Grignard reagents is isomerization of alkyl halides. It turned out that, in the presence of these reagents, n-chloroalkanes undergo partial isomerization to produce a mixture of secondary chloroalkanes. The catalytic turnover number is as large as 20. 

Losses of catalyst which limit the catalytic turnover numbers to finite values. 

The observed reaction rate constants, kobs, have been normalized to Ist-order constants when necessary. The catalytic turnover number, CTN, is the number of moles of substrate reacted per minute divided by the moles of enzyme present. 

A totally different approach to metal-catalyzed SNAr reactions of chlorobenzene involves reversible -coordination of the metal to PhCl, leading to the increase in electron deficiency of the benzene ring, sufficient for nucleophilic displacement of chlorine via the Meisenheimer-type path (Sect. 2.4) [85,86,203]. This way, anisole can be prepared from chlorobenzene in a catalytic manner [86, 203], although with very low catalytic turnover numbers of 2-6 (Eq. 26). 

The catalytic turnover number (TON) is the number of moles of product per mole of catalyst this number indicates the number of catalytic cycles for a given process, e.g. after 2 h, the TON was 2400. The catalytic turnover frequency (TOP) is the catalytic turnover per unit time the number of moles of product per mole of catalyst per unit time, e.g. the TOF was 20min. ... 

Defining the catalytic turnover number and frequency is not without problems. For example, if there is more than one product, one should distinguish between values of the total TON and TOF for aU the catalytic products, and specific values for individual products. The term catalytic turnover number is usually used for batch processes, whereas catalytic turnover frequency is usually apphed to continuous processes (flow reactors). 

Very recently, it has been demonstrated [76] that the hosts (RR)-(29) and (R)- 59), complexed to KOCMej or KNHj, catalyse the Michael additions of methyl vinyl ketone and methyl acrylate to the phenyl acetic esters (61) and (62), and the )8-ketoester (63) with high catalytic turnover numbers (CTN = mmoles of product... 

Each of the catalysts listed earlier in the hydroformylation reaction are found to be catalysts for the reduction of nitrobenzene to aniline the rhodium, osmium, and ruthenium species are particularly eflFective although with osmium higher temperatures must be used. (A. F. M. Igbal previously has reported that several derivatives of rhodium, including Rh6(CO)i6 can act as catalysts for the reduction of nitrobenzene to aniline using CO + H2O (19).) The catalysts listed are also much sturdier than was found in the case of iron carbonyl, and in the experiments listed in Table III the total amount of nitrobenzene and catalyst in a 1000 molar ratio was added to the reaction at the outset. In no case was there observed any precipitate of metal oxides or carbonates, and presumably much higher catalytic turnover numbers could be realized if the reaction were run in a continuous-type reactor. 

Studies already carried out have revealed that the catalytic turnover numbers of acetylglycosylated metalloporphyrins were doubled when compared with those of the same metalloporphyrins without sugar groups. Certainly the improvement of such catalytic methods requires the development of new synthetic methodologies. 

The catalytic turnover number (TON) is the number of moles of product per mole of catalyst this number indicates the number of catalytic cycles for a given process, e.g. after 2 h, the TON was 2400. 

In turning to the pressure-gap problem, we note that this same reaction carried out under UHV would show a marked decrease in the rate of reaction as measured by the catalytic turnover number. The turnover number is defined as the rate of a reaction normalized per reactive surface site. 

---