Turn over number, TON

Figure 3.6. Turn over number (TON) displayed as function of time for the hydroformylation of 1-octene using a set-up for continuous processes with SCCO2 as mobile phase and supported catalyst 2...

Constant rates k (mol/s-gPd ) have been determined from the slope of the experimental curves plotting acetylenic molar concentration versus time. Turn over numbers (TONs = mol/s-atom Pd ) were calculated from the following equation ... 

The influence of reaction conditions upon activity was explored, revealing that 13 is 16 times more active than is 14, a fact that can perhaps be attributed to the enhanced steric bulk of the former. This property has previously been identified as fundamentally important in avoiding termination by the p-hydride elimination pathway. 71,172 The activity of the 13/MAO system was further probed, revealing a significant increase in turn-over number (TON) upon varying the pressure in the range 1.1 >30... 

The poor turn-over numbers (TON) in the hydrocyanation reactions are another limitation, because of degradation of the catalyst, which still has to be overcome. The maximum TON reached so far have been in the order of 500-750, which is extremely low compared with other homogenous catalytic reactions. 

Turn over number (TON) moles of ester formed at 5 hours/moles of in the catalyst... 

The activity of these catalysts are expressed in terms of Turn Over Number (TON) calculated as... 

The first application of phosphinines in catalysis was reported by Zenneck et al. in 1996 in the case of t 6-Fe complexes [46, 98], It was shown that complex 73 could catalyse the cyclotrimerization of dimethyl acetylenedicarboxylate as well as the formation of pyridines from alkynes and nitriles. Importantly, the catalytic activity of this complex was found to be superior to that of the corresponding benzene [Fe(n6-C6FI6)(COD)] complex. Reactions of methylpropargyl ether with butyronitrile in the presence of complex 73 as catalyst in a ratio 620 2,720 1 afforded a mixture of functional benzenes and pyridines. Turn over numbers (TON) for the conversion into pyridines reached 160 and those for the formation of functional benzenes reached 326, thus corresponding to a chemoselectivity of 0.49 (Scheme 26). 

The specific rate (mol.g.m 2.h-l), which varies like the Turn Over Number (TON), can be calculated from the following equation R = F/S.X, F being the initial molar flow rate of hydrocarbon (mol.lrl), S die specific surface area (m. g-l) and X the conversion. 

Under UV light, all forms of titania oxidize propane to carbon dioxide. The conversion was followed by periodical illumination with dark periods of 5 min during which propane was found to be the only weakly adsorbed in the dark. Analysis of the carbon mass balance (Figure 4.2) obtained by online MS indicates the formation and accumulation of intermediate reaction products at the catalyst surface whose concentration increases with reaction time in the order anatase > rutile >= mixed anatase/rutile > P25. Taking into account the specific surface areas, the turn over number (TON) increases in the order anatase (9) rutile (15) P25 (112). The activity of titania P25 is higher by a factor of 10 compared to rutile, anatase, or their physical mixture. 

Gold derivatives have also been found to facilitate the Mannich reaction.Thus, the heterogeneous catalyst, gold supported on nanocrystalline Ce02 or Zr02, was found to accelerate the reaction of aldehyde 26, amine 54, and acetylide 55 to produce 56, with a turn-over number (TON) 50-fold greater than the homogeneous variation. 

The amount of A converted, that is, the absolute number of passes through the catalytic cycle before the catalyst becomes deactivated is called the turn over number (TON) ... 

While many heterogeneous catalysts and some homogenous catalytic complexes are known to racemize optically active scc-alcohols via corresponding ketones [18, 19], there is little precedence for the racemization of amines [20, 21]. Moreover, most of them do not meet industrial criteria for turn over number (TON), price of the catalyst, loading capacity of the catalyst or reaction conditions, in particular when high temperatures are required. 

To date, several different catalysts, both organocatalysts and metal-based catalysts, are available for the asymmetric Michael-type addition reactions. Indeed, a high level of achievement has been reached in terms of enanatioselectiv-ity and product yield. However, specihc windows for particular substrates, especially in natural product motif synthesis, are stdl in great demand. Thus, the exploration of more gen-eraL as well as more operationally simple (e.g., moisture stable and air stable), catalysts is attainable. Through the further in-depth structural investigation of catalyst-substrate interaction in Michael addition, a more sophisticated, yet more efficient, catalyst can be developed, and thus, the Turn Over Number (TON) can be expected to be increased. These future developments certainly will be fmitfiil to pharmaceutically and industrially related processes. 

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