Catalysis of Organic..

Tanielyan et al. 127complete conversion was achieved over 105 min reaction time at significantly lowerTOF of 28.6 h -1 . In the third run, at three-fold increase in the substrate concentration(48mmol scale, 4.0M, 50.0 % v/v) the oxidation surprisingly entered into severeinhibition at 44.2% conversion level (curve 3). When the initial concentration ofhexan-1-ol was further increased to 64 mmol scale (5.3 M, 66.7% v/v), the catalystsystem was completely deactivated at 7.4% conversion over 300 min reaction time(curve 4).Oxygen Uptake, mmol403530252015[ROH] o(1) 1.3 M(2) 2.7 M(3) 4.0 M(4) 5.3 M95.5%244.2%a b c34Theoretical Uptake10 120 0.17.4%5Sub/Cat=133300 0.00 100 200 300 0 50 100 150 200 0.2 0.4 0.6Time, minTime, min[NBS], mmolFig 4. Effect of the initial concentration of the Hexanol-1 on the conversion (a), theconcentration of the NBS on the oxygen uptake (b) and the NBS concentration onthe rate of oxygen uptake (c-curve1), selectivity to 2 (c-curve 2) and the amount ofthe acid 8 by-product (c-curve 3) at T= 48°C, P (O 2 )=15psi, [AA TEMPO] =0.64mmol and Mg(NO 3 ) 2 = 1.2 mmol.Conditions for (a): [NBS] = 0.048mmol, [Hexanol-1] = 2mL (16mmol) (1), 4mL(32mmol) (2), 6mL (48mmol) (3) and 8mL (64mmol) (4), CH 3 COOH = balance to12mL total liquid phase.Conditions for (b,c): [Hexanol-1] = 8mL (64mmol), CH 3 COOH = 4mL, [AATEMPO] = 0.48mmol (0.75 mol%), [Mg(NO 3 ) 2 ] = 0.48mmol, [NBS] = 0.191mmol(1), 0.231mmol (2), 0.287mmol (3), 0.48mmol (4), 0.55mmol (5) and 0.61mmol (6).The data in Figure 4a indicated that at least one of the components of the ternarycatalyst had been gradually consumed or slowly degraded at high substrateconcentrations. To determine the true reason of this deactivation phenomenon, thesame 64 mmol scale reaction was repeated using either 10% excess AA-TEMPO or10% excess MNT. Both reactions (not shown in the plot) produced the samenegative result. When the concentration of the NBS was incrementally increasedfrom 0.29 mol% to 0.95 mol%, a rapid and complete conversion of 1 was achieved atTOF = 33 h -1 and at S/C ratio of 133. The data in Figure 4c show that the amount ofthe NBS used at these high S/C ratios affects not only the overall rate of oxidation(curve 1) but, to a large extent, controls the level of the acid by-product (curve 3).Using the same optimized substrate to catalyst ratios of hexan-1-ol : AA TEMPO :65432121100806040Selectivity to 2 and to acid, 8, %0.50.40.30.2Rate Uptake, mmol/min