Catalysis of Organic..

128TEMPO Oxidation of AlcoholsMNT : NBS of 133 : 1 : 1 :1.19, a twelve fold scaled up reaction was carried out atTable 2. Oxidation of alcohols using the X-TEMPO-NBS-Mg(NO 3 ) 2 system a .Run Substrate Scale Substrate/ X-TEMPO Yield (time)CatalystMmol Mol/mol % (min)1 1-Hexanol 16 33 MeO- TEMPO 91 (47)2 1-Hexanol 16 33 TEMPO 92 (60)3 1-Hexanol 16 33 HO TEMPO 92 (36)4 1-Hexanol 16 33 AA-TEMPO 95 (25)5 1-Hexanol 64 133 AA-TEMPO 92 (280)6 2-Hexanol 64 133 AA-TEMPO 33 (600)7 1-Heptanol 64 133 AA-TEMPO 99 (400)8 1-Octanol 64 133 AA-TEMPO 99 (400)9 1-Dodecanol 64 133 AA-TEMPO 89 (400)10 Benzyl alcohol 64 133 AA-TEMPO 93 (30)11 1 Phenylethanol 64 133 AA-TEMPO 89 (240)Conditions for 1-4: [1-Hexanol] = 16mmol (2 cc), [CH 3 COOH] = 10 cc, [X-TEMPO] = 3 %mol, Mg(NO 3 ) 2 = 0.48 mmol, [NBS] = 0.048 mmol. For 5-11: [1-Hexanol]= 64 mmol (8cc),[CH 3 COOH]=4cc, [X-TEMPO] = 0.75 %mol, Mg(NO 3 ) 2= 0.48mmol, [NBS] = 0.55 mmol. T= 46°C, Pressure O 2 =15 psi48°C and an air pressure of 200 psi. The 800 mmol reaction was completed in 3hours for full conversion of 1 at 93.1% selectivity to 2.Scope of ApplicationThe data in Table 2 show the potential of the triple X-TEMPO / Mg(NO 3 ) 2 / NBSbased catalyst system tested over large number of representative alcohols at low(entry 1-4) and at high C/S ratio (5-11).The primary alcohols were oxidized to thecorresponding aldehydes at complete conversion of the alcohol and at 90-93%selectivity with the only by-product detected were the corresponding acid and someminor amounts of the symmetrical ester. The best performing TEMPO derivativeunder the optimized conditions (T 46°C and [MgNO 3 ] 2 = 3mol%), was the AA-TEMPO catalyst (entry 4) in the presence of which complete conversion of 1 wasachieved over a 25 min reaction time with a turnover frequency of 80h -1 , which is thehighest reported to date for a TEMPO based aerobic oxidation. At high S/C ratios,the triple catalyst system shows the characteristic for other TEMPO based oxidationsystems; preference in oxidation of primary over secondary alcohols (19). Forexample the oxidation of hexan-1-ol was nearly an order of magnitude faster as theoxidation of hexan-2-ol under comparable conditions (entry 5, 6). Benzyl alcoholand 1-Phenylethanol were both quantitatively converted to the respectivebenzaldehyde and acetophenone (entry 10,11).