Catalysis of Organic..

Tanielyan et al. 129ConclusionsIt has been shown that the aerobic oxidation of alcohols takes place only when allthree components of the catalyst are present; AA TEMPO, Mg(NO 3 ) 2 , NBS (23).The reaction can be run under mild conditions: temperature 310-330K; oxygenpressure of 0.1-0.5Mpa; alcohol concentration of 5.4M in HOAc; ratio of substrate :AA TEMPO:Mg(NO 3 ) 2 :NBS = 133:1:1:1.19. Non-activated primary alcohols arequantitatively converted to the corresponding aldehydes at high selectivity. The onlyby-product observed in some instances is the corresponding carboxylic acid. Somesecondary alcohols were also oxidized with high selectivity to the correspondingketones but at lower conversions. Both benzyl alcohol and the sec-phenylethanolwere smoothly converted to their respective aldehyde or ketone oxidation products.Experimental SectionA. Experimental Setup. The oxidation reactions were performed using an in-housemade Multi Autoclave Glass Volumetric system (24). All reactions were carried outin Ace Glass reaction flasks with Teflon heads, equipped with Swagelock basedinjection and thermocouple ports. Digital stirrers and Fisher cross stir bars were usedfor providing an efficient and controlled stirring. The Multi Autoclave reactor systemallows conducting five simultaneous oxidations with five independent variables. Theonly common parameter for all five reactions is the reaction temperature. The reactorsystem permits the recording of the oxygen uptake with the time, thus allowingprecise monitoring the progress of the oxidation. The system was described in detailin our earlier work (24).B. Oxidation procedure for the small-scale experiments. The required amounts ofhexan-1-ol, AA-TEMPO, Mg(NO3)2, NBS and HOAc were loaded in the reactorand the flask was connected to the volumetric manifold. The flask was flushed threetimes with oxygen and immersed in the thermostated water bath held at the reactiontemperature for two minutes to equilibrate the system. The oxygen was admitted tothe reaction pressure and the continuous monitoring of the oxygen uptake initiatedand recorded against the time. After the reaction was completed the productcomposition was analyzed by GC using dioxane as an internal standard.C. Large-scale oxidation protocol. The large-scale oxidations reactions were carriedout in a 300mL Parr autoclave equipped with an injection port, a thermocouple port,a septa sealed addition port and port connected to the volumetric measurement andgas supply module. The module consists of a forward pressure regulator and acalibrated ballast reservoir. The pressure in the reactor and in the ballast reservoir ismonitored constantly and the pressure drop in the ballast reservoir is constantlyconverted into moles of oxygen uptake recorded vs. the time.In a typical oxidation reaction, the autoclave was charged with hexan-1-ol (100mL,800 mmol), HOAc (50 mL, 0.87mol), AA-TEMPO (1.28g, 6.0 mmol, 0.75 mol%),Mg(NO 3 ) 2 .6H 2 O (1.54g, 6mmol) and NBS (1.21g, 6.8mmol). The system waspurged three times with nitrogen, the nitrogen pressure increased to 150 psi and theautoclave heated to the desired temperature. When the target temperature wasreached, oxygen was admitted at 200 psi and the computer monitoring of the oxygen