Selective Oxidation Of Alcohols To Corresponding Aldehydes And Ketones By Molecular Oxygen

The selective oxidation of alcohols to the corresponding aldehydes or ketones is a fundamental transformation in both laboratory synthesis and industrial production. Numerous oxidizing reagents(e.g.CrO₃/H₂SO₄,CrO₃(Py)₂,PCC,DMSO/(COCl)₂,MnO₂ and SeO₂)in stoichiometric amounts have been traditionally employed to accomplish this transformation with considerable drawbacks,such as use of expensive reagents and volatile organic solvents,and discharge of environmentally pernicious wastes.From economic and environmental perspectives,the development of new catalytic oxidation systems with cheap and green oxidation reagents such as air,molecular oxygen and hydrogen peroxide is very attractive.Of particular interest are the use of molecular oxygen and air,which have several benefits,including low cost,improved safety,abundance,and water as the sole byproduct.Therefore,study on this type of oxidation is of great value in laboratory scope as well as industrial applications.In this dissertation,the selective oxidation of alcohols to corresponding aldehydes and ketones using molecular oxygen as primary oxidant was studied.The ionic liquid immobilized TEMPO(TEMPO-IL)was prepared and used in TEMPO-IL/CuCl catalytic system,which was applied for the aerobic oxidation of alcohols using[bmim][PF₆]as solvent or under solvent-flee conditions.The system exhibits favorable catalytic activity for the oxidation of benzylic and allylic alcohols,in spite of low activity observed for the oxidation of heterocyclic and aliphatic alcohols.The catalytic system shows high selectivity,no acid product was detected,and double bonds of allylic alcohol were not oxidized.The catalytic system was easily recovered and reused in the reaction.In the case of the oxidation of benzyl alcohol,the catalyst was recovered and reused for 5 times without significant loss of catalytic activity.The catalytic mechanism of TEMPO-IL/CuCl was discussed.The results show that copper ion is the active centre of the oxidation.To improve the catalytic activity of TEMPO/CuCl,effects of bases on alcohols oxidation were studied.It was found that most inorganic and organic bases speed up the reaction except sodium bicarbonate,and the promotion effect of pyridine, N-methylimidazole and ethanol solution of sodium hydroxide was remarkable.It is suggested that the promotion activity of base was due to the basicity and the coordination capacity.The TEMPO/CuCl/pyridine catalytic system was applied to the aerobic oxidation of types of alcohol.The results show that in the presence of pyridine the selective oxidation of alcohols proceeded rapidly.The oxidation of benzylic,allylic and heterocyclic alcohols in the presence of pyridine,is about 10 times faster than without pyridine as co-catalyst.Because of the loss of TEMPO and base in the extraction process,the TEMPO/CuCl/pyridine system can not be recycled and reused.Alternatively,TEMPO-IL and 3A molecular sieve(MS3A)would be used to instead of TEMPO and base respectively. The TEMPO/CuCl/3AMS catalytic system was as reactive as the TEMPO/CuCl/pyridine system was,and can be easily recovered and reused.The TEMPO/Cu(NO₃)₂ catalytic system was developed and used in the oxidation of a series of alcohols in ionic liquid[bmim][PF₆].It was found that active spieses in this system includes TEMPO,Cu(NO₃)₂ and halide ions.A highly efficient transition-metal-free catalytic system-TEMPO/X^-/HNO₃ was developed.Compared with other transition-metal-free catalytic systems,the TEMPO/X^-/HNO₃ catalytic system is environmental benign.The catalytic mechanisms of TEMPO/X^- /HNO₃ and TEMPO/Cu(NO₃)₂ were discussed.The oxidation of alcohols in both systems proceeds via nitric oxide activated molecular oxygen.The aerobic oxidation of alcohols can be achieved by TEMPO/CuCl catalytic system in water,in spite of the low conversion and selectivity.With the addition of base and surfactant,the conversion and selectivity can be improved.The recycling of ionic liquid and silica immobilized TEMPO was investigated.Because of the break of the bond between TEMPO and the supporter,the recycling of the catalytic system was difficult.A series of OMS-2 materials were prepared and characterized by BET,TG,XRD, SEM and EDS.OMS-2 materials were applied to the aerobic oxidation of alcohols.The results show that OMS-2 materials have favorable catalytic activity and the corresponding catalytic system shows high selectivity.Metal ion doping on OMS-2 materials has little promotion effects on the catalytic activity in ionic liquid and decreases the selectivity of the oxidation of alcohols.The possibility of selective oxidation of solid alcohols by solid phase grinding in mortar or ball grinder was explored.The results indicated that highly selective oxidation of alcohols can also be achieved by grinding.However,the conversion of oxidation is low due to the effect of water produced in the reaction.The reaction catalyzed by OMS-2 was found to follow the Mars-van Krevelen oxidation mechanism.