【作者】 刘霖；

【导师】 魏运洋；

【作者基本信息】 南京理工大学 ， 应用化学， 2008， 博士

【摘要】 由醇选择性氧化制备相应的醛或酮是有机合成中一个非常重要的官能团转换。传统的氧化工艺大多采用化学计量氧化剂如CrO₃/H₂SO₄、CFO₃（Py）₂、PCC、DMSO/（COCl）₂、MnO₂和SeO₂等,这些氧化剂存在影响环境和成本较高等问题,并且反应要消耗大量有机溶剂。为了解决这一问题,近年来开发绿色、温和、经济、高效的反应催化体系,以H₂O₂、O₂或空气作为清洁氧化剂液相催化氧化醇类至醛酮化合物成为研究热点,特别是氧气或空气,因为氧气（空气）是所能得到的最丰富、廉价、安全及环境友好的氧化剂。因此,深入研究此类氧化反应不但对于实验室范围内很有价值,而且对于工业生产也有重要意义。本论文在以分子氧为氧化剂的醇选择性氧化体系方面作了一些有益的探索。制备了离子液体固定化TEMPO（TEMPO-IL）,并将其应用于TEMPO-IL/CuCl催化体系,以离子液体[bmim][PF₆]为溶剂或无溶剂条件下催化醇类的氧化,该体系对苄醇和烯丙醇的氧化均有较好的催化效果,但对于脂肪醇和杂环醇的催化效果较差,即使延长反应时间也很难完全反应。研究还发现,该催化体系的选择性很高,各种醇类均未发现氧化到酸的情况,且烯丙醇的双键也不会被氧化。TEMPO-IL/CuCl催化体系在离子液体中和无溶剂条件下都有很好的循环使用性能,经多次循环使用转化率和收率无明显下降。探讨了TEMPO-IL/CuCl催化体系的催化机理,铜离子是反应的活性中心。针对TEMPO/CuCl催化体系反应速度较慢的问题,研究了碱对TEMPO/CuCl体系的促进作用。研究发现,除了碳酸氢钠以外,其他碱无论是无机碱和有机碱都对TEMPO/CuCl催化体系有促进作用,其中吡啶、N-甲基咪唑、NaOH的醇溶液的促进效果较好。研究发现,碱类能起促进作用的原因之一是其碱性,在碱性环境中可能有利于醇上氢的离去;另一个原因可能是有些碱如吡啶和N-甲基咪唑具有一定的配位能力,与Cu离子形成的络合物与醇的结合能适中,更有利于反应的进行。将TEMPO/CuCl/pyridine催化体系应用于多种醇的分子氧氧化发现,该体系能高效、选择性地将苄醇、杂环醇和烯丙醇氧化为醛或酮,对于一些活泼醇（如肉桂醇）,反应体系中存在吡啶情况下,反应速率比不加吡啶快近十倍。由于TEMPO和碱的流失,TEMPO/CuCl/pyridine催化体系难以回收和循环使用,为了解决此问题,改用3A分子筛（MS3A）与TEMPO-IL分别代替碱与TEMPO也能很好的提高氧化反应的速度,且具有很好的回收和循环使用性能。在离子液体[bmim][PF₆]中,TEMPO/Cu（NO₃）₂体系能催化各种醇的氧化,研究了该体系的反应机理,发现该催化体系的催化作用实际是TEMPO、Cu（NO₃）₂和卤素离子共同作用的结果。提出了TEMPO/X^-/HNO₃无过渡金属催化醇氧化体系,该体系反应效率高,选择性好,和其他无过渡金属催化氧化体系相比,对环境的不良影响更小。讨论了TEMPO/Cu（NO₃）₂体系和TEMPO/X^-/HNO₃体系催化醇氧化的机理,认为这两种体系都是氧化氮活化分子氧从而催化醇的氧化。水相中TEMPO/CuCl体系能将醇催化氧化为醛或酮,但转化率和选择性较低。TEMPO/CuCl/H₂O体系中加入碱和表面活性剂均能提高反应的转化率和选择性。考察了离子液体固定化和SiO₂负载TEMPO在反应中的循环使用性能,由于TEMPO与载体材料之间的连接键容易断裂而使体系的循环使用性能较低。合成了系列OMS-2材料,并对其进行了BET、TG、XRD、SEM和EDS分析。将系列OMS-2材料应用于催化醇的分子氧氧化,结果表明,OMS-2材料在离子液体中有较好的催化氧化性能,反应的选择性较高。金属离子的掺杂对OMS-2在离子液体中催化氧化并无明显促进作用,反而降低了其催化选择性。采用手工研磨或球磨机研磨的方法,探索了OMS-2催化固相研磨选择性氧化固态醇的可能性,结果表明,采用研磨的方式也能高选择性地氧化醇,但由于反应生成水的不利影响,使转化率偏低。OMS-2材料催化醇的氧化可能按Mars-van Krevelen机理进行。更多还原

【Abstract】 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.更多还原