【摘要】：以分子氧為氧化劑,在非常溫和條件下實(shí)現(xiàn)將醇選擇氧化為醛或酮是一個(gè)非常具有挑戰(zhàn)的課題。利用二氧化鈦?zhàn)贤夤夤獯呋梢栽谑覝氐臈l件下實(shí)現(xiàn)分子氧的活化進(jìn)而進(jìn)行醇的選擇氧化,因此受到科學(xué)研究者的廣泛關(guān)注,目前已有許多成果。但是利用可見光光催化實(shí)現(xiàn)醇的選擇氧化仍然是一個(gè)難題。在論文中我們以分子氧或空氣中的分子氧為氧化劑,采用染料敏化二氧化鈦的策略在可見光照射下成功實(shí)現(xiàn)了醇選擇氧化為相應(yīng)的醛或酮的過程,取得了如下所示的兩方面的進(jìn)展:(1)利用曙紅染料敏化銳鈦礦二氧化鈦可以吸收可見光,通過2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)氧化還原中介引發(fā)相應(yīng)的醇的選擇氧化反應(yīng)。在綠光LED照射下,染料敏化二氧化鈦的可見光光催化過程可以與TEMPO的催化氧化循環(huán)進(jìn)行協(xié)同作用。TEMPO是一種實(shí)現(xiàn)醇類選擇氧化的有效催化劑,這可以進(jìn)一步以分子氧為氧化劑實(shí)現(xiàn)醇的選擇氧化。動(dòng)力學(xué)和同位素效應(yīng)(KIE)的結(jié)果表明醇的Ca-H的活化是反應(yīng)的決速步。這表明可見光光催化與TEMPO催化的協(xié)同作用在氧化轉(zhuǎn)化過程中具有很大的潛力。(2)實(shí)現(xiàn)了以空氣中的分子氧為氧化劑,茜素紅染料為敏化劑在二氧化鈦表面有效地收集可見光以誘導(dǎo)直接的光催化醇的選擇氧化反應(yīng)。二氧化鈦為茜素紅的光催化反應(yīng)提供了平臺(tái),在電子轉(zhuǎn)移和氧活化中起著氧化還原活性的作用。在這個(gè)可見光光催化體系中,活性醇如苯甲醇及其衍生物可以轉(zhuǎn)化為相應(yīng)的醛,具有良好的轉(zhuǎn)化率和優(yōu)異的選擇性。其它代表性的醇如烯丙基醇,仲醇和伯醇也有不錯(cuò)的轉(zhuǎn)化率和選擇性。結(jié)果表明選擇合適的染料分子與二氧化鈦結(jié)合可以直接用來實(shí)現(xiàn)挑戰(zhàn)性的有氧氧化反應(yīng)�？傊�,我們利用染料敏化二氧化鈦的可見光光催化體系,在室溫下以純氧或空氣為氧化劑,實(shí)現(xiàn)了多相可見光催化選擇性氧化醇類為醛或酮的體系,只有水作為副產(chǎn)品形成,實(shí)現(xiàn)了高效和高選擇性的產(chǎn)物的形成,是到目前為止最為有效的多相光催化的有機(jī)轉(zhuǎn)化體系。
[Abstract]:The selective oxidation of alcohols to aldehydes or ketones under very mild conditions with molecular oxygen as oxidant is a challenging subject. Ultraviolet photocatalysis of titanium dioxide can activate molecular oxygen at room temperature and then selective oxidation of alcohols, so it has been widely paid attention to by scientific researchers and many achievements have been made. However, the selective oxidation of alcohols by visible light catalysis is still a difficult problem. In this paper, the selective oxidation of alcohols to corresponding aldehydes or ketones was successfully realized by using the strategy of dye sensitized titanium dioxide under visible light, using molecular oxygen or oxygen in air as oxidant. Two advances have been made as follows: (1) the selective oxidation of alcohols can be initiated by using the eosin dye sensitized anatase titania to absorb visible light and to initiate the selective oxidation of alcohols through the redox intermediation of (TEMPO). Under green LED irradiation, the visible photocatalytic process of dyestuff sensitized titanium dioxide can be synergized with the catalytic oxidation cycle of TEMPO. Tempo is an effective catalyst for selective oxidation of alcohols. The selective oxidation of alcohols can be realized by using molecular oxygen as oxidant. The kinetic and isotopic effects of (KIE) indicate that the activation of Ca-H of alcohols is a critical step in the reaction. This indicates that the synergistic effect of visible light catalysis and TEMPO catalysis has great potential in the process of oxidation and conversion. (2) the molecular oxygen in air is used as oxidant. Alizarin red dyes were used as sensitizers to effectively collect visible light on the surface of titanium dioxide to induce direct photocatalytic selective oxidation of alcohols. Titanium dioxide provides a platform for the photocatalytic reaction of alizarin red and plays an active role in electron transfer and oxygen activation. In this visible light catalytic system, active alcohols such as benzyl alcohol and its derivatives can be converted to corresponding aldehydes with good conversion and excellent selectivity. Other typical alcohols such as allyl alcohols, secondary alcohols and primary alcohols also have good conversion and selectivity. The results show that the suitable dye molecules can be directly combined with titanium dioxide to realize the challenging aerobic oxidation reaction. In a word, we have realized the selective oxidation of alcohols to aldehydes or ketones under room temperature with pure oxygen or air as oxidant, using dye sensitized TIO _ 2 as visible light catalysis system. Only water is formed as by-product. The formation of highly efficient and highly selective products is the most effective organic conversion system of multiphase photocatalysis up to now.
【學(xué)位授予單位】：華中師范大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O621.251

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