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Selective and mild oxidation of suldes to sulfoxides by H2O2 using DBUH-Br3 as catalyst DBUH-Br3 catalyzed selective conversion of suldes to sulfoxides in the presence of H2O2 as oxidizing agent is described. The reaction was performed selectively at room temperature and relatively short reaction times. Sulfoxides are important intermediates in the synthesis of various natural products . Omeprazole and Figpronil pesticides are two typical examples of extensive applications of these important intermediates in pharmaceutical and nechemical industries . Syntheses of sulfoxides are usually achieved by oxidation of their corresponding suldes. During the last years, various procedures for H2O2 oxidation of suldes including the use of various heterogeneous catalyst systems have been reported . The application of this oxidant has been developed due to its effective oxygen content,eco-friendly nature, low cost, and also safety in storage and operation . Recently various heterogenous catalyst-oxidizing agent systems including gold(III)–hydrogen peroxide silica-immobilized vanadyl alkyl phosphonate–sodium bromate, silica sulfuric acid–hydrogen peroxide , and titanium based catalyst-oxidizing agents have been reported for oxidation of suldes. Although, many reagents have been employed for the oxidation of suldes to sulfoxides,the most common problem encountered during the reaction is the over-oxidation of sulfoxides to their corresponding sulfones . Prompted by these reports and due to the potential oxidation of sulfur-containing compounds by H2O2, in the presence of heterogenous catalysts, in this study we wish to report on a new and efcient method for selective oxidation of suldes to sulfoxides by H2O2 as oxidant and in the presence of DBUH-Br3 as catalyst Experimental All chemicals were purchased from Merck and Fluka chemical companies. The oxidation products were characterized by comparison of their spectral and physical data with authentic samples. 1.1. General procedure for the selective oxidation of suldes to sulfoxides To a mixture of various suldes (1 mmol) and DBUH-Br3 (0.1 mmol, 0.039 g) in CH3CN (15 mL), H2O2 30% (v/v)(1.4 mmol) was added gradually. After the completion of the reaction which was monitored by TLC using n-hexane:EtOAc (7:3), the solvent was removed and CH2Cl2 (20 mL) was added and the mixture was washed with water(15 mL), 5% HCl solution (15 mL) and water (15 mL), respectively. The organic phase was then dried over anhydrousNa2SO4 and the solvent was removed under reduced pressure. The resulting products were determined by their 1HNMR spectrums and compared with the authentic samples. The synthesis and X-ray structure of DBUH-Br3 as the catalyst have already been reported elsewhere (Fig. 1)[13].In order to get an insight into the optimum catalytic conditions for the selective oxidation of suldes to sulfoxides,the oxidation reaction of methylphenylsulde by hydrogen peroxide as a model experiment was studied at different temperatures and catalyst/H2O2 ratios. The results are summarized in Table 1. Different solvents were also screened. or the oxidation of methylphenylsulde, and as the result acetonitrile was found to be the best solvent in terms of activity and selectivity. In order to show the catalytic role of DBUH-Br3, the reaction of methylphenylsulde was performed in the absence of DBUH-Br3. The reaction was not completed within 24 h . Consequently, it was performed in different molar ratios of the catalyst in the presence of oxidant in order to obtain the optimum reaction conditions . The chemoselectivity of the system was also investigated. Several suldes containing an unsaturated C–C bond,nitrile or an alcoholic group were subjected to the sulfoxidation reaction, and it was observed that the functional groups remained intact during the reaction . The suggested mechanism of this selective oxidation is shown in Scheme 2. DBUH-Br3 might in situ generate Br2.Subsequently, Br+ can be produced via oxidation with H2O2. The nal step of oxidation involves nucleophilic attack of sulfur of the sulde compound on the Br+ followed by concerted oxygen transfer from water to give the corresponding sulfoxide. In summary, we have described an efcient method for the selective oxidation of suldes to sulfoxides under very mild reaction conditions. Also, chemoselectivity, easy and clean work-up, green oxidant, high yields and the easy preparation of the catalyst were the remarks of this method which could be the priority of the other existing methodologies. |
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8814402
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飲雪(金幣+5, 翻譯EPI+1): 謝謝，就這段吧Sulfoxides are important intermediates in the synthesis of various natural products . Omeprazole and Figpronil pesticides are two typical examples of extensive applications of these important intermediates in pharmaceutical and nechemical industries . Syntheses of sulfoxides are usually achieved by oxidation of their corresponding suldes. During the last years, various procedures for H2O2 oxidation of suldes including the use of various heterogeneous catalyst systems have been reported . The application of this oxidant has been developed due to its effective oxygen content,eco-friendly nature, low cost, and also safety in storage and operation . Recently various heterogenous catalyst-oxidizing agent systems including gold(III)–hydrogen peroxide silica-immobilized vanadyl alkyl phosphonate–sodium bromate, silica sulfuric acid–hydrogen peroxide , and titanium based catalyst-oxidizing agents have been reported for oxidation of suldes. Although, many reagents have been employed for the oxidation of suldes to sulfoxides,the most common problem encountered during the reaction is the over-oxidation of sulfoxides to their corresponding sulfones . Prompted by these reports and due to the potential oxidation of sulfur-containing compounds by H2O2, in the presence of heterogenous catalysts, in this study we wish to report on a new and efcient method for selective oxidation of suldes to sulfoxides by H2O2 as oxidant and in the presence of DBUH-Br3 as catalyst 2011-05-26 21:28:30
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2樓2011-05-25 22:31:50
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飲雪(金幣+10, 翻譯EPI+1): 多謝，有勞您了 2011-05-27 21:16:13
| Sulfoxides are important intermediates in the synthesis of various natural products . 亞砜是各種天然產(chǎn)物合成中重要的媒介。Omeprazole and Figpronil pesticides are two typical examples of extensive applications of these important intermediates in pharmaceutical and nechemical industries . 奧美拉唑和Figpronil 殺蟲(chóng)劑是這類媒介在制藥和化工業(yè)中廣泛應(yīng)用的兩個(gè)典型例子。Syntheses of sulfoxides are usually achieved by oxidation of their corresponding suldes. 亞砜通常由其相應(yīng)的suldes氧化制得。During the last years, various procedures for H2O2 oxidation of suldes including the use of various heterogeneous catalyst systems have been reported .近年間，各種H2O2氧化suldes的操作程序包括各種非均相催化體系的使用已經(jīng)有報(bào)道。 The application of this oxidant has been developed due to its effective oxygen content, eco-friendly nature, low cost, and also safety in storage and operation .由于其有效的氧含量、環(huán)境友好特性、低廉的費(fèi)用以及在儲(chǔ)存和使用中的安全性，這種氧化劑的應(yīng)用得到很好的開(kāi)發(fā)。 Recently various heterogenous catalyst-oxidizing agent systems including gold(III)–hydrogen peroxide silica-immobilized vanadyl alkyl phosphonate–sodium bromate, silica sulfuric acid–hydrogen peroxide , and titanium based catalyst-oxidizing agents have been reported for oxidation of suldes. 近來(lái)，已有在suldes的氧化中使用多種非均相催化劑-氧化劑體系包括金（III）-過(guò)氧化氫二氧化硅-固定化氧釩基磷酸鹽-溴化鈉、硫酸二氧化硅-過(guò)氧化氫和鈦基催化劑-氧化劑的報(bào)道。Although, many reagents have been employed for the oxidation of suldes to sulfoxides, the most common problem encountered during the reaction is the over-oxidation of sulfoxides to their corresponding sulfones . 盡管有許多試劑已經(jīng)被用來(lái)氧化suldes為亞砜，但反應(yīng)中還普遍存在著亞砜被過(guò)度氧化為砜類的難題。Prompted by these reports and due to the potential oxidation of sulfur-containing compounds by H2O2, in the presence of heterogenous catalysts, in this study we wish to report on a new and efcient method for selective oxidation of suldes to sulfoxides by H2O2 as oxidant and in the presence of DBUH-Br3 as catalyst受這些報(bào)道所啟發(fā)，基于在非均相催化劑存在下含硫化合物能被過(guò)氧化氫氧化，在本研究中，我們報(bào)道了一種新的有效的在DBUH-Br3催化劑存在下、以過(guò)氧化氫為氧化劑選擇性氧化suldes為亞砜的方法。 |
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