Triphase, solvent-free catalysis over the TS-1/H2O2 system in selective oxidation reactions
Triphase, solvent-free catalysis over the TS-1/H2O2 system in selective oxidation reactions
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DOI：
10.1016/s1387-1811(98)00074-2
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发表时间：
1998-05
影响因子：
5.2
通讯作者：
R. Kumar;A. Bhaumik
中科院分区：
文献类型：
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作者：
R. Kumar;A. Bhaumik
无溶剂、三相条件（固-液-液）用于在TS-1/ h2o2体系上氧化各种有机底物（见-à-vis在共溶剂存在下通常使用双相条件）显示：(i)芳香化合物（如苯、甲苯、苯甲醚和氯化苄）的羟基化反应速率显著提高（3-10倍），同时取代苯产物的区域选择性逆转；（ii） Baeyer-Villiger （BV）氧化/重排环己酮和苯乙酮。在氯化苄的情况下，三相条件导致环羟基化形成对羟基和邻羟基氯化苄（75%）（对邻位比85:15），以及侧链氧官能化，然后去除HCl直接形成苯甲醛（不通过水解生成苯甲醇）。在BV氧化过程中，环己酮和苯乙酮分别生成己内酯和乙酸苯酯为主要产物（选择性70-90%）。另一种反应是环氧化（30-10%）生成羟基环己酮和相应的二酮（环己酮）或羟基苯乙酮（苯乙酮）。添加一定量的无机酸（H2SO4）可显著提高转化率。在双相条件下，这种反应途径在共溶剂的存在下根本不发生。导致活性增强、区域选择性改变和新途径的因素有：(1)硅酸钛的相对疏水性和受限制的孔径；（ii）基材与助溶剂的竞争扩散；（iii） Brönsted在h2o2和水存在下硅酸钛的酸度。因此，本研究开辟了一个新的领域，硅酸钛将在各种有机转化中非常有用，以一种生态安全的方式。
Solvent-free, triphase conditions (solid-liquid-liquid) used in the oxidation of various organic substrates over the TS-1/H2O2system (vis-à-vis conventionally used biphase conditions in the presence of a co-solvent) exhibit: (i) significant enhancement (3–10 times) in the reaction rates in the hydroxylation of aromatics (such as benzene, toluene, anisole and benzyl chloride), along with a reversal in regioselectivity of the products of substituted benzenes; and (ii) Baeyer-Villiger (BV) oxidation/rearrangement of cyclohexanone and acetophenone. In the case of benzyl chloride, triphase conditions resulted in the ring hydroxylation forming p-hydroxy and o-hydroxy benzyl chloride (75%) (para:ortho ratio 85:15) along with side-chain oxyfunctionalization followed by HCl removal directly forming benzaldehyde (no formation of benzyl alcohol through hydrolysis). During BV oxidation, cyclohexanone and acetophenone gave caprolactone and phenyl acetate, respectively, as major products (70–90% selectivity). The other reaction was ring oxidation (30-10%) to hydroxy cyclohexanone and corresponding diketones (cyclohexanone) or hydroxy-acetophenones (acetophenone). Addition of a catalytic amount of mineral acid (H2SO4) significantly increased the conversion. Such reaction routes do not occur at all in the presence of co-solvent under biphase conditions. Factors responsible for enhancement in activity, change in regioselectivity and new routes are: (i) relative hydrophobic nature and restricted pore dimensions of titanium silicates; (ii) competitive diffusion of substrate with co-solvent; and (iii) Brönsted acidity of titanium silicates in the presence of H2O2and water. Thus the present study opens up a new area where titanium silicate will be quite useful in various organic transformations, in an eco-safer way.