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排序方式: 共有1072条查询结果,搜索用时 46 毫秒
1.
Michiel Janssen Prof. Dirk E. De Vos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(45):10724-10734
The practical application of Shilov-type Pt catalysis to the selective hydroxylation of terminal aliphatic C−H bonds remains a formidable challenge, due to difficulties in replacing PtIV with a more economically viable oxidant, particularly O2. We report the potential of employing FeCl2 as a suitable redox mediator to overcome the kinetic hurdles related to the direct use of O2 in the Pt reoxidation. For the selective conversion of butyric acid to γ-hydroxybutyric acid (GHB), a significantly enhanced catalyst activity and stability (turnover numbers (TON)>30) were achieved under 20 bar O2 in comparison to current state-of-the-art systems (TON<10). In this regard, essential reaction parameters affecting the overall activity were identified, along with specific additives to attain catalyst stability at longer reaction times. Notably, deactivation by reduction to Pt0 was prevented by the addition of monodentate pyridine derivatives, such as 2-fluoropyridine, but also by introducing varying partial pressures of N2 in the gaseous atmosphere. Finally, stability tests revealed the involvement of PtII and FeCl2 in catalyzing the non-selective overoxidation of GHB. Accordingly, in situ esterification with boric acid proved to be a suitable strategy to maintain enhanced selectivities at much higher conversions (TON>60). Altogether, a useful catalytic system for the selective hydroxylation of primary aliphatic C−H bonds with O2 is presented. 相似文献
2.
Nagendranath Mahata V. Vishwanathan 《Journal of molecular catalysis. A, Chemical》1997,120(1-3):267-270
Kinetics of vapor phase hydrogenation of phenol to cyclohexanone over Pd/MgO system has been studied in a flow microreactor under normal atmospheric pressure. The reaction rate is found to be negative order with respect to the partial pressure of phenol and has increased from −0.5 to 0.5 with increasing temperature (473 to 563 K). The apparent activation energy (Ea) of the process is found to be close to 65 kJ per mol. On the basis of kinetic results a surface mechanism is proposed. 相似文献
3.
Two new compounds have been isolated from the whole plant of Monochoria vaginalis and characterized as: (10Z)‐1‐(2,6‐dihydroxyphenyl)octadec‐10‐en‐1‐one ( 1 ) (20R, 24R)‐campest‐5‐ene‐3β, 4β‐diol ( 2 ) together with nine known ones. The structures of these compounds were elucidated on the basis of spectral data and chemical evidence. 相似文献
4.
以合成土样为对象,研究了超声波辅助提取苯酚的条件及其提取效率。用中档超声波场辐射试样2×30s,30ml丙酮-正己烷(体积比1:1)分两次萃取10.0g合成土样中的苯酚,这时所获收率最高。在选定条件下用于实际土样分析,以索氏萃取4h的结果为对照基准,本方法的平均回收率为97.8%,RSD为1.5%。 相似文献
5.
芳环羟基化HPLC分离荧光法检测Cu(Ⅱ)-H2O2体系中产生的·OH 总被引:4,自引:3,他引:1
采用L-苯丙氨酸为探针,使用液相色谱分离荧光检测(FLD)和荧光分光光度分析(FS)两种方法平行检测Cu(Ⅱ)-H2O2 体系中产生的·OH.试验采用的激发波长277 nm,发射波长306 nm.体系在反应前后的荧光变化,可反映·OH产生量.对FLD与FS所得数据进行了比较分析,结果显示两种方法具有较高一致性.FS使用混合体系检测,易对荧光的产生造成干扰,而FLD法没有干扰. 相似文献
6.
Highly Effective Phenol Hydroxylation over Ti-ZSM-5 Catalyst Prepared Using B-ZSM-5 as Precursor 以B-ZSM-5为母体合成Ti-ZSM-5高效苯酚羟基化催化剂 总被引:3,自引:0,他引:3
以改进方法合成的B-ZSM-5为母体,采用气固相同晶取代法合成了较小晶粒的Ti-ZSM-5分子筛. 考察了样品的物化性能和催化苯酚羟基化性能. 结果表明: 所合成的小晶粒Ti-ZSM-5具有较高的结晶度,尺寸为100~200 nm,且不含锐钛矿型TiO2,对苯酚羟基化反应的催化性能优异. 相似文献
7.
8.
铬(Ⅲ)邻菲咯啉,8—羟基喹啉配合物/Y型分子筛的制备及苯酚催化羟化 总被引:2,自引:0,他引:2
制备了铬(Ⅲ)邻菲咯啉,8-羟基喹啉配合物/Y型分子筛,利用元素分析,SEM,UV-VisBET及XRD等方法确定了分子筛选笼中金属配合物的生在及其晶体结构,考察了实验参数对苯酚转化率及产物选择性的影响。 相似文献
9.
The [4+2] cyclodimerization of cyclohexa-2,4-dienone derivatives of the orthoquinone monoketal and orthoquinol types has been the topic of numerous investigations over the last 50 years in the aim of rationalizing the extraordinary level of regio-, site-, and stereoselectivities observed in these processes. In particular, the double diastereo-π-facial differentiation expressed in cyclodimerizations of chiral orthoquinols (i.e., 6-alkyl-6-hydroxycyclohexa-2,4-dienones) is an important aspect of these transformations, for they relate to the construction of several natural products. The experimental and theoretical results that are described in this article offer a comprehensive understanding of the factors controlling these site-specific regio- and diastereoselectivities. Our interpretation of these results relies on a combination of Woodward-Hoffmann and Salem-Houk secondary orbital interactions and Cieplak-type hyperconjugative effects in bispericyclic C2-symmetric transition states. 相似文献
10.
Halina Y. Neujahr 《Applied biochemistry and biotechnology》1982,7(1-2):107-111
The enzyme phenol 2-hydroxylase was immobilized on Sepharose and used in conjunction with an O2 electrode for quantitating phenol. Similarly, catechol 1,2-oxygenase was used for quantitating catechol. A third probe was
prepared by immobilization ofTrichosporon cutaneum cells rather than purified phenol 2-hydroxylase for phenol quantitation. The whole cell system gave results comparable to
the immobilized enzyme system. 相似文献