质谱法研究角型二氢吡喃香豆素双酯化物酰基连接位置

研究了角型二氢吡喃香豆素双酯化物的ＥＩＭＳ，并结合Ｘ－射线单晶衍射分析，证实Ｃ－３′连接的酰氧基较容易和４′－Ｈ脱去羧酸，生成Ｍ－Ｒ１ＣＯＯＨ的碎片离子。而Ｃ－４′连接的酰氧基不能以羧酸的形式脱去，只能脱去酰氧基，生成Ｍ－Ｒ２ＣＯＯ碎片离子，故当两个酰基的质量数不同时，可实际应用ＥＩＭＳ确定酰基的连接位置。

First Asymmetric Synthesis of (-)Methyl 2, 2-dimethyl-3-hydroxychromanyl-6-formate

Aim To synthesize naturally occurring (-) methyl2,2-dimethyl-3-hydroxychromanyl-6-formate. Methods Sharpless' asymmetric dihydroxylation wasemployed to construct the 3-hydroxychroman. Results First asymmetric synthesis of (-) methyl 2,2-dimethyl-3-hydroxychromanyl-6-formate (1) was accomplished starting from methyl 4-hydroxy-benzoate(2), and the absolute configuration was established. Conclusion A useful method for constructingchiral 3-hydroxychroman by employing Sharpless' asymmetric dihydroxylation is achieved.

Solid base catalysts derived from Ca-M-Al(M = Mg, La, Ce, Y) layered double hydroxides for dimethyl carbonate synthesis by transesterification of methanol with propylene carbonate

Composite solid base catalysts derived from Ca‐M‐Al(M=Mg,La,Ce,Y)layered double hydroxides(LDH)were synthesized,characterized and applied to the transesterification of methanol with propylene carbonate.X‐ray diffraction analyses of the catalysts show that all of the catalysts were in the form of composite oxides.Compared with the Ca‐Al LDH catalyst,the specific surface areas and pore volumes of the catalysts were increased with the introduction of Mg,La or Ce.The catalytic performance of these catalysts increases in the order of Ca‐Y‐Al<Ca‐Al<Ca‐Ce‐Al<Ca‐La‐Al<Ca‐Mg‐Al,which is consistent with the total surface basic amounts of these materials and the formation of especially strong basic sites following modification with Mg and La.The Ca‐Mg‐Al catalyst shows the highest(Ca+Mg):Al atomic ratio,indicating that it likely contains more unsaturated O2?ions,providing it with the highest concentration of very strong basic sites.The recyclability of these catalysts is improved following the addition of Mg,La,Ce or Y,with the Ca‐Mg‐Al maintaining a high level of activity after ten recycling trials.X‐ray diffraction analyses of fresh and used Ca‐Mg‐Al demonstrate that this catalyst is exceptionally stable,which could be of value in practical applications related to heterogeneous catalysis.

Spectroscopic Analysis of Structural Transformation in Biodiesel Oxidation

The oxidation behavior of three biodiesels of different origins,viz.rapeseed oil derived biodiesel,soybean oil derived biodiesel and waste oil based biodiesel,were tested on an oxidation tester.The chemical compositions of the biodiesels were characterized by gas chromatography.Thereafter,the structural transformation of fatty acid methyl ester(FAME)of the biodiesels was analyzed by an infrared spectrometer and an ultraviolet absorption spectrometer.The results demonstrated that the oxidation behavior of biodiesels of different origins was closely related to the composition and distribution of FAMEs.Higher concentration of unsaturated FAME with multi-double bonds exhibited poorer oxidation resistance.Furthermore,cis-trans isomerization transformation occurred in the unsaturated FAME molecules and conjugated double-bond produced during the oxidation process of biodiesel.Greater cis-trans variations corresponded to deeper oxidation degree.The higher the content of unsaturated FAME with multi-double bonds in a biodiesel,the more the conjugated double bonds was formed.