Microwave-Assisted Preparation of Trifluoroacetaldehyde (Fluoral): Isolation and Applications

A novel method for the preparation of trifluoroacetaldehyde (fluoral, TFAc, CF₃CHO) from commercially available trifluoroacetaldehyde ethylhemiacetal (TFAE) by microwave irradiation is described. The isolation, characterization and reaction of fluoral with various nucleophiles were studied to verify the diverse applicability of this new method.     

Spectroscopic properties of the photoproducts of pyridoxal-5′-P irradiation: Catalytic site recognition of ribonuclease A

Photoproducts of pyridoxal-5-P, i.e., 4-pyridoxic-5-P and bis-pyridoxal-5-P, have been studied by spectroscopic methods. The spectroscopic properties of bis-pyridoxal-5-P (bis-PLP) resemble those of pyridoxal-5-P (PLP) under similar experimental conditions. The coupling of methylen hydrogens to the phosphorus atom has been shown by NMR spectroscopy. The singlet in the³¹P-NMR spectra and the triplet in¹H-undecoupled experiments confirm the presence of the phosphate group in the 5 position of the structure of the vitamin. The effect of pH and solvent composition on the relative distribution of species of bis-pyridoxine-5-P (bis-PNP) has been investigated by absorption and fluorescence spectroscopy. The acid-base dissociation of the phosphate group is easily detected by emission spectroscopy. Bis-PNP and bis-PLP bind to the enzyme RNase A and they behave as competitive inhibitors with respect to the substrate cytidine-2-3-cyclic phosphate. The natural forms of vitamin B₆, pyridoxine, and pyridoxine-5-P have no effect on the catalytic activity of the protein. Experimental evidence derived from fluorescence and inhibition experiments is consistent with the hypothesis that bis-PNP recognizes the catalytic site of RNase A.     

Synthesis and Diels-Alder reaction of a sapphyrin derivative

Sapphyrins participate in Diels-Alder reactions with pentacene affording novel barrelene-fused sapphyrins. The new compounds were synthesized using traditional heating and microwave irradiation conditions. The experiments carried out under microwave irradiation proved cleaner, affording only the monoadduct and in higher yields.     

Solid-supported Hantzsch—Biginelli reaction for syntheses of pyrimidine derivatives

The microwave-assisted dry media technology was utilized for the synthesis of some novel derivatives in the Hantzsch—Biginelli reaction. In this eco-friendly approach, the usage of organic solvents and hazardous reagents resulting in corrossion of materials was minimized, giving high yields of products within a short reaction time.     

The effect of nanosized titania-silica film composition on the photostability of adsorbed methylene blue dye

The effect of nanosized porous films (average density 10 g/m²) of TiO₂. TiO₂/SiO₂, and SiO₂ on the photostability of adsorbed methylene blue (MB) dye during UV irradiation in air was investigated by optical spectroscopy and laser-induced mass spectrometry. The effectiveness of the photodecomposition of MB decreases in the order TiO₂ > TiO₂/SiO₂ > SiO₂ with rate constants 1E-2, 0.6E-2, and 0.3E-2 min⁻¹ respectively. A mechanism including the participation of both excited states of the dye molecules and photoexcited titanium dioxide is proposed for the photodecolorization of MB adsorbed on the surface of the investigated films. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 220–225, July–August, 2007.     

Green method for ultrasensitive determination of Hg in natural waters by electrothermal-atomic absorption spectrometry following sono-induced cold vapor generation and ‘in-atomizer trapping’

Sono-induced cold vapor generation (SI-CVG) has been used for the first time in combination with a graphite furnace atomizer for determination of Hg in natural waters by electrothermal-atomic absorption spectrometry after in situ trapping onto a noble metal-pretreated platform (Pd, Pt or Rh) inserted into a graphite tube. The system allows ‘in-atomizer trapping’ of Hg without the use of conventional reduction reactions based on sodium borohydride or tin chloride in acid medium for cold vapor generation. The sono-induced reaction is accomplished by applying ultrasound irradiation to the sample solution containing Hg(II) in the presence of an organic compound such as formic acid. As this organic acid is partly degraded upon ultrasound irradiation to yield CO, CO₂, H₂ and H₂O, the amount of lab wastes is minimized and a green methodology is achieved.     

Improvement in the synthesis of metallophthalocyanines using microwave irradiation

A successful application of microwave irradiation, in which phthalocyanines were synthesized under solventless conditions from 1,2-phthalonitrile or phthalic anhydride and urea in the presence of metal templates is described. It was found that in comparison with conventional heating, the microwave process is a very useful alternative for cyclotetramerization processes because of reduction of the reaction time, better yield, and easy-to-perform procedure.     

水溶液中锌粉促进邻二醇合成的研究

邻二醇是有机合成中重要的合成子,是合成烯烃、酮类化合物的重要中间体,广泛用于农药、医药等精细化工品的合成.合成邻二醇最有效的方法是羰基化合物的还原偶联,通常由羰基化合物与相应的金属试剂或金属络合物作用而实现,往往反应时间长,要求的条件苛刻,有的收率比较低.     

毛细管电泳在拮抗药物对氨基苯甲酸、对羟基苯甲酸和磺胺分析测定中的应用

本文报道了一种用毛细管区带电泳法(CZE)分离与测定对氨基苯甲酸、对羟基苯甲酸及磺胺类药物的新方法.电泳条件为:用 20mmol/L硼砂-20mmol/L H_3PO_4-20 mmol/Lβ-环糊精-4％乙醇(pH 7.0)作电泳液,L-抗坏血酸为内标,280nm为检测波长,样品由电进样方式(10kV/10s)引入毛细管(51.2 cm×50μm i.d.,有效分离长度为 38.5 cm).在24.5°C下,6 min内三者可达基线分离(电泳电压 25kV),且在一定范围内可进行定量分析,保留时间(Tr)及A_(样品)/A_(内标)的RSD值分别小于1.0％和5.0％.本法的建立为研究这三者共存于高等动物及微生物体内时的生理作用提供了一种可共选择的新方法.