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Investigation of urotropine thermal decomposition reaction in self-generated atmosphere by means of thermal analysis method
Evgeni A. Gusev*, a, Sergei V. Dalidovicha and Lidiya I. Krasovskayaa
Thermochimica Acta
1985, Volume 93, Pages 21-24
doi:10.1016/0040-6031(85)85006-1
Abstract
Urotropine decomposition in self-generated atmosphere was studied by means of differential thermal analysis. It was found out that under such conditions the urotropine was not sublimated with heat absorption as in case of investigations in the air or in the vacuum. At constant volume the urotropine decomposition enthalpy amounted to ?98±5 . By means of mass-spectrometric, gas-chromatographic and X-ray analysis we identified pyrolysis products, which were hydrogen, nitrogen, ammonia, methan, methyl-amines and amorphous tar-form sediment.
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Microwave-assisted extraction of phenolic compounds from tea residues under autohydrolytic conditions
Shuntaro Tsubaki, a, , Masahiro Sakamotoa and Jun-ichi Azumaa
Food Chemistry
2010, Volume 123, Issue 4, Pages 1255-1258
doi:10.1016/j.foodchem.2010.05.088
Abstract
Phenolic compounds were extracted from three kinds of tea residues (green, oolong and black tea residues) by microwave-assisted extraction in water under autohydrolytic conditions without using any catalyst or organic solvent. Productions of phenolic compounds were enhanced by microwave heating at 230 °C. The main phenolic constituent in the extract from green tea residue was pyrogallol (24.6%) which was estimated to be originated from degradations of catechins. Derivatives of guaiacyl units of lignin such as dihydroconiferyl alcohol (10.3%) and vanillin (8.1%) were, however, the main constituents in oolong tea residue. In the case of black tea residue, derivatives of both catechins and lignin were comparably extracted. These phenolic compounds are interesting as a bio-based chemical feedstock such as phenolic precursors and antioxidants.
Keywords: Microwave-assisted extraction, Autohydrolysis, Tea residue, Phenolic compound,
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Application of ionic liquids in the microwave-assisted extraction of polyphenolic compounds from medicinal plants
Fu-You Dua, Xiao-Hua Xiaoa, Xue-Jun Luoa and Gong-Ke Li
Talanta
2009, Volume 78, Issue 3, Pages 1177-1184
doi:10.1016/j.talanta.2009.01.040
Abstract
Ionic liquids (ILs) solutions as solvents were successfully applied in the microwave-assisted extraction (MAE) of polyphenolic compounds from medicinal plants. ILs, its concentration and MAE conditions were investigated in order to extract polyphenolic compounds effectively from Psidium guajava Linn. (P. guajava) leaves and Smilax china (S. china) tubers. The results obtained indicated that the anions and cations of ILs had influences on the extraction of polyphenolic compounds as well as the ILs with electron-rich aromatic ?-system enhanced extraction ability. Under the optimized conditions, the extraction yields of the polyphenolic compounds were in the range of 79.5–93.8% with one-step extraction, and meanwhile the recoveries were in the range of 85.2–103% with relative standard deviations (R.S.D.s) lower than 5.6%. Compared to conventional extraction procedures, the results suggested that the proposed method was effective and alternative for the extraction of polyphenolic compounds from medicinal plants. In addition, the extraction mechanisms and the structures of samples before and after extraction were also investigated. ILs solutions as green solvents in the MAE of polyphenolic compounds from medicinal plant samples showed a great promising prospect.
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Ionic liquid-based microwave-assisted extraction of rutin from Chinese medicinal plants
Huan Zenga, Yuzhi Wang, a, , Jinhuan Konga, Chan Niea and Ya Yuana
Talanta
2010, Volume 83, Issue 2, Pages 582-590
doi:10.1016/j.talanta.2010.10.006
Abstract
An ionic liquid-based microwave-assisted extraction (ILMAE) method has been developed for the effective extraction of rutin from Chinese medicinal plants including Saururus chinensis (Lour.) Bail. (S. chinensis) and Flos Sophorae. A series of 1-butyl-3-methylimidazolium ionic liquids with different anions were investigated. The results indicated that the characteristics of anions have remarkable effects on the extraction efficiency of rutin and among the investigated ionic liquids, 1-butyl-3-methylimidazolium bromide ([bmim]Br) aqueous solution was the best. In addition, the ILMAE procedures for the two kinds of medicinal herbs were also optimized by means of a series of single factor experiments and an L9 (34) orthogonal design. Compared with the optimal ionic liquid-based heating extraction (ILHE), marinated extraction (ILME), ultrasonic-assisted extraction (ILUAE), the optimized approach of ILMAE gained higher extraction efficiency which is 4.879 mg/g in S. chinensis with RSD 1.33% and 171.82 mg/g in Flos Sophorae with RSD 1.47% within the shortest extraction time. Reversed phase high performance liquid chromatography (RP-HPLC) with ultraviolet detection was employed for the analysis of rutin in Chinese medicinal plants. Under the optimum conditions, the average recoveries of rutin from S. chinensis and Flos Sophorae were 101.23% and 99.62% with RSD lower than 3%, respectively. The developed approach is linear at concentrations from 42 to 252 mg L?1 of rutin solution, with the regression coefficient (r) at 0.99917. Moreover, the extraction mechanism of ILMAE and the microstructures and chemical structures of the two researched samples before and after extraction were also investigated. With the help of LC–MS, it was future demonstrated that the two researched herbs do contain active ingredient of rutin and ionic liquids would not influence the structure of rutin.
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On the electrosynthesis of sodium borohydride
D.M.F. Santos, a, and C.A.C. Sequeiraa
International Journal of Hydrogen Energy
2010, Volume 35, Issue 18, Pages 9851-9861
doi:10.1016/j.ijhydene.2010.01.129
Abstract
Sodium borohydride (NaBH4) is a versatile reducing agent used in many industrial processes. These include organic and pharmaceutical synthesis, wastewater treatment, and paper pulp bleaching. Additionally, it is a unique material in its ability to carry large amounts of hydrogen in a safe and innocuous form. In order for NaBH4 to serve as a valuable support of the hydrogen economy, it is estimated that its cost must be reduced by at least one order of magnitude from its present price. Therefore, considerable research is required on the development of innovative NaBH4 synthesis processes that have been reported in the open literature. It is anticipated that the most likely route to achieving the low-cost production of NaBH4 lies in the electrochemical methods. A process for synthesising a NaBH4 solution using a two-compartment electrolytic cell with conversion of metaborate to borohydride ions is described. Several cathode materials and electrolytic compositions are tested to select the most appropriate experimental conditions for the NaBH4 electrosynthesis. To avoid erroneous results leading to false conclusions, the electrolysed solutions were in situ monitored by a newly developed potentiometric technique, whose resulting data are explained by thermodynamic and kinetic considerations.
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