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81.
Summary A synthesis of the potential pharmaceutical agents 3,4,5-trigalloylquinic acid and 1,3,4,5-tetragalloylquinic acid is described. It involves three steps starting from commercially available quinic acid and provides overall yields of about 15%. The acylation of benzyl or 4-nitrobenzyl quinate with tribenzylgalloyl chloride is the key step. It leads selectively to the triacyl product in the case of benzyl quinate and can be either stopped at the triacyl stage or driven to the tetraacyl derivative in the case of the 4-nitrobenzyl quinate. From the chiroptical properties of the two compounds their stereochemistry was derived by means of the benzoate rule.
Zu Synthese und chiroptischen Eigenschaften der Tri- und Tetragalloylchinasäuren
Zusammenfassung Eine Synthese von 3,4,5-Trigalloylchinasäure und 1,3,4,5-Tetragalloylchinasäure. die potentielle Pharmaka darstellen, wird beschrieben. Sie umfaßt drei Stufen, welche ausgehend von kommerziell erhältlicher Chinasäure Gesamtausbeuten um 15% ergeben. Die entscheidende Stufe dabei ist die Acylierung von Benzyl- oder 4-Nitrobenzylchinat mit Tribenzylgalloylchlorid. Sie führt im Falle des Benzylchinats selektiv zum Triacylprodukt und kann im Fall des 4-Nitrobenzylchinats entweder auf der Stufe des Triacylderivates abgebrochen oder bis zum Tetraacylprodukt durchgezogen werden. Aus den chiroptischen Eigenschaften der beiden Verbindungen wurde ihre Stereochemie abgeleitet.相似文献
82.
2,2-Dimethyl-3-(2-methyl-3-indolyl)cyclopropylacetic acid, its amide and esters, and the corresponding alcohol, viz., the product of ester reduction by LiAlH4, were synthesized. The chemoselectivity of N- and O-alkylation of these compounds was studied. Selective monoalkylation at the nitrogen atom of the heterocycle, O-alkylation to the side chain, or dialkylation at both nucleophilic sites can be carried out under conditions of phase-transfer catalysis. The N-acylation at the indole fragment of nitrile of this acid occurs only under the Vilsmeier—Haak formylation conditions. 相似文献
83.
A straightforward and stereospecific synthesis of (+)-polyoxamic acid is disclosed. The key step of the synthesis involves the regio- and stereospecific bromohydration of an olefin via intramolecular participation by the sulfinyl group. 相似文献
84.
O. Slisenko E. Lebedev P. Pissis A. Spanoudaki E. Kontou O. Grigoryeva 《Journal of Thermal Analysis and Calorimetry》2006,84(1):15-19
The structure-property relationships of thermoplastic
polymer blends based on poly(ether-urethane) ionomer (PEUI) and ion-containing
styrene-acrylic acid copolymer (S-co-AA(K))
have been investigated by using DMTA, DSC and TGA, as well as tensile tests.
Convergence of the glass transition temperature (Tg)
values of the PEUI and the S-co-AA(K) components
in the blends studied, as compared to the individual polymers, was found and
explained by improving compatibility of the components due to increasing effective
density of physical networks formed by ion-dipole and ion-ion interactions
of ionic groups of the components. Character of E'=f(T) and E'=f(T) dependencies confirms the increase of the effective
density of physical networks in the compositions studied compared to individual
PEUI and S-co-AA(K). Improvement of end-use
properties, i.e. thermal stability and tensile properties has been found for
the PEUI/S-co-AA(K) compositions with lower
content of S-co-AA(K) (i.e. <10 mass%)
and explained by formation of additional network of intermolecular ionic bonds
between the functional groups of PEUI and S-co-AA(K). 相似文献
85.
P. V. Katsikopoulos C. D. Papaspyrides 《Journal of polymer science. Part A, Polymer chemistry》1994,32(3):451-456
Loss of diamine and distinct transition phenomena from the solid to the melt state restrain solid-state polymerization (SSP) of nylon salts from industrial application. To depress these phenomena temperatures well below the melting point of the starting material are employed, resulting however in low reaction rates. The need to use catalysts arises and accordingly in this study hexamethylenediammonium adipate (HMA) particles were polymerized containing a strictly controlled amount of uniformly distributed catalyst. The catalysts included boric, sulphuric, and phosphoric acids with boric acid being the most effective in accelerating the reaction while eliminating the tendency to agglomeration. In general, catalyst concentration up to a critical value plays a considerable role in the overall behavior. Furthermore, in agreement with non catalytic processes, the reaction temperature remains an influential parameter. © 1994 John Wiley & Sons, Inc. 相似文献
86.
E. V. Gert 《Cellulose (London, England)》1996,3(1):217-228
For preparation of various modified forms of microcrystalline cellulose, an optional combination is proposed of hydrolytic activity with other properties of nitric acid such as, adduct forming ability (manifested as Knecht compound formation), oxidizing, bleaching and nitrating. The manifestation of a chosen acid function is reached by variation of the reaction conditions: concentration, temperature, time, etc. The sole-reagent continuous procedure involving several operations made in a predetermined sequence allows the use of a more simple technological scheme and saves energy, time and materials. The features of transformation of fibrous and microcrystalline forms of native cellulose into cellulose-II through the Knecht compound are discussed. Purely acidic transformation schemes of native cellulose into microcrystalline cellulose hydrate and amorphous low-nitrate powder cellulose according to the above scheme are considered. Morphological features as well as distinguishing properties — enhanced hydrophilicity, sorption activity and degree of whiteness — of the prepared materials are pointed out. The possibility of obtaining uniformly oxidized forms of powder cellulose according to this scheme and the outlook for the use of nitrogen(IV) oxide as a multifunctional reagent are discussed. 相似文献
87.
Ying-nan Xuan Yan Gao Yong Huang Xi-gao Jian Laboratory of Cellulose Lignocellulosics Chemistry Guangzhou Institute of Chemistry Chinese Academy of Sciences Guangzhou China Institute of Chemistry Chinese Academy of Sciences Beijing China Department of Polymer Science College of Chemical Engineering Dalian University of Technology Dalian China 《高分子科学》2002,(3):225-229
A kind of novel heat-resistant, high performance engineering thermoplastic phthalazinone poly(aryl ether sulfoneketone) (PPESK) containing a carboxyl group in its side chain was prepared by the nucleophilic displacement reaction of 4-(4-hydroxylphenyl)-1(2H)-phthalazinone with di(4-chlorophenyl) sulfone, 4,4'-difluoro-benzophenone and phenolphthalin insulfolane in the presence of K_2CO_3 to produce high molecular weight polymers which can be dissolved in some polarsolvents such as chloroform and nitrobenzene at room temperature and can be easily can into flexible, yellowish andtransparent films. PPESK is an amorphous polymer having a decomposition temperature above 400℃, which indicates that ithas high thermal stability. At the same time, the thermal properties of PPESKs with dicyandiamide (DICY) as curing agentindicated that the heat-resistance properties of the PPESKs are improved after curing. The apparent activation energy (ΔE) ofthe cross-linking reaction and the reaction order (n) of PPESK/DICY were found to be 52.2 kJ/mol and ca. 1.0, respectively.Therefore, the cross-linking reaction is approximately a first order reaction. 相似文献
88.
A sequential injection UV method was developed to determine benzophenone-4 (BZ4) and phenylbenzimidazole sulphonic acid (PBS) simultaneously, these being the most commonly used UV-filters in aqueous formulations used as sunscreen sprays. The selective elution of both was performed by on-line solid-phase extraction, by retention on a SAX microcolumn and separation by varying the pH of elution. The sensitivity obtained was 0.042±0.001 ml μg−1 for PBS and 0.0159±0.0003 ml μg−1 for BZ4. The limit of detection was 1.6 μg ml−1 for PBS and 0.6 μg ml−1 for BZ4. The R.S.D. of the results was 1-6% for PBS and 1-12% for BZ4. The method was validated using commercial sunscreen formulations with concentrations determined by a liquid chromatographic procedure. The two procedures gave comparable results. Automation of the method means the amount of reagents used and residues generated are decreased. The system allows the required analysis sequence to be programmed using suitable software. 相似文献
89.
Isabelle FavierElisabet Duñach 《Tetrahedron》2003,59(10):1823-1830
Mandelic acid and some aryl substituted derivatives were oxidised under molecular oxygen and a catalytic amount of Bi(0). The corresponding aldehydes and/or the carboxylic acids were obtained selectively depending on the nature of the substituent. Aldehydes and α-keto acids were oxidised under the same Bi(0)/O2 system and α-keto acids were proposed as intermediates in the formation of benzoic acid derivatives. 相似文献
90.
Static pressure usually increases the transition temperatures of polymers by decreasing their free volume. If the pressurizing medium is soluble in the polymer matrix, the opposing effect of increasing the free volume is possible. Those shifts of transition temperatures were monitored with a medium-pressure Differential Scanning Calorimetry (DSC) device. The influences of sorbed and surrounding gas molecules are demonstrated by changes occurring in the transition temperature regions. The results show the severe plasticizing effect of CO2 on poly(p-phenylene sulphide) (PPS). The glass transition temperature TG and the temperature of crystallization TC are influenced by sorbed gas molecules. They decrease due to sorbed CO2 molecules. Glass transition is lowered, but is difficult to interpret, as relaxation phenomena which diminish with increasing pressure occur during DSC runs. In crystallites no gas solution is usually possible, so that the melting point of PPS is mainly affected by influences other than plasticization. 相似文献