Improved One-pot Synthesis of 4,6-Dihydroxyisophthalic Acid and 2,3-Dihydroxyterephthalic Acid

An improved method for the large-scale preparation of 4,6-dihydroxyisophthalic acid and 2,3-dihydroxyterephthalic acid has been developed.Compared to the previous procedures,this new process-requires much lower CO2 pressure of 0.3 Mpa and shorter reaction time.thus providing a convenient access for large-scale synthesis.The yield is high （93% and 65%,respectively）, and the oxidation of phenol is nearly inhibited,neither decolorization nor further chromatographic purification is required.     

An Efficient Procedure for Esterification of Aryloxyacetic Acid and Arylthioacetic Acid Catalyzed by Silica Sulfuric Acid

Aryloxyacetate and arylthioacetate are wildly used in herbicides, plant regulator and insecticides. Recently, Wille et al. have reported that methyl aryloxyacetate is an efficient agent to prevent and treat allergic contact dermatitis.[1] The most popular synthesis is by heating sodium phenoxide (mercaptide) with ethyl chloroacetate in DMF,[2] or by the esterification of acid with alcohol using concentrated H2SO4 as catalyst.[3] In this paper, synthesis of aryloxyacetate and aryl thioacetate from aryloxyacetic acid and arylthioacetic acid respectively in ether catalyzed by silica sulfuric acid in 83%～94% yields is described. The catalyst is reused for 3 times without significant loss of activity (Entry 4). Compared with common procedures, the present procedure possesses the advantages of the operational simplicity, short reaction time,less-corrosion, high yield and reusable catalyst.     

Preparation and Characterization of Molybdotungstoniobogermanic Acid

Recently,thepreparationandpropertiesofheteropolycomplexeshaveincreasinglyattractedattentioninvariousfieldsofchendstIy,especiallyincatalysicapplicationsfortheiruniqueproperties'.Sincel988,thestudiesoffour-baseheteropolycomplexeswiththeKegginstructurehavebeenreported.Asthespecialbifunctionalcatalyticand.-lantisepsispropertyoftheheteropolycomplexescontainingniobium',andsofarthemolybdotungstoniobogermanicheteropolycomplexesinwhichthecentralatomisgermanium,havenotbeenreportedyet,ennea-tungsto-bi-mo…     

Esterification of Glycerol by Oleic Acid and Selective Hydrogenation of Oleic Acid Methylester Over Acid and Ru-Sn-B Supported Mesoporous AlMCM-41

Demand for large pore size molecular sieves has given rise to great interests in a new family of silica-based mesoporous materials designated as M41s, which expand typical molecular sieves into an extra-large pore range and generate the potential for the applications of these materials in catalysis and sorption for very bulky molecules1-6. MCM-41 possesses a hexagonal arrangement of uniform mesopore ranging from 15 to 100 ? and can be prepared with varied Si/Al ratios. The investigations of …     

Synthesis and α-Glucosidase Inhibitory Activity of Ursolic Acid,Lupeol, and Betulinic Acid Derivatives

Chemistry of Natural Compounds - Seven synthetic derivatives of ursolic acid, lupeol, and betulinic acid (1a–1b, 2a–2b, and 3a–3c) were synthesized to study their...     

Crystal Structures of β-Cyclodextrin Complexes with Formic Acid and Acetic Acid

β-Cyclodextrin (β–CD)-formic acid (1) andβ-CD–acetic acid (2) inclusion complexes crystallizeas β-CD...0.3HCOOH...7.7H₂O andβ-CD...0.4CH₃COOH...7.7H₂O in themonoclinic space group P2₁ with comparable unit cell constants.Anisotropic refinement of atomic parameters against X-ray diffractiondata with F_o ² > 2σ (F_o ²) (986/8563 and 991/8358)converged at R-factors of 0.051 and 0.054 for 1 and 2,respectively. In both complexes, the β-CD molecularconformation, hydration pattern and crystal packing are similar,but the inclusion geometries of the guest molecules are different.The β-CD macrocycles adopt a ``round'' conformationstabilized by intramolecular, interglucose O3(n)...O2(n + 1)hydrogen bonds and their O6–H groups are systematically hydratedby water molecules. In the asymmetric unit, each complex contains oneβ-CD, 0.3 formic acid (or 0.4 acetic acid), and 7.7 water moleculesthat are distributed over 9 positions. Water sites located in theβ-CD cavity hydrogen bond to the guest molecule. In thecrystal lattice, β-CD molecules are packed in a typical ``herringbone'' fashion. In 1, the formic acid (occupancy 0.3) is entirely included in the β-CD cavity such that its C atom is shifted from the O4-plane center to the β-CD O6-side by 2.90 Å and C=O, C–-O bonds point to this side. In 2, the acetic acid (occupancy 0.4) is completely embedded in the β-CD cavity, in which the carboxylic C atom is displaced from the O4-plane centerto the β-CD O6-side by 0.87 Å; the C=O bond directsto the β-CD O6-side and makes an angle of 15°to the β-CD molecular axis. Furthermore, bothdimethyl-β-CD-acetic acid and β-CD-acetic acidcomplexes form a cage structure, showing that the small guestsenclosed entirely in the cavity either in β-CD or indimethyl-β-CD do not affect the packing of the host macrocycles.     

Purification and Structure Identification of Hyaluronic Acid

Polysaccharide produced by mutated strain of Streptococcus zooepidemicus was purified by the procedures including Savage method, quaternary ammonium compound precipitation, DEAE-cellulose(DE52) chromatography and Sephadex G-75 gel filtration. The structure of the purified polysaccharide has been characterized by means of chemical composition analysis,13C NMR spectrum, infrared spectrum and circular dichroism (CD). All the results showed that the purified polysaccharide was hyaluronic acid (HA). The single helix conformation of the purified HA was determined by Congo red experiment. The molecular weight of the HA was about 1.16×106D, which was measured by viscosity method.     

Synthesis of L-Aspartic Acid and Lactone Copolymers

Recently,thesynthesisandapplications0fbiodegradablepolydepsipeptides,alternatingcopolymersofa-aminoacidanda-hydroxyacidwithfunctionalside-chaingroupshavedrawnmoreandmoreattentionl'2.Thisisbecausethefunctionalizedpendantgroups0fthep0lydepsipeptidesmakethemusefulf0rthepreparationofavarietyofpolymer-drugconjugates.However,thepolymerizati0nofdepsipeptideswithfuncti0nalgr0upsisratherdifficultduetotheirbigstructuresandsterichindrance.Furthermore,high-molecular-weightpr0ductsofsuitablephysicalpropert…     

Crystal and Molecular Structure of Cyanuric Acid

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Synthesis and Characterization of the Terpolymer of Itaconic Acid with Acrylamide and 2-Acrylamido-2-methylpropanesulfonic Acid

The thermal stability of the polymer is of great significance in paper, ceramics and oil industry1. Conventional polymers such as polyanionic cellulose can not meet high temperature limitations2-4. Aggour5-6 and Collette7 etc. have conducted extensive research on synthesis and characterizations of the copolymer or terpolymer containing 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS). Till now, very few research works have been reported on the terpolymer of itaconic acid (IA), acrylamid…     

Self-assembled Monolayers of n-Hexadecanoic Acid and α-Hydroxyl n-Hexadecanoic Acid on Titanium Surfaces

Ｄｕｒｉｎｇｔｈｅｌａｓｔｔｗｏｄｅｃａｄｅｓ ,ｐｅｏｐｌｅｈａｖｅｐａｉｄｍｕｃｈｉｎｔｅｒｅｓｔｉｎｔｈｅｃｈｅｍｉｓｔｒｙｏｆｓｅｌｆ ａｓｓｅｍｂｌｅｄｍｏｎｏｌａｙｅｒｓ(ＳＡＭｓ) ,ｗｈｉｃｈｓｈｏｗｓｐｏｗｅｒｆｕｌａｐｐｌｉｃａｔｉｏｎｓｉｎｔｈｅｆｉｅｌｄｓｏｆｂｉｏｓｅｎｓｏｒｓａｎｄｔａｉｌｏｒｅｄｓｕｒｆａｃｅｓ .Ｐａｒｔｉｃｕｌａｒｌｙ ,ｔｗｏｔｙｐｅｓｏｆＳＡＭｓ ,ｉ.ｅ .,ｔｈｉｏｌｓ/ｔｈｉｏｌａｔｅｓｏｎｇｏｌｄａｎｄｓｉｌａｎｅｓｏｎｓｉｌｉｃｅｏｕｓｓｕｒｆａｃｅ…     

γ-Hydroxyacetylenic Acid Derivatives: Generation from Propiolic Acid and Ester Anions and Their Use in Butenolide Synthesis

γ-Hydroxyacetylenic acids and esters have been found to be conveniently prepared in our laboratory by the addition of the propiolic acid dianion¹ or the acetylide of methylpropiolate² to an aldehyde or to a ketone (Scheme I, Table I). These polyfunctional compounds have been shown previously to be useful synthetic intermediates in route to such compounds as 1,3-dienes,² carbohydrates³ and butenolides.^4–7     

Dielectric Relaxation of the β-Cyclodextrin Complexes with Tridecanoic Acid and 1,13-Tridecanedioic Acid

The frequency and temperature dependence of the real (') and imaginary (') parts of the dielectric permittivity of the polycrystalline complex-cyclodextrin-tridecanoic acid in two hydration forms (with 16.2 and 10.7 water molecules) and -cyclodextrin-1,13-tridecanedioic acid with 16.4 and 10.5 water molecules have been investigated, in the frequency range 0.1–100 kHz and temperature range 120–310 K. The dielectric behavior is described well by Debye-type relaxation dispersion. All systems except for the complex of partially dehydrated monocarboxylic acid, exhibit an additional -dispersion, at low frequencies (f < 1000 Hz). Only one-step was found in the ' vs. Tplots of both complexes in the two hydration forms, a fact indicating that the watermolecules cannot be divided into strongly bound and easily movable molecules. The'vs. T plots, at a fixed frequency (200 Hz), show the characteristic peakattributed to a transition between ordered and disordered -CD hydroxyl groupsand water molecules. The transition temperature was 202.7 K for all systems examinedexcept for the complex -CD-tridecanoic acid.16.2 H₂O (214.5 K). This means that the order to disorder transformation process was unaffected by the dehydration process in the case of the dicarboxylic acid complex, whereas in the case of the monocarboxylic acid, it was unexpectedly facilitated. The relaxation time varies with temperature, in a like curve (in the range 8–14 s), with maximum values located at the corresponding order-disorder transition temperatures. The activation energies of the fully hydrated complexes have absolute values of 5 kJ/mol in the range 1.98–3.82 K_{BT transition} which are higher than the corresponding values of :2 kJ/mol of the dehydrated complexes. A thermal hysteresis observed in all complexes is a result of the order-disorder transformation.     

Cross-linking Copolymerization of Acrylic Acid and Multi-armed Cross-linkers

Polymer gels are of considerable interests in material science1-3. Many theoretical and experimental studies have been made on the cross-linking copolymerization4-6 of these systems. Recently, in situ interferometry is applied in studying this process7-9. As shown in Figure 1, the common two-armed cross-linkers will lead to defects in the network, while multi-armed cross-linkers will enhance the integrity of the network. This paper studies the cross-linkers influence on cross-linking and t…     

The Preparation and Characterization of Conjugated Linolenic Acid

Conjugated Linolenic Acid (CLN) has recently been shown to have a more strong cytotoxic effect on various human tumor cell lines than CLA. In CLN, all the three double bonds are conjugated, whereas they are methylene-interrupted in LN. Some seed oil, such as tung oil and pomegranate seed oil,principally consist of CLN, accounting for 76.5% and 75.5%, respectively. CLN can be characterized using the combination of gas chromatography (GC), high - performance liquid chromatography (HPLC…     

Synthesis of (+)- and (−)-Phaselic Acid

The syntheses of both enantiomers of phaselic acid (2-O-caffeoylmalate) are described. The previously unreported acetate-protected caffeic acid anhydride was used with appropriately protected malic acid derivatives as coupling partners to provide fully protected phaselic acid. Sequential unmasking of the protecting groups afforded phaselic acid in an acceptable overall yield.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

N-Phospho-α-Amino Acids and Co-Evolution of Nucleic Acid and Protein

N-phospho-α -amino acids obtainable from aqueous condition were different from their corresponding β -analogues intrinsically. As the self-reproduction unites, N-phospho-α -amino acids were capable to produce non-random oligopeptides. As the phosphoryl donor, they were able to phosphorylate the nucleosides much faster than the deoxynucleosides.     

Coulometric Titration of Thiocyanate,Mercaptoacetic Acid,and β-Mercaptopropionic Acid with Electrogenerated Hypobromite

Abstract

Several sulfur containing ligands have been determined by coulometric titration using biamperometric end point detection. Satisfactory results were obtained for the direct determination of thiocyanate, mercaptoacetic acid and β-mercaptopropionic acid. Silver has been determined by an indirect method involving the determination of excess precipitant.     

Synthesis and Molecular Recognition of Novel Cyclic Pseudopeptides Containing L-Glutamic Acid or L-Aspartic Acid Backbones

Novel cyclic pseudopeptides containing L-glutamic acid or L-aspartic acid backbone structures were efficiently synthesized and characterized. Their chiral recognition properties for L- and D-amino acid methyl ester hydrochloride were discussed also.     

Monitoring Homovanillic Acid and Vanillylmandelic Acid in Human Urine by Capillary Electrophoresis with Electrochemical Detection

A simple,rapid and low-cost method of separation and determination of homovanillic acid and vanillylmandelic acid in human urine was developed based on capillary zone electrophoresis/amperometric detection with high sensitivity and good resolution.