Cerimetry in non-aqueous media - Oxidation of oxalic acid through the intermediate formation of ceric oxalate

It was found that ceric oxalate is an intermediate product in the oxidation of oxalic acid by ammonium hexanitrato cerate in solvents such as acetonitrile, and a mixture of acetonitrile and glacial acetic acid. Conditions for the formation of ceric oxalate and its decomposition into carbon dioxide and cerous oxalate have been studied. An analytical method for the estimation of oxalic acid in non-aqueous media has been evolved based on this reaction.

Cerimetry in nonaqueous media - Oxidation of ascorbic acid

The reaction between ascorbic acid and ammonium hexa nitrato cerate was studied potentiometrically in the mixed solvent glacial acetic acid acetonitrile medium. It was found that one mole of ascorbic acid consumes four equivalents of cerate in non-aqueous medium. This reaction can be made use of to estimate potentiometrically ascorbic acid with ammonium nitrato cerate in non-aqueous media, using either glass or antimony as reference electrode and platinum as indicator electrode.

Hybrid Polypeptides: Gabapentin as a Stereochemically Constrained gamma-Amino Acid Residue

The design of folded structures in peptides containing the higher homologues of alpha-amino acid residues requires the restriction of the range of local conformational choices In alpha-amino acids stereochemically constrained residues like alpha,alpha-dialkylated residue, aminoisobutyric acid (Aib), and D-Proline ((D)Pro) have proved extremely useful in the design of helices and hairpins in short peptides Extending this approach, backbone substitution and cyclization are anticipated to bc useful in generating conformationally constrained beta- and gamma-residues This brief review provides a survey of work on hybrid peptide sequences concerning the conformationally constrained gamma-amino acid residue 1-aminomethyl cyclohexane acetic acid, gabapentin (Gpn) This achiral, beta,beta-disubstituted, gamma-residue strongly favors gauche-gauche conformations about the C-alpha-C-beta (0(2)) and C-alpha-C-gamma (0(1)) bonds, facilitating local folding The Gpn residue can adopt both C-7 (NH1 -> CO1) and C-9 (CO1 (I)<- NH1+I) hydrogen bonds which are analogous to the C-5 and C7 (gamma-turn) conformations at alpha-residues In conjunction with adjacent residues, Gpn may be used in ay and gamma alpha segments to generate C-12 hydrogen bonded conformations which may be considered as expanded analogs of conventional beta-turns The structural characterization of C-12 helices, C-12/C-10 helices with mixed hydrogen bond directionalities and beta-hairpins incorporating Gpn residues at the turn segment is illustrated (C) 2010 Wiley Periodicals, Inc Biopolymers (Pept Sci) 94 733-741 2010

Probing acid-amide intermolecular hydrogen bonding by NMR spectroscopy and DFT calculations

Benzene carboxylic acids and Benzamide act as their self-complement in molecular recognition to form inter-molecular hydrogen bonded dimers between amide and carboxylic acid groups, which have been investigated by H-1, C-13 and N-15 NMR spectroscopy. Extensive NMR studies using diffusion ordered spectroscopy (DOSY), variable temperature 1D, 2D NMR, established the formation of heterodimers of benzamide with benzoic acid, salicylic acid and phenyl acetic acid in deuterated chloroform solution. Association constants for the complex formation in the solution state have been determined. The results are ascertained by X-ray diffraction in the solid state. Intermolecular interactions in solution and in solid state were found to be similar. The structural parameters obtained by X-ray diffraction studies are compared with those obtained by DFT calculations. (C) 2012 Elsevier B.V. All rights reserved.

Stabilization of poly(lactic acid) by polycarbodiimide

Polycarbodiimide (CDI) was used to improve the thermal stability of poly(L-lactic acid) (PLA) during processing. The properties of PLA containing various amounts of CDI were characterized by GPC, DSC, rheology, and tensile tests. The results showed that an addition of CDI in an amount of 0.1-0.7 wt% with respect to PLA led to stabilization of PLA at even 210 degrees C for up to 30 min, as evidenced by much smaller changes in molecular weight. melt viscosity, and tensile strength and elongation compared to the blank PLA samples. In order to examine the possible stabilization mechanism, CDI was reacted with water, acetic acid, L-lactic acid, ethanol and low molecular weight PLA. The molecular structures of the reaction products were measured with FTIR.

Synergistic extraction and recovery of Cerium(IV) and Fluorin from sulfuric solutions with Cyanex 923 and di-2-ethylhexyl phosphoric acid

Synergistic extraction and recovery of Cerium(IV) (Ce(IV)) and Fluorin (F) from sulfuric solutions using mixture of Cyanex 923 and di-2-ethylhexyl phosphoric acid (D2EHPA) in n-heptane have been carried out. in order to investigate the synergistic extraction of Cyanex 923 + D2EHPA, extraction Ce(IV), F, Ce(III) and Ce-F mixture solution using D2EHPA or Cyanex 923 as extractant alone were studied firstly, and then Synergistic extraction of Ce(IV), F and Ce(IV)-F mixture solution with D2EHPA + Cyanex 923 were carried out. The largest synergistic coefficient of Ce(IV) is obtained at the mole fraction X-Cyanex (923) = 0.8. The synergistic enhancement coefficients (R-max) obtained for Ce(IV) are 23.12 in Ce(IV) solution, and in Ce-F mixed solution R-max for Ce(IV) and F are 2.24 and 3.25 respectively.

Synergistic extraction of rare earths using acid-base coupling extractants of calix[4]arene carboxyl derivative and primary amine N1923

Synergistic effect in the extraction of rare earth (RE) metals by the acid-base coupling (ABC) extractants of calix[4]arene carboxyl derivative Bu-t[4]CH2COOH (H(4)A) and primary amine N1923 (RNH2) has been investigated. The extraction of RE was enhanced by the addition of sodium cations into the aqueous phase not only in the extraction system of Bu-t[4]CH2COOH alone but also in the mixture of Bu-t[4]CH2COOH and N1923. The separation factors (SFs) indicating the extraction selectivity of adjacent RE elements became higher in the mixture system.

Solvent extraction of rare earths from chloride medium with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 and sec-octylphenoxyacetic acid

The extraction of rare earth elements from chloride medium by mixtures of sec-nonylphenoxy acetic acid (CA100) with bis(2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex301) or bis(2,4,4-trimethylpentyl) monothiophosphinic acid (Cyanex302) in n-heptane has been studied. The synergistic enhancement of the extraction of lanthanum (III) by mixtures of CA100 with Cyanex301 has been investigated using the methods of slope analysis and constant mole. The extracted complex of lanthanum (III) is determined. The logarithm of the equilibrium constant is calculated as - 1.41. The formation constants and the thermodynamic functions, Delta H, Delta G, and Delta S have also been determined.

Bronsted guanidine acid-base ionic liquids: Novel reaction media for the palladium-catalyzed Heck reaction

Bronsted acid-base ionic liquids (GILs) based on guanidine and acetic acid are efficient reaction media for palladium-catalyzed Heck reactions. They offer the advantages of high activity and reusability. GIL2 plays multiple roles in the reaction: it could act as solvent, as a strong base to facilitate beta-hydride elimination, and as a ligand to stabilize activated Pd species.

Catalytic behavior of concentrated heteropolyacid solution in acylation of anisole with acetic anhydride

The catalytic behavior of concentrated heteropolyacid solution in acylation. of anisole with acetic anhydride has been investigated under the reaction conditions such as molar ratio of anisole to acetic anhydride, reaction temperature and mass ratio of reactant to catalyst. When the molar ratio of anisole to acetic anhydride is changed from 2:1 to 1:1, the yield of methoxyacetophenone (MOAP) increases a little, but when it is changed from 1: 1 to 1: 2, the yield has a greater increase from 15% to 30%. The yield of MOAP at the reaction temperature of 363 K doubles that at 333 K. The highest yield is obtained when the mass ratio of reactant to catalyst is 12.8. The conclusion is therefore that the heteropolyacid in acetic acid can effectively catalyze the acylation of anisole with acetic anhydride, and its activity and selectivity are comparable to those of acid clay and molecular sieve.

Immobilization of the heteropoly acid (HPA) H4SiW12O40 (SiW12) on mesoporous molecular sieves (HMS and MCM-41) and their catalytic behavior

Supported catalysts, consisting of SiW12 immobilized on hexagonal mesoporous silica (HMS) and its aluminum-substituted derivative (MCM-41) with different loadings and calcination temperatures, have been prepared and characterized by X-ray diffraction, FT-IR and NH3-temperature programmed desorption. It is shown that SiW12 retains the Keggin structure on the mesoporous molecular sieves and no HPA crystal phase is developed, even at SiW12 loadings as high as 50 wt%. In the esterification of acetic acid by n-butanol, supported catalysts exhibit a higher catalytic activity and stability and held some promise of practical application. In addition, experimental results indicate that the loaded amount of SiW12 and the calcination temperatures have a significant influence on the catalytic activity, and the existence of aluminum has also an effect on the properties of supported catalysts.

Vapor phase esterification catalyzed by immobilized dodecatungstosilicic acid (SiW12) on activated carbon

The vapor phase esterification of acetic acid with ethanol and n-butanol catalyzed by SiW12 supported on activated carbon was studied in a flow fixed-bed reactor in the range of 358 to 433 K. The effects of the reaction temperature, liquid hourly space velocity (LHSV) as well as the molar ratio on the catalytic activity have been investigated. The kinetic studies showed that the rate of esterification was dependent on the partial pressures of the reactants and the addition of argon, an inert diluent in the system when the total pressure was kept at 1 atm. Also the alcohol structure has a profound effect on not only the rate of esterification, but also on the mechanism of esterification changing from a dual site mechanism for ethanol to a single site mechanism for n-butanol.

Simultaneous determination of monoamine and amino acid neurotransmitters in rat endbrain tissues by pre-column derivatization with high-performance liquid chromatographic fluorescence detection and mass spectrometric identification

A sensitive and efficient method for simultaneous determination of glutamic acid (Glu), gamma-amino-butyric acid (GABA), dopamine (DA), 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) in rat endbrains was developed by high-performance liquid chromatography (HPLC) with fluorescence detection and on-line mass spectrometric identification following derivatization with 1,2-benzo-3,4-dihydrocarbazole-9-ethyl chloroformate (BCEOC). Different parameters which influenced derivatization and separation were optimized. The complete separation of five neurotransmitter (NT) derivatives was performed on a reversed-phase Hypersil BDS-C-18 column with a gradient elution. The rapid structure identification of five neurotransmitter derivatives was carried out by on-line mass spectrometry with electrospray ionization (ESI) source in positive ion mode, and the BCEOC-labeled derivatives were characterized by easy-to-interpret mass spectra. Stability of derivatives, repeatability, precision and accuracy were evaluated and the results were excellent for efficient HPLC analysis. The quantitative linear range of five neurotransmitters were 2.441-2 x 10(4) nM, and limits of detection were in the range of 0.398-1.258 nM (S/N = 3:1). The changes of their concentrations in endbrains of three rat groups were also studied using this HPLC fluorescence detection method. The results indicated that exhausting exercise could obviously influence the concentrations of neurotransmitters in rat endbrains. The established method exhibited excellent validity, high sensitivity and convenience, and provided a new technique for simultaneous analysis of monoamine and amino acid neurotransmitters in rat brain. (C) 2008 Elsevier B.V. All rights reserved.

Intramolecular carbenoid insertions : the reactions of [alpha]-diazoketones derived from furanyl, thienyl, benzofuranyl and benzothienyl acetic acids with rhodium (II) acetate /

A number of synthetically useful ring systems can be prepared via the intramolecular insertion of a metal-stabilized carbenoid into a heteroaromatic systems. The chemical outcome of these reactions are dependent not only on the nature of the heteroatom but also on the length of the aliphatic tether linking the carbenoid moiety with the aromatic fragment. Our work with furanyl and thienyl systems containing a single methylene tether have allowed for some rather atypical chemistry. For example, treatment of l-diazo-3-(2-thienyl)-2-propanone (6) with catalytic rhodium (II) acetate yields 5,6- dihydro-4^-cyclopenta[Z>]thiophen-5-one (3) while, the isomeric l-diazo-3-(3-thienyl)-2- propanone(15) gives a spiro-disulphide (20). Novel chemistry was also exhibited in the analogous furanyl systems. While treatment of l-diazo-3-(3-furanyl)-2-propanone (52) with Rh2(OAc)4 resulted in the expected 2-(4-Oxo-2-cyclopentenyliden)acetaldehyde (54), isomeric l-diazo-3-(2- furanyl)-2-propanone (8) undergoes vinylogous Wolff rearrangement to give a mixture of 6a-methyl-2,3,3a,6a-tetrahydrofuro[2,i-^>]furan-2-one (44) and 2-(2-methyl-3-furyl)acetic acid (43). Rhodium acetate catalyzed decomposition of l-diazo-3-(3-benzofuranyl)-2- propanone (84) and l-diazo-3-(2-benzofuranyl)-2-propanone (69)also allows for vinylogous Wolff rearrangement, a chemistry unseen in benzofuranyl systems with longer tethers. A number of interesting products were isolated from the trapping of intermediate ketenes. Decomposition of l-diazo-3-(3-benzothienyl)-2-propanone (100) resulted in the formation of 2,3-dihydro-l//-benzo[^]cyclopenta[^thiophen-2-one (102). However, in addition to (102), a dimer was also generated from the decomposition of l-diazo-3-(2- benzothienyl)-2-propanone (109). The insight into the mechanistic underpinnings of the above reactions are provided by molecular modeling at a PM3 level.

Attempted asymmetric synthesis of Lactobacillic acid / |nFawzy F. Z. Georges. -- 260 St. Catharines, Ont. : [s. n.],

This research work has been planned with the intention of proving the absolute configuration of lactobacillc acid. During the course of this work, attempts have been made to synthesize cis-2-carboxycyclopropane- l-.acetic acid as,v,a suitable resolvable material. As the results were not satisfactory, the synthesis of ci,s-2-carboxycyclopropane-l-propionic acid has been alternatively attempted by ring opening of bicyclo- [4.1.~-heptan-2-onewithout much success. Attempts to resolve or prepare bicyclo[ 4.1.~-hePtan-2-one optically active are also reported. On the other hand, a complete scheme is described for the possible synthesis of optically active lactobacillic acid. If only bicyclo- ~.1.~ -heptan-2-one can be resolved or prepared optically active, this described scheme can be applied smoothly to the synthesis of enant~omeric lactobacillic acid.