Showing papers in "Pure and Applied Chemistry in 1985"

Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984)

Abstract: Mise au point comportant des definitions generales et la terminologie, la methodologie utilisee, les procedes experimentaux, les interpretations des donnees d'adsorption, les determinations de l'aire superficielle, et les donnees sur la mesoporosite et la microporosite

Palladium catalyzed coupling of organotin reagents with organic electrophiles

Abstract: A novel, synthetically useful palladium catalyzed cross-coupling reaction of organotin reagents with a variety of organic electrophiles that generates a new carbon—carbon bond has been discovered recently. Because this mild, versatile reaction is tolerant of a wide variety of organic functionality on either coupling partner, is stereospecific, and gives high yields, it is ideal for use in the synthesis of complicated organic molecules. In the presence of carbon monoxide, instead of a direct coupling reaction, carbon monoxide insertion takes place, stitching the coupling partners together and generating a ketone. The utility of this coupling reaction has been demonstrated by the synthesis of a macrodiolide antibiotic, marine sesquiterpenes, insect pheremones and a number of key synthetic intermediates.

The corona discharge, its properties and specific uses

Abstract: The main properties of corona discharges are reviewed, with emphasis on the features which make them unique for use as non-equilibrium chemical reactors : Their stability and ease of operation over a wide range of gases and pressures, including atmospheric ; their sharply confined ionization regions where hot electrons interact with cold gas, inducing reactions without back reactions ; and their extended low field drift regions which act as gaseous electrolytes, inducing electrochemical reactions on surfaces. Present and future applications are discussed : Synthesis of ozone and ammonia, promotion of flames and combustion, surface treatment, and electrical insulation improvement.

Organoboron compounds in new synthetic reactions

Abstract: A general and convenient method for the stereoand regiospecific synthesis of conjugated alkadienes, alkenynes, arylated alkenes, and other olefinic compounds is described. The reaction of (E)or (Z)-lalkenyldisiamylboranes, or 2-(E)-l-alkenyl-l ,3,2-benzodioxaboroles easily obtainable by hydroboration, with either (E)or (Z)-l-alkenyl halides in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium and bases such as sodium alkoxides gives the corresponding (E,E)-, (_,_)-, or (Z,Z)-conjugated alkadienes stereoand regiospecifically, while retaining the configurations of both the starting alkenylboranes and haloalkenes. The reaction of (E)and (Z)-l-alkenyldisiamylboranes with 1-haloalkynes similarly provides a stereoand regiospecific synthesis of conjugated ()_ and (Z)-alkenynes. A mechanism of this crosscoupling reaction, which involves the transmetallation between a 1-alkenylborane and an alkoxopalladium(II) complex generated through the metathetical displacement of a halogen atom from RPd(II)X with sodium alkoxide, is proposed. The versatility of this method has been demonstrated by the stereospecific synthesis of natural products bearing conjugated alkadiene or alkenyne structures, e.g., trans(C10)-allofarnesene, bombykol and its three geometrical isomers, humulene, and trisporol B.

Catalytic asymmetric synthesis of cyclopropanecarboxylic acids: an application of chiral copper carbenoid reaction

Abstract: Reaction of alkyl diazoacetate with an olefin catalyzed by a chiral copper complex gives an optically active alkyl cyclopropanecarboxylate. This chiral copper carbenoid reaction was successfully applied to the synthesis of industrially valuable cyclopropanecarboxylic acids: (÷)-trans-chrysanthem ic acid, (÷)-cis-permethrinic acid and (+)-2,2-dimethylcyclopropanecarboxylic acid. A series of effective catalysts, chiral Schiff base-copper complexes, was prepared starting with an optically active a-amino acid to achieve more than 90% e.e. of the products. The chirality of the products was correlated with that of the catalyst on the basis of metallacyclobutane intermediates. CHIRAL COPPER CARBENOID REACTION (ref. 1) AND ITS APPLICATION TO CHRYSANTHEMIC ACID SYNTHESIS In 1966, the first example of asymmetric catalysis (ref. 2) by means of a soluble transition metal complex was reported by Prof. Nozaki and his coworkers. They decomposed ethyl diazoacetate in styrene in the presence of chiral copper complex (1) as a catalyst to give the products, transand cis-2-phenyl-cyclopropanecarboxylate (3 and 4), both in an optically active form (Eq 1). This finding demonstrated that the carbene derived from ethyl diazoacetate is not free but is combined with the chiral copper complex to form a carbene-copper complex (ref. 3), which is responsible for the asymmetric induction. Furthermore, the reaction provided a new method for the preparation of optically active cyclopropane derivatives of practical value, although the enantiomeric excess (e.e.) attained at that time was less than 10%. Ph COOEt

The physical chemistry of natural waters

Abstract: Symbols, Physical Constants, and Conversion Factors. Introduction. Basic Thermodynamic Concepts. Basic Kinetic Concepts. Ionic Interactions. Physical Chemical Properties of Natural Waters. Chemical Equilibria in Natural Waters. Estimation of the Thermodynamic Properties of Natural Waters. The Kinetics of Oxidation and Reduction of Metals in Natural Waters. The Oxidation of Hydrogen Sulfide in Natural Waters. Author Index. Subject Index.

Absorption, retention and metabolic transformations of carotenoids in rainbow trout, salmon and chicken

Abstract: Absorption and piginenting efficacy of astaxanthin, canthaxanthin and zeaxanthin were studied in rainbow trout (Salmo crairdneri, R.). Astaxanthin is the best pigmenter, followed by canthaxanthin and astaxanthin dipalmitate. Metabolites present in the skin were isolated, identified and compared with those in the skin of Atlantic salmon (Salmo salar) . The di stribution of zeaxanthin and astaxanthin in the body of the chicken was also studied comparatively. Emphasis was laid on the configurational analysis of the administered carotenoids as well as of their metabolites. absorption and deposition of the single stereoisomers were compared. No epimerization of astaxanthin at C(3)/C(3') was detected in rainbow trout, nor was there one in chicken after zeaxanthin administration. A biological function of astaxanthin, canthaxanthin and zeaxanthin as vitamin A (retinol and 3,4-didehydroretinol) precursors was found in vitamin A depleted rainbow trout.

Thermodynamics of binary liquid organic mixtures

Abstract: Recent studies on the thermodynamic properties of binary organic liquid mixtures are reviewed. Emphasis is placed on structure-property correlations and pseudo-lattice group contribution models. The examples of application cover low-pressure phase diagrams, excess enthalpies and excess heat capacities for several classes of polar or nonpolar systems containing alkanes, cyclohexane, benzene, ethers, alkanones, chloroalkanes, or alkanols.

Resonance Raman spectroscopy of carotenoids and carotenoid-containing systems

Abstract: The application of Raman and resonance Raman spectroscopies to biochemical problems has developed mainly during the past decade. Among naturally occuring chromophores,carotenoidshave proved to be very suitable for studies in resonance Raman spectroscopy. Vibrational spectra can be obtained at very low concentration (until 108M) even if the chromophore is included in a complex biological medium ; thus a very active research area has been developed. After a brief presentation of resonant Raman spectroscopic properties of carotenoids, free and bound to proteins, a re— view, with some examples is given with special emphasis on two distinct advantages of Raman spectroscopy. Time resolution allows short lived spe— cies to be analysed onthe nanosecond and picosecond time scales. Further— more space resolution enables vibrational spectra of carotenoids to be obtained even from single living cells, circumventing the difficult biochemical purification of these pigments.

The inductively coupled R.F. (radio frequency) plasma

Abstract: A review is made of the basic principals and the main design features of the inductively coupled radio frequency (r.f.) plasma. Special attention is given to diagnostic measurements carried out by different investigators in order to determine the charasteristics of the electric and magnetic fields, the temperature, velocity and concentration distributions in the discharge region. Mathematical modelling is discussed giving an overview of the different models proposed and typical results obtained. Applications of the inductively coupled plasma technology in material processing, synthesis of ultra fine powders and spectrochemical elemental analysis are briefly reviewed.

Carotenoids in photosynthesis

Abstract: Carotenoids are usually considered to perform two major functions in photosynthesis. They serve as accessory light harvesting pigments, extending the range of wavelengths over which light can drive photosynthesis, and they act to protect the chlorophyllous pigments from the harmful photodestructive reaction which occurs in the presence of oxygen. Drawing upon recent work with photosynthetic bacteria, evidence is presented as to how the carotenoids are organized within both portions of the photosynthetic unit (the light harvesting antenna and the reaction centre) and how they discharge both their functions. The accessory pigment role is a singlet-singlet energy transfer from the carotenoid to the bacteriochlorophyll, while the protective role is a triplet-triplet energy transfer from the bacteriochlorophyll to the carotenoid.

Thermodynamic functions of transfer of single ions from water to nonaqueous and mixed solvents: Part 3 - Standard potentials of selected electrodes

Abstract: Donnees sur les potentiels standards d'electrode a 298,15 K et sur leurs coefficients thermiques, dans le cas d'electrodes a hydrogene, huit electrodes ion metallique/metal et six electrodes anion, sel d'Ag/Ag, dans 20 solvants. Ils sont calcules a partir de l'energie de Gibbs molaire standard et de l'energie de transfert de l'ion correspondant de l'eau dans ces solvants. Donnees numeriques

The particle in the box model for resonance Raman scattering in polyacetylene

Abstract: The anomalous resonance Raman effect in trans—polyacetylene is described quantitatively by assuming that the conjugations on the polymer chain are statistically interrupted by defects (particle in the box model). The A-term of the Albrechttheory and the Huckel approximation are used to evaluate the Raman cross section and the optical transition energies and transition moments, respectively. The good agreement with experimental results allowed to determine the distribution function for the defects on the chain. In the second part of the paper the particle in the box model is used to interpret Raman spectra taken during the cis—trans—isomeri— zation, during sample degradation by exposure to air, and during the electrochemical doping process. In the latter case evidence for a reversible order—disorder tran— sition is deduced from the experiments.

Mesophase pitch and its carbon fibers

Abstract: Preparation, structure et proprietes des fibres de carbone preparees a partir de brai a l'etat de mesophase

Copper-catalyzed additions of organic polyhalides to olefins: a versatile synthetic tool

Abstract: Mise en evidence de l'utilite des adduits 1:1 fonctionalises pour les syntheses selectives de composes du type pyrones-2, composes aromatiques, acides pyrethroides, pyridines, α-aminoacides halogenes et pyrrolidones-2

Synthesis, structure and properties of liquid crystalline polymers

Abstract: A number of new liquid crystalline polymers have been synthesized and their mesophase behaviour studied. Two different approaches have been chosen to chemically vary the \"classical\" thermotropic side group polymers in order to obtain more insight into the structure—property—relationships of these molecules. (i) The constituents (polymer main chain, spacer and mesogenic units) have been widely varied. Thus, side group polymers with polyester main chains, spacers with oligoethylene oxide or siloxane units, non—mesogenic comonomers (dyes), and disc— like mesogenic units (as side groups as well as within the polymer main chain) have been investigated. (ii) The structural principles of liquid crystalline polymers have been varied by synthesizing side group polymers with paired mesogens (containing two mesogenic units per monomer unit) and of combined main chain and side group polymers (containing mesogenic units as side groups and within the polymer main chain).

Rheology of liquid crystalline polymers

Abstract: Revue des concepts pouvant etre utilises pour interpreter la rheologie complexe des polymeres cristallins liquides

Recent advances in arene transformation reactions via chromium complexes

Abstract: L'addition sequentielle de carbanions reactifs et d'electrophiles carbones a des complexes arene Cr(CO) 3 donne apres decomplexation, des cyclohexadienes trans disubstitues. L'alkylation des complexes anioniques cyclohexadienyles, formes initialement a lieu avec une selectivite elevee

Biodegradation of carotenoids - an important route to aroma compounds

Abstract: In the group of compounds referred to as degraded carotenoids the majority of the members are volatile compounds comprising 13 to 9 carbon atoms. A fair number of these are important aroma constituents occurring in many higher plants, some of which are widely used and of considerable economic importance. The discussion will be focused on the formation of selected representatives encountered in tobacco, since this is the richest single source of these compounds and also since it comprises a large number of degraded diterpenoids of known structure and stereochemistry providing additional information on possible degradative pathways. Although degraded carotenoids constitute a large group of compounds, only the function of a few mainly those which play a vital role in life processes is known. Many, however, possess highly attractive aroma properties and it is primarily selected members of this group and their formation which will be considered here. The degraded carotenoids retaining the largest number of original carbon atoms are the nor-. carotenoids, which have 39, 38 or 37 carbon atoms. However, these are of little interest here, since neither do they appear to be precursors of any of the aroma compounds under consideration, nor do the reactions leading to their formation have any bearing on the generation of the aroma compounds. In contrast, both the formation and the structures of the apo-carotenoids are of importance, since, being present in higher plants and frequently possessing the same end groups as the four carotenoids predominant here, they are potential precursors of the carotenoid-like aroma compounds. Remarkably little, however, is known about their immediate precursors and the reactions by which they are formed. In fact, it is still unclear whether they result from direct cleavage of the bonds indicated in Fig. 1, or by a stepwise mechanism of the Glover-Redfearn type. Moreover, it is still an open question in virtually all cases whether the cleavage is enzyme-assisted or accomplished by singlet oxygen or autooxi dation. More detailed information on enzymatic in-chain cleavages is only available for the conversion of /3carotene to retinal, which is postulated to occur as shown in Fig. 2 (Ref. 1). However, has also been shown that a tea enzyme preparation in the presence of tea flavanols converted C-labelled -. carotene into /%-ionone, and several other, unidentified volatile substances including some derived exclusively from the central part of the polyene chain (Ref. 2). Furthermore, soy bean lipoxygenase is known to effect the conversion of violaxanthin into 3-hydroxy-,3-ionone epoxide (Ref. 3). It seems therefore that there are site-specific as well as non-sitespecific enzymes capable of effecting cleavage of the polyene chain. 693 024

Order and disorder in transition metal carbides and nitrides: experimental and theoretical aspects

Abstract: A general overview of the experimental data concerning long and short—range order of metalloid vacancies in rocksalt structure transition metal carbides and nitrides is given. Hexagonal compounds M2C and M2N are also briefly considered. Emphasis is put on neutron scattering experiments, and mew information is given, in particular on the TiCX system. Some data concerns the vacancy—induced lattice distortions. Recent theoretical calculations of the stability of ordered phases and of pair interaction potem— tials, starting from the band structure of the stoichiometric compounds, are briefly presented.

Optical diagnostics of low pressure plasmas

Abstract: The techniques of optical emission spectroscopy with actinome- try, laser induced fluorescence spectroscopy, laser optogalvanic spectroscopy and absorption spectroscopy are discussed. Examples of the application of these techniques to probing low pressure plasmas of the type used in microe- lectronics materials processing are presented.

Applications of solubility parameters and other cohesion parameters in polymer science and technology

Abstract: Cohesion parameters (solubility parameters) provide o,ne of the simplest methods of correlating and predicting the cohesive and adhesive properties of polymers and solvents from a knowledge of the properties of the individual components alone. It is therefore not surprising that there are severe limitations on their precision. Whether or not any correlation or prediction is 'satisfactory\" depends on the precision that is expected or needed. When one is looking for relatively minor differences in behaviour, such as solubility differences between isomeric liquids or between polymers with different degrees of cross-linking, cohesion parameters may not be appropriate. The most important situation where caution is required in using Hildebrand parameters or Hansen parameters is where the extent of donor-acceptor (Lewis acid-Lewis base) interactions (particularly hydrogen bonding) within a component is very different from that between components. There is a group of parameters of dimension (pressureY which are concerned with the cohesive properties of materials, and the term cohesion parameter is a good general description (ref. 1,2). The original solubility parameter defined by J.H. Hildebrand and R.L. Scott (ref. 3) 1 6 = [(LiII RT)/V]2 is now most appropriately called the Hildebrand parameter, and the widely used subdivision into dispersion (d), polar (p) and hydrogen bonding (h) components by C.M. Hansen (ref. 4) gave rise to Hansen parameters, 6d' The significance of the term \"cohesion\" and the dimension (pressureY are clear when one considers that when mixing of i and j occurs, the change in cohesive energy density or cohesive pressure (c) is given by the exchange energy density or interchange cohesive pressure, A:

Thermodynamic functions of transfer of single ions from water to nonaqueous and mixed solvents: Part 2 - Enthalpies and entropies of transfer to nonaqueous solvents

Abstract: Literature data on the enthalpies and entropies of transfer of ions from water to non-aqueous solvents to the end of 1982 are compiled and evaluated according to stated critena, including the extra-thermodynamic assumption. Data, for which the tetraphenylarsonium tetraphenylborate assumption was not used were assigned low weights in the evaluation. The entropy data were subjected to the additional criterion of yielding with the enthalpy data the previously established Gibbs free energy data. Selected values are suggested on the basis of a weighted averaging procedure. INTRODUCTION The literature has been surveyed to the end of 1982, and a critical evaluation of the data has been made. Similarly to the previous report (ref. 1), which has dealt with the Gibbs free energies of transfer of individual ions from water to non-aqueous solvents, this report too concerns the transfer of single ions. Extrathermodynamic assumptions are necessary for dividing the thermodynamic data for complete electrolytes into ionic contributions. Those cases, where the data have not been treated in this manner by the original authors, and where this division cannot either be carried out by the compiler, have been left out from this survey. Included therefore are only cases where this division has been or can be made. These are classified into the following categories: (i) The division into the ionic contributions has been or can be made according to a reliable extrathermodynamic assumption. These cases have been given full weight in the evaluation. (ii) The division has been made according to a not completely satisfactory extrathermodynamic assumption, but data have been provided for both cations and anions, and data are available for some of these ions, that belong to category (i). In such cases adjustments have been made, the criterion of additivity being adhered to. Such data have been given less than full weight in the evaluation. (iii) The division has been made according unsatisfactory extrathermodynamic assumptions. Such data have been recorded in the compilation but have been given zero weight in the evaluation. Contrary to the case of the Gibbs free energies of transfer, only the \"reference electrolyte\" assumption has been used for the enthalpies of transfer, since nothing that corresponds to the \"Fic/Foc\" assumption is available for the enthalpies. Entropies of transfer of individual ions have been estimated by means of the \"reference electrolyte\" assumption too, but also by means of other ones. These include the use of electrostatic terms (the temperature derivative of the Born expression) and so-called neutralsolute terms in theoretical calculations, and the use of the correspondence principle. The most widely used \"reference electrolyte\" assumption, the PhAsBPh one, is that H(PhAs, W÷S) LH(BPh, W÷S) and similarly AS(PhAs, W÷S) S(BPh, W÷S), for the transfer from water, W, to all solvents 5, at any temperature. This is tantamount to assuming that the PhAsBPh assumption that has been used for the Gibbs free energy of transfer at a given reference temperature (usually 298.15 K) (ref. 1) is valid for all temperatures. It is indeed difficult to see a reason why this assumption should not be valid at other temperatures, provided its validity at one is accepted, on the grounds of the largeness, low charge, and nearly same size of the constituent ions of this reference electrolyte.

Source-based nomenclature for copolymers (Recommendations 1985)

Abstract: Titular Members: G. Allegra (Italy), 1977—1985; R. E. Bareiss (FRG), 1983—1985; N. M. Bikales (USA), 1977—1985, Secretary, 1979—1985; P. Corradini (Italy), 1968—1977; R. B. Fox (USA), Secretary, 1968—1979; A. D. Jenkins (UK), 1975—1985, Chairman, 1977—1985; P. Kratochvfl (Czechoslovakia), 1979—1985; K. L. Loening (USA), Chairman, 1968—1977; I. Mita (Japan), 1979—1985; I. M. Papisov (USSR), 1979—1985; N. A. Plate (USSR), 1971—1983; W. Ring (FRG), 1971—1981; P. Sigwalt (France), 1975—1983; U. W. Suter (Switzerland), 1981—1985; T. Tsuruta (Japan), 1968—1979.

Metal-ligand bond-energies in organometallic compounds

Abstract: The energy contributions of metal-carbon and metal-ligand bonds in a variety of organometallic compounds are examined to seek trends as the metal or the ligand changes. In general, the bond energies D(M-X) for metals from the same group increase as the energy of atomization of the metal increases. Metal—carbon bond dissociation energies fall along the sequence D0(MC) in diatomic carbides > D(M-Cp) in cyclopentadienyls > D(M-arene) > D(M-alkyl) > D(M-CO) in metal carbonyls. For transition metals, the ligand bonding power of phosphine donors (PEt3 > PPh3) is larger than for nitrogen donors (pyridine > MeCN > NH3), and olefine donors have similar bonding power to CO and pyridine. The irregular changes in the dissociation energies, D(M2), of transition dimetals on moving across the Periodic Table are considered in relation to the 'valence-state' adopted by the metal in forming metal-metal bonds.

Asymmetric isomerization of allylic compounds and the mechanism

Abstract: Les complexes de rhodium de type [Rh(diphosphine)L n ]ClO 4 (L n =n/2 molecules de solvant, diene ou diphosphine) sont de bons catalyseurs pour la migration d'hydrogene-1,3 de composes allyliques fonctionnalises comme les allyl-amines, -alcools ou -ethers. Le coordinat le plus favorable est le bis-diphenylphosphino-2,2' binaphtyle-1,1' (binap) et l'allylamine est le substrat le plus convenable

The activation of carbon-hydrogen bonds

Abstract: On decrit des reactions dans lesquelles l'etape d'activation a lieu par addition oxydante d'une liaison C-H sur un centre de metal de transition, suivie de reactions conduisant a un produit fonctionnalise