Synthesis Path Research Articles

Influence of sequence of chemical reactions on kinetics and solid state behavior for bisphenol A diglycidyl ether—bisphenol A—sulfanilamide ternary blends

The kinetics of reaction of ternary blends based on Bisphenol A diglycidyl ether, Bisphenol A and sulfanilamide curing agent was investigated using FTIR, HPLC, SEC following two different synthesis paths. Four the same initial composition prepolymers differing by the cross-link point distribution and the chain length between cross-links have been synthesized and their solid state behavior has been studied. For the formulation DGEBA: SAA: BA = 4.0: 1.25: 1.5 mol (catalyst—0.005 e.e.w. DGEBA), though the schedules have different kinetics, finally the prepolymers with equal conversion of epoxy groups and mass-average molar mass were obtained by both schedules. The dynamic mechanical spectroscopy performed in the glass transition region displays the evolution of the viscoelastic characteristics as a function of cross-link density. For similar formulations networks obtained by schedule 1 have higher values of Tg and ö than networks obtained by schedule 2, perhaps due to a higher real cross-link density.

ChemInform Abstract: Investigation of Paths for the Synthesis of 5,5-Dialkyl-3-perfluoroalkyl-5,6-dihydro-1,2,4-triazolo [3,4-a]isoquinolines.

Substituted 3-trifluoromethyl-5,6-dihydro-1,2,4-triazolo[3,4-a]isoquinolines were obtained by the reaction of substituted 1-methylthio-3,4-dihydroisoquinolines with hydrazine hydrate and trifluoroacetic acid. The corresponding 3-perfluoroalkyl derivatives are formed in the course of dehydration of 2-(3,3-dimethyl-3,4-dihydro-1-isoquinolyl)hydrazides of perfluorocarboxylic acids.

Modeling the Nitrogenase FeMo Cofactor

Density functional calculations are used to describe the nitrogenase FeMo cofactor and its interaction with N2, H2, H2O, and CO. Different models of the active part of the cofactor are investigated, and it is shown that a detailed description of the adsorption of different substrates can be obtained in good agreement with available experimental information. In addition, we propose a reaction path for the catalytic synthesis of ammonia through the gradual hydrogenation of molecular N2 adsorbed on the Fe part of the cofactor.

Energetics of kaolin polymorphs

The enthalpy of formation of kaolin polymorphs at 298 K has been determined by dropsolution calorimetry into molten lead borate at 975 K. Corrections have been made for impurities in the samples. The standard enthalpy of formation from the elements is: kaolinite -4120.2 ± 6.6 kJ/mol, dickite -4107.6 ± 5.7 kJ/mol, nacrite -4104.0 ± 7.6 kJ/ mol, and halloysite -4097.5 ± 5.6 kJ/mol. Using entropy data from the literature, the standard free energy of formation from the elements at 298 K is -3799.4 ± 6.4 kJ/mol for kaolinite, -3785.1 ± 5.6 kJ/mol for dickite, and -3776.8 ± 5.8 kJ/mol for halloysite. The effect of crystallinity (Hinckley index ranging from 1.6 to 0.4) on the enthalpy of formation of kaolinite is smaller than 5 kJ/mol, the experimental error. The relative stability of the polymorphs probably does not change significantly with pressure and temperature over their range of occurrence. Thus the geological occurrence of halloysite, nacrite, and dickite, which are metastable phases, must be interpreted in terms of kinetics or as the result of a specific synthesis path, rather than as resulting from changes in the thermodynamically stable phase assemblage.

New ionic polymers by cellulose functionalization

The unique structure and reactivity of cellulose opens up various possibilities for the design of advanced materials based on this biomacromolecule. In the present feature the state of the art of selected cellulose functionalization reactions is discussed adequately considering own research results. In particular, new synthesis paths to ionic cellulosics, both with controlled functionalization patterns and unconventional combinations of different functional groups (hydrophilic-lipophilic), as well as new synthesis concepts are presented. An important approach to new cellulosics is the reaction via an induced phase separation with solid alkali hydroxide particles. Starting from solutions of cellulose in N,N-dimethylacetamide/LiCl or from organo-soluble cellulose derivatives of different hydrolytic stability dissolved in dimethyl sulfoxide, subsequent etherification and esterification yield cellulose products of unconventional functionalization patterns and properties. Not only reactions directed towards the hydroxyl groups - the primary reactive sites - is given attention but also nucleophilic displacement reactions at the carbon atoms appear as synthesis tool to new polysaccharide materials.

Particle formation paths in the synthesis of silicon nitride powder in a laser-heated aerosol reactor

The Laser-chemical vapour precipitation of Si 3N 4 powder by reacting SiH 4 and NH 3 was studied using a newly developed laminar gas mixing system. Thermophoretic sampling enabled monitoring of the formation process on a milli-second basis and shows the existence of two synthesis paths: the nitridation of Si particles and the sintering of directly formed Si 3N 4. The latter route leads to almost stoichiometric α- and β-Si 3N 4, with particle sizes up to 150 nm. The Si 3N 4 particles do not decompose above the thermodynamic decomposition temperature, probably due to kinetic reasons since the residence time is of the order of milliseconds.

Preparation of modified monomer and studies on EB radiation curing of polyurethane-acrylate in the air

Preparation of the monomer modified by phosphite is described. According to the results of IR, MS and 1H-NMR, the possible synthesis path was deduced. The coating was made up of polyurethane acrylate, modified monomer, active diluent and so on. A non-tacky transparent film can be obtained after EB curing in the air. The experiment indicated that the modified monomer plays a great role in resisting oxygen inhibition. Furthermore, it reduces the radiation dose that the curing needs, and takes effect on radiation sensitization. The optimum radiation condition is 40 KGy. The gel content was used to express the curing extent and the relationship between dose and P-H bond conversion was studied.

Synthesis path versus distribution of functional groups in cellulose ethers

AbstractDifferent ways for carboxymethylation of cellulose are discussed exemplary for cellulose ether synthesis in terms of the resulting structural features. The industrially applied slurry process yields polymers with statistic amounts of the four differently substituted repeating units glucose, mono‐, di‐, and tri‐O‐carboxymethylglucose. Surprisingly, the newly developed totally homogeneous carboxymethylation in the efficient cellulose solvent Ni[tris(2‐aminoethyl)amine](OH)2 gives exactly the same result. Thus, the polymer is evenly accessible during both reaction paths. In contrast the carboxymethylation starting from homogeneous solutions of cellulose in N,N‐dimethyl acetamide /LiCl or solutions of reactive derivatives of cellulose in dimethyl sulfoxide (DMSO) yields polyelectrolytes with a nonstatistic content of the building units. This is achieved via an induced phase separation forming highly reactive microstructures.

First-Principles Study on High-Pressure Synthesis of Hetero-Diamond BC2N.

We propose probable synthesis paths using high pressure condition for well-crystallized energeticallyfavored structures of BC2N heterodiamonds, and further show their expected mechanical and electronic properties, from a viewpoint of material design by first-principles calculations. The results indicate that BN/C2 (111) superlattice is the most stable among atomically-mixed heterodiamond structures, and that compression of a graphitic superlattice at low temperature will be a promising way for the well-crystallized sample. The bulk modulus is found to be comparable to that of diamond. It is also found that the band-edge states of the superlattices dramatically change depending on the stacking orientation of boron and nitrogen.

Methanol synthesis pathway over Cu/ZrO2 catalysts : a time-resolved DRIFT 13C-labelling experiment

To provide additional evidence on the synthesis path of methanol over Cu/ZrO2 catalysts, a three‐step in situ experiment was performed in a DRIFT cell. 13C‐labelled as well as common 12C paraformaldehyde and formic acid were adsorbed and subsequently hydrogenated under reaction conditions (0.5 MPa and 423 K). It was found that methanol was generated exclusively from the 2‐H2CO intermediate, not from adsorbed surface formate. Furthermore, the intermediacy of CO2-3 in the reverse/water–gas shift reaction was shown.

A study of the electrochemical synthesis of ZnO thin films

The principal characteristics of the cathode deposition of zinc oxide from slightly acidified aqueous zinc nitrate solution at 65 °C were studied via potentiodynamic electrolysis, potentiostatic electrolysis, and X-ray diffraction patterns. The results indicate the reliability of a low-temperature electrolytic path of synthesis, and avenues of further exploration. Keywords: zinc oxide, cathode deposition, XRD patterns, FBM theory.

Life-Cycle Assessment of Chemical Production Processes: A Tool for Ecological Optimization

Life-cycle assessment (LCA) has gained in recent years widespread acceptance as an environmental management tool to assess and valuate the environmental impacts (resource consumption and emissions to nature) of products and processes, covering the whole life cycle from cradle (extraction of raw material) to grave (final disposal). Applied to chemical manufacturing, LCA allows to compare the ecological performance of synthesis processes, guide process developers to weak points and improvement options, and avoid suboptimizations. In our Consumer Care Chemicals Division, we apply LCA routinely to sales products as well as manufacturing-process chains, and we developed a specialized LCA computer system ECOSYS for that purpose. Material flow, energy, and waste data for all in-house manufacturing processes are extracted from our company data bases into ECOSYS. For meaningful comparisons of whole life cycles, we must include LCA results for the raw materials bought from other suppliers, and since such data are rarely available, appropriate estimation procedures were developed. The multitude of ecological burdens calculated over the life cycle can be judged and compared by a variety of valuation schemes, e.g. according to the Swiss BUW AL or the modern Eco-indicator 95 method. ECOSYS is not restricted to existing, operational processes, but allows the process developer to test his hypothetical designs (e.g. derived from a simulation tool) at a very early stage. If process alternatives use different raw materials, a narrow judgement on data for the process step alone may lead to suboptimization, whereas LCA results that consider all preceding syntheses of intermediates allow a more objective comparison. As an example, two synthesis paths for DNS (4,4?-dinitro-2,2?-stilbenedisulfonic acid disodium salt) were compared: The older, established route uses NaOCI in aqueous media as an oxidant, whereas the method more recently introduced in one of our production plants is based on air oxidation in liquid ammonia. The latter produces considerably less waste and is favorable with respect to many ecological parameters, including energy consumption, over the whole life cycle.

Social Structuration of the Field of Entrepreneurship: A Case Study

AbstractAs part of the emergence of an epistemology specific to the field of entrepreneurship research, this article aims to reveal the social structuration of knowledge in entrepreneurship, through the empirical study of articles published in the Journal of Business Venturing between its founding in 1986, and 1993. This research, by virtue of its empirical approach based on methods of network analysis widely used in the sociology of science and technology, tends to substitute a social representation of the field of entrepreneurship research for the essentially cognitive and formal representation characteristic of most epistemological reflections in this field. At the end of this study, the field of entrepreneurship research appears as an intricate network, where researchers and institutions are involved in a social and collective game of strategic struggles and alliances. Furthermore, this field of research appears as a largely fragmented space fraught with the traps inherent to disciplinary introversion.RésuméS'inscrivant dans l'émergence d'une épistémologie propre au champ de recherche en entrepreneurship, l'article vise à mettre au jour la structuration sociale des connaissances en entrepreneurship, par l'étude empirique das articles parus dans le Journal of Business Venturing depuis sa fondation en 1986 jusqu'en 1993. Par sa démarche empirique fondée sur les méthodes d'analyse de réseau largement utilisées en sociologie des sciences et des techniques, cette recherche conduit alors à substituer une représentation sociale du champ de recherche en entrepreneurship à la représentation essentiellement cognitive et formelle qui marque la plupart des réflexions d'ordre épistémologique que l'on trouve dans le champ. Au terme de cette recherche, le champ de recherche en entrepreneurship se présente sous la forme d'un enchevêtrement de réseaux oà chercheurs et institutions sont engagés dans un jeu social et collectif de luttes et d'alliances stratégiques. En outre, le champ de recherche se présente comme un espace largement fragmenté au prise avec les pièges inhérents au cloisonnement disciplinaire.

Properties of regioselectively substituted anionic cellulose polyelectrolytes

AbstractIn relation to recent results of regioselective reactions in cellulose chemistry, the synthesis and properties of important cellulose polyelectrolytes, namely of carboxymethyl cellulose and cellulose sulfate are described. Synthesis paths leading to such cellulose polyelectrolytes with an unusual pattern of the distribution of functional groups were developed using protecting group technique, activation effects, as well as phase separation phenomena. The regioselective distribution of functional groups within the anhydroglucose repeating unit at fixed degree of substitution and along the polymer chain is shown to be especially relevant, e.g., to solubility, salt tolerance, and interaction with human blood.

96/03303 - Polyfluorinated dibenzodioxins, dibenzofurans, biphenyls, synthesis, analysis, and potential paths of formation

96/03303 - Polyfluorinated dibenzodioxins, dibenzofurans, biphenyls, synthesis, analysis, and potential paths of formation

Kinetic of a liquid/liquid/solid fine chemicals reactions – modelling of a continuous pilot plant reactor

AbstractIn the field of fine chemicals batch process the implementation of synthesis paths results most often in the determination of the optimal operating conditions on a bench scale apparatus; successive scale‐ups are then handled in an empirical way.For multi‐phase reactions, this approach can be limited due to the coupling between the chemical kinetics and the physical kinetics of the mass transfer. This work proposes a more rational approach for the overall synthesis of Amiodarone, a widely used anti‐arrhythmic drug produced by a liquid/liquid/solid reaction. After analysing the reaction scheme and identifying the limiting steps of the process, a simplified model is proposed to describe the overall process kinetics. The latter is used to model a continuous pilot loop‐reactor packed with static mixers.

Divergent pathways for δ-aminolevulinic acid synthesis in two species of Arthrobacter

Secretion of coproporphyrin III by suspensions of Arthrobacter photogonimos and A. globiformis facilitated analysis of the paths of synthesis of δ-aminolevulinic acid, the precursor of tetrapyrroles. Sensitivity of coproporphyrin accumulation to gabaculine and incorporation of 14C from [1- 14C]glutamate indicated that suspensions of A. photogonimos synthesized δ-aminolevulinic acid from glutamate by the widespread C5 pathway. In contrast, A. globiformis cells switched from predominantly the C5 pathway for δ-aminolevulinic acid synthesis in early exponential phase cultures to δ-aminblevulinic acid synthase in stationary phase cultures.

Divergent pathways for δ-aminolevulinic acid synthesis in two species ofArthrobacter

Secretion of coproporphyrin III by suspensions of Arthrobacter photogonimos and A. globiformis facilitated analysis of the paths of synthesis of δ-aminolevulinic acid, the precursor of tetrapyrroles. Sensitivity of coproporphyrin accumulation to gabaculine and incorporation of 14C from [1-14C]glutamate indicated that suspensions of A. photogonimos synthesized δ-aminolevulinic acid from glutamate by the widespread C5 pathway. In contrast, A. globiformis cells switched from predominantly the C5 pathway for δ-aminolevulinic acid synthesis in early exponential phase cultures to δ-aminblevulinic acid synthase in stationary phase cultures.

Confused? Frustrated? Can't find the right synthesis path?

Confused? Frustrated? Can't find the right synthesis path?

Oscillating prostacyclin and thromboxane generation by human vessels: biological and mathematical evidence for negative feedback control

The presented study investigates the time-dependent release of PGI 2 and TXA 2 by isolated human umbilical veins in vitro using the radio-immunoassay for measurement. After changing the nutritional fluid—Krebs-Henseleit solution at pH 7.4, 37°C, 95% O 2/5% CO 2—the release graph oscillates. These oscillations with time were verified by variance analysis and are very similar for both substances. This indicates one or several negative feedback mechanisms acting on the common path of synthesis from the membrane-bound phospholipids to PGH 2, which are effective in the regulation of eicosanoid biosynthesis in vitro. A mathematical function describing the observed PGI2 and TXA 2 synthesis is communicated.