Active Hydrogen Atoms Research Articles

Electrocatalytic dechlorination of atrazine

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), a photosynthetic inhibitor that is used in large quantities for weed control in corn and sorghum, is dechlorinated in aqueous solution upon electrolysis at a reticulated vitreous carbon cathode in the presence of noble-metal catalysts. Electrocatalytic hydrogenolysis to 2-ethylamino-4-isopropylamino-s-triazine occurs in quantitative yield, and is most efficient with palladium-based catalysts. Current efficiency increases with atrazine and catalyst concentration, and decreasing current density. A previously unobserved phenomenon with Pd catalysts is that current must be passed for a certain time before dechlorination commences. This lag time is explained in terms of the palladium lattice absorbing a finite amount of hydrogen before catalytically active hydrogen atoms appear on the catalyst surface.Key words: electrocatalytic hydrogenoloysis, dechlorination, atrazine, palladium catalysts.

One-Stage Determination of the Number of Hydroxyl Groups in Polyatomic Phenols by Gas Chromatography Using Mixed Reagents 1

The use of mixtures of compounds of similar chemical nature is recommended for derivatization in chromatographic analysis. It is assumed that every initial compound containing Nreaction centers in the molecule yields (N + 1) derivatives as a set of approximately equidistant retention peaks in the index scale with the intensity ratios close to binomial coefficients. A one-stage procedure for obtaining volatile derivatives of polyatomic phenols by the action of mixed perfluoroacylating reagents is proposed as the simplest way to determine the number of hydroxyl groups in their molecules. The possibility to extend this method to other classes of organic compounds with active hydrogen atoms and mixtures of other reagents is considered.

1-(3,3-Dimethyl-3,4-dihydroisoquinoline-1-yl)-1-(quinoline-2-yl)-methane: Structure and Peculiarities of Its Complexation with Metal Salts

1-(3,3-Dimethyl-3,4-dihydroisoquinoline-1-yl)-1-(quinoline-2-yl)methane (I) is studied using X-ray diffraction analysis. Molecule I is shown to have a flattened structure and to exist in the enamine tautomeric form: the active hydrogen atom is at the N(1) atom of the dihydroisoquinoline fragment. Molecule I is stabilized by the N–H...N intramolecular hydrogen bond.

Pathways targeting solvent-free PUR coatings

In the last 10 years, an intense rivalry, driven by increasingly restrictive VOC emission regulations, has developed between water-based, powder-based and high-solids coatings as each of these technologies has attempted to establish itself in the market for low-solvent and solventless systems. Polyurethanes (PUR) are especially important for outdoor applications, thanks to their excellent physical and chemical properties — gloss, hardness, UV stability and chemical resistance. In the past, much effort has been put in to develope high-solids PUR systems. The approach taken was to lower the viscosity of the binder, or that of the polyisocyanate crosslinking agent, by reducing molar mass or narrowing the molar mass distribution by means of chemical modification or some special process. Unfortunately, the result was often only a moderate increase in the solids content, and often a worsening of the curing time compared with conventional high-molecular systems. Another approach, the use of reactive diluents, indeed increases the solids content considerably. But such formulations are also much more expensive because of the higher amount of crosslinker required. In this paper, self-crosslinking isocyanates (SCIs) will be presented as a new way of formulating “super high-solids” systems. SCIs are low-viscosity, bifunctional resins that contain NCO and blocked OH (or NH) groups. Upon activation, the OH and NH groups react with NCO groups to form polyurethanes and polyureas, respectively. The building blocks of SCI systems are diisocyanates (HDI, IPDI, etc.), trifunctional compounds containing active hydrogen atoms (triols, amino alcohols, etc.) and blocking compounds (ketones, aldehydes, etc.). SCIs can be synthesized as urethane- or allophanate-group-based systems. The groups containing active hydrogen are activated by dissociation of the blocking groups due to the action of atmospheric moisture after the coating formulation has been applied. By using SCIs as self-crosslinking reactive diluents, solids contents of standard PUR systems can be increased drastically. In the formulation of moisture-curing one-pack coatings, solid contents of more than 90% are achievable. The properties of the coatings can be tailored to meet requirements through a suitable choice of the SCIs components and, in the case of two-packs, the resin binder or the type of hardener.

Hyperbranched Copolymers Made from A2, B2 and BB′2 Type Monomers, 3. Comparison of Copoly(sulfone-amine)s Containing Piperazine and 4,4′-Trimethylenedipiperidine Units

Hyperbranched copoly(sulfone-amine)s with various lengths of linear segments between two branching units were synthesized by copolymerization of A2 type monomer with B2 and BB′2 type monomers without any catalysts. Herein, A2 is divinyl sulfone (DV); B2 is piperazine (PZ) or 4,4′-trimethylenedipiperidine (TMDP), and BB′2 is 1-(2-aminoethyl)piperazine (AP) or N-methyl-1,3-propanediamine (NPA). Analysis by FTIR and LC-MSD confirmed the polymerization path that has been presented in previous papers of this series. The rapid reaction of secondary-amino groups of BB′2 and B2 with vinyl groups of A2 results in the formation of the intermediate containing one reactive vinyl group and two active hydrogen atoms. Further polymerization of this AB′2 type intermediates gives hyperbranched copoly(sulfone-amine)s. The analysis of DSC showed that the resulting branched copolymers were semi-crystalline when the feed ratio of B2 to BB′2 was equal to or higher than two. Furthermore, double-melting endotherms were observed in the corresponding DSC curves of the sample with TMDP units, while only one melting peak was observed for the sample with PZ units. The degree of branching (DB) of the copolymers obtained increased with decreasing the feed ratio of B2 to BB′2 monomers.

Some New Directions of Development of Polymers and Plastics

Three new possibilities of obtaining resins and plastics are shortly signalised. New liquid anhydrous reactive solvents (RSs) have been obtained from different compounds containing active hydrogen atoms and formaldehyde have been obtained. These RSs dissolve monomers condensating with formaldehyde, especially melamine (Mel) and urea into anhydrous solutions, liquid at temperature of dissolving, containing up to 100% of polymerising substances and up to 70% Mel. At temperature of dissolving these solutions can be fast formed and cured, combining synthesis with processing of polymers in the common process of reactive forming. They can be used for fast bonding of natural fibers. Plastified PVC crosslinks with aliphatic amines under gelling conditions into synthetic poromeric leatherlike materials with hygienic properties of natural leather and 30–40% water vapour sorption and desorption. It was found out that new ecological polyurethanes can be obtained from vegetable oil. urea and formaldehyde

Determination of hair polyamines as N-ethoxycarbonyl- N-pentafluoropropionyl derivatives by gas chromatography–mass spectrometry

An efficient method is described for the simultaneous determination of hair polyamines, such as 1,3-diaminopropane, putrescine, cadaverine, spermidine and spermine, by gas chromatography–mass spectrometry (GC–MS) with the selected ion-monitoring (SIM) mode. The method is based on the extractive two-phase ethoxycarbonyl (EOC) reaction of amino functions in aqueous solutions combined with subsequent pentafluoropropionyl (PFP) derivatization of the remaining active hydrogen atoms for the direct analysis by GC–SIM-MS. The detection limits for SIM of the polyamines as N-EOC- N-PFP derivatives ranged from 1 to 10 ng/g hair, while their recovery rates varied in the range of 76.42–93.38%. This method demonstrated a good overall accuracy (% bias) and precision (% C.V.) as 3.32–11.05% and 5.88–14.71%, respectively. When applied to 0.6 M HCl extracts of hair samples from 11 healthy men and 19 healthy women, all five polyamines were positively detected at the concentrations of 8.82–871.87 ng/g. Both in median and mean concentrations, the most abundant hair polyamine was spermidine, followed by spermine, putrescine, 1,3-diaminopropane and cadaverine in the male group, while the order of 1,3-diaminopropane and cadaverine was reversed in the female group. The levels of polyamines, except for cadaverine, in hair specimens studied were found to be higher in men than in women.

Hydrogen-deuterium exchange reactions of cis- and trans-cyclopropane derivatives with D(2)O and CD(3)OD in the gas phase

Gas-phase hydrogen-deuterium (H/D) exchange reactions involving four isomeric cyclopropane derivatives were investigated under chemical ionization (CI) conditions, using D(2)O and CD(3)OD as reagent gases. There are abundant ions at [M + 1](+), [M + 2](+) and [M + 3](+) in the D(2)O and CD(3)OD positive-ion CI mass spectra of the two isomer pairs 1, 2 and 3, 4. Their CI mass spectra are identical with each pair, and so are the collision-induced dissociation (CID) spectra of ions [M + 1](+), [M + 2](+) and [M + 3](+) of each of the two isomer pairs. The CID spectra of [M + 1](+) ions indicate that they have common D/H exchange reactions within each pair, which take place between molecular ions and deuterium-labeling reagents to form the [M - H + D](+) ions. Those of their [M + 2](+) ions show that they have common D/H exchange reactions within each pair, which form the [M(d1) + H](+) ions. Those of their [M + 3](+) ions show that they have common D/H exchange reactions within each pair, which take place between the [M(d1)] and deuterium-labeling reagents to produce [M(d2) + H](+) for the isomer pair 1, 2 and [M(d1) + D](+) for the isomer pair 3, 4. The number and position, and active order of the active hydrogen atoms of the isomer pairs 1, 2 and 3, 4 were determined. Copyright 2000 John Wiley & Sons, Ltd.

Structural factors determining the inhibitive effect of alkyl(aryl)ammonium salts of functionalized perfluoropolyethers

Thirty homologous series of functionalized perfluoropolyethers (FP) based on alkyl(aryl)ammonium salts were studied, by correlation analysis and statistical data processing, as inhibiting constituents of perfluoropolyether lubricating greases. The basic adsorption and colloid-chemical factors responsible for the inhibitive effect of FPs are the high critical micell concentration, surface activity, hydrophobicity, and formation of chemoadsorption complexes, in which FPs function as electron-donating agents. Contributions from ten basic structural factors of FPs (carboxylate and arylsulfonate anions, electronic structure of an anchor heteroatom, active hydrogen atoms of NH- and OH-acids in aliphatic and aromatic fragments, aliphatic radicals, aromatic fragment in an alkylammonium cation, etc.), influencing their inhibitive effect in low-polarity media, were quantitatively estimated.

水素-アルゴンプラズマアーク溶解による鉄およびコバルトの脱酸，脱窒

Removal of oxygen and nitrogen of pure liquid iron and cobalt has been examined by Ar and (0.5% to 20%)H2+Ar plasma arc melting under atmospheric pressure. While the removal rates of oxygen and nitrogen were very low when the plasma gas was noly Ar, they rose remarkable with addition of a small amount of hydrogen such as 0.5 to 1%H2 and increased with hydrogen content of the plasma gas. The oxygen and nitrogen concentrations finally decreased to the very low levels as follows; O<2 and N<1 mass ppm for iron and O<5 and N<1 mass ppm for cobalt. This excellent refining effect is supposed to be caused by activated hydrogen atoms dissociated in the high temperature plasma arc and to be expressed as the following reactions; O+2H=H2O for deoxidation and N+3H=NH3 for nitrogen removal.The deoxidation of iron proceeded through two steps by the fast 1st step at the beginning of melting and, thereafter, the slow 2nd step. Both steps were of a first order rate low and the deoxidation rate of 1st step was found to increase in proportion to the about 1/2th power of the hydrogen content in the plasma generating gas. So, it is considered that, for the 1st step of deoxidation, the chemical reaction on the surface of the liquid iron is the rate determining step.

Accumulation of Caffeoyl-D-quinic Acids and Catechins in Plums Affected by the Fungus Taphrina pruni

Plums (Prunus domestica) affected by the fungus Taphrina pruni and healthy ones were harvested in intervals of about four days. Photometric comparison of their methanolic extracts proved that infected fruits contained ten times more compounds with phenolic hydroxyl groups. Further structure elucidation and quantification of these phenolic differences by gas chromatography and gas chromatography / mass spectrometry revealed that the content of caffeoyl-ᴅ-quinic acid isomers and (+)-catechin had changed: The amount of chlorogenic acid and its isomers was increased in infected fruits about 15 times compared to nonaffected ones. Contrary, (+)-catechin content was decreased. Additional photometric assays demonstrated that (+)-catechin reduction is accompanied by a corresponding increase of proanthocyanidins in infected fruits. All the compounds identified in infected plums in increased concentrations had a common structural feature: they were o-diphenols. After oxidation to corresponding o-quinones they are able to add to substances with active hydrogen atoms, e.g. fungal enzymes. Consequently, the accumulation of a high concentration of odiphenols may be a defence response directed towards fungal enzymes.

Phase Behavior of Nematic-Nonnematic Binary Systems II - The Effect of Hydrogen Bonding -

Binary mixtures of nematic 4-pentyl-4′-cyanobiphenyl (5CB) with some kinds of non-nematic solutes were found to show the increase in nematic-isotropic transition temperature, contrary to usually observed decrease. All these ‘unusual’ solutes found in this work have active hydrogen atoms which can act as hydrogen bond donor. ‘Unusual’ increase in the clearing temperature was attributed to the hydrogen bonding interaction between 5CB and solutes. The effect of hydrogen bonding interaction between 5CB and various non-nematic solutes on thermal and spectroscopic properties were studied in detail.

5600020 Process for the preparation of alkoxylates using ester compounds as catalyst

According to the invention, the alkoxylation of compounds containing active hydrogen atoms is carried out in the presence of specific alkaline earth metal salts of alkylor alkenylsuccinic monoesters as catalyst. The alkoxylates obtained have a narrow homolog distribution and a good appearance.

Correlation of Kováts Retention Indices on Polar Stationary Phase with That on Non-polar Stationary Phase

A retention equation, , was developed to correlate the Kováts retention indices on polar stationary phases with that on non-polar stationary phases. Some differences of interaction forces of solutes on polar and non-polar stationary phases were taken into account. The dispersive interaction of a solute was treated in two parts, the carbon chain and the functional group(s), which led to a good fit for this correlation. In addition, the hydrogen bonding interaction should be considered in this correlation for compounds with active hydrogen atoms due to the absence of hydrogen bonding interaction on non-polar stationary phases. However, the dipole-induced-dipole interaction might be omitted for its less importance in the retention, unless compounds with great polarity are used. Correlations of some cited retention data for compounds with various functional groups were presented in the present paper, and the results were satisfactory.

Ab Initio Molecular Orbital Study of Reactivity of Active Alkyl Groups. III. Nitrosation of Acyclic Carbonyl Compound with Methyl Nitrite via Na+ Chelated Transition State.

The mechanism of the nitrosation of sodium enolate of acetone [CH3COCH2]-Na+ (1) with methyl nitrite CH3ONO (2) to give 1-hydroxy-imino-2-oxo-propane CH3COCH=NOH (3) was studied by the ab initio molecular orbital (MO) method. The complex [CH3COCH2NO(OCH3)]-Na+ (C-II) was first formed from the adduct (C-I) of 1 and 2 through the pericyclic transition state (TS1). Finally, Z-hydroxyimino compound (3Z) was obtained through demethoxylation of 2 moiety and abstraction of an active hydrogen atom in C-II with a base. In the final formation of 3Z, two leaving groups, the methoxy group and the active hydrogen atom in C-II, should be situated in positions with respect to each other which permit their elimination, i.e., they are antiperiplanar to one another. It has become apparent that 3Z tends to be formed predominantly when a countercation of a base coordinates to the oxygen atom of the enolate of acetone.

Interaction of Hydrogen and Methane with Inp100) and GaAs(100) Surfaces

The interaction of thermally activated hydrogen atoms and methane molecules with Inp100) and GaAs(100) surfaces was studied by X-ray and UV-induced photoelectron spectroscopy (XPS, UPS), high resolution electron energy loss spectroscopy (HREELS), low energy electron diffraction (LEED), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and desorption spectroscopy (DS). In most cases the interaction causes a strong decomposition of the surface due to a preferential loss of the group-V and an enrichment of the group-III elements. Hydrogenation of the clean Inp100) 4×2 surface can be divided into three stages. First, there is a saturation of dangling bonds, where the 4×2 reconstruction is preserved. Then, there is a breaking of the In dimers present at the surface, resulting in a 4×1 LEED structure. Finally, a loss of phosphorus and the build-up of metallic indium droplets follows. Bombardment of Inp100) surfaces with methane ions results in the formation of In–C and P–C species. Hydrogen exposure of GaAs(100) surfaces is more effective, since it changes the surface structures already at the initial stages of interaction. This is corroborated by the HREELS and DS data, which give strong evidence for a preferential loss of arsenic. Desorption spectra were taken during the hydrogen exposure and they show for low hydrogen pressure directly the desorption of AsH3. For high hydrogen pressure (p ≥ 1×10−4 Torr) GaH3 is detected in addition. The intensity ratio of desorbing species (AsH3/GaH3) decreases with increasing hydrogen pressure. After extrapolation a value of one results at a pressure of p = 1×10−3 Torr. Models for the interaction of hydrogen and methane with Inp100) and GaAs(100) are discussed in detail.

Probable optimum hydrogen coverage of chemical vapor deposited diamond (111) surface

The isolated single dangling bonds on the diamond growth surfaces are believed to be the active bond sites for the surface growth of diamond in chemical vapor deposition (CVD) systems. If more than one dangling bonds connect with each other at some areas of the surface, they may reconstruct and form π-chain or dimer bonds because of the higher partial surface energies at such areas. These π-chain or dimer bonds are the templates for graphite growth and can be restrained by the etching action of the active hydrogen atoms in the deposition atmosphere. Assuming that the occurrence probability of each dangling bond at any site of the surface is random, the probability functions of a bond site occupied by an isolated dangling bond or one of the dangling bonds in a dangling bond cluster have been worked out respectively. Then, the typical experimental curve of the CVD diamond growth rate can be reasonably explained. When the probability of a surface bond site occupied by an isolated single dangling bond is maximum, an optimum hydrogen coverage of 0.86 monolayer (ML) of the CVD (111) diamond surface can be achieved and this corresponds to the highest surface growth rate of diamond. This mechanism is proposed by us as a reduced diamond surface growth model.

Interfacial polycondensation. I.

Interfacial polycondensation is a rapid, irreversible polymerization at the interface between water containing one difunctional intermediate and an inert immiscible organic solvent containing a complementary difunctional reactant. It is based on the Schotten-Baumann reaction in which acid chlorides are reacted with compounds containing active hydrogen atoms (—OH, —NH and —SH). A large number of polymers (heat-sensitive and infusible as well as stable and meltable) can be prepared. The method has been applied to the preparation of polyurethanes, polyamides, polyureas, polysulfonamides, and polyphenyl esters. Interfacial polycondensations are run in simple, open laboratory equipment with or without stirring. With suitable agitation granular or powdered polymers with high molecular weight are prepared at room temperature and isolated within a few minutes. The intermediates need not be absolutely pure or in balance nor is a quantitative yield needed in order to obtain high polymer. The major variables in the interfacial polycondensation process are discussed and the laboratory techniques and principles are contrasted with melt polycondensation.

Retention of Optical Purity in H-D Exchange Reactions Catalysed by Cobalt-Aluminium Alloy in Na2CO3-D2O

Co-Al alloy in a sodium carbonate-deuterium oxide solution catalyzes the H-D exchange reaction of optically active benzylic hydrogen atom without racemization.

The bimolecular hydrogen-deuterium exchange behavior of protonated alkyl dipeptides in the gas phase

As part of an ongoing characterization of the intrinsic chemical properties of peptides, thermal hydrogen-deuterium exchange has been studied for a series of fast-atom-bombardment-generated protonated alkyldipeptides and related model compounds in the reaction with D2O, CH3OD, and ND3 in a Fourier transform ion cyclotron resonance mass spectrometer. Despite the very large basicity difference between the dipeptides and the D2O and CH3OD exchange reagents, efficient exchange of all active hydrogen atoms occurs. From the kinetic data it appears that exchange of the amino, amide, and hydroxyl hydrogens proceeds with different efficiencies, which implies that the proton in thermal protonated dipeptides is immobile. The selectivity of the exchange at the different basic sites is governed by the nature of both the dipeptide and the exchange reagent. The results indicate that reversible proton transfer in the reaction complexes, which effectuates the deuterium incorporation, is assisted by formation of multiple hydrogen bonds between the reagents. Exchange is considered to proceed via the intermediacy of different competing intermediate complexes, each of which specifically leads to deuterium incorporation at different basic sites. The relative stabilization of the competing intermediate complexes can be related to the relative efficiencies of deuterium incorporation at different basic sites in the dipeptide. For all protonated dipeptides studied, the exchange in the reaction with ND3 proceeds with unit efficiency, whereas all active hydrogen atoms are exchanged equally efficiently. Evidently specific multiple hydrogen bond formations are far less important in the reversible proton transfers with the relatively basic ammonia, which allows effective randomization of all active hydrogen atoms in the reaction complexes.