Suitable Reactions Research Articles

Preparation of Fatty Acid Methyl Esters for Gas-Chromatographic Analysis of Marine Lipids: Insight Studies

Assays for fatty acid composition in biological materials are commonly carried out by gas chromatography, after conversion of the lipid material into the corresponding methyl esters (FAME) via suitable derivatization reactions. Quantitative derivatization depends on the type of catalyst and processing conditions employed, as well as the solubility of said sample in the reaction medium. Most literature pertinent to derivatization has focused on differential comparison between alternative methods; although useful to find out the best method for a particular sample, additional studies on factors that may affect each step of FAME preparation are urged. In this work, the influence of various parameters in each step of derivatization reactions was studied, using both cod liver oil and microalgal biomass as model systems. The accuracies of said methodologies were tested via comparison with the AOCS standard method, whereas their reproducibility was assessed by analysis of variance of (replicated) data. Alkaline catalysts generated lower levels of long-chain unsaturated FAME than acidic ones. Among these, acetyl chloride and BF(3) were statistically equivalent to each other. The standard method, which involves alkaline treatment of samples before acidic methylation with BF(3), provided equivalent results when compared with acidic methylation with BF(3) alone. Polarity of the reaction medium was found to be of the utmost importance in the process: intermediate values of polarity [e.g., obtained by a 1:1 (v/v) mixture of methanol with diethyl ether or toluene] provided amounts of extracted polyunsaturated fatty acids statistically higher than those obtained via the standard method.

A hierarchical approach for fast and accurate equilibrium calculation

In the present paper an improved stoichiometric algorithm based on the successive single reaction equilibrium has been described, avoiding the solution of large systems. The algorithm calculates the equilibrium composition adding automatically suitable new reactions to improve the convergence. The algorithm has been tested for plasma composition calculation for a pure nitrogen and air plasma mixtures. The algorithm proposed always converges and it is significantly faster than other hierarchical algorithms.

Ring‐Opening Polymerization of the Cyclic Ester Amide Derived from Adipic Anhydride and 1‐Amino‐6‐hexanol in Melt and in Solution

AbstractThe ring‐opening polymerization (ROP) of the cyclic ester amide (cEA) 5 (systematic name, 1‐oxa‐8‐aza‐cyclotetradecane‐9,14‐dione) ‐ prepared from adipic anhydride and 1‐amino‐6‐hexanol ‐ in the melt at 165 °C and in solution at 100 °C and 120 °C with Bu2Sn(OMe)2 or Ti(OBu)4 as initiator yields the alternating poly(ester amide) (PEA) 4 (systematic name, poly(5‐(6‐oxyhexylcarbamoyl)‐pentanoate) with regular microstructure. Kinetic studies for different monomer‐to‐initiator ratios, different reaction media, initiators and temperatures reveal that the ROP is a first‐order reaction with respect to the monomer. Under suitable polymerization conditions termination and transfer reactions are suppressed. The elementary chain growth reaction proceeds by a coordination insertion mechanism in analogy to the polymerization of lactones. By using monohydroxy‐ and bishydroxy‐functional telechelic poly(ethylene oxide) and Sn(octoate)2 as the initiating system poly(ethylene oxide)‐block‐poly(ester amide)s and poly(ester amide)‐block‐poly(ethylene oxide)‐block‐poly(ester amide)s are obtained. The poly(ester amide) 4 is a semicrystalline material with a melting point of 140 °C, the block copolymers are phase separated systems showing two melting points characteristic for the respective homopolymers.

Mechanochemical synthesis of nanoparticles

The results of recent investigation of the mechanochemical synthesis of inorganic nanoparticles are reviewed. It was demonstrated that, by selecting suitable chemical reaction paths, stoichiometry of starting materials and milling conditions, mechanochemical processing can be used to synthesise a wide range of nanocrystalline particles dispersed within a soluble salt matrix. Selective removal of the matrix phase by washing the resulting powder with appropriate solvents can yield nanoparticles of the desired phase. This technique has been shown to have advantages over other methods of producing nanoparticles in terms of low cost, small particle sizes, low agglomeration, narrow size distributions and uniformity of crystal structure and morphology.

Novel fluorinated polymer from 18-crown-6 by radical polyaddition

Radical polyaddition of bis(α-trifluoromethyl-β,β-difluorovinyl) terephthalate [CF 2C(CF 3)OCOC 6H 4COOC(CF 3)CF 2] (BFP) with 18-crown-6 to produce fluorinated polymer bearing crown ether moiety in main chain is described. Prior to polyaddition, the model reaction of 2-benzoxypentafluoropropene [CF 2C(CF 3)OCOC 6H 5] (BPFP) with 18-crown-6 was investigated to afford suitable reactions condition for polyaddition. The polyaddition of BFP with 18-crown-6 yielded a soluble polymer bearing M n=5.5×10 4 with unimodal molecular weight distribution after purification by reprecipitation with cold ethanol.

Dislocation and twin interactions with polytwin interfacesin L1 0-ordered FePd

The frequent polytwin (PT) interfaces present in L1 0-phases after appropriate heat treatments strongly influence the properties and behavior of this interesting class of intermetallics. The interactions of dislocation glide and twinning with the PT-interfaces has been studied through crystallographic and geometric analyses for {101}-conjugated PT-L1 0-phases. The most suitable boundary reactions for the shear transfer of hard dislocation glide and microtwinning across {101}-conjugated PT-interfaces in L1 0-phases have been determined. Defect-interface interactions in lightly deformed PT-FePd, which exhibits {101}-conjugated PT-interfaces, have been documented by experimental observations using transmission electron microscopy (TEM). A model for the defect-interface interactions in PT-FePd, based on the most suitable boundary reactions identified through theoretical analyses, has been proposed and is consistent with the experimental TEM observations. This model enables a micro-mechanism based rationalization of the plastic flow behavior typical of polycrystalline PT-FePd. Defect-interface interactions in PT-L1 0-FePd and their role for the deformation behavior have been discussed.

Density Functional Calculations on the Heats of Formation of Certain Aromatic Nitro Compounds

AbstractIn order to select suitable isodesmic reactions, heats of formation at 298 K of seven aromatic nitro compounds were calculated by various density functional theories, together with different basis sets. The calculated heats of formation for nitrobenzene, 1,2‐dinitrobenzene, 1,3‐dinitrobenzene, 1,4‐dinitrobenzene, 1,3,5‐trinitrobenzene, 1,2,3‐trinitrobenzene, and 1,2,4‐trinitrobenzene by various DFT methods were averaged to be 14.84, 23.23, 12.84, 12.89, 14.71, 30.61, and 25.73 kcal/mol, respectively. These values are very close to the experimental or multivariable linear regression results.

ChemInform Abstract: Structure, Biological Activity and Synthesis of Polyamine Analogues and Conjugates

The structure and the biological significance of naturally occurring and synthetic polyamine analogues and conjugates are presented and the available methodologies for their synthesis are described. These methodologies involve either the selective functionalization of the amino functions, using suitable protecting groups or acylating agents, or fragment synthesis protocols. The latter employ suitable amino components and simple reactions, like Michael addition to α,β-unsaturated nitriles, alkylation of amines and sulfonamides, reductive alkylation and acylation followed by reduction of the thus-obtained amides, as key-reactions, or azides as key-intermediates, for the assembly of the polyamine skeleton. Syntheses performed in solution as well as in the solid phase are discussed.

Deeply bound levels in kaonic atoms

Using a microscopic antikaon–nucleus optical potential recently developed by Ramos and Oset [? ] from a chiral model, we calculate strong interaction energy shifts and widths for K − atoms. This purely theoretical potential gives an acceptable description of the measured data ( χ 2/ num.data=3.8 ), though it turns out to be less attractive than what can be inferred from the existing kaon atomic data. We also use a modified potential, obtained by adding to the latter theoretical one a s-wave term which is fitted to known experimental kaonic data ( χ 2/ degree of freedom =1.6 ), to predict deeply bound K − atomic levels, not yet detected. This improved potential predicts, in general, states even narrower than those recently reported by Friedman and Gal [? ]. This reinforces the idea that these deeply atomic states can be detected and resolved by using suitable nuclear reactions. Besides, we also study K − and K ̄ 0 nuclear bound states and compute binding energies and widths, for both species of antikaons, in 12 C, 40 Ca and 208 Pb. Despite of restricting our study only to potentials obtained from best fits to the known kaonic atom data, the dynamics of these nuclear bound states depends dramatically on the particular optical potential used.

Studies on the microstructure of vinyl/N-phenylmaleimide copolymers by NMR and their applications

The micro- and stereostructures and sequence distribution of methyl methacrylate (MMA)/N-phenylmaleimide (PMI) and styrene (St)–PMI copolymers were studied in detail with NMR spectroscopy. The MMA–PMI copolymer was in a random sequence distribution and the St–PMI copolymer was alternating in structure. Some micro- and stereoinformation of the MMA–PMI copolymers could be obtained from 1H-NMR spectra. The average number sequence length obtained from the copolymer triad by 13C-NMR spectra was in agreement with that calculated from the reactivity ratios measured by an elemental analyzer. From the triad fraction of the copolymer measured by 13C-NMR, the copolymer chain of MMA–PMI was proved to be a one-order Markov chain. More suitable propagation reactions were proposed from the deviation of sequence distribution of the St–PMI copolymer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2581–2587, 2000

Development of synthetic methods for 4-substituted indoles and their applications for the syntheses of natural products

In our continuing work on synthesizing 4-substituted indole alkaloids as simple as possible by creating suitable reactions, we developed synthetic methods for 4-substituted indoles having a nitrogen or oxygen functional group at the 4-position starting from indole-3-carbaldehyde and one step conversion method of indole-3-carbaldehydes into indole-3-acetonitriles. Utilizing them, we could establish a practical synthetic route to 1,3,4,5-tetrahydropyrrolo[4,3,2-de]-quinoline in three steps from indole-3-carbaldehyde. On the basis of these results, short step total syntheses of marine indole alkaloids, such as isobatzelline C, batzelline C, makaluvamine A, and damirones A and B, were achieved. Furthermore, a novel preparative method of psilocin was established in only five steps from indole-3-carbaldehyde. The syntheses of psilocin analogs having a formyl group or bromine in the benzene part were also achieved.

β-K4La6I14Os: A New Structure Type for Rare-Earth-Metal Cluster Compounds That Contains Discrete Tetrahedral K4I3+ Units

Suitable reactions of KI, La, LaI3, and Os in niobium tubes at 800−850 °C result in black, air- and moisture-sensitive crystals of the quaternary title phase. Isostructural K4Pr6I14Z also exist for Z = Fe, Ru. The title phase was characterized by single-crystal X-ray diffraction (tetragonal, P4/ncc (No. 130), Z = 4; a = 13.117(3), c = 25.17 (1) Å at 23 °C). The important structural feature is the constitution (K4I)3+(La6I13Os3-) with a new type of 3D anion network of [(La6Os)Ii8Ii-a4/2Ia-i4/2Ia-a2/2] clusters that are connected into puckered layers through Ii-a and Ia-i atom pairs that bridge diagonally in the a−b plane. These cluster layers are further interlinked along c⃗ at trans-vertexes through simple bridging Ia-a. The 14th iodine atom occurs in the unique K4I3+ ions which lie in columns that interpenetrate the La6OsI13 network along c. The present 16-e- clusters, in contrast with the optimal 18-e- octahedral cluster configuration, exhibit an uncommon tetragonal elongation and evidently become closed shell, with only a small temperature-independent (van Vleck-like) paramagnetism, ∼4 × 10-4 emu mol-1.

The Physics and Chemistry of Small Translucent Molecular Clouds. XII. More Complex Species Explainable by Gas‐Phase Processes

We have observed 10 molecular species of complexity (four to seven atoms) in three translucent clouds and in TMC-1 and L183. Of these species HNCO, HOCO+, H2CCO, CCH, and CH3CCH are detected in all five objects, while HCOOH, CH3CHO, CH3CN, CH2NH, and VyCN are detected in fewer objects. These species are chosen because they are expected to mark the transition between simpler species that are formed in the gas phase and complex hydrogenated species [NH2CHO, EtOH, EtCN, (CH3)2O, and CH3OCHO] that are believed to form by grain chemistry. The C/O ratio and the metal abundances are determining factors in the abundances of most of the species. The gas-phase chemistry of HNCO is set out for the first time. HNCO, H2CCO, CCH, and CH3CCH are successfully modeled for a wide range of C/O, metals, and cloud conditions. HOCO+, HCOOH, CH3CN, and VyCN are well modeled under fewer conditions, while CH3CHO and CH2NH are fitted in only a small range of conditions. For most species, the models tend to underestimate the observed abundances. By introducing or modifying a number of gas-phase reactions in the New Standard Model we are able to explain the abundances of most species for specific sets of physical conditions (density, temperature, extinction), abundances (metals, C/O), and time epoch. The parameter sets for the different species are largely non overlapping. However, we have been able to find a single, unique set of parameters including a specific epoch for each of TMC-1, L183, and the translucent clouds that explains eight of the 10 species. The exceptions are CH2NH, which requires higher C/O than other species, and CH3CHO, which is possibly modeled in dark clouds but not in translucent objects. For the eight well-fitted species, C/O=0.4 is favored, and the time epoch is 5(5)±4(5) yr for each type of object. In this exercise we cannot distinguish between high and low metals. Previously studied species (HCN, C3H2, CCS, and HC3N) fit the same set of conditions. It is possible that all 10 species may be explained by gas-phase chemistry, perhaps when suitable neutral-neutral reactions are found for species such as CH3CHO and CH2NH. Until then, grain processes cannot be ruled out for these and other species such as HOCO+ (formed from desorbed CO2) or VyCN (highly saturated). Ortho/para and E/A ratios are found to lie within the thermal limits for all cases except O/P (H2CCO), whose value of 5.9 in TMC-1 exceeds the limit of 3.0, which confirms an earlier result by Ohishi. This result cannot be explained by grain interactions. Nevertheless, in the species of intermediate complexity, we may be encountering the boundary between gas and grain chemistry for partly hydrogen-saturated species. The transition to grain chemistry seems clearly to occur at the next level of complexity, which includes NH2CHO, EtOH, EtCN, (CH3)2O, and CH3OCHO, species we have failed to detect after exhaustive searches in translucent and dark clouds.

Incorporating Organic Name Reactions and Minimizing Qualitative Analysis in an Unknown Identification Experiment

We have developed a new type of unknown identification experiment for the introductory organic chemistry laboratory. The unknown sample the student is provided with is the product of an organic name reaction. The student is only informed of the starting material and conditions used in the compound's synthesis, and must then: (1) deduce the compound's structure, (2) determine the name reaction and corresponding mechanism that yields the compound, and (3) present his/her results to the class. Structure determination is accomplished through the acquisition and interpretation of NMR and IR spectra. Numerous suitable name reactions are suggested.

Structural Novelties in Anionic Cluster Halide Phases. Discrete Tetrahedral A(4)Br(+) Ions in Two New Zirconium Bromide Structures (A = Na-Cs).

Suitable reactions of ABr, Zr, ZrBr(4), and an interstitial Z element in Ta containers at 850 degrees C afford two series of quaternary cluster phases containing A(4)Br(3+) ions. Cubic (A(4)Br)(2)Zr(6)(Z)Br(18) phases occur for various combinations of A = Na-Cs, Z = Be, B, H, Mn. The combination with A = K, Z = B was structurally characterized (inverse fluorite, Fm&thremacr;m, Z = 4, a = 16.191(2) Å). The 15-e cluster exhibits the appropriate magnetic moment, and this decreases toward the diamagnetic 14-electron limit in products with potassium deficiencies, (K(4)(-)(x)())(2)Zr(6)Br(18)B, x </= approximately 0.5. The tetragonal Cs(4)Br[Zr(6)(B)Br(12)]Br(4) (P&fourmacr;2(1)m, Z = 2, a = 12.5482(7) Å, c = 11.5610(9) Å) contains a new type of puckered M(6)Br(16) layers with Cs(4)Br(3+) in tunnels normal to the layers. Both examples of A(4)Br(3+) ions have short central Br-A bonds plus three to nine more distant bromines in neighboring clusters about each A, respectively.

Chromatographic investigations of polyacetals in the critical range of liquid chromatography, 2. Determination of functionality and molecular weight distributions in α,ω‐bis(9‐anthrylmethylpoly(1,3,6‐trioxacyclooctane))s obtained by “active chain‐end mechanism”

AbstractThe fractions obtained by cationic active chain‐end polymerization of 1,3,6‐trioxacylooctane initiated with (CF3SO2)2O (I), CF3SOOCC6H4CO⊕⊖O3SCF3( II) and (C6H5)3C⊕PF (III) were investigated using high‐performance liquid chromatography (HPLC) at the “critical point” of adsorption. The propagating species were converted into 9‐anthrylmethyl groups by suitable reactions of termination of transformation. Their incorporation made the chain ends detectable in the ultraviolet spectrum. The samples were separated at conditions specified for poly(1,3,6‐trioxacyclooctane)s (polyTOCs) obtained with (CF3SO2)2O as initiator. The functionality and molecular weight distribution of polyTOCs obtained with mono‐ and bifunctional initiators and with different counterions were compared and discussed. In the reaction mixtures oligomers of undesired functionality were detected irrespective of the usage of mono‐ or even bifunctional initiators. A correct method was used to determine the completeness of the separation and to calculate the percentages of the individual fractions. The order of initiators depending on the amount of the undesired end‐functionality fractions in the products obtained has been established. Attempts were made to elucidate the reactions complicating the cationic chain‐end polymerization of cyclic acetals and leading to a mixture of cyclic, dead, monofunctional and bifunctional oligomers and polymers. The results were summarized and compared with functionality and molecular weight distributions of oligo(1,3,6‐trioxacyclooctane)s obtained by “activated monomer mechanism” which have been discussed in the first paper of this series.

Interconversion Pathways of Chalcogen Rings. AnAb InitioMO Study of Model Reactions Involving Hypervalent Sulfur and Selenium Hydrides

Chalcogen ring molecules are known to undergo facile interconversion reactions in organic solvents and in the melts, e.g. polymerization of liquid sulfur or the formation of Se6 and Se7 upon dissolving Se8 in CS2. These interconversion reactions have been suggested to proceed via the homolytic cleavage of the chalcogen-chalcogen bonds or through the formation of hypervalent intermediates. The experimental evidence on the actual mechanism, however, is rather sparse. The energetics of the various suggested interconversion pathways have been studied by ab initio MO techniques using suitable model reactions involving sulfur and selenium hydrides. Full geometry optimization has been performed for hypervalent chalcogen hydrides H2EE and H2E(EH)2 as well as for the radicals HE · and HEE · (E = S or Se in the case of each chalcogen atom) utilizing the MIDI-4∗ basis sets. The energy changes in their formation from appropriate unbranched chalcogen hydrides HEnH(n = 1,2 or 4) and HEnE′mH (m,n = 0–4; n + m = 2,4; E,E...

Oligomeric Rare-Earth-Metal Halide Clusters. Three Structures Built of (Y(16)Z(4))Br(36) Units (Z = Ru, Ir).

Suitable reactions in sealed Nb tubing at 850-950 degrees C gave good yields of a family of oligomeric cluster phases that were characterized by single-crystal X-ray diffraction means. The basic Y(16)Z(4) units ( approximately &fourmacr; symmetry) can be derived from 2+2 condensation of centered Y(6)Br(12)Z-type clusters or as tetracapped truncated tetrahedra Y(16) that are centered by a large tetrahedral Z(4). These are surrounded by 36 bromine atoms which bridge edges or cap faces of the Y(16)Z(4) nuclei and, in part, bridge to metal atoms in other clusters. The principal bonding appears to be Y-Z and Y-Br, with weaker Y-Y (&dmacr; approximately 3.70 Å) and negligible Z-Z interactions. The phase Y(16)Br(20)Ru(4) (P4(2)/nnm, Z = 2; a = 11.662(1) Å, c = 16.992 (2) Å) is isostructural with Y(16)I(20)Ru(4) and with the new Sc(16)Br(20)Z(4) (Z = Fe, Os). Syntheses only in the presence of Ir and ABr-YBr(3) fluxes (A = K-Cs) produce Y(16)Br(24)Ir(4) (Fddd, Z = 8; a = 11.718(3) Å, b = 22.361(7) Å, c = 44.702(2) Å), in which the electron-richer Ir interstitials are compensated by four additional bromine atoms and altered bridging between macroclusters. Larger amounts of YBr(3) yield a third example, Y(20)Br(36)Ir(4) (Y(16)Br(24)Ir(4).4YBr(3), I4(1)a, Z = 4; a = 12.699(1) Å, c = 45.11(1) Å). Here infinite zigzag chains of YBr(6/2) octahedra that share cis edges lie between and bridge to the Y(16)Ir(4) clusters. All of these phases contain 60-electron, closed-shell macroclusters. Y(16)Br(20)Ru(4) and Y(20)Br(36)Ir(4) were found to exhibit temperature-independent (Van Vleck) paramagnetism with values typical of those found for other rare-earth-metal, zirconium, niobium, and tantalum cluster halides.

A search for neutron reactions that may be useful for Hiroshima dose reconstruction

Results are presented of a detailed search for neutron reactions that could potentially be useful in reconstructing the neutron fluence in Hiroshima, with emphasis on fast neutrons in the 1-MeV range. Searches were made for suitable reactions in several neutron cross-section libraries from the U.S., Europe, Japan, China, and the former U.S.S.R. Because of the long time (∼ 50 yr) since the atomic bombing of Hiroshima, reaction products evaluated in this search were limited to those with half-lives between 5 and 10 9 yr. From the about 100 reactions within this category, only six appear to have some potential utility for fast neutron measurements of suitable materials from Hiroshima. The technology may currently be available to measure two of these reactions if suitable materials can be obtained.

The use of in situ NMR spectroscopy and parahydrogen as tools for chiral synthesis

1. In situ 1H NMR spectroscopy and using parahydrogen (p-H 2) allows to characterize the stereochemistry of suitable hydrogenation reactions instantaneously. 2. The rhodium(I)-catalyzed homogeneous hydrogenation of the unsaturated racemic alcohols ( R,S)-2-(1-hydroxy-ethyl)-acrylic acid methyl ester ( I) and ( R,S)-2-methoxy-1-phenyl-buta-2,3-dien-1-ol ( II) leads to the formation of different diastereomeric products which can be distinguished unambiguously due to their characteristic polarization multiplets.