Synthesis and polymerisation of polycyclic compounds with strained C—C single bonds

Ring opening polymerisation of bicyclobutanes possessing electronegative substituents (CN, COOCH₃, etc.) at one or both bridgeheads can be accomplished readily with either radical or anionic initiators. The polymer chains consist exclusively of cyclobutane rings linked through the 1,3 positions. Readily obtained in high molecular weight, they possess attractive physical properties for the formation of fibres and films. These new monomers copolymerise readily with vinyl compounds, exhibiting reactivities comparable to the latter, and provide a wide variety of new copolymers. Other bicyclic compounds containing strained C—C bonds whose polymerisation has been demonstrated include bicyclo-[2.1.0]-pentane-1-carbonitrile, 1-methyl-2,3-benzocyclopropenecarbonitrile, and 1,3-dehydroadamantane. The ability to polymerise requires a high strain energy, but a high degree of p character in the C—C single bond as well.     

Zur Kinetik der Bildung von löslichen Polymeren beim Metathese-Abbau von C—c-vernetztem 1,4-Polybutadien

1,4-Polybutadiene was crosslinked with dicumyl peroxide. Samples with different degree of crosslinking were ground to particles with a diameter of < 0,1 mm and degraded in a metathesis reaction with a small amount of 4-octene and the catalyst WCl₆/(CH₃)₄Sn at 20°C. The fraction of the soluble polymer (soluble in chlorobenzene and precipitable by methanol) was determined as a function of reaction time and investigated by gel permeation chromatography. This fraction and in particular the higher molecular part (M > 120 000 g/mol) passes a maximum, which is more evident at a lower degree of crosslinking. The kinetics show peculiarties of the metathesis degradation and crosslinking.     

Palladium‐Catalysed Regioselective Sequential C‐5 and C‐2 Direct Arylations of 3‐Acetylpyrroles with Aryl Bromides

The PdCl(C₃H₅)(dppb)/KOAc system was found to be effective for the direct regioselective C‐5 arylation of 3‐acetylpyrroles with ortho‐substituted aryl bromides. This procedure has been found to be tolerant to a variety of functional groups at C‐2 of the aryl bromide such as methyl, formyl, nitrile, nitro, hydroxymethyl, chloro, fluoro or trifluoromethyl. The sequential direct C‐5 arylation followed by C‐2 arylation of such 3‐substituted pyrroles allows the synthesis of 2,5‐diaryl‐3‐acetylpyrroles in high yields.     

Synthesis and Electronic Spectra of Some Disperse Dyes Derived from N—2—Cyanoethyl—1,2,3,4—tetrahydroquinoline

Various monoazo dyes suitable for transfer printing have been prepared from N—2cyanoethyl—1, 2, 3, 4—tetrahydroquinoline and compared with the corresponding N—methyl (kairoline) derivatives. The presence of a β—cyanoethyl group brings about significant hypsochromic shifts of the first absorption band and leads to some improvement in light—fastness properties on polyester fibre.     

利用二元体系的C H红外光谱推算汽液平衡数据

Prediction of vapor-liquid equilibrium （VLE） is extremely necessary to separate liquid mixture in chemical production, especially when the required experimental data are difficult to measure, or the measurement is not economical. The infinite dilution activities can be used to predict VLE. However, it needs both the ends of the activities that are difficult to obtain for many systems. In the present study, a new model is proposed for correlating the frequency shift of C-H stretching band of IR spectra over the whole concentration. Investigated mixtures in- clude water/2-propanol, water/N, N-dimethylformamide （DMF）, water/methanol, water/ethanol, water/1, 4-dioxane, and water/dimethylsulfoxide （DMSO） systems. Simultaneous correlations of C--H frequency shift and VLE data are made. Furthermore, the VLE data were predicted with satisfactory results by the parameters obtained from IR spectra coupled with one ot the intinite chlution activity coefficients.     

siRNA Modified with 2′‐Deoxy‐2′‐C‐methylpyrimidine Nucleosides

(2′S)‐2′‐Deoxy‐2′‐C‐methyluridine and (2′R)‐2′‐deoxy‐2′‐C‐methyluridine were incorporated in the 3′‐overhang region of the sense and antisense strands and in positions 2 and 5 of the seed region of siRNA duplexes directed against Renilla luciferase, whereas (2′S)‐2′‐deoxy‐2′‐C‐methylcytidine was incorporated in the 6‐position of the seed region of the same constructions. A dual luciferase reporter assay in transfected HeLa cells was used as a model system to measure the IC₅₀ values of 24 different modified duplexes. The best results were obtained by the substitution of one thymidine unit in the antisense 3′‐overhang region by (2′S)‐ or (2′R)‐2′‐deoxy‐2′‐C‐methyluridine, reducing IC₅₀ to half of the value observed for the natural control. The selectivity of the modified siRNA was measured, it being found that modifications in positions 5 and 6 of the seed region had a positive effect on the ON/OFF activity.     

Plasma Processing of B4C–TiB2 Eutectic Composite Powders

The production of a composite powder of eutectic B₄C–TiB₂ is demonstrated via an atmospheric plasma processing method. Feedstock material is prepared for plasma processing by mixing and spray drying monolithic B₄C and TiB₂ to produce a flowable precursor powder. These powders are fed through a plasma torch, where they are melted and actively quenched in flight with argon gas. Plasma processed powders are composed of crystalline B₄C and TiB₂, with some additional B₂O₃ oxide phase. The plasma processing method results in the production of monolithic B₄C and TiB₂ nanoparticles, but some larger particles (generally ≥10 μm in diameter) are shown to contain the traditional lamellar eutectic microstructure. The eutectic interphase spacing ranges from 100 to 650 nm, and the composite microstructure is present through the entire thickness of the eutectic particles. Future work on plasma processing of eutectic powders should focus on methods utilizing passive in‐flight quenching to increase the average particle size.     

COMPLEX DYNAMIC BEHAVIOR IN THE CASE OF CO—NO—O2—H2O REACTION SYSTEM ON Pt/γAl2O3 CATALYST

Self-sustained, isothermal oscillations in outlet species concentrations were observed under certain steady inlet conditions in the case of the CO—NO—O₂—H₂O reaction system on Pt/γAl₂O₃ catalyst in a fixed-bed tubuiar reactor. The oscillations were mostly aperiodic, and for fixed inlet concentrations of the other species, they occurred in a rather narrow window of inlet oxygen concentrations near the stoichiometric point. The amplitude and frequency of these oscillations were affected by temperature and by the inlet concenlrations of CO and NO. Systemalic experiments, conducted to understand the cause of these oscillations, revealed that the catalyst aging procedure and the presence of water vapor induced the complex dynamic behavior observed in the CO—NO—O₂—H₂O system. The oscillations are explained qualitatively in terms of the competition among the various reactants for adsorption and subsequent reaction on the catalyst surface.     

Copper‐Catalyzed C–N,C–O Coupling Reaction of Arylglyoxylic Acids with Isatins

The copper(II)‐catalyzed decarboxylative coupling reactions of arylglyoxylic acids with isatins afford 4H‐benzo[d][1,3]oxazin‐4‐ones via decarbonylation and concurrent C–N, C–O bond formation.

     

Studies on the C–H/C–D Exchange in Imidazolium (Pilocarpinium) and in 2- and 4-Hydroximinomethyl Pyridinium Compounds

The H–D exchange of methylene protons in a side-chain when situated between a positively charged N-atom (α–CH₂) and a ketone function was studied in various pilocarpinium (N-methyl imidazolium) and hydroximinomethyl pyridiniums using NMR measurements. Structural factors which determine the course of the exchange are reported, and the role of the solvent was examined. Mass-spectra of nondeuteriated and deuteriated 4-hydroximinomethyl-1-phenacyl-pyridinium chloride confirmed the fast exchange of the α–CH_a. An alternative H–D exchange of the C₂–H in the imidazolium moiety of certain pilocarpinium compounds without a ketone in the N-chain was detected. Mechanisms for the two types of exchanges involving an ylid as intermediate and attack of a deuteron were proposed.     

Palladium‐Catalyzed Intermolecular C‐2 Alkenylation of Indoles Using Oxygen as the Oxidant

A general and efficient palladium‐catalyzed intermolecular direct C‐2 alkenylation of indoles using oxygen as the oxidant has been developed. The reaction is of complete regio‐ and stereoselectivity. All products are E‐isomers at the C‐2‐position with no Z‐isomers and 3‐substituted products were detected.

     

Reactions of phenolic ester alcohol with aliphatic isocyanates—transcarbamoylation of phenolic to aliphatic urethane: A 13C‐NMR study

Reactions of aliphatic isocyanates with a phenolic ester alcohol (PHEA) were investigated using ¹³C‐NMR spectroscopy. PHEA has two reactive sites: a phenolic  OH group and a secondary aliphatic  OH group. Both  OH groups react with the isocyanate groups. With an organotin catalyst, dibutyltin dilaurate (DBTDL), the aliphatic  OH group reacts first. With a tertiary amine catalyst, 1,4‐diazabicyclo[2.2.2]octane (DABCO), or triphenylphosphine (Ph₃P) or even in the absence of a catalyst at room temperature (RT) the phenolic  OH group reacts first. With the organotin catalyst, the reactions are generally complete in a day at RT. With DABCO or triphenylphosphine or DNNDSA catalysts, the reactions are almost complete only in 3–4 days at RT in ethyl acetate or acetonitrile. Uncatalyzed reactions are slower. With an acid catalyst such as dinonylnaphthalenedisulfonic acid (DNNDSA), both  OH groups react with the isocyanate. When equimolar quantities of PHEA and hexamethylenediisocyanate (HDI) polymerize at RT or reflux in the presence of a catalyst, both  OH groups react, with the phenol reacting slowly. Upon refluxing, the phenolic  OH‐based urethane slowly rearranges (transcarbamoylation) to the aliphatic  OH‐based urethane. DABCO and Ph₃P catalysts effect this rearrangement at a much slower rate than does the acid catalyst. In the presence of a catalytic amount of DBDTL in a refluxing solvent, this rearrangement is complete in 2 h. By refluxing the phenolic–OH‐based urethane in isopropanol, the mechanism of transcarbamoylation was found to be intermolecular. The mechanism is likely to involve deblocking of the phenolic urethane and subsequent reaction of the isocyanate generated, with the aliphatic  OH group. This conclusion was confirmed by differential scanning calorimetry (DSC) experiments. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2212–2228, 2000     

Crack Healing in Ti2Al0.5Sn0.5C–Al2O3 Composites

Oxidation induced crack healing of Al₂O₃ composites loaded with a MAX phase based repair filler (Ti₂Al_0.5Sn_0.5C) was examined. The fracture strength of 20 vol% repair filler loaded composites containing artificial indent cracks recovered fully to the level of the virgin material upon isothermal annealing in air atmosphere after 48 h at 700°C and 0.5 h at 900°C. SEM‐EBSD analysis of crack microstructure indicates two different oxidation reaction regimes to govern the crack filling: near the surface SnO₂, TiO₂, and Al₂O₃ were formed whereas deeply inside the cracks Al₂O₃ and TiO₂ and metallic Sn were detected. The presence of elemental Sn was attributed to partial oxidation of aluminum and titanium which lowered the local oxygen concentration below a threshold value required for Sn oxidation to SnO₂. Thus, Ti₂Al_0.5Sn_0.5C may represent an efficient repair filler system to trigger oxidation induced crack healing in ceramic composites at temperatures below 1000°C.     

The controlled reaction of active carbons with air at 350°C—I: Reactivity and changes in surface area

Two activated carbons prepared from almond shells and olive stones were reacted with air at 350°C to different percentages burn-off. The reactivity was studied in the temperature range 350–500°C where the reaction is relatively slow. The activated carbon from almond shells is more resistant to the reaction with air and the activation energy of that reaction is 101 kJ mol⁻¹. The adsorption of N₂ at 77 K has been used to characterize the adsorptive properties and surface area of all the obtained products, which have high surface areas (around or above 1000 m² g⁻¹). The gas adsorption results, together with mercury porosimetry have allowed a study of the variation of surface area and porosity as a function of the burn-off. In any case, the exposure of the active carbons to air at 350°C for several days does not considerably affect their adsorptive properties even for a weight loss up to 50%.     

Feststoff-Bioreaktoren — Teil 2: Bewegte Anlagen

Solid State Fermentation Plant - Part 2: Non-Stationary Units . Western experience with solid state fermenters in which the fermenting substrate is circulated is still limited to the laboratory scale (< 20 kg of substrate). In contrast, automated industrial plant with capacities of 10 to 100 t of inoculated substrate per charge have been in operation in Japan for several decades for the semi-continuous production of enzyme mixtures. However, the substrate is only occasionally circulated in these plant. It is shown from the literature cited that stationary solid state fermentation processes employing the tablet method give significantly better results (lower plant costs, shorter process duration, high enzyme product yields, higher product quality, less pronounced gradient formation, etc.) than processes with occasional product circulation. Stationary solid state fermentation plant (tablet method) therefore appear to represent the method of choice, especially for the production of secondary metabolites, pigments, flavours, etc., whose production optima lie within fairly narrow limits which cannot be met by non-stationary units.     

Reactivity of Electrogenerated N‐Heterocyclic Carbenes in Room‐Temperature Ionic Liquids. Cyclization to 2‐Azetidinone Ring via C‐3/C‐4 Bond Formation

The intrinsic chemistry of imidazolium‐based room‐temperature ionic liquids, related to the acidity of the C‐2 imidazolium cation, can be modified via cathodic cleavage of the C‐2/hydrogen bond. N‐Heterocyclic carbenes, electrogenerated by electrolysis of imidazolium‐based room‐temperature ionic liquids, are stable bases that are strong enough to deprotonate bromoamides 1a–k yielding the azetidin‐2‐one ring via C‐3/C 4 bond formation. The electrosynthesis of β‐lactams 2a–k has been achieved under mild conditions, elevated yields and avoiding the use of toxic, volatile, molecular solvents.