Shape-selective isopropylation of biphenyl over a highly dealuminated mordenite: effect of propylene pressure

A highly dealuminated H-mordenite (H-M) catalyzed the selective isopropylation of biphenyl to 4,4-diisopropylbiphenyl (4,4-DIPB). The high selectivity is ascribed to the shape-selective catalysis in mordenite pores. The selectivity of 4,4-DIPB decreased during the isopropylation of biphenyl due to isomerization of 4,4-DIPB under low propylene pressure. The increase of propylene pressure suppressed the isomerization in the isopropylation. 4,4-DIPB itself was isomerized over highly dealuminated H-M under low propylene pressure.     

Phosphinated linear polystyrene as a ligand of palladium catalysts for ethoxycarbonylation of 4,4′-dibromobiphenyl

Phosphinated linear polystyrene was synthesized and used as a ligand of palladium catalysts. It showed high activity for the ethoxycarbonylation of 4,4-dibromobiphenyl (I) in the presence of triethylamine. The catalysts acted as homogeneous under the reaction conditions (150°C, p(CO) = 10 kg/cm²), and precipitated as solid materials after the reaction. Catalytic performances highly depended on the compositions of the solvent, and the highest activity was achieved in ethanol.     

Silyl Triflate-Initiated Ring-Opening Polymerizations of Cyclosiloxanes

Polymer yields between 70 and 85% form in ring-opening polymerizations of trimeric cyclosiloxanes initiated with trimethylsilyl triflate in the presence of a selective scavenger for protic acids, 2,6-di-t-butylpyridine. Examples include the polymerization of 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (F₃) and hexamethylcyclotrisiloxane (D₃). Siloxane bond redistribution is essentially absent and data are presented establishing a nonterminating polymerization giving an average of roughly one trimethylsilyl group per chain. The present observations contrast with other work that suggests that the presence of free triflic acid is required for initiation with trimethylsilyl triflate.     

Suppression of the α → β-nickel hydroxide transformation in concentrated alkali: Role of dissolved cations

The presence of dissolved cations such as Al and Zn in alkaline electrolyte (6 M KOH) suppresses the -nickel hydroxide transformation. The uptake of Al (10 mol%) and Zn (30 mol%) exhibited by the active material likely stabilizes the -phase. Dissolved Al is deleterious to the performance of the nickel hydroxide electrode, whereas, dissolved Zn enhances the specific discharge capacity of nickel hydroxide by approximately 25% showing that the mode of metal uptake is different in the two cases.     

Syntheses and thermal properties of (sulfonylbisphenoxy)-containing cyclotriphosphazene polymers

A (sulfonylbisphenoxy)-containing cyclotriphosphazene polymer system has been prepared by polycondensation of (phenoxy)chlorocyclotriphosphazene and 4,4-sulfonylbisphenol. The syntheses by polycondensation using sodium salt of 4,4-sulfonylbisphenol and by interfacial polycondensation were carried out for comparison. The characterization, thermal stability, and fire resistance of the synthesized polymers were studied. Thermogravimetric analysis showed that the polymers prepared were stable to above 400°C in nitrogen and exhibited high char contents at elevated temperature. The result indicated that the presence of a sulfonyl group was helpful for enhancing thermal stability and the presence of a phosphphazene ring was the cause of the high char residue at elevated temperature.     

Syntheses and properties of aromatic polyamides derived from 4,4′-oxydibenzoic acid and aromatic diamines

A series of aromatic polyamides were synthesized by direct polycondensation of 4,4-oxydibenzoic acid with various aromatic diamines inN-methyl-2-pyrrolidone (NMP) solution containing dissolved calcium chloride, using triphenyl phosphite and pyridine as condensing agents. The resultant polyamides had inherent viscosities of 0.21-1.48 dL/g. Most of the polymers were organo-soluble and could be solution-cast into flexible and strong films. The glass transition temperatures (T_gs) of most polyamides could be determined with the help of differential scanning calorimetry (DSC) traces, which were recorded in the range of 170–275 °C. Thermogravi metric data of these polymers indicated that most of the polyamides showed no significant weight loss before 450 °C in either air or nitrogen atmospheres.     

Synthesis and properties of aromatic polyesters and brominated polyesters derived from α,α′-bis(4-hydroxyphenyl)-1,4(or 1,3)-diisopropylbenzene

The interfacial polycondensation technique was used for the preparation of polyarylates and brominated polyarylates. Polyarylates and brominated polyarylates were prepared by mixing a solution of diacid chloride such as terephthaloyl chloride, isophthaloyl chloride, or their mixture in dichloromethane with an aqueous alkaline solution of ,-bis(4-hydroxyphenyl)-1,4(or 1,3)-diisopropylbenzene or ,-bis(4-hydroxy-3,5-dibromophenyl)-1,4(or 1,3)-diisopropylbenzene using triethylbenzylammonium chloride as the phase transfer agent. Moderate to high molecular weight polyarylates with _inh up to 1.27 dL/g were obtained, and most of them could be cast into tough and flexible films depending on the polymer composition. In general, polymers containing more 1,3-isomer or isophthaloyl chloride moieties gave transparent and flexible films and had lower glass transition temperatures and higher solubility. Although these polymers have two isopropylidene linkages in their repeating units, they still exhibit moderately high thermal stability and show no obvious weight loss before 400 °C. The introduction of bromine on the polymer backbone caused a decrease of inherent viscosity, crystallinity, and thermal stability of the polyarylates, while causing an increase in glass transition temperature and a great enhancement of fire retardancy.     

Synthesis and Properties of Soluble 3,3′,4,4′-Benzophenonetetracarboxylic Dianhydride Copolyimides Based on 1,1-Bis[4-(4-aminophenoxy)phenyl]-1-phenylethane and Commercial Dianhydrides

1,1-Bis[4-(4-aminophenoxy)phenyl]-1-phenylethane (BAPPE) is a useful monomer for preparing soluble polyimides, but polyimide synthesized from BAPPE and 3,3,4,4-benzophenonetetracarboxylic dianhydride (BTDA) shows poor solubility. Insoluble BTDA/BAPPE polyimide can copolymerize with soluble polyimides at certain molar ratios (m₂/m₁) to produce arbitrarily soluble copolyimides. To prepare soluble copolyimides, the smallest m₂/m₁ ratio changes due to the matching dianhydrides, depending on the structure of the dianhydride component. When polymers contain the same m₂/m₁ ratio, copolyimides formed through thermal imidization show poorer solubility than these formed through chemical imidization, and copolyimide cyclized at 250°C has a better solubility than that cyclized at 300°C; this is due to the formation of intermolecular linkages during the high-temperature thermal cyclization. Additional, these copolyimides are characterized by good mechanical properties together with good thermal stability, and a comparative study on the properties of the homopolyimide and copolyimide are also presented.     

Unexpected products of the allyldiethylamine hydroformylation homogeneously catalyzed by rhodium complexes

Attempts to carry out the hydroformylation of allyldiethylamine homogeneously catalyzed by rhodium complexes led to unexpected formation of N,N,N,N-tetraethyl-1,4-diaminobutane and 4-(diethylamino)-1-butanole as final products. The role of the catalyst on the product formation and the reaction mechanism are briefly discussed.     

Hydroformylation of functional alkenes with heterodonor phosphine rhodium catalysts: substrate or ligand directed regioselectivity?

The catalytic activity and selectivity of heterodonor phosphine rhodium catalysts prepared in situ were tested in the hydroformylation of functional alkenes (ethyl acrylate, methyl methacrylate, styrene, 4-vinyl-1-cyclohexene, dicyclopentadiene and cis-1,2,3,6-tetrahydrophthalic anhydride). Systematic variation of the heterodonor atom in the ortho position of the ligand showed that the heterodonor atom has a significant influence on the activities and selectivities of the reaction. However, the activity seems to depend mainly on the modifying ligand, and the regioselectivity mainly on the substrate (i.e., the structure and functionality of the alkene). Nevertheless, regioselective control is only obtained through synergy between the substrate and the catalyst. Clear regiocontrol was observed in the hydroformylation of ,-unsaturated esters and styrene with an in situ formed o-(thiomethylphenyl)diphenylphosphine rhodium catalyst.     

Organic-Inorganic Hybrid Materials Based on the Incorporation of Polysilicic Acid Nanoparticle (PN) with Organic Polymers. 3. Shrinkage Characteristics in the Cure of Unsaturated Polyester Resin in the Presence of a Modified PN

The polysilicic acid nanoparticle (PN) was modified by the reaction of silanol group on its surface with silyl group (–Si(OR)₃) containing modifiers such as phenyltrimethoxylsilane (PTS), 2-(p-styryl)ethyltrimethoxylsilane (SETS), and 3-(trimethoxylsilyl)propyl methacrylate (TPMA), respectively, to afford modified PNs (M-PNs) including P-PN, S-PN, and T-PN. P-PN, S-PN and T-PN were mixed, respectively, with unsaturated polyester resin (UP) in styrene, UP/St, and then let homogeneous solutions cure at 150°C to produce transparent hybrid materials, UP/St/P-PN, UP/St/S-PN, and UP/St/T-PN. It was found that the M-PNs could not only act as low-profile additives (LPAs) to reduce the shrinkage of the hybrids during curing but also enhance their dynamic mechanical properties. The shrinking mechanism of the hybrids during curing and the interfacial force between M-PNs and UP/St matrix, which plays an important role in shrinking control and properties of hybrid, were studied in detail.     

Effect of the naturally occurring salt ‘Kanwa’ as a fertilizer on the productivity ofStylosanthes in the subhumid zone of Nigeria

Soil nutrient deficiencies pose a serious limitation to higher crop and forage yields in the Nigerian subhumid zone. Some of the deficiencies may be alleviated by using as a fertilizer a salt mined locally called Kanwa which is traditionally used as a cattle lick. Yields ofStylosanthes hamata cv Verano andS. guianensis cv Cook seed and dry matter increased with Kanwa application at different locations. The effect of Kanwa was enhanced when phosphorus was adequately supplied. Improvements to soil physical properties were proportional to the yield of the legume. The implications of good quality fodder and improved soil conditions in Agro-pastoral Systems in the Nigerian SHZ are discussed.     

High-Performance Directional Metallopolyamides. I. Synthesis and Thermal Analysis

High-performance polyamides containing the 4,4-disubstituted-2,2-bipyridyl moiety were synthesized by phosphorylation polycondensation from 2,2-bipyridyl-4,4-dicarboxylic acid and a series of primary aromatic diamines with triphenylphosphite and pyridine as the agents to facilitate condensation. Polyamides exhibiting improved solubility in organic solvents and strong acids, melting transitions at low temperatures, and good thermal properties were prepared by introducing bulking methyl and fluoro groups and flexible ether and propyl linkages and by using monomers with reduced symmetry. Solutions of the polyamides with rigid main chains (III, IV, V, VI, and VIII) showed birefringence (colorful spherulites) at concentrations of 5, 10, and 15% (w/v) polymer/solvent. The chelation of ruthenium(II) ions resulted in the preparation of directional metallopolyamide systems based on the geometrically favorable tris(2,2-bipyridyl)ruthenium(II) complex. The three-dimensional polyamides, which absorbed at a _max of 476 mm and emitted at a _max of 620 nm, exhibited a high thermal stability and improved solubility, making them suitable candidates for compressive strength studies and cyclic voltammetry studies as part of an effort to address the corrosion of graphite fiber-reinforced composites.     

2,2′-OXO-1,1′-azobenzene: Selective toxicity of rye (Secale cereale L.) allelochemicals to weed and crop species: II

Three allelochemicals from rye or its breakdown products were evaluated for activity on garden cress (Lepidum sativum L.), barnyardgrass [Echinochloa crus-galli (L.) Beauv.], cucumber (Cucumis sativus L.), and snap bean (Phaseolus vulgaris L.). 2,4-Dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA), 2(3H)-benzoxazolinone (BOA), and 2,2-oxo-1,1-azobenzene (AZOB) were all applied singly at 50, 100, and 200 ppm and in two- and three-way combinations each at 50 and 100 ppm. AZOB at 100 and 200 ppm produced 38–49% more inhibition than DIBOA, while combinations of BOA/ DIBOA, which contained AZOB at 100 ppm had 54–90% more inhibition when compared to DIBOA/BOA combinations. All combinations were slightly antagonistic to barnyardgrass, while several combinations caused a synergistic response to garden cress germination and growth. Cucumbers and snap beans exhibited both types of responses, depending on the allelochemical combination and application rate. The plant-produced benzoxazinones were more inhibitory to crops than weeds. Therefore, improved herbicidal selectivity would be expected if there were rapid transformation of the benzoxazinones to the microbially produced AZOB.     

Residual effects of growing mungbean and uridbean on the yield and nitrogen uptake of a succeeding wheat crop

A two year field experiment was carried out at the Indian Agricutural Research Institute, New Delhi - 110012, India to assess the effect of mungbean (Vigna radiata L.) and uridbean (Vigna mungo L.) residues on the yield and N uptake of a succeeding wheat crop as compared to sorghum fodder. Sorghum produced 3.5–7.5 times more dry matter and removed 2–3 times more nitrogen than mungbean or uridbean during same duration (80 ± 10 days) of their growth. Without N application the grain yield of wheat following mungbean and uridbean (without residue incorporation) was 0.45 and 0.48 t ha^–1 more than the yield of wheat following sorghum fodder. These yields were equivalent to that predicted when 36 and 38 kg urea-N ha^–1, respectively, was directly applied to wheat. The residual effects of these grain legumes were higher when succeeding wheat was fertilized with 60 kg urea-N ha^–1; at this level mungbean and uridbean spared 52 and 43 kg urea-N ha^–1, respectively, in succeeding wheat. The residual effect of mungbean and uridbean further increased when their residue was incorporated in soil; with this practice they spared 94 and 115 kg urea-N ha^–1, respectively, without N application to wheat and 74 and 82 kg urea-N ha^–1, respectively, with an application of 60 kg urea-N ha^–1 to wheat.Mungbean and uridbean, without residue incorporation, increased aboveground plant-N uptake of succeeding wheat by 11.5–34.9 and 10.8–34.0 kg N ha^–1, respectively; whereas with residue incorporation, they increased aboveground plant-N content of succeeding wheat by 26.1–45.8 and 32.7–47.7 kg N ha^–1, respectively.The results of the present study indicate that there is both an indirect sparing effect and a direct residual effect of mungbean and uridbean on the nitrogen needs of succeeding wheat, more so when their residues are incorporated in soil.     

The ring transformations of 1,2,3,4-diepoxybutane (2,2′-bioxirane) catalysed by various aluminosilicates

The transformations of a molecule containing two adjacent epoxide rings, 2,2-bioxirane that is, were studied over various acidic aluminosilicates (HZSM-5, HY-FAU, AlMCM-41), for the first time, In the 373–473 K temperature range, in a pulse reactor, a ring-opening–ring-enlargment reaction producing furan only occured over the zeolites and it was the predominant reaction on AlMCM-41 as well. The driving force of this transformation route is water formation via elimination from 2,2-bioxirane. Suprising is the lack of the mono- or dialdehyde, the would-be products of the cleavage of the sterically more hindered C–O bonds – an acid-catalysed reaction typical for alkyl-substituted oxiranes.     

Experimental Study of Ignition of a Gasoline–Air Mixture in a Constant‐Volume Combustion Chamber

The characteristics of flamekernel development in a premixed gasoline–air mixture in a cylindrical constantvolume combustion chamber are measured. The experiments are performed with an initial temperature of 393 K, pressure of 6 bar, and equivalence ratio = 0.8 with the use of various ignition systems and spark plugs. The schlieren pictures of the process are presented, and the measured results for flame velocity, heatrelease rate, and mass fraction of the burnt fuel are analyzed.     

Catalytic Methoxycarbonylation of Aromatic Diamines with Dimethyl Carbonate to Their Dicarbamates Using Zinc Acetate

The methoxycarbonylation of 2,4-toluene diamine and 4,4-diphenylmethane diamine with dimethyl carbonate to the corresponding dicarbamates using zinc acetate was carried out at 453 K. Zn(OAc)₂, prepared by evacuating Zn(OAc)₂2H₂O at 383 K for 2 h, yields dimethyltoluene-2,4-dicarbamate in 96% yield in 2 h, while Zn(OAc)₂2H₂O yields dimethyl-4,4-methylenediphenyldicarbamate in 98% yield at 453 K in 2 h.The structure of methyl 3-amino-4-methyl phenyl carbamate, which is one of the intermediates for the reaction of 2,4-toluene diamine with dimethyl carbonate into dimethyltoluene-2,4-dicarbamate, has been determined by measuring the NOE spectrum of ¹H NMR.     

Acetone conversion to isobutene in high selectivity using zeolite β catalyst

The catalytic activity of the proton forms of zeolite and ZSM-5 are compared for the conversion of acetone. Zeolite demonstrates markedly enhanced selectivity to isobutene and selectivities of >80% can be achieved for conversions up to 65%. In contrast high selectivities to isobutene with ZSM-5 can be attained only at very low conversions (5%).     

Mechanisms of Iron Activation on Fe-Containing Zeolites and the Charge of α-Oxygen

According to previous Mössbauer data [1] -sites formation at the activation of Fe-containing zeolites is accompanied by irreversible self-reduction of the iron, proceeding without participation of an external reducing agent. Reduced Fe²⁺ ions are inert to O₂ but are reversibly oxidized to Fe³⁺ by N₂O, generating the -oxygen species, O, which provide selective oxidation of hydrocarbons.In this work, the mechanism of -sites formation was studied via quantitative measurement of the dioxygen amount desorbed into the gas phase at the step of self-reduction. A prominent role of the zeolite matrix chemical composition has been revealed. For example, with zeolites of Al–Si composition (FeZSM-5 and Fe-), heating to 900 °C in a closed vacuum space leads to irreversible evolution of O₂, which is accompanied by the immediate formation of -sites. Similar heating of B–Si and Ti–Si zeolites also leads to dioxygen evolution; however, this evolution is reversible and is not accompanied by formation of -sites. Activation of these zeolites occurs only in the presence of water vapor. Stoichiometric measurements showed that in terms of charge one regular O^2- ion, removed at the activation, is equivalent to two -oxygen atoms. So, -oxygen is identified as an ion-radical species O ^-., whose unique oxidation properties still distinguish it from the generally observed O^-. radicals.The mechanism of -sites formation is proposed, in which the process of strong chemical stabilization of reduced Fe²⁺ atoms in the zeolite structure is a key step, making impossible the reoxidation of the iron with O₂.