Dicyclopentadienoxidation. I,Unkatalysierte Flüssigphasenoxidation von Dicyclopentadien

Dicyclopentadiene Oxidation I. Uncatalyzed Liquid-Phase Oxidation of Dicyclopentadiene Dicyclopentadiene is oxidized by molecular oxygen to a mixture of the monoepoxides 2 and 3 . The identification of the epoxides 2 , 3 and 4 was executed with authentic samples prepared by epoxidation with peracetic acid or with tert-butylhydroperoxide in the presence of MoO₂(acac)₂

1 acac — Acetylacetonat

The main product is the substituted norbornene oxide 2 . Allylic oxidation is also observed. Remarkable amounts of hydroperoxides can be determined iodometrically. The formation of allylic oxidation products 7 , 8 , 9 and 10 was proved by GC-MS-analysis. It is shown that in the uncatalyzed liquid phase oxidation of dicyclopentadiene no more than 50% of epoxides are formed. The bisepoxide 4 was found in small amounts only at higher conversions of the dicyclopentadiene.     

Über die katalysierte Flüssigphasenoxidation von cis- und trans-Oct-4-en

The Catalyzed Liquid-Phase Oxidation of cis- and trans-Oct-4-ene The influences of MoO₂(acac)₂

1 acac-Acetylacetonat.

, MoO ₃ and Co(acac) ₃ on the liquid-phase oxidation of cis- and trans-oct-4-ene at 110°C were studied. In the presence of molybdenum catalysts the yield of epoxides and the stereoselectivity of epoxide formation are increased. The results are in good agreement with the hypothesis that molybdenum compounds effect only the stereospecific reaction of the hydroperoxides formed with the starting olefin yielding the corresponding epoxide. The cobaltic complex increases the rate of autoxidation, but has no remarkable influence on the yield of epoxides. In the presence of Co(acac)₃ more trans-epoxide is formed from cis-oct-4-ene than in the uncatalyzed reaction. This can be explained by an increase of the lifetime of the intermediate peroxyalkyl radical, effected by complex formation of the radical with a cobalt species.     

Dicyclopentadienoxidation. II 5. Katalysierte Flüssigphasenoxidation von Dicyclopentadien

Dicyclopentadiene Oxidation. II. Catalyzed Liquid-Phase Oxidation of Dicyclopentadiene The liquid-phase oxidation of dicyclopentadiene 1 by molecular oxygen was studied in the presence of MoO₂(acac)₂

1 Acac- Acetylacetonat

as a typical epoxidation catalyst. The yield of the mono-epoxides 2 and 3 is increased to 56,4% (uncatalyzed reaction: 43,6%). The ratio of the two mono-epoxides is decreased to 2/3 = 2,6 in relation to the uncatalyzed reaction ( 2/3 = 7,1). The influence of temperature, conversion and solvents is described. The bisepoxide 4 is formed at lower conversions than in the uncatalyzed reaction. But also at higher conversions of 1 not more than 10% of the bisepoxide 4 is formed     

Simultaneous fluorine elimination and alkylation of poly(tetrafluoroethylene)

PTFE (powder or foils) was defluorinated and derivatized in a one-step process by alkyl- and aryllithium in the presence of tetramethylethylenediamine

1 Systematic name: 1,2-Bis-[dimethylamino]ethane.

(TMEDA) as a catalyst. As evidenced by infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and elemental analysis the C₄H₉-, C₈H₁₇-, C₁₂H₂₅- or phenyl groups were attached to a partly defluorinated macromolecular chain. Analogous reactions with dilithioaryl or dilithioalkyl agents presumably lead to crosslinking of the polymeric chains through alkyl or aryl groups. When the PTFE powder is treated with more concentrated RLi (>3 mol L^?1) at temperatures >150°C, the defluorination is almost quantitative even in the absence of the catalyst. The TMEDA-catalyzed reaction proceeds via elimination and nucleophilic addition. On the other hand, more concentrated RLi in the absence of the catalyst seems to react via a radical mechanism.     

Modeling of Ethylene‐Norbornene Copolymer Microstructure in Solution Polymerization with Homogeneous Metallocene Catalysts

Summary: The microstructure of ethylene‐norbornene copolymer produced in solution polymerization is analyzed through kinetic modeling and experiments using homogeneous rac‐Et(1‐indenyl)₂ZrCl₂/methylaluminoxane catalyst in toluene at 70 °C. The sequence distribution function and average chain length equations are derived for terminal model and penultimate model. The model simulations show that both models provide similar predictions of average copolymer composition, especially at low norbornene concentration in the copolymer. However, at higher norbornene concentrations the penultimate model yields much better predictions of norbornene sequence length distribution than the terminal model. The terminal model has been inadequate in describing the copolymerization rate, whereas the penultimate model yields excellent predictions of rate behavior. The model calculations also indicate that at norbornene concentration in the copolymer larger than about 10 mol‐%, the maximum ethylene block length is smaller than 70, prohibiting the formation of crystalline copolymer.

Ethylene sequence distribution curves at different mol‐% of norbornene in copolymer.     

Norbornene polymerization and ethylene/norbornene copolymerization catalyzed by constrained geometry cyclopentadienyl-phenoxytitanium catalysts

Norbornene polymerization and ethylene/norbornene copolymerization were studied using constrained geometry complexes 2-(tetramethylcyclopentadienyl)-4,6-di-tert-butylphenoxytitanium dichloride (1), 2-(tetramethylcyclopentadienyl)-6-tert-butylphenoxytitanium dichloride (2), and 2-(tetramethylcyclopentadienyl)-6-phenylphenoxytitanium dichloride (3) as catalysts with AlⁱBu₃ and Ph₃CB(C₆F₅)₄ as cocatalysts. Polymerization results indicate that these catalyst systems are highly active for both the homopolymerization of norbornene and the copolymerization of ethylene with norbornene. The norbornene homopolymerization is vinyl addition polymerization. Ethylene/norbornene copolymers with high norbornene incorporation (>50%) were easily obtained with these catalyst systems by increasing the norbornene feed concentration. The produced polymers were characterized by ¹³C NMR, IR, DSC and GPC.     

Synthesis and Photocatalytic Properties of HTaWO<Subscript>6</Subscript> Intercalated with Oxide Materials

Transition metal oxides (TiO₂, MnO₂, Cr₂O₃, Fe₂O₃, NiO, CuO) were intercalated into the interlayer of HTaWO₆ by (1) hydrothermal reaction on HTaWO₆ with 1 M soluble metal nitrate aqueous solution at 130C for 12 h followed by calcination at 250C for 3 h and (2) sol reaction on HTaWO₆/n-C₃H₇NH₂ precursor with metal oxide sol, followed by UV irradiation. The gallery height of transition metal oxide in the interlayer of HTaWO₆ is changed from 0.42 to 0.71 nm, the band gap energies of intercalated materials are less than 3 eV. HTaWO₆/Cr₂O₃, HTaWO₆/MnO, HTaWO₆/Fe₂O₃, HTaWO₆/NiO and HTaWO₆/CuO porous materials are capable of photocatalytic decomposing methyl orange, and the photocatalytic activity of HTaWO₆/TiO₂ is superior to that of unsupported TiO₂.     

Esterification of styrene–maleic anhydride copolymer by mixed alcohols

A copolymer (MW = 1800) of styrene (St) and maleic anhydride (MAn) was esterified with an excess amount of an alcohol mixture, and then the relation between the esterification rates of the individual alcohols and the contents of the esters in the esterific copolymer was examined. At first, the rate constant of an individual esterification was obtained for four different alcohols (n-butanol, i-amylalcohol, and benzylalcohol) in a noncatalyst system. Then, the mixed esterification of n-butanol and i-amylalcohol was carried out; from the analysis of the ester contents, the following equation was obtained: From this result, it was concluded that, in esterification with alcohols involving n species, the content of the individual ester can be expressed by the following equation: where [P] = concentration of esters in the copolymer, [B]₀ = initial concentration of alcohols, and k = rate constant of esterification (i,j = 1,2…,n).     

Synthesis and characterization of phenolic and amino resins based on α, β-unsaturated aldehydes

Phenolic and amino resins on the basis of α,β-unsaturated aldehydes were synthesized in bulk or solution. Catalysts were HCl, H₃PO₄, or formic acid, and in some cases NaOH. The course of the reactions was followed by GPC and NMR while the structure of the reaction products was determined by one- and two-dimensional NMR. The course of the reactions is influenced by experimental conditions: the type of monomers, their molar ratio, the type and quantity of the catalyst, the reaction time and temperature, and the reaction medium. At the beginning of the reaction the addition of a nucleophile to an aldehyde takes place through parallel 1,2-addition to and 1,4-addition to group. Oligomers with ? OH, , and ? CHO functional groups are able to add new monomer units or to react mutually to form higher molecular weight addition and condensation products. The overall rate constants for the beginning of the reactions were between 10^?3 L/mol s for the high reactive mixtures and 10^?7 L/mol s for the less reactive mixtures. The resins were cured by heating at temperatures above 135°C with the addition of hexamethylenetetramine.     

The STOBBE Condensation with Pyrrolyl Aldehydes – a synthesis of indole derivatives

The condensation of pyrrolyl-2-aldehyde or 1-methyl-pyrrolyl-2-aldehyde with dimethyl succinate, using sodium hydride as condensing agent, gave predominantly the halfesters 1a and 1c respectively. Their structure and (E)-configuration

1 i. e., pyrrol ring and COOCH₃ group are in trans position. This nomenclature follows the IUPAC 1968 Tentative Rules, Section E, Fundamental Stereochemistry, J. org. Chemistry 35 , 2849 (1970).

were confirmed by their cyclisation to the corresponding indole derivatives 2a–h .     

Fracture behavior of coated/uncoated graphite-epoxy composites

The static delamination behavior of graphite/epoxy composite specimens subjected to mode I tensile opening (using UDCB

1 Uniform double cantilever beam.

specimens), and pure mode II shear loading (using ENF

2 End-notched flexural.

specimens) were studied. The graphite epoxy composites for the study were made from commercially treated fibers, with and without an electropolymerized interlayer. The mode I fracture energy (G_IC) was found to be significantly higher (more than 50 percent) for the coated fibers. However, this improvement was accompanied by a high reduction (more than 3 times) in the mode II fracture energy (G_IIC). This effect is apparently related to poor adhesion between the interlayer and the epoxy resin, which may be corrected by use of a “top layer” of appropriate composition to form chemical bonds between the phases. The fracture toughness (K_IC) of composites made with commercially treated fibers was also evaluated, using double side-notched specimens.     

A Stereoselective Access to Cyclic cis‐1,2‐Amino Alcohols from trans‐1,2‐Azido Alcohol Precursors

A unique one‐pot synthesis of cyclic cis‐1,2‐amino alcohols from trans‐1,2‐azido alcohol precursors was developed. The key step is highlighted by the stereoselective reduction of the cyclic α‐alkoxy imines, which could be prepared from the corresponding azides by ruthenium catalysis under photolytic conditions. Remarkably, this unprecedented reaction pathway offers a stereodivergent access to structurally diverse cyclic 1,2‐amino alcohols.

     

Oxidative Alkoxycarbonylation of Alkynes by Means of Aryl α‐Diimine Palladium(II) Complexes as Catalysts

The straightforward in situ synthesized bis(2,6‐diisopropyl)acenaphthenequinonediimine palladium triflate catalyst was generally employed for both the mono‐alkoxycarbonylation of terminal alkynes, and the bis‐alkoxycarbonylation of 1,2‐disubstituted alkynes by using mild reaction conditions [carbon monoxide pressure (P_CO)=4 bar, temperature=20 °C]. Utilizing low catalyst loading (down to 0.5 mol%), a variety of propiolic esters were synthesized with good to excellent isolated yields. Most importantly the system was very efficient not only with methanol but also with a range of different alcohols, starting from the less hindered benzyl alcohol to the most hindered ones, such as isopropyl alcohol and tert‐butyl alcohol. In addition, aromatic and aliphatic 1,2‐disubstituted alkynes were converted into maleic acid derivatives, together with an acid‐catalyzed isomerization reaction, showing modest to good selectivity and excellent combined yields. In particular 3‐hexyne showed a satisfactory degree of selectivity for the maleic diesters of methanol and benzyl alcohol, obtaining the corresponding products with good isolated yields.

     

Stevensanaloge,Durch Nickelkomplexe Katalysierte Umlagerung Von Triarylphosphoryliden Und Darstellung Sowie Strukturbestimmung Von Phosphorylid-Nickeltricarbonylkomplexen

The Stevens rearrangement of the triarylphosphorusylids R₃ P=CHR′ (III) (R′ = H, CH₃, C₂ H₅) to diarylbenzylphosphines (V) is catalyzed by nickel complexes (e.g., (COD)₂ Ni (I)). Attempts to prepare trimesitylphosphine-methylene result in direct formation of dimesityl (mesitylmethyl) phosphine (XII) — the first recorded direct Stevens rearrangement of a phosphorusylid. Phosphorusylids react with nickeltetracarbonyl without rearrangement to give complexes of the type R₃P=CH_a · Ni(CO)₃ (XIV). The structure of XIV has been established by the IR and NMR spectra and confirmed by an X-ray structural determination.

1 B. L. Barnett and C. Krüger, J. Cryst. Mol. Struct., im Druck.

The ylid is bonded to the nickel through the C-atom with resulting hybridization from sp² towards sp³.     

Vinyl polymerization of norbornene with bispyrazolylimine dinickel(II)/methylaluminoxane catalytic system

The polymerization of norbornene has been investigated in the presence of two novel bispyrazolylimine dinickel(II) complexes bis-2-(C₃HN₂Me₂-3,5)(C(Ph) = N(4-RC₆H₄)Ni₂Br₄ (complex 1, R = H; complex 2, R = OCH₃) activated by methylaluminoxane. The two catalytic systems show high activity (up to 1.83 × 10⁶ gPNBE/(molNi·h)) for norbornene polymerization and provide polynorbornene (PNBE) with higher molecular weights (M _w = 4.44 × 10⁵–11.57 × 10⁵ g/mol) and narrower molecular weight distributions about 2.0. The electron-donating of methoxyl group in complex 2 could enhance the catalytic activity for norbornene polymerization, however, the molecular weights of polymers were decreased. The influences of polymerization parameters such as polymerization temperature, Al/Ni molar ratio, reaction time and catalyst concentration on catalytic activity, and molecular weight of the PNBEs were investigated in detail. The obtained PNBEs were characterized by means of ¹H NMR, FTIR, and thermogravimetric analyses. The analyses results of PNBE indicated that the norbornene polymerization is vinyl-type polymerization rather than ring-opening metathesis polymerization.     

Antioxidants and stabilizers, 107. Reaction of N-phenyl-1,4-benzoquinoneimine with the 1-cyano-1-methylethyl-radical

The reaction of N-phenyl-1,4-benzoquinoneimine (I)

1 Decoding of abbreviations see p. 103/104.

and 4-hydroxydiphenylamine (II) with the carbon centred 1-cyano-1-methylethyl radical (R^·) was studied in connection with an investigation of the action mechanism of industrial antidegradants, such as N-phenyl-N′-sec-alkyl-1,4-phenylenediamines. The mixture of I and II reacts very readily with R^·, giving rise to III , VI , and VIII . I alone reacts much slowlier, and the reaction mixture contains more products. IV and VII were identified along with III . Under the conditions used, II alone does not react at all. IV exists in two isomeric forms, syn and anti. VIII is very labile; XI was isolated from its transformation products. Reduction of IV gives V , which is labile, similarly to VIII .     

Silver Hexafluoroantimonate‐Catalyzed Direct α‐Alkylation of Unactivated Ketones

A practically simple and direct α‐alkylation of unactivated ketones using benzylic alcohols has been achieved. The in situ formed acetals are the key for the success of the reaction. The catalyst, silver hexafluoroantimonate(V) (AgSbF₆) provides double activation by converting the ketone into an enol ether via acetal and generation of carbocationic center at the benzylic position of the benzylic alcohol. The alcohols include benzylic propargyl alcohols, cinnamyl alcohols, and diarylmethanols.

     

A polymeric amine–copper(II) complex as catalyst for the hydrolysis of 1,2,2-trimethylpropyl methylphosphonofluoridate (soman) and bis (1-methylethyl) phosphorofluoridate (DFP)

The Cu (II) complex of poly-4-vinylpyridine, quaternized with 19 mol % ethyl bromide and 36 mol % 4-chloromethyl-4′-methyl-2,2′-bipyridine, was examined as a catalyst for the hydrolysis of the toxic organophosphorous compounds bis (1-methylethyl) phosphorofluoridate ( 1 ,

1 Registry no.: 1 , 55-91-4; 2 , 96-64-0.

DFP) and 1,2,2-trimethylpropyl methylphosphonofluoridate ( 2 , soman). Studies were carried out at 25.0 and 37.0°C for both substrates in MOPS buffer at pH 7.0. In the presence of 7.31 × 10^?3 M catalyst at 25.0°C, soman is hydrolyzed with a first-order rate constant of 0.019 min^?1 (t_1/2 = 37.5 min), whereas DFP hydrolyzes with a rate constant of 0.011 min^?1 (t_1/2 = 63.8 min). For soman, this represents a 14-fold increase over the uncatalyzed rate in the same buffer. Other studies examined the effect of a strongly sorptive polymeric resin on catalysis by this copper-containing polymer and found a dramatic decrease in the hydrolysis rate of soman in the presence of the polymeric sorbent.     

Copolymerization of ethene with norbornene using palladium(II) α-diimine catalysts: Influence of feed composition, polymerization temperature, and ligand structure on copolymer properties and microstructure

Four cationic palladium(II) α-diimine complexes, [{ArNC(R)-C(R)NAr}Pd(Me)(CH₃CN)] (1, R=H, Ar=2,6-Me₂C₆H₃, =B[3,5-C₆H₃(CF₃)₂]₄; 2, R=CH₃, Ar=2,6-iPr₂C₆H₃; 3, R=CH₃, Ar=2-tBuC₆H₄; 4, R,R=An, Ar=2,6-iPr₂C₆H₃) were used for the copolymerization of ethene with norbornene. The copolymerization behavior of the catalysts and the influence of the polymerization temperature were investigated. The copolymers were characterized using ¹³C NMR spectroscopy, differential scanning calorimetry, and gel permeation chromatography techniques. Sterically demanding ortho -N-aryl substituents and rigid bulky bridge units increase the copolymer molar masses, while the incorporation level of norbornene is decreased. Microstructures with isolated norbornene units and alternating sequences are predominant. Less bulky substituted catalysts yield copolymers with higher norbornene contents and lower molar masses. Norbornene diblock sequences are dominant which are exclusively racemic connected, indicating that the insertion proceeds under chain end control. Optimal polymerization results are achieved at temperatures between 10 and 30 °C, while temperatures below 0 °C result in lower polymerization rates and molar masses. Above 30 °C, activities, molar masses, and norbornene incorporation decreases due to catalyst decomposition.     

Properties of standard materials for reflection

This article gives a short survey of some literature on the calibration, suitability, properties, and use of various materials which are used as standards of reflectance. The classical ultimate reference standard, smoked magnesium oxide, is discussed briefly, and information is given on the properties of materials presently used: BaSO₄, Russian opal glasses, ceramic tiles, and Halon.

1 Halon is a registered trade name of the Allied Chemical Corporation.

The suitability of these materials for use as transfer standards or working standards is discussed.