Electrocatalytic reduction of tert-butyl hydroperoxide at iron electrodes

The electrochemical reduction of tert-butyl hydroperoxide has been investigated in dimethylformamide and 1,2-dichloroethane. Voltammograms at platinum or at glassy carbon electrodes were indistinguishable from the background, whereas at iron electrodes a well-defined cathodic peak was observed. The electrocatalytic reduction of tert-butyl hydroperoxide was enhanced at freshly electrodeposited iron. A study of the reduction mechanism at iron electrode showed that both the electron transfer and the cleavage of the peroxidic bond occurred in a single step, consuming two electrons per mole with the production of tert-butanol. The electrocatalytic effect of iron was also observed for the cumyl hydroperoxide reduction. Organic peroxides are not implicated in an electrocatalytic reduction at iron surfaces.     

Synthesis of disubstituted amine-functionalized diene-based polymers

Diene-based polymers with two amine groups within each repeat unit were successfully synthesized by bulk and solution free radical polymerization techniques. All polymers have exclusive 1,4-microstructure. The number average molecular weights of the materials obtained were in the range of 30–52 × 10³ g/mol using 2,2′-azobisisobutyronitrile (AIBN), t-butyl peracetate (t-BPA), or t-butyl hydroperoxide (t-BHP) as the initiators. The highest molecular weight achieved was 72 × 10³ g/mol when t-butyl peroxide (t-BPO) was used as the initiator. Quantitative quaternization was achieved yielding hydrophilic water soluble polymers. Prior to quaternization, the polymers are hydrophobic and dissolve in most organic solvents.     

Effect of the nature of an extractant on the composition and properties of lipids extracted from peat

The effect of an extractant on the yield of lipids depending on the moisture content of peat was studied. A maximum yield of lipids was obtained upon extraction with a mixture of methyl tert-butyl ether and ethanol in a ratio of 1: 1. It was found that the use of an ethyl acetate-ethanol or methyl tert-butyl ether-ethanol solvent mixture led to a decrease in the acid and peroxide numbers of lipids regardless of the moisture content of peat. The antioxidant activity of lipids increased with the moisture content of peat.     

Regioselective Alcoholysis of Silychristin Acetates Catalyzed by Lipases

A panel of lipases was screened for the selective acetylation and alcoholysis of silychristin and silychristin peracetate, respectively. Acetylation at primary alcoholic group (C-22) of silychristin was accomplished by lipase PS (Pseudomonas cepacia) immobilized on diatomite using vinyl acetate as an acetyl donor, whereas selective deacetylation of 22-O-acetyl silychristin was accomplished by Novozym 435 in methyl tert-butyl ether/n-butanol. Both of these reactions occurred without diastereomeric discrimination of silychristin A and B. Both of these enzymes were found to be capable to regioselective deacetylation of hexaacetyl silychristin to afford penta-, tetra- and tri-acetyl derivatives, which could be obtained as pure synthons for further selective modifications of the parent molecule.     

Crystalline Di-Tert-Butyl Trioxide and Dicumyl Trioxide

Di-tert-butyl trioxide has been prepared at ?50° by photolysis of solid di-tert-butyl diperoxymonocarbonate and, more conveniently, by the reaction of ozone in Freon 12 (CF₂Cl₂) or methyl chloride with either dissolved tert-butyl hydroperoxide or suspended hydrated sodium tert-butyl peroxide. A low-temperature procedure for freeing the product from accompanying tert-butyl alcohol and other impurities is described. The ozone - sodium salt method has also been applied to the preparation of crystalline dicumyl trioxide. These trioxides have the properties previously observed in solution. They are unstable at temperatures above ?30°. NMR spectra of the trioxides are reported and compared with those of related compounds. Approximate rate constants for the thermal decomposition of dicumyl trioxide are reported.     

Emulsion polymerization of ethylene. V. Kinetics and mechanism

The solubility of ethylene was measured in water, water–tert-butyl alcohol, water-emulsifier, water-tert-butyl alcohol-emulsifier, and water–tert-butyl alcohol–emulsifier–polyethylene. The polymerization of ethylene in an emulsion system differs from that of other vinyl monomers in several ways: the rate of polymer formation is inversely proportional to the emulsifier concentration and to the number of particles, the molecular weight of the polymer increases as the particle size increases, the polymer contains bound emulsifier whose concentration depends inversely on the particle diameter. These peculiarities are attributed to a transfer reaction between polymer radicals and emulsifier adsorbed on the surface of the polymer particle. In the presence of a fatty-acid soap, the transfer probably occurs primarily at the carbon α to the carboxyl group.     

Effects of hydrogen peroxide concentration and ultraviolet light intensity on methyl tert-butyl ether degradation kinetics

This paper aims to study methyl tert-butyl ether (MTBE) degradation in the presence of ultraviolet (UV) light and hydrogen peroxide, and to determine the effects of operating conditions on the reaction kinetics. Two key parameters investigated in this study include the concentration of hydrogen peroxide and the average UV light intensity in the solution. A 1000 W xenon arc lamp was used as the light source. The degradation of MTBE was found to follow a pseudo-first-order kinetics in terms of MTBE concentration. Although reaction rate increased with the addition of hydrogen peroxide, higher levels of hydrogen peroxide had a diminishing return since the excessive hydrogen peroxide could act as a scavenger for the hydroxyl radicals. On the other hand, the average UV light intensity in the solution was found to proportionally increase the reaction rate constant. A regression model was developed for the pseudo-first-order rate constant (k) as a function of the hydrogen peroxide concentration and the average light intensity in the solution:

     

Copolymers from tert-butyl methacrylate and 2-propenyl isocyanate—polymers for photoresist application

Free radical copolymerisation of tert-butyl methacrylate (1) with 2-isopropenyl isocyanate (2) has been investigated. Reactivity ratios of r₁=3.48±0.60 for 1 and r₂=0.004±0.04 for 2 were obtained. As 2-propenyl isocyanate has almost no tendency to homopolymerise maximum isocyanate content is reached in an alternating copolymer. The reaction of the isocyanate functionality with morpholine was used to obtain compounds for determination of the composition by NMR-spectroscopy. Glass transition temperature of the copolymers increases with increasing tert-butyl methacrylate content. It was found that thermal cis-elimination of isobutylene from the tert-butyl ester is followed by two further reactions: formation of six-membered anhydride rings by two neighbouring acid functionalities and formation of 3,4-dimethyl-pyrrolidin-2-one from one acid group and an adjacent isocyanate functionality. The reactions could be observed in the solid state and in solution at about 200 °C. Molecular weights of the copolymers as determined by size exclusion chromatography decreases with increasing isocyanate content which is due to chain transfer reactions of isopropenyl isocyanate. Conversion per minute decreases with increasing isocyanate content in the monomer feed.     

Selective oxidation of indole by chloroperoxidase immobilized on the mesoporous molecular sieve SBA-15

The selective oxidation of hydrocarbons is an important value-enhancing chemical transformation in particular with respect to fine chemicals and pharmaceuticals production. Enzymatic oxidations operate under mild reaction conditions and produce little if any waste. However, its industrial use is still limited mainly due to their high cost and the low space time yields. In the present work, chloroperoxiase from Calariomyces fumago immobilized on the mesoporous molecular sieve SBA-15 was applied for the oxidation of indole to 2-oxoindole using hydrogen peroxide or tert.-butyl hydroperoxide as oxidants. The performance of the immobilized enzyme was found to be superior to native chloroperoxidase with respect to maximum conversion and pH range applicable. However, immobilized CPO is still sensitive to high concentrations of hydrogen peroxide. The use of tert.-buty hydroperoxide is found to avoid this problem, but the reaction rate is significantly reduced.     

Model study of the crosslinking of polydimethylsiloxanes by peroxides

The decompositions of di-t-butyl peroxide (TBP) and diaroyl peroxides in permethylated silicone oil (47V20) have been studied by differential scanning calorimetry (DSC). Results show the importance of the solubility of the peroxide in the silicone on their rate of disappearance. For the diaroyl peroxides, according to the nature of the substituents on the phenyl ring and the concentration of the peroxide, the decomposition occurs in solution and/or in the solid phase. Decomposition in solution began at a lower temperature than in the solid phase, which took place immediately after melting and was quite instantaneous. Decomposition of these peroxides was also performed in octamethylcyclotetrasiloxane (D₄) and decamethyltetrasiloxane (DMTS). According to DSC results, D₄ seems to be a better model of the silicone than the linear one. Analyses of the products of the decomposition of TBP and dibenzoyl peroxide (BP) in this model showed that the dehydrodimer of D₄ was produced in low yield relative to peroxide. The main compounds obtained were high molecular weight compounds, which were apparently different for the two peroxides. The free radical origin of these products has been proven in the case of TBP by the addition of TEMPO in the reaction medium.     

Radical bulk polymerization of N-vinylcaprolactam

Bulk radical polymerization of N-vinylcaprolactam was studied at temperatures between 60 and 120°C. with different initiators. Satisfactory results were obtained with azobisisobutyronitrile, tert-butyl perbenzoate, and tert-butyl peroxide as initiators. The polymerization reaction of N-vinylcaprolactam with these initiators is first order with respect to the monomer and 0.5 order with respect to the initiator. A linearity of the kinetic curves up to high conversions was observed. The cause of this behavior is a feeble gel effect, which also induces an increase of the molecular weight during polymerization.     

Electrosynthesis and structural characterization of a novel aryl ether trimer

The structure of a novel trimer formed by three p-tert-butyl anisole moieties via the controlled potential electrolysis of p-tert-butyl anisole was determined by X-ray diffraction method. By cyclic voltammetry, we report a multistep electron transfer, each followed by a chemical reaction, resulting in an ECECEC mechanism. Preparative scale oxidation of p-tert-butyl anisole in dry acetonitrile leads to its two first oligomers. The symmetrical dimer, 2,2′-dimethoxy-5,5′-di-tert-butylbiphenyl, shows that the favored coupling sites are those in the ortho position of the methoxy group. The title compound, namely the 1-methoxy-bis-2,3-(2′-methoxy-5′-tert-butylphenyl)-4-tert-butylbenzene crystallizes in triclinic space group P-1 with a = 10.571(3) Å, b = 11.739(1) Å, c = 12.733(2) Å, α = 74.64(1)°, β = 88.71(2)°, γ = 76.58(2)°, V = 1480.8(5) Å³, and Z = 2. The structural analysis reveals that two p-tert-butyl anisole moieties are linked in ortho position on a third p-tert-butyl anisole fragment.     

Allyl functionalized telechelic linear polymer and star polymer via RAFT polymerization

Reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene using bisallyl trithiocarbonate as a chain transfer agent (CTA) was studied. The polymerization exhibited first-order kinetics and the molecular weight increased linearly with increase of monomer conversion. Well defined allyl-functionalized telechelic polystyrene (PS), poly(tert-butyl acrylate) (PtBA) and corresponding triblock copolymers, polystyrene-b-poly(n-butyl acrylate)-b-polystyrene (PS-b-PnBA-b-PS) and poly(tert-butyl acrylate)-b-polystyrene-b-poly(tert-butyl acrylate) (PtBA-b-PS-b-PtBA) were prepared as characterized with GPC and NMR analysis. The allyl-end groups of the telechelic PS have been switched to 1,2-dibromopropyl groups quantitatively by bromine addition reaction, further substitution of the bromide with azide was also made. Furthermore, star PS with allyl-end-functionalized arms was synthesized by RAFT polymerization of divinyl benzene using allyl-functionalized PS as a macro-CTA via arm-first approach. Star polymer with a thiol-functionalized core was generated by aminolysis reaction of the star polymer and ethylenediamine. As a result, difunctionalized star polymer with allyl and thiol groups was obtained and was used as a stabilizer for the formation of gold nanoparticles.     

Enhancement of MTBE photocatalytic degradation by modification of TiO2 with gold nanoparticles

The photocatalytic degradation of methyl tert-butyl ether by gold-modified TiO₂ has been studied by a combination of high resolution electron microscopy, X-ray photoelectron spectroscopy and reactor measurements. The optimum gold loading corresponded to a mean Au particle size of ⩽ 3 nm at which point the gold may no longer be metallic. Such catalysts exhibited a threefold rate enhancement compared to unmodified TiO₂, possibly due to injection of photo-excited electrons from semiconducting Au into the TiO₂ conduction band. Since the presence of dissolved oxygen was crucially important to good performance, it is possible that an additional factor was lowering of the local work function, thus promoting electron transfer to dioxygen molecules adsorbed at the Au/TiO₂ interface.     

Morphology of poly[(t-butyl acrylate)-b-styrene-b-isobutylene-b-styrene-b-(t-butyl acrylate)] pentablock terpolymers and their thermal conversion to the acrylic acid form

The morphology of a synthesized poly[(tert-butyl acrylate)-b-styrene-b-isobutylene-b-styrene-(tert-butyl acrylate)] pentablock terpolymer was determined using transmission electron microscopy, atomic force microscopy and small angle X-ray scattering methods. The outer blocks of this material were converted to the acrylic acid form by a thermal process that caused a beta-scission reaction in a simple thermal process, as verified by FTIR and NMR spectroscopies as well as thermogravimetric analysis. An initial heat-vacuum treatment induced a morphology that was more disordered relative to the precursor material, but when these samples were recast in THF solvent and annealed again, a considerably more refined and ordered morphology consisting of hexagonally packed cylinders resulted. This simple heat treatment allows for the tert-butyl groups to be converted to acrylic acid groups without dissolving the polymer or further sample cleaning. A dynamic mechanical investigation of the PtBuA form revealed three or two relaxation features depending interpretations based on the presence of three-phase morphology or a two-phase morphology in which there are mixed hard block domains.     

Synthesis of reactive copolymers with peroxide functionality for cross-linking water-soluble polymers

A series of reactive copolymers with peroxide functionality (RCPFs) were synthesized via radical copolymerization of monomer mixtures in an organic solvent comprised of a peroxide monomer 5-(tert-butyl peroxy)-5-methylhex-1-en-3-yne, acrylamide, maleic anhydride, and butyl methacrylate. Peroxide functionality allows the RCPFs to initiate a variety of radical processes, including cross-linking of organic polymers. Hydrophilic monomer subunits (acrylamide and maleic anhydride) within the RCPF macromolecules promote cross-linking of water-soluble polymers. We aimed to investigate RCPF comonomer ratio and its effects on copolymerization kinetics and composition, as well as physico-chemical and colloidal properties. We also evaluated and characterized the kinetic parameters of the thermal decomposition of peroxide moieties in the synthesized RCPF. Findings revealed that RCPF possessed surface-active properties and reduced surface tension at its aqueous solution–air interface. The data indicated that the decomposition process complied with the first-order kinetics, and complex thermal analysis confirmed the presence of peroxide moieties. RCPFs' ability to cross-link water-soluble polymers was demonstrated on poly(acrylamide) and poly(vinyl alcohol).     

Copolymerisation of ethylene and vinyl acetate under high pressure with a peroxide/triethylaluminium system

The present study was carried out to examine the effectiveness of an addition of triethylaluminium to tert-butyl perpivalate which is frequently used in industrial applications for initiating the copolymerisation of ethylene with vinyl acetate. For this purpose, polymerisation tests were carried out in the laboratory on a continuous basis at 1900 bar and 150°C. Vinyl acetate was added in concentrations of up to 36 wt.-% in the feed to the reactor. The organic peroxide concentration was 50 mole ppm; the concentration of organoaluminium alkyl was varied within the range of 0–75 mole ppm. The effects observed, namely an increase in the conversion and a decrease in the peroxide consumption were more marked than with the homopolymerisation of ethylene. This is attributable to the increased rate of chain growth in addition to the increased amount of radicals available. The properties of the copolymers obtained are changed only moderately by aluminium alkyl. Apart from a decrease in density and an increase in the melting point, a decrease in the polydispersity was observed.     

Amphiphilic poly(acrylic acid-b-styrene-b-isobutylene-b-styrene-b-acrylic acid) pentablock copolymers from a combination of quasiliving carbocationic and atom transfer radical polymerization

Amphiphilic poly(acrylic acid-b-styrene-b-isobutylene-b-styrene-b-acrylic acid) (PAA-PS-PIB-PS-PAA) block copolymers were prepared using a combination of quasiliving carbocationic and atom transfer radical polymerization (ATRP) techniques. Poly(styrene-b-isobutylene-b-styrene) (PS-PIB-PS) block copolymer macroinitiators with targeted molecular weights and high degrees of chain end functionality (F_n>1.7) were prepared by quasiliving carbocationic polymerization of isobutylene followed by sequential addition of styrene. Poly(tert-butyl acrylate-b-styrene-b-isobutylene-b-styrene-b-tert-butyl acrylate) (PtBA-PS-PIB-PS-PtBA) pentablock terpolymers with targeted molecular weights and low polydispersities (PDIs) were synthesized from the PS-PIB-PS macroinitiators via ATRP of tBA using either a Cu(I)Cl/1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) or Cu(I)Cl/tris[2-(dimethylamino)ethyl]amine (Me₆TREN) catalyst system. Deprotection of the tert-butyl groups using trifluoroacetic acid at 25 °C resulted in the formation of PAA-PS-PIB-PS-PAA pentablock terpolymers. Comonomer composition of the final terpolymers, determined by ¹H-NMR spectroscopy, was very close to theoretical.     

Hydrogen peroxide improving crystallinity of TiO2 nanoparticle in layer compound

TiO₂ nanoparticle in the pillared montmorillonite was crystallized to become anatase phase by treatment with aqueous hydrogen peroxide at room temperature without losing both the porous structure and the hydrophobicity of the pillared clay. The resulting pillared clay showed higher photocatalytic activity than the untreated pillared clay in degradation of di-n-butyl phthalate in water.     

Bioconversion process for synthesis of tert-butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate using liquid-core immobilized Saccharomyces cerevisiae CGMCC No 2233

Tert-butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate was synthesized using asymmetric reduction of tert-butyl (S)-6-chloro-5-hydroxy-3-oxo-hexanoate with liquid-core immobilized Saccharomyces cerevisiae CGMCC No. 2233. The optimum conditions for preparation of the liquid-core immobilized cells were found to be 2% guar gum, 5% CaCl₂, 0.8% sodium alginate, capsule diameter 2mm, 0.3% chitosan (1.0×10⁵) solution, and 30 min for formation of the film of liquid-core immobilized cells. The optimum re-cultivation time was 32 h. The optimum reduction conditions were found to be pH 6.8–7.2, 160 r/min, and 30 °C. Conversion was found to reach 100% when initial concentration of substrate was less than 50 g/L. The diastereomeric excess of tert-butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate exceeded 99%. The liquid-core immobilized cells retained their effectiveness even after 15 uses.