Showing papers on "Ether published in 1984"

Regioselective reductive ring-opening of 4-methoxybenzylidene acetals of hexopyranosides. Access to a novel protecting-group strategy. Part 1

Abstract: Reduction of fully protected 4,6-O-(4-methoxybenzylidene) hexopyranosides with sodium cyanoboro-hydride–trifluoroacetic acid in NN′-dimethylformamide, or trimethylsilyl chloride in acetonitrile, gives the 6- and 4-O-(4-methoxybenzyl) ethers, respectively, in good yield and good regioselectivity. The 4-methoxybenzyl ether linkage in products containing benzyl ethers or other protective groups is selectively cleaved upon treatment with cerium(IV) ammonium nitrate in aqueous acetonitrile.

Lignin-degrading enzyme from Phanerochaete chrysosporium

Abstract: The extracellular fluid of ligninolytic cultures of the white-rot wooddestroying fungus,Phanerochaete chrysosporium Burds., contains an enzyme that degrades lignin model compounds as well as lignin itself (1). Like ligninolytic activity, the enzyme appears during idiophasic metabolism, which is triggered by nitrogen starvation. The enzyme has been purified to homogeneity by DEAE-Biogel A chromatography, as assessed by SDS polyacrylamide gel electrophoresis, isoelectric focusing, and gel filtration chromatography. These techniques also revealed a molecular weight of 42,000 daltons, and an isoelectric point of 3.4. The purified enzyme exhibits low substrate specificity. It is an oxygenase, but requires hydrogen peroxide for activity. The activity is optimum at 0.15 mM H2O2; at concentrations above 0.5 mM, H2O2is inhibitory. Model compound studies have shown that the enzyme catalyzes cleavage between Cα and Cs in compounds of the type aryl-CαHOH—CsHR-(R = -aryl or -O-aryl), and in the Cα-hydroxyl-bearing propyl side chains of lignin. This cleavage produces an aromatic aldehyde moiety from the Cα-portion, and a Cs-hydroxylated moiety from the Cα-portion. Cleavage between Cα and Cs in arylglycerol-Β-aryl ether structures leads indirectly to cleavage of the Β-aryl ether linkage, which is the most abundant intermonomer linkage in lignin. The Cs-hydroxyl oxygen comes from molecular oxygen, and not from H2O2, as determined by18O isotope studies. The pH optimum for these reactions is between 2.5 and 3.0; no activity is observed above pH 5. Formation of the expected aldehydes from spruce and birch lignins, and partial depolymerization of the lignins results from the action of the purified enzyme. In addition to Cα—Cs cleavage, the enzyme catalyzes aromatic alcohol oxidation, aryl methylene oxidation, hydroxylation at Cα and Cs in models containing a Cα—Cs double bond, intradiol cleavage in phenylglycol structures, and phenol oxidations.

Absorption of some glycol ethers through human skin in vitro

Abstract: To assist evaluation of the hazards of skin contact with selected undiluted glycol ethers, their absorption across isolated human abdominal epidermis was measured in vitro. Epidermal membranes were set up in glass diffusion cells and, following an initial determination of permeability to tritiated water, excess undiluted glycol ether was applied to the outer surface for 8 hr. The appearance of glycol ether in an aqueous "receptor" phase bathing the underside of the epidermis was quantified by a gas chromatographic technique. A final determination of tritiated water permeability was compared with initial values to establish any irreversible alterations in epidermal barrier function induced by contact with the glycol ethers. 2-methoxyethanol (EM) was most readily absorbed (mean steady rate 2.82 mg/cm2/hr), and a relatively high absorption rate (1.17 mg/cm2/hr) was also apparent for 1-methoxypropan-2-ol (PM). There was a trend of reducing absorption rate with increasing molecular weight or reducing volatility for monoethylene glycol ethers (EM, 2.82 mg/cm2/hr; 2-ethoxyethanol, EE, 0.796 mg/cm2/hr; 2-butoxyethanol, EB, 0.198 mg/cm2/hr) and also within the diethylene glycol series: 2-(2-methoxyethoxy) ethanol (DM, 0.206 mg/cm2/hr); 2-(2-ethoxyethoxy) ethanol (DE, 0.125 mg/cm2/hr) and 2-(2-butoxyethoxy) ethanol (DB, 0.035 mg/cm2/hr). The rate of absorption of 2-ethoxyethyl acetate (EEAc) was similar to that of the parent alcohol, EE. Absorption rates of diethylene glycol ethers were slower than their corresponding monoethylene glycol equivalents. Combination of intrinsic toxicity and ability to pass across skin contribute to assessment of hazards of contact with undiluted glycol ethers.

Dimethylboron bromide and diphenylboron bromide: cleavage of acetals and ketals

Abstract: Reactivite des boranes du titre vis-a-vis du clivage d'acetals cycliques et acycliques, de cetals, de perhydropyrannyl- et perhydrofuryl ethers, de glycosides de methyle, d'acetonides, d'ethers de -methoxymethyle, -methoxyethoxymethyl et methylthiomethyle

Photochemistry of phosphate esters : an efficient method for the generation of electrophiles

Abstract: The photochemical cleavage of benzyl diethyl phosphates has been examined in tert-butyl alcohol, which produces the corresponding benzyl tert-butyl ether as the major solvolysis product upon direct irradiation. The multiplicity of the reactive excited state has been established as the singlet state

Experimental studies on toxicity of ethylene glycol alkyl ethers in Japan.

Abstract: Past studies on the toxicological effects of ethylene glycol alkyl ethers as well as the recent data on these chemicals in Japan are reviewed. Only a few researchers have participated in the study of ethylene glycol alkyl ethers in Japan. The effects of ethylene glycol alkyl ethers on testis and embryotoxic effects of ethylene glycol monomethyl ether (EGM) have been studied, as has the teratogenicity of ethylene glycol dimethyl ether (EGdM). Studies on ethylene glycol alkyl ethers and related compounds administered to mice by oral gavage revealed the occurrence of testicular atrophy and decreased white blood cell count by EGM, EGdM, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether and ethylene glycol monoethyl ether acetate, and the toxicity was related to their chemical structure. On the other hand, ethylene glycol, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monoacetate or ethylene glycol diacetate showed no such an effect. Studies on EGM using hamsters or guinea pigs revealed the occurrence of testicular atrophy similar to that observed in mice. In regard to the methyl ethers of other glycols, there is no convincing evidence that propylene glycol monomethyl ether, diethylene glycol monomethyl ether or diethylene glycol dimethyl ether causes testicular atrophy in mice. Teratological studies of EGM and EGdM revealed embryotoxic effects in mice.

Linoleate hydroperoxides are cleaved heterolytically into aldehydes by a Lewis acid in aprotic solvent.

Abstract: Treatment of isomeric methyl linoleate hydroperoxides with a Lewis acid, BF3, in anhydrous ether led to a carbon-to-oxygen rearrangement that caused cleavage into shorter-chain aldehydes. Methyl (9Z,11E)-13-hydroperoxy-9,11-octadecadienoate afforded mainly hexanal and methyl (E)-12-oxo-10-dodecenoate, whereas methyl (10E,12Z)-9-hydroperoxy-10,12-octadecadienoate cleaved into 2-nonenal and methyl 9-oxononanoate. The 2 aldehydes obtained from each hydroperoxide isomer were uncharacteristic of the complex volatile profile usually obtained by β-scission of oxy radicals derived from homolysis of the hydroperoxide group. Rather, the reaction resembled the one catalyzed by the plant enzyme, hydroperoxide lyase.

Optically anisotropic melt forming copolyesters

Abstract: Copolyesters useful for fibers from hydroquinone, hydroxybenzoic acid or 6-hydroxy-2-naphthoic acid, 3,4'-dicarboxydiphenyl ether and optionally isophthalic acid or resorcinol.

Synthesis and characterization of soluble aromatic polyazomethines from 2,5‐bis(4‐aminophenyl)‐3,4‐diphenylthiophene and aromatic dialdehydes

Abstract: New soluble aromatic polyamides with inherent viscosities of 1.0–1.7 dL/g were prepared by the low temperature solution polycondensation of 2,5-bis(4-aminophenyl)—3,4-diphenylthiophene, bis(4-aminophenyl) ether, and aromatic diacid chlorides in N,N-dimethylacetamide. The polyamides and copolyamides are generally soluble in amide-type solvents. They have glass transition temperatures in the range of 280–325°C and showed no weight loss below 390°C on thermogravimetry curves in both air and nitrogen atmospheres.

Review of glycol ether and glycol ether ester solvents used in the coating industry.

Abstract: Ethylene oxide-based glycol ether and glycol ether ester solvents have been used in the coatings industry for the past fifty years. Because of their excellent performance properties (evaporation ra...

Two stage process for improving the catalyst life of zeolites in the synthesis of lower olefins from alcohols and their ether derivatives

Abstract: A process for improving the catalyst life of zeolites employed in the conversion of alcohols (e.g. methanol) and/or their ether derivatives (e.g., dimethyl ether) wherein a suitable zeolite is modified in a 2-stage procedure by providing a controlled low amount of a coke precursor deposit on the external surface of the zeolite, and then heating this treated zeolite in an inert gas at specifically controlled temperatures for a minimum time is disclosed. A process of employing this modified zeolite to produce lower olefins is also disclosed.

Stability constants, enthalpies, and entropies for metal ion-lariat ether interactions in methanol solution

Abstract: Log K/sub n/, ..delta..H/sub n/, and T..delta..S/sub n/ values valid in CH/sub 3/OH at 25/sup 0/C have been determined for the interaction of Na/sup +/, K/sup +/, Cs/sup +/, and Ca/sup 2 +/ with 15-crown-5 and several lariat ethers. The lariat ethers studied are based on both 15-crown-5 and 18-crown-6 frameworks and contain various pendant arms extending from either carbon or nitrogen atoms on the crown framework. In comparable cases, enlarging the ring size from 15 to 18 members resulted in increased stability. The inclusion on the aza-15-crown-5 ring of a pendant arm bound to nitrogen and having an oxygen atom in the 3 position increases complex stability. The inclusion on the aza-15-crown-5 ring of a pendant arm bound to nitrogen and having an oxygen atom in the 3 position increases complex stability about ten-fold for Na/sup +/, K/sup +/, and Ca/sup 2 +/ compared to the crown ether with the same ring structure but lacking a heteroatom in the side arm. Generally, little effect on the log K/sub n/ value is found either by lengthening the pendant arm (and by including an additional donor atom) on the 18-crown-6 compounds or by appending pendant arms having oxygen atoms on themore » carbon pivot atom of the 15-crown-5 macrocycles. 25 references, 1 figure, 2 tables.« less

Process of presulfurizing catalysts for hydrocarbons treatment

Abstract: Catalysts for the treatment of hydrocarbons are presulfurized or presulfided ex-situ, in the absence of hydrogen, by means of a polysulfide of the general formula R--S.sub.(n) --R' wherein n is an interger from 3 to 20 and R and R' are each an organic radical having from 1 to 150 carbon atoms, R' being optionally a hydrogen atom, the so-presulfurized or presulfided catalysts being subsequently activated with hydrogen during their use in the hydrotreatment process of a hydrocarbon charge, i.e. in-situ. An aldehyde or an alcohol or a ketone, an ether or an organic acid, may be added, as promoter, to the polysulfide.

Regioselective reductive ring opening of 4-methoxybenzylidene acetals of hexopyranosides. Access to a novel protective group strategy

Abstract: Reduction of fully protected 4,6,-O-(4-methoxybenzylidene)hexopyranosides with sodium cyanoborohydride-trifluoracetic acid in N,N-dimethylformamide, or with trimethylsilyl chloride in acetonitrile, gives the 6-and 4-O-(4-methoxybenzyl) ethers, respectively, in good yields and with good regioselectivity; the 4-methoxybenzyl ether linkage in products containing benzyl ethers or other protective groups is selectively cleaved upon treatment with cerium(IV) ammonium nitrate in aqueous acetonitrile.