958 resultados para Organic products
Resumo:
Volatile organic compounds (VOCs) have a great influence on tropospheric chemistry; they affect ozone formation and they or their reaction products are able to take part in secondary organic aerosol formation; some of the VOCs are themselves toxic. Knowing the concentrations and sources of different reactive volatile organic compounds is essential for the development of ozone control strategies and for studies of secondary organic aerosol formation. The objective of this work was to study volatile organic compounds in urban air, develop and validate determination methods for them, characterize their concentrations and estimate the contributions of different VOC sources. Of the different compound groups detected in the urban air of Helsinki, alkanes were found to have the highest concentrations, but when the concentrations were scaled against the reactivity with hydroxyl radicals (OH), aromatic hydrocarbons and alkenes were found to have the greatest effect on local chemistry. Comparisons with rural sites showed that concentrations at Utö and Hyytiälä were generally lower than those in Helsinki, especially for the alkenes and aromatic hydrocarbons, but concentrations of halogenated hydrocarbons at Utö and carbonyls at Hyytiälä were at the same level as in Helsinki. Most halogenated hydrocarbons do not have any significant sources in Helsinki, and carbonyls are formed in the atmosphere in the reactions of other VOCs, and are therefore also produced in other than urban areas. At Hyytiälä carbonyls were found to have an important role in the local chemistry. The contribution of carbonyls as an OH sink was higher than that of the monoterpenes and aromatic hydrocarbons. Based on the emission profile and concentration measurements, the contributions of different sources were estimated at urban (Helsinki) and residential (Järvenpää) sites using a chemical mass balance (CMB) receptor model. It was shown that it is possible to apply CMB in the case of a large number of different compounds with different properties. According to the CMB analysis, the major sources for these VOCs in Helsinki were traffic and distant sources. At the residential site in Järvenpää, the contribution due to traffic was minor, while distant sources, liquid gasoline and wood combustion made higher contributions. It was also shown that wood combustion can be an important source at some locations of VOCs usually considered as traffic-related compounds (e.g., benzene).
Resumo:
Syntheses of the isomers of the C11 acid, 1(a),3(a)- dimethylcyclohexane-1 (e),2(e),3(e)-tricarboxylic acid (A) and 1(a),3(e)-dimethylcyclohexane-1(e),2(e),3(a)-tricarboxylic acid (B), the latter by two different routes, are reported. Two of the four possible isomers of the precursor triester, trimethyl 1-methylcyclohexane-1,2,3-tricarboxylate, on individual methylation followed by hydrolysis, gave the trans,meso-acid (A), identified by comparison with an authentic sample, and the cis,trans-form (B) whose structure and configuration were proved by comparison with a specimen obtained by the unambiguous and highly stereoselective second synthesis. This demonstrated that methylation of the triester isomers occurs stereospecifically and exclusively at C-3. In the second sequence, it has been possible to assign definite conformations to four key intermediates and the final product, directly from n.m.r. spectra, from changes in these spectra accompanying specific steps, and from chemical evidence. Comparison of the n.m.r. spectra of the isomeric triesters (A) and (B) has provided unequivocal proof of the accepted trans,meso configuration for the abietic acid degradation product (A).
Resumo:
A one-step synthesis of (IIb), an isomerization product of 7-methoxychromano3,4-disoxazole, from (III) is reported.
Resumo:
Peroxydisulfuric acid oxidation of testosterone propionate, progesterone, and cholest-4-en-3-one has been shown to yield 3-oxo-17β-hydroxy-4-oxa-5α-androstane (I, after saponification), 3,20-dioxo-4-oxa-5α-pregnane (V) and 3-oxo-4-oxa-5α-cholestane (VII) respectively. Boron trifluoride etherate-lithium aluminum hydride reduction of δ-lactones I, V, and VII led to the corresponding tetrahydropyran derivatives (IIb, VIa, and VIII). Similar reduction of 3β-hydroxy-17-oxo-17a-oxa-D-homo-5α-androstane (XI) gave 3β-hydroxy-17a-oxa-D-homo-5α-androstane (XIIa). Diborane-boron trifluoride etherate was also found to reduce lactones to cyclic ethers, while reduction with diborane gave hemiacetals. Evidence in support of the structures and stereochemistry assigned to the lactones and their unusual reduction products has been summarized. A tentative mechanism is proposed for lactone → ether reduction employing diborane-boron trifluoride etherate.
Resumo:
Reduction of smilagenin acetate (Va) using a boron trifluoride etherate-lithium aluminum hydride reagent, followed by hydrogen peroxide oxidation and acetylation, was found to yield: 3β-ethoxysmilagenin (Vb), 3β-ethoxydihydrosmilagenin acetate (VIa), dihydrosmilagenin diacetate (VIb), and a complex mixture of partially acetylated products. Similar reaction conditions were employed to convert dihydrodiosgenin (II) to dihydrochlorogenin (III). Boron trifluoride etherate-lithium aluminum hydride reduction of 3β-acetoxy-5α-cholestane and 3β-acetoxy-5α-lanostane (VIIIa) was shown to yield the corresponding 3β-ethoxy (e.g., VIIIb) derivatives.
Resumo:
Molybdenum-doped TiO2 organic-inorganic hybrid nanoparticles were synthesized under mild hydrothermal conditions by in situ surface modification using n-butylamine. This was carried out at 150 degrees C at autogeneous pressure over 18 h. n-Butylamine was selected as a surfactant since it produced nanoparticles of the desired size and shape. The products were characterized using powder X-ray diffraction, Fourier transform infrared spectrometry, dynamic light-scattering spectroscopy, UV-Vis spectroscopy and transmission electron microscopy. Chemical oxygen demand was estimated in order to determine the photodegradation efficiency of the molybdenum-doped TiO2 hybrid nanoparticles in the treatment of pharmaceutical effluents. It was found that molybdenum-doped TiO2 hybrid nanoparticles showed higher photocatalytic efficiency than untreated TiO2 nanoparticles.
Resumo:
A synthetic approach toward the geranylated PPAP natural products, prolifenones A and B. employing Effenberger cyclization as the key step, is delineated. The efficacy of this approach is further expanded through access to an advanced precursor of hyperforin. (C) 2010 Elsevier Ltd. All rights reserved.
Resumo:
Potassamide induced in situ alkylation of 1-alkyl- 4-cyano-3-methoxy-5,6-dihydroisoquinolines (2a & 2b) with alkyl iodides (CH3I, CH3CH2I & cyclohexyl iodide) gave the 5-alkyl- and 5,9-dialkyl-5,6-dihydroisoquinolines (4–ad & 3a–e), isoquinoline derivatives, (5a–b) and diastereomeric mixture of 4- alkyl-1,2,3,4-tetrahydroisoquinolin-3(2H)-ones (6a–e & 6′a–e). Structures were assigned on the basis of spectral data [Mass, 1H & 13C NMR, 2D NOESY & HC-COLOC]. Amide induced in situ alkylation of compounds 3a and 4a with CH3I gave in almost quantitative yield the dimethylated compounds 3d and 3a respectively. While KNH2/liq.NH3 methylation of 1,2- dihydroisoquinoline, 1 with CH3I gave the mixture of compounds, 6a & 6′a and the isoquinoline derivative 5a, NaH/benzene reaction of 1 with CH3I gave exclusively 5a. N-methylation of the mixture of compounds 6a & 6′a with NaH/CH3I gave the methylated derivatives, 7 & 8. A suitable mechanism has been proposed for the formation of products.
Resumo:
A mechanism involving the intermediacy of nitrene 5, formed from the oxime of spironaphthalenone 1 by acid catalysed dehydration, has been proposed to explain the formation of pyrrolotropones/pyrrolo esters from spironaphthalenones. The initially formed nitrene rearranges to the isopyrrole 6, which either undergoes sigmatropic migration to the pyrrolotropone 2 or adds alcohol to form the pyrrolo ester depending on substitution at 1′ position. The isopyrrole intermediate 6 has been trapped as a Diels-Alder adduct 8.
Resumo:
We present a simple template-free method for the synthesis of interconnected hierarchical porous palladium nanostructures by controlling the aggregation of nanoparticles in organic media. The interaction between the nanoparticles is tuned by varying the dielectric constant of the medium consistent with DLVO calculations. The reaction products range from discrete nanoparticles to compact porous clusters with large specific surface areas. The nanoclusters exhibit hierarchical porosity and are found to exhibit excellent activity towards the reduction of 4-nitrophenol into 4-aminophenol and hydrogen oxidation. The method opens up possibilities for synthesizing porous clusters of other functional inorganics in organic media.