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[en] In this work, we tested the applicability of several methyl substituted benzyl groups as an alternative to the methyl group for the protection of the hydroxyl groups in the nucleophilic aromatic radiofluorination. As a model synthesis, the no-carrier-added (n.c.a.) preparation of 2-[18F]fluoro-3-hydroxy-6-methylpyridine from O-protected 3-hydroxy-6-methyl-2-nitropyridine was chosen. Conditions for acidolytic and hydrogenolytic cleavage of heteroaryl esters were studied. Among various protecting groups tested, 4-methylbenzyl and 2,4-dimethylbenzyl groups proved to be the best by resulting in about 70% yields of [18F]-labelled product after hydrolysis with 32% HCl at 120 deg C for 10 min. Furthermore, 4-methylbenzyl ester cleaved readily under catalytic transfer hydrogenation condition using ammonium formate and 10% Pd/C in boiling methanol to give 2-[18F]fluoro-3-hydroxy-6-methylpyridine in radiochemical yield of 75% within a reaction time of 10 min. Conditions for the cleavage of both 4-methylbenzyl and 2,4-dimethylbenzyl esters are well suited for the implementation into an automated synthesis module. (author)
[en] In this study, a nation-wide field measurement has been carried out in Chinese residence to obtain BTEX(benzene series) concentration levels and characteristics. Concentrations of benzene series (benzene, toluene, xylene and ethylbenzene) indoor were sampled in 223 dwellings covering 5 climate zones in China during 2016.12-2017.12. The arithmetic mean concentrations of benzene, toluene, xylene and ethylbenzene were 6.78μg/m3, 17^g/m3, 17.68μg/m3 and 9.87μg/m3, respectively. Higher concentration of BTEX and higher standard limit were founded in China than that in other countries and organizations. We identify some reasonable sources for specific data group, impact factors on decoration year, frequency of smoking and cooking of benzene series concentration were studied. Toluene concentration decreased with increase of decoration year, and concentration of benzene concentration in smoking families were higher than that in non-smoking families. No direct correlation between cooking frequency and indoor benzene concentration were founded. This study also provided statistical data on benzene exposure in new decorated residences and a discussion on setting limit values for standard. (paper)
[en] A semicontinuous slurry-microcosm method was applied to mimic trichloroethylene (TCE) cometabolic biodegradation field results at the Que-Jen in-situ pilot study. The microcosm study confirmed the process of aerobic cometabolism of TCE using toluene as the primary substrate. Based on the nucleotide sequence of 16S rRNA genes, the toluene-oxidizing bacteria in microcosms were identified, i.e. Ralstonia sp. P-10 and Pseudomonasputida. The first-order constant of TCE-degradation rate was 0.5 day-1 for both Ralstonia sp. P-10 and P.putida. The TCE cometabolic-biodegradation efficiency measured from the slurry microcosms was 46%, which appeared pessimistic compared to over 90% observed from the in-situ pilot study. The difference in the TCE cometabolic-biodegradation efficiency was likely due to the reactor configurations and the effective time duration of toluene presence in laboratory microcosms (1 days) versus in-situ pilot study (3 days). The results of microcosm experiments using different toluene-injection schedules supported the hypothesis. With a given amount of toluene injection, it is recommended to maximize the effective time duration of toluene presence in reactor design for TCE cometabolic degradation
[en] Energy flow and C-Hmethyl and C-Hring bond dissociations in vibrationally excited toluene in the collision with N2 and O2 have been studied by use of classical trajectory procedures. The energy lost by the vibrationally excited toluene upon collision is not large and it increases slowly with increasing total vibrational energy content between 5,000 and 45,000 cm-1. Intermolecular energy transfer occurs via both of V-T and V-V transfers. Both of V-T and V-V transfers increase as the total vibrational energy of toluene increases. When the total energy content ET of toluene is sufficiently high, either C-H bond can dissociate. The C-Hmethyl dissociation probability is higher than the C-Hring dissociation probability, and that in the collision with N2 is larger than with O2
[en] Full text:There has been carried out direct metallization of toluene and isotropy benzene with alkali metals. It has been established, that alkali metal is substituted only for benzyl hydrogen. It is shown that in contrast to alkyl aromatic hydrocarbons with tertiary benzyl hydrocarbon at direct metallization of toluene and further treatment of reaction mixture consecutively by artificial ice water and concentrated HCI phenyl melon acid is generated
[en] Recently we have reported on the α-iodination reaction of some cyclic enaminones.1 The required cyclic enaminones have been synthesized by the reaction of cyclohexane-1,3- dione and amines such as aniline in the presence of ptoluenesulfonic acid as the catalyst.2 During the reaction small amounts of cyclic vinamidinium salt was isolated. From the reaction mixture we could not find and isolate any salt-free vinamidine itself. Elimination of p-toluenesulfonic acid from the salt could be carried out by treatment with triethylamine to afford the cyclic vinamidine (vide infra). The synthesis of vinamidine in a direct method in high yield could not be achieved with excess use of aniline (up to 5 equiv.). The failure might be arisen from the basic nature of vinamidine, which trap the acid catalyst and presented as its salt, namely vinamidinium salt. Electronic interactions between p-donor atoms (saturated nitrogen atom in this case) and π-acceptor groups (imino group in this case) through an intervening carbon-carbon double bond make vinamidine as a strong base.
[en] Trans fats, unsaturated fatty acids with at least one double bond in the trans configuration, have received a great amount of attention in the field of oleo chemistry and safety. In this work, the cis-trans isomerization of unsaturated fatty acids in edible oils has been successfully developed using simple and cheap p-toluenesulfinic acid as catalyst. The effects of reaction time, temperature, catalyst loading, and the amounts of water and antioxidants on the cis-trans isomerization have been systematically investigated. The results indicate that the amount of water (0–20 wt %) and antioxidants (0–200 mg/kg) had no significant effect on this cis-trans isomerization of unsaturated fatty acids in edible oils. The final products (trans fats) from the cis-trans isomerization reaction were characterized by both GC and React IR. The yield of trans double bonds from the isomerized fat can reach 79.6% after heating at 100 oC for 90 min without changing either the location of the double bonds or the degree of unsaturation. In addition, this convenient method has been applied to various vegetable oils (e.g., olive oil, camellia seed oil, corn oil, sesame oil, sunflower oil and soybean oil) and nearly 80.0% yields of TFA were generated, which shows a promising method to provide trans-fat products for research related to oleo and food chemistry.
[es]Las grasas trans, ácidos grasos insaturados con al menos un doble enlace en la configuración trans, han recibido muchas atenciones en oleoquímica y seguridad. En este trabajo, se ha llevado a cabo con éxito la isomerización cis-trans de ácidos grasos insaturados en aceites comestibles usando mediante un método simple y barato utilizando ácido p-toluenosulfínico como catalizador. Los efectos del tiempo de reacción, la temperatura, la carga del catalizador, la cantidad de agua y los antioxidantes en la isomerización cis-trans se han investigado sistemáticamente. Los resultados indicaron que la cantidad de agua (0–20% en peso) y antioxidante (0–200 mg/ kg) no tuvo un efecto significativo sobre la isomerización cis-trans. Los productos finales (grasas trans) de la reacción de isomerización cis-trans se caracterizaron por GC y React IR. El rendimiento en dobles enlaces trans de la manteca isomerizada puede alcanzar el 79,6% tras calentar a 100 ºC durante 90 minutos sin cambiar tanto la posición de los dobles enlaces como el grado de insaturación. Además, este método tan útil se ha aplicado a diferentes aceites vegetales (por ejemplo, oliva, semilla de camelia, maíz, sésamo, girasol y soja) y casi se forma alrededor del 80.0% de ácidos grasos trans, lo que demuestra ser un método prometedor para proporcionar productos grasos trans para investigaciones relacionadas en la química del aceite y los alimentos.
[en] A novel compound, 6,6'-(butane-1,1-diyl)bis(4-methylbenzene-1,2-diol) (BMB), was synthesized through an acid-catalyzed condensation reaction between 4-methylcatechol (HPC) and butyraldehyde. When evaluated by the Rancimat and deep frying methods, BMB exhibited a stronger antioxidant activity than TBHQ. Its DPPH radical scavenging activity was also fairly higher than TBHQ, but lower compared to its mother phenol, HPC, due to its relative ease of binding DPPH•. BMB had the strongest scavenging ability of the 4-methylcatechol analogues reported to date. It could be used effectively to retard lipid peroxidation in both moderate and high temperature food preparations.
[es]Un nuevo compuesto, 6,6'-(butano-1,1-diil)bis(4-metilbenceno-1,2-diol) (BMB) fue sintetizado mediante una reacción de condensación catalizada por ácido entre el 4-metilcatecol (HPC) y el butiraldehído. Cuando se evaluó mediante los métodos Rancimat y de fritura, el BMB mostró una actividad antioxidante más fuerte que el TBHQ. Su actividad de eliminación de radicales DPPH también fue bastante mayor que la del TBHQ, pero menor en comparación con el fenol de partida, HPC, debido a su relativa facilidad para unirse a DPPH• .BMB tiene una actividad de eliminación más fuerte que los análogos de 4-metilcatecol reportados hasta la fecha. Podría usarse eficazmente para retardar la peroxidación de lípidos en la preparación de alimentos a temperatura moderada y alta.