7,828 research outputs found
Halide- and base-free Wittig reaction: phosphonium methylcarbonate salts as ylide precursors
No full textMethylphosphonium methylcarbonate, ylide precursor for halyde- and base-free Wittig reactions
No full textThe phosphonium salt triphenylmethylphosphonium methylcarbonate [PΦ,Φ,Φ,1][OCOOCH3] was obtained by methylation of triphenylphosphine (Ph3P) with dimethylcarbonate, adopting a green and sustainable procedure1.
The [PΦ,Φ,Φ,1][OCOOCH3] phosphonium salt was observed to possess significant P-CH3 proton acidity, and deuterium exchange experiments showed the formation of the analogous PhP3-CD3 phosphonium salt. Spontaneous deprotonation of the methyl group lead therefore to formation of the corresponding phosphorus ylide, Ph3P=CH2.
This Ph3P=CH2 ylide was tested for the Wittig reaction with benzaldehyde PhCHO, generating the desired PhC=CH2 olefination product. It was noteworthy that this Wittig reaction protocol did not require an alkyl halide or a strong base for the formation of the ylide, and could be conducted in air, making it a greener procedure.
The scope of the olefination reaction was extended to a number of carbonyl substrates, both aldehydes and ketones, with high conversions and selectivity. It was performed under mild conditions (34 – 80 °C), using a ratio ylide:carbonyl between 1.0 -3.0, in 2-methyl tetrahydrofuran (2-Me-THF) as solvent.
The study was also extended to other alkylphosphonium methylcarbonate ionic liquids ([P8,8,8,1][OCOOCH3] and [P4,4,4,1][OCOOCH3]). It was demonstrated that, depending on the reaction conditions, it was possible to achieve not only the transfer of a =CH2 fragment, but also the selective transfer of the bulkier alkyl group e.g. =CH(CH2)nCH3, giving access to a variety of olefins. Cis-trans selectivity was in the range 20-80
Data for: Sensitivity test and ensemble hazard assessment for tephra fallout at Campi Flegrei, Italy
No full textEnsemble conditional Hazard Curves (cHC) for tephra load given an eruption at the Campi Flegrei caldera, considering the weighted ensemble of 5 models. The conditional Hazard Curves (cHC) are conditional upon an eruption, and more specifically, cHC are reported for: i) different levels of aggregation of the volcanic sources: Small explosive size, Medium explosive size, Large explosive size, and all sizes in all potential vents;ii) intensity thresholds 50, 100, 200, 300, ..., 3000 kg/m^2;iii) different statistics for the epistemic uncertainty: mean, median, 16th and 84th percentiles.For more details, see the linked paper: Selva J, Costa A, De Natale G, Di Vito MA, Isaia R, Macedonio G, "Sensitivity test and ensemble hazard assessment for tephra fallout at Campi Flegrei, Italy"
Le galle della Selva di Gallignano [The insect galls of the "Selva di Gallignano"]
No full textSome of the most common insect induced galls found in the "Selva di Gallignano" are reported. In particular: on Quercus spp. are described galls induced by Andricus quercustozae, A. kollari, A. dentimitratus, A. caputmedusae and Neuroterus quercusbaccarum; on Rosa canina galls of Diplolepsis rosae; on Salix spp. galls by Pontania proxima; on Ulmus minor leaf galls of Tetraneura ulmi; on Medicago sativa flower galls of Contarinia medicagins; on Fraxinus ornus leaf galls of Dasineura affinis; on Quercus ilex leaf galls of Dryomyia lichtensteini
Non Catalytic Continuous-Flow Transesterification of Dialkyl Carbonates with Glycerol Acetals
No full textTransesterificazione di carbonati organici con acetali del glicerolo in condizioni di flusso continuo
No full textAl Pla de la Selva (1.700 m.)
No full textBoExcursió del 21 al 24 de setembre de 1974. Itinerari: Port de Comiols (1.105 m.) – Santuari d’Arboló-Alins (1.048 m.) – Àreu (1.220 m.) – Pla de la Selva (1.700 m.) – Cabana de Boet (1.900 m.) – Estany de Sozllo (2.390 m.) – Estany d’Estats (2.500 m.) – Port de Sozllo (2.894 m.) – Refugi de Vall Ferrera (1.940 m.) – Pica Roja (2.902 m.) – Cabana de Boet – Pla de la Selva – Àre
Composición florística y estructura de bosque reservado de la universidad nacional agraria de la selva, en parcela permanente de medición, Tingo María - Perú
No full textEn los bosques tropicales, los árboles desarrollan estrategias de supervivencia,
así como el incremento y establecimiento de plántulas dentro de sus
poblaciones, motivo por el cual se realizó el estudio con el objetivo de
caracterizar la composición florística y determinar la diversidad del Bosque
Reservado de la UNAS, en parcela permanente de medición (PPM). Se instaló
un PPM de 100 m x 100 m en el Bosque Reservado de la Universidad Nacional
Agraria de la Selva (BRUNAS) ubicado en la región de Huánuco, provincia de
Leoncio Prado, distrito Rupa Rupa. Se evaluó fustales y árboles maduros
identificadas en el herbario HOXA Selva Central y las variables consideradas
fueron cualitativas (infestación de lianas, calidad de fustes y forma de copa) y
cuantitativas (altura, diámetro a la altura del pecho, abundancia, dominancia,
fecuencia, índice de valor de importancia, índice de homogeneidad, cobertura,
índice de Shannon-Wiener, índice de dominancia de Simpson). En los
resultados se determinó que el BRUNAS está conformado por Senefeldera
inclinata, Pourouma minor, Cedrelinga cateniformis, Otoba parvifolia, Hevea
guianensis, Dacryodes nitens, Cecropia sciadophylla, Osteophloeum
platyspermum, Schizocalyx peruvianus, Pseudolmedia laevis, Guatteria
guentheri, Tapirira guianensis y Theobroma subincanum. Además, la mayoría
de los individuos presentan fuste deformado, forma de copa buena, sin la
presencia de lianas y en dicha área en estudio las especies fueron equitativas.
Se concluye que el BRUNAS es un bosque heterogéneo estándo en proceso
de sucesión de bosque secundario a bosque primario.Tesi
Attilio Selva
No full textL'attività dello scultore Attilio Selva (1888-1970) fino al 1920 e i suoi rapporti con Federigo Tozzi
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