Dimetildioxirano. 1. Oxidação de compostos de enxofre

A brief review of the chemistry of dimethyldioxirane is presented. This article specifically foccus on the preparation of dimethyldioxirane, its chemical reactivity, and specially on the oxidation of sulfur compounds.

Síntese e caracterização de compostos organometálicos de estanho (IV)

Organotin(IV) derivatives containing bulky R groups have been synthesized and characterized. It is discussed how their syntheses depend on the reaction conditions, such as stoichiometry of starting materials, bulkiness of the organo group attached to the Sn centre as well as temperature in which the reaction is carried out. Finally the molecular structure of Sn2Ph6, determined by X-ray diffraction is reviewed.

Componentes voláteis do café torrado. Parte I: compostos heterocíclicos

A review of heterocyclic compounds in roasted coffee is presented. The contents, precursors and sensorial properties of furans, pyrroles, oxazoles, thiazoles, thiophenes, pyrazines and pyridines are discussed. The impact heterocyclic compounds of coffee aroma are described.

Compostos fosfatados ricos em energia

The chemical and biological properties of energy-rich phosphate compounds, e.g. ATP and acetyl phosphate, were revised. The role of water in the formation of this class of energy-rich compounds in biological systems is also discussed.

Reações de Diels-Alder entre compostos carbonílicos a,b-insaturados e ciclopentadieno

We review herewith the use of solids such as activated alumina and other modern Lewis acid catalysts, as well as the influence of different solvents, including water, on the title reactions, described in the last seven years.

Presença de compostos carbonílicos no ar em ambientes internos na cidade de São Paulo

The presence of low carbonyl compounds (C1-C4) and glutaraldehyde was observed in 14 work-locations in São Paulo city, Brazil, during January to July 1997 period. The quantification of other carbonyls was not possible due to a sampling artifact caused probably by undesirable reactions between the ambient ozone and the organic substract of C18 cartridge used to collect carbonyls. High indoor concentrations, compared to outdoor levels, were observed for all compounds. Formaldehyde was the most abundant species (29 ppb) followed by acetone and acetaldehyde (25 and 17 ppb) with a small contribution of propanal, crotonaldehyde and C4 isomers (0.7 to 1.5 ppb) when related to the total indoor carbonyls level. Glutaraldehyde was observed only in two different occupational locations in a hospital at high concentrations (121 ppb). In general, high individual carbonyl levels as well as total carbonyls levels found in several locations indicated an unpropitious air quality for the occupants of these non-industrial sites.

7-Epiclusianona, a nova benzofenona tetraprenilada e outros constituintes químicos dos frutos de Rheedia gardneriana

Phytochemical investigation of the fruits of Rheedia gardneriana led to the isolation of sesquiterpenes mixture, methyl esters of fatty acids (palmitate, estearate, oleate, linoleate, linolenate), sugars (galactose, glucose, fructose), triterpene (oleanolic acid), steroids mixture (stigmasterol and sitosterol) and the new tetraprenylated benzophenone 7-epiclusianone.

Sobre os nomes dos elementos químicos, inclusive dos transférmios

The names of the chemical elements in Brazilian portuguese are presented, including a discussion of corresponding Brazilian nomenclature rules and translation of some parts of the pertinent IUPAC rules. The rules for naming groups of elements in the periodic table, as well as those for the symbolic indication of atomic number, mass number and electric charge of atoms, are also presented.

Reações de inserção intramolecular de diazo compostos polifuncionais catalisadas por ródio(II): síntese de oxetan-3-ona-2-carboxilato e outros heterociclos funcionalizados

gamma-Hydroxy-alpha-diazo-beta-ketoesters are key intermediates in the chemistry of penicilin-based antibiotics and natural products. The method developed here for the synthesis of ethyl 2-diazo-4-hydroxy-3-oxo-butanoate 17 (in two steps from the diazo mercurial 2) compares very favorably with those reported in the literature for similar compounds. The Rh2(OAc)4-mediated intramolecular OH-insertion reaction of the diazo hydroxy ester 17 was investigated, furnishing the oxetan-3-one-2-carboxilate 18 in good yield. When the diazo ester lacks a free hydroxyl group as in the case of the phenoxy diazo ester 11 an intramolecular CH-insertion takes place, affording the 2H-chromene 20 in almost quantitative yield. The behavior of other functionalized diazo esters towards Rh2(OAc)4 was also investigated.

Constituintes químicos das raízes de Pyrostegia Venusta e considerações sobre a sua importância medicinal

This paper describes the chemical constituents isolated from roots of Pyrostegia venusta. From ethanol extract of the roots allantoin, beta-sitosterol, 3b-O-beta-D-glupyranosylsitosterol and hesperedin were isolated. The structures of these natural products were identified on the basis of spectral data, including 2D NMR of the peracetyl derivative of hesperidin.

Extração e pré-concentração de compostos orgânicos voláteis por permeação em membrana para análise cromatográfica

This work discusses sample preparation processes for gas chromatography (GC) based on the technique of extraction through membrane permeation (MPE). The MPE technique may be easily coupled to GC via a relatively simple device, which is a module that holds the membrane and is directly connected to the GC column. The possibility of operational errors due to sample handling is substantially reduced in an MPE-GC system because the sample preparation and the chemical analysis are accomplished as a one-step process. The MPE technique is of relatively wide application as it can be used for aqueous samples, solid samples and gaseous samples. Depending on the type of sample the extraction is performed with the membrane in direct contact with the sample or in contact with its headspace. The MPE-GC technique is very useful in trace analysis, due to the time-dependent enrichment of the analyte. A typical application of MPE-GC is the analysis of VOCs present in water that may be accomplished with detection limits at the low ppb (mugL-1) level.

Estudo de alguns compostos organolantanídeos: [LnCp2Cl.PPh3]

In this work we present the synthesis and characterization of some organolanthanide compounds [LnCp2Cl.PPh3], Ln = La, Nd, Eu, Yb and Lu. The catalytic activity of these compounds has been verified in cyclohexene hydrogenation. Cyclohexane was identified by¹H NMR analysis in the reaction products.

Componentes voláteis do café torrado. Parte II. Compostos alifáticos, alicíclicos e aromáticos

This review is about the aliphatic, alicyclic and aromatic compounds (non-heterocyclic compounds) that are present in the volatile fractions of roasted coffees. Herein, the contents, aroma precursors and the sensorial properties of volatile phenols, aldehydes, ketones, alcohols, ethers, hydrocarbons, carboxylic acids, anhydrides, esters, lactones, amines and sulphur compounds are discussed. Special attention is given to the compounds of these groups that are actually important to the final aroma of roasted coffees.

RMN 2D: Detecção inversa e gradiente de campo na determinação estrutural de compostos orgânicos

A view of the general aspects involving the 2D NMR spectroscopy using inverse detection and field gradient techniques is presented through the analysis of a sesquiterpene.

Separação e identificação de constituintes químicos polares dos galhos de Porcelia Macrocarpa

This paper describes a methodology to separate and identify polar compounds as flavonoid and lignan glucosides, amino acids, salt of quaternary ammonium amino acid and carbohydrates from branches of Porcelia macrocarpa (Annonaceae).