Cu(I) catalysed cyclopropanation of olefins: Stereoselectivity studies with Arylid-Box and Isbut-Box ligands

In our quest to find new ligands for highly stereoselective reactions, we tested a variety of chiral non-racemic pseudo-C₂ symmetric bis-oxazolines derived from malonic acid containing an arylidene bridge unit (and appropriately termed Arylid-Box) in the catalytic asymmetric cyclopropanation (CAP) reaction of styrene and ethyl diazoacetate using between only 1-2 mol% of a Cu(I) pre-catalyst. Some very good e.e.s (up to 86%), were obtained. It was possible to isolate 10a′-[Cu(CH₃CN)₄]PF₆ which existed as a bench stable solid that proved to be more efficient than the catalyst prepared in situ. Cu(I) pre-catalysts were used for the first time in the CAP reaction with the Isbut-Box ligands 13a and 13b and, although, the e.e.s were better for ligand 13a using these pre-catalysts, in the case of ligand 11b this was not the case. Spectroscopic studies (UV-Vis and ¹H NMR) were carried out to gain an insight into the nature of the catalytic species at work so that the conditions could be optimised giving better results. Some theoretical studies were conducted to try to explain the better enantioselectivities obtained using Evans’ tert-Box-Cu(I) complex over our complex.     

Determination of citric acid in soft drinks using flow injection with potentiometric detection

A flow injection analysis (FIA) system with potentiometric detection has been developed for the determination of citric acid in commercial fruit juices using a copper-selective tubular electrode. It consists of the complexation of citrate ion with copper (II) ion, monitoring the free copper (II) concentration. Linear relationships between the potential and log concentrations of citric acid in the range of 1 × 10^–3 mol/L – 1 × 10^–2 mol/L were attained with samples injected in the system without prior treatment. Repeatability was determined by assessing the relative standard deviation for ten replicate injections of different juice samples which varied from 1.2% to 3.0%. The results provided by the automated system were compared with those of an enzymatic conventional method used for the analysis of citric acid in food and a relative deviation of less than 4.0% was found. Recovery trials resulted in values from 97.0% to 101.0%. The system allows a sampling frequency of 60 samples/h.     

Exact master equation for a noncommutative Brownian particle

We derive the Hu-Paz-Zhang master equation for a Brownian particle linearly coupled to a bath of harmonic oscillators on the plane with spatial noncommutativity. The results obtained are exact to all orders in the noncommutative parameter. As a by-product we derive some miscellaneous results such as the equilibrium Wigner distribution for the reservoir of noncommutative oscillators, the weak coupling limit of the master equation and a set of sufficient conditions for strict purity decrease of the Brownian particle. Finally, we consider a high-temperature Ohmic model and obtain an estimate for the time scale of the transition from noncommutative to ordinary quantum mechanics. This scale is considerably smaller than the decoherence scale.     

Synthesis and Characterization of Polymeric Materials from Vegetable Oils

Although the petrochemical polymers have revolutionized the technological development, the intensive use of these materials have contributed to the global pollution. In this context, researches involving ecofriendliness materials are growing up, as well as, a current interest in developing materials from inexpensive and renewable resources, such as vegetable oils. In this work, is described the synthesis of polymeric materials by thermal polymerization from linseed oil (Linum usitatissimum L.) and passion fruit oil (Passiflora edulis) and their characterization by gas chromatographic (GC), Fourier transform infrared (FTIR) spectroscopy, solubility in organic solvents, thermogravimetry (TG), differential scanning calorimetry (DSC) and Raman spectroscopy. The TG curve shows that those polymeric materials present two stages of decomposition. DSC plots of the vegetable oils showed some endothermic and exothermic transitions which are not present in the DSC curves corresponding to oil-based polymers. The Raman spectra of the polymers indicate declining of absorbance in the region of CC stretching (∼1600 cm⁻¹). This absorption was used to estimate the degree of polymerization (79% and 67.5% for linseed and passion fruit oils, respectively).     

Influence of physical-chemical interactions on the thermal stability and surface properties of poly(vinyl chloride)-b-poly(hydroxypropyl acrylate)-b-poly(vinyl chloride) block copolymers

The synthesis of poly(vinyl chloride) (PVC) homopolymers and poly(vinyl chloride)-b-poly(hydroxypropyl acrylate)-b-poly(vinyl chloride) (PVC-b-PHPA-b-PVC) block copolymers via a single electron - degenerative transfer mediated living radical polymerisation was carried out on a pilot scale in industrial facilities. The thermal stability of the products was assessed conductimetrically. The block copolymers, that contained a low content of PHPA (below 12 wt.%), showed thermal stability that was approximately three times greater than that of conventional PVC. Inverse gas chromatography study of the copolymers surface showed that there was a decrease in the dispersive component and greater Lewis acidity and basicity constants were observed relative to those of PVC. The thermal stabilisation of PVC when in the presence of PHPA is explained by the interactions between its functional groups and the structures formed during the thermal degradation. The thermal stability and the surface properties of PVC-b-PHPA-b-PVC were strongly dependent on the molecular weight of the block copolymer. Lewis acid-base interaction parameters were determined and are interpreted as evidence of the PVC-b-PHPA-b-PVC compatibilising function in PVC-wood flour composites.     

Identification of alkyl carbazoles and alkyl benzocarbazoles in Brazilian petroleum derivatives

The present work describes (a) the identification and characterization of an impurity, 2,4,5,7-tetrabromo-6-hydroxy-9-(2,3,4,5-tetrachlorophenyl)-3H-xanthen-3-one (BCPX), in the color additives D&C Red Nos. 27 and 28 (phloxine B) and (b) the determination of the extent and level of BCPX contamination in certified lots of these colors. For these purposes, BCPX (a compound not previously reported in the literature) was synthetically prepared. Test portions from 42 certified lots of D&C Red Nos. 27, 28 and 27 lakes were analyzed for BCPX using an HPLC method that included gradient elution and UV-vis photodiode array detection. Those lots were submitted for certification by both domestic (six) and foreign (six) manufacturers during the past 4 years. Of the test portions analyzed, 32 (76.2%) contained BCPX in amounts ranging from 0.01 to 3.21%. The remaining 10 test portions (23.8%) contained no detectable BCPX or less than 0.008%, which is the limit of quantification for the present method. The analyses revealed substantial differences in the level of BCPX across different manufacturers. The wide range of BCPX levels found in the analyzed lots suggests that the presence of BCPX in D&C Red Nos. 27 and 28 may be avoided or significantly reduced during the manufacturing process.     

The Stille reaction in the synthesis of the C37-norcarotenoid butenolide pyrrhoxanthin. Scope and limitations

The sequential Stille cross-coupling reactions of the dihalogenated gamma-alkylidenebutenolide 7 with stannanes 9 and 6 afforded the carbon skeleton of pyrrhoxanthin, a highly functionalized C7'-C8' acetylenic C37-norcarotenoid butenolide. Although the first halogen-selective Stille coupling takes place in 90% yield at ambient temperature, double isomerization of the Z,E- to the E,Z-C7'-C10' enyne, likely induced by the catalyst, accompanyied the bond formation, leading to 9'Z-20 and, ultimately, to 9'Z-pyrrhoxanthin 9'Z-1.     

Four-component assembly of chiral N-B heterocycles with a natural product-like framework

The dative N-B bond was used to simply assemble heterocycles with a skeleton akin to the 5-oxofuro[2,3-b]furan motif. Twenty-five new N-B heterocycles were prepared via a highly efficient one-pot four-component reaction in yields and diastereoselectivities up to 95% and >97%, respectively. Several reaction intermediates were discovered using electrospray ionization mass spectroscopy which set the basis for the mechanism elucidation using DFT calculations.     

Microwave-assisted headspace solid-phase microextraction to quantify polycyclic aromatic hydrocarbons in pine trees

A methodology for the extraction and quantification of 16 polycyclic aromatic hydrocarbons (PAHs) based on microwave-assisted extraction coupled with headspace solid-phase microextraction followed by gas chromatography/mass spectroscopy was validated for needles and bark of two pine species (Pinus pinaster Ait. and Pinus pinea L.). The limits of detection were below 0.92 ng g(-1) (dry weight) for needles and below 0.43 ng g(-1) (dw) for bark. Recovery assays were performed with two sample masses spiked at three levels and the overall mean values were between 70 and 110 % for P. pinaster and 75 and 129 % for P. pinea. In the first species, the increase in sample mass lowered the recoveries slightly for most PAHs, whereas for the second, the recoveries were higher for the needles. Naturally contaminated samples from 4 sites were analysed, with higher levels for urban sites (1,320 and 942 ng g(-1) (dw) vs. 272 and 111 ng g(-1) (dw) for needles and 696 and 488 ng g(-1) (dw) vs. 270 and 103 ng g(-1) (dw) for bark) than for rural ones and also for P. pinaster samples over P. pinea. It is also shown that gas-phase PAHs are predominant in the needles (over 65 % of the total PAHs) and that the incidence for particulate material in bark, reaching 40 % as opposed to a maximum below 20 % for the needles. The method has proved to be fit and improved some of the existing approaches, on the assessment of particulate PAHs and bark levels.