Second generation N-heterocyclic carbene-Pt(0) complexes as efficient catalysts for the hydrosilylation of alkenes

A new class of benzimidazolylidene carbene-Pt(0) complexes was developed and used to efficiently catalyse the hydrosilylation of alkenes.     

Wang-aldehyde resin as a recyclable support for the synthesis of alpha,alpha-disubstituted amino acid derivatives

Merrifield resin was functionalised with hydroxybenzaldehyde under microwave irradiation. The resultant resin was used as a means for immobilisation and activation of alpha-amino acid esters for alkylation reactions. Alpha,alpha-disubstituted and cyclic amino acid esters were prepared in good yields.     

New hydrothermal synthesis and structure of Th2(PO4)2(HPO4).H2O: the first structurally characterized thorium Hydrogenphosphate

Th(2)(PO(4))(2)(HPO(4)).H(2)O was synthesized under wet hydrothermal conditions starting from a mixture of H(3)PO(3) and Th(NO(3))(4).5H(2)O. The crystal structure was solved by powder X-ray diffraction data. The unit cell parameters are a = 6.7023(8) Angstroms, b = 7.0150(8) Angstroms, c = 11.184(1) Angstroms, beta = 107.242(4) degrees, space group P2(1), and Z = 2. The structure consists of layers of both thorium atoms and PO(4) groups, alternating with a layer formed by HPO(4) entities and water molecules. By thermal treatment, this compound turns into Th(4)(PO(4))(4)P(2)O(7), a ceramic already described in the field of the immobilization of tetravalent actinides.     

Size-exclusion chromatographic determination of polymer molar mass averages using a fractal calibration

The characterization of polymers by size-exclusion chromatography basically consists of the determination of the weight-average molar mass (Mw), number-average molar mass (Mn), and polydispersity index (I). An accurate estimation of these magnitudes requires the use of a reliable and trusted calibration curve. Three procedures for building up a calibration curve are analyzed in this work. The first is the classical universal calibration (UC), based on the elution of tetrahydrofuran-polystyrene in a system as reference. The second is based on the proper calibration curve made with standards of the sample under study. However, two main drawbacks arise when using these methodologies: the nonfulfilment of the UC when secondary mechanisms, other than pure size-exclusion, are present in the separation process; and the lack of a broad set of narrow standards of the sample under analysis in the second procedure. In order to circumvent these difficulties, a third, recently-proposed approach based on fractal considerations is applied. The accuracy and reliability of this method is proven through the calculation of the deviations observed in the estimation of the Mw values for polymer samples in different solvent-gel chromatographic systems. Whereas the classical UC shows a mean deviation of approximately 80% relative to the values given by the manufacturer, the fractal calibration yields a mean deviation of approximately 16%, similar to that obtained from the proper calibration. Moreover, the fractal procedure only needs one polymeric sample to generate the calibration curve.     

Capillary electrophoresis enhanced by automatic two-way background correction using cubic smoothing splines and multivariate data analysis applied to the characterisation of mixtures of surfactants

Mixtures of the surfactant classes coconut diethanolamide, cocamido propyl betaine and alkylbenzene sulfonate were separated by capillary electrophoresis in several media containing organic solvents and anionic solvophobic agents. Good resolution between both the surfactant classes and the homologues within the classes was achieved in a BGE containing 80 mM borate buffer of pH 8.5, 20% n-propanol and 40 mM sodium deoxycholate. Full resolution, assistance in peak assignment to the classes (including the recognition of solutes not belonging to the classes), and improvement of the signal-to-noise ratio was achieved by multivariate data analysis of the time-wavelength electropherograms. Cubic smoothing splines were used to develop an algorithm capable of automatically modelling the two-way background, which increased the sensitivity and reliability of the multivariate analysis of the corrected signal. The exclusion of significant signals from the background model was guaranteed by the conservativeness of the criteria used and the safeguards adopted all along the point selection process, where the CSS algorithm supported the addition of new points to the initially reduced background sample. Efficient background modelling made the application of multivariate deconvolution within extensive time windows possible. This increased the probability of finding quality spectra for each solute class by orthogonal projection approach. The concentration profiles of the classes were improved by subsequent application of alternating least squares. The two-way electropherograms were automatically processed, with minimal supervision by the user, in less than 2 min. The procedure was successfully applied to the identification and quantification of the surfactants in household cleaners.     

Feedstock characterization and prediction of product yields for industrial naphtha crackers on the basis of laboratory and bench-scale pyrolysis

A new severity function has been introduced in order to plot and evaluate the yield data from hydrocarbon pyrolysis. It is demonstrated that the new severity function can also be used for the presentation of product yields obtained from hydrocarbon mixtures and naphtha fractions.In order to characterize and evaluate available feedstocks for olefin production, yields for seven naphtha fractions were determined in a bench-scale reactor. It was established that the yields of ethylene and propylene obtained from the different naphtha fractions increase proportionally with the increase in the characterization factor.On the basis of pyrolysis experiments carried out in laboratory, bench-scale and pilot reactors and in a commercial furnace it is shown that by using the new severity function the yield data obtained in reactors of different sizes and operating under different conditions can be directly compared and uniformly evaluated.The feasibility of micro-scale pyrolysis-gas chromatography for predicting product yields and evaluating naphtha feedstocks is also discussed.     

On the iodometric determination of the bromide ion

The oxidation of bromide effected by chlorine was investigated and it was established that it runs down in two steps. In the course of the first step in a medium of pH between 6.5-7.5, Br⁺ùOH^- electromer hypobromous acid forms. This BrOH electromer leads, on further oxidation, to the product BrCl₅, furnishing on hydrolysis bromate. In a medium, in which the pH is adjusted to about 8.5-9 the hydrolysis takes place at such a rate that it can be used for analytical purposes.On the basis of these investigations the determination of the bromide ion amounting to 0.1-25 mg can be carried out rapidly with an error of a few tenths of one per cent. Besides the oxidizing substances only iron, copper, mercury and molybdenum ions interfere with the procedure. The interfering ions can either be eliminated by treatment with soda and hydrogen sulphide, or by the distillation of bromine.