Comparative tests to improve the gas chromatographic analysis of chlorobornanes in fish samples

A comparison was made between electron capture negative ionization quadrupole mass spectrometry (ECNI-MS) and electron capture detection (ECD) with regard to repeatability and reproducibility for the gas chromatographic (GC) analysis of toxaphene congeners [chlorobornanes (CHBs)]. The tests, including standard solutions and several cleaned fish extracts, showed larger relative standard deviations (RSDs) for the repeatability of ECNI-MS but no differences in the reproducibility of the 2 techniques. The sensitivity of the GC-ECNI-MS was considerably better than that of GC/ECD. Four stepwise-designed comparative tests were also conducted on GC analysis, cleanup, and the complete method. The results showed that, according to the current state-of-the-art, coefficients of variation for the between-laboratory performance were not < 20% and were usually between 20 and 30%. In spite of separation problems, e.g., for CHB 26, which cannot be separated into a single-component peak, a 95% methyl 5% phenyl polysiloxane (CP Sil 8) column was preferred to more polar columns for the analysis of CHBs 26, 40, 41, 44, 50, and 62. CHB 62 was more difficult to determine than CHB 26 and 50. Addition of the CHBs 40, 41, and 44 to the standard set of 3 chlorobornanes (26, 50, and 62) resulted in more separation problems. A 3-step cleanup method was recommended.     

Gas chromatography-mass spectrometry analysis of alkylphenols in cod (Gadus morhua) tissues as pentafluorobenzoate derivatives

A highly selective and sensitive method for the determination of 30 meta- and para-substituted alkylphenols from phenol (C0) to nonylphenol (C9) in biota is described. Dichloromethane extracts of spiked cod liver and muscle samples are cleaned up by gel permeation chromatography, derivatised with pentafluorobenzoyl chloride and analysed by gas chromatography-mass spectrometry with negative-ion chemical ionisation. Quantification is done with isotope dilution of five internal standards of different chain length. The detection limits were in the low microg/kg levels. There were encountered problems with background levels of 4-nonylphenol. 4-Nonylphenol isomers were found in a number of plastic and rubber products used in the laboratory.     

Nitropyridyl isocyanates in 1,3‐dipolar cycloaddition reactions

The reactivity of 3‐nitro‐4‐pyridyl isocyanate ( 7 ) and 5‐nitropyridin‐2‐yl isocyanate ( 9 ) in 1,3‐dipolar cycloaddition reactions with azides and pyridine N‐oxides has been investigated. 1,3‐Dipolar cycloaddition to trimethylsilylazide (TMSA) afforded the respective tetrazolinones, 1‐(3‐nitropyridin‐4‐yl)‐1H‐tetrazol‐5(4H)one ( 8 , 50 %) and 1‐(5‐nitropyridin‐2‐yl)‐1H‐tetrazol‐5(4H)one ( 11 , 64 %). Respectively, 1,3‐dipolar cycloaddition of nitropyridyl isocyanates 7 and 9 to 3,5‐dimethylpyridine N‐oxide ( 14 ), 3‐methylpyridine N‐oxide ( 21 ) and pyridine N‐oxide ( 22 ) gave the substituted amines, 3,5‐dimethyl‐N‐(3‐nitropyridin‐4‐yl)pyridin‐2‐amine ( 17 ), 3,5‐dimethyl‐N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 20 ), N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 24 ), 5‐methyl‐N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 23 ) and 3‐methyl‐N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 25 ) in 65 ‐ 80 % yield, obtained by cycloaddition, rearrangement and decarboxylation. The results demonstrate that the nitropyridyl isocyanates ( 7,9 ) readily undergo 1,3‐dipolar cyloaddition reactions similar to phenyl isocyanates.     

1,3‐Dihydro‐2H‐imidazo[4,5‐c]pyridin‐2‐one

A facile acid catalysed cyclisation method for the preparation of the cyclic urea 2H‐imidazo[4,5‐c]pyridin‐2‐one ( 2 ) in > 95 % yield is reported. The biologically active compound 2 can be obtained by heating (3‐amino‐4‐pyridinyl)‐carbamic acid methyl, ethyl or tert‐butyl esters ( 1a‐c ) in sulfuric acid (0.1 %) or in aqueous HBF₄ (3.5 equivalents) for 10 min. ‐ 3 hrs at 90 °C. The corresponding microwave‐promoted (MW) reactions afforded the pure product 2 within few minutes. The 6‐butylamino‐substituted analogue ( 2a ) was correspondingly obtained by MW irradiation in 99 % yield by cyclisation of 2‐(butylamino)‐5‐amino‐4‐pyridylcarbamic acid isopropyl ester ( 1d ). Quantitative precipitation of product 2 was obtained by pH adjustment. The process represents a solvent‐free, “green” method for the preparation of 2 .     

Application of phosphine-oxazoline ligands in Ir-catalyzed asymmetric hydrogenation of acyclic aromatic N-arylimines

[reaction: see text] A new class of chiral phosphine-oxazoline ligands have been developed. Chiral Ir complexes prepared from these ligands induced high enantioselectivities (66-90% ee) when applied to the asymmetric hydrogenation of acyclic aromatic N-arylimines.     

Nitropyridyl isocyanates

We hereby report the first preparation of 3‐nitro‐4‐pyridyl isocyanate 9 and 5‐nitro‐2‐pyridyl isocyanate 18 . They were formed by Curtius rearrangement of the corresponding acyl azides 8 and 17 , prepared from methyl 3‐nitro‐4‐pyridinecarboxylate 6 via the hydrazide 7 and 5‐nitro‐picolinic acid 16 , respectively. The substrates 6 and 16 were generated by nitration of methyl 4‐pyridinecarboxylate 5 and nitration and oxidation of 2‐picoline 14 . 3‐Nitro‐4‐pyridyl isocyanate 9 can be stored in dry solution and is stable at room temperature for several weeks while 5‐nitro‐2‐pyridyl isocyanate 18 was less stable and should be used for synthetic purposes immediately.     

A method for analysing nesting techniques for the linearized shallow water equations

A method for analysing different nesting techniques for the linearized shallow water equations is presented. The problem is formulated as an eigenvector–eigenvalue problem. A necessary condition for stability is that the spectral radius of the propagation matrix is less than or equal to one. Two test cases are presented. The first test case is analysed, and effects of enforcing volume conservation and nudging in time are studied. A nesting technique is found that causes no growth of any eigenvectors for reasonable time steps. This nesting technique is then used on both test cases, and results are compared to an everywhere refined model and a coarse grid model. Copyright © 2002 John Wiley & Sons, Ltd.     

Asymmetric hydrogenation of di and trisubstituted enol phosphinates with N,P-ligated iridium complexes

The iridium-catalyzed asymmetric hydrogenation of various di- and trisubstituted enol phosphinates has been studied. Excellent enantioselectivities (up to >99% ee) and full conversion were observed for a range of substrates with both aromatic and aliphatic side chains. Enol phosphinates are structural analogues of enol acetates, and the hydrogenated alkyl phosphinate products can easily be transformed into the corresponding alcohols with conservation of stereochemistry. We have also hydrogenated, in excellent ee, several purely alkyl-substituted enol phosphinates, producing chiral alcohols that are difficult to obtain highly enantioselectively from ketone hydrogenations.