An investigation of microbore reverse-phase columns containing 3 μm packing materials

A procedure for packing 15 cm × 1 mm id reverse-phase microbore columns with 3 μm silicas obtained from different manufacturers is described. The speed of analysis and detection limits are compared to those obtained with a 50 cm × 1 mm id column packed with 10 μm ODS. The effect of detector time constant on the system, and flow rates on column efficiency are also examined.     

Preparation of some silyl esters and study of their vibration spectra in gas and condensed phases

A new preparative route for silyl esters is described, involving reaction of silyl bromide and trisalkyltin esters. The far infrared spectrum of some simple esters are reported; an investigation of the shifts in the carbonyl stretching band on condensation shows no significant differences in behaviour between methyl and silyl esters.

---

Darstellung einiger Silylester und Untersuchung der Vibrationsspektren in der Gasphase und in kondensierter Phase

Zusammenfassung Es wird ein neuer präparativer Weg (über Silylbromid und Trisalkylzinnester) für die Synthese von Silylestern beschrieben. Das ferne IR einiger Ester wird angeführt; eine Untersuchung der Verschiebung der Carbonyl-Streck-Frequenz bei Kondensation zeigt keine signifikanten Unterschiede zwischen Methyl- und Silyl-Estern.

     

Darstellung und Charakterisierung von Halogeno(diethyldithiocarbamato) (triethyl- und triphenylphosphin)palladium(II)-Komplexen

The Complexes [Pd(PEt ₃)₂ dtc]X (1) and Pd(PR ₃)Xdtc (2, 3) (dtc=S₂CNEt ₃;X=Cl, Br, I;R=Et, Ph) have been prepared. Conductivity, susceptibility, UV and IR measurements show that the cations [Pd(PEt ₃)₂ dtc]⁺ of1 and the complexes2, 3 have square-planar structure.

     

Polymerization of methyl methacrylate in the presence of iron(II) complex with tetradentate nitrogen ligands under conditions of atom transfer radical polymerization

Four tetradentate nitrogen ligands, viz. dichloro{[N,N^′-diphenyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (1), {[N,N^′-dioctyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (2), {[N,N^′-dibenzyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (3), and (1R,2R)-(−)-N,N^′-di(quinoline-2-methyl) di-iminocyclohexane (4), were investigated as novel complexing ligands in iron-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate where ethyl-2-bromoisobutyrate was the initiator in o-xylene at 90 °C. With ligands 1 and 2 the experimental molecular weights increased gradually with monomer conversion. High to moderate conversions (87%, 43%) were obtained in relatively short times (90 min for 1 and 30 min for 2), which indicates an efficient catalyst system, but after these times a dramatic increase in viscosity of the polymerization medium led to loss of control. It is noteworthy that polymerization proceeded in a controlled manner with ligand 1, which has two rather bulky substituents on the N-atom. Such bulky ligands did not work for a copper-based system, where they led to excessive terminations or other side reactions. When the bulkiness of the substituents was significantly increased, as in ligand 3, a decrease in polymerization rate and loss of control occurred. Ligand 4 was less efficient than the other ligands, probably because the ethylene bridge was replaced by cyclohexane bridge.     

Diastereoselective addition of diethyl difluoromethylphosphonate to enantiopure sulfinimines: synthesis of α,α-difluoro-β-aminophosphonates, phosphonic acids, and phosphonamidic acids

Addition of diethyl lithiodifluoromethylphosphonate to enantiomerically pure aromatic, heteroaromatic, and aliphatic aldehyde-derived sulfinimines afforded N-sulfinyl α,α-difluoro-β-aminophosphonates with generally good enantioselectivity and in high yield. The reaction with acetophenone-derived sulfinimine resulted in the formation of the addition product with high diastereoselectivity and in only moderate yield. A two-step deprotection involving treatment of diastereomerically pure N-sulfinyl α,α-difluoro-β-aminophosphonates with trifluoroacetic acid in EtOH followed by refluxing with 10 N HCl provided enantiopure α,α-difluoro-β-aminophosphonates and α,α-difluoro-β-aminophosphonic acids. The N-Cbz derivative of (R)-2-amino-1,1-difluoro-2-phenylethylphosphonate was a convenient starting point for the preparation of corresponding difluorophosphonate monoester, difluorophosphonic acid, and difluorophosphonamidic acid. At 21 °C difluorophosphonamidic acid was stable in aqueous solution at pH above 5.     

Chloro(η6‐p‐cymene)(phosphoramidite)ruthenium(II), a 16‐Electron Fragment Stabilized by an η2‐Aryl–Metal Interaction,and Its Use in Asymmetric Cyclopropanation

Chloride abstraction from the half‐sandwich complexes [RuCl₂(η⁶‐p‐cymene)(P*‐κP)] ( 2a : P* = (S_a,R,R)‐ 1a = (1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl bis[(1R)‐1‐phenylethyl)]phosphoramidite; 2b : P* = (S_a,R,R)‐ 1b = (1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl bis[(1R)‐(1‐(1‐naphthalen‐1‐yl)ethyl]phosphoramidite) with (Et₃O)[PF₆] or Tl[PF₆] gives the cationic, 18‐electron complexes dichloro(η⁶‐p‐cymene){(1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl {(1R)‐1‐[(1,2‐η)‐phenyl]ethyl}[(1R)‐1‐phenylethyl]phosphoramidite‐κP}ruthenium(II) hexafluorophosphate ( 3a ) and [Ru(S)]‐dichloro(η⁶‐p‐cymene){(1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl {(1R)‐1‐[(1,2‐η)‐naphthalen‐1‐yl]ethyl}[(1R)‐1‐(naphthalen‐1‐yl)ethyl]phosphoramidite‐κP)ruthenium(II) hexafluorophosphate ( 3b ), which feature the η²‐coordination of one aryl substituent of the phosphoramidite ligand, as indicated by ¹H‐, ¹³C‐, and ³¹P‐NMR spectroscopy and confirmed by an X‐ray study of 3b . Additionally, the dissociation of p‐cymene from 2a and 3a gives dichloro{(1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl [(1R)‐(1‐(η⁶‐phenyl)ethyl][(1R)‐1‐phenylethyl]phosphoramidite‐κP)ruthenium(II) ( 4a ) and di‐μ‐chlorobis{(1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl [(1R)‐1‐(η⁶‐phenyl)ethyl][(1R)‐1‐phenylethyl]phosphoramidite‐κP}diruthenium(II) bis(hexafluorophosphate) ( 5a ), respectively, in which one phenyl group of the N‐substituents is η⁶‐coordinated to the Ru‐center. Complexes 3a and 3b catalyze the asymmetric cyclopropanation of α‐methylstyrene with ethyl diazoacetate with up to 86 and 87% ee for the cis‐ and the trans‐isomers, respectively.     

Synthesis and Structure of MnCl2(HDpyF) (HDpyF = N,N′‐di(2‐pyridyl)formamidine): New Crystallographic Disorder and Bonding Mode of the HDpyF Ligand

The reaction of N,N′‐di(2‐pyridyl)formamidine (HDpyF) with MnCl₂‐4H₂O afforded the complex MnCl₂(HDpyF), which was characterized by X‐ray crystallography. The HDpyF ligand chelates to the Mn(II) center through the first and the third nitrogen atoms to form a six‐membered ring, leaving the second and the fourth nitrogen atoms uncoordinated. The HDpyF ligand is crystallographically disordered such that two different molecules can be solved. The neutral HDpyF ligand adopts the new s‐cis‐syn‐s‐trans conformation.     

Evaluation of a synergetic effect between Rh as permanent chemical modifier and acetylacetone as complexing agent in Sc determination in sediment slurry samples by ETAAS

In the present work, scandium was determined in sediment slurry samples (from three different rivers) by electrothermal atomic absorption spectrometry (ETAAS). Slurries were prepared by weighting 100 mg of dry sediment samples (≤53 μm particle sizes) and adding 6 ml of HCl:HNO₃:HF (3:1:2, v/v). Accurate results were only possible due to the synergetic effect between Rh as permanent chemical modifier and acetylacetone (Acac) as complexing agent. The same platform was used for 400 heating cycles. The performance of the chemical modification was evaluated by using scanning electron microscopy (SEM), synchrotron radiation X-ray fluorescence (SRXRF) and some figures of merit (precision and detectability). The best analytical conditions were attained using 1500 and 2550 °C as pyrolysis and atomization temperatures. The scandium content in the liquid phase of the slurries ranged from 61 to 73%, thus indicating, in this study, that both liquid and solid phases play an important role in slurry analyses. An amount of 5.0–20.0 μg l⁻¹ Sc linear range as well as LOD and LOQ of 0.19 and 0.62 μg l⁻¹, respectively, were obtained under these conditions. The accuracy was checked by using microwave-assisted decomposition, and the results compared to those obtained with the proposed methodology (slurry analysis). By checking both sets of the results, there is no statistical difference at the 95% confidence levels.     

Nanometer-sized zirconium dioxide microcolumn separation/preconcentration of trace metals and their determination by ICP-OES in environmental and biological samples

A new method is proposed using a microcolumn (20 mm × 2.0 mm) packed with nanometer-sized zirconia as solid-phase extractor for the separation/preconcentration of Mn, Cu, Cr, Zn, Ni and Co prior to their determination by inductively coupled plasma optical emission spectrometer (ICP-OES) in environmental samples. The factors affecting the separation and preconcentration of analytes such as pH, sample flow rate and volume, eluent concentration and volume were determined, interfering ions were studied, and the optimal experimental conditions were established. The adsorption capacity of nanometer-sized ZrO₂ for Mn, Cu, Cr, Zn, Ni and Co was found to be 1.3, 1.3, 1.7, 2.0, 3.9 and 1.5 mg g⁻¹, respectively. The detection limits of the method were 12, 58, 24, 2, 7 and 36 ng L⁻¹, respectively, with a preconcentration factor of 25. The precision of this method was 1.7% (Mn), 2.9% (Cu), 5.9% (Mn), 3.8% (Mn), 6.2% (Mn) and 4.3% (Mn) with 9 determinations of 10 ng mL⁻¹ of target analytes, respectively. The method was successfully applied to the determination of trace metals in lake water, dried fish samples, certified reference materials of human hair and milk, and provided satisfactory results.     

über die Reaktionen von CH3OCl,CF3OCl,CF3OF und CF3OH mit dem supersauren System HF/MF5 (M = As,Sb) Darstellung und Charakterisierung von CH3OCl(H)+MF6− und CF3OCl(H)+MF6−

On the Reactions of CH₃OCl, CF₃OCl, CF₃OF, and CF₃OH with the Superacid System HF/MF₅ (M = As, Sb). Preparation and Characterization of CH₃OCl(H)⁺MF₆^? and CF₃OCl(H)⁺MF₆^? The preparation of the chlorine oxoniumsalts CH₃OCl(H)⁺MF₆^? and CF₃OCl(H)⁺MF₆^? by protonation of CH₃OCl and CF₃OCl in the superacid solution of HF/MF₅ (M = As, Sb) is described. However CF₃OF and CF₃OH have not been protonated under the same conditions. In the case of CF₃OH the formation of F₂CO · MF₅ is observed. The novel compounds are characterized by nmr- and vibrational spectroscopy.