Volume 88, Issue 5

New magnetically recoverable catalysts have been synthesized by deposition of 1% palladium (Pd)-metal on the polymer poly(1-oxo-trimethylene), containing 15% of magnetite. The magnetite allows the complete recovery of the catalyst with the simple application of an external magnetic field. The activity of such a catalyst has been studied under phosphine-free conditions in the alkoxycarbonylation of iodobenzene to the corresponding benzoic acid esters.

Aza- and diazafulvenium methide systems are versatile building blocks for the synthesis of pyrroles and pyrazoles. These extended dipoles participate in sigmatropic [1,8]H shifts and 1,7-electrocyclizations giving vinyl pyrroles and pyrazoles. Under flash vacuum pyrolysis conditions these heterocycles undergo interesting rearrangements. Aza- and diazafulvenium methides can be intercepted by dipolarophiles. Derivatives with carboxylate groups at C-4 and/or C-5 act exclusively as 1,7-dipoles affording products resulting from the addition across the 1,7-positions. These 1,7-cycloadducts include chlorin and bacteriochlorin type macrocycles as well as steroidal analogues, compounds with relevance in medicinal chemistry. In contrast with this chemical behavior, 5-trifluoromethylazafulvenium methides can participate in both 1,7- and 1,3-dipolar cycloadditions. The generation and reactivity of benzodiazafulvenium methides is also discussed.

The classification, modeling, and quantification of human errors in routine chemical analysis are described. Classifications include commission errors (mistakes and violations) and omission errors (lapses and slips) in different scenarios at different steps of the chemical analysis. A Swiss cheese model is used to characterize error interaction with a laboratory quality system. The quantification of human errors in chemical analysis, based on expert judgments, i.e. on the expert(s) knowledge and experience, is applied. A Monte Carlo simulation of the expert judgments was used to determine the distributions of the error quantification scores (scores of likelihood and severity, and scores of effectiveness of a laboratory quality system against the errors). Residual risk of human error after the error reduction by the laboratory quality system and consequences of this risk for quality and measurement uncertainty of chemical analytical results are discussed. Examples are provided using expert judgments on human errors in pH measurement of groundwater, multi-residue analysis of pesticides in fruits and vegetables, and elemental analysis of geological samples by inductively coupled plasma mass spectrometry.

Approaches for analytical-scale extraction are developing rapidly as new strategies are implemented to improve sample throughput, to minimize material use in laboratory methods, and to develop on-site capabilities. In this contribution, definitions and recommendations for symbols for the terms used in analytical extraction are presented. Exhaustive, microextraction, elevated temperature, microwave- and ultrasound-assisted, parallel batch, flow through systems, and membrane extraction approaches are discussed. An associated tutorial titled “Extraction” provides a detailed introduction to the topic.