The ETACS European project for testing the comparability of sensors and analysers

ETACS is the official acronym for the European project "European Testing and Assessment of Comparability of On-line Sensors/Analysers". This project has three main objectives to achieve the comparability of performance data for sensors and analysers in the environmental field. First, to develop a test protocol for validation and comparison of the performance of on-line sensors/analysers. The test protocol is intended to be generic, that is independent of the specific sensors/analysers and the specific parameters to be monitored. Second, the practical testing of this test protocol to assess its applicability and to develop the techniques used. Finally, to achieve widespread acceptance of the test protocol by producer/suppliers, users and relevant authorities to assist its early adoption as an agreed European standard. Laboratory tests for producing the test protocol have been carried out and completed to check the applicability of such a protocol.     

Synthesis and properties of monodisperse oligofluorene-functionalized truxenes: highly fluorescent star-shaped architectures

This paper describes the strategy toward novel monodisperse, well-defined, star-shaped oligofluorenes with a central truxene core and from monofluorene to quaterfluorene arms. Introduction of solubilizing n-hexyl groups at both fluorene and truxene moieties results in highly soluble, intrinsically two-dimensional nanosized macromolecules T1-T4. The radius for the largest oligomer of ca. 3.9 nm represents one of the largest known star-shaped conjugated systems. Cyclic voltammetry experiments reveal reversible or quasi-reversible oxidation and reduction processes (Eox = +0.74 to 0.80 V, Ered = -2.66 to 2.80 eV vs Fc/Fc+), demonstrating excellent electrochemical stability toward both p- and n-doping, while the band gaps of the oligomers are quite high (EgCV = 3.20-3.40 eV). Close band gaps of 3.05-3.29 eV have been estimated from the electron absorption spectra. These star-shaped macromolecules demonstrate good thermal stability (up to 400-420 degrees C) and improved glass transition temperatures with an increase in length of the oligofluorene arms (from Tg = 63 degrees C for T1 to 116 degrees C for T4) and show very efficient blue photoluminescence (lambdaPL = 398-422 nm) in both solution (PhiPL = 70-86%) and solid state (PhiPL = 43-60%). Spectroelectrochemical experiments reveal that compounds T1-T4 are stable electrochromic systems which change their color reversibly from colorless in the neutral state (approximately 340-400 nm) to colored (from red to purple color; approximately 500-600 nm) in the oxidized state.     

Ultrasonic and Raman Scattering Spectroscopy of Zinc Thiocyanate Complexes in Water at 25<Superscript>∘</Superscript>C: Kinetics of Complex Formation Determined by Multivariate Analysis

Advances have been made recently in broadening the accessible ultrasonic absorption frequency range and improving the detectability of minor species present in solution using Raman spectroscopy. Development of chemometric techniques in these areas needs to keep pace with the improvement of these experimental methods. Refinements in the analysis of ultrasonic and Raman data based on multivariable least squares and factor analysis, respectively, are examined to investigate the kinetics of zinc thiocyanate complex formation in water. Analysis of ultrasonic absorption relaxation spectra verified that the observed process in aqueous Zn(SCN)₂ involves substitution of water from the first coordination shell of Zn²⁺. Use of a multivariable least-squares error surface is described that enhances the reliability of assigned frequencies of ultrasonic absorption maxima. Factor analysis of Raman scattering data provided direct evidence that at least four complex species, such as Zn(SCN)⁺ and Zn(SCN)₂, are simultaneously present in the aqueous zinc thiocyanate solutions.     

A model of the chemical composition and pyrolysis kinetics of lignin

This study presents a novel approach for the chemical representation of lignin for modelling the reaction kinetics of lignin in lignocellulosic biomass. This methodology relies on the definition of dimeric pseudo-components containing phenolic functionalities, i.e., p-hydroxyphenyl, guaiacyl and syringyl groups, as measured in real biomass and native lignin through wet chemistry and spectroscopic techniques. The reactivities of the lignin pseudo-components are modelled through a series of lumped unidirectional reactions, whose product formation and reaction rate constants are optimised to replicate a comprehensive experimental dataset gathered from several works available in the literature. The new kinetic model contributes to the state-of-the-art by providing a more accurate depiction of the conversion rates, selectivity of char vs. volatiles, and aromatic composition in condensable products in line with the inherent reactivity of lignin functionalities and the empirical observations of lignin depolymerisation and thermal degradation at low (<1?K/s) and high heating rates (>50?K/s).     

Challenges in Catalytic Hydrophosphination

Despite significant advances, metal‐catalyzed hydrophosphination has ample room for discovery, growth, and development. Many of the key successes in metal‐catalyzed hydrophosphination over the last decade have indicated what is needed and what is yet to come. Reactivity that is absent from the literature also speaks to the challenges in catalytic hydrophosphination. This Concept article discusses and highlights recent developments that address the ongoing challenges, and identifies areas in metal‐catalyzed hydrophosphination that are underdeveloped. Advances in product selectivity, catalyst design, and both unsaturated and phosphine substrates illustrate the ongoing development of the field. Like all catalytic transformations, the benefits are realized through catalyst, ligand, and conditions, and consideration of those features are the route to a yet more efficient and broadly applicable reaction.     

Group transfer from nickel imido, phosphinidene, and carbene complexes to ethylene with formation of aziridine, phosphirane, and cyclopropane products

The reactions of nickel complexes bearing terminal imido, phosphinidene, and carbene ligands with ethylene are reported. In all three cases, corresponding three-membered rings, aziridine, phosphirane, and cyclopropane, were produced in moderate to excellent yields. NMR spectra of the phosphinidene (dtbpe)Ni=P(dmp) reaction with ethylene show a [2+2] cycloaddition adduct before phosphirane formation. A labeling study with trans-ethylene-d2 shows formation of aziridine and phosphirane proceeds with net retention of relative stereochemistry.     

Hyperaromatic stabilization of arenium ions

Benzene-cis- and trans-1,2-dihydrodiols undergo acid-catalyzed dehydration at remarkably different rates: k(cis)/k(trans) = 4500. This is explained by formation of a β-hydroxycarbocation intermediate in different initial conformations, one of which is stabilized by hyperconjugation amplified by an aromatic no-bond resonance structure (HOC(6)H(6)(+) ? HOC(6)H(5) H(+)). MP2 calculations and an unfavorable effect of benzoannelation on benzenium ion stability, implied by pK(R) measurements of -2.3, -8.0, and -11.9 for benzenium, 1-naphthalenium, and 9-phenanthrenium ions, respectively, support the explanation.     

The ETACS European Project for testing the comparability of sensors and analysers: Part II. Field tests

 The results of field tests performed within the European Testing and Assessment of Comparability of On-line Sensors/Analysers (ETACS) European Project are presented in this article. This work is complementary to the laboratory tests, already published in Part I in this Journal. The objective was to consider the complete measuring chain, including the sensor/analyser, sampling elements, pumping and conditioning devices needed for a particular application. These aspects were not included in the laboratory tests and, therefore, new facets were involved. Field tests are considered site specific in terms of the sample dynamic range and matrix composition, as well as event dependent with respect to environmental conditions. A protocol for checking the performance of sensors/analysers working in a field location is presented. The protocol is a general guide and, therefore, can be used independently of the nature of the sensor/analyser under evaluation.     

Taming Tin(IV) Polyazides

The first charge‐neutral Lewis base adducts of tin(IV) tetraazide, [Sn(N₃)₄(bpy)], [Sn(N₃)₄(phen)] and [Sn(N₃)₄(py)₂], and the salt bis{bis(triphenylphosphine)iminium} hexa(azido)stannate [(PPN)₂Sn(N₃)₆] (bpy = 2,2′‐bipyridine; phen = 1,10‐phenanthroline; py = pyridine; PPN = N(PPh₃)₂) have been prepared using covalent or ionic azide‐transfer reagents and ligand‐exchange reactions. The azides were isolated on the 0.3 to 1 g scale and characterized by IR and NMR spectroscopies, microanalytical and thermal methods and their molecular structures determined by single‐crystal XRD. All complexes have a distorted octahedral Sn[N]₆ coordination geometry and possess greater thermal stability than their Si and Ge homologues. The nitrogen content of the adducts of up to 44 % exceed any Sn^IV compound known hitherto.     

Hyperaromatic stabilization of arenium ions: a remarkable cis stereoselectivity of nucleophilic trapping of β-hydroxyarenium ions by water

Cis- and trans-1,2-dihydrodiol isomers of benzene undergo acid-catalyzed dehydration to form phenol. In principle the isomeric substrates react through a common β-hydroxybenzenium (cyclohexadienyl) carbocation. Notwithstanding, the isomers show a large difference in reactivity, k(cis)/k(trans) = 4500. This difference is reduced to k(cis)/k(trans) = 440 and 50 for the 1,2-dihydrodiols of naphthalene and 9,10-dihydrodiols of phenanthrene, respectively, and to 6.9 for the dihydrodiols of the nonaromatic 7,8-double bond of acenaphthylene. Because the difference in stabilities of cis- and trans-dihydrodiols should be no more than 2-3-fold, these results imply a high cis stereoselectivity for nucleophilic trapping of a β-hydroxyarenium cation by water in the reverse of the carbocation-forming reaction. This is confirmed by studies of the 10-hydroxy-9-phenanthrenium ion generated from aqueous solvolyses of the trans-9,10-bromohydrin derivative of phenanthrene and the monotrichloroacetate ester of the phenanthrene cis-9,10-dihydrodiol. The cis stereoselectivity of forward and reverse reactions is explained by the formation (in the "forward" reaction) of different conformations of carbocation from cis- and trans-dihydrodiol reactants with respectively β-C-H and β-C-OH bonds in pseudoaxial positions with respect to the charge center of the carbocation optimal for hyperconjugation. Formation of different conformations is constrained by departure of the (protonated) OH leaving group from a pseudoaxial position. The difference in stability of the carbocations is suggested to stem (a) from the greater hyperconjugative ability of a C-H than a C-OH bond and (b) from enhanced conjugation arising from the stabilizing influence of an aromatic ring in the no-bond resonance structures representing the hyperconjugation (C(6)H(6)OH(+) ? C(6)H(5)OH H(+)). This is consistent with an earlier suggestion by Mulliken and a demonstration by Schleyer that the benzenium ion is subject to hyperconjugative aromatic stabilization. It is proposed that, in analogy with the terms homoconjugation and homoaromaticity, arenium ions should be considered as "hyperaromatic".