Libor Dušek

Differentiation between phenol- and amino-substances in voltammetry determination of synthetic antioxidants in oils

AbstractThe paper describes a method of voltammetric determination of antioxidants in lubricating oils developed with the use of Linear Sweep Voltammetry (LSV) and Fast Scan Differential Pulse Voltammetry (FSDPV). Experimental conditions have been found for simultaneous determination of phenol-based antioxidants and amino-antioxidants: the phenols can be electrochemically oxidized using the polarisation of gold disc electrode (AuDE) in the potential range of 0–1400 mV in 0.2 M H2SO4 in the presence of ethanol and acetonitrile at the ratio of 3:1. Secondary aromatic amines can be determined directly in this supporting electrolyte; the presence of phenolic antioxidants does not interfere with this analysis. On the other hand, secondary aromatic amines interfere with the determination of phenolic substances; therefore, the amines present have to be eliminated in a suitable way. A procedure for masking the aromatic amines using their reaction with nitrous acid has been suggested and optimised. The nitrosamines thus formed can be used for sensitive and selective determination of amino-antioxidants by means of cathodic reduction on the hanging mercury drop electrode (HMDE) using Fast Scan Differential Pulse Voltammetry. The method was applied in analysis of real samples of lubricating oils.

C,N-Chelated organotin(iv) azides: synthesis, structure and use within click chemistry

A set of tri- and diorganotin(IV) azides bearing 2-(N,N-dimethylaminomethyl)phenyl as a C,N-chelating ligand (LCN) has been prepared and structurally characterized. Triorganotin(IV) azides of the type LCNR2SnN3 (R = n-Bu (1) and Ph (2)) and (LCN)2(n-Bu)SnN3 are monomeric both in solution and in the solid state. The central tin atom in these species is five-coordinated with distorted trigonal bipyramidal geometry. Diorganotin(IV) azides of the type LCNRSn(N3)2 (R = n-Bu and Ph) are monomeric with trigonal bipyramidal geometry around the tin atom as well. Finally, (LCN)2Sn(N3)2 contains a six-coordinated tin atom with heavily distorted octahedral geometry due to the presence of two LCN units. The potential use of selected organotin(IV) azides 1 and 2 as useful building blocks within click chemistry was investigated. The reactions of 1 and 2 with various nitriles resulted in the formation of corresponding triorganotin(IV) tetrazolides (i.e. κ-N1: LCN(n-Bu)2Sn(5-MeCN4), LCNPh2Sn(5-MeCN4), LCN(n-Bu)2Sn(5-Me2NCH2CN4), LCNPh2Sn(5-Me2NCH2CN4); and κ-N2: LCN(n-Bu)2Sn(5-t-BuCN4), LCNPh2Sn(5-t-BuCN4), LCN(n-Bu)2Sn(5-PhCN4), LCNPh2Sn(5-PhCN4)). Similarly, the reaction of 1 and 2 with cyclooctyne provided corresponding C,N-chelated di-n-butyl/diphenyltin(IV) κ-N1 4,5,6,7,8,9-hexahydrocycloocta[d][1,2,3]triazol-1-ides. All azido complexes and products of the [3+2] cycloaddition reactions were characterized by the combination of elemental analysis, mass spectrometry, IR spectroscopy, multinuclear NMR spectroscopy and, in the case of crystalline materials, XRD analysis. In addition, DFT calculations were carried out within the click chemistry reactions in order to corroborate the preferred formation of the respective tetrazolide regioisomer.

Triorganotin(IV) esters of 2-{[ N -(2-oxo-2H-naphthalene-1-yliden)hydrazo]}benzoic acid, instability of the cyclohexyl derivative

Three triorganotin(IV) esters of 2-{[N-(2-oxo-2H-naphthalene-1-yliden)hydrazo]}benzoic acid were prepared and studied by IR and NMR spectroscopy and X-ray crystallography for the tributyl- and triethyltin(IV)-2-{[N-(2-oxo-2H-naphthalene-1-yliden)hydrazo]}benzoates (2, 3). These compounds are monomeric in solution with four-coordinate tin. The hydrazo tautomeric forms are present in chloroform solution as well as in the solid state. The coordination geometries of tin in 2 and 3 are trigonal bipyramidal with all three carbons in equatorial positions, one carboxylic oxygen and the quinone-type oxygen from adjacent molecules are in axial positions forming centrosymmetric dimers with the ring containing 20 members. The yield of the tricyclohexyltin(IV) derivative (4) is much lower than 2 or 3, with instability towards moisture in solution. The product of the reaction with water is the bis(µ2-hydroxo)-bis{2-{[N-(2-oxo-2H-naphthalene-1-yliden)hydrazo]}benzoato}tetracyclohexylditin (4a) dimer. The tin is five-coordinate in the solid state by two cyclohexyl and two hydroxy groups, the last coordination site is occupied by a monodentate carboxy group. The dimeric form of this compound remains in chloroform solution.

Kinetics and mechanism of the reaction of substituted O‐benzoylbenzamidoximes with sodium methoxide in methanol

The kinetics of reaction of substituted O-benzoylbenzamidoximes with sodium methoxide in methanol were studied at 25 °C. The only reaction products are substituted benzamidoximes and methyl benzoates. The slope of the dependence of rate constant on sodium methoxide concentration gradually increases, but in the presence of C18 crown ether the dependence becomes linear and the rate constant is lower than in the absence of the crown ether, which means that the reaction is catalysed by sodium cation. The rate constants of reactions with the ion pair and with methoxide ion were determined with the presumption that the rate-limited step of the catalysed reaction is the reaction of substituted O-benzoylamidoximes with the ion pair of sodium methoxide. The rate constants of the reaction with the ion pair are about 20 times higher than those of the non-catalysed process. The slopes of the dependence of log k of the non-catalysed and catalysed reactions on the pKa of substituted benzamidoximes are 1.05 and 0.94, respectively. These high values indicate the rate-limiting step involving the splitting off of substituted benzamidoxime from the tetrahedral intermediate. On the basis of the relatively high ρ constant of methanolysis at the benzoyl group substituted derivatives (2.17 and 1.98 for the non-catalysed and catalysed reactions, respectively), it can be presumed that the transition state structure will be close to the tetrahedral intermediate. Copyright

Electrochemical dissolution of steel as a typical catalyst for electro-Fenton oxidation

Although traditional Fenton reaction is known for a long time, it is still a perspective method for removal of pollution from wastewater. Applications of electro-Fenton oxidation are commonly used in wastewater treatment. These methods are classified into groups—electrochemical advanced oxidation processes. Typical catalysts for these technologies are Fe2+ ions. Comparison between two material types of steel was investigated in this paper. Alloy steel Cr–Ni and non-alloy steel were used as a source of Fe2+ ions as catalyst for electro-Fenton oxidation. Electrochemical dissolution was chosen as a method of catalyst dosage. Various parameters were tested depending on the type of material of alloy and non-alloy steel at a time. Corrosion properties were also experimentally tested of both materials of steel anodes. Electrochemically dissolved Fe2+ and Fe3+ sludge could be very well removed from treated water by the sedimentation process. At first the solutions were adjusted, then loosely precipitated, and at the end sedimented. Residual concentrations of iron in the solutions determined by UV/VIS spectrophotometry were in compliance with the threshold limits stated by the government regulation.Graphical abstract