Activity coefficients of hydrocarbons at infinite dilution in di-n-octyltin dichloride. Comparison with results obtained in other alkyltin solvents

The gas chromatographic method was employed to measure the infinite dilution activity coefficients of twenty-eight hydrocarbons of different types in di-n-octyltin dichloride between 50 and 80°C, and of seven branched alkanes in tri-n-octyltin chloride between 40 and 60°C. A comparison is made between the results obtained for all the solutes in both solvents and in tetra-n-octyltin.     

Structural diversity in the coordination of amidines and guanidines to monovalent metal halides

A series of structurally characterised, monovalent metal-halide complexes incorporating neutral amidine and guanidine ligands is reported. N,N'-diphenylbenzamidine reacted with copper(I) chloride to afford the bis-ligand complex [CuCl(PhC[NPh][NHPh])2]2 (1), that exists as a chlorine bridged dimer in the solid state, with a non-symmetrical distribution of NH...Cl interactions within the 'Cu2Cl2' metallacycle. In contrast, only one equivalent of the guanidine, Me2NC[NiPr][NHiPr] (2), is coordinated in the copper(I) iodide complex [CuI(Me2NC[NiPr][NHiPr])]2 (3), which was also isolated as the dimer with bridging halide atoms. The molecular structure of the bicyclic guanidine, 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-alpha]pyrimidine (hppH), is reported, revealing a hydrogen bridged dimer with extensive delocalisation throughout the ligand framework. Coordination of hppH to lithium chloride afforded the dimeric bis-ligand complex [LiCl(hppH)2]2 (4) in which each hppH molecule interacts with a different chlorine atom of the central 'Li2Cl2' core of the molecule via NH...Cl hydrogen bonding. In contrast the 2:1 ligand to metal complex is formed with silver(I) chloride to afford AgCl(hppH)2 (5), a unique example of a monomeric, three-coordinate silver chloride supported by nitrogen-based ligands. The series of mixed ligand complexes [CuX(hppH)(PPh3)]n (6, X = Cl, n= 1; 7, X = Br, n= 2; 8 X = I, n= 2) have also been synthesised and structurally characterised, allowing comparisons of the relative coordinating behaviour of hppH and PPh3 as neutral donors at copper(I) centres to be made.     

Synthesis of tris- and tetrakis(pyrazol-1-yl)borate gold(III) complexes. Crystal structures of [Au[kappa(2)-N,N'-BH(Pz)(3)]Cl(2)] (pz = pyrazol-1-yl) and [Au[kappa(2)-N,N'-B(Pz)(4)](kappa(2)-C,N-C(6)H(4)CH(2)NMe(2)-2)]ClO(4).CHCl(3)

Na[BH(pz)(3)] and Na[AuCl(4)].2H(2)O react in water (1:1) to give [Au[kappa(2)-N,N'-BH(pz)(3)]Cl(2)] (1) or, in the presence of NaClO(4) (2:1:1), the cationic complex [Au[kappa(2)-N,N'-BH(pz)(3)](2)]ClO(4) (2). The reactions of Na[B(pz)(4)] with the cyclometalated gold complexes [AuRCl(2)] and NaClO(4) (1:1:1) produce [Au[kappa(2)-N,N'-B(pz)(4)](R)]ClO(4) [R = kappa(2)-C,N-C(6)H(4)CH(2)NMe(2)-2 (3)] or [Au[kappa(2)-N,N'-B(pz)(4)](R)Cl] [R = C(6)H(3)(N=NC(6)H(4)Me-4')-2-Me-5 (4)], respectively, although 4 is better obtained in the absence of NaClO(4). The crystal structures of 1 and 3.CHCl(3) are reported. Both complexes display the gold center in square planar environments, two coordination sites being occupied by the chelating poly(pyrazolyl)borate ligands.     

Pyrimidine N-oxides. Oxidation of 5-nitroso-2,4,6-triaminopyrimidine

The peroxytrifluoroacetic acid oxidation of 5-nitroso-2,4,6-triaminopyrimidine ( 1b ) led to the formation of two products: 5-nitro-2,4,6-triaminopyrimidine 1-N-oxide ( 2 ) and 5-nitro-2,4,6-triaminopyrimidine 1-3-di-N-oxide ( 3 ). On the basis of previous experience 2 was the sole expected oxidation product. However, 3 represents a rather unexpected development in that di-N-oxides in the pyrimidine series are uncommon. The yields are good for both products and structures are assigned on the basis of elemental analysis, mass spectral data, and chemical reactions. The reaction sequence is also discussed.     

Comparison of normal-phase and reversed-phase gravity-flow column methods for provitamin A determination

Summary Considering the high cost of HPLC, the use of preparative C₁₈ packing material as stationary phase in classical gravity-flow columns is proposed as an alternative for developing countries. In the present study, three methods were compared, one utilizing a normal-phase MgO: HyfloSupercel column, developed with increasing concentration of acetone in petroleum ether and two utilizing C₁₈ reversed-phase columns developed with acetonitrile-methanol-chloroform (RP-C₁₈ method) or with decreasing concentration of water in acetone (modified RP-C₁₈ method). Percent recoveries of -carotene from the columns were 98, 96 and 98% and of the entire analysis (-carotene added to kale) 92, 89 and 92%, for the normal phase, RP-C₁₈ and modified RP-C₁₈ methods respectively. No significant difference was observed in the provitamin A contents (exclusively -carotene) of two leafy vegetables determined by the modified reversed-phase and normal-phase methods; however, significantly lower values were obtained by the RP-C₁₈ method. The situation became more complicated when samples containing other provitamins were analyzed. For squash both types of stationary phase could separate - and -carotene; however, for tomato and red-fleshed papaya, part of lycopene remained mixed with -carotene in both reversed-phase columns. Although -cryptoxanthin was separated in the modified RP column, it was also mixed with lycopene in the RP column. For all samples, the normal-phase column demonstrated much better separation.     

Enantioselective Formation of 2‐Azetidinones by Ring‐Assisted Cyclization of Interlocked N‐(α‐Methyl)benzyl Fumaramides

The synthesis of optically active interlocked and non‐interlocked 2‐azetidinones by intramolecular cyclization of N‐(α‐methyl)benzyl fumaramide [2]rotaxanes is described. Two different strategies of asymmetric induction were tested in which the chiral group was located either proximal or distal to the reacting center of the thread. During these experiments, an interesting equilibration process inside the macrocyclic void occurred, thus leading to the cyclization through the (α‐methyl)benzyl carbon atom and giving rise to β‐lactams, with a quaternary carbon atom, in an enantio‐ and diastereocontrolled manner. This cyclization also proceeds in kinetically stable chiral pseudo[2]rotaxanes, thus allowing further dethreading to provide enantioenriched 3,4‐disubstituted trans‐2‐azetidinones. The stereochemical outcomes of the cyclizations inside and outside the macrocycle demonstrated noticeable differences.     

Geobacter species enhances pit depth on 304L stainless steel in a medium lacking with electron donor

Geobacter sulfurreducens bacteria increased the open circuit potential of 304L stainless steel by around 320 mV in only a few hours after inoculation. This represents a significant increase in the corrosion risk. In contrast, the oxidation of acetate, which is catalysed by well-established biofilms, shifted the pitting potential towards positive values. In acetate-lacking media, pitting occurred with and without bacteria in the same range of potential values, but the presence of bacteria drastically increased the size of pits. AFM showed pits more than 10 times broader and deeper due to the presence of bacteria.In the absence of acetate, the masking effect due to acetate oxidation disappeared and the full corrosive effect of the biofilm was revealed.This also fully explains why pitting was predominantly observed close to surface areas where bacterial settlement was the densest.     

Survey on thermodynamic properties for the complexation behaviour of some calixarene and cucurbituril receptors

Some aspects of the complex formation reaction between amino acids, short peptides, and nucleobases with calixarenes and cucurbiturils in solution are presented. A brief survey of their stability constants, enthalpies, and entropies data obtained by different techniques in various solvents is reported, along with the ability of these receptors to be employed as carriers through liquid membrane in view of separating biological compounds.