Effets cinetiques de sels lors de la methanolyse de l'acetate de phenyle par catalyse basique en milieu methanolique: Etude perturbationnelle des effets de sels lors de l'hydrolyse ou de la méthanolyse d'esters aliphatiques ou aromatiques

Methanolysis of phenyl acetate shows a slight rate increase in the presence of NaClO₄ or NaBr or a rather large rate decrease in the presence of LiClO₄ or LiBr. These results are different from those obtained for alkaline hydrolysis of an aliphatic ester. They are interpreted in terms of a frontier orbital controlled reaction. For aliphatic esters, complexation phenomena

is predominant; for aromatic esters, due to a stabilisation of the π^* CO orbital energy level, two opposite effects are possible:

complexation inducing a rate increase, and association of the nucleophile HO^- or CH₃O^- with M⁺ leading to a rate decrease. The relative importance of these two opposite effects depends on the nature of the ester.     

Synthesis of 6-amino-1,2,3-triazolo[4,5-c] pyridin-4(5H)one (8-aza-3-deazaguanine) and 6-amino-1-(β-D-ribofuranosyl)-1,2,3-triazolo[4,5-c] pyridin-4(5H)one (8-Aza-3-deazaguanosine) via novel ring closure procedures

The total synthesis of 6-amino-1,2,3-triazolo[4,5-c]pyridin-4(5H)one (8-aza-3-deazaguanine, 3 ) and 6-amino-1-(β-D-ribofuranosyl)-1,2,3-triazolo[4,5-c]pyridin-4(5H)one (8-aza-3-deazaguano-sine, 22 ) has been described for the first time by a novel base-catalyzed ring closure of 4(5)-cyanomethyl-1,2,3-triazole-5(4)carboxamide (14) and methyl 5-cyanomethyl-1-(2,3,5-tri-O-ben-zoyl-β-D-ribofuranosyl)-1,2,3-triazole-4-carboxylate (17) , respectively. Under the catalysis of DBU, 2,4-dinitrophenylhydrazone of dimethyl 1,3-acetonedicarboxylate (7) was converted to methyl 5-methoxycarbonylmethyl-1-(2,4-dinitroanilino)-1,2,3-triazole-4-carboxylate (12) via dimethyl 2-diazo-3-iminoglutarate (8) . Catalytic reduction of 12 gave methyl 4(5)methoxycar-bonylmethyl-1,2,3-triazole-5(4)carboxylate (11) from which methyl 4(5)carbamoylmethyl-1,2,3-triazole-5(4)carboxylate (10) was obtained by ammonolysis. Dehydration of 10 provided methyl 4(5)cyanomethyl-1,2,3-triazole-5(4)carboxylate (13) which on amination gave 14 . The 1,2,3-triazole nucleosides 17, 18 and 19 were obtained from the stannic chloride-catalyzed condensation of the trimethylsilyl 13 and a fully acylated β-D-ribofuranose. The yield and ratio of the ribofuranosyl derivatives of 13 markedly depends on the ratio of stannic chloride used. The structures of the nucleosides 22 and 23 were established by a combination of NOE, ¹H-nmr and ¹³C-nmr spectroscopy.     

Potential energy curves for ground and excited states of NaLi from ab initio calculations with effective core polarization potentials

Sixteen low-lying electronic states of NaLi are investigated by SCF/valence Cl calculations including core polarization effects by means of an effective potential. Spectroscopic constants are obtained with estimated uncertainties of ΔR_e ? 0.01 Å, Δω_e ? 0.6 cm^?1 and ΔD_e ? 80 cm^?1. From a comparison of experimental and theoretical G(υ) values, we suggest a ground-state dissociation energy of 7093 ± 5 cm^?1. Using our rovibrational energies and recently measured excitation lines, we are able to improve the T_e values and dissociation energies of five excited states to an accuracv of ±8 cm^?1.     

Os(II)-nitrosyl and Os(II)-dinitrogen complexes from reactions between Os(VI)-nitrido and hydroxylamines and methoxylamines

Reactions between the Os(VI)-nitrido salts (e.g., trans-[Os(VI)(tpy)(Cl)(2)(N)]PF(6) (tpy = 2,2':6',2"-terpyridine), cis-[Os(VI)(tpy)(Cl)(2)(N)]PF(6), and fac-[Os(VI)(tpm)(Cl)(2)(N)]PF(6) (tpm = tris(pyrazol-1-yl)methane)) and the hydroxylamines (e.g., H(2)NOH and MeHNOH) and the methoxylamines (e.g., H(2)NOMe and MeHNOMe) in dry MeOH at room temperature give three different types of products. They are Os(II)-dinitrogen (e.g., trans-, cis-, or fac-[Os(II)-N(2)]), Os(II)-nitrosyl [Os(II)-NO](+) (e.g., trans- or cis-[Os(II)-NO](+)), Os(IV)-hydroxyhydrazido (e.g., cis-[Os(IV)-N(H)N(Me)(OH)](+)), and Os(IV)-methoxyhydrazido (e.g., trans-/cis-[Os(IV)-N(H)N(H)(OMe)](+), and trans-/cis-[Os(IV)-N(H)N(Me)(OMe)](+)) adducts. The products depend in a subtle way on the electron content of the starting nitrido complexes, the nature of the hydroxylamines, the nature of the methoxylamines, and the reaction conditions. Their appearance can be rationalized by invoking the formation of a series of related Os(IV) adducts which are stable or decompose to give the final products by two different pathways. The first involves internal 2-electron transfer and extrusion of H(2)O, MeOH, or MeOMe to give [Os(II)-N(2)]. The second which gives [Os(II)-NO](+) appears to involve seven-coordinate Os(IV) intermediates based on the results of an (15)N-labeling study.     

Polarographisches Verhalten der C2-Halogenkohlenwasserstoffe

Summary Investigations on the polarographic and voltammetric behaviour of organic halogen compounds were carried out in order to obtain information on the redox properties and how to develop determination and detection methods. In this second report the dp-polarographic behaviour of the halogen substituted C₂-compounds has been studied in different supporting electrolytes and in various solvents. The electrode processes are discussed and the possibilities for the polarographic determination of the C₂-halogen hydrocarbons. The detection limit is 0.25 g · ml^–1 and the linear current-concentration relationship is observed up to 25 g · ml^–1. A simple and rapid method is proposed for the dp-polarographic determination of 1,2-dibromoethane in gasoline; the relative standard deviation for 20 g · ml^–1 is ±1.8%.     

Application of an androgen receptor assay for the characterisation of the androgenic or antiandrogenic activity of various phenylurea herbicides and their derivatives.

The potency of different substances for [3H]dihydrotestosterone ([3H]DHT) displacement from the bovine androgen receptor was tested. The phenylurea herbicide linuron and its derivative 3,4-dichloroaniline (3,4-DCA), which are found in sediments and surface waters, are known to displace bound testosterone from the rat androgen receptor. Because 3,4-DCA is rapidly taken up by fish and metabolised into 3,4-dichloroacetanilide (3,4-DCAc), it was investigated whether the displacement effects are attributable to 3,4-DCA or to 3,4-DCAc. The potency of 3,4-DCAc androgen receptor binding was compared with that of several phenylurea compounds. In a radioreceptor assay with calf uterus cytosol as androgen receptor preparation, the specific binding of [3H]DHT, the endogenous ligand, was completely displaceable by increasing concentrations of 3,4-DCAc. The relative binding affinities (RBA) of the various compounds were about 1/10(4) to 1/10(5) of that of DHT. 3,4-DCAc had the relative highest affinity (1.31 x 10(-4)), followed by linuron, 3,4-dichlorophenylurea, flutamide, 3,4-DCA and diuron with the lowest RBA (2.4 x 10(-5)). Hence the metabolism of xenobiotic compounds has to be considered to estimate potential ecotoxiocological effects. This test not only can be used to screen for androgen- and antiandrogen-like substances in environmentally relevant samples such as surface waters, but might also be applied for drug testing and for residue monitoring.     

Selten‐Erd‐Metall‐Koordinationspolymere: Synthesen und Kristallstrukturen von drei neuen Glutaraten, [Pr2(Glu)3(H2O)4] · 10,5H2O, [Pr(Glu)(H2O)2]Cl und [Er(Glu)(GluH)(H2O)2]

Rare‐Earth‐Metal Coordination Polymers: Syntheses and Crystal Structures of Three New Glutarates, [Pr₂(Glu)₃(H₂O)₄] · 10.5H₂O, [Pr(Glu)(H₂O)₂]Cl, and [Er(Glu)(GluH)(H₂O)₂] The new rare‐earth dicarboxylates [Pr₂(Glu)₃(H₂O)₄] · 10.5H₂O ( 1 ), [Pr(Glu)(H₂O)₂]Cl ( 2 ) and [Er(Glu)(GluH)(H₂O)₂] ( 3 ) were obtained from the reactions of glutaric acid with PrCl₃·6H₂O and Er(OH)₃, respectively. The crystal structures were determined by single‐crystal X‐ray diffraction. [Pr₂(Glu)₃(H₂O)₄] · 10,5H₂O crystallizes in the orthorhombic space group Pnma (no. 62) with a = 871.7(4), b = 3105.0(9), c = 1308.3(9) pm and Z = 4. The crystals of [Pr(Glu)(H₂O)₂]Cl are monoclinic (I2/a; no. 15) with a = 786.2(1), b = 1527.6(2) c = 801.2(1) pm, β = 99.78(1)° and Z = 4. [Er(Glu)(GluH)(H₂O)₂] crystallizes in the monoclinic space group P2₁/a (no. 14) with lattice parameters of a = 882.4(1), b = 1375.3(2), c = 1267.4(2) pm, β = 107.13(1)° and Z = 4. The rare‐earth cations have the coordination numbers 10 ( 1 ), 8 + 1 ( 2 ) and 9 ( 3 ). The individual polyhedra are connected to chains and further to sheets in 1 and 2 and to double chains in 3 . Only in the water‐rich compound 1 there are channels that contain crystal water molecules. It, therefore, has a considerably lower density than 2 and 3 .     

Ternäre Halogenide vom Typ A3MX6. IV. [1]. Ternäre Halogenide des Scandiums mit Natrium,Na3ScX6 (X = F,Cl, Br): Synthese,Strukturen, Ionenleitfähigkeit

Ternary Halides of the A₃MX₆ Type. IV. Ternary Halides of Scandium with Sodium, Na₃ScX₆ (X = F, Cl, Br): Synthesis, Structures, Ionic Conductivity X-ray studies on single crystals of Na₃ScF₆ and Na₃ScBr₆ show, that Na₃ScF₆ crystallizes with the cryolite type (monoclinic, P2₁/n, Z = 2, a = 560.16(9), b = 580.31(8), c = 812.1(2)pm, β = 90.720(14)°) and Na₃ScBr₆, as the only ternary bromide of the rare earth elements with sodium, in the Na₃CrCl₆ type (trigonal, P3 1c, Z = 2, a = 728.95(7), c = 1309.29(17)pm). The ionic conductivity of powder samples of Na₃ScF₆, Na₃ScBr₆ and of Na₃ScCl₆ was studied by impedance spectroscopy. Activation energies were determined as 1.22 eV, 0.80 eV and 0.71 eV for the fluoride, chloride and bromide, respectively. The differences are explained from the crystal structures and the sizes and polarizabilities of the anions.