Oxidative nucleophilic substitution of hydrogen in nitroarenes by silyl enol ethers

Enolates generated by treatment of silyl ketene acetals and enol ethers with fluoride ion sources add to nitroarenes to produce σ^H adducts that oxidize either with KMnO₄ to give substituted nitroarenes or with dimethyldioxirane to give substituted phenols. In the latter case the oxidation results in replacement of the nitro group with a hydroxy group. It was shown that high effectiveness of these reactions is not due to stabilization of the σ^H adducts via O-silylation but due to the nature of the accompanying cation.     

Oxidative nucleophilic substitution of hydrogen in nitroarenes with phenylacetic acid derivatives

Oxidative nucleophilic substitution of hydrogen (ONSH) in nitroarenes with carbanion of isopropyl phenyl acetate gives various products depending on the conditions and oxidant. The reaction carried out in liquid ammonia and KMnO₄ oxidant gives iso-propyl α-hydroxy-α-nitroarylphenylacetates formed via hydroxylation of the initial ONSH products. In some cases additionally dimeric, trimeric and tetrameric products are formed. In THF and Bu₄N⁺MnO₄⁻ or DDQ oxidants simple ONSH products are formed whereas oxidation by dimethyl dioxirane (DMD) gave iso-propyl hydroxyaryl phenyl acetates. The dimeric and trimeric products are apparently formed via coupling of nitrobenzylic radicals generated in course of oxidation with nitrobenzylic carbanions of the ONSH products.     

On the complex formation equilibria between dioxouranium(VI) and sulfate ions

The complexation equilibria between UO2(2+) and SO4(2-) ions have been studied at 25 degrees C in the ionic medium 3 M NaClO4 by potentiometry, by spectrophotometry and by solubility measurements of UO2(IO3)2. The potentiometric investigation was carried out with the Hg-Hg2SO4(s)-SO4(2-) half-cell and glass electrode in the sulfate concentration range 0.005 to 0.07 M. The optical absorbances in the UV-visible region and the solubility data cover the ligand concentration range 0.005 to 0.3 M. The data could be explained by assuming the complexes and equilibrium constants [Table: see text]. The constants in the infinite dilution reference state, log beta1o = 3.08 +/- 0.15 and log beta2o = 4.28 +/- 0.15, estimated by assuming the validity of the specific interaction theory, are practically coincident with literature data.     

Oxidative nucleophilic substitution: transformation of alkylboronic derivatives

An efficient amidation reaction is described in this paper. Potassium alkyltrifluoroborate salts can be transforming to amides from nitriles in the presence of copper acetate and boron trifluoride. An extension of this reaction allowed the formation of amines, ethers, and C-C bond.     

Oxidative nucleophilic substitution of hydrogen in nitroarenes with trifluoromethyl carbanions. Synthesis of trifluoromethyl phenols

Trifluoromethyl carbanions generated from the Ruppert reagent and TASF add to highly electron-deficient nitroarenes to produce σ^H adducts subsequently oxidized with dimethyldioxirane to substituted trifluoromethyl phenols.     

Mechanism of nucleophilic substitution of hydrogen in azines

A study of the kinetics of the reaction of N-methylacridinium iodide with arylamines shows that the reaction proceeds via a stepwise bimolecular mechanism with the formation of an intermediate.See [1] for communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, September, 1976.     

Hydroxylation of nitro-(pentafluorosulfanyl)benzenes via vicarious nucleophilic substitution of hydrogen

Para- and meta-nitro-(pentafluorosulfanyl)benzenes react with anions of cumyl hydroperoxide in the presence of t-BuOK in liquid ammonia to form nitro-(pentafluorosulfanyl)phenols. Their reduction with hydrogen in the presence of Raney-Nickel provides amino-(pentafluorosulfanyl)phenols.     

Cathodically activated nucleophilic aromatic substitution of hydrogen: a novel electrochemical mechanism

Cathodically activated nucleophilic aromatic substitution of hydrogen (SNArH) is reported for the first time; the 1,3,5-trinitrobenzene radical anion reacts with the nucleophile N-methylformamide leading to high yields of the sigma H-complex radical anion; this intermediate can be easily oxidised electrochemically by means of a three-electron mechanism giving rise to the nucleophilic aromatic substitution product (NASH product) in good yield.     

Sequestering ability of polycarboxylic ligands towards dioxouranium(VI)

In this paper we report a comparison on the sequestering ability of some polycarboxylic ligands towards dioxouranium(VI) (UO(2)(2+), uranyl). Ligands taken into account are mono- (acetate), di- (oxalate, malonate, succinate and azelate), tri- (1,2,3-propanetricarboxylate) and hexa-carboxylate (1,2,3,4,5,6-benzenehexacarboxylate). The sequestering ability of polycarboxylic ligands towards UO(2)(2+) was quantified by a new approach expressed by means of a sigmoid Boltzman type equation and of a empirical parameters (pL(50)) which defines the amount of ligand necessary to sequester 50% of the total UO(2)(2+) concentration. A fairly linear correlation was obtained between pL(50) or log K(110) (log K(110) refers to the equilibrium: UO(2)(2+)+L(z-)=UO(2)L((2-z)); L=generic ligand) and the polyanion charges. In order to complete the picture, a tetra-carboxylate ligand (1,2,3,4-butanetetracarboxylate) was studied in NaCl aqueous solutions at 0相似文献   

On the hydrolysis of the dioxouranium(VI) ion in sulfate solutions

The formation of ternary UO2(2+)-(OH-)-SO4(2-) complexes has been studied at 25 degrees C in 3 M NaClO4 ionic medium by measurements with a glass electrode. The solutions had uranium concentrations between 0.3 and 30 mM, sulfate between 20 and 200 mM, and 1.66 < or = [SO4(2-)]/[U(VI)] < or = 300. The hydrogen ion concentration ranged from 10(-3) M to incipient precipitation of basic sulfates. This occurred, depending on the metal concentration, at [H+] between 10(-4) and 10(-5.3) M. In the interpretation of the data the stabilities of binary complexes were assumed from independent sources. The data could be explained with the mixed complexes and equilibria (beta(pqr)(3sigma) refers to pUO2(2+) + qH2O + rSO4(2-) <==> (UO2)p(OH)q(SO4)r(2p-q-2r) + qH+): logbeta222 = -2.94 +/- 0.03, logbeta341 = -9.82 +/- 0.06, logbeta211 = -0.30 +/- 0.09, logbeta212 = 1.09 +/- 0.09, logbeta351 = -15.04 +/- 0.09 and logbeta462 = -14.40 +/- 0.06. The fit could be improved by including UO2OH+ with logbeta110 = -5.1 +/- 0.1. The identity of the minor species remains, however, an open question.     

Reactions of oxidative nucleophilic substitution of hydrogen in nitroarenes

The review summarizes information on the reactions of oxidative nucleophilic substitution of hydrogen in nitro derivatives of carboaromatic substrates with N-, C-, O-, and P-nucleophiles.     

Structural model of dioxouranium(VI) with hydrazono ligands

Synthesis and characterization of several new coordination compounds of dioxouranium(VI) heterochelates with bidentate hydrazono compounds derived from 1-phenyl-3-methyl-5-pyrazolone are described. The ligands and uranayl complexes have been characterized by various physico-chemical techniques. The bond lengths and the force constant have been calculated from asymmetric stretching frequency of OUO groups. The infrared spectral studies showed a monobasic bidentate behaviour with the oxygen and hydrazo nitrogen donor system. The effect of Hammett's constant on the bond distances and the force constants were also discussed and drawn. Wilson's matrix method, Badger's formula, Jones and El-Sonbati equations were used to determine the stretching and interaction force constant from which the UO bond distances were calculated. The bond distances of these complexes were also investigated.     

Synthesis and characterization of heavier dioxouranium(VI) dihalides

The synthesis and characterization of the dioxouranium(VI) dibromide and iodide hydrates, UO(2)Br(2)x3H(2)O (1), [UO(2)Br(2)(OH(2))(2)](2) (2), and UO(2)I(2)x2H(2)Ox4Et(2)O (3), are reported. Moreover, adducts of UO(2)I(2) and UO(2)Br(2) with large, bulky OP(NMe(2))(3) and OPPh(3) ligands such as UO(2)I(2)(OP(NMe(2))(3))(2) (4), UO(2)Br(2)(OP(NMe(2))(3))(2) (5), and UO(2)I(2)(OPPh(3))(2)(6) are discussed. The structures of the following compounds were determined using single-crystal X-ray diffraction techniques: (1) monoclinic, P2(1)/c, a = 9.7376(8) A, b = 6.5471(5) A, c = 12.817(1) A, beta = 94.104(1) degrees , V = 815.0(1) A(3), Z = 4; (2) monoclinic, P2(1)/c, a = 6.0568(7) A, b = 10.5117(9) A, c = 10.362(1) A, beta = 99.62(1) degrees , V = 650.5(1) A(3), Z = 2; (4) tetragonal, P4(1)2(1)2, a = 10.6519(3) A, b = 10.6519(3) A, c = 24.0758(6) A, V = 2731.7(1) A(3), Z = 4; (5) tetragonal, P4(1)2(1)2, a = 10.4645(1) A, b = 10.4645(1) A, c = 23.7805(3) A, V = 2604.10(5) A(3), Z = 4, and (6) monoclinic, P2(1)/c, a = 9.6543(1) A, b = 18.8968(3) A, c = 10.9042(2) A, beta =115.2134(5) degrees , V = 1783.01(5) A(3), Z = 2. Whereas 1 and 2 are the first UO(2)Br(2) hydrates and the last missing members of the UO(2)X(2) hydrate (X = Cl --> I) series to be structurally characterized, 4 and 6 contain room-temperature stable U(VI)-I bonds with 4 being the first structurally characterized room temperature stable U(VI)-I compound which can be conveniently prepared on a gram scale in quantitative yield. The synthesis and characterization of 5 using an analogous halogen exchange reaction to that used for the preparation of 4 is also reported.     

Solvent extraction of dioxouranium(VI) with dialkyldithiophosphoric acids

The extraction of dioxouranium(VI) species from acidic aqueous solutions into benzene, in the presence of dialkyldithiophosphoric acids occurs with moderate partition coefficients, increasing with the length of the alkyl chain. The mechanism involves the formation of neutral [UO₂[S₂P(OR)₂]₂] species soluble in benzene, the partition is strongly affected by complexation in the aqueous phase, when the alkyl chain is short. Distribution coefficients and extraction constants have been determined under various conditions.     

On the hydrolysis of the dioxouranium(VI) ion in oxalate solutions

The complex formation between the dioxouranium (VI) and the oxalate ions has been investigated by measuring the potential of a glass electrode, at 25.00 degrees C, in 1 and 3 M NaClO4, at lower acidities than 10(-4.5) M, in order to favour the formation of (mixed) ternary species. The upper limits of concentration of all the analytical parameters have been imposed by the modest solubility of Na2C2O4 in the ionic media. The experimental measurements at different ionic strengths have been treated by means of the computerised least square programme LETAGROP - ETITR. Ternary complexes of general composition (p, q, r) are formed according to reaction (1), in addition to the already reported binary complexes. pUO2(2+) + qH2O + rC2O4(2-) <==> (UO2)p(OH)q(C2O4)r(2p-q-2r)(+) + qH+ (1). The stoichiometric compositions of the ternary species are (1, 1, 1), (2, 4, 2), (2, 2, 4). Their formation constants, expressed in molality, obtained in the two ionic media, are listed below. [table: see text]. For reasons discussed in the present work in the last column only the value of the constant in 1 M ionic medium is reported for the species (2, 4, 2). Additional evidence on the stoichiometric composition of the species formed is afforded by the mass-spectrometric measurements, collected in solutions of known composition.     

Ab initio and DFT benchmark study for nucleophilic substitution at carbon (SN2@C) and silicon (SN2@Si)

To obtain a set of consistent benchmark potential energy surfaces (PES) for the two archetypal nucleophilic substitution reactions of the chloride anion at carbon in chloromethane (S(N)2@C) and at silicon in chlorosilane (S(N)2@Si), we have explored these PESes using a hierarchical series of ab initio methods [HF, MP2, MP4SDQ, CCSD, CCSD(T)] in combination with a hierarchical series of six Gaussian-type basis sets, up to g polarization. Relative energies of stationary points are converged to within 0.01 to 0.56 kcal/mol as a function of the basis-set size. Our best estimate, at CCSD(T)/aug-cc-pVQZ, for the relative energies of the [Cl(-), CH(3)Cl] reactant complex, the [Cl-CH(3)-Cl](-) transition state and the stable [Cl-SiH(3)-Cl](-) transition complex is -10.42, +2.52, and -27.10 kcal/mol, respectively. Furthermore, we have investigated the performance for these reactions of four popular density functionals, namely, BP86, BLYP, B3LYP, and OLYP, in combination with a large doubly polarized Slater-type basis set of triple-zeta quality (TZ2P). Best overall agreement with our CCSD(T)/aug-cc-pVQZ benchmark is obtained with OLYP and B3LYP. However, OLYP performs better for the S(N)2@C overall and central barriers, which it underestimates by 2.65 and 4.05 kcal/mol, respectively. The other DFT approaches underestimate these barriers by some 4.8 (B3LYP) to 9.0 kcal/mol (BLYP).     

The solvation of the dioxouranium(VI) ion by dimethyl sulfoxide

The species UO₂(DMSO) ₅ ²⁺ is shown from¹H NMR studies to be the predominant dioxouranium(VI) species existing in dilute anhydrous acetonedimethyl sulfoxide (DMSO) solutions, and this result is compared with data reported for the analogous water-acetone-dimethyl sulfoxide system. Complete line-shape analyses of exchange-modified¹H NMR line shapes indicate that the mechanism for DMSO exchange on UO₂(DMSO) ₅ ²⁺ is probably of theD orI _D type. A typical set of rate parameters arek _ex (260°K) =273±14 sec^–1, H ^#=38.9±0.5 kJ-mole^–1, and S ^#=–47.5±1.8 J-^oK^–1-mole^–1 for a solution in which [UO₂(DMSO)₅ ²⁺], [DMSO], and [d ₆ acetone] are, respectively, 0.01155, 0.0875, and 13.00 moles-dm^–3.