Kinetics of radiation-induced abstraction of hydrogen atoms by CCl3 radicals in the liquid phase: 2,3-dimethylbutane

The kinetics of the gamma-radiation induced free radical reactions in carbon tetrachloride solutions of 2,3-dimethylbutane (DMB) were studied in the temperature range 32–118 °C. The kinetics of the following reactions were measured: and the following rate constants expression was obtained: . The activation energy and the A factor obtained are in good agreement with the values obtained at the gaseous phase, considering the activation energy for self-diffusion of CCl₄.     

Organosilver(I) chemistry: On the reaction of RAg and R2AgMgCl compounds with conjugated enynenitriles

The addition of RAg and R₂AgMgCl to enynenitriles

is described. RAg reagents prefer to transfer their R group to the double bond of these nitriles, so that after protolysis 2,3-alkadienenitriles are obtained, while the homoargentates generally give 2,4-alkadienenitriles. The regio- and stereo-chemical course of the reactions are compared with those in additions of RCu and R₂CuMgCl to the enynenitriles.     

Reactions of palladium (II) chloride with 1,4 - diphenyl - 2,3 - dimethyl - 1,4 - diazabutadiene and 1,4-DI(p-methoxyphenyl)-2,3-dimethyl- 1,4 - diazabutadiene

The reactions of palladium(II) chloride with 1,4 - diphenyl - 2,3 - dimethyl - 1,4 - diazabutadiene and 1,4 - di(p - methoxyphenyl) - 2,3 - dimethyl - 1,4 - diazabutadiene are described. With 1,4 - diphenyl - 2,3 - dimethyl - 1,4 - diazabutadiene diimine fission is produced, giving rise to a product identified by elemental analysis, IR and Raman spectra, and X-ray diffraction, as trans-dichlorobis(aniline) palladium(II). The complex is soluble in dimethylformamide and crystallizes with two molecules of solvent. The substance crystallizes in the monoclinic space group P2₁/n. The X-ray data were refined to R = 0.047 and R_w = 0.046. Final distances are PdN = 2.060(5)Åand PdC1 = 2.299(2)Å. There are two bifurcated intermolecular NH ... C1 and CH... C1 hydrogen bonds which, together with one more intermolecular hydrogen bond NH... O, are responsible for the packing of the molecules. However, when 1,4 - di(p - methoxyphenyl) - 2,3 - dimethyl - 1,4 - diazabutadiene was treated with palladium chloride under the same conditions cis - dichloro - 1,4 - di(p - methoxyphenyl) - 2,3 - dimethyl - 1,4 - diazabutadiene was formed, as deduced from elemental analysis, and IR and Raman spectra.     

Silaheterocyklen. I Reaktionen von H2CCHSiCl3 mit LiBut

Silaheterocycles. I. Reactions of H₂C?CHSiCl₃ with LiBu^t The reactions of H₂C?CHSiCl₃ ( 3 ) with LiBu^t in n-pentane are studied under various conditions (stoichiometry, concentration, temperature). They yield complex product-mixtures which are analysed by GC/MS and GC/IR techniques. The reaction pathways are determined by several factors: (a) The number of Cl atoms and the polarity of the Si-Cl bond, (b) the nucleophilicity of and (c) the participation of the ylidic form in the ground-state of 3 . Under mild conditions the addition of LiBu^t to the vinyl group mainly leads to the ã-lithio adduct Cl₃SiCH(Li)CH₂Bu^t, which, in competition to substitution, undergoes different following reactions: (a) 1,2-LiCl elimination to silaethenes, (b) 2,3-LiH elimination to trans-silyl/butylethenes and (c) intermolecular Si-C-coupling with the formation of chains of high molecular weights. The primary compound Cl₂Si?CHCH₂Bu^t undergoes self-dimerization or reacts with butylated Si?C species to 1,3-disilacyclobutanes. Furthermore ethene derivatives R¹R²R³SiCH?CHBu^t are produced by the addition of LiBu^t to the SiC double bond and 2,3-LiH elimination. The product pattern suggests the participation of silaethenes BuCl_(2-n)Si?CHCH₂Bu^t (n = 0–2) in the reaction course.     

N-Atom measurements in high temperature C2N2/NO/Ar reaction systems

N-atom concentration profiles were measured in highly diluted C₂N₂/NO/Ar reaction systems behind reflected shock waves at temperatures between 3050 K and 4430 K by applying atomic resonance absorption spectroscopy (ARAS). C₂N₂ served as a thermal source for CN radical which react with both, NO and the subsequently formed N atoms. Computer simulations based on a simplified reaction mechanism revealed strong sensitivity of the measured N atoms to the elementary reactions: A fitting procedure of all experiments allowed determination of individual values of the rate coefficients: The present results enlarge the temperature range of the recommended Arrhenius expression of k₅ |1| and confirm recent measurements of the backward reaction of (R-9) |2,3|. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 35–41, 1997.     

Functionalization of Non‐activated C?H Bonds of Alkanes: An Effective and Recyclable Catalytic System Based on Fluorinated Silver Catalysts and Solvents

The complexes F_n‐TpAg(L) (F_n‐Tp=a perfluorinated hydrotris(indazolyl) borate ligand; L=acetone or tetrahydrofuran) efficiently catalyze the functionalization of non‐activated alkanes such as hexane, 2,3‐dimethylbutane, or 2‐methylpentane by insertion of CHCO₂Et units (from N₂CHCO₂Et, ethyl diazoacetate, EDA) into their C? H bonds. The reactions are quantitative (EDA‐based), with no byproducts derived from diazo coupling being formed. In the case of hexane, the functionalization of the methyl C? H bonds has been achieved with the highest regioselectivity known to date with this diazo compound. This catalytic system also operates under biphasic conditions by using fluorous solvents such as Fomblin or perfluorophenanthrene. Several cycles of catalyst recovery and reuse have been performed, with identical chemo‐ and regioselectivities.     

Synthesis and Spectral and Electrochemical Characterization of Novel Substituted 1,4-Naphthoquinone Derivatives

The novel substituted 2,3-dichloro-1,4-naphthoquinone derivatives were synthesized from the reactions of (1) and related nucleophilles in sodium carbonate (Na₂CO₃) solution of ethanol, chloroform with Et₃N, or potassium carbonate (K₂CO₃) solution of acetonitrile. The structures of novel compounds were characterized by using microanalysis, Fourier transform–infrared, ¹H NMR, ¹³C NMR, mass spectrometry, and cyclic voltammetry (CV).

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

A calorimetric study of the silver (I) complexes of some sulfur-containing amines

The enthalpies of the reactions in 0.5 M KNO₃ at 25°C between the hydrogen and silver(I) ions and a number of sulfur-containing amines of the general formula R'-S-(CH₂)NR₂ where

and n=2,3, have been determined by means of direct calorimetric titrations. By the use of the ΔG values reported elsewhere, the corresponding ΔS values have been calculated. the complex formation in acid, neutral and alkaline medium is discussed.     

Anion sensing by Phenazine-based urea/thiourea receptors

The novel colorimetric receptors 2,3-bis-N-(9,10-diaza-anthracen-1-yl)-N′-phenylurea and 2,3-bis-N-(9,10-diaza-anthracen-1-yl)-N′-phenylthiourea have been prepared by the reaction of 2,3-diaminophenazine with phenylisocyanate and phenylisothiocyanate, respectively, in quantitative yields. The interaction and colorimetric sensing properties of receptor = 2 and 3 with different anions were investigated by naked eye, UV-vis and fluorescence spectroscopy in DMSO. The receptors effectively and selectively recognized biologically important F⁻, CH₃COO⁻, H₂P in the presence of other anions, such as Cl⁻, Br⁻, I⁻ and HS in DMSO.     

Pyrido[2,3-d]pyrimidines 3. Synthesis and properties of 7-chloro- and 6-nitro-7-chloropyrido[2,3-d]pyrimidine-2,4,5-triones

7-Chloropyridopyrimidine was obtained by diazotization of 1,3-dimethyl-7-amino-8H-pyrido[2,3-d]pyrimidine-2,4,5-trione in HCl, and its nitration and reactions with nucleophilic reagents were studied. An imidazo[1,2:1, 6]pyrido[2,3-d]pyrimidine derivative was synthesized.See [1] for Communication 2.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 497–501, April, 1991.     

Role of reactive intermediates in the radiolytic degradation of Acid Red 1 in aqueous solution

The role of reactive intermediates of water radiolysis (e_aq⁻, H, HO, O₂⁻/HO₂) in decoloration and mineralization of aqueous solutions of Acid Red 1 dye was investigated. The decoloration is highly effective in the reactions of e_aq⁻ and H, and less effective in HO reactions. The O₂⁻/HO₂ pair does not take part in decoloration. For mineralization, which is an oxidative degradation, HO radicals are needed: the efficiency increases with the dissolved oxygen concentration. The reactions of the O₂⁻/HO₂ radical pair slightly increase the rate of mineralization. Iron and copper ions (possible constituents of waste waters) in low concentration do not influence the reactions.     

Synthesis and characterization of 2,3-bis(hydroxyimino)-1,2,3,4-tetrahydro-pyrido[2,3-b]pyrazine and its nickel(II), cobalt(II), copper(II), palladium(II), cadmium(II) and cobalt(III) complexes

Summary 2,3-Bis(hydroxyimino)-1,2,3,4-tetrahydro-pyrido[2,3-b]pyrazine (H₂L), prepared from 2,3-diaminopyridine and cyanogen-di-N-oxide has been converted into nickel(II), palladium(II), copper(II), cobalt(II), and cobalt(III) complexes (H₂L) with a 12 metal:ligand ratio. The ligands coordinate through the two N atoms, as do most vicinal dioximes. [(LH)Cl(H₂O)Cd], contains a six-membered chelate ring. [Co(HL)₂(L)Cl] has also been prepared using triphenylphosphine, triphenylarsine, thiophene and chloride as axial ligands. The structure of thevic-dioxime and its complexes are proposed on the basis of elemental analysis, i.r.,¹H-n.m.r. and uv-visible measurements.     

Cp2TiCl2-Catalyzed hydroalkylation of α-olefins with ButBr—Et3Al

The reactions of olefins with alkyl halides and Et₃Al in the presence of catalytic amounts of Cp₂TiCl₂ were studied. Unbranched -olefins of the aliphatic series underwent hydroalkylation under the action of tert-butyl bromide to form 2,3-dimethylalkanes.     

Photoredox reactions of Cr(III) mixed-ligand complexes

Irradiation of chromium(III) complexes with oxalate and pyridinedicarboxylate ligands (pda = 2,3-, 2,4-, or 2,5-dicarboxylate) leads to diverse behaviors, dictated by light energy, presence of oxygen and the ligand nature. Irradiation within the MC bands is unaffected by O₂ and results in ligand substitution. The LMCT excitation is effective only when oxalate is coordinated to Cr(III); then electron transfer from oxalate to central ion generates an intermediate, consisted of a Cr(II)species and the C₂O₄^? radicals. The species undergo fast redox reactions dependent on the presence of O₂ and the pda ligand.(1) In anoxic medium the fast outersphere electron transfer from Cr(II) to solvent, generates hydrated electrons and re-oxidizes the chromium centre to Cr^III. Then geminate recombination regenerates substrate, whereas competitive release of the C₂O₄^? radical leads to substitution of one oxalate ligand by two water molecules (aquation induced by the LMCT excitation). In the presence of the pda ligand the outersphere electron transfer is accompanied by the innersphere CT, generating Cr(III) coordinated to two radical ligands: C₂O₄^? and pda^3?; the intermediate releases also e_aq^?, but this reaction is slower than that of the homoleptic oxalate complex. Hydrated electrons are scavenged also by the released radicals. All these processes are completed within microseconds and in consequence, the Cr(III) complexes irradiated in deoxygenated solutions are insensitive to subsequent oxygenation.(2) When UV-irradiation is carried out in oxygenated medium reaction of Cr(II) species with molecular oxygen competes with the outer- or inner electron transfer observed in anoxic medium. Both these pathways result in generation of chromate(VI). Quantum yield of the Cr(VI) production is sensitive to the presence and structure of pda ligand, decreasing within the series 2,3-pda > 2,4-pda > 2,5-pda.     

Phenomenon of isoparametricity in reactions of <Emphasis Type="Italic">trans</Emphasis>-2,3-diaryloxiranes with arenesulfonic acids. Mechanistic interpretation

Nonadditive effects of substituents X and Y are manifested in reactions of symmetrically X-substituted trans-2,3-diaryloxiranes with Y-substituted arenesulfonic acids. The isoparametric point is reached experimentally: close to the point τ _X ^IP = 4.73 on substituent Х the rate of the oxirane ring opening of trans-2,3-bis(3-bromo-5-nitrophenyl)oxirane (τ_X = 4.38) practically does not depend on substituent Y (ρ _Y ^X = 0.10±0.05). The results of cross correlation analysis of the kinetic data are applied to interpretation of the mechanism of the studied reactions.     

Free radical addition of F-alkyl compounds to unsaturated carboxylic anhydrides and their derivatives

Many perfluoroalkyl-substituted organic compounds have been obtained through free radical addition of F-alkyl iodides to a center of unsaturation:

X, Y, and Z may include carbon chains, rings and various substituents. During the course of these synthetic studies—done over a span of several years—significant discoveries in mechanism and structure have been made.Today I wish to report some free radical additions of F-alkyl iodides to unsaturated anhydrides and their derivatives. Among the compounds recently discovered are the norbornene products 5 to 10.

Spectroscopic properties of the adducts varied with position and nature of the substituents. Somewhat surprisingly, the chemical shift of protons on the R_F side of the molecule was affected by changes in substituents on the other side of the molecule.Various reactions of the adducts were studied. Unusual stereospecificity in lactone formation and in base- induced cyclization to nortricyclene derivatives was observed. Only when the iodo group was in an endo position did these reactions occur.Analogous free radical addition of fluorinated thiols (R_FCH₂CH₂SH) to norbornene anhydrides produced a series of 5-polyfluoroalkylthionorbornane-2,3-dicarboxylic acid anhydrides(11, 12; U S Patent 3,989,725 (1976). As in previous studies the entering group took up the exo position exclusively. Reaction with acids, esters or norbornene carboxylic imides of the fluorinated thiol also gave analogous products.Because of the hydrophobic nature of the F-alkyl groups the entire range of compounds displayed pronounced surface-activity and would appear to have utility in a wide range of applications.