Influence de la structure sur l'hydrolyse des N-pyrrolylmethylene-2 anilines

Hydrolysis of the imine function of a series of Schiff bases derived from pyrrole-2-carboxaldehyde and substituted anilines (X = H, p-OCH₃, p-OC₂H₅, p-CH₃, p-Cl, p-Br, m-CN, m-NO₂, p-NO₂) was studied in all of the pH ranges. The hydrolysis curves log k_abs (mn^?1) = f(pH) were established in buffered aqueous methanol by polarography or amperometry. The shapes of the curves obtained for pH > 5 indicates that N-pyrrolylmethylene-2 anilines hydrolyse according to the same mechanism as N-benzylidene anilines. The particular stability of these products for pH < 5 permits one to obtain complete hydrolysis curves in acid media. A very good Hammett correlation (k_obs = + 1,73) has been established from the maxima which appear for strong acidity. This stability is interpreted as due to the specific electron-donating effect of the pyrrole nucleus. The influence of the structural parameter X on the morphology of the curves log k_abs = f(pH) and on the hydrolysis mechanism of the imine function is discussed in all of the pH ranges.     

Application of spin trapping to redox-initiated vinyl polymerization with thiourea as the reductant

An electron spin resonance (ESR) study confirms a free radical mechanism for aqueous vinyl polymerization initiated by three redox systems involving thiourea. The primary radical, NH₂? C (?NH)S^., could not be detected by ESR spectroscopy, perhaps because of its large g anisotropy and/or very short relaxation time. Propagating radicals are trapped from methyl-methacrylate by 2-methyl-2-nitroso propane (MNP) and their structures are found to be the same as those produced by either azo-bis-isobutyrnitrile or di-t-butyl peroxylate. The latter monomer, however, reacts with MNP in the absence of any initiator, giving different ESR lines.     

Kinetics and mechanism of the aminolysis of O-ethyl S-aryl dithiocarbonates in acetonitrile

The aminolysis reactions of O-ethyl S-(Z-phenyl) dithiocarbonates (Z=p-CH₃, H, p-Cl, and p-NO₂) with anilines (AN) and N,N-dimethylanilines (DMA) in acetonitrile at 30.0°C are investigated. Relatively small values of β_X (β_nuc,0.4 ca. 0.7) and β_Z (β_lg −0.1 ca. −0.4) for both ANs and DMAs, significantly large k_H/k_D values (1.1 ca. 1.9) involving deuterated anilines, and large negative ρ_XZ values for ANs (−0.56) are interpreted to indicate a concerted mechanism for both ANs and DMAs but with a hydrogen bonded four-center type transition state (TS) for ANs. The relative leaving ability, k(Z=p-NO₂)/k(Z=p-CH₃), is smaller for ANs than for DMAs, especially for a weaker nucleophile (1.9 and 4.7 for AN and DMA, respectively, with X=p-Cl). This suggests that the rate enhancement by the hydrogen-bond formation in the four-center type TS for AN is greater for a weaker nucleofuge (Z=p-CH₃), especially when the nucleophile (X=p-Cl) is weaker. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 419–423,1998     

Effects of substituents on the anionic copolymerization of ring-substituted cinnamonitriles

trans-Cinnamonitrile (M₁) was copolymerized with several of its ring-substituted derivatives (M₂) in toluene at 25°C, calcium zinc tetraethyl being used as catalyst. The ring substituents investigated include H, p-CH₃O, m-CH₃O, p-CH₃, m-CH₃, p-Cl, and m-Cl. It was found that the values of log (1/r₁) are linearly correlated with Hammett's σ constants with the reaction constant σ ρ 0.7. The effects of coordination between monomer and catalyst sites upon the Hammett relation are discussed.     

Novel Copolymers of Halogen Ring Substituted 2-Cyano-3-Phenyl-2-Propen- Amides and Styrene

ABSTRACT

Electrophilic trisubstituted ethylene monomers, halogen ring substituted 2-cyano-3-phenyl-2-propenamides, RC₆H₄CH=C(CN) CONH₂ (where R is o-Cl, m-Cl, p-Cl, p-Br, and p-F) were prepared by Knoevenagel condensation. Novel copolymers of the propenamides and styrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator at 80°C. The order of reactivity (1/r ₁) for the monomers (M₁=styrene) was o-Cl (1.42) > p-F (1.19) > p-Cl (0.70) > m-Cl (0.60) > p-Br (0.44).     

Reactions of aromatic compounds with nucleophilic reagents in liquid ammonia: XVII. Effect of ionic association on the orientation in aryloxydefluorination of 2,4-difluoronitrobenzene

The analysis of dependence of fluorine replacement orientation in 2,4-difluoronitrobenzene effected by nucleophiles Y-C₆H₄OM (Y =p-OMe,p-Me,m-Me, H,p-F,p-Cl,m-F,m-Cl; M = Li, Na, K, Et₄N, Bu₄N) in liquid ammonia medium at -35‡C on the nature of M, Y, on nucleophile concentration, on addition of crown ethers, diaminoalkanes, and dimethoxyethane indicates the occurrence of ionic association at M = K, Na. For communication XVI, see [1].     

NOVEL COPOLYMERS OF TRISUBSTITUTED ETHYLENES WITH STYRENE. I. 2-HALOPHENYL-1,1-DICYANOETHYLENES

Electrophilic trisubstituted ethylene monomers, 2-halophenyl-1,1-dicyanoethylenes, RC₆H₄CH=C(CN)₂ (where R is o-Cl, m-Cl, p-Cl, p-Br, and p-F) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and malononitrile, and characterized by CHN elemental analysis, IR, ¹H and ¹³C-NMR. All the ethylenes were copolymerized with styrene (M₁) in solution with radical initiation (AIBN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, ¹H and ¹³C-NMR. The order of relative reactivity (1/r ₁) for the monomers is p-Cl (14.8) >m-Cl (2.67)> o-Cl (1.82) > p-Br (1.52) > p-F (1.36). High T _g's of the copolymers (> 150°C) in comparison with that of polystyrene indicate a substantial decrease in the chain mobility of the copolymers due to the high dipolar character of the trisubstituted monomer unit. Gravimetric analysis indicated that the copolymers decompose in the range 300–400°C.     

Study of substituted aryldiazonium salts and their crown ethers complexes by XPS

The complexes of fourteen substituted aryldiazonium salts RC₆H₄N₂+BF₄^? (R?H, p-CH₃, p-NO₂, p-I, p-Cl, p-F, m-Br, m-Cl. m-CH₃, o-CH₃, o-OCH₃, o-NO₂, o-Br, o-Cl) with crown ethers 18-C-6 (1) and dibenzo-24-c-8 (2) have been studied by XPS. The results show that the chemical shifts of α-N1s and β-N1s of substituted aryldiazonium salts are closely related to the induction and conjugation effects of R groups. It is interesting to note that charge transfer(β-N→O) take place upon complexation of substituted aryldiazonium salts with crown ethers. Therefore the decrease of binding energy of crown ether oxygen may be used as a measurement of the stabilities of these complexes.     

Organosilicon compounds : LI. Further studies of the base-catalysed solvolysis of N-(triorganosilyl)anilines

Relative rates of solvolysis of some N-triorganosilylanilines in mixtures of ethanol and aqueous potassium hydroxide have been determined, with results as follows. (i) For XC₆H₄NHSiEt₃ compounds in MeOH (5 vol) + aq. alkali (2 vol) at 50°: (X =) H, 1.0;p-Me, 0.80;p-OMe, 0.83;m-Me, 0.90; o-Me, 0.87; p-SMe, 1.90; p-F, 1.7; p-Cl, 2.8; o-Cl, 14; m-Cl, 4.2; m-NO₂, 18; p-CN, ca. 43; p-NO₂, ca. 120. (ii) For PhNHSi(C₆H₄Y)₃ compounds in MeOH (10 vol) + aq. alkali (1 vol) at 50°: (Y =) H, 1.0; p-OMe, 0.12; p-Cl, ca. 32; m-Cl, ca. 84. (iii) For PhNHSiR₃ compounds in MeOH (5 vol) + aq. alkali (2 vol) : (R₃ =) Et₃, 1.0; Et₂Me, 18 (at 30°); Me₂-i-Pr, 8 (at 30°);Me₂-t-Bu, 0.012 (at 50°);i-Pr₃, 0.006 (at 50°). In series (i) the relative rates correlate with σ, or where appropriate σ^?-constants, with a ? value of 1.6. It is suggested that in the transition state of the rate-determining step the OSi bond is fully formed, or almost so, the SiN bond approximately 20—50% broken, and the bond between the nitrogen atom and a proton from the solvent ca. 10—30% formed.     

Preparation of Complexes of Nickel(II) Aryl Carboxylates with Morpholine and Piperidine

Complexes of nickel(II) aryl carboxylates with a general formula Ni(RC₆H₄COO)₂L₂ where R=H, p-CH₃. p-Cl, m- & p-NO₂; and L = morpholine and piperidine; have been prepared by the interaction of nickel(II) aryl carboxylates with a large excess of appropriate amine. Unlike parent anhydrous nickel(II) aryl carboxylates all these complexes are soluble in common organic solvents.     

The reactivity of areneseleninato complexes. New pentacoordinate nickel(II) complexes with benzeneseleninato ions and ethylenediamine as ligands

Summary Five-coordinate bis(Se-benzeneseleninato)tris(ethylenediamine)nickel(II) complexes are obtained by reaction of the Ni(H₂O)₂(XC₆H₄SeO₂)₂ complexes (X = H,p-Cl,m-Cl,m-Br orp-Me) with ethylenediamine. All the diaquo complexes react with three moles of ethylenediamine to form Se-seleninato derivatives. The compounds are characterized on the basis of far i.r. and near i.r. spectroscopy, electronic spectra and magnetochemical investigations. The most attainable geometry is the square pyramidal, probably slightly distorted; tentative assignments for the electronic spectra are proposed. Conductivity data indicate that these new complexes are nonelectrolytes; both areneseleninato and ethylenediamine behave as monodentate ligands. The magnetic moments show that all the complexes are of high-spin type, the values lying within the ranges observed for other high-spin five-coordinate nickel(II) complexes.     

Paradoxes in Thermal Stability of the Liquid-Crystal Phase of Phenylpropargyl Phenyl Ethers: I. Synthesis and Mesogenic Properties of Phenylpropargyl Phenyl Ethers

The ethers PhCCCH₂OC₆H₃RR' were prepared in 51-83% yields by reactions of phenylpropargyl tosylate in alkaline solution with appropriate p- and o-substituted phenols. Below are given R, R', and the ranges of existence of the nematic mesophase (°C): p-I, H, 104-137; p-Cl, H, 65-117; p-F, H, 33-53; p-OMe, H, 79-120; H, H, 44-115; p-(Me)₃C, H, 74-82; p-COOH, H; p-NO₂, H, 77-96; o-NO₂, H, 83-139; o-CHO, H, 75-115; p-Br, o-NO₂, 95-132; p-Cl, o-NO₂, 71-123; p-F, o-NO₂, 79-120; o-Cl, H, none; p-COOPr, H, none; and p-COOPh, H, 116-134. In contrast to the traditional views, the presence of the o-nitro group enhances, rather than distorts, the thermal stability of the mesophase. The stability increases in parallel with the -R effect of the o-substituent.     

Synthesis,characterization, and olefin polymerization of half-sandwich Ir,Rh, Ru metallacycle enclosing a nickel in the center

Reactions of binuclear [Cp*Ir(μ-Cl)Cl]₂ (Cp* = pentamethylcyclopentadienyl), [Cp*Rh(μ-Cl)Cl]₂ and [(p-cymene)Ru(μ-Cl)Cl]₂ with 2 equiv. AgOTf (OTf = O₃SCF₃) followed by addition of one equiv. (m-pyridyl)N=C(C₁₀H₆)C=N(m-pyridyl) (mPy-bian) linker and NiCl₂·DME (DME = 1,2-dimethoxyethane) in methanol gave heterometallic cationic metallacycles [Cp*₄Ir₄(μ-Cl)₄(μ-mPy-bian)₂NiCl₂](OTf)₄ (1a), [Cp*₄Rh₄(μ-Cl)₄(μ-mPy-bian)₂NiCl₂](OTf)₄ (1b), and [(p-cymene)₄Ru₄(μ-Cl)₄(μ-mPybian)₂NiCl₂](OTf)₄ (1c), respectively. All the complexes are characterized by IR, NMR spectroscopy, and elemental analysis. Ni K-edge X-ray absorption spectroscopy (XAS) studies on 1a–1c reveal that nickel is six-coordinate with four nitrogens and two chlorides. Upon activation with MAO, 1a–1c showed moderate to good catalytic activity for ethylene and norbornene polymerization.     

Zum basenkatalysierten H/D-Austausch des acetylenischen Wasserstoffatoms in aromatischen Alkinylverbindungen

On the Base-Catalysed H/D-Exchange of the Acetylenic Hydrogen Atom in Aromatic Alkynyl Compounds H/D-exchange rates for a number of compounds of the general type 1 (X = p-CH₃O, m-CH₃O, p-CF₃, m-CF₃, p-CH₃, p-Cl, H; Z ? O, NH, CH₂) were determined in N-methyl-pyrrolidine (NMP)/D₂O mixtures at 25° (see Table 1). It is shown that the log k values of the H/D-exchange correlate nicely (r = 0.995) with the chemical shift of the acetylenic proton in 1 . Thus, the H/D-exchange rate is given by log k (min^?1) = 2.91 · δ (ppm) - 7.79 for the NMP/D₂O mixture at 25°.     

para‐Phenylene‐Bridged Spirobi(triarylamine) Dimer with Four Perpendicularly Linked Redox‐Active π Systems

para‐Phenylene‐bridged spirobi(triarylamine) dimer 2 , in which π conjugation through four redox‐active triarylamine subunits is partially segregated by the unique perpendicular conformation, was prepared and characterized by structural, electrochemical, and spectroscopic methods. Quantum chemical calculations (DFT and CASSCF) predicted that the frontier molecular orbitals of 2 are virtually fourfold degenerate, so that the oxidized states of 2 can give intriguing electronic and magnetic properties. In fact, the continuous‐wave ESR spectroscopy of radical cation 2 ^.+ showed that the unpaired electron was trapped in the inner two redox‐active dianisylamine subunits, and moreover was fully delocalized over them. Magnetic susceptibility measurements and pulsed ESR spectroscopy of the isolated salts of 2 , which can be prepared by treatment with SbCl₅, revealed that the generated tetracation 2 ⁴⁺ decomposed mainly into a mixture of 1) a decomposed tetra(radical cation) consisting of a tri(radical cation) moiety and a trianisylamine radical cation moiety (≈75 %) and 2) a diamagnetic quinoid dication in a tetraanisyl‐p‐phenylendiamine moiety and two trianisylamine radical cation moieties (≈25 %). Furthermore, the spin‐quartet state of the tri(radical cation) moiety in the decomposed tetra(radical cation) was found to be in the ground state lying 30 cal mol^?1 below the competing spin‐doublet state.     

Electron spin resonance study of the radiation-induced polymerization of N-vinylcarbazole

When crystals of N-vinylcarbazole are γ-irradiated at 77°K., the ESR spectrum observed before warming consists of three peaks attributed to a radical–cation with the unpaired spin associated mainly with the nitrogen atom. Above 90°K. polymerization occurs, initiated by the cation, and the spectrum changes to that of an alkyl type of radical, ?N? ?H? CH₂, trapped in the polymer. Single crystals were used for a detailed analysis of the nuclear hyperfine parameters of the observed radicals.     

Anionic copolymerization of isocyanates with ketenes

Diphenyl-, phenylethyl, and phenylmethylketene have been copolymerized with phenyl isocyanate by use of sodium naphthalene in dimethylformamide (DMF) at ?45°C. Reactivity ratios of phenyl isocyanate (r₂) with diphenylketene (r₁) were r₁ = 0.10, r₂ = 0.29; with phenylethylketene (r₁) were r₁ = 1.6, r₂ = 0.10; and with phenyl methyl ketene (r₁) were r₁ = 4.8, r₂ = 0.02. The same initiator and solvent system were used for homopolymerization of phenylethylketene and copolymerization with m-chloro-, p-chloro-, p-methoxy-, and m-methoxyphenyl isocyanate as well as with phenyl isocyanate. Molecular weights ranged from 1740 to 4000. The effect of substituents on the order of isocyanate incorporation into the copolymer was m-Cl = p-Cl > m-MeO > H > p-MeO. Phenylethylketene was also copolymerized with m-methoxyphenyl, p-methoxyphenyl, and p-tolyl isocyanate in tetrahydrofuran (THF) at ?78°C. Molecular weights ranged from 2800 to 10,500. The least reactive isocyanate was incorporated into the copolymer to a greater extent in this solvent than in the more polar DMF. DTA showed the presence of crystallinity only in polymers of high isocyanate content. The ketenes copolymerized less readily with alkyl isocyanates, such as ethyl, n-butyl, n-hexyl, and cyclohexyl isocyanate, than with the aromatic isocyanates when sodium naphthalene was used in either DMF or THF.     

ESR studies of α-hydro p-substituted phenyl nitroxides and correlation analysis of their HFSC values

Well-resolved ESR spectra of a series of α-hydro p-substituted phenyl nitroxides were obtained in the fast ET reactions of p-substituted anilines with perfluoroacyl peroxides in F113 (CCl₂FCClF₂) solutions and one parameter (σ or σ^·) as well as dual-parameter (σ, σ^·) correlation analyses of their hyperfine splitting constants were conducted.     

COMPLEXATION OF METAL IONS WITH 3,5-DI-TERT-BUTYL-1,2-BENZOQUINONE-1-MONOOXIME,ESR STUDIES OF RADICAL INTERMEDIATES

Abstract

The possibility of chelate formation of 3,5-di-terf-butyl-o-benzoquinone-1-monooxime with Cu(II), Co(II), Ni(II), Mn(II), Pd(II) metal ions under N₂ and in air have been investigated. It was found that complexation of metals except Cu(II) and Mn(II) was accompanied by formation of various stable radical species under air. The complexation of Co(II) even under N₂ unlike other metal ions, results in the formation of very stable radical species, which are assigned to phenazinyl type radical. ESR examination of reduction of bis(3,5-di-tert-butyl-o-benzoquinone-1-monooximato)M(II) (M = Cu, Pd) with triarylphosphines P(C₆H₄ X)₃ (X = H, m-Cl, m-CH₃, p-Et₂N) reveal the formation of the N-(2′-hydroxy-3,5-di-tertbutylphenyl)-4′,6′-di-tertbutyl-o-benzosemiquinone iminate radical. Finally, ESR spectra of Cu(II), Ni(II), and Mn(II) complexes at 300 and 130 K, as well as reaction of bis(oximato)Ni(II) with PPh₃ have been studied.     

Identification of radicals spin-trapped in autoxidized linoleic acids: A high performance liquid chromatography and electron spin resonance study

Radicals generated in linoleic acid and deuterated linoleic acid have been trapped by the spin trap 2-methyl-2-nitroso-propane (MNP) and identified by electron spin resonance (ESR) and ENDOR spectroscopy. The formation of two distinct secondary alkyl radical adducts (one conjugated, the other non-conjugated, as shown by their UV absorption spectra) was demonstrated by 11, 11-dideuterio-9-cis-12-cis-linoleic acid using HPLC and ESR spectroscopy.