Struktur und Reaktivität heterosubstituierter Nitrile. XVIII [1]. Kinetik und Mechanismus der Alkohol-Addition an Arylcyanate in Gegenwart tertiärer Amine

Structure and Reactivity of Heterosubstituted Nitriles. XVIII. Kinetics and Mechanism of the Addition of Alcohols to Aryl Cyanates in Presence of Tertiary Amines The mechanism of the carbonic acid arylester imide or carbamic acid arylester formation by the addition of alcohols or water to aryl cyanates in the presence of tertiary amines has been studied. After a slow formation of an autocatalyst, an intermediate is formed in a fast equilibrium between this one and a molecule of aryl cyanate and tertiary amine. This intermediate is slowly alcoholyzed to carbonimidic acid diester which in part is fragmented by the base to phenole and alkyl cyanate. The alkyl cyanate undergoes further reaction with the alcohol and the amine to dialkyl ether and trialkyl ammonium cyanate in the reaction mixture.     

Struktur und Reaktivität heterosubstituierter Nitrile. XIX [1]. Kinetik und Mechanismus der Addition sekundärer aliphatischer Amine an Arylcyanate

Structure and Reactivity of Heterosubstituted Nitriles. XIX. Kinetics and Mechanism of the Addition of Secondary Aliphatic Amines to Aryl Cyanates The N,N-dialkyl-O-aryl isourea formation by the addition of secondary aliphatic amines to aryl cyanates was studied by kinetic methods in dioxane and dioxane water mixtures. Linear relationships between the rate constants and the water concentrations, the basicity of the amines and the electrophilicity of the aryl cyanates have been found. These data and the activation parameters support two concurrent reactions, a direct nucleophilic attack of the amine to aryl cyanate and one involving a six membered transition state between a molecule of cyanate, amine and water.     

Struktur und Reaktivität heterosubstituierter Nitrile. XX [1]. Kinetik und Mechanismus der Addition primärer aliphatischer Amine an Arylcyanate

Structure and Reactivity of Heterosubstituted Nitriles. XX. Kinetics and Mechanism of the Addition of Primary Aliphatic Amines to Aryl Cyanates The addition rate of primary aliphatic amines to aryl cyanates in water/dioxane mixtures was measured by u.v.-spectroscopy. The second order rate constants give a linear correlation with the concentration of water. The rate of the addition is increased by growing electrophilicity of the aryl cyanates and decreased by steric hindrance of the amine substituents. The nucleophilicity of the amine has no influence on the reaction rate. The results are explained by a six-membered cyclic transition state, in which the nucleophilic attack and the proton transfer proceed with equal rate.     

Struktur und Reaktivität heterosubstituierter Nitrile. 24 Kinetik und Mechanismus der Reaktion von o-Phenylendiamin mit Arylcyanaten

Structure and Reactivity of Heterosubstituted Nitriles. 24. Kinetics and Mechanism of the Reaction of o-Phenylen diamine with Aryl Cyanates The second and third order rate constants for the reaction of o-phenylene diamine with aryl cyanates to 2-amino benzimidazole phenylester imide in water/dioxane have been determined by i.r. measurements. The reaction proceeds through a bimolecular and a trimolecular mechanism simultaneously. In the slow step of the bimolecular process an electrophilic attack of the aryl cyanate on o-phenylene diamine takes place in a seven membered cyclic transition state. The slow step of the trimolecular mechanism consists of a nucleophilic attack of the diamine on a phenole aryl cyanate associate by a six membered cyclic transition state. The final products of both reactions are formed by successive fast reactions.     

Acylierung von Heterocyclen mit Kohlensäurederivaten. I. Kinetik und Mechanismus der Reaktion von 2-Aminobenzimidazolen mit Arylcyanaten

Acylation of Heterocycles with Carbonic Acid Derivatives. I. Kinetics and Mechanism of the Reaction of 2-Aminobenzimidazoles with Aryl Cyanates The second order rate constants for the reaction of 2-amino-benzimidazoles (2-ABI) with aryl cyanates forming 2-amino-benzimidazole aryl ester imide 3 have been determined in dependence on substituent effects by u. v. measurements. The results are interpreted by a six-membered cyclic transition state in which the electrophilic attack of the cyanate on the endocyclic N atom is catalyzed by an H bridge interaction of the exocyclic amino group of 2-ABI with the OCN group.     

Organische Phosphorverbindungen. X. [1]Quantitative Untersuchungen über das Alkylierungsvermögen mehrfach kernsubstituierter O,O-Dimethyl-O-phenyl-phosphate und -thiophosphate

Organic Phosphorus Compounds. X. Quantitative Studies on the Alkylation Capacity of Polysubstituted O-Phenyl O,O-Dimethyl Phosphates and Thiophosphates The alkylation capacity of polysubstituted O-phenyl-O, O-dimethyl phosphates and thiophosphates towards tertiary amines can be described quantitatively using the HAMMETT′S substituent constants σ by multiparameter equations which are reducable to lg k₂ = lg k₀ + ϱ · Σσ with σ_ortho = σ_para (r = 0,976–0,999). Satisfactory results are obtained by correlation of the rate constants with the pK_a-values of the phenolic ester components, whereas the chemical shift δ_CH3_O of the ester group in the case of m,p-substituted compounds is only partly or — with the inclusion of orthoderivatives — little suited as correlation parameter.     

Untersuchungen zum photochemischen Ausbleichverhalten von tautomeriefähigen Azofarbstoffen. V. Oxidation substituierter 1-Phenylazo-2-naphthole durch Singulettsauerstoff in polymerer Matrix

Studies on Photo Fading of Tautomeric Azo Dyes. V. Oxydation of Substituted 1-Phenylazo-2-naphtholes by Singlet Oxygen in a Polymeric Matrix The logarithms of rate constants of methylene blue sensitized photolysis of substituted 1-phenylazo-2-naphthols ( 1a–y ) in polymer matrix show no linear correlationship with respect to Hammett-δ-constants of the substituents. The slope of the function lg k = f(δ), where k represents rate constants, differs for positive and negative δ-values in sign but decomposition is oxydative at all substituents. It is possible to explain the nonlinear correlation, when singlet oxygen ¹O₂ attacks only the anti-hydrazone-tautomer in the dyes investigated.     

Säurestärke und Komplexbildung von Curcuminoiden

Acidity and Complex Formation of Curcuminoids The stoichiometric acid dissociation constants of curcumin 1a and derivatives as well as the stoichiometric stability constants of the Cu(II)- and Ni(II)-complexes of these substances have been determined by pH-potentiometric titrations in dioxane-water mixture. The influence of different substituents on the pK_a-values and the stability constants is discussed. The complexing properties of the  CO CH₂ CO structural element of the ligands are not significantly changed when the phenyl group is substituted by the styryl group. Solid CuL₂-complexes have been characterized. The coordination of the ester group in the tricarbonyl ligand systems 4 was excluded by i.r. spectroscopy.     

31P-NMR-Untersuchungen N-Aryl-substituierter Iminotriphenylphosphorane: Hammettbeziehung zwischen 31P-Verschiebung und Substituentenkonstanten

³¹P-NMR Investigation of N-Aryl-substituted Iminotriphenylphosphoranes: Hammett Relationship between ³¹P Chemical Shift and Substituent Constants The ³¹P chemical shifts of p- and m-substituted N-arylimino-triphenylphosphoranes reflect the electronic influence of the substituents and can be correlated by a Hammett relationship. This new correlation was used for the estimation of σ- resp. σ-values for p-(CH₃)₂N-, p-C₆H₅CO- and p-C₆H₅ N  N-groups as well as for β-naphthyl- and pyridyl(4)-rings. The applicability of a similar Hammett equation for the o-substituted compounds is not possible.     

Photochemie arylsubstituierter Δ2-1,3,4-Oxadiazoline. II. Zum Einfluß der Substituenten und des Lösungsmittels auf die Absorptions- und Fluoreszenzeigenschaften arylsubstituierter Δ2-1,3,4-Oxadiazoline

Photochemistry of Arylsubstituted Δ²-1,3,4-Oxadiazolines. II. The Influence of the Substituents and the Solvent on the Absorption and Fluorescence Properties of Arylsubstituted Δ²-1,3,4-Oxadiazolines The electronic absorption and the fluorescence spectra of 16 arylsubstituted Δ²-1,3,4-oxadiazolines were measured in benzene at room temperature. The push-pull effect of the substituents supports an increasing intramolecular charge-transfer in the electronically excited singlet state, which increases its dipole moment relative to the ground state. The significant linear correlation of the Hammett σ_p-values with the energies of the fluorescence and absorption maxima of the Δ²-oxadiazolines, p-substituted in the phenylring at the C 2-atom, demonstrate these intramolecular charge transfer. The titel compounds demonstrate with increasing solvent polarity a bathochromic shift of the absorption maxima. For some oxadiazolines the dipole moment for the excited singlet state proved to be about 30 Cm as Stoke's shift dipendency from the solvent indicate.     

Hammett-Beziehungen zwischen 1H-NMR- bzw. 31P-NMR-chemischen Verschiebungen und Substituenten-konstanten in ω-Diphenylphosphinyl-und ω-Diphenylthiophosphinyl-trans-styrenen

Hammett Relationships between ¹H-NMR and ³¹P-NMR Chemical Shifts, Respectively, and Substituent Constants in ω-Diphenylphosphinyl and ω-Diphenylthiophosphinyl trans-Styrenes A well linear correlation between the chemical shifts of the ethylenic protons H_B and the ³¹P nuclei, respectively, and the Hammett constants σ_p of substituents R in 4-position for diphenylphosphinyl trans-styrenes 1 and the analogous diphenylthiophosphinyl trans-styrenes 2 has been found. A similar relationship for the proton H_A has been observed in the case of 1 only, but the substituent-induced shifts are not so sensitive. Donor substituents R in 1 and 2 effect an increase in the shielding of H_B and a deshielding of the P atom being connected with shifts of the i. r. PO absorption bands in 1 in the direction of lower wavenumbers. A mesomeric interaction between R and PY substituents (Y = O, S) is concluded to produce polymethin-like π-electron density distribution.     

Untersuchungen zur Hydrolysestabilität von 4-Arylmethyliden-2-pyrazolin-5-onen

Investigations on the Hydrolytic Stability of 4-Arylmethylidene-2-pyrazolin-5-ones The 4-Arylmethylidene-2-pyrazoline-5-ones S are not stable under aqueous alkaline conditions. By the substitution of R³ with electron donor substituents S reacts preferably yielding aldehyde A and 2-pyrazoline-5-one P , while with electron acceptor substituents S forms 4,4′-aryl-methylidene-bis-2-pyrazoline-5-one B . The intermediate of hydrolysis is 4-(arylhydroxymethyl)-2-pyrazoline-5-one SOH . The second order rate constants of the reaction of S with hydroxidions and with 2-pyrazoline-5-ones P ⁻ are determined. The dependence of the hydrolytic decomposition of S on the pH vaue substituents and temperature is suitable for the intermediate formation of SOH .     

Die UV-Spektren α,β-ungesättigter Ester und ihre Beeinflussung durch Lösungsmittel und Komplexbildung

UV Spectra of α,β-Unsaturated Esters and the Influence of Solvents and Complex Formation Positions and intensities of partially overlapped π-π* and n-π* transitions in spectra of methyl and ethyl esters of acrylic, methacrylic and crotonic acid are discussed. Reproducible values were determined by graphical and mathematical band-separations. n-π* bands in gaseous methyl acrylate show vibrationally fine structures. These are compared with fine structures in the spectra of α-methylene-γ-butyrolactone and α, β-dehydrobutyrolactone. In solutions with C_ester lt; 0,1 m self-associations are negligible. The transition-displacements Δv _max due to solvent effects closely correlate with the solvent parameters of KOSOWER . These correlations allow to calculate λ_max-values at which solvents absorb strongly. Equilibrium constants K of EDA-complexes with TCNE and chloranile were determined. With a competition method K was found in the range of 0.9 to 10.3 l · mol⁻¹.     

Der Substituenteneinfluß auf IR-Spektrenparameter von 4′-phenylsubstituierten (E)-Styryl-methyl-sulfonen

The Influence of Substituents on the I.R. Spectral Parameters of 4′-Phenylsubstituted (E)-Styryl-methyl-sulphones The positions and integrated intensities of the bands corresponding to characteristic vibrations of eight 4′-phenylsubstituted (E)-styryl-methyl-sulphones were determined and correlated with substituent constants. The results demonstrate a linear dependence of the wavenumbers of vSO₂ and VCC vibrations, respectively, with the electrophilic substituent constants σ. Otherwise the square roots of the integrated intensities A^1/2 (v^sso₂) and σ gave no linear correlation. The influence of the substituents on the i.r. spectral parameters is discussed and compared with π-bond orders and π-electron densities. These magnitudes reflect qualitatively the behaviour of i.r. frequencies and intensities of selected absorption bands.     

Reaktivität und Toxizität homologer Brom- und Dibromalkane

Reactivity and Toxicity of Homologous Bromo- and Dibromoalkanes The rate constants of the reactions of 4-(4-nitrobenzyl)-pyridine (NBP) with ω,ω′-dibromoalkanes Br (CH₂)_n Br (n = 2–4), alkyl bromides C_nH_2+n1Br (N = 2–4) and allyl bromide in acetophenone were measured and compared with the LD₅₀-values of these compounds estimated on mice. The tested dibromoalkanes show a contrary graduation of reactivity and acute toxicity.     

Untersuchungen zur Spin-Trapping-Kinetik in Systemen von Radikalen unterschiedlicher Reaktivität. Die Photolyse von α-Phenylbenzoin in Gegenwart von Benzyliden-tert.-butylamin-N-oxid

Investigations on Spin-Trapping Kineties in Radical Systems with Different Reactivity. Photolyses of α-Phenylbenzoine in the Presence of Benzylideneter. -butylamine N-oxide As a model system to study the spin-trapping kinetics of systems forming two radicals of different reactivity α-phenylbenzoine (PhB) was chosen. The photolysis of PhB forms benzoyl (B·) and diphenylketylradikals (K·), respectively, which can be trapped by benzylidene-tert-butyl-amine N-oxide (PBN), as a spin trap. The rate constants of radical addition to PBN and their reactions with the spin adducts were determined by means of flash photolysis and kinetic calculations of the PBN concentration dependence. For B· and K· addtion rate constants to PBN of k₁ = 8,1 × 10⁵ M⁻¹s⁻¹, and k₂ = 5,8 · 10⁴ M⁻¹s⁻¹, respectively, were found. The rate constants for the reactions of B· and K· with the spin adducts are in the order of 10⁹…10¹⁰ M⁻¹s⁻¹.     

Phenoxaphosphino‐Modified Xantphos‐Type Ligands in the Rhodium‐Catalysed Hydroformylation of Internal and Terminal Alkenes

The solubility of the modifying ligand is an important parameter for the efficiency of a rhodium‐catalysed hydroformylation system. A facile synthetic procedure for the preparation of well‐defined xanthene‐type ligands was developed in order to study the influence of alkyl substituents at the 2‐, and 7‐positions of the 9,9‐dimethylxanthene backbone and at the 2‐, and 8‐positions of the phenoxaphosphino moiety of ligands 1 – 16 on solubility in toluene and the influence of these substituents on the performance of the ligands in the rhodium‐catalysed hydroformylation. An increase in solubility from 2.3 mmol⋅L⁻¹ to >495 mmol⋅L⁻¹ was observed from the least soluble to the most soluble ligand. A solubility of at least 58 mmol⋅L⁻¹ was estimated to be sufficient for a large‐scale application of these ligands in hydroformylation. Highly active and selective catalysts for the rhodium‐catalysed hydroformylation of 1‐octene and trans‐2‐octene to nonanal, and for the hydroformylation of 2‐pentene to hexanal were obtained by employing these ligands. Average rates of >1600 (mol aldehyde) × (mol Rh)⁻¹×h⁻¹ {conditions: p(CO/H₂) = 20 bar, T = 353 K, [Rh] = 1 mM, [alkene] = 637 mM} and excellent regio‐selectivities of up to 99% toward the linear product were obtained when 1‐octene was used as substrate. For internal olefins average rates of >145 (mol aldehyde)×(mol Rh)⁻¹×h⁻¹ {p(CO/H₂) = 3.6–10 bar, T = 393 K, [Rh] = 1 mM, [alkene] = 640–928 mM} and high regio‐selectivities up to 91% toward the linear product were obtained.     

Elektrochemische Reduktion und Azokupplung kernchlorierter p-Dimethylaminobenzendiazoniumsalze Hammett-Korrelationen

Electrochemical Reduction and Azo-coupling of Ring Chlorinated p-Dimethylaminobenzenediazonium Salts. Hammett-Correlations The polarographic half-wave potentials of ring halogenated 4-dimethylaminobenzenediazonium salts ( 6a–6j ) can be linearly correlated with the total σ-constants Σσ_korr (E_1/2 = (0.25 Σσ_korr + 0.33) V; r = 0.995), if for the dimethylamino group of the 3- or 3,5-halogenated derivatives corrected σ′_p-constants are used. The Σσ_korr-values determined can be used to correlate the influence of substituents on the azo-coupling kinetics (lg k/k₀ = 2.46 Σσ_korr; r=0,988).     

1-Amino-4-aryl-2(1H)-pyrimidinthione: Acidität und Komplexbildung mit Mn(II), Co(II), Ni(II), Zn(II), Cd(II), Pb(II) und Ag(I)

1-Amino-4-aryl-2(1H)-pyrimidinethiones: Acidity and Complex Formation with Nonferrous Metal Ions and Ag(I) Acid dissociation constants of new 2, 3 and already known 1 substituted 1-amino-4-aryl-2(1H)-pyrimidinethiones and stability constants of their nonferrous metal ion and silver complexes have been measured pH-potentiometrically in a 75% (v/v) mixture of dioxane/water. The influence of the substituents on pK_a- and lgβ_n-values is discussed. The X-ray structure analysis of bis[1-(4-toluenesulfonamido)-4-(4-tolyl)-2(1H)-pyrimidinethionatol]-nickel(II) 5 proves that pyrimidinethiones coordinate via their thione sulphur and aminonitrogen. However, the bond lengths are not levelled in the chelating ring.     

Protonierung und Solvatation schwacher organischer Basen. I. Zur Basizität von ω-Chloracetophenonen

Protonation and Solvation of Weak Organic Bases. I. Basicity of ω-Chloroacetophenones The protonation equilibria of ω-chloroacetophenone and some p-substituted derivates have been studied in the acid system H₂O/H²SO⁴/SO₃ by u.v. and ¹H-n.m.r. spectroscopy. From the determined H₀ values for half-protonation _pK_BH+ values were calculated by means of the solvation parameters m of YATES and McCLELLAND . The (H₀)_1/2 and the _pK_BH+ values were successfully correlated with σ_p and σ_p⁺ substituent constants.