(N-benzoyl)trichloroacetimidoylphosphonate

A method for the synthesis ofO,O-diethyl (N-benzoyl)trichloroacetimidoylphosphonate (1) by successive reaction ofN-(1-diethoxyphosphoryl-2,2-dichlorovinyl)benzamide with Me₃SiCl and Cl₂ was proposed. The reaction of phosphonate1 with R₃P follows the [4+1] cycloaddition mechanism to give phosphoranes, whose stability and further transformations are controlled by the nature of R. Dedicated to the memory of Academician M. I. Kabachnik on his 90th birthday. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2101–2104, October, 1998.     

Catalytic synthesis of N-benzoyl (N-nitrobenzoyl) derivatives of ɛ-aminocaproic acid oligomers

The synthesis of N-benzoyl [N-(m-nitrobenzoyl)] derivatives of ?-aminocaproic acid oligomers by the reaction of ?-caprolactam with benzoic (nitrobenzoic) acid in the presence of p-toluenesulfonic acid as catalyst was studied.     

Luminescent cyclometallated platinum(II) complexes with N-benzoyl thiourea derivatives as ancillary ligands

A series of cyclometallated 2-phenylpyridine Pt(II) complexes having N-benzoyl thiourea derivatives as ancillary ligands were prepared and characterised by elemental analysis, IR and UV–Vis spectroscopy, ¹H and ¹³C NMR spectroscopy as well as by X-ray diffraction on single-crystal. All complexes were obtained as a single isomer with N atom of the 2-phenylpyridine ligand and S atom of the N-benzoyl thiourea derivatives coordinated in trans positions to the platinum metal as evidenced by using X-ray crystallography and NMR spectroscopy. All Pt(II) complexes show good luminescence properties at room temperature, both in dichloromethane solution and in solid state.     

Thermolysis reaction of 2-acetyl-1-oxo-five-, six-, and seven-membered ring

The rates of gas-phase thermolysis reactions of 2-acetylcyclopentanone 1,2-acetylcyclohexanone 2, N-acetylcaprolactam 3,2-acetylbutyrolactone 4,2-acetyl-2-methylbutyrolactone 5, and 3-acetyl-2-oxazolidinone 6 have been measured over a temperature range of 50 K. They undergo unimolecular first-order elimination reactions for which log A = 11.7, 11.7, 11.2, 11.4, 11.5, and 11.1 s^?1 and E_a = 193.4, 189.5, 153.2, 201.0, 206.8, and 176.1 kJ mol^?1, respectively. The effect of the ring size together with the effect of a heteroatom in the ring on the rate of thermolysis reactions for compound 1–6 is the subject of this work. © 1995 John Wiley & Sons, Inc.     

Hydrolysis of amides. Kinetics and mechanism of the basic hydrolysis of N-acylpyrroles,N-acylindoles and N-acylcarbazoles

The hydroxide ion catalyzed hydrolysis of N-formyl, N-acetyl and N-benzoylpyrroles, -indoles and -carbazoles has been studied in water at 25.0°. The rate constants of formation of the tetrahedral intermediate are strongly increased by releasing steric hindrance in the acyl portion as shown by the higher reactivity of N-formyl derivatives in comparison with N-acetyl and N-benzoyl derivatives.     

Synthesis,X-Ray Crystallography,and Reactions of N-Acyl and N-Carbamoyl Succinimides

A collection of N-acyl and N-carbamoyl succinimides were prepared by acylation of succinimide with acyl chlorides or by ethylene dichloride (EDC) coupling of carboxylic acids. The x-ray crystal structures of N-benzoyl and N-p-nitrobenzoyl succinimides were determined. The N-acyl succinimides were effective in acylating primary amines, a secondary amine, and an aromatic amine.

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The pyrolysis kinetics of ethyl esters in the gas phase. The alkyl substituent effect at the acyl carbon

The gas-phase elimination of ethyl 3-methylbutanoate and ethyl 3,3-dimethylbutanoate has been studied, in a static system, over the temperature range of 360–420°C and in the pressure range of 71–286 torr. The reactions are homogeneous, unimolecular, and follow a first-order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for ethyl 3-methylbutanoate, log k₁ (s^?1) = (12.70 ± 0.36) – (202.5 ± 4.4) kJ/mol/2.303RT, and for ethyl 3,3-dimethylbutanoate, log k₁ (s^?1) = (13.04 ± 0.08) – (207.1 ± 1.0) kJ/mol/2.303RT. Alkyl substituents at the acyl carbon of ethyl esters yield very close values in rates. Consequently it is rather difficult to offer some conclusion concerning the effect of these substituents.     

The kinetics and mechanisms of the gas-phase pyrolysis of ethyl 4-bromobutyrate. The ion-pair mechanism revisited

The gas-phase pyrolysis of ethyl 4-bromobutyrate has been investigated in a static system over the temperature range of 354.6–374.7°C and the pressure range of 51–126 torr. The elimination reaction in seasoned vessels and in the presence of at least twofold of a chain radical inhibitor is homogeneous, unimolecular, and obeys a first-order rate law. The rate coefficients are given by the Arrhenius equation log k₁(s^?1) = (13.31 ± 0.82) – (205.1 ± 8.6)kJ/mol/2.303RT. The partial rates for the parallel eliminations to normal dehydrobromination, lactone formation, and bromobutyric acid product have been estimated and reported. The carboethoxy substituent of the bromoester has been found to assist anchimerically the elimination process, where dihydrobromination and lactone formation arise from an intimate ion-pair mechanism.     

Thermal behaviour and electro-optical properties of a series of liquid crystals based on palladium complexes with mixed ligands

A series of ortho-metallated palladium(II) complexes with two dimeric liquid crystals Schiff base (methoxy and decyloxy as terminal groups) as cyclometallated ligands and N-aryl-N′-benzoyl thiourea derivatives as co-ligands were prepared and investigated for their liquid crystalline properties. Their structures were assigned based on elemental analysis, FT-IR and ¹H NMR spectroscopy while the thermal behaviour was investigated by differential scanning calorimetry and polarising optical microscopy. The complexes with Schiff base ligand bearing methoxy group as terminal group show extensive decomposition during melting while the complexes with Schiff base having decyloxy group as terminal group show monotropic nematic phases, with the mesophase stability strongly related to the type of N-aryl-N′-benzoyl thiourea derivative used. Their liquid crystalline properties are compared with their analogues having N,N-dialkyl-N′-benzoyl thiourea as co-ligands which were reported previously. One of the latter complexes was also investigated by thermally stimulated depolarisation currents method while the optical transmission was recorded simultaneously. The thermally stimulated depolarisation currents and optical transmission spectra confirmed the previous observation regarding the phase transition temperatures. The current intensity–applied voltage dependencies of this complex were investigated by specific electrical measurements.     

Kinetics of the gas-phase thermal elimination of N-alkyl-pyrazoles

The kinetic study of the gas-phase thermal elimination reactions of N-ethyl-3,5 dimethyl-pyrazole (I), N-ethyl-pyrazole (II), N-sec-butyl-pyrazole (III), and N-tert-butyl-pyrazole (IV) using a flow system is reported. After obtaining activation parameters for I we carried out competitive reactions with II, III and IV using I as internal standard to obtain their E_a. The values of Δ(ΔH) calculated for II, III and IV agree with the little differences in E_a experimentally found.     

Theoretical Study of Molecular Structure,Reactivity, Lipophilicity,and Solubility of N-Hydroxyurea,N-Hydroxythiourea,and N-Hydroxysilaurea

Ab initio molecular orbital methods at the CBS-QB3 level of theory have been used to study the structure and gas-phase stability of various tautomers and rotamers of N-hydroxyurea, N-hydroxythiourea, and N-hydroxysilaurea, their anions and protonated forms. The geometries of N-hydroxyurea, N-hydroxythiourea, and N-hydroxysilaurea, their anions and cations were optimized at the Becke3LYP/CBSB7 level of theory. For all compounds studied, the amidic form is computed to be substantially more stable than the iminolic tautomer. N-Hydroxyurea and its thio and sila derivatives are computed to behave as Nacids in the gas phase. These compounds are in gas-phase weak acids with a calculated acidity of about 1425 to 1355 kJ-mol^–1. Basicities increase in the order: N-hydroxyurea < N-hydroxythiourea < N-hydroxysilaurea. The most stable protonated structures are represented by several isomers with almost equal stability. Thus, in the N-hydroxyurea, N-hydroxythiourea, and N-hydroxysilaurea, both protonation at the double bonded (C=O, C=S and Si=O) oxygen and sulfur atoms, as well as the protonation at the N(H)OH nitrogen basic center is equally probable. The experimental pK _a value (10.6) of N-hydroxyurea and the computed value (9.7) for its monohydrated complex with the specifically hydrogen-bonded water molecule to the ionizable OH group are in a good agreement. The experimental partition coefficient of N-hydroxyurea is best reproduced by the Alog P_s method. The formation of nitroxide radical in the reaction of N-hydroxyurea and its sulfur and silicon substituted derivatives with the phenol radical is an exothermic process. Thus, the \bondN(H)OH moiety of these compounds may quench the structurally related tyrosyl radicals in the active site of ribonucleotide reductase.     

The benzoylation of uracil and thymine

Uracil and thymine react with benzoyl chloride in acetonitrile-pyridine solution at room temperature to give first their 1-$\text{N}$-benzoyl (2b and 3b) and then their 1-$\text{N}$, 3-$\text{N}$-dibenzoyl derivatives (4a and 4b, respectively); the latter compounds are converted into the corresponding 3-$\text{N}$-benzoyl derivatives (5a and 6a) under mild conditions of basic hydrolysis.     

Quinoline nitroxide radicals. Ipso-attack in the reaction between 2-methoxy and 2-cyanoquinoline N-oxide,and phenylmagnesium bromide

2-Methoxy and 2-cyanoquinoline N-oxide, when treated with phenylmagnesium bromide, undergo a nucleophilic ipso-attack at C-2, yielding, by elimination of methoxymagnesium bromide or cyanomagnesium bromide, the corresponding 2-phenylquinoline N-oxides, which react with the excess of Grignard reagents forming 2,2-diphenylquinoline 1-oxyls. Even when the methoxy and cyano groups are in position 4, the attack by the Grignard reagent takes place at C-2 giving 2-phenylquinolines and 2-phenylquinoline N-oxides by elimination of hydroxymagnesium bromide and bromomagnesium hydride, respectively; the formation of 2,2-diphenylquinoline l-oxyls in these reactions is discussed.     

Thermal synthesis and characterisation of N,N'-di(chlorobenzyl) ureas

The thermal stability of the Schiff base ethylacetoacetate-o-chlorobenzylamine (bdII), N-o-chlorobenzyl-C-benzoyl acetamide (bdIII), and N-p-chlorobenzyl-C-benzoyl acetamide (bdIV) were studied by thermogravimetric analysis. II Gave N,N'-di(o-chlorobenzyl) urea (bdIa) at 60° C, whereas the thermogravimetric curves of III and IV indicate that reactions other than formation of I may occur. The urea derivatives (I) have also been prepared from benzylamines and the corresponding β-ketoester and identified.     

Carbene and radical pathways in pyrolysis of benzisoxazolones and benzotriazoles

A comparative study of the flash vacuum pyrolysis of a number of N‐alkyl and N‐acyl benzotriazoles and benzisoxazolones has confirmed that carbene derived pathways predominate at lower temperatures, and radical pathways at highter temperatures. Two new general unimolecular thermal reactions are also highlighted.     

Photoactivated α-ketocarbenes: Formation and isomerization reactions. RRKM calculations with semi-empirical parameters (AM1, MNDOC)

The dynamical aspects of some α-diazoketones (DZ) photolysis are investigated within the framework of statistical theories (RRKM formulation). On the whole, the results agree satisfactorily with the gas-phase experimental observations (quantum yields). In particular, the reactions DZ + hv → α-ketocarbene (KC) + N₂, appear to be mainly governed by statistical behavior. The two channel isomerizations KC → ketene (KE), i.e, the Wolff Rearrangement, and KC → α,β-unsaturated ketone (ON) are also considered. It is suggested that the trapping of the α-ketocarbenes and oxirenes (OX) species would be favored under appropriate conditions (among them the irradiation wavelength and the relaxation processes involved in the reactive medium). The parametrization of the model relies on semi-empirical quantum calculations and is improved by some adjustments with experimental data. © 1994 John Wiley & Sons, Inc.     

Collision-Induced Dissociation of Diazirine-Labeled Peptide Ions. Evidence for Brønsted-Acid Assisted Elimination of Nitrogen

Gas-phase dissociations were investigated for several peptide ions containing the Gly-Leu* N-terminal motif where Leu* was a modified norleucine residue containing the photolabile diazirine ring. Collisional activation of gas-phase peptide cations resulted in facile N₂ elimination that competed with backbone dissociations. A free lysine ammonium group can act as a Brønsted acid to facilitate N₂ elimination. This dissociation was accompanied by insertion of a lysine proton in the side chain of the photoleucine residue, as established by deuterium labeling and gas-phase sequencing of the products. Electron structure calculations were used to provide structures and energies of reactants, intermediates, and transition states for Gly-Leu*-Gly-Gly-Lys amide ions that were combined with RRKM calculations of unimolecular rate constants. The calculations indicated that Brønsted acid-catalyzed eliminations were kinetically preferred over direct loss of N₂ from the diazirine ring. Mechanisms are proposed to explain the proton-initiated reactions and discuss the reaction products. The non-catalyzed diazirine ring cleavage and N₂ loss is proposed as a thermometer dissociation for peptide ion dissociations.

The mechanism of thermal elimination of urea and thiourea derivatives. Part 1. Rate data for pyrolysis of N-acetylurea,N-acetylthiourea,N,N -diacetylthiourea,and N-acetylthiobenzamide

Rates of thermal decomposition of N-acetylurea (1), N-acetylthiourea (2), N,N′-diacetylthiourea (3), and N-acetylthiobenzamide (4) have been measured over a 45 K range for each compound. The molecules were found to undergo unimolecular first-order elimination reactions for which log A = 11.9, 11.6, 11.8, and 13.4 s^-1, and E_a = 181.2, 135.9, 128.3, and 130.3 kJ mol^-1, respectively. The reactivities of these compounds have been compared with those of amide derivatives and with each other. Product analysis together with the kinetic data were used to outline feasible pathways for the elimination reactions of the compounds under study. © 1996 John Wiley & Sons, Inc.     

Gas-phase kinetics of N-substituted diacetamide

Gas-phase elimination reactions of number of N-substituted diacetamides have been studied. The rates of N-phenyl, 4-methoxyphenyl, 4-nitrophenyl, and benzyl diacetamide have been measured between 643–683, 642–693, 673–725, and 555–610 K, respectively. They undergo unimolecular first-order elimination reactions, for which log A = 12.8, 12.9, 12.8, and 11.0 s^?1 and E_a = 185.7, 191.4, 193.4, and 143.6 kJ mol^?1, respectively. The reactivity of these compounds has been compared with the unsubstituted diacetamide at 600 K. The kinetic data reveals that each of the N-aryldiacetamides is less reactive than the parent molecule. We attribute this observation to the resonance of the lone pair of electrons on the nitrogen with either the two carbonyl oxygen atoms or with the 6π electrons in the aromatic ring which will result in the stabilization of the N-aryldiacetamides related to the parent molecules. © 1994 John Wiley & Sons, Inc.     

The Saunders-Bell Analysis of Tunnel Effects in Reactions with Kinetic Isotope Effects

The primary kinetic isotope effects of deuterium were investigated in 22 hydrogen and deuterium transfer reactions, including enzymatic and nonenzymatic hydride transfer reactions, elimination reactions, and reactions catalyzed by enzymes lipooxygenase, amine dehydrogenase, and methylmalonyl-CoA mutase. In each case, the Saunders-Bell analysis was applied to calculate the tunnel effects and the corresponding thermodynamic parameters. The Saunders-Bell analysis was effective in 14 cases out of 22. A high degree of correlation was found between the barrier factor, the tunnel factor, and the entropy factor among all reactions studied. From this, a general relationship between the three factors was derived, based on the Saunders-Bell analysis of the Bell equation; the Saunders-Bell analysis is valid within certain limits of the barrier factor. This general relationship is universally valid for all hydrogen/deuterium transfer reactions in nature with moderate tunneling, when the Saunders-Bell analysis applies.