Kinetic study on the acid hydrolysis of 1-aryl-2-phenyl-2-imidazolines. Basicity-rate of hydrolysis and structure relationships

Rate constants (k_obs) of hydrolysis in sulfuric acid-water mixtures at 100° for five 1-aryl-2-phenyl-2-imidazolines were determined. The influence of substituents in the phenyl group at N-1 upon the rate of hydrolysis was studied. When the imidazoline ring is considered to be a substituent of the benzene ring at N-1, a good correlation with the Hammett equation is found. In opposition to the behavior in alkaline media it was observed that reaction rates were enhanced by electron-withdrawing phenyl substituents and reduced by electron-releasing groups providing, similarly, a change in the mechanism of the reaction in the second case that was not observed in the first. Agreement with the Hammett equation allowed comparison between experimental and “calculated” rate constants which are fairly close. An equation relating the rate constants with the pK_a values of the imidazolinium ions is given.     

Acid-catalyzed hydrolysis of ring-substituted phenyl vinyl sulfides

The acid-catalyzed hydrolysis of phenyl vinyl sulfide and its ring-substituted derivatives has kinetically been investigated in 40% aqueous dioxane and 90% aqueous tetrahydrofuran. The observed rate constants were satisfactorily correlated with the Hammett acidity function H₀. The effect of substituents on the hydrolysis rates was found to conform to the Hammett σ- constants with ? = ? 1.98 (40% dioxane, 30°). The ? value was compared with that found for the hydrolysis of phenyl vinyl ether in terms of the transmission efficiency of the S and O atoms.     

Mechanism of (Salen)manganese(III)‐Catalyzed Oxidation of Aryl Phenyl Sulfides with Sodium Hypochlorite

The oxidation of 4‐substituted phenyl phenyl sulfides was carried out with several oxo(salen)manganese(V) complexes in MeCN/H₂O 9 : 1. The kinetic data show that the reaction is first‐order each in the oxidant and sulfide. Electron‐attracting substituents in the sulfides and electron‐releasing substituents in salen of the oxo(salen)manganese(V) complexes reduce the rate of oxidation. A Hammett analysis of the rate constants for the oxidation of 4‐substituted phenyl phenyl sulfides gives a negative ρ value (ρ=?2.16) indicating an electron‐deficient transition state. The log k₂ values observed in the oxidation of each 4‐substituted phenyl phenyl sulfide by substituted oxo(salen)manganese(V) complexes also correlate with Hammett σ constants, giving a positive ρ value. The substituent‐, acid‐, and solvent‐effect studies indicate direct O‐atom transfer from the oxidant to the substrate in the rate‐determining step.     

Reaction of 4‐benzylidene‐2‐methyl‐5‐oxazolone with amines,Part 2: Influence of substituents in para‐position in the phenyl ring and a substituent on amine nitrogen atom on the reaction kinetics

An influence of a structure of the amine (benzylamine, N‐methyl‐benzylamine, N‐isopropyl‐benzylamine, N‐methyl‐butylamine, N‐ethyl‐butylamine, sec‐butylamine, and tert‐butylamine) on a rate constant of the ring‐opening reaction of 4‐benzylidene‐2‐methyl‐5‐oxazolone (Ox) was studied. The good correlation between logarithm of the rate constants and Charton's steric substituent constant ν as well as good correlation with a form of the simple branching equation indicate that there is a steric effect because of substitution at C1 carbon atom of nucleophile which decreases the reaction rate. Additionally, an influence of a structure of the benzylidene moiety of Ox on a rate of the oxazolone ring‐opening reaction was studied. The substituents (? OH, ? OCH₃, ? N(CH₃)₂, ? Cl, ? NO₂) in para‐position of the phenyl ring of Ox substantially modified the rate of the reaction with benzylamine in acetonitrile. The rate of the Ox ring‐opening reaction decreased with increase of the electron‐donating properties of the substituent. A good correlation between the rate constants of the reaction of 4‐(4′‐substituted‐benzylidene)‐2‐methyl‐5‐oxazolones with benzylamine and the electron density at the reaction center (carbon C5 of the oxazolone ring), calculated using ab initio method, and the Hammett substituent constants, and CR equation were established. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 148–155, 2002; DOI 10.1002/kin.10039     

Nitrogen Bridgehead Compounds. Part 81. Synthesis of 9-(benzylidenehydrazono)-6-methyl-4-oxo-6,7,8,9-tetrahydro- and 9-(benzylidenehydrazine)-6-methyl-4-oxo-6,7-dihydro-4H-pyrido[1,2-a]-pyrimidine-3-carboxylates

Reaction of ethyl 9-hydrazono-6-methyl-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylate and benzaldehyde and its derivatives give a tautomeric mixture of 9-arylidenehydrazono-6,7,8,9-tetrahydro- and 9-arylidenehydrazine-6,7-dihydropyrido[1,2-a]pyrimidine derivatives. In the same case the enhydrazine and hydrazone tautomers were separated. The structure of the products were characterised by uv, ir, ¹H and ¹³C nmr. The equilibrium of the tautomers was affected by the substituent of the phenyl ring. A fair linear correlation exists between the logarithms of the equilibrium constants and Hammett σ_m and σ^? constants of the substituents present on the phenyl ring.     

Kinetics and mechanism of base-catalyzed hydrolysis of Cu(II)-salicylamide complex

The kinetics of hydrolysis of Cu(II)-salicylamide complex have been studied in sodium hydroxide solution (0.5 to 2.5M). The observed pseudo-first-order rate constants vary according to the empirical equation 1/??_obs = B₁ + B₂/[ōH] up to 2.0 M sodium hydroxide concentration. The mechanism of base-catalyzed hydrolysis has been proposed and it is concluded that the reaction proceeds by the interaction of complex with the nucleophile, forming tetrahedral intermediate which then breaks down to products. The rate equation has been derived. Thermodynamic parameters have also been reported.     

Activation of the aromatic system by the SO2CF3 group: Kinetics study and structure–reactivity relationships

The rate constants for the reaction of 2,6‐bis(trifluoromethanesulfonyl)‐4‐nitroanisole with some substituted anilines have been measured by spectrophotometric methods in methanol at various temperatures. The data are consistent with the S_NAr mechanism. The effect of substituents on the rate of reaction has been examined. Good linear relationships were obtained from the plots of log k₁ against Hammett σ_para constants values at all temperature with negative ρ values (?1.68 to ?1.11). Activation parameters Δ^≠H varied from 41.6 to 54.3 kJ mol^?1 and Δ^≠S from ?142.7 to ?114.6 J mol^?1 K^?1. The δΔ^≠H and δΔ^≠S reaction constants were determined from the dependence of Δ^≠H and Δ^≠S activation parameters on the σ substituent constants, by analogy with the Hammett equation. A plot of Δ^≠H versus Δ^≠S for the reaction gave good straight line with 177°C isokinetic temperature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 203–210, 2010     

Vinyl polymerization. 178. Copolymerizations of p-substituted phenyl vinyl sulfides

The copolymerizations of p-substituted phenyl vinyl sulfides (M₂) having OCH₃, CH₃, H, Cl, and Br substituents with styrene and methyl methacrylate (M₁) and their intercopolymerizations at 60°C. were studied. From the results of copolymerizations with styrene and methyl methacrylate, the monomer reactivity ratios and the Q₂e₂ values were determined. For example, the Q and e values for unsubstituted phenyl vinyl sulfide were 0.45 and ?1.26 in the copolymerization with methyl methacrylate. This result indicated the importance of the 3d orbital resonance between the sulfur atom and the adjacent carbon atom in the transition state of copolymerizations. The relative reactivities of these monomers toward the polymer radicals were found to be correlated with the Hammett σ constants of the substituents. In the intercopolymerizations of these monomers, it was also found that the relative reactivities followed the Hammett equation approximately.     

Carbon‐13 NMR and PM3 Study on the Substituent Effect of 1‐Aryl‐3,3‐Difluoro‐2‐Halocyclopropenes

The substituent‐induced chemical shifts (SCS) of C2 and C3 on the ¹³C NMR spectra of 1‐aryl‐3,3‐difluoro‐2‐halocyclopropenes were studied. The correlation between SCS and Hammett constants shows that the tendency of effect by the substituents on the phenyl ring is BrC2(ρ = 4.66) > ClC2(ρ = 4.50) and ClC3(ρ = ?1.63) > BrC3(ρ = ?1.41). The DSP treatment further confirms the SCS of C2 and C3 are the main contribution of the resonance effect and field effect, respectively. Those results of the incremental shifts reveals that the gem‐difluorocyclopropenyl bearing the phenyl group possesses a triple bond character, which is also observed in IR spectra with high n?_C=C (1768–1945 cm^?1).     

Alkaline hydrolysis of ethiofencarb: Kinetic study and mechanism degradation

The present paper deals with the hydrolysis of ethiofencarb [2‐ethylthiomethyl(phenyl)‐N‐methylcarbamate] in alkaline solution. The reaction kinetics has been investigated using spectrophotometric and liquid chromatographic techniques. The rate constants were determined following a proposed first‐order kinetic model. The positive activation entropy Δ S^≠ = +100.07 J mol^?1 K^?1 and the absence of general basic catalysis indicated an E1cB hydrolytic mechanism, involving the formation of methyl isocyanate. This result was confirmed by the fact that ethiofencarb fits well into Brönsted and Hammett lines, obtained for a series of substituted N‐methylcarbamate whose decomposition in aqueous media was established to follow an E1cB mechanism. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 118–124, 2013     

1H‐4,5,6,7‐Tetrahydro‐1,3‐diazepines. part II: basicity and hydrolysis of 1, 2‐diaryl derivatives

Basicity and alkaline hydrolysis of 1,2‐diaryl‐1H‐4,5,6,7‐tetrahydro‐1,3‐diazepines 1 are studied. Results are analyzed on the basis of Hammett and Swain‐Lupton constants, finding good structure‐basicity correlation when both, inductive and mesomeric effects, are considered together. Regioselectivity is observed in the alkaline hydrolysis of compounds 1 , and it is analyzed in light of the stereoelectronic control theory. Results are compared with those previously obtained for five and six membered ring homologues: 1H‐4, 5‐dihydroimidazoles and 1,4,5,6‐tetrahydropyirimidines respectively.     

Correlation of substituted aromatic β‐diketones' characteristic protons chemical shifts with Hammett substituent constants

Influence of dibenzoylmethane's substituents in meta and para positions on chemical shift values of tautomers' characteristic protons was investigated in four solvents with ¹H NMR spectroscopy: acetone‐d₆, benzene‐d₆, CDCl₃ and deuterated dimethyl sulfoxide (DMSO‐d₆). It was proved that the influence of substituents on chemical shifts strongly depends on the kind of the solvent; the greatest changes were observed in benzene‐d₆ and the smallest in CDCl₃. In acetone‐d₆ and DMSO‐d₆, the influence of substituents on chemical shifts is similar and the most regular. It allowed a fair correlation of chemical shifts of para‐substituted dibenzoylmethane derivatives' characteristic protons with Hammett substituent constants in these solvents. In CDCl₃, characteristic protons' chemical shifts were near ¹H NMR spectroscopy measurement error limits, and, therefore, correlation with Hammett substituent constants in this solvent was unsatisfactory. In benzene, although the changes of chemical shifts are the most evident, the changes are also the most irregular, and, therefore, correlation in this solvent failed completely. Results of meta‐substituted derivatives were much more irregular, and their correlation with Hammett substituent constants was poor in all investigated solvents. Copyright © 2013 John Wiley & Sons, Ltd.     

Kinetic Studies of Donor–Acceptor Cyclopropanes: The Influence of Structural and Electronic Properties on the Reactivity

The kinetics of (3+2) cycloaddition reactions of 18 different donor–acceptor cyclopropanes with the same aldehyde were studied by in situ NMR spectroscopy. Increasing the electron density of the donor residue accelerates the reaction by a factor of up to 50 compared to the standard system (donor group=phenyl), whereas electron‐withdrawing substituents slow down the reaction by a factor up to 660. This behavior is in agreement with the Hammett substituent parameter σ. The obtained rate constants from the (3+2) cycloadditions correlate well with data from additionally studied (3+n) cycloadditions with a nitrone (n=3) and an isobenzofuran (n=4). A comparison of the kinetic data with the bond lengths in the cyclopropane (obtained by X‐ray diffraction and computation), or the ¹H and ¹³C NMR shifts, revealed no correlation. However, the computed relaxed force constants of donor–acceptor cyclopropanes proved to be a good indicator for the reactivity of the three‐membered ring.     

Importance of steric effect and evaluation of quantitative structure reactivity relationship (QSRR) in the quaternization reaction of benzothiazoles and phenacyl bromide

The kinetics of reaction of substituted 2-aminobenzothiazoles and phenacyl bromide have been followed conductometrically and in some cases, argentometrically. Both the methods produced almost the same rate constants. Substituents at position 5 of the benzothiazole nucleus behave like para substituents of the benzene ring. A correlation with Hammett σ_p substituent constants has been obtained with a rho value of ?1.04. The rate data of quaternization reaction of 4, 5, and 6 substituted 2-aminobenzothiazoles with phenacyl bromide have been correlated with F_k, R_k, and V_w values by multiple regression analysis with the equation suggested by Williams and Norrington and modified by us. The values are found to correlate well with the equation, log k = ?4.4979 ? 0.4815f_jF_k + 0.5933r_jR_k ? 0.0277V_w.     

A study concerning the synthesis,basicity and hydrolysis of 4‐amino‐2‐(N,N‐diethylamino)quinazoline derivatives

A group of 2‐(N,N‐diethylamino)‐4‐aminoquinazoline derivatives have been synthesized in the reaction of N¹,N¹‐diethyl‐N²‐arylchlorocarboxyamidines with cyanamide in the presence of T1Cl₄ as a catalyst. Such quinazolines decompose into the corresponding quinazolones in dilute aqueous HC1 solutions at higher temperature. Hydrolysis rates of 2‐(N,N‐diethylamino)‐4‐aminoquinazoline and 2‐(N,N‐diethylamino)‐4‐(N,N‐dimethylamino)‐quinazoline have been determined to observe the influence of substituents at the 4‐amino group upon the hydrolysis. pK_a values have been also determined for these compounds and analyzed in conjunction with the Hammett σ constants.     

Solvent and Substituent Effects in the Solvolysis of 9‐Aryl‐9‐bromofluorenes

The solvolysis of eight 9‐aryl‐9‐bromofluorenes ( 6b～6i ) in a variety of solvents were studied. Correlation analysis using single‐parameter Grunwald‐Winstein equation (Eqn. 1) with different Y scales showed good linearity (R ≥ 0.98) for most cases if Y_xBnBr was employed. Linear relationships were observed from Hammett‐type analysis of logarithm of rate constants using Brown‐Okamoto σ⁺ constants (Eqn. 3), although inverse order of k(p‐CF₃)/k(m‐ CF₃) was realized in a number of cases. The ρ values were found to vary slightly with different solvent systems. Calculated atomic charge reveals the similarity between 9‐phenyl‐9‐fluorenyl cation ( 7 ) and triphenylmethyl cation ( 8 ). An extended charge delocalization throughout the fluorenyl ring led to the conclusion of the insignificance of antiaromaticity, which was in harmony with that obtained in previous studies. The variation of relative k_Br/k_Cl rate ratios was attributed to the electrophilic pull by solvents in solvolysis.     

Hydrolysis of 2-aminoethanethiolsulfate ions

The kinetics of the acid catalyzed hydrolysis of 2-aminoethanethiolsulfate (AETS) ions were investigated. The dependence of the hydrolysis rate constant on acidity and temperature was determined. The hydrolysis rate equation can be expressed as where H_o is the Hammett acidity function. The rate constant, k, can be expressed as The pK_a's for the compound were measured and literature value of pK_a was found to be in error. The values determined in this study are pK_a1 < ?0.5 and pK_a2 = 9.1 ± 0.1. General acid catalysis of the hydrolysis reaction was found not to proceed to a significant degree. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Vinyl polymerization. 179. Effects of substituents on chain transfer reaction of substituted cumenes toward poly(methyl methacrylate) radical

In order to study the effects of substituents on the chain transfer reaction to cumenes, the polymerization of methyl methacrylate in a series of nuclear-substituted cumenes with α,α′-azobisisobutyronitrile as initiator was carried out at 60°C. and the chain transfer constants C were determined. The C values obtained for all substituted cumenes were greater than that (C₀) for unsubstituted cumene, regardless of the electronattracting or -repelling nature of the substituents. Hence the plot of log (C/C₀) against the Hammett σ constants gave no linear relationship. When the plots were made by the modified Hammett equation including resonance effect of the substituents: log (C/C) = ρσ + γE_R, however, a straight line with ρ = 0.03 and γ = 0.9 was obtained. From these results, it may be concluded that the effect of the substitutents on the chain transfer reactivities of cumenes toward attack of a poly(methyl methacrylate) radical is attributable mainly to the resonance contribution in the transition state. These results are also compared with those for polystyryl radical reported previously and discussed.     

Electron ionization mass spectra and tautomerism of substituted 2‐phenacylquinolines

Tautomerism has been studied conventionally in solutions or in the solid state. However, the importance of mass spectrometry in the gas phase was realized relatively late. 2‐Phenacylquinolines are known to undergo ketimine‐enaminone tautomerism. The ratio of tautomers is dependent on the nature of the phenyl ring substituent and the Hammett substituent constants σ. Theoretical calculations indicate the presence of ketimine and enaminone tautomers in the gas phase. The electron ionization mass spectra of eight 2‐phenacylquinolines (ketimine form) were recorded at 70 eV in order to determine the fragmentation routes and to screen for the presence of their enaminone tautomers, (Z)‐2‐benzoylmethylene‐1,2‐dihydroquinolines, in the gas phase. The relative abundances or total ion currents of some ions correlated with the Hammett substituent constants and Hammett‐Brown constants. The product ions [M–CO]^{+ .} and [M–HCO]⁺ were observed. A reaction mechanism is suggested for the formation of these ions, requiring skeletal rearrangements. The results furnish information relating to tautomerism in the gas phase. Copyright © 2009 John Wiley & Sons, Ltd.     

The psuedo‐michael reaction of 2‐aminoimidazolines 2. Part 1. Synthesis and structure assignment of isomeric 5(1H)‐Oxo and 7(1H)‐Oxo‐2,3‐dihydroimidazo[1,2‐a]pyrimidine‐6‐carboxylates

The pseudo‐Michael reaction of 1‐aryl‐2‐aminoimidazolines‐2 with diethyl ethoxymethylenemalonate (DEEM) was investigated. Extensive structural studies were performed to confirm the reaction course. For derivatives with N1 aromatic substituents, it was found that the reaction course was temperature dependent. When the reaction temperature was held at ?10 °C only the formation of 1‐aryl‐7(1H)‐oxo‐2,3‐dihydroimi‐dazo[1,2‐a]pyrimidine‐6‐carboxylates ( 4 ) was observed in contrast to earlier suggestions. Under the room temperature conditions, the same reaction yielded mixtures, with varying ratio, of isomeric 1‐aryl‐7(1H)‐oxo‐ ( 4a‐4f ) and 1‐aryl‐5(1H)‐oxo‐2,3‐dihydroimidazo[1,2‐a]pyrimidine‐6‐carboxylates ( 5a‐5f ). The molecular structure of selected isomers, 4b and 5c , was confirmed by X‐ray crystallography. Frontal chro‐matography with delivery from the edge was applied for the separation of the isomeric esters. The isomer ratio of the reaction products depended on the character of the substituents on the phenyl ring. The 1‐aryl‐7(1H)‐oxo‐carboxylates ( 4a‐4f ) were preferably when the phenyl ring contained H, 4‐CH₃, 4‐OCH₃ and 3,4‐Cl₂ substituents. Chloro substitution at either position 3 or 4 in the phenyl ring favored the formation of isomers 5a‐5f . The isomer ratios were confirmed both by ¹H NMR and chromatography. The reaction of the respective hydrobromides of 1‐aryl‐2‐aminoimidazoline‐2 with DEEM, in the presence of triethylamine, gave selectively 5(1H)‐oxo‐esters ( 5a‐5f ).