Vinyloge Acylverbindungen. XXI. 1H-NMR-spektroskopische Untersuchungen an 3-Chlor-propen-iminiumsalzen

Vinylogous Acyl Compounds. XXI. ¹H-N.M.R. Spectroscopic Investigations on 3-Chloropropen-iminium Salts The ¹H-n.m.r. data of a series of 3-aryl-3-chloropropeniminium salts 5 are reported. From the vicinal coupling constants ³J(H¹, ²H) as well as from NOE difference spectra follows that salts of type 5 have throughout E(1,2)Z(2,3) configuration.     

Vinyloge Acylverbindungen. XVIII [1]. Einfluß sterischer Faktoren auf das Reaktionsverhalten vinyloger Carbonamidiumsalze

Vinylogous Acyl Compounds. XVIII. Influence of Steric Factors on the Reaction Behaviour of Vinylogous Carbonamidium Salts Depending on the size of their N-alkyl groups vinylogous carbonamidium salts show a markedly graduated reactivity under suitable conditions. Thus 2-formyl-vinyl trimethylammonium perchlorate 1a is decomposed by sodium hydroxide yielding only trimethylamine and salts of malondialdehyde 2 , while the analogous triethylammonium salt 1b additionally undergoes a fragmentation to triethylamine, acetylene and formic acid. The reaction of 4-(4-nitrobenzyl)-pyridine with 1 and the analogous 2-benzoylvinylammonium salts 3 to the 1,4-dihydropyridine dye 4 and 5 , respectively, is faster by orders of magnitude in the case R′ = CH₃ than in the case R′ = C₂H₅. Contrary to the 1a -p-nitrophenylhydrazone 6a which can be transformed into the pyrazole 7 the 1b -hydrazone 6b withstands such a ring closure. Depending on the reaction conditions and nature of the substituent R the action of aniline on 1 leads either to the monoanils 8 or to the malondialdehyde dianil salt 9 . While piperidine reacts with 3a as well as with 3b to give N-(2-benzoylvinyl)-piperidine 10 , aniline forms a corresponding vinylogous amide 11 only with 3a. 3b , however, on reaction with aniline · HCl via the intermediate monoanil 12 , yields the vinylogous amidinium salt 13 which is not obtainable from 3a or 11 . Using o-phenylendiamine this reactivity graduation can be utilized for preparing 2-aryl-substituted 1H-1,5-benzodiazepinium salts, e.g. 17 .     

Vinyloge Acylverbindungen. XX. Reaktivität und Toxizität arylsubstituierter β-Chlorvinylketone, β-Chlorvinylaldehyde und β-Chlorvinylmethyleniminiumsalze

Vinylogous Acyl Compounds. XX. Reactivity and Toxicity of Aryl-substituted β-Chlorovinyl Ketones, β-Chlorovinyl Aldehydes, and β-Chlorovinyl Methyleniminium Salts Based on kinetic measurements, the nucleophilic replaceability of the chlorine in aromatic β-chlorovinyl ketones ArCO-CH  CH-Cl ( 1 ), isomeric β-chlorovinyl aldehydes OCH CHC(Cl)Ar( 2 ), and corresponding β-chlorovinyl methyleniminium salts Me₂N^⊕;CH CHC(Cl)Ar X^⊖ ( 3 ) is compared and related to toxicological findings. The chemical reactivity of these important synthetic building blocks increases in the order 2 < 1 < 3 , the acute toxicity (24 h LD₅₀ i. p. in the mouse) shows the graduation 2 < 3 < 1 . Compounds of type 1 prove to be relatively toxic (LD₅₀ 24–42 mg/kg) and display a marked necrotic action after percutaneous absorption, whereas the aldehydes 2 have not only a minor acute toxicity (LD₅₀ 158–298 mg/kg) but also a somewhat less marked skin damaging activity. In addition, the LD₅₀ values of selected β-chlorovinyl carbonyl compounds are compared with those of corresponding halogen-free compounds as well as of vinylogous carbonamidium salts ArCO CHCH N^⊕R₃X^⊖. The latter, which can be used as synthetic equivalents of 1 , differ in both the reduced acute toxicity and missing skin damaging properties.     

Inter- und intramolekulare Acylwanderungen an 1(9)H-2,3-Dihydro-imidazo[1,2-a]benzimidazolen

Inter- and Intramolecular Acyl Transfer on 1(9)H-Imidazo[1,2-a]benzimidazoles The new imidazo[1,2-a]benzimidazoles ( 3 ) react with electrophiles like aroyl chlorides, isocyanates, cyanates, chloroformates and chlorothioformates to give the 9-acyl derivatives ( 4a – 1 ). At higher temperatures intermolecular acyl transfer takes place to give the l-acyl compounds ( 5a – m ). In the case of 1-carbamoyl imidazo[1,2-a]benzimidazoles ( 5 ) was observed intramolecular acyl transfer in the presence of strong bases and 1-benzimidazol-2-yl-hydantoins ( 6 ) were isolated. The structures of the prepared compounds could be inferred from their ¹H and ¹³C n.m.r., mass spectra and were corroborated by the comparison with the data of similar derivatives as well as by chemical means.     

Acylierung von Heterocyclen mit Kohlensäurederivaten. II. Endo- und exo-Carbamoylierung von 2-Amino-benzimidazol-Derivaten mit Isocyanaten. Mechanismus der Acylgruppenwanderung

Acylation of Heterocycles with Carbonic Acid Derivatives. II. Endo and Exo Carbamoylation of 2-Amino-benzimidazole Derivatives with Isocyanates. Mechanism of the Acyl Group Migration 2-Amino-benzimidazoles react with isocyanates with good yields to give 2-amino-1-carbamoyl-aminobenzimidazoles 1 at −30°C and the corresponding 2-carbamoyl isomeres 2 at room temperature, respectively. The isomerization mechanism was studied by crossover experiments and kinetic measurements and has been found to consist of inter- and monomolecular acyl transfer.     

Diels-Alder-Reaktionen. VII. Über die Isomerisierung von 2-Vinylbicyclo[2,2,1]hepten-(5)

Diels-Alder Reactions. VII. The Isomerization of 2-Vinylbicyclo[2,2,1]hept-5-ene The isomerization of exo/endo-2-vinylbicyclo[2,2,1]-hept-5-ene in the presence of Na/Al₂O₃ rapidly gives the thermodynamic equilibrium between exo- and endo-2-vinylbicyclo-[2,2,1]hept-5-ene and cis- and trans-2-ethylidenbicyclo[2,2,1]-hept-5-ene. Far more slowly vinylnortricyclene is formed, which enriches to an equilibrium concentration of about 75% at 60°C. The dependence of equilibrium constants of isomerization on temperature allows the calculation of enthalpies and entropies of isomerization.     

Pyryliumverbindungen. XXII. 1H-NMR- und UV-spektroskopische Untersuchungen zur Isomerisierung von Pseudobasen unsymmetrisch substituierter 2, 4, 6-Triarylpyryliumsalze

Pyrylium Compounds. XXII. ¹H-N.M.R. and U.V. Spectroscopic Investigations on the Isomerization of Pseudobases of Unsymmetrically Substituted 2, 4, 6-Triarylpyrylium Salts The kinetics and mechanism of the isomerization of the title compounds, the pentene 1,5-diones 2 and 3 , were studied by ¹H-n.m.r. and u.v. spectroscopy. The equilibrium constants measured vary little near 1, indicating the small influence of substituents on the equilibrium position. The mutual rearrangement 2 ⇄ 3 proved to be a base-catalized reaction which is characterized by strictly linear Hammett correlation between 1g k and Σσ_p. The results obtained suggest resonance-stabilized anions of type 4 as intermediates. - Pseudobases of 3-alkyl-2, 4, 6-triarylsubstituted pyrylium salts do not undergo a reversible isomerization.     

Zur Umkupplung von 4-Arylazo-2-pyrazolin-5-onen mit p-Chinondiiminkationen

Recoupling of 4-Arylazo-2-pyrazoline-5-ones with p-Quinonediimine Cations 4-Arylazo-2-pyrazoline-5-ones ( 1a – j ) readily undergo coupling reaction with p-quinonediimine cations ( 2a , b ) to form azomethin dyes ( 3a , b ). The dependence of the rate constants k_K of the dye formation on the substituents of 1a – j as well as on the ionic strength show that the rate-determining step of the coupling reaction is the formation of the intermediate 4 in a bimolecular reaction between the carbanions of 1a – j and p-quinonediimine ( 2a , b ). It became evident that the benzenediazoniumion ( 5a – j ) is eliminated in the reaction of 4 to 3a , b . Under the coupling conditions used, substituted benzene is formed in the reduction reaction of 5a , b by the p-phenylendiamine ( 7a , b ) or by the leuco dye ( 6a , b ).     

Isomerization of α-pinene to camphene

The catalytic isomerization reaction of α-pinene to camphene over a clinoptilolite catalyst was investigated in a batch reactor open to the atmosphere between 130 and 155°C. The catalyst was selective to the isomerization of α-pinene to camphene. The effects of several variables, such as reaction temperature, amount of catalyst, stirring speed and catalyst particle size, on the conversion of α-pinene and selectivity to camphene were determined. The reaction fits a first-order parallel reaction with rate constants of k ₁ = 3.020·10^?2 e ^?33381.6/RT for the production of camphene and of k ₂ = 1.576·10^?2 e ^?31096.53/RT for the production of limonene.     

Comparison of physically mixed and separated MgO and WO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> catalyst for propylene production via 1-butene metathesis

We examined the catalyst bed design of MgO and WO₃/SiO₂ for production of propylene via metathesis of 1-butene. WO₃/SiO₂ was used as a bi-functional catalyst for isomerization and metathesis reactions. Addition of MgO was proposed to help improve the isomerization activity and hence the propylene yield. Experimental studies were carried out to determine activity and reaction kinetics of 1-butene isomerization over MgO isomerization catalyst and 1-butene metathesis over WO₃/SiO₂ bi-functional catalyst for designing a suitable catalyst bed. Two types of catalyst bed arrangement—physically mixed bed and separated bed—were considered and compared by computer simulation. The simulations reveal that adding MgO in the separated bed by packing MgO before WO₃/SiO₂ offers superior propylene yield to the physically mixed bed. The appropriate %MgO loading in catalyst bed which offers a maximum propylene yield was found to vary (3 and 23%), depending on operating condition.     

Strukturvariationen durch Reaktionen der Thiocarbonylgruppe

Structural Variations by Reactions of the Thiocarbonyl Group The 2,3‐dihydrothiazol‐2‐thiones 1a—c have been methylated to the 2‐methylsulfanylthiazolium iodides 2a—c , which could be reacted with double activated CH‐acidic compounds like 4‐nitrophenylacetonitrile ( 3 ) to yield 5 and 6a,b , with malonic acid derivatives 7a—c to yield the push pull substituted ketene‐S,N‐acetales 8a—c or with 3‐aminorhoda‐nine derivatives to yield 12a,b . Vinylogous CH‐acidic compounds like 9a—d reacted with 2b to the push‐pull substituted butadienes 10a—d . With p‐phenethidine 2b formed depending on the reaction conditions either the rare structure of an ortho‐dithiocarbonic diester diamide ( 14 ) or the isothiourea 15 . With hydrazino compounds, 16a—c with hydrazono partial structure resulted. Efforts to acylate the unsubstituted nitrogen of 17 with carbonic acid ester derivatives always yielded the S‐acylated products 18 and 20a,b .     

Multi‐Step Controlled Kinetics of the Transesterification of Crude Soybean Oil with Methanol by Mg(OCH3)2

This work focuses on a kinetic model that can be expressed as three significant controlled regions, i.e., a mass transfer controlled region in the internal surface of a heterogeneous catalyst, an irreversible chemical reaction controlled region in the pseudo‐homogenous fluid body and a reversible equilibrium chemical reaction controlled region near to the transesterification equilibrium stage. With the help of MATLAB7.0 software, the apparent reaction rate constants, k₂, k₂⁺ and k₂^–, were calculated and the corresponding apparent activation energies were calculated to be 67.450, 60.680 and 58.279 kJ·mol^–1, respectively. According to the confirmation experiments, it is indicated that the results can be applied for predicting the FAME yield at other reaction temperatures.     

Acylwanderungen am 3(5)-Amino-pyrazol

Acyl Migrations on 3(5)-Amino-pyrazole 3(5)-Amino-pyrazole 1 form 3 isomeric monoacylation products, 4 diacylation products and 3 triacylation products by reaction with electrophiles like cyanates, isocyanates or carboxylic and chlorides, respectively. Acyl migrations are observed depending on the reaction temperature and the structure of the acyl residue. The structures of the acyl derivatives of 3(5)-amino-pyrazole were characterized by nmr-spectroscopy.     

Kinetics of the aminolysis of hydrogenated tallow by allylamine and other primary amines in methanol

Kinetics of the aminolysis of hydrogenated tallow by allylamine in methanol solution under sodium methoxide catalysis was studied at several temperatures (60 to 90C) and catalyst concentrations. Under the experimental conditions the triglycerides were rapidly converted to the mixed methyl esters, which slowly reacted with the amine to produce the mixed amides. At constant catalyst concentration, disappearance of triglyceride was found to be first order in triglyceride and in amine. Because rate was found to be directly proportional to catalyst concentration, the experimental over-all rate was −d[Triglyceride]/dt=k₃[Triglyceride] [Amine] [RO⁻], and k₃ was 2.022 kg² mole⁻² hr⁻¹. A mechanism proposed by Bunnett and Davis for ester aminolysis involving an ester-amine complex formed in a rapid pre-transition-state equilibrium is consistent with thermodynamic terms which reconcile a large negative entropy of activation (−44.17 cal deg⁻¹ equivalent⁻¹) and relatively small energy of activation (11.60 kcal equivalent⁻¹). Relative rate constants at 70C under sodium-methoxide catalysis for the aminolysis of hydrogenated tallow by a variety of structurally different primary amines agreed, in general, with those found by others for the ethylene glycol-catalyzed reaction of methyl acetate with the same amines at 25C. However, monoethanolamine reacted nineteen times faster than predicted, which suggested a mechanism involving initial attack by the alkoxy anion of the ethanolamine in the rate detering step, followed by rapid, base-catalyzed, acyl acyl oxygen-to-nitrogen (O→N) migration. The velocity constants and thermodynamic constants reported enable prediction of the time required for specific yields under a variety of experimental conditions. Presented at AOCS Meeting, Chicago, 1964. E. Utiliz. Res. Dev. Div., ARS, USDA.     

Skeletal isomerization kinetics of 1-pentene over an HZSM-22 catalyst

Synthesis of the oxygenate fuel additive TAME (tertiary amyl methyl ether) is based on the reaction between reactive isopentene compounds (2-methyl-1-butene and 2-methyl-2-butene) and methanol. Skeletal isomerization of n-pentenes is an important reaction route in production of the raw material for TAME synthesis. In this work the kinetics of skeletal isomerization of 1-pentene was studied using HZSM-22 as a catalyst, and the effect of temperature (523–598 K) and WHSV (weight hourly space velocity) on product composition were investigated. The observed main reaction products were cis- and trans-2-pentenes, 2-methyl-2-butene, 2-methyl-1-butene and 3-methyl-1-butene. Minor products found in the output stream were C₂, C₃, C₄, C₆, C₇, C₈ and C₁₀ – alkenes and – alkanes. Only traces of methane and C₉ compounds were detected. Two different reaction mechanisms have been proposed in literature for skeletal isomerization of n-pentenes and their side reactions (dimerization and fragmentation); the monomolecular and the bimolecular skeletal isomerization mechanisms. In the current work a pseudohomogeneous reaction model for both mechanisms is fitted to experimental data. The fitting results show that both reaction mechanisms explain the skeletal isomerization of 1-pentene to isopentenes well. However, the monomolecular reaction mechanism explained the formation of dimerization and fragmentation products slightly better. The reliability of the estimated Arrhenius parameters was analyzed using Bayesian inference and Markov chain Monte Carlo methods (MCMC) which are rarely used in chemical engineering.     

Reactions with 2-thiazolin-5-ones. III. The behaviour of 4-Arylazo-2-alkoxy-2-thiazolin-5-ones toward amines and Grignard reagents

Treatment of 4-arylazo-2-alkoxy-2-thiazolin-5-ones 4a – f with glycine or phenylhydrazine effects their conversion into 1-aryl-5-alkoxy-1 H-1,2,4-triazole-3-carboxylic acid derivatives 5a – j , with the loss of hydrogen sulfide. On the other hand, the reaction of the 2-ethoxy ( 4a – c ) and the 2-isopropyloxy ( 4g – i ) derivatives with strong basic amines involves the loss of an alkyl mercaptan to yield the N-substituted amines 7d – j of 1-aryl-Δ²-1,2,4-triazolin-5-one-3-carboxylic acids. The 2-benzyloxy derivatives 4d – f react with the same reagents to give the N-substituted amides 2a – g of 1-aryl-Δ²-1,2,4-triazolin-5-thione-3-carboxylic acids, with the loss of benzyl alcohol. Hetero-ring opening of 4 , followed by recyclisation, occurs upon treatment with ethyl or phenyl magnesium halides to yield the triazolinethione derivatives 13 a – c .     

Effect of copolycondensation temperature on the reactivity ratios of bis(4-hydroxybutyl) terephthalate and bis(2-hydroxyethyl) terephthalate

Summary The effect of copolycondensation temperature on the monomer reactivity ratios of bis(4-hydroxybutyl) terephthalate (BHBT) and bis(2-hydroxyethyl) terephthalate (BHET) was investigated at 260, 270, and 280 °C, in the presence of titanium tetrabutoxide as a catalyst. Adopting 2nd order kinetics to polycondensation, the rate constants of polycondensation of BHBT and BHET, k ₁₁ and k ₂₂, were calculated to be 2.58, 1.30; 3.87, 2.24; and 5.29, 4.06 min⁻¹. In addition, the rate constants k ₁₂ and k ₂₁ of cross reactions could be determined as 0.91, 3.00; 1.49, 4.42; and 2.13, 5.85 min⁻¹ from a proton nuclear magnetic resonance spectroscopic analysis. The monomer reactivity ratios of BHBT were much larger than those of BHET, indicating the block nature of the copolycondensation, but the differences between monomer reactivity ratios were decreased with increasing polycondensation temperature, indicating that a probability of randomization was increased. Received: 15 October 1998/Revised version: 3 December 1998/Accepted: 8 December 1998     

Polymerization of butadiene with tii4-Al(i-Bu)3 Catalyst: Part II: Kinetic model development

Expressions for conversions, Mn and Mw have been derived for the proposed kinetic scheme for the polymerization of butadiene using Til₄ — Al(i-Bu)₃ as catalyst. The rate constants k_p, k_ta and k_d and the active sites were estimated from experimental data of conversion and molecular weight averages. The logarithm of both k_p and k_ta are linearly related to Al/Ti ratio. On the other hand, k_d and C_o appear to be uncorrelated with the reaction variables studied in this investigation. The activation energy for propagation reaction was found to be 12.05 ± 1.31 which agrees well with those reported previously. The small difference in the activation energies for k_p and k_ta accounts for the independence of the molecular weight of the polymer on the reaction temperature.     

Catalytic oxidation of benzene to maleic anhydride in a continuous stirred tank reactor

The kinetics of the vapor phase oxidation of benzene has been studied over an industrial catalyst in a continuous stirred tank reactor in the temperature range from 280 to 430°C and at atmospheric pressure. The products obtained are maleic anhydride, carbon oxides and water. The rate of the overall reaction (disappearance of benzene) is represented by the following expression based upon a steady state adsorption model The rate of formation of maleic anhydride is correlated by the equation which allows for a homogeneous depletion of maleic anhydride. The rate constants k_B, k_O, k_2(g) were found to follow Arrhenius behavior.      

The isomerization and metathesis of n-butenes: I. Unreduced molybdena-alumina catalysts

A significant change in the catalytic characteristics of an unreduced molybdena-alumina catalyst occurred at room temperature with increasing duration of contact with the reactant cis-2-butene. Butene isomerization over the fresh catalyst was effected by an acidic mechanism with the concomitant intermolecular transfer of H and D. The chief diagnostic characteristics for this mechanism were maintained throughout pulse experiments, but changed to those characteristic of isomerization by metathesis after soaking in butene for 15 min or when a static recirculation reactor was used, i.e., with increasing contact time, the acidic character of the catalyst decreased and the activity for metathesis increased. Thus, in the later stages of the reaction, equimolar mixtures of cis-2-butene d₀ and d₈ isomerized to produce cis- and trans-C₄H₄D₄, C₄H₈, and C₄D₈ in ratios of 2:1:1 without other hydrogen scrambling.