Temperature vs. time sequences to palliate deactivation in parallel and in series-parallel with the main reaction: parametric study

The calculation of temperature vs. time sequences to palliate catalyst deactivation in an integral reactor has been studied either by maintaining constant the conversion at the reactor outlet in a simple reaction or by maintaining constant the concentration of a given component at the outlet in a complex reaction system. The experimental systems studied, which are a simple one (dehydration of 2-ethylhexanol) and a complex one (isomerization of cis-butene), have kinetic models of the Langmuir-Hinshelwood-Hougen-Watson type for the main reaction and deactivation, with deactivation by coke dependent on the concentration of the reaction components. In the reaction of dehydration of 2-ethylhexanol deactivation occurs in parallel with the main reaction and in the isomerization of cis-butene deactivation occurs in series-parallel with the main reaction. A parametric study has been carried out for both reaction systems. The sequences calculated have been experimentally proven in an automated reaction apparatus.     

Recent advances in oxidative C–C coupling reaction of amides with carbon nucleophiles

The C–C coupling reaction of N-electron withdrawing group (EWG) protected amides with coupling partners is one of the most important methods for C–C bond formation at the α-position of amides to directly give α-substituted amides. Of the four reactions, namely, the reaction via the generation of carbanion with an electrophile, that via the generation of carbon radical with a radical donor, that via the generation of iminium ion species with a nucleophile (oxidative coupling reaction), and that using a transition metal carbenoid, the oxidative coupling reaction presents a challenge although the reaction products are very useful for the transformation of a wide range of nitrogen-containing derivatives. In this review, recent developments in the oxidative coupling reaction of N-EWG protected amides with nucleophiles are summarized with focus on the reaction using a transition metal, the transition-metal-free reaction, the enantioselective reaction using a chiral catalysts, and the organocatalyzed oxidative coupling reaction.     

Study of the reaction between 1,5-naphtalene diisocyanate and polycaprolactone in different solvents

The reaction between polycaprolactone and 1,5-naphtalene diisocyanate has been investigated in solvents with different dielectric constants and hydrogen bonding powers (toluene, ethyl acetate, ethyl methyl ketone), and in the same solvents with the addition of a catalytic amount of dimethyl sulfoxide (DMSO). The reaction was considered to proceed over two steps, the reaction of the first NCO group being faster. The course of the reaction was measured by titration of the unreacted NCO groups, ¹H- and ¹³C-NMR spectroscopy, and size exclusion chromatography. By titration only the overall reaction order and reaction rate constants could be determined. DMSO accelerated the reaction in all three solvents, which was explained by the stabilization of the activation complex by DMSO. Both steps of the reaction could be specified by NMR spectroscopy. The ratio between the reaction rate constants for the first and the second step decreased with the increased hydrogen bonding strength of the solvent and with DMSO. By SEC only the reaction of the first NCO group could be determined due to the low resolution for higher molar mass reaction products with a broad distribution. The values obtained for the first step reaction rate constants were in good agreement with NMR values. © 1995 John Wiley & Sons, Inc.     

DMAP-catalyzed four-component one-pot synthesis of highly functionalized spirooxindole-1,4-dihydropyridines derivatives in aqueous ethanol

An efficient, clean, and environmental friendly ‘one-pot’ four-component reaction was developed for assembling a novel type of spirooxindole derivatives containing dihydropyridine and pyrrolidinone. The reaction could be easily performed in aqueous ethanol with 4-DMAP as catalyst in good yields. The high efficiency and the simple and mild condition of the reaction, in addition with its avoidance of time-consuming, costly syntheses, and tedious workup, endowed the reaction with application significance. A series of spirooxindole derivatives were therefore prepared in excellent yields by using this ‘one-pot’ four-component reaction method.     

Chloracylierung und Bromacylierung von Carbonylverbindungen. IV. Bildungsmechanismus von Carbonsäure-(1-halogenalkyl)estern

Chloroacylation and bromoacylation of carbonyl compounds IV. Investigations of the reaction mechanism The kinetics of the Lewis acid catalyzed reaction between acyl chlorides and carbonyl compounds (especially aldehydes) is investigated by ¹H-NMR.-spectroscopy. With acetyl chloride as starting material a second order reaction is observed; the rate of the reaction increases in polar solvents as well as with increasing electron-donating capacity of the aldehyde. - With benzoyl chloride as starting material the reaction is first order with respect to benzoyl chloride, but zero order with respect to the aldehyde. The reaction rate is strongly influenced by the substituents of the benzoyl chloride. - Two polar reaction mechanisms which are in accord with these results are outlined and discussed.     

Theoretical study on the reaction mechanism of CN radical with ketene

The bimolecular single collision reaction potential energy surface of CN radical with ketene (CH2CO) was investigated by means of B3LYP and QCISD(T) methods. The calculated results indicate that there are three possible channels in the reaction. The first is an attack reaction by the carbon atom of CN at the carbon atom of the methylene of CH2CO to form the intermediate NCCH2CO followed by a rupture reaction of the C-C bond combined with -CO group to the products CH2CN CO. The second is a direct addition reaction between CN and CH2CO to form the intermediate CH2C(O)CN followed by its isomerization into NCCH2CO via a CN-shift reaction, and subsequently, NCCH2CO dissociates into CH2CN CO through a CO-loss reaction. The last is a direct hydrogen abstraction reaction of CH2CO by CN radical. Because of the existence of a 15.44 kJ/mol reaction barrier and higher energy of reaction products, the path can be ruled out as an important channel in the reaction kinetics. The present theoretical computation results, which give an available suggestion on the reaction mechanism, are in good agreement with previous experimental studies.     

Synthesis of Substituted Phosphonates and Their Reactions with Carbonyl Compounds

Abstract

The reaction of the derivatives of 3-phenyl-3-chloro-2-oxopropionic acid with the trivalent phosphorus compounds has been studied. The esterification or amidation of this acid have been shown to influence the course of reaction with Ph₃P. In the reaction with esters enolphosphonium salts are produced, ketophosphonium salts are obtained when amides are involved. Properties of these compounds have also been studied in the Wittig reaction. 3-(α-chlorobenzyl)-2-oxoquinoxaline which reacted with trialkyl phosphates (Arbuzov reaction) has been synthesized. These phosphonates are obtained in nearly quantitative yields, in alkaline conditions (Horner-Emmons reaction) they react smoothly with aromatic aldehydes to give the substituted vinylyuinoxalines.     

Polymerization of lignin model compounds with formaldehyde in acidic aqueous medium

The reaction of formaldehyde with lignin model compounds in acidic medium was shown to give fast crosslinking of alkyl-substituted phenolic and etherified phenolic lignin model compounds at positions meta to the aromatic hydroxy groups. This reaction differs from the reaction of formaldehyde with phenolic lignin model compounds in alkaline conditions, where the reaction with formaldehyde always occurs at positions ortho/para to the aromatic hydroxy group., The reaction of formaldehyde with lignin in acidic medium have considerable potential for the crosslinking of lignin, particularly heavily condensed alkali lignin, for use in polymeric products.     

MECHANISM OF THE REACTION OF SOME STABLE HEMIMERCAPTALS WITH Secondary-AMINES: EVIDENCE AGAINST THE INTERMEDIACY OF A METHYLENESULFONIUM ION

Abstract

The reaction of the arenethiols 4a-b with formaldehyde and the sec-amines 5a-c gave the aminomethyl aryl sulfides 6a-d. The reaction of the hemimercaptals 3a-b with 5a in methanol gave 6a-b in high yield. In acetonitrile reaction media, 6b was obtained by the reaction of 3b with 5a which suggested that 7b was not an intermediate in the formation of 6b in methanolic media. The absence of 7b in methanolic media suggests that the methylenesulfonium ion 8b is not an reaction intermediate. The formation of 7b was observed in the reaction of 3b with methanol when catalyzed by the Lewis acid tetrafluoroboric acid diethyl ether complex. The experimental observations are best explained by a mechanism whereby 3a-b are in rapid equilibrium with 4a-b under the basic reaction conditions. Rapid reaction of the liberated formaldehyde with 5a leads to the normal Mannich reaction pathway. Consistent with this mechanism, the reaction of a mixture of 3a-b and 12 with 5a gave both 6a-b and 13.     

Model studies on the kinetics and mechanism of polyarylate synthesis by acidolysis

Model reactions were carried out to simulate the acidolysis process for polyarylate synthesis by using p-tert-butylphenyl acetate (ptBuPhOAc) and benzoic acid in diphenyl ether. p-tert-Butylphenol was formed in the reaction mixture and its concentration stayed constant throughout the reaction. Acetic benzoic anhydride and benzoic anhydride were detected by NMR. Based on this experimental evidence, a mechanism for the acidolysis was proposed involving the mixed anhydride. The kinetics of the acidolysis reaction was studied for this model reaction. The overall reaction order is two and the reaction order with respect to each reactant is one. Second-order reaction rate constants were measured at different reaction conditions (200–250°C). The activation energy (E_a), activation enthalpy (ΔH^≠), and activation entropy (ΔS^≠) were calculated from these data. The thermodynamic parameters of the acidolysis reaction were also measured for the analogous reaction of p-tert-butylphenyl pivalate (ptBuPhOPiv) and benzoic acid. The kinetics of two other elementary reactions involved in the acidolysis reaction were also studied: p-tert-butylphenol with acetic anhydride or benzoic anhydride, and p-tert-butylphenyl pivalate with benzoic acid.     

Ab initio Mechanism Study on the Reaction of Chlorine Atom with Formic Acid

The potential energy surface(PES) for the reaction of Cl atom with HCOOH is predicted using ab initio molecular orbital calculation methods at UQCIDS(T,full)6-311 G(3df,2p)//UMP2(full)/6-311 G(d,P) level of theory with zero-point vibrational energy (ZPVE) correction.The calculated results show that the reaction mechanism of Cl atom with formic acid is a C-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom with a 3.73kJ/mol reaction barrier height,leading to the formation of cis-HOCO radical which will reacts with Cl atom or other molecules in such a reaction system.Because the reaction barrier height of O-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom which leads to the formation of HCO2 radical is 67.95kJ/mol,it is a secondary reaction channel in experiment,This is in good agreement with the prediction based on the previous experiments.     

Mechanistic Studies on the SCS‐Pincer Palladium(II)‐Catalyzed Tandem Stannylation/Electrophilic Allylic Substitution of Allyl Chlorides with Hexamethylditin and Benzaldehydes

This paper describes a mechanistic study of the SCS‐pincer Pd^II‐catalyzed auto‐tandem reaction consisting of the stannylation of cinnamyl chloride with hexamethylditin, followed by an electrophilic allylic substitution of the primary tandem‐reaction product with 4‐nitrobenzaldehyde to yield homoallylic alcohols as the secondary tandem products. As it turned out, the anticipated stannylation product, cinnamyl trimethylstannane, is not a substrate for the second part of the tandem reaction. These studies have provided insight in the catalytic behavior of SCS‐pincer Pd^II complexes in the auto‐tandem reaction and on the formation and possible involvement of Pd⁰ species during prolonged reaction times. This has led to optimized reaction conditions in which the overall tandem reaction proceeds through SCS‐pincer Pd^II‐mediated catalysis, that is, true auto‐tandem catalysis. Accordingly, this study has provided the appropriate reaction conditions that allow the pincer catalysts to be recycled and reused.     

Syntheses of Polycyclic Natural Products Employing the Intramolecular Double Michael Reaction

The one-pot intramolecular double Michael reaction of compounds having two different α, β-unsaturated carbonyl groups to form polycyclic compounds can be carried out by three different methods: in the first the substrate is treated with lithium hexamethyldisilazide, in the second with chlorotrimethylsilane, triethylamine, and zinc chloride at an elevated temperature, and in the third with tert-butyldimethylsilyl trifluoromethanesulfonate and triethylamine. The reaction proceeds with complete regioselectivity and high stereoselectivity following a stepwise mechanism. Spiro-fused bicyclo[2.2.2]octane derivatives can be constructed with high stereoselectivity by the intromolecular double Michael reaction by using the first method. Enantiomerically pure atisine and the enantiomer of atisirene were synthesized stereoselectively by application of this methodology. The syntheses of steroids and angular triquinane-type sesquiterpenoids were possible with the second method. Heterocyclic compounds with a bridgehead nitrogen atom were obtained by the reaction of α, β-unsaturated amides following the second and third methods. The asymmetric synthesis of tylophorine with diastereofacial control was achieved by the intramolecular reaction according to the third method. The sulfur-mediated intramolecular double Michael reaction utilizing the third method produced trans-hydroindane derivatives. Furthermore, the intramolecular Michael-aldol reaction can be employed in synthesizing polycyclic systems with cyclobutane units by treatment with tert-butyldimethylsilyl trifluoromethanesulfonate in the presence of triethylamine. The intermolecular double Michael reaction and related reactions will also be described.     

The synthesis of a fluorinated phthalocyanine

The reaction of perfluoroalkylcopper with 4-iodophthalonitrile provides a convenient route to fluorinated phthalonitriles which readily form phthalocyanines in the presence of stannous chloride dihydrate.During the course of preparing 4-perfluoroheptylphthalonitrile $\text{1}$, a secondary reaction was observed when the reaction time was extended beyond two hours. This reaction involves the interaction of the orthodinitrile with copper and/or cuprous iodide to afford the phthalocyanine nucleus. This coaction is portrayed by the appearance of a green color in the reaction media.     

Reaction of trifluororacemic acid methyl ester with 1,3-dienes

The reaction of trifluororacemic acid with 1,3-dienes affords Diels-Alder reaction products in a high yield and with a high degree of specificity. Catalysis by SnCl₄ changes the course of the reaction of the ester with isoprene, affording an ene reaction product.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 141–145. January, 1991.     

New synthesis of multisubstituted cyanocyclopropanes by the intramolecular SN2 alkylation and 1,3-CC insertion reaction of magnesium carbenoids as the key reactions

Addition reaction of 1-chlorovinyl p-tolyl sulfoxides derived from ketones and aldehydes with lithium α-cyano carbanions gave nitrile adducts in high to quantitative yields. Treatment of the nitrile adducts derived from acetonitrile with excess i-PrMgCl in THF resulted in the formation of cyanocyclopropanes via the intramolecular S_N2 alkylation of the generated magnesium carbenoids. The intermediate of this reaction was proved to be a cyclopropylmagnesium chloride and was reactive with electrophiles to give multisubstituted cyanocyclopropanes. On the other hand, the reaction of the nitrile adducts derived from arylacetonitriles with i-PrMgCl resulted in the formation of 2-arylcyanocyclopropanes by the 1,3-carbon–carbon (1,3-CC) insertion reaction of the generated magnesium carbenoid intermediates. This reaction was found to proceed in a highly stereospecific manner. The key reactions, intramolecular S_N2 alkylation and 1,3-CC insertion reaction of the magnesium carbenoids, are the first examples for the reaction of the magnesium carbenoids bearing a nitrile functional group.     

Cross-linking epoxide resins with hydrolysates of chrome-tanned leather waste

Differential scanning calorimetry was employed to investigate the reaction of diglycidyl ethers of bisphenol A (DGEBA) of mean molecular mass 348–480 Da, with collagen hydrolysate of chrome-tanned leather waste in a solvent-free environment. The reaction leads to biodegradable polymers that might facilitate recycling of plastic parts in products of the automotive and/or aeronautics industry provided with protective films on this basis. The reaction proceeds in a temperature interval of 205–220°C, at temperatures approx. 30–40°C below temperature of thermal degradation of collagen hydrolysate. The found value of reaction enthalpy, 519.19 J g⁻¹ (= 101.24 kJ mol⁻¹ of epoxide groups) corresponds with currently found enthalpy values of the reaction of oxirane ring with amino groups. Reaction heat depends on the composition of reaction mixture (or on mass fraction of diglycidyl ethers in the reaction mixture); proving the dependence of kinetic parameters of the reaction (Arrhenius pre-exponential factor A (min⁻¹) and activation energy E _a (kJ mol⁻¹)) did not succeed. Obtained values of kinetic parameters are on a level corresponding to the assumption that reaction kinetics is determined by diffusion.     

The reaction between solid lead and chlorine gas

When lead reacts with a chlorine atmosphere the reaction rate shows a logarithmic rate law followed by a parabolic one. Both reaction rates can be explained by assuming that electron holes in the reaction product are rate-determining. In the beginning, the reaction of holes with lead (I) ions on lead ion lattice sites in PbCl₂ is the rate-determining step; later, the transport of holes by diffusion through the growing PbCl₂ layer becomes rate-determining.An oxide layer on the lead before chlorination retards the reaction, while, on the contrary, traces of oxygen in the chlorine gas accelerate the reaction. Both phenomena can be explained by assuming that a mixed compound PbO_1?xCl_2x is formed. It is concluded that the presence of impurities in the system may influence the reaction rate drastically.     

β-Homoamino acids as catalysts in enantioselective intra- and intermolecular aldol reactions

β³-Homoamino acids catalyze the intra- (cf. the Hajos-Parrish-Eder-Sauer-Wiechert reaction) as well as the intermolecular aldol reaction. The stereochemical outcome with selectivities of up to 83% ee is reversed in the intramolecular reaction, when we go from the proteinogenic amino acids to the homologues, and reaction time increases dramatically for both reactions. In contrast, in the intermolecular reaction Me-β³hPhe-OH gives the same enantiomer as (S)-proline does, but with lower enantiomeric excess (54% vs 48% ee).     

The Mechanism of Schiff Base Formation of Some Arylidenes-p-Aminosalicylic Acid

Formation of a series of Schiff bases derived from p-aminosalicylic acid I and various aromatic aldehydes has been studied kinetically in ethanol medium in presence of piperidine as a basic catalyst. The order of the reaction is determined to each reactant by following the concentration of the Schiff base formed during the reaction. The reaction is Kinetically third-order in the presence of low concentration of piperidine, first-order to each of I , aldehyde and piperidine. On the other hand, in presence of ≥5×10^?4 M of piperidine the order of the reaction changed to second-order, thus much the reaction is independent of piperidine concentration. The rate determining step is suggested to be the dehydration of the carbinolamine intermediate step 4. Variation in reaction rate constants with the different substituent of the aromatic aldehyde, with substituents of aromatic amine and with the nature of the hydroxylic organic solvents as reaction medium are studied and discussed.