Mechanism for acetic acid-catalyzed ester aminolysis

A computational study is described to elucidate the mechanism for acetic acid-catalyzed ester aminolysis to produce amides. A concerted acyl substitution mechanism is proposed to involve concurrent acyl-O bond cleavage and acyl-N bond formation where acetic acid acts as a bifunctional catalyst connecting to both the alkoxide and the amino moieties. This mechanism does not involve the intermediacy of a tetraheral adduct nor the rehybridization of acyl carbon, in sharp contrast to classic stepwise acyl substitution mechanism.     

Neighboring amide group participation in ester aminolysis in aprotic solvents

The piperidinolysis of 8-quinolyl-, p-nitrophenyl-, o-, and p-piperidinocarbonylphenyl acetates in acetonitrile and in chlorobenzene was studied at 25°C. The strictly second order kinetic behaviour and the weaks solvent-dependence of the rate of the reaction of o-piperidinocarbonylphenyl acetate indicate anchimeric assistance by the o-amide group, and support the suggestion that amide groups of hydrophobic enzyme active sites may act as general base catalysts.

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8--, --, - - 25°C. - - , .

     

Microwave effects in solvent-free esters aminolysis

Solvent-free ester aminolysis was studied under microwave or conventional heating either in the absence of base or induced by KOtBu with or without a phase transfer agent. The specific microwave effects were shown to be dependent on the conditions and discussed in terms of relative polarities of ground and transition states.     

Crown ether salt catalysis of ester aminolysis in an aprotic solvent

The RCO ₂ ^– catalyzed n-butylaminolysis of 4-nitrophenyl acetate in chlorobenzene has been studied. Logarithms of the catalytic rate constants can be linearly correlated with Taft polar substituent constants for the R groups. Product analysis as well as the lack of steric hindrance by bulky R substituents indicate that the carboxylates act as general base catalysts.

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- 4- . R. , R , .

     

Vanadium-titanium oxides: Sol-gel synthesis and catalytic properties in chlorobenzene oxidation

Vanadium-titanium mixed oxides with V/Ti = 0.025, 0.050, and 0.100 have been synthesized by sol-gel processing. The anatase-rutile transition temperature decreases from 750 to 600°C as the vanadium content of the TiO₂ phase is increased. The most important texture parameters and the photoelectron and IR spectra of the oxides are reported. The oxides exhibit high catalytic activity in chlorobenzene oxidation, which is due to their specific electronic and crystal structures.     

A new reaction pathway in the ester aminolysis catalyzed by glymes and crown ethers

Butylaminolysis of p-nitrophenyl acetate in chlorobenzene in the presence of different kinds of phase-transfer catalysts (crown ethers and glymes) supports the existence of a reaction pathway exhibiting a first-order dependence on the concentration of the phase transfer catalyst and a second-order dependence on the concentration of butylamine. This novel reaction pathway must be included in the mechanism traditionally accepted for the catalysis by phase-transfer agents of aminolysis reactions in aprotic solvents.     

Spirobicyclic diamines 1: synthesis of proline-derived spirolactams via thermal intramolecular ester aminolysis

Proline-derived [4.4]-spirolactams have been synthesised in good yields by a reductive-amination reaction followed by thermal cyclisation of the resulting amine onto the proline ester group in refluxing toluene. The synthesis of the corresponding [4.5]-spirolactams by the same method gave much reduced yields.     

Rate enhancement of PFP sulfonate ester aminolysis by chloride salts in organic and aqueous media

We report here, a method of accelerating the rate of aminolysis of PFP sulfonates to yield sulfonamides using tetrabutylammonium salts. We have previously explored the utility of employing PFP sulfonates in the formation of sulfonamides; however we demonstrate here the advantages of combining the existing methodology with a revised protocol which allows the diversity within both the sulfonate ester and the amine to be extended.     

Catalysis of ester aminolysis by cyclodextrins. The reaction of alkylamines with p-nitrophenyl alkanoates

The effects of four cyclodextrins (alpha-CD, beta-CD, hydroxypropyl-beta-CD, and gamma-CD) on the aminolysis of p-nitrophenyl alkanoates (acetate to heptanoate) by primary amines (n-propyl to n-octyl, isobutyl, isopentyl, cyclopentyl, cyclohexyl, benzyl) in aqueous solution have been investigated. Rate constants for amine attack on the free and CD-bound esters (k(N) and k(cN)) have ratios (k(cN)/k(N)) varying from 0.08 (retardation) to 180 (catalysis). For the kinetically equivalent process of free ester reacting with CD-bound amine (k(Nc)), the ratios k(Nc)/k(N) vary from 0.2 to 28. Either way, there is evidence of catalysis in some cases and retardation in others. Changes in reactivity parameters with structure indicate more than one mode of transition state binding to the CDs. Short esters react with short alkylamines by attack of free amine on the ester bound by its aryl group, but for longer amines, free ester reacts with CD-bound amine. Reaction of long esters with long amines, which is catalyzed by beta-CD and gamma-CD, involves inclusion of the alkylamino group and possibly the ester acyl group. The larger cavity of gamma-CD may allow the inclusion of the ester aryl group, as well as the alkylamino group, in the transition state. Reaction between an ester bound to the CD by its acyl group and free amine appears not to be important.     

Polyamide synthesis by ester aminolysis. I. A new route for nylon-6,6 synthesis

A new route for nylon-6,6 synthesis has been studied. The process is grounded on the synthesis of an α-amino ω-ester monoamide precursor (AME-6,6) easily available in reacting in the bulk hexamethylene diamine and dimethyl adipate at a low temperature (T ≅ 50°C) preferably in the presence of a phenol derivative. In such conditions AME-6,6 precipitates with a very good yield (90–95%). One of the greatest advantages of AME-6,6 is to keep the stoichiometric balance for further polyamidation; that is not the case in other processes. Moreover AME-6,6 is very stable, e.g., even stored at room temperature under air during 50 days. Polyamides-6,6 have been obtained from AME-6,6 (used freshly prepared or after storage) in glass laboratory reactors by direct heating under vacuum (T = 270°C) with number-average molecular weights of roughly 20,000. © 1996 John Wiley & Sons, Inc.     

The synthesis of l-proline derived tetraazamacrocyclic ligands of C2 symmetry via intramolecular ester aminolysis

A convenient and efficient synthesis of enantiomerically pure 12-, 14-, and 16-membered tetraazamacrocyclic ligands, able to form complexes with transition metal cations, is discussed. Linear α,ω-aminoesters, prepared from l-proline, undergo intramolecular aminolysis to afford the corresponding macrocyclic amides in good yields.     

Asymmetric aminolysis of aromatic epoxides: a facile catalytic enantioselective synthesis of anti-beta-amino alcohols

[reaction: see text] The first asymmetric aminolysis of trans-aromatic epoxides with anilines is described. The process affords enantioenriched anti-beta-amino alcohols in up to 99% ee. The complete regio- and diastereoselectivity observed uses commercially available [Cr(Salen)Cl] as a Lewis acid catalyst and in combination with a very simple experimental procedure renders the present reaction a facile and practical tool for the synthesis of chiral nonracemic anti-beta-amino alcohols.     

The synthesis of l-proline derived hexaazamacrocyclic ligands of C3 symmetry via intramolecular methyl ester aminolysis

A convenient synthesis of enantiomerically pure 18-, 21-, and 24-membered hexaaza-crown ligands is presented. Linear α,ω-aminoesters, prepared from l-proline, undergo intramolecular aminolysis to afford the corresponding 18-, 21-, and 24-membered macrocyclic amides in satisfactory yields (42, 65, and 22%, respectively). These were subsequently transformed into the title macrocyclic hexamines via exhaustive reduction with a borane–dimethylsulfide complex. X-Ray structures of two larger macrocyclic amides are also presented.     

Active intermediates for the selective chlorination of chlorobenzene in the antimony pentachloride–sulfur-containing compound catalytic system

Ionic complexes of trichlorosulfonium, phenyldichlorosulfonium, and bis(p-chlorophenyl)chlorosulfonium hexachloroantimonates have been synthesized. Chlorination of chlorobenzene with the synthesized complexes and chlorine in the presence of the catalytic systems SbCl₅-sulfur-containing compounds (SCl₂, Ph₂S, Ph₂S₂) has been carried out. The close values of the para/ortho ratio of the dichlorobenzenes in these pairs of reactions provides a basis for considering that chlorosulfonium hexachloroantimonates are the para-selective intermediates in the chlorination of chlorobenzene.     

Asymmetric effects in catalytic membranes

A catalytic membrane hybrid system based on a cermet membrane with a channel size 〈d〉 of ～0.12 μm has been produced using sol-gel processing. A layer of a superfine methanol conversion catalyst with the composition Cr₂O₃ · Al₂O₃ · ZnO has been formed on the inner surface of the channels, and a thin oxide coating of composition P_0.03Ti_0.97O_{2 ± δ} with a homogeneous porous structure and 〈d〉 ～ 2 nm has been formed on the geometric membrane surface. The methanol conversion rate and the gas permeability of the membrane depend considerably on the methanol vapor and gas (H₂, He, CO₂, Ar, CH₄) flow directions. When methanol vapor diffuses toward the mesoporous layer, the catalytic activity is one order of magnitude higher and the gas permeability coefficients are 3–8 times lower than in the case of the reverse flow of the gaseous molecules. The temperature dependence of the gas permeability taking into account the possible types of mass transfer in porous solids suggests that, when the gases move toward the mesoporous coating consisting of phosphorus-modified titanium oxide, surface flow and activated diffusion dominate, whereas the reverse gas motion is dominated by free molecular flow.     

Novel catalytic effects of Mn3O4 for all vanadium redox flow batteries

A new approach for enhancing the electrochemical performance of carbon felt electrodes by employing non-precious metal oxides is designed. The outstanding electro-catalytic activity and mechanical stability of Mn(3)O(4) are advantageous in facilitating the redox reaction of vanadium ions, leading to efficient operation of a vanadium redox flow battery.     

High catalytic activity and stability of palladium nanoparticles prepared by the laser electrodispersion method in chlorobenzene hydrodechlorination

Palladium nanoparticles deposited on thermally oxidized silicon and on the carbon support Sibunit by the laser electrodispersion method are extremely active in the gas-phase hydrodechlorination of chlorobenzene at 100–200°C. High conversion of chlorobenzene (above 90%) has been achieved with catalysts with an unusually low metal content (from 10^?4 to 10^?3 wt %). The cyclohexane-to-benzene ratio in the reaction products depends on the process duration, palladium content, and support nature. According to X-ray photoelectron spectroscopy (XPS) data, palladium in the catalysts retains its metallic state over a long time under the reaction conditions. Possible causes of the high catalytic activity (10⁵ mol (mol Pd)^?1 h^?1) of the palladium nanoparticles and their stability to chlorination are discussed.