Mechanism of the condensation of homocysteine thiolactone with aldehydes

Chemical reactivity of homocysteine thiolactone (HTL) has been implicated in cardiovascular disease. Owing to its aminoacyl-thioester character, HTL undergoes facile electrophilic and nucleophilic reactions at its amino and activated-carboxyl group, respectively. To gain insight into the mechanism of the reactions involving its amino group, the kinetics of the condensation of homocysteine thiolactone with formaldehyde, acetaldehyde, and pyridoxal phosphate, were analyzed in the pH range from 5 to 10. The reactions were first order with respect to HTL, aldehyde, and hydroxide ion concentrations. Of the two ionic species of HTL (pKa=6.67+/-0.05), the acid form HTL+ was approximately 100-fold more reactive than the base form HTL(0). The reactions of HTL with aldehydes involve intermediate adducts. The conversion of the intermediate carbinolamine to a product, 1,3-tetrahydrothiazine-4-carboxylic acid or its 2-substituted analogue, occurs in a two-step reaction. The first step involves hydrolysis of the thioester bond in the intermediate, facilitated by anchimeric assistance by the oxygen of the carbinolamine group of the intermediate. The second step involves an attack of the liberated thiolate on the aldehyde-derived carbon of the intermediate, affording 1,3-tetrahydrothiazine-4-carboxylic acid or its 2-substituted analogue. An unusual feature of these reactions is that the formation of the carbinolamine group increases the reactivity of the thioester bond of HTL approximately 10(4)-fold. The facile formation of tetrahydrothiazines may contribute to HTL elimination from the human body.     

Mechanism of the oxidative condensation of acridines with nucleophiles

The kinetics of the reaction of acridine hydrochloride with the alkiodides of 2- and 4-picolines, 2- and 4-methylquinolines, 2-methylbenzothiazole, and 1,2-dimethylbenzimidazole in the presence of air oxygen were investigated. It is shown that the reaction is second order overall and first order in each of the components at a constant oxygen concentration. The reaction rate constants were calculated, and a mechanism is proposed for the reaction.     

Mechanism of the condensation of acetone on the surface of aluminum oxide

The condensation of acetone on the surface of aluminum oxide was studied by the methods of the temperature-program surface reaction, mass spectrometry, and infrared spectroscopy, and a reaction mechanism is proposed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 3, pp. 333–338, May–June, 1985.     

Mechanism of dehydration and condensation of CuHPO4· H2O

The dehydration of CuHPO₄·H₂O was followed by means of thermogravimetric measurements under quasi-isothermal-quasi-isobaric conditions. The intermediates and products formed during The thermal analysis and during the calcination of the starting hydrogen phosphate in an electric furnace at various temperatures were analysed by means of thin-layer chromatography, IR spectroscopy, X-ray diffraction analysis and electron microscopy.

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Zusammenfassung Mittels thermogravimetrische Messungen wurde die Dehydration von CuHPO₄·H₂O unter quasiisothermen-quasiisobaren Bedingungen untersucht. Die bei der Thermoanalyse und dem Kalzinieren des ursprünglichen Hydrogenphosphates in einem elektrischen Ofen bei verschiedenen Temperaturen entstehenden Produkte und Zwischenprodukte wurde mit Hilfe von Dünnsichtchromatographie, IR-Spektroskopie, Röntgendiffraktion und Elektronenmikroskopie untersucht.

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- CuHPO₄·H₂O. , , , , .

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The authors thank Prof. E. Pungor for valuable discussions.     

Catalysis of the knoevenagel condensation

Xonotlite alone or made more basic by doping of potassium $\text{t}$-butoxide catalyses the title reaction between aromatic aldehydes and malononitrile or alkyl cyanoacetates. At ambient temperatures, this procedure specifically gives high yields of $\text{E}$ olefinic Knoevenagel products.     

Transformed steroids Communication 151. Mechanism of the condensation of Δ16-20-ketosteroids with S.S-diphenylsulfilimine

Conclusions Taking 16-dehydrocorticosterone 16-acetate as am example, a new mode of stabilization of the intermediate products of addition of S,S-diphenylsulfilimine to 21-acetoxy-¹⁶-20-ketosteroids has been observed, the steroidal S M ylide (21-acetoxy-16-S,S-diphenylsulfiliminopregn-4-en-11,21-diol-3,20-dione) being formed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1181–1184, May, 1986.     

On the condensation of salicylaldehyde with hydrazine

A simple procedure for preparing uncontaminated salicylaldehyde hydrazone is outlined. The condensation reaction of salicylaldehyde and hydrazine in 2:1 molar ratio usually gives initially a mixture of the three geometrical isomers of salicylaldazine: one isomer is bright yellow, another is cream, the third is light pink. The earlier reports of Feigl and of Terentev et al. on the use of salicylaldehyde in the detection of hydrazine have been found to be misleading and the later report of Jain et al. incomplete. A detailed account is now given and improved salicylaldehyde tests for hydrazine are recommended. The structure given by Jain et al. for the copper(II) complex of salicylaldehyde hydrazone is confirmed by means of infrared spectroscopy and microanalysis. Preliminary studies on the copper(II) complex of salicylaldazine are reported.     

Mechanism of the condensation reaction between 1-aryl- and heteroaryl-1,4-dihydro-3(2H)-isoquinolinones and aldehydes

4-Benzylidene-1-phenyl-1,4-dihydro-3(2H)-isoquinolinone, the intermediary product of the carbonyl condensation reaction between 1-phenyl-1,4-dihydro-3(2H)-isoquinolinone and benzaldehyde, rearranges in the presence of an equivalent quantity of sodium hydride into 4-benzyl-1-phenyl-3(2H)-isoquinolinone. As the possibility of the migration of the hydrogen at C-1 in the form of a proton or a hydrogen atom (radical reaction) was excluded, the mechanism of the rearrangement could be depicted as an intermolecular hydride anion migration. In case of the 1-(4-pyridyl)- and 1-(3-pyridyl)-1,4-dihydro-3(2H)-isoquinolinones, however, the rearrangement can be carried out also in polyphosphoric acid and in this case a proton loss-proton gain mechanism was proved.     

On the condensation of water on hexadecane

The impulse-adiabatic method of measuring the critical supersaturation (lnS _c ) at water condensation on hexadecane is improved; the experiments are conducted with purer hexadecane than in previous work [2]. The dependence of InS _c on -lnS _c (undersaturation in the initial state) obtained earlier has been confirmed and the asymptotic value of lnS _c at sufficiently low humidity is established with better accuracy: InS _c =0.2550.26. With this value of lnS _c , the line tension is estimated to be –1.50×10^–5 dyn, assuming that the established critical supersaturation refers to the onset of barrierless phase formation.     

Concentration oscillations in the condensation of organosilanols

Auto-oscillations were discovered by TLC in a study of the condensation of RR'Si(OH)₂ (R=R′=Me, Et, Ph; R=Me, R′=CH₂=CH, Ph, OH) in aqueous organic solvents in the pH range −1–15 up to large degrees of conversion of the monomer (70–100%). The process is characterized by complicated profiles of the kinetic curves containing sections of acceleration and deceleration of the reaction. The nonequilibrium character of the process was established. It was assumed that the phenomena observed arise as a result of association of the monomer and oligomers during the reaction. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2256–2259, December, 1997.     

Size-dependent enthalpy of condensation

A thermodynamic model for the size dependence of enthalpy of condensation, DeltaH(con), is discussed. The model is valid over a range of radii where the arrangement of surface layer and surface tension remain invariable; it provides a way of calculating enthalpy and entropy changes and equilibrium vapor pressures. The difference between DeltaH(con) for two liquid bodies of the same chemical nature is equal to the variation of the autoadsorption energies on their surfaces.     

Topologies of capillary condensation

Calculations are presented to illustrate the dependence of capillary adsorption upon the interactions present in model pores. The sequence of phase transitions at zero temperature is determined for a Lennard-Jones lattice gas in a pore consisting of 4 × 4 × sites. The dependence of the specific filling sequence upon the comparative strength of the gas-pore wall and the gas-gas interaction well-depths is determined. Grand canonical Monte Carlo simulations of sorption at finite temperature in the continuum version of the same model pore are also reported. Both the theory and the simulations were performed with variable gas-solid and gas-gas energy well-depths. At a temperature of 90 K, the gas-solid heterogeneity associated with atoms adsorbed in the corners, on the walls and in the interior pore volume gives rise to sequential adsorption similar to that observed in the lattice gas calculation at 0 K. A gradual approach to non-wetting behavior is observed as the gas-solid well-depth decreases. Values of the gas-solid well-depth needed to produce pore filling at saturation (i.e., pore-wetting) are discussed.     

Polyene condensation of aldehydes

Summary The effects of catalyst, temperature, and duration of reaction were studied for the polyenic condensation of crotonaldehyde and senecialdehyde.     

The condensation of trimethylolphenol

The intermolecular condensation reactions of 2,4,6-trimethylolphenol (TMP) have been studied. The rate of disappearance of TMP from aqueous solutions at 40°C was measured over a range of pH 2–11. Concentrations of TMP were determined by HPLC. Major products, separated on the chromatograph and identified by PMR, were the o,p- and p,p-dimers and a trimer. Reaction kinetics were second order in TMP concentration at low pH. At high pH kinetics were first order in total TMP concentration, contrary to the findings of earlier investigators. The reaction rate varied with pH in a complex manner. The variation is explained by separate acid-catalyzed and base-catalyzed mechanisms. A kinetic model is proposed in which the rate constants are independent of pH.     

Biomimetic condensation copolyesters

Copolyterephthalates of bis(4-hydroxy-3-methylphenyl)-2,2-propane and N-methyldiethanolamine and their hydrochloric salts of various compositions and microstructures have been prepared by the copolycondensation of hydrophilic and hydrophobic comonomers. It has been shown that the transition from random proteinlike structures to the block structures makes it possible to preserve biomimetic properties of the copolymers at a smaller content of charged units in macromolecules. The ability of charged polymers to survive in aqueous solutions has been used for the synthesis of copolyterephthalate of N-bis(hydroxyethyl)tetradecylmethylammonium bromide and N-methyldiethanolamine demonstrating fungicidal activity.     

Kinetic simulation of the oxidative condensation of methane

The kinetics of the oxidative condensation of methane (OCM) over a mixed-oxide lithium-manganese-tungsten-silicate catalyst has been simulated, and systems of stoichiometric chemical equations possible under the OCM conditions have thereby been discriminated. A phenomenological kinetic model has been developed to fit the observed rates of formation and disappearance of the compounds involved in OCM.     

Mechanism of the formation of 1,2,4‐thiadiazoles by condensation of aromatic thioamides and of N‐substituted thioureas

The condensation reaction of thiobenzamide, (as well as thionicotinamide and isothionicotinamide) in the presence of dimethyl sulfoxide and of an acid, affords 3,5‐diphenyl‐1,2,4‐thiadiazole. Under the same experimental conditions, N‐substituted thioureas are also condensed to 1,2,4‐thiadiazole derivatives; their structure is ascertained by spectroscopic properties and by X‐ray diffraction. Some information on the mechanism of thiadiazoles formation from both starting classes of compounds, thiobenzamides and N‐substituted thiourea, is collected and discussed.