Stoichiometric number molecularity and multiplicity

On the basis of the polynomial to which the system of pseudo-steady-state equations corresponding to the nonlinear single-route mechanism is reduced (kinetic polynomial), the known concepts of stoichiometric number and molecularity have been studied. A set of the minimal-integer stoichiometric coefficients is shown to correspond to the kinetic characteristics in the neighborhood of equilibrium.

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Prediction of retention indexes. III. Silylated derivatives of polar compounds.

Polar compounds containing hydroxyl, amino and carboxyl groups, singly or in combination, can be chromatographed after the polar functional groups are silylated. The silylated derivatives of acids, alcohols, amines, diols, amino alcohols, amino acids are shown to behave chromatographically as hydrocarbons, and their retention indexes can be readily predicted from their base values. The column difference, namely, the difference between the retention indexes of the analyte on polar and non-polar columns is minimal for the silylated derivatives in comparison to that observed for the underivatized analytes. This minimal column difference is attributed to the hydrocarbon-like chromatographic characteristics of the silylated derivatives. The retention indexes of the silyl derivatives appear to correlate with the atom number Z of the analyte.     

The diazo route to diazonamide A: studies on the tyrosine-derived fragment

Various approaches to the tyrosine-derived fragment of the marine secondary metabolite diazonamide A are described. Initial efforts were focused on the originally proposed structure of the natural product, and a feasibility study established that a model 4-aryltryptamine could be readily prepared. Protected 4-bromotryptamine underwent Pd0-catalyzed coupling with the boronic acid derived from 2-bromophenyl allyl ether by Claisen rearrangement, O-methylation and lithiation-boration. The resulting biaryl was elaborated into an alpha-diazo-beta-ketoester, dirhodium(II)-catalyzed reaction of which with N-Z-valinamide gave the desired tryptamine-oxazole following cyclodehydration of the intermediate ketoamide. A potential precursor to the benzofuran ring of the original structure of diazonamide A was prepared in eight steps from N-Z-tyrosine tert-butyl ester. Iodination, O-protection and Stille coupling gave the cinnamyl alcohol 25, converted via the bromide into the allyl aryl ether 27. Subsequent Claisen rearrangement and oxidative cleavage of the alkene gave the lactol 29, converted into the desired benzofuranone 31. The revision in the structure of diazonamide A to 2 resulted in the targeting of an alternative tyrosine-derived model benzofuranone 41 synthesized in four steps from N-Z-tyrosine methyl ester 36 by a route involving Claisen rearrangement of cinnamyl ether 37. Poor yields in this sequence prompted an investigation into the intramolecular Heck reaction as a route to benzofuranone 50. Coupling of 3-iodotyrosine 44 with 2-phenylbutenoic acid 48 gave ester 49 that readily underwent intramolecular Heck reaction to give benzofuranone 50, albeit with poor stereocontrol.     

Intramolecular alkylative arylation of oxabicylic alkene: a potential diene approach for the synthesis of estrone and analogous steroid structures

Regioselective and stereospecific intramolecular alkylative arylation of unsaturated oxabicyclic diol 6, mediated by Lewis acid or strong protic acid to give the tetracyclic products 7a and 7b, as shown above, represents the first example of an electrophilic (cationic in character) ring-opening-cyclization of oxabicyclic alkene. This constitutes the key cyclization step for a long-standing and potentially useful diene approach for the synthesis of estrone and analogous steroid structures. [structure: see text]     

Synthesis and molecular structure of 3-(2-aryl-2-oxoethyl)-3-methoxy-2-oxo-2,3-dihydroimidazo-[1,2-<Emphasis Type="Italic">a</Emphasis>]pyridine hydrochlorides

Reactions between 2-pyridylamides of Z-4-aryl-2-hydroxy-4-oxobut-2-enoic acids with diazomethane have been used to synthesize 3-(2-aryl-2-oxoethyl)-3-methoxy-2-oxo-2,3-dihydroimidazo[1,2-a]pyridines, which form hydrochlorides with hydrochloric acid. The structure of the latter has been demonstrated by XRD for the hydrochloride of 3-methoxy-2-oxo-3-(2-phenyl-2-oxoethyl)-2,3-dihydroimidazo[1,2-a]pyridine. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 464–468, 2007.     

Crystal and molecular structures of binuclear caesium complexes with 1,3-calix[4]-bis-crown-6 and 1,3-calix[4]-bis-benzo-crown-6

The crystal structures of two binuclear complexes between caesium and 1,3-calix[4]-bis-crowns have been determined. Cs₂ Bis-benzoC6(NO₃)₂. 3CHCl₃ (1) in whichBis-benzoC6 is 1,3-calix[4]-bis-benzo-crown-6, crystallizes in the orthorhombic system: space groupPca2 ₁ a=19.513(10),b=15.382(5),c=23.708(9) Å,V=7116(5) ų,Z=4. Refinement led to a final conventionalR value of 0.065 for 2321 reflections. The structure of (1) is analogous to those already reported withBis-C6, (in whichBis-C6 is, 1,3-calix[4]-bis-crown-6) and NO ₃ ^– as a counter-ion. Cs₂ Bis-C6(NCS)₂ (2) crystallizes in the monoclinic system: space, groupC2 a=36.57(2),b=11.47(1),c=13.65(1) Å, =109.03(5)°.,V=5415(6) ų,Z=4. Refinement led to a final conventionalR value of 0.063 for 2227 reflections. Compound (2) is made of dimers bridged by a disordered NCS^– ion. The crown ether chain conformations are discussed. Supplementary data relating to this article (atomic coordinates, anisotropic displacement parameters, bond distances and angles and observed and calculated structure factors) are deposited with the British Library as Supplementary Publication No. SUP 82199 (52 pages).     

Effect of stirring on the Belousov-Zhabotinskii reaction: A problem of interpretation

It is probable that different phenomena attributed to mechanical stirring during the Belousov-Zhabotinskii (BZ) reaction are caused by atmospheric oxygen and, as far as our experiments show, they have nothing to do with dissipative structures or with the turbulence of the reacting mixture.

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Susceptibility of Ni?P?O?Te catalyst to modification by products of ethylbenzene oxidehydrogenation

Washing conditions of phosphate slurry from which Ni–P–O–Te catalyst had been obtained had practically no effect on the initial H _surf. ⁺ concentration but affected substantially the degree of acidification of the catalyst surface during the first stage of ethylbenzene oxidehydrogenation, and thereby the catalyst activity.

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, Ni–P–O–Te, H _. ⁺ , .

     

Aziridine and hydroxy- and chloroethylamine derivatives of colchicine and their biological activity

With the aim of enhancing the cytostatic properties of the initial alkaloid, new aziridine and bis(chloroethyl)amine derivatives of colchicine have been synthesized by the direct interaction of colchicine with chloroethylamine hydrochloride and also via the mono- and diethanolamine derivatives. The structures of the compounds obtained have been studied by spectral methods. An increased radiomodifying and antitumoral activity and a decreased toxicity of the substances synthesized as compared with the initial colchicine has been shown. Results obtained in the National Cancer Institute of the USA from the study of the cytostatic activity of the bis(chloroethyl)amino derivative of 60 tumor lines are presented. Institute of Oncology and Radiology, Academy of Sciences of the Republic of Uzbekistan. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 782–789, November–December, 1998.     

Kinetic Spectrophotometric Determination of Chromium (VI) by Oxidation of Sodium Pyrogallol-5-sulphonate by Hydrogen Peroxide

Summary. A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of chromium (VI). The method is based on the catalytic effect of Cr(VI) on the reaction of sodium pyrogallol-5-sulphonate (PS) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 437nm within 1min after addition of H₂O₂. The optimum reaction conditions are PS (1.32·10^–3mol·dm^–3), H₂O₂ (0.32mol·dm^–3), HClO₄ (2.6·10^–3mol·dm^–3) at 25°C. Following this procedure, chromium (VI) can be determined with a linear calibration graph up to 0.25ng·cm^–3 and a detection limit of 0.024ng·cm^–3, based on the 3 criterion. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cr(VI) and total Cr in river waters and total Cr in herbal samples.