Structure and the properties of 18α,19βH-ursane derivatives with a lactone bridge to ring E

1980 ◽  
Vol 45 (5) ◽  
pp. 1366-1378 ◽  
Author(s):  
Eva Klinotová ◽  
Hana Skorkovská ◽  
Jiří Protiva ◽  
Alois Vystrčil
Keyword(s):  
Alkaline Medium ◽  
Hydroxy Acid ◽  
Lead Tetraacetate

Oxidation of ketolactone II in alkaline medium led predominantly to hydroxy acid VI with an oxabicycloheptane arrangement of the E ring. Further oxidation of hydroxy acid VI with lead tetraacetate or the pyrolysis of its diacetate, VII, gave ketone XV which on further oxidation gave either lactone XVIII or XXIV, depending on conditions. The structure of both lactones was confirmed by reduction to tetrol XIX or pentol XXV, from lactone XXIV diketone XXXI was also obtained.

Oxidation of 3β,28-Diacetoxy-18-lupen-21-one with Peroxy Acids: A Way to Des-E-lupane Derivatives

1993 ◽  
Vol 58 (10) ◽  
pp. 2505-2516 ◽  
Author(s):  
Eva Klinotová ◽  
Martin Rejzek ◽  
Hana Zůnová ◽  
Jan Sejbal ◽  
Jiří Klinot ◽  
...  
Keyword(s):  
Alkaline Medium ◽  
Peracetic Acid ◽  
Lead Tetraacetate ◽  
Epoxy Derivative ◽  
Oxidative Removal ◽  
Acid Catalyzed ◽  
Peroxy Acids ◽  
Strong Acids

Oxidation of 3β,28-diacetoxy-18-lupen-21-one (I) and its 18β, 19β-epoxy derivative III with peracetic acid, catalyzed with strong acids, proceeds with cleavage of the bond between C-19 and C-21 under formation of E-seco derivatives with hydroxyl and isobutyryl groups on C-18 (spiro lactones V - VII and acid VIII). Oxidative removal of the isobutyryl fragment in spiro lactone VI by treatment with lead tetraacetate leads to the tetranor derivative - keto lactone XI which in an alkaline medium loses formaldehyde from C-17 to give des-E acid XVI.

Kinetics and Mechanism of Oxidation of Labetalol by Hexacyanoferrate(III) in Alkaline Medium

2012 ◽  
Vol 3 (2) ◽  
pp. 131-133
Author(s):  
ANNAPURNA NOWDURI ◽  
◽  
Apparao Babu Duggada ◽  
Vijaya Raju Kurimella
Keyword(s):  
Alkaline Medium ◽  
Kinetics And Mechanism ◽  
Mechanism Of Oxidation

Binding of calcium and lead ions to carboxystarch prepared by action of nitrogen dioxide on native starch and its 2,3-dialdehyde derivatives

1986 ◽  
Vol 51 (6) ◽  
pp. 1340-1351 ◽  
Author(s):  
Rudolf Kohn ◽  
Karol Tihlárik
Keyword(s):  
Nitrogen Dioxide ◽  
Alkaline Medium ◽  
Binding Capacity ◽  
Lead Ions ◽  
Carbonyl Groups ◽  
Weakly Alkaline ◽  
Exchange Cations ◽  
Counter Ions ◽  
The Stability ◽  
Derivatives Of

The binding of calcium and lead ions to carboxy derivatives of starch prepared by allowing nitrogen dioxide to act on native maize starch (procedure A) and on starch 2,3-dialdehyde derivatives of degrees of oxidation DO(d.a.) ≥ 0.94 (procedure B) was studied. The carboxy group content of the samples in the H+ form was 4.6 - 12.1 mmol g-1. The effect of alkaline medium on the stability of the carboxy derivatives and on their ability to bind and exchange cations was examined. The Ca2+ → 2K+ exchange was evaluated in terms of the decrease in the electrostatic free enthalpy Δ(Gel/N)KCa, determined by alkalimetric potentiometric titrations, and the binding of Pb2+ ions was evaluated in terms of the activity of the Pb2+ counter-ions determined in suspensions of Pb salts of the carboxy derivatives by means of an ion specific electrode. The IR and CD spectra revealed that the carboxystarch preparations obtained by procedure A contained, in addition to free carboxy groups, a considerable amount of carbonyl groups. During the conversion of the latter groups to the former, even in a weakly alkaline medium, the carboxy derivatives undergo an appreciable degradation and lose, to a great extent, their ability to bind and exchange cations. Procedure B, on the other hand, leads to highly selective starch and amylose carboxy derivatives, exhibiting a small amount of carbonyl groups and featuring a relative stability towards alkaline medium; their binding capacity is as high as 12 milliequivalents of cations per g of sample.

Oxidation of polysubstituted pyridinium salts

1982 ◽  
Vol 47 (5) ◽  
pp. 1494-1502 ◽  
Author(s):  
Petr Nesvadba ◽  
Josef Kuthan
Keyword(s):  
Alkaline Medium ◽  
Electrophilic Substitution ◽  
Pyridine Ring ◽  
Potassium Ferricyanide ◽  
Pyridinium Salts ◽  
Complex Reaction

Oxidation of 1-substituted 2,4,6-triphenylpyridinium salts Ia-Ij with potassium ferricyanide in an alkaline medium was accompanied by contraction of the pyridine ring and formation of 1,2,3,5-tetrasubstituted pyrroles II. The derivative IIf underwent facile electrophilic substitution in the position 4. Contrary to compounds Ia-Ij, the 1-substituted-2,6-diphenylpyridinium salts IIIa,b were oxidized to give a complex reaction mixture containing 4-pyridones IVa,b.

Outer-sphere interaction of (S)-asparagine and (S)-glutamine with [Co(NH3)6]3+ ion and its possible role in ligand substitution

1987 ◽  
Vol 52 (10) ◽  
pp. 2457-2459
Author(s):  
František Jursík
Keyword(s):  
Amino Acids ◽  
Transition Region ◽  
Alkaline Medium ◽  
Optical Activity ◽  
Substitution Reaction ◽  
Outer Sphere ◽  
Ligand Substitution ◽  
Cotton Effect ◽  
Negative Cotton Effect

Optical activity of the achiral cation [Co(NH3)6]3+ is induced both by (S)-AsnONa and (S)-GlnONa, as shown by a negative Cotton effect in the 1A1g → 1T1g transition region. An outer-sphere interaction by three-point attachment of the amides can explain the fact that substitution reaction of [Co(NH3)6]3+ with the mentioned amides in an alkaline medium is unusually slow as compared with other amino acids.

Adsorption and Oxidation of Thiosulfate on the Platinum Electrode in a Slightly Alkaline Medium

2000 ◽  
Vol 65 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Tomáš Loučka
Keyword(s):  
Alkaline Medium ◽  
Oxidation Reaction ◽  
Open Circuit Potential ◽  
Platinum Electrode ◽  
Adsorbed Layer ◽  
Open Circuit ◽  
Adsorbed Hydrogen ◽  
Oxidation Number ◽  
Hydrogen Electrode ◽  
Layer Region

The aim of this research was to study the oxidation and reduction of the adsorbed thiosulfate on the platinum electrode in a slightly alkaline medium. The adsorption was performed at the open circuit conditions. The reduction of the adsorbed layer in the hydrogen region is slower in a slightly alkaline medium than in acid. The mechanism of reduction and oxidation of adsorbed molecules is probably the same. The nonstationary currents measured in presence of thiosulfates showed that the change in the oxidation number does not take place during the adsorption in the double layer region. In the hydrogen region, thiosulfate replaces the adsorbed hydrogen while beeing reduced. Nonstationary currents at higher concentrations of thiosulfate indicate the presence of more layers on the electrode. Upon reaching higher concentrations of thiosulfate the oxidation reaction takes place between thiosulfate in solution and adsorbed product of its reduction. The open circuit potential of the platinum electrode measured in a thiosulfate solution was 0.780 and 0.783 V against the hydrogen electrode in the same solution.

2D metal azolate framework as nanozyme for amperometric detection of glucose at physiological pH and alkaline medium

2021 ◽  
Vol 188 (3) ◽  
Author(s):  
Muhammad Adeel ◽  
Vincenzo Canzonieri ◽  
Salvatore Daniele ◽  
Alberto Vomiero ◽  
Flavio Rizzolio ◽  
...  
Keyword(s):  
Alkaline Medium ◽  
Amperometric Detection
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