Kinetics and mechanism of the oxidation of some α‐hydroxy acids by 2,2′‐bipyridinium chlorochromate

The oxidation of glycolic, lactic, malic, and a few substituted mandelic acids by 2,2′‐bipyridinium chlorochromate (BPCC) in dimethylsulphoxide leads to the formation of corresponding oxoacids. The reaction is first order each in BPCC and the hydroxy acids. The reaction is catalyzed by the hydrogen ions. The hydrogen ion dependence has the form: k_obs = a + b [H⁺]. The oxidation of α‐deuteriomandelic acid exhibited a substantial primary kinetic isotope effect (k_H/k_d = 5.29 at 303 K). Oxidation of p‐methylmandelic acid was studied in 19 different organic solvents. The solvent effect has been analyzed by using Kamlet's and Swain's multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 248–254, 2002     

Kinetics and mechanism of the oxidation of some organic sulfides by morpholinium chlorochromate

The oxidation of organic sulfides by morpholinium chlorochromate (MCC) resulted in the formation of the corresponding sulfoxides. The reaction is first order with respect to both MCC and the sulfide. The reaction is catalyzed by toluene‐p‐sulfonic acid (TsOH). The oxidation was studied in 19 different organic solvents. An analysis of the solvent effect by Swain's equation showed that both the cation‐ and anion‐solvating powers of the solvents play important roles. The correlation analyses of the rate of oxidation of 34 sulfides were performed in terms of various single and multiparametric equations. For the aryl methyl sulfides, the best correlation is obtained with Charton's localized‐delocalized‐resonance and localized‐delocalized‐resonance‐steric equations. The oxidation of alkyl phenyl sulfides exhibited a very good correlation in terms of the Pavelich–Taft equation. The polar reaction constants are negative, indicating an electron‐deficient sulfur center in the rate‐determining step. A mechanism involving formation of a sulfonium cation intermediate in the slow step has been proposed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 65–72, 2009     

Kinetics and mechanism of the oxidation of formic and oxalic acids by quinolinium fluorochromate

Kinetics and mechanism of oxidation of formic and oxalic acids by quinolinium fluorochromate (QFC) have been studied in dimethylsulphoxide. The main product of oxidation is carbon dioxide. The reaction is first-order with respect to QFC. Michaelis-Menten type of kinetics were observed with respect to the reductants. The reaction is acid-catalysed and the acid dependence has the form: k_obs =a +b[H⁺]. The oxidation of α-deuterioformic acid exhibits a substantial primary kinetic isotope effect (k_H/k_D = 6.01 at 303 K). The reaction has been studied in nineteen different organic solvents and the solvent effect has been analysed using Taft’s and Swain’s multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical cyclic transition state in the rate-determining step. Suitable mechanisms have been proposed.     

Neighbouring group participation in reactions of sulphides with chloramine-t

Neighbouring group participation in reactions of chloramine-T with ortho-substituted aryl methyl sulphides and diaryl sulphides has been studied. The reaction is markedly hindered by the steric effect of the ortho substituent of the phenyl ring, but groups having a CO moiety show an anchimeric effect in the following order: o-CH₂CO₂Me ~ o-CH₂CO₂H < o-CH₂CO₂^- < o-CO₂Me ~ o-CO₂H < o-CO₂^- ? 2o-CO₂ in the rate-determining step may be ruled out on the basis of salt and isotope effect. Substituents with neighbouring group participation diminish the yield of sulphilimine in solvents containing water. The electrophilic chlorination of sulphides by TsNHCl may be assumed to be the rate-determining step with the positively charged sulphonium centre stabilized by the negatively polarized or charged carbonyl-oxygen in the transition state. This type of interaction hinders the nucleophilic attack of sulphonamidate ion at the sulphonium centre in the fast product-controlling steps, decreasing the yield of sulphilimine.     

Friessche Verschiebung vonortho- undpara-Methoxyphenylacetaten. Die Bildung von Ketoestern

During theFries rearrangement ofo- andp-methoxy phenyl acetates with AlCl₃ in nitromethane at 20°C substitution occurs mainly in thep-position of the phenolic residue to yieldp-acylphenols. Larger quantities ofo-acylphenols are obtained only, if thisp-position is already substituted. Witho-methoxy phenyl acetates the substitution of the acid residue to yield ketoesters is observed as a side reaction. Those ketoesters are obtained as main products if TiCl₄ is taken as a catalyst.

     

Kinetics and mechanism of the oxidation of substituted benzylamines by cetyltrimethylammonium permanganate

Oxidation of meta- and para-substituted benzylamines by cetyltrimethylammonium permanganate (CTAP) to the corresponding aldimines is first order with respect to both the amine and CTAP. Oxidation of deuteriated benzylamine (PhCD₂NH₂) exhibited the presence of a substantial kinetic isotope effect (k _H /k _D = 5.60 at 293 K). This confirmed the cleavage of an α-C-H bond in the rate-determining step. Correlation analyses of the rates of oxidation of 19 monosubstituted benzylamines were performed with various single and multiparametric equations. The rates of the oxidation showed excellent correlations in terms of Yukawa—Tsuno and Brown’s equations. The polar reaction constants are negative. The oxidation exhibited an extensive cross-conjugation, in the transition state, between the electron-donating substituents and the reaction centre. A mechanism involving a hydride-ion transfer from the amine to CTAP in the rate-determining step has been proposed.     

Synthesis and recyclization reactions of 4-(o-R-phenyl)-3-imidazolines

1-Hydroxy-4-phenyl-3-imidazoline reacts with butyllithium to give the product oforthometallation of the phenyl group. Reactions of this compound with electrophiles followed by oxidation afford 4-(o-R-phenyl) derivatives of nitroxyl radicals. When a hydroxyalkyl group is present in theortho-position, an unusual pathway of the decay of stable nitroxyl radicals of the imidazoline series has been observed due to the existence of a spirobicyclic tautomer. The reaction of theo-metallated derivative with CS₂ leads to a profound transformation of the imidazoline ring and to the formation of isoindolethione. Fast recyclization into isoquinolines occurs in the case of the 4-(o-benzoyl)phenyl derivative of 3-imidazoline. The product ofo-metallation reacts with methyl nitrate to yield the 4-(o-hydroxy)phenyl derivative (a potential paramagnetic chelate-forming reagent) and theo-nitro derivative, the starting material for further chemical transformations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 899–903, May, 1994.     

Chemotherapeutic agents. IX. Synthesis and pesticidal activities of bis[4-aryl/alkyl-1, 2, 4-triazoline-5-thione-3-yl]alkanes and 1 -Aryl/alkyl-3-[4-(4-aryl/alkyl-1, 2, 4-triazoline-5-thione-3-yl)phenyl]thiourea and related compounds

Various bis[4-aryl/alkyl-1, 2, 4-triazoline-5-thione-3-yl]alkanes ( 3 ) were prepared from base cyclization of bis thiosemicarbazide 2 and transformed into sulphides by reaction with different alkyl halides in alkaline medium. These compounds were further oxidised to sulphones 5 with acidic potassium permanganate. 1-Aryl-3-[4-(4-aryl/alkyl-1, 2, 4-triazoline-3-thione-5-yl)phenyl]thioureas ( 8 ) were prepared in two steps from p-aminophenylhydrazide ( 6 ) and aryl/alkylisothiocyanates. Alkylation of 8 with different alkyl halides yielded exclusively sulphides 9 . Some sulphides 12 and Mannich bases 13 from 5-(p-fluorophenyl)-1, 3, 4-oxadiazol-2-thione ( 11 ) were also prepared to evaluate their pesticidal activities. All the prepared compounds were screened for pesticidal activities but none of them exhibited any significant activity.     

Lösungsmitteleinsehlüsse in Kristallen von p-substituierten Benzoesäurederivaten

Zusammenfassung p-Hydroxybenzoesäure, p-Aminobenzoesäure und p-Aminosalicylsäure vermögen aus einzelnen Lösungsmitteln in Form von Addukten auszukristallisieren. Die analogeno- und m-Verbindungen zeigen diese Fähigkeit nicht. Ebenso fehlt Adduktbildung bei p-Chlor-, p-Brom- und p-Nitrobenzoesäure.

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Solvent inclusions in crystals of p-substituted benzoic acid derivatives

Summary p-Hydroxybenzoic acid,p-aminobenzoic acid andp-aminosalicylic acid are capable of crystallizing out of various solvents in the form of adducts. The correspondingo- andm-compounds do not exhibit this characteristic. Similarly there is no adduct-formation in the cases ofp-chloro-,p-bromo- andp-nitrobenzoic acid.