D. N. Kursanov

Acidity of niccolocene in dimethyl sulfoxide and methanol solutions

The acidity of niccolocene in dimethyl sulfoxide-methanol solution during potassium methoxide catalysis was determined by measuring the isotopic hydrogen-exchange rate constants of 9-phenylxanthene and niccolocene in this mixture of solvents.

Acidity of nickelocene and kinetic isotope effect during the hydrogen exchange with bases

1. n nThe rate constants for the deuterium and tritium exchange of nickelocene (NC), ferrocene (FC), triphenylmethane (TPM) and diphenylmethane (DPM) with bases were measured, and it was established that the kinetic acidity of these compounds and cyclopentadienylmanganese tricarbonyl (CMT) increases in the order: FC ≪ CMT < DPM < TPM < NC. n n n n n2. n nThe kinetic isotope effect for the exchange reaction of NC with bases was determined, the same as in the case of FC and CMT; the reaction proceeds by the mechanism of protophilic hydrogen substitution.

Hydrogen-exchange reaction of alkyl halides with formic and acetic acids

1. n nAn investigation was made of the hydrogen exchange of alkyl halides in media differing in dielectric constant, namely formic and acetic acids. n n n n n2. n nTertiary halides (chloride, bromides, and iodides) undergo hydrogen exchange with formic acid-d, whereas secondary alkyl halides do not undergo hydrogen exchange under the same conditions. Tertiary chlorides do not undergo hydrogen exchange with acetic acid-d, whereas under the same conditions tertiary bromides exchange hydrogen atoms for deuterium, though at a much lower rate than with formic acid. n n n n n3. n nIt is suggested that the hydrogen exchange of alkyl halides is a consequence of their dissociation, which depends on the dielectric constant of the medium, the nature of the halogen atom, and the structure of the alkyl group.

Effect of positive charge on metal atom on photic mobility of hydrogen atoms in π-cyclopentadienyl complexes of cobalt

The positive charge on the cobalt atom in the di-π-cyclopentadienyl complex of cobalt exerts a noticeable effect on the rate of hydrogen isotope exchange of the cyclopentadienyl ligand in basic media: the acidity of the C-bonds of cobalticene was estimated.

Proton mobility of hydrogen atoms in bis-arene complexes of chromium

1. n nThe reaction of isotopic exchange of hydrogen of two types of bis-π-arene complexes of chromium (Arene)2Cr (where Arene=benzene, toluene, ethylbenzene) with deuteroethanol in the presence of sodium ethylate and [(Arene)2Cr]⊕I⊖ with deuterium oxide in the presence of KOD, was studied. The rate of isotopic exchange of the hydrogen of both types of chromium complexes increases in proportion to the concentration of the bases, and not only the hydrogen atoms of the aromatic ring, but also the hydrogens of the side chain participate in the exchange. n n n n n2. n nThe factors of the partial rate were determined for the phenyl and methyl hydrogen atoms in bisπ-toluenechromium. On the basis of the data of IEH, the acidity of the C-H bonds in bis-π-benzenechromium was estimated (pKa26.3 +- 0.2).

Hydrogen exchange of saturated hydrocarbons in homogeneous media Communication 2. Hydrogen exchange of methylcyclohexane in solutions of trifluoroacetic and sulfuric acids at various values of the acidity function

1. n nThe kinetics of the hydrogen exchange of methylcyclohexane was studied in solutions of trifluoroacetic and sulfuric acids at various values of the acidity function of the initial solutions. n n n n n2. n nA linear relationship was found between the acidity functions of the solutions and the logarithms of the rate constants of the hydrogen exchange of methylcyclohexane.

Hydrogen isotope exchange in esters of trifluoracetic acid

1. n nA study has been made of the hydrogen exchange reaction of tertiary, secondary, and primary alkyl trifluoracetates (tertiary butyl, methylcyclohexyl-, 2-methylpentyl-, secondary butyl-, isopropyl-, and n-butyltrifluoracetates) in trifluoracetic acid. n n n n n2. n nThe tertiary alkyl trifluoracetates enter into a hydrogen exchange reaction with trifluoracetic acid. Hydrogen exchange of secondary trifluoracetates can be produced only by increasing the acidity of the medium by adding sulfuric acid to the trifluoracetic acid solutions. The primary trifluoracetates are incapable of hydrogen exchange even under these conditions. n n n n n3. n nThe proposal is made that hydrogen exchange of tertiary and secondary trifluoracetates is the result of ionization of these esters to form carbonium ions that are capable of exchange.

The reaction of isotopic exchange of hydrogen with alkyl halides

1. n nWe have studied the kinetics of hydrogen exchange in 2-chloro-2-methylpentane and 1-chloro-1 -methylcyclohexane in anhydrous acetic acid in the presence of the Lewis acids: FeCl3, SbCl5, SnCl4, ZnCl2, HgCl2, and BF3. Under the same conditions, the rate constants of hydrogen exchange in the alkyl chlorides depend essentially on their structures. n n n n n2. n nOn the basis of the results of hydrogen exchange in different tert-alkyl chlorides we have arranged a series of relative activities FeCl3 ≥SbCl5 > SnCl4 > ZnCl2> HgCl2 > BF3. n n n n n3. n nThe relative activities of the different Lewis acids remain constant for the tert-aliphatic chlorides and differ only somewhat for the alicyclic chloride. n n n n n4. n nWe have suggested that the method of hydrogen exchange is suitable for quantitative estimation of the Lewis acids.

Hydrogen exchange in heterolytic reactions. Exchange of hydrogen atoms in the replacement of iodine in alkyl iodides

1. n nThe possibility of applying the hydrogen-exchange reaction in the study of the, mechanism of heterolytic reactions was investigated. A study was made of hydrogen exchange a) in the hydrolysis of tertiary alkyl iodides (tert-C4H9I and tert-C5H11I) with water enriched with deuterium oxide, and b) during the exchange of iodine for another iodine atom in alkyl iodides (C2H5I, i-C3H7I, tert-C4H9I, and tert-C5H11I) in reaction with 56% HI enriched with deuterium iodide. n n n n n2. n nIt was shown that hydrogen exchange in C-H bonds is observed in those reactions which, according to kinetic investigations, proceed by a unimolecular mechanism, i.e. with intermediate formation of carbonium ions. It was shown, in particular, that the hydrolysis of tertiary alkyl iodides (C4H9I and C5H11I) and replacement of iodine by iodine in tertiary alkyl iodides, which proceed by an SN1 mechanism, are accompanied by hydrogen exchange reactions of secondary and primary alkyl iodides, which permits us to assume a bimolecular mechanism for these reactions.