Yu. A. Lisitsyn

Electrochemical amination of unsaturated and aromatic compounds

The mechanism and synthetic perspectives of an indirect cathodic amination of unsaturated and aromatic substrates are considered. The influence of experimental conditions on the state and reactivity of the aminating reagent in solution is studied. The key role of the electrolyte acidity and redox properties of the reagents and intermediates in the obtained isomeric composition and the yield of the amination products is demonstrated.

Electrochemical amination of anisole in 4–6 M solutions of H2SO4 and acetonitrile

Indirect cathode amination of anisole with Ti(IV)/Ti(III) and NH2OH in media containing 4 or 6 M H2SO4, CH3CN, and H2O (in small amounts) was studied. Para- and ortho-anisidines were the major products of radical cation substitution at 15–45°C. The total yield of monoamino compounds based on the source of amino radicals (with its full conversion) may be up to 84% in these conditions.

Electrochemical amination. Functionalization of anisole in solutions of 4.0–6.0 M H2SO4 and acetic acid

The electrochemical amination of anisole in 4.0–6.0 M H2SO4 solutions containing CH3COOH and small amounts of water is studied with the use of the Ti(IV)/Ti(III)-NH2OH system. Under these conditions, the products of radical substitution are para- and ortho-anisidines. Their total current efficiency and yield by hydroxylamine are 82.0% at a complete conversion of the source of amine radicals. Owing to the chain mechanism, the electrochemical process is terminated upon consumption of no more than 0.5 electrons per NH2OH molecule. At a small charge passed through the electrolyte, the anisidines current efficiency can exceed 380%.

Electrochemical amination. Dilute aqueous organic solutions of sulfuric acid

The electrochemical process of anisole amination is studied in 1.5–9 M H2SO4 solutions containing acetonitrile or acetic acid. It is shown that the synthesis of aromatic monoamino compounds is better performed in moderately acidic media with high concentrations of organic solvents. Due to the chain mechanism of the electrochemical process, the current efficiency of amines can exceed 150% under these conditions.

Selectivity of electrochemical amination of anisole in water solutions of H 2 SO 4

During amination of anisole in 8-15 M sulfuric acid solutions with the consumption of the amount of electricity theoretically necessary for the complete conversion of NH2OH in the process with the expenditure of one electron per its molecule the main products of substitution are orto-, para-anisidines, and 4-methoxy-1,3-phenylenediamine. meta-Anisidine and 4-methoxy-1,2-phenylenediamine are found in insignificant amounts.

Electrochemical amination. Ti(IV)/Ti(III) mediator system in aqueous solutions of sulfuric acid

As a result of polarographic and spectrophotometric studies, and mathematical modeling, the dependence of electrochemical properties of the Ti(IV)/Ti(III) pair on the composition of the Ti(IV) complexes is established in sulfuric acid solutions. It is found that Ti(IV) in 1–17 M H2SO4 at the metal ion concentrations used in the process of amination of aromatic compounds can exist in the form of twelve basic complex forms, of which seven, including the binuclear and two tetranuclear ones, are observed for the first time. Ten forms are electrochemically active. An increase in the overall amount of reversibly reducing cationic mononuclear hydrosulfate complexes of Ti(IV) among these at a growing H2SO4 concentration results in an increase in the redox potential of the Ti(IV)/Ti(III) mediator system and therefore in an increase in the yield of the electrochemical amination products.

Electrosynthesis of anisidines in aqueous sulfuric and acetic acids

The influence of the concentrations of acetic and sulfuric acids on the efficiency of anisole amination by means of hydroxylamine and Ti(IV)/Ti(III) mediator was studied. Ortho- and para-anisidines were obtained with the total yields of about 79% by current and hydroxylamine.

Electrochemical Amination in the System Ti(IV)–NH2OH–C6H6: The Efficiency of the Process in a Sulfuric Acid Solution Containing an Organic Solvent

Electrolysis of the system Ti(IV)–NH2OH–C6H6 in an 11 M H2SO4 solution shows that using an organic solvent (acetic acid, acetonitrile) during cathodically initiated amination of aromatic substrates permits the production of aromatic amines with the overall yield by hydroxylamine reaching 91%. Due to a chain mechanism of radical substitution, the benzene amination in electrolytes containing 5 M CH3COOH and 5.5 M CH3CN terminates largely upon consuming 70–75 and 50–55% of the charge required theoretically for a one-electron process. The maximum efficiency of electrochemical amination is observed at low hydroxylamine conversions and the overall current efficiency for mono- and disubstituted products of the benzene amination may exceed in these conditions 750%.

Electrochemical amination. Selective introduction of two amino groups into an aromatic ring

Indirect cathodic amination of anisole via a Ti(IV)–NH2OH system in aqueous solutions of sulfuric acid is studied. The major products of the radical cation substitution in these media are para- and ortho-anisidines and 4-methoxy-1,3-phenylenediamine. The most efficient electrochemical process takes place in 10–12 М H2SO4. Under these conditions, complete conversion of the source of amino radicals is observed, and the total current yields, which correspond to the yields per hydroxylamine, reach 60%.

Selective synthesis of benzene-1,3-diamines by amination of anilines containing ortho/para-orienting substituents in the para position

Electrochemical radical cation amination of aniline with hydroxylamine and Ti(IV)–Ti(III) mediator system in aqueous sulfuric acid gives isomeric benzenediamines in good overall yield [1]. In the present communication we describe selective synthesis of benzene-1,3-diamines via functionalization of p-anisidine and p-chloroaniline in aqueous sulfuric acid. These substrates contain an ortho/para-orienting substituent in the para position and are more (MeO) and less (Cl) activated than aniline toward electrophiles.