Electrochemical amination. Dilute aqueous organic solutions of sulfuric acid

ISSN 1023-1935, Russian Journal of Electrochemistry, 2009, Vol. 45, No. 2, pp. 132–138. © Pleiades Publishing, Ltd. 2009.Original Russian Text © Yu.A. Lisitsyn, L.V. Grigor’eva, 2009, published in Elektrokhimiya, 2009, Vol. 45, No. 2, pp. 141–147.

132

INTRODUCTION

Indirect cathode amination of aromatic compoundsin sulfuric acid solutions containing Ti(IV) and NH

2

OHenables synthesis of the corresponding mono anddiamines in one technological stage [1, 2]. One of themain factors determining the efficiency, degree, andselectivity of substitution is the H

2

SO

4

concentration.In the absence of the sulfonation reaction, its effect onthe radical chain process is displayed in changes in thecomposition of complexes of oxidized and reducedforms in the Ti(IV)/Ti(III) mediator system and in theassociation of protonated monoamino compounds withsulfate and hydrosulfate ions.

The most efficient amination is observed in electro-lytes with an H

2

SO

4

concentration of more than 7 M.Under these conditions aromatic diamines are the finalsubstitution products. The use of organic solvents(CH

3

COOH and CH

3

CN) for the amination of sub-strates with low solubility in water makes it possible toobtain amines with the total current efficiency (CE) andhydroxylamine yields close to numerical, with the sourceof amino radicals being completely converted [3].

However, in terms of economy, it is desirable toelectrosynthesize organic compounds in dilute electro-lyte solutions with high electrical conductivity, whichconsiderably reduces the problem of electrolyte con-tamination of electrolysis products. For the aminationof aromatic substrates, H

2

SO

4

solutions with a concen-tration of less than 7 M are of special interest becausesubstitution here ends in forming only monoaminocompounds. Still it should be noted that the maximumcurrent efficiency for the latter, obtained by optimiza-tion of the anisole amination process in the potentiostatmode [4], does not exceed 10.5%; and the majority of

aminyl radicals disappear during the ammonia forma-tion reaction competitive to substitution.

With regard to the results of CH

3

COOH and CH

3

CNuse in strong acidic media, the present work studies theeffect of the nature and concentration of organic solventon the yield of monoanino compounds in dilute H

2

SO

4

solutions.

EXPERIMENTAL

Electrolyses of aqueous and aqueous organic H

2

SO

4

solutions containing anisole and the Ti

(

IV

)–

NH

2

OHsystem were conducted in a three-electrode glass cellwith cathode and anode spaces separated by a ceramicdiaphragm.

A catholyte, an aqueous solution of 25 ml, contained0.1 M Ti(IV), 0.2 M NH

2

OH, the required concentra-tions of H

2

SO

4

, and either CH

3

COOH or CH

3

CN. Theamount of anisole added to the catholyte was 5 ml. Ahighly dispersed emulsion of the aromatic compound inthe electrolyte was maintained by magnetic stirring.Oxygen dissolved in the emulsion was removed beforeelectrolysis with an argon flow passed preliminarythrough a Drechsel bottle containing the emulsion com-ponents. During electrolysis the inert gas was passedover the catholyte.

Anisole amination was performed at 40

°

C, and thecurrent density on the mercury cathode was 2 mA/cm

2

.The construction of the electrochemical cell describedin the works [5, 6] provided the constant mercury elec-trode area (11 cm

2

), while the emulsion was vigorouslystirred. The galvanostatic mode of electrolysis wasachieved by P-5848 or PI-50-1 potentiostats. In order toprecisely control and automatically record the cathodepotential, measured relative to the silver-chloride refer-ence electrode, a Shch-4313 voltammeter and KSP-4 or

Electrochemical Amination. Dilute Aqueous Organic Solutionsof Sulfuric Acid

Yu. A. Lisitsyn

z

and L. V. Grigor’eva

Kazan State University, Kazan, Butlerov Institute of Chemistry, Kazan, 420008 Russia

Received April 21, 2008

Abstract

—The electrochemical process of anisole amination is studied in 1.5–9 M H

2

SO

4

solutions containingacetonitrile or acetic acid. It is shown that the synthesis of aromatic monoamino compounds is better performedin moderately acidic media with high concentrations of organic solvents. Due to the chain mechanism of theelectrochemical process, the current efficiency of amines can exceed 150% under these conditions.

Key words

: hydroxylamine, cathode, Ti(IV)/Ti(III) mediator system, electrophilic amination, radical aromaticsubstitution

DOI:

10.1134/S1023193509020025

z

Corresponding author: [email protected] (Yu.A.Lisitsyn).

RUSSIAN JOURNAL OF ELECTROCHEMISTRY

Vol. 45

No. 2

2009

ELECTROCHEMICAL AMINATION. DILUTE AQUEOUS ORGANIC SOLUTIONS 133

LKD4-003 recorders, respectively, were used. Thecharge passed through the electrolyte was 250 C, as inthe works [4, 5]. The Pt wire covered with platinumblack served as the anode, while an aqueous H

2

SO

4

solution was used as the anolyte, and its concentrationwas equal to that of the catholyte.

After electrolysis was completed, the cooledcatholyte was diluted with water to a sulfuric acid con-centration of 1–1.5 M, and then it was neutralized bysuccessive treatment with a saturated aqueous NaOHsolution and sodium hydrocarbonate. Electrolysis prod-ucts were extracted by chloroform.

Quantitative analysis of isomeric anisidines wascarried out on a Chrom-4 chromatograph with a flameionization detector. The temperature of the glass col-umn [

2500

×

3

mm, 5% XE-60 on a Chromaton N-AW-DMCS (0.160-0.200 mm)] was 150

°

C, the carrier gas(helium) flow rate was 15 ml/min (the qualitative com-position of amino compounds was confirmed by a heatconductivity detector and three phases: XE-60, SE-30,and OV-17).

Polarographic studies were conducted at 25

°

C in aglass cell equipped with a thermostating jacket. Polaro-grams were recorded in an argon atmosphere in thethree-electrode mode by means of a PU-1 polarographand an LKD4-003 X-Y recorder with a potential sweeprate of 5 mV/sec. The dropping mercury electrode(DME, mercury mass flow rate is 3.6 mg/sec) and mer-cury pool were used as the working and auxiliary elec-trodes respectively. The DME potential was measuredwith respect to the silver-chloride electrode. Therequired drop time of the DME (0.51s) was provided byan electromagnetic drop time controller.

Voltammetric curves were recorded in the elec-trosynthesis cell in a three-electrode mode using aP-5848 potentiostat and a KSP-4 recorder. The rate ofchange of the stationary mercury electrode (SME)potential corresponded to the polarographic one; exper-iment details are similar to those in the above describedanisole amination.

In the work we used 15 % solution of titan (IV) sul-fate in 4 M H

2

SO

4

(analytical grade), H

2

SO

4

(chemi-cally pure), hydroxylamine sulfate salt (Acros, 99%)recrystallized from the aqueous solution, NaOH (ana-lytical grade), NaHCO

3

(chemically pure), distilled ani-sole (chemically pure), chloroform (analytical grade),acetic acid (chemically pure), isomeric anisidines(reagent grade) purified by distillation in vacuum overKOH, and acetonitrile (analytical grade) treated byKMnO

4

and distilled over P

2

O

5

. All solutions were pre-pared with bidistilled water.

RESULTS AND DISCUSSIONS

Specificity of the amination of aromatic compoundsin aqueous organic solutions of dilute H

2

SO

4

was stud-ied by the example of anisole functionalization. In1

−

7 M aqueous H

2

SO

4

solutions the scheme of this

electrochemical process can be represented by a set ofequations (1)–(10) [1, 2, 4, 5]

Cathode:

Ti

(

IV

) +

e

Ti

(

III

), (1)

Catholyte:

(2)

Ti

(

III

) +

NH

2

OH

[

Ti

(

IV

)

NH

2

]

•

+

OH

–

, (3)

(4)

[

Ti

(

IV

)

NH

2

]

•

+

Ti

(

III

) 2

Ti

(

IV

) +

NH

3

, (5)

(8)

(9)

(10)

The choice of C

6

H

5

OCH

3

as a test subject was deter-mined by its activity relative to electrophilic reagentsand also by complete oxidation of methoxyaminocyclohexadienyl radicals by Ti(IV) ions (equations (8)and (9)) in solutions with a low concentration of sulfu-ric acid [4, 5]. Electrolysis was performed under condi-tions close to optimal for benzene amination in stronglyacidic aqueous organic solutions [3]. Anisole was takenin large excess with respect to the source of amino rad-icals (amounts of C

6

H

5

OCH

3

and NH

2

OH were, respec-tively, 0.046 and 0.005 mole), and the substitution effi-ciency was evaluated by the total current efficiency ofanisidines.

Amination of Anisole in Aqueous Organic Solutionsof 1.5 M H

2

SO

4

In the absence of organic solvent the electrochemi-cal amination of anisole to anisidines proceeds mosteffectively in 1–2 M H

2

SO

4

solutions [4, 5], thereforethe dependence of the yield and isomeric distribution ofamino compounds on concentrations of CH

3

COOH andCH

3

CN were analyzed in 1.5 M H

2

SO

4

. Since CE andsubstitution selectivity depend on the water/sulfuricacid mole ratio (WSAMR) in the solution, and waterwas replaced with organic solvent, in order to evaluatemore correctly the effect of the solvent nature on theresults of amination at the same WSAMR, acetonitrile

NH2OH H+ NH3OH,++

Ti IV( )NH2[ ]• H+ Ti IV( ) NH3,++•+

H+

H3COC6H5NH2Ti IV( )[ ]•,

C6H5OCH3

H3NC6H5OCH3[ ]•+,

(6)

(7)NH3•+

[Ti(IV)NH2]•

H3COC6H5NH2Ti IV( )[ ]•

H3COC6H4NH2 Ti III( ) H+,+ +

H3NC6H5OCH3[ ]•+ Ti IV( )++

NH3C6H4OCH3 Ti III( ) H+,+ +

H3COC6H4NH2 H+ H3COC6H4NH3.++

134

RUSSIAN JOURNAL OF ELECTROCHEMISTRY Vol. 45 No. 2 2009

LISITSYN, GRIGOR’EVA

and acetic acid were added in equal volume concentra-tions. Molar concentrations of solvents in electrolytescompared by pairs differed by approximately 10%.Electrolyses proceeded in the region of potentialswhere electrochemical hydrogen evolution on the mer-cury cathode almost did not occur (Fig. 1).

In the aqueous 1.5 M H2SO4 solution, the currentefficiency of anisidines is 6.4%. Anisole is a water insol-uble substrate [6], therefore a main partof the radicalaminating reagent turns into ammonia (equation (5)).The amination efficiency is by 2% lower than the effi-ciency reported in [5] because of a somewhat highercathode current density and lower temperature used inthe present work. Introduction of small concentrationsof organic solvents into the catholyte, unlike introduc-tion into strongly acidic solutions [7], not only does notincrease the yield of anisidines, but on the contrary,decreases it (Fig. 2). As in the media with a high con-

centration of H2SO4 [3, 7], the yield of amination prod-ucts is higher in solutions containing CH3CN.

In dilute H2SO4 solutions with increasing acid con-centration the equilibrium of (2) shifts to the right. Adecrease in the concentration of the unprotonated formof hydroxylamine leads to an increase in the concentra-tion of cathodically generated Ti(III), to increased con-tribution of reaction (5) to the disappearance of the ami-nating reagent, and to a decrease in the total currentefficiency of isomeric anisidines [5]. Taking intoaccount that an increase in the concentration of organicsolvent in 1.5 M H2SO4 is also accompanied bydecreasing WSAMR, the lowered efficiency observedin aqueous organic media can be explained by that atsmall concentrations of CH3COOH or CH3CN theincreased rate of reaction (5) affects to a larger extentthe amination process than an increase in the aromaticsubstrate concentration in the electrolyte.

Voltammograms of Ti(IV) reduction obtained in 1.5 MH2SO4 under conditions of convective diffusion (Fig. 3,curves 1 and 2) indicate the presence of catalytic cur-rents in aqueous and aqueous organic media containinghydroxylamine (note that under polarographic condi-tions catalytic currents of Ti(IV) reduction in aqueousH2SO4 solutions (0.001 M Ti(IV), 25°C) in the presenceof NH2OH are detected only in media with an acid con-centration lower than 1 M [8]). In the solution contain-ing CH3CN (Fig. 3b), the catalytic current of Ti(IV)reduction even exceeds the similar current recorded inthe absence of solvent (Fig. 3a); though, as known [8],a decrease in the WSAMR value in the aqueous solu-tion lowers the apparent rate constant of the reactionbetween Ti(III) and hydroxylamine. At 15°C, for exam-ple, the constant rate, evaluated by the polarographicmethod of the decreasing with time limiting current of

–1.0

–0.8

–0.6

–0.4

–0.2

–0.6

–0.4

–0.2

0

0 60 120 180t, min

(‡)

(b)

12

10

0

135

1.1

0

5.5

8.815.3

E, V

Fig. 1. Changes in the mercury cathode potential duringelectrolysis of the Ti(IV)–NH2OH–C6H5OCH3 system in1.5 M H2SO4 containing CH3COOH (a) CH3CN (b). Figu-res denote molar concentrations of organic solvents.cTi(IV) = 0.1 å, i = –2 mA/cm2, T = 40°C.

12

10

8

6

4

2

0 164 8 12[Solvent], M

CE, %

1

2

Fig. 2. Effect of CH3CN (1) and CH3COOH (2) concentra-tions on the total current efficiency of isomeric anisidinesduring the electrochemical amination of anisole in 1.5 MH2SO4.



the Ti(III) oxidation wave in the presence of hydroxy-lamine [8], is almost quartered as the sulfuric acid con-centration rises from 1 to 2.3 M. The rate of reaction (3)determines the total rate of Ti(IV) regeneration duringthe indirect electrochemical reduction of hydroxy-lamine to ammonia, and its increase in the aqueousorganic H2SO4 solution, as compared to the aqueoussolution of the acid with the same concentration, indi-cates a rise in the Ti(III) reduction potential. This islikely to occur due to the formation of complexes con-taining acetonitrile or acetic acid molecules (and prob-ably acetate-ions in acetic acid media) in the coordina-tion sphere. Hence, a decrease in the efficiency of ani-sole amination at low and moderate concentrations oforganic solvents is caused by the enhanced rate of reac-tion (5) due to an increase both in the concentration andthe reduction potential of Ti(III) complexes.

At a concentration of CH3COOH and CH3CN ofabout 10 and 11 M respectively the current efficiency ofanisidines reaches minimum values (Fig. 2). Furtherincrease in the fraction of organic solvents in electro-lytes results in an enhanced role of the increasing ani-sole concentration in determining the substitution effi-ciency. However, the use of high CH3COOH andCH3CN concentrations in 1.5 M H2SO4 is limited by thesolubility of supposedly mixed Ti(IV) complexes. Theinclusion of CH3CN and CH3COOH molecules (maybe,acetate-ions as well) into the coordination sphere ofTi(IV) is evidenced, in particular, in the results ofpolarographic studies (Fig. 4a). The introduction oforganic solvents in concentrations usually used for theelectrosynthesis of amines in strongly acidic media(5 M CH3COOH or 5.5 M CH3CN [3, 9]) into the 1 MH2SO4 solution containing 0.001 M Ti(IV) leads to achange in the form of the polarogram for Ti(IV) reduc-tion. The first wave of titanum (IV) reduction increasesand shifts to the region of more anodic potentials. Thesecond wave, on the contrary, shifts to the cathoderegion. It shifts so far in the acetonitrile solution thatoverlaps the reduction wave of hydroxonium ions(Fig. 4a). In 1.5 M H2SO4 solutions containing alsoTi(IV) in the concentration used in electrosynthesis, achange in characteristics of voltammograms in thepresence of organic solvents is observed too (Fig. 4b).Apart from voltammetric data, a possible change in thecomposition of Ti(IV) complexes, when organic sol-vents are introduced, is evidenced by white precipitateappearing during the preparation of solutions. The pre-cipitate formed during the addition of organic solvent tothe sulfuric acid solution of metal ions dissolves whenwater or sulfuric acid is added. Note that the aqueoussolution containing 0.1 M Ti(IV), 0.5 M CH3COOH,and 6 M CH3COOH becomes yellow when the precipi-tate dissolves [10].

A comparison of Ti(IV) reduction potentials onDME (Fig. 4) and SME in the cell for synthesis ofamino compounds (Fig. 3) with potentials at whichelectrolysis of the Ti(IV)–NH2OH–C6H5OCH3 systemproceeds (Fig. 1) indicates that in anisole amination not

all but only electrochemically most active Ti(IV) com-plexes, which reduce at potentials of first polarographicwaves, take part. Oxidation potentials of these complexescan be assumed to be higher that those of particles reduc-ing at potentials of second waves, therefore it is theseTi(IV) complexes that oxidize amino cyclodienyl radicalsand participate in the chain amination process.

In the aqueous 1.5 M H2SO4 solution, in accordancewith the nature of the substituent and previously pub-lished data [4, 5], the amino cation-radical is mainlyattacked at ortho- and para-positions of the aromaticring of anisole [(ortho + para)/meta = 12.3, ortho/2para = 1.3, 2 para/meta = 6.8]. Because of the positiveeffect of the field [11, 12] of oxygen atoms from meth-oxy-groups the ortho-position of the ring is more acti-vated than the para-position.

An addition of organic solvent to the electrolyteresults in a definite change in the isomeric compositionof anisole amination products (Fig. 5). A rise in the sol-vent concentration is accompanied by the increasedfraction of para-anisidine.

Dependences presented in Figures 2 and 5 are simi-lar to dependences of the current efficiency of ani-

–1.2

–0.8

–0.4

–1.2 –1.6

0

–0.4 –0.800.4

–1.2

–0.8

–0.4

0

I, A

(b)

(‡) 1

3

2

4

1

2

3

4

E, V

Fig. 3. Voltammetric curves of 0.1 M Ti(IV) reduction onSME in the aqueous solution of 1.5 M H2SO4 not contain-ing (a) and containing (b) 5.5 M CH3CN, in the absence(2) and presence of 0.2 M NH2OH (1) or 0.2 M NH2OH +C6H5OCH3 (3), (4) is 1.5 M H2SO4. v = 5 mV/s.

136



sidines and their isomeric distribution on the concentra-tion of sulfuric acid obtained in aqueous media [5].However, in aqueous organic solutions of 1.5 M H2SO4

the increased yield of anisidines, after passing the min-imum value, and the intersection of fractional distribu-tion curves of ortho- and para-anisidines are observedat substantially larger WSAMR values. Thus, if in theabsence of solvent WSAMR values close to 6.9 and 5.6(6 and 7 M H2SO4) correspond to the minimum yield ofanisidines and the cross point of the above curves, thenin the solution containing CH3CN they are close to 13.6and 15.7 (molar ratios approximately corresponding to3.5 and 3.1 M H2SO4). Moreover, unlike the aqueoussolutions of sulfuric acid, an increase in the total yieldof anisidines in electrolytes containing organic solventsis not accompanied by the appearance of disubstitutedproducts of amination. These results agree with a con-clusion of the effect of acetic acid and acetonitrile onthe amination process drawn previously in the study ofstrongly acidic aqueous organic media [7, 13].

Effect of the Sulfuric Acid Concentration

Results of anisole amination in 1.5 M H2SO4 indi-cate that aqueous organic electrolytes containing 1.5and less mole/l acid are not suitable for the synthesis ofaromatic monoamino compounds. However, a sharpincrease in the total current efficiency of anisidines athigh concentrations of organic solvents (Fig. 2) shows apotential possibility to obtain monoamines in somewhatmore acidic solutions, in the media where the formationprocess of diamino compounds has not started yet.

With regard to these data, in the present work wehave performed a series of electrolyses of the Ti(IV)–NH2OH–C6H5OCH3 system in solutions with increas-ing H2SO4 concentration and close to maximum possi-ble concentrations of CH3CN. It should be noted thatwhen 5 ml of anisole is added to 25 ml of the electro-lyte, the ratio of volumes of two liquid phases contain-ing the aromatic substrate or titanium ions changes sub-stantially. In particular, if, after electrolyses are com-pleted, in 2 and 6 M H2SO4 the ratios of volumes, inwhich anisole is dissolved, to volumes of sulfuric acid

–5

–3

–1

1

–1.2–0.80.4 0 –0.4

–300

–200

–100

0

1

2

3

1

2

3

(b)

(‡)

E, V

I, µÄ

Fig. 4. Classical polarograms of 0.001 (a) and 0.1 M Ti(IV)(b) reduction in 1 (a) and 1.5 M H2SO4 (b) in the absence (1)and presence of 5 M CH3COOH (2) or 5.5 M CH3CN (3).

75

60

45

30

15

0

0 2 4 6 8 10 12

P, %

75

60

45

30

15

0

0 4 8 12 16[CH3CN], M

[CH3COOH], M

para

ortho

meta

para

ortho

meta

(‡)

(b)

Fig. 5. Isomeric distribution of anisidines depending on theconcentration of CH3COOH (a) and CH3CN (b) during ani-sole amination in 1.5 M H2SO4 solutions.



aqueous phases are of about 2.5 and 0.3 respectively,then a single phase system is observed in 9 M acid.

In all media considered, isomeric anisidines areobtained as anisole amination products; diamino com-pounds are not found even in 9 M sulfuric acid, inwhich disubstituted products form in significantamounts in the absence of solvents [1, 2]. The para-iso-mer prevails among anisidines (Table 1), whereas meta-anisidine almost does not form under the given condi-tions.

Some increase in the H2SO4 concentration (Table 1,experiment No. 2) eliminates the problem of solubilityof Ti(IV) complexes at high concentrations of organicsolvent, provides the possibility to raise the anisoleconcentration in the catholyte and boost the efficiencyof cation-radical substitution. Due to the chain mecha-nism of the electrochemical process (see the scheme;Ti(III) is regenerated by reactions (8) and (9)) the cur-rent efficiency of anisidines in electrolytes containingH2SO4 of 3 and more mole/l exceeds 100%. The maxi-mum total yield of amino compounds is observed in6 M acid (experiment No. 6).

In the absence of organic solvent, the current effi-ciency of anisidines, having passed through the mini-mum in 5–6 M H2SO4 solutions, increases up to an acidconcentration of 13 M [5]. Since in the above experi-ments concentrations of both sulfuric acid and acetoni-trile changed simultaneously, in order to evaluate theeffect of the former parameter on the substitution effi-ciency in aqueous organic electrolytes, anisole wasaminated in acetic acid media at fixed concentrations oforganic solvent. Taking into account that in the pres-ence of CH3CN the highest yield of amino compoundsis observed in 6 M H2SO4, the studies were performedat two concentrations of acetic acid that are close tomaximum possible for solutions containing 6 and 9 MH2SO4 (Table 2), 11 and 7.6 M, respectively.

Data given in Table 2 show that in aqueous organicmedia an increase in the H2SO4 concentration up to 8 Mpromotes the rise of CE of targeted amino compounds.In acetic acid solutions (Table 2) as well as in electro-lytes containing acetonitrile (Table 1), the highest yieldof anisidines was obtained in 6 M H2SO4.

Table 1. Effect of catholyte composition on the results of electrochemical amination of anisole. [Ti(IV)] = 0.1 M, [NH2OH] = 0.2 M,i = –2 mA/cm2, Q = 250 C, T = 40°C

Experiment No. M MCE, %

2 para/ortho ortho para Σ

1 1.5 15.3 2.26 9.00 11.3 8.02 2 16.0 26.3 57.9 84.2 4.43 3 14.9 37.4 78.6 116.0 4.24 4 13.8 45.2 90.3 135.5 4.05 5 12.7 48.5 94.7 143.2 3.96 6 11.6 51.6 95.4 147.0 3.77 7 10.5 56.1 89.8 145.9 3.28 8 9.4 50.4 90.1 140.5 3.69 9 8.3 42.5 78.9 121.4 3.7

cH2SO4, cCH3CN,

Table 2. Results of anisole electrochemical amination in sulfuric acid solutions containing CH3COOH

Experiment No. M MCE, %

2 para/ortho ortho para Σ

1 1.5 11 0.73 1.47 2.20 4.02 2 11 1.34 4.62 5.96 6.93 3 11 5.17 19.77 24.94 7.64 4 11 27.6 65.7 93.3 4.85 5 11 48.6 97.9 146.5 4.06 6 11 53.7 98.7 152.4 3.77 6 7.6 27.6 54.8 82.4 4.08 7 7.6 41.8 78.5 120.3 3.89 8 7.6 45.9 79.2 125.1 3.5

10 9 7.6 41.2 73.7 114.9 3.6

cH2SO4, cCH3COOH,

138



CONCLUSIONSThe study of anisole amination in 1.5–9 M H2SO4

shows that electrosynthesis of monoamino compoundsfrom aromatic substrates should be performed in elec-trolytes with a sulfuric acid concentration of 4–8 M athigh concentrations of organic solvents. A high concen-tration of CH3CN or CH3COOH prevents the formationof disubstituted amination products and provides theconcentration of the aromatic substrate in the catholytesufficient to substantially suppress the reduction reac-tion of amino radicals to ammonia. The use of solventsin sulfuric acid electrolytes allows a 17–18 timesincrease in the efficiency of the electrochemical processunder galvanostatic conditions.

ACKNOWLEDGMENTSThe work was supported by Russian Foundation for

Basic Research (project No. 06-03-32936a).

REFERENCES1. Lisitsyn, Yu.A. and Kargin, Yu.M., Elektrokhimiya,

2000, vol. 36, p. 103 [Russ. J. Elektrochem. (Engl.Transl.), vol. 36, p. ].

2. Lisitsyn, Yu.A., Busygina, N.V., and Kargin, Yu.M.,Ross. Khim. Zh., 2005, vol. 49, p. 121.

3. Lisitsyn, Yu.A. and Kargin, Yu.M., Elektrokhimiya,2004, vol. 40, p. 1129 [Russ. J. Elektrochem. (Engl.Transl.), vol. 40, p. ].

4. Mel’nikov, B.V., Lisitsyn, Yu.A., and Kargin, Yu.M., Zh.Obshch. Khim., 1992, vol. 62, p. 2745.

5. Lisitsyn, Yu.A. and Kargin, Yu.M., Zh. Obshch. Khim.,1993, vol. 63, p. 1312.

6. Spravochnik khimika. T. 2. Osnovnye svoistva neorgan-icheskikh i organicheskikh soedinenii. L.- (ChemistGuide. V.2, Main Properties of Inorganic and OrganicCompounds), Moscow: GNTIKhL, 1963, p. 422.


8. Mel’nikov, B.V., Lisitsyn, Yu.A., Mingazova, G.I., andKargin, Yu.M., Zh. Obshch. Khim., 1991, vol. 61, p. 528.


10. Lisitsyn, Yu.A., Belyaeva, L.V., Sinyashin, O.G., andKargin, Yu.M., Zh. Obshch. Khim., 1999, vol. 69,p. 1196.

11. Nomenklaturnye pravila IYuPAK po khimii. T. 5. Fiz-icheskaya organicheskaya khimiya (IUPAC Nomencla-ture of Chemistry, V. 5, Physical Organic Chemistry),Moscow: VINITI, 1985, 380 p.

12. Syks, P., Mekhanizmy reaktsii v organicheskoi khimii (AGuidebook to Mechanism in Organic Chemistry), Mos-cow: Khimiya, 1991, 448 p.

13. Lisitsyn, Yu.A., Makarova, O.N., and Kargin, Yu.M., Zh.Obshch. Khim., 2001, vol. 71, p. 1249.

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Electrochemical amination. Dilute aqueous organic solutions of sulfuric acid