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Russ.Chem.Bull., Int.Ed., Vol. 56, No. 3, March, 2007
Lyalin and Petrosyan
out at a current of 108 mA and 50 °С. After 4 F mol–1 electricity
were passed, ButOН was salted out from the reaction solution by
the addition of solid NaCl followed by the separation of the
aqueous and organic phases. Under reduced pressure ButOH
was distilled off from the organic fraction. The residue obtained
after distillation (unreacted starting alcohol with an admixture
of NaCl) was mixed with water (5 mL), and the mixture was
treated with СHCl3 (2×10 mL). The organic layer was dried
over Na2SO4, and 2ꢀ(2,4,6ꢀtrimethylphenyl)ethanol (0.67 g) was
obtained after the solvent was distilled off (the substance was
arylacetic acids and revealed the factors determining the
selectivity of the process. It is found that the yield of
benzoic acid formed as the byꢀproduct depends on the
electronic properties of the aryl substituent in a molecule
of the initial alcohol.
Experimental
Experiments were carried out under constant current using a
Bꢀ5ꢀ8 dc source and a temperatureꢀcontrolled (with a Uꢀ1 therꢀ
mostat) undivided cell with the Ni anode (S = 45 cm2) and
Ti cathode (S = 20 cm2). The electric circuit included the couꢀ
lometer designed at the Special Design Bureau of the N. D.
Zelinsky Institute of Organic Chemistry, Russian Academy of
Sciences. The solution was magnetically stirred during elecꢀ
trolysis. Before the process, the Ni anode was activated accordꢀ
ing to an earlier described procedure8: the electrolysis of the
solution containing 0.1 М NiSO4, 0.1 М NaOAc, and 0.005 М
NaOH was carried out at Ja = 1 mA cm–2 with periodical reꢀ
verse of polarity of the electrodes. The latter is necessary to form
a NiOOHꢀcontaining multilayer coating on the anode surface.
The initial 2ꢀphenylethanol, 2ꢀ(2,4,6ꢀtrimethylphenyl)ethaꢀ
nol, 2ꢀphenoxyethanol, 2ꢀ(2ꢀhydroxyethyl)pyridine, and
3ꢀphenylpropanꢀ1ꢀol (Acros) were used without additional puꢀ
rification.
1
identified by Н NMR spectroscopy). Aqueous fractions (after
the alcohol was isolated) were mixed together, acidified with
concentrated НС1 (to pH 1), and extracted with CHCl3
(3×25 mL). The extract was dried over Na2SO4, the solvent was
distilled off, and a white powder (0.12 g) was obtained. Accordꢀ
ing to the data of 1Н NMR spectroscopy, the powder was a
mixture of 2,4,6ꢀtrimethylphenylacetic acid, 2,4,6ꢀtrimethylꢀ
benzoic acid, and 2ꢀ(2,4,6ꢀtrimethylphenyl)ethanol. The molar
ratio of these components in the reaction mixture was deterꢀ
mined as 1 : 0.1 : 0.3 from the integral intensities of signals of
2,4,6ꢀtrimethylphenylacetic acid, 2,4,6ꢀtrimethylbenzoic acid,
and 2ꢀ(2,4,6ꢀtrimethylphenyl)ethanol with δ 6.75 (s, 2 Н,
H arom.), 6.80 (s, 2 Н, H arom.), and 6.70 (s, 2 Н, H arom.),
respectively. Taking into account these data, the yield of
2,4,6ꢀtrimethylphenylacetic and 2,4,6ꢀtrimethylbenzoic acids
was 10 and 1%, respectively, and the conversion of 2ꢀ(2,4,6ꢀtriꢀ
methylphenyl)ethanol was 16%.
The acids obtained by the EO of the alcohols were identified
by 1Н NMR spectroscopy by comparing with the spectra of
authentic samples of benzoic, 2ꢀpyridinecarboxylic, (2ꢀpyriꢀ
dyl)acetic, and 3ꢀphenylpropionic acids (Acros). Authentic
samples of phenoxyacetic9 and 2,4,6ꢀtrimethylbenzoic10 acids
were synthesized by known procedures. The spectra of phenylꢀ
acetic11 and 2,4,6ꢀtrimethylphenylacetic12 acids described in
Electrooxidation of 2ꢀphenoxyethanol. C. A 50% aqueous
solution of ButOH (100 mL), KOH (1.68 g, 0.03 mol), and
2ꢀphenoxyethanol (0.69 g, 0.005 mol) were placed in the cell.
Electrolysis in an alkaline aqueousꢀalcohol medium was carried
out according to method B. After the completion of the elecꢀ
trolysis and isolation of the products (see above), unreacted
2ꢀphenoxyethanol (0.27 g, identified by 1Н NMR spectroscopy,
58% conversion) and a solid substance, being (according to the
1
the literature were used. H NMR spectra were recorded on a
Bruker ACꢀ200 instrument in DMSOꢀd6.
1
Electrooxidation of 2ꢀphenylethanol in an aqueous solution of
NaOH (see Table 1, entry 2). A. A 1 М solution of NaOH
(100 mL) and 2ꢀphenylethanol (0.6 mL, 0.005 mol) were placed
in the cell, and electrolysis was carried out at a current of 270 mA
and 50 °С. After 4 F per mole of starting substance of electricity
were passed (Q = 1930 C), the electrolysis was stopped, the
reaction mixture was stirred for 0.5 h, and the unreacted alcohol
was extracted with CHCl3 (3×30 mL). The extract was dried
over Na2SO4, and CHCl3 was distilled off under reduced presꢀ
sure. A yellow oil, being 2ꢀphenylethanol (according to the data
data of Н NMR spectroscopy) 2ꢀphenoxyacetic acid containꢀ
ing ∼5% 2ꢀphenoxyethanol (0.43 g), were obtained. To purify
the acid, the latter was transformed into the salt by the treatꢀ
ment with a solution of NaOH (0.2 g, 0.005 mol) in water
(5 mL), and 2ꢀphenoxyethanol was extracted with CHCl3
(2×3 mL). The organic extract was rejected, and the aqueous
solution was acidified with concentrated HCl (to pH 1) and
extracted with СНС13 (2×3 mL). After the solvent was distilled
off, 2ꢀphenoxyacetic acid was obtained (0.33 g, 43%), m.p.
100 °С (cf. Ref. 9: m.p. 99 °С). 1H NMR, δ: 6.90—7.25 (m, 5 Н,
H arom.); 4.55 (s, 2 Н, СН2).
1
of Н NMR spectroscopy), was obtained (0.22 g). The aqueous
solution was acidified with concentrated HCl (to рН 1) and
extracted with CHCl3 (2×30 mL). The organic extract was dried
over Na2SO4, the solvent was distilled off, and a crystallizing oil
was obtained (0.35 g), being a mixture (according to the data of
1Н NMR spectroscopy) of phenylacetic and benzoic acids. The
molar ratio of phenylacetic and benzoic acids was determined as
1 : 0.5 from the integral intensities of signals of phenylacetic and
benzoic acids with δ 7.25 (s, 5 Н, H arom.) and 8.05—7.50 (m,
5 Н, H atom.), respectively. Taking into account these data, the
yields of phenylacetic and benzoic acids were 34 and 19%, reꢀ
spectively, and the conversion of 2ꢀphenylethanol was 64%.
Electrooxidation of 2ꢀ(2,4,6ꢀtrimethylphenyl)ethanol.
B. A 50% aqueous solution of ButOH (100 mL), KOH (1.68 g,
0.03 mol), and 2ꢀ(2,4,6ꢀtrimethylphenyl)ethanol (0.83 g,
0.005 mol) were placed in the cell, and electrolysis was carried
Electrooxidation of 2ꢀ(2ꢀhydroxyethyl)pyridine. A solution
of NaOH (100 mL) and 2ꢀ(2ꢀhydroxyethyl)pyridine (0.57 mL,
0.005 mol) were placed in the cell. Electrolysis was carried out
according to method A. After the completion of the electrolysis,
the unreacted alcohol was removed by extraction with СНС13
(3×35 mL). The extract was dried over Na2SO4, the solvent was
distilled off, and an oil (0.15 g) was obtained, which was
unreacted 2ꢀ(2ꢀhydroxyethyl)pyridine identified by 1Н NMR
spectroscopy. The aqueous phase was acidified with concentrated
HCl (to pH 1), water was distilled off under reduced pressure,
and the solid residue was treated with acetone (1×15 mL) and
EtOH (3×25 mL) and filtered. The filtrates were mixed, the
solvents were distilled off, and an oil (0.75 g), which was (acꢀ
cording to the data of 1Н NMR spectroscopy) a mixture
of 2ꢀpyridinecarboxylic acid, (2ꢀpyridyl)acetic acid, and