Primary alkanols: oxidative homocondensation in water and cross-condensation in methanol

Article abstract of DOI:10.1007/s11172-015-1236-4

Water was used as a reaction medium and a reagent in oxidation of primary alkanols to dimeric esters and alkanoic acids using either molecular bromine or a hydrogen peroxide—hydrobromic acid mixture as the oxidants. The similar reaction in methanol produced methyl alkanoates.

Full text of DOI:10.1007/s11172-015-1236-4

Russian Chemical Bulletin, International Edition, Vol. 64, No. 12, pp. 2845—2850, December, 2015
2845
Primary alkanols: oxidative homocondensation in water
and crossꢀcondensation in methanol
G. I. Nikishin, L. L. Sokova, A. O. Terent´ev, and N. I. Kapustina
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
4
7 Leninsky prosp., 119991 Moscow, Russian Federation.
Eꢀmail: kap@ioc.ac.ru
Water was used as a reaction medium and a reagent in oxidation of primary alkanols to
dimeric esters and alkanoic acids using either molecular bromine or a hydrogen peroxide—
hydrobromic acid mixture as the oxidants. The similar reaction in methanol produced methyl
alkanoates.
Key words: oxidation, water, methanol, alkanols, carboxylic acids, esters, bromine, hydrogen
peroxide, hydrobromic acid.
2
8
Oxidation of alkanols to aldehydes, ketones, and
alkanoic acids is one of the fundamental reactions in orꢀ
ganic chemistry widely used in science and technology
and is still of academic interest. In recent years, a new
approach to oxidation of primary alkanols was developed.
This is oxidative condensation of primary alkanols to
alkanoates without the use of the corresponding alkanoic
acids as the starting reagents. This strategy was impleꢀ
mented in the synthesis of two type of esters, namely,
methyl esters (by crossꢀcondensation of alkanols and arylꢀ
alkanols with methanol) and "dimeric" esters (by homoꢀ
condensation of two molecules of the same alkanol). Synꢀ
thesis of methyl alkanoates was accomplished in the
sized by oxidation of alkanols with Pb(OAc) —MHal
4
2
9
and Ce(NH ) (NO ) —LiBr using mechanochemical
4
2
3 6
3
0
activation, as well as with Ce(SO ) —LiBr in water.
4
2
It is of note that the role of water in the homoꢀ and
crossꢀcondensations of alkanols has not been yet discussed
in detail. However, water strongly affects these processes:
the oxidations in pure water and in the dispersion water—
alkanol proceed in different directions and with different
selectivities.
In the present work, we evaluated the role of water as
both a reaction medium and a reagent in oxidation of
primary alkanols to alkanoic acids and alkanoates. Oxidaꢀ
tion was mediated by either molecular bromine or a hyꢀ
drogen peroxide—hydrobromic acid system as a source of
bromine.
1
presence of the following oxidizing agents: Ca(OCl) ,
2
t
2
3
4
Bu OCl/pyridine , PhIO/KBr, I /K CO , TsNBr2/
K CO , and trichloroisocyanuric acid. Methyl benzoates
2
2
3
5
6
2
3
were synthesized by the reactions of benzylic alcohols with
Results and Discussion
7
8
methanol mediated with NaIO /LiBr, MnO /NaCN,
4
2
9
10
ZnBr /H O , and H O /HBr oxidizing systems. The
2
2
2
2
2
Oxidation with molecular bromine. In the present work,
we pioneered in using molecular bromine as a stoichioꢀ
metric reagent for selective homoꢀ and crossꢀcoupling of
primary alkanols 1a—h. Treatment of solutions of primary
alkanols 1b,c,e,g in methanol with bromine yielded methyl
esters 2b,c,e,g (Scheme 1, Table 1).
reactions under aerobic conditions were performed with
1
1
12,13
14
15
CBr or catalytic systems involving Pd
, Au , Co ,
4
1
6
17
Ru, and Ir in the presence of hydrogen acceptor inꢀ
stead of the oxidizing agent. In the reactions with benzylic
alcohols, not only methanol was used but also other esterꢀ
ifying alcohols1
2—14,15,18
19
and Nꢀhydroxysuccinimide.
Crossꢀcondensations of alkanols to give dimeric esters
have been carried out in the presence of redox catalysts
Scheme 1
(
mediators) in the reaction media consisting of water/
waterꢀmiscible organic solvent. The oxidizing systems were
2
0
21
22
NaBrO —HBr, H O —HBr, oxone—NaBr, oxone—
3
2
2
NaCl,23 H O —KBr—PhSO H, and PhI(OAc) —KBr
24
2
2
3
2
2
4
in ethyl acetate, pyridinium chromate—Al O (solventꢀ
2
3
free),2 pyridinium hydrobromide perbromide in water.
6
27
In our research group, dimeric esters have been syntheꢀ
R = Pr (b), Bu (c), C H (e), C H (g)
6
13
8 17
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2845—2850, December, 2015.
066ꢀ5285/15/6412ꢀ2845 © 2015 Springer Science+Business Media, Inc.
1

2
846
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015
Nikishin et al.
Table 1. Oxidation of alkanols with bromine in methanola
Conversions of alkanols 1c,e,g at 40 °C for 18—20 h at
a reagent molar ratio 1 : Br = 1 : 4 were 94—98% and
2
b
Entry Alkanol
Molar
ratio 1 : Br2
t/°C Conversion Yield (%)
show a decrease (up to ∼ 90%) with a decrease in the reacꢀ
tion temperature (to 20 °C). These conditions are optimal
for the synthesis of methyl esters 2. The only exception is
butanꢀ1ꢀol (1b), whose conversions were 65—47% deꢀ
pending on the reaction temperature. The reaction perꢀ
formed with 1.6ꢀfold less amount of bromine (from 4 to
of 1 (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1b
1b
1c
1c
1c
1c
1e
1e
1e
1e
1g
1g
1g
1g
1 : 4
1 : 4
1 : 2.5
1 : 2.5
1 : 4
20
40
20
40
20
40
20
40
20
40
20
40
20
40
47
65
61
83
75
94
71
82
89
98
65
82
83
96
2b, 90
2b, 93
2c, 95
2c, 95
2c, 94
2c, 93
2e, 96
2e, 94
2e, 95
2e, 95
2g, 97
2g, 95
2g, 96
2g, 96
2
.5 mol per 1 mol of alkanol) proceeds with a 1.2ꢀfold
reduced conversion (see Table 1, cf. entries 4 and 6, 8 and
0, 12 and 14). The amount of bromine exceeding the
1 : 4
1 : 2.5
1 : 2.5
1 : 4
1
stoichiometric value is consumed in the side reaction,
namely, in oxidation of methanol. It is of note that under
all oxidation conditions the yields of methyl esters 2b,c,e,g
were above 90%. Due to the large excess of methanol over
alkanols 1b,c,e,g (125 : 1), the yields of dimeric esters
0
1
2
3
4
1 : 4
1 : 2.5
1 : 2.5
1 : 4
1 : 4
(
RCOOCH R) 3b,c,e,g were very low (see Table 1).
2
At the same time, oxidation of alkanols 1c,e,g in water
(Scheme 2, Table 2, entries 5—8, 17, and 18) produces
esters 3c,e,g in high yields and selectivity.
a
b
Reaction conditions: 1 (1 mmol), MeOH (4 mL), 18—20 h.
Conversion of compound 1 and yields of products 2 and 3
(
RCOOCH R) were determined by GC using internal standard.
2
Yields are calculated on the basis of the converted alkanol 1.
Yields of compounds 3b,c,e,g were ∼ 1—2%.
Surprisingly, alkanoic acids were obtained only in trace
amounts. This is especially characteristic of acids 4e,g,
Table 2. Oxidation of alkanols with bromine in water and water—methanol solutiona
b
Entry
Alkanol
Molar
Solvent
Conversion
Yield (%)
ratio 1 : Br2
of 1 (%)
2
3
4
1
2
3
4
5
6
7
8
9
1a
1a
1b
1b
1с
1с
1e
1e
1e
1 : 2.5
1 : 4
1 : 2.5
1 : 4
1 : 2.5
1 : 4
1 : 2.5
1 : 4
H O
60
87
76
89
92
96
98
99
95
—
—
—
—
—
—
—
—
2e, 94
—
—
4a, 95
4a, 96
4b, 76
4b, 87
4c, 11
4c, 15
2
H O
2
H O
3b, 17
3b, 81
3c, 87
3c, 84
3e, 96
3e, 93
3e, 21
2
H O
2
H O
2
H O
2
c
H O
4e
4e
2
c
H O
2
c
1 : 2.5
H O—MeOH
4e
2
(
1 : 1)
10
11
12
13
14
15
16
1e
1e
1e
1e
1e
1e
1e
1 : 4
H O—MeOH
97
97
99
96
98
95
99
2e, 92
2e, 40
2e, 38
2e, 27
2e, 21
—
3e, 41
3e, 55
3e, 53
3e, 67
3e, 70
3e, 71
3e, 37
4ec
4ec
2
(1 : 1)
1 : 2.5
1 : 4
H O—MeOH
2
(5 : 1)
H O—MeOH
4ec
2
(5 : 1)
1 : 2.5
1 : 4
H O—MeOH
4ec
2
(
10 : 1)
H O—MeOH
4ec
2
(
10 : 1)
1 : 2.5
1 : 4
H O—MeCN
4e, 26
4e, 60
4gc
2
(1 : 4)
H O—MeCN
—
2
(1 : 4)
1
1
7
8
1g
1g
1 : 2.5
1 : 4
H O
H O
96
98
—
—
3g, 97
3g, 94
2
c
4g
2
a
b
Reaction conditions: 1 (1 mmol), solvent (4 mL), 18—20 h, 20 °C.
Conversion of compound 1 and yields of products 2, 3, and 4 were determined by GC using internal
standard. Yields are calculated on the basis of the converted alkanol 1.
c
Yield was ∼ 1—3%.

Oxidation of alkanols
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015 2847
Scheme 2
water and methanol favored highly selective formation of
methyl ester 2e (see Table 2, entries 9 and 10). As methaꢀ
nol content decreases, the solution turns into two phases
(
see Table 2, entries 11—14). However, not all heptanꢀ1ꢀ
ol (1e) forms the dispersed phase, some amount of 1e is
present in continuous phase (water—methanol). Under
these conditions, despite a 50ꢀfold molar excess of methaꢀ
nol relative 1e (entries 13 and14), heptanꢀ1ꢀol 1e oxidizes
mostly to dimeric ester 3e and in lesser extent to methyl
ester 2e. As expected, oxidation of 1e in a homogeneous
i.e., water does not participate in oxidations carried out in
water as a solvent. This fact can be explained by different
types of the oxidation media. In methanol, the reaction
proceeds in homogeneous solution; while in water, the
reaction takes place in dispersion containing water and
waterꢀinsoluble aggregated alkanol particles. Vigorous stirꢀ
ring of the reaction mixture results in formation of the
emulsion and drops of alkanols. Alkanols are oxidized to
dimeric esters inside of the aggregated particles; the oxiꢀ
solution H O—MeCN follows two directions producing
2
both dimeric ester 3e and heptanoic acid 4e (see Table 2,
entries 15 and 16).
Oxidation with hydrogen peroxide—hydrobromic acid.
Bromine is an efficient, convenient, and easy to use oxiꢀ
dizing agent for alkanols; however, its application for the
synthesis of esters leads to sideꢀreactions giving large
amounts of hydrogen bromide. Taking this fact into acꢀ
count, we elaborated another approach to methyl esters
and dimeric esters, which is more economically favorable
and more attractive from the viewpoint of green chemisꢀ
try. Hydrogen peroxide was chosen as a stoichiometric
oxidizing agent and hydrobromic acid was chosen as a
redox catalyst. Oxidation of alkanols 1d—g under optiꢀ
mum conditions in MeOH results in methyl esters 2d—g
in the yields up to 93% (Table 3, entries 3, 4, 6, and 8).
Similarly to oxidation with bromine, it is more difficult to
oxidize butanꢀ1ꢀol (1b) even under these conditions. The
reaction starts from generation of bromine from hydroꢀ
bromic acid, then both oxidation of alkanols and regenerꢀ
ation of bromine from a newly formed HBr molecules
occur in the repeating cycles. Syntheses of methyl esters
are shown on Scheme 4 and are summarized in Table 3.
dation involves formation of aldehyde, acid bromide, and
its subsequent alcoholysis2
,7,10,21
(another plausible mechꢀ
3,4
anism involves formation and oxidation of hemiacetal ).
Alkanols can react with water only on the surface of these
particles to give alkanoic acids in yields not exceeding 1—2%.
In contrast to alkanols 1b,c,e,g, propanꢀ1ꢀol (1a) is suffiꢀ
ciently miscible with water; consequently, the oxidation
proceeds in the homogeneous water—propanol solution.
This process results selectively in propionic acid (4a), no
dimeric propyl propionate (3a) is detected (Scheme 3, see
Table 2). In this case, water is not only solvent, but also
plays a role of reagent actively participating in hydrolysis
of propionyl bromide.
Scheme 3
Scheme 4
Butanꢀ1ꢀol (1b) is poorly water soluble (7.9 g per 100 mL
of water at 20 °C), but this is enough to cause the oxidaꢀ
tion of 1b predominantly in solution to give butyric acid
1
, 2: R = C H (d), EtCH(Me)CH (h)
5 11 2
(
4b) with small traces of butyl butyrate (3b) (see Table 2).
Pentanꢀ1ꢀol (1c) is soluble in water in lesser extent
∼ 2.7 g per 100 mL of water at 20 °C); therefore, its reacꢀ
Along with methyl esters, the reaction produces dimeric
(
esters and alkanoic acids but in noticeably lower yields.
The product ratio depends on both the reagent ratio and
the water solubility of alkanols. The oxidation procedure
involves portionwise addition of hydrogen peroxide at
a uniform rate to a stirred solution of alkanol and hydroꢀ
bromic acid in methanol. During first hours of the reacꢀ
tion, the mixture is homogeneous containing a large
amount of methanol; these conditions favor formation of
tion produces pentanoic acid (4c) in 11—15% yield with
the major product (84—87%) being pentyl pentanoate (3c).
The effects of a reaction medium are clearly seen not
only for the reactions carried out in water but also in waꢀ
ter—methanol solution (see Table 2, entries 9—14). Using
heptanꢀ1ꢀol (1e) as an example, it was shown that the use
of a homogeneous solution containing equal amounts of

2
848
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015
Nikishin et al.
a
Table 3. Oxidation of alkanols 1 with HBr—H O in methanol
Table 4. Oxidation of alkanols 1 with HBr—H O in water and
2
2
2
2
water—methanol solutiona
b
Entry Alkanol
Conversion
Yield (%)
b
of 1 (%)
Entry Alkanol
Solvent Conversion
Yield (%)
2
3
4
of 1 (%)
2
3
4
1
2
3
4
5
6
7
8
9
1
1b
1c
1d
1e
1e
1f
65
90
88
83
98
90
98
92
98
80
2b, 65
2c, 77
2d, 89
2e, 91
2e, 80
2f, 92
2f, 79
2g, 93
2g, 81
2h, 86
—
3c
3d
4b, 32
4c, 22
4d, 9
d
1
2
3
1a
1b
H O
60
82
60
—
—
—
—
4a, 96
2
d
H O
3b, 10 4b, 88
3b, 31 4b, 95
2
3e, 3
3e, 15 4e, 3
3f, 7
3f, 19
3g, 4
4e, 4
1b H O—MeOH
2
с
с
(5 : 1)
d
4f
4f
4g
4
5
6
1e
1e
H O
98
80
95
—
—
—
3e, 86 4e, 12
3e, 99
3e, 24 4e, 73
2
d
c
1f
H O
—
2
d
d
1g
1g
1h
1e H O—MeCN
2
с
3g, 17 4g
3h, 12 4hd
(1 : 9)
0
7
8
9
1e H O—MeOH
93
96
98
2e, 7 3e, 89 4e, 21
2e, 12 3e, 83 4e, 31
2e, 45 3e, 50 4e, 41
2
(
5 : 1)
a
Reaction conditions: 1 (1 mmol), reagent ratio is 1 : HBr : H O =
1 : 1.5 : 10, MeOH (3 mL), 7—9 h, 65—70 °C.
Conversion of compound 1 and yields of products 2, 3, and 4
were determined by GC using internal standard. Yields are calꢀ
culated on the basis of the converted alkanol 1.
2
2
1e H O—MeOH
2
=
b
(5 : 2)
1e H O—MeOH
2
(1 : 1)
1
1
0
1
1f
1f
H O
H O—MeOH
98
93
—
3f, 90 4f, 71
2f, 71 3f, 91
2
c
MeOH (2 mL).
Yield was ∼ 1—2%.
—
2
d
(5 : 1)
1
1
2
3
1g
H O
98
95
—
3g, 96 4g, 21
2
1g H O—MeOH
2g, 8 3g, 90
—
2
methyl esters. For instance, 4 h after the reaction onset
(5 : 1)
(
2
see Table 3, entry 8) the molar ratio of esters 2e : 3e was
4; whereas after completion of the reaction (9 h after the
a
Reaction conditions: 1 (1 mmol), reagent ratio is 1 : HBr : H2O2
1 : 1.5 : 10, solvent (5 mL), 7—9 h; 65—70 °C.
=
reaction onset), 2e : 3e was 4. As the reaction goes to comꢀ
pletion, the increase in the water content makes the reacꢀ
tion mixture cloudy and partially twoꢀphase thus leading
to the formation of dimeric esters. This explanation is in
agreement with the results of the experiments 4, 6, 8 and
b
Conversion of compound 1 and yields of products 2, 3, and 4
were determined by GC using internal standard. Yields are calꢀ
culated on the basis of the converted alkanol 1.
c
Reagent ratio was 1e : HBr : H O = 1 : 1.5 : 5.
2
2
5
, 7, 9 (see Table 3). Note that the methanol content in
experiments 5, 7, and 9 was decreased 1.5ꢀfold. A decrease
in the content of methanol in the reaction mixture causes
formation of a two phase dispersion, which favors the
dimeric ester formation. As a result, the yield of the dimeric
esters increases from 3—7% to 15—19%. Alkanols disꢀ
solved in water phase are oxidized to alkanoic acids.
In contrast to oxidation in methanol, upon aqueous
oxidation of alkanols 1e—g the twoꢀphase system is formed
immediately after the reaction onset. Under these condiꢀ
tions, alkanols nearly quantitatively produce the correꢀ
sponding dimeric esters 3e—g (Table 4). Addition of acetoꢀ
nitrile destroys two phase system water—heptanꢀ1ꢀol (1e);
as a result, oxidation occurs in homogeneous medium giving
heptanoic acid 4e as a major product instead of dimeric
ester 3e, the product ratio 4e : 3e being 3 : 1 (Scheme 5;
see Table 4, entry 6). In these cases, water actively particꢀ
ipates in the reaction.
Aqueous oxidation of propanꢀ1ꢀol (1a) and butanꢀ1ꢀol
(1b) with the H O —HBr system proceeds analogously to
2
2
oxidation with bromine: compound 1a gives selectively
propionic acid (4a), compound 1b produces butanoic acid
(4b) and butyl butyrate (3b) in a ratio of ∼ 9 : 1 (see Table 4,
entries 1 and 2).
Alkanols 1e—g are oxidized in the water—methanol
(5 : 1) solution in two phase system. Under these condiꢀ
tions, similarly to oxidation with bromine, despite a 50ꢀfold
Scheme 5

Oxidation of alkanols
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015 2849
excess of MeOH relative to 1e—g, the yields of dimeric
esters 3e—g exceed by one order of magnitude those of
methyl esters 2e—g (see Table 4, entries 7, 11, and 13).
gen peroxide (35% aqueous solution, pure grade) and bromine
(
99%+) available from Acros Organics were used as purchased.
Hydrobromic acid (48% aqueous solution, pure grade) was used
without additional purification.
Bromineꢀmediated oxidation of primary alkanols 1a—h in
methanol (general procedure). A mixture of alkanol 1 (1 mmol)
and MeOH (4 mL) was vigorously stirred with bromine at 20 °C
An increase in the methanol content (H O : MeOH =
2
=
5 : 2, see Table 4, entry 8) does not virtually effect the
outcome of oxidation of alkanol 1e. At H O : MeOH =
2
=
1 : 1, the dispersion phase is partially destroyed and
oxidation follows two directions affording two esters
2e and 3e) in nearly equal amounts (see Table 4, entries 8
(
or 40 °C) for 18—20 h (the reagent molar ratios are given in
Table 1). After completion of the reaction indicated by a color
change of the reaction mixture from red to lightꢀorange, water
(10—15 mL) was added and the mixture was extracted with diꢀ
ethyl ether ((3×20 mL). The combined organic layers were
washed with saturated aqueous NaHCO3 (10—15 mL), water
(
and 9). A divergence in the reaction outcome between
experiments 8 and 9 from Table 4 and experiments 9 and
1
0 from Table 2, which were carried out at the same ratio
(
10—15 mL), dried with MgSO , and the solvent was removed
4
MeOH : H O (1 : 1), can be explained by actually higher
2
in vacuo. The conversions of the starting alkanols and the prodꢀ
uct yields were determined by GC using an internal standard.
Bromineꢀmediated oxidation of primary alkanols 1a—h in
methanol—water (general procedure). A mixture of alkanol 1
(1 mml) and a methanol—water mixture (4 mL) was vigorously
stirred with bromine at 20 °C for 19—20 h (the reagent molar
ratios are given in Table 2). Then water (10—15 mL) was added,
the mixture was extracted with diethyl ether (3×20 mL). The
combined organic layers were washed with water (2×15 mL),
content of water in experiments 8 and 9 from Table 4 due
to the use of aqueous solutions of hydrogen peroxide and
hydrobromic acid.
1H NMR spectra of methyl (2) and dimeric (3) esters
exhibit signals characteristic of these molecules: at δ 2.3—2.4
(
t, CH COO) and 3.5—3.6 (s, C(O)OCH ) for 2; at
2
3
δ 2.3—2.4 (t, CH COO) and 4.0—4.1 (t, C(O)OCH ) for 3.
2
2
13
C NMR spectra contain signal of the C=O group carbon
dried with MgSO , and the solvent was removed in vacuo.
4
atoms at δ 171—174.
The conversions of alkanols and the product yields were deterꢀ
mined by GC.
In summary, formation of the disperse medium is
a decisive factor promoting oxidative homocondensation of
primary alkanols in water. Destruction of the dispersion
by adding acetonitrile leads to oxidation in homogeneous
solution giving predominantly alkanoic acids. Water
soluble alkanols producing homogeneous solutions are
oxidized to alkanoic acids, formation of dimeric esters
under these conditions was not detected. In methanol,
alkanols are oxidized to methyl esters; in water—methaꢀ
nol mixture they produce alkanoic acids, methyl and
dimeric esters in the ratio depending on both the water
solubility of alkanols and the water : methanol ratio. Oxiꢀ
dative homocondensation of alkanols and crossꢀcoupling
with methanol upon treatment with bromine were taken
as the basis for elaboration of the simple and versatile
preparative procedures towards dimeric and methyl esters
of alkanoic acids.
Oxidation of primary alkanols 1a—h with H O —HBr in methꢀ
2
2
anol or in a water—methanol mixture (general procedure). To
a vigorously stirred solution of alkanol 1 (1 mmol) in 48% HBr in
MeOH or MeOH—H O, a solution of H O (35%) in the correꢀ
2
2
2
sponding solvent (1—1.5 mL) was added by portions (0.2—0.25 mL)
at 65—70 °C (the reagent molar ratios are given in Tables 3 and 4).
After addition of the first portion of the H O solution, the reacꢀ
2
2
tion mixture turned to light yellow and after 20—30 min was
colorless. Then the next portion of hydrogen peroxide was added.
After completion of the reaction, the mixture was cooled, exꢀ
tracted with diethyl ether (3×15 mL), the combined organic
layers were washed with water, dried with MgSO , and the solꢀ
4
vent was removed in vacuo. The conversions of alkanols and the
product yields were determined by GC.
The structures of all synthesized compounds 2, 3, and 4 were
1
13
confirmed by H and C NMR spectroscopy and IR spectroꢀ
scopy. The products were isolated by silica gel column chromatoꢀ
graphy.
Experimental
This work was financially supported by the Russian
Science Foundation (Project No. 14ꢀ23ꢀ00150).
GC analysis was performed on a Chromꢀ5 chromatograph
with the flameꢀionization detector and 3000×3 mm analytical glass
columns with 5% SEꢀ30 and 5% FFAP on Chromaton NꢀAWꢀ
HMDS (0.16—0.20 mm). The product yields were determined
by an internal standard method with the empirical correlation
coefficients. IR spectra were recorded on a Perkin—Elmer 577
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Received June 3, 2015;
in revised form September 8, 2015