Bromination of ketones with the systems H2O2-LiBr- CeIII and H2O2-LiBr-CeIV

Article abstract of DOI:10.1007/s11172-013-0166-2

A new method for the synthesis of α-bromoketones was suggested. The C₅-C₁₁ linear and branched ketones in the reaction with the systems H₂O₂-LiBr-Ce^III and H ₂O₂-LiBr-Ce^IV in acetonitrile were brominated at α-position. The reaction is highly selective.

Full text of DOI:10.1007/s11172-013-0166-2

1
214
Russian Chemical Bulletin, International Edition, Vol. 62, No. 5, pp. 1214—1217, May, 2013
Bromination of ketones with the systems
III
IV
H O —LiBr—Ce and H O —LiBr—Ce
2
2
2
2
G. I. Nikishin, L. L. Sokova, 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
A new method for the synthesis of ꢀbromoketones was suggested. The C —C linear and
5
11
III
IV
branched ketones in the reaction with the systems H O —LiBr—Ce and H O —LiBr—Ce
2
2
2
2
in acetonitrile were brominated at ꢀposition. The reaction is highly selective.
Key words: bromination, ketones, bromo ketones, hydrogen peroxide, lithium bromide,
oxidation, cerium(III) nitrate, cerium(IV) ammonium nitrate.
Halogenation processes take one of the central places
The purpose of the work was to develop a new approach in
the use of cerium salts in organic reactions, where the
in organic synthesis, are widely represented in chemical
laboratory practice, are used in industry. Besides tradiꢀ
tional technique of halogenation with aggressive, toxic,
and frequently inconvenient in handling chlorine, bromine,
and iodine, other methods using milder halogenating
agents are developed. Halogenation with such agents is
most often used for compounds containing carbon—carbꢀ
on multiple bonds, aromatic rings, and activated methyl
and methylene groups. Hydrohalic acids and their Li, Na,
and K salts in the combination with oxidants serve as the
source of halogen. Hydrogen peroxide is especially effiꢀ
IV
III
Ce and Ce salt performed the function of the redox
catalyst in the combination with the stoichiometric oxiꢀ
dant, hydrogen peroxide. We effected this approach for
the first time in the oxidation of alkanols to esters by the
III
system H O —LiBr—Ce (see Ref. 14) and in the bromiꢀ
2
2
1
5
nation of alkenols to vicinal dibromoalkanols. This apꢀ
proach resulted in the decrease of the consumption of
expensive and not quite convenient (because of the high
molecular weight) oxidant CAN, replacing it with the enꢀ
vironmentally friendly and chip hydrogen peroxide.
The bromination of ketones was performed using three
modifications: with the stoichiometric amount of CAN
with respect to the ketone (procedure A), with the catalytꢀ
ic amount of CAN in the combination with H O (proceꢀ
1
cient in the role of the oxidant (see review and references
2
—4
sited therein). tertꢀButyl peroxide,
a complex of hydroꢀ
6,7
5
gen peroxide with urea, and oxone were also used.
Among other oxidant, ceric ammonium nitrate (CAN)
successfully used in many reactions of organic synthesis,
including bromination reactions, also attracted the attenꢀ
tion.8 Thus, alkenes, cycloalkenes, alkenylarenes add
bromine upon the action of CAN and KBr to be converted
to the corresponding vicinal dibromides. Methyl 2,3ꢀdiꢀ
bromoꢀ3ꢀphenylpropionate was obtained from methyl cinꢀ
2
2
dure B), and with the catalytic amount of CN in the comꢀ
bination with H O (procedure C). Bromine involved in
2
2
the bromination reaction was generated from LiBr upon
IV
III
the action of Ce . The Ce salt used as the starting reꢀ
IV
agent (or formed from Ce in the course of the reaction)
was oxidized by hydrogen peroxide to Ce . Thus, several
IV
9
namate . Cinnamic acid itself under similar conditions
oxidationꢀreduction cycles were subsequently repeated inꢀ
IV
decarboxylates to be converted to -bromostyrene, no adꢀ
dition of bromine is observed in this case.1 The solidꢀ
phase reactions of -arylacrylic acids with CAN—LiBr
volving Ce salt as the redox catalyst in the bromination
0
process (Scheme 1). The steps of this cycle we described
1
4,16,17
in the preceding publications.
1
1
also lead to ꢀbromostyrenes. Alkylaromatic hydroꢀ
carbons undergo bromination in this oxidation system at
the side chain,12 whereas activated aromatic compounds
Scheme 1
are reacted at the aromatic ring.1 In the cited works,
CAN was exclusively used as a stoichiometric oxidant.
In the present work, we report the results on the bromꢀ
ination of aliphatic ketones upon the action of the oxidaꢀ
tive systems H O —LiBr—Ce(NH ) (NO ) (CAN) and
3
Hydrogen bromide formed in the bromination reacꢀ
tion together with -bromoketone was oxidized by hydroꢀ
gen peroxide and Ce salt to bromine. Under the optimal
2
2
4 2
3 6
IV
H O —LiBr—Ce(NO ) •6H O (cerium nitrate (CN)).
2
2
3 3
2
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1214—1217, May, 2013.
066ꢀ5285/13/6205ꢀ1214 © 2013 Springer Science+Business Media, Inc.
1

Bromination of ketones
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 5, May, 2013
1215
conditions, the conversion of LiBr and the yields of
Table 2. Bromination of ketones 1a—f by the system H2O2—
LiBr—Ce /Ce
III
IVa

ꢀbromoketones were close to the quantitative.
Six C —C linear and branched ketones (1a—f) were
chosen as the objects of our studies (Scheme 2, Tables 1
and 2).
5
11
Ketone
a—f
Proceꢀ
dure
Converꢀ
sion of
Product
Yieldb
of 2a—f
(%)
1
1
a—f (%)
EtCOEt (1a)
A
B
C
A
B
C
A
B
C
A
99
97
96
95
93
93
98
92
78
95
EtCOCHBrMe (2a)
97
96
95
92
90
89
95
90
75
93
Scheme 2
1
1
a
a
2a
2a
PrCOPr (1b)
PrCOCHBrEt (2b)
1
1
b
b
2b
2b
BuCOBu (2c)
BuCOCHBrPr (2c)
2
2
c
c
2c
2c
i. CAN, LiBr (A); ii. CANcat, H O , LiBr (B); iii. CN , H O ,
2
2
cat
2
2
AmCO C H
AmCOCHBrBu (2d)
5
11
LiBr (C)
(1d)
1
1
d
d
B
C
93
65
95
97
96
85
63
45
2d
2d
90
65
94
95
95
83
60
40
a: R = Et, R´ = H, R = Me; b: R = Pr, R´ = H, R = Et;
c: R = Bu, R´ = H, R = Pr; d: R = Am, R´ = H, R = Bu;
e: R = Bu , R´ = R = H; f: R = Pr , R´ = R = Me
t
i
t
t
Bu COMe (1e) A
1
1e
Pr COPr (1f)
1f
1
Bu COCH Br (2e)
2
e
B
С
A
B
C
2e
2e
Dibutylketone (1c) was chosen as a model compound
to study the dependence of the conversion and the yields
of 4ꢀbromononanꢀ5ꢀone (2c) from the procedure of bromꢀ
ination (A, B, C) and the ratio of reagents (see Table 1).
The selection of the bromination conditions was considꢀ
i
i
i
Pr СOCBrMe (2f)
2
2f
2f
f
a
Reaction conditions: 1a—f (1 mmol), the molar ratio
: Ce : LiBr : H O : H SO
: Ce : LiBr : H O : H SO
IV
1
1
=
1 : 2.5 : 1 : 0 : 0.2 (A),
= 1 : 0.3 : 1 : 10 : 0.2 (B),
2
2
2
4
IV
2
2
2
4
Table 1. Bromination of ketone 1c by the system H O —LiBr—
III
2
2
1 : Ce : LiBr : H O : H SO = 1 : 0.3 : 1 : 10 : 0.2 (C), CH CN
2 2 2 4 3
III
IVa
Ce /Ce
(
10 mL), 65—70 C, 5—6 h and 10—12 h (procedure A and proꢀ
III
cedure B, respectively), 10—12 h (procedure C), Ce
Ce(NO ) •6H O, Ce is Ce(NH ) (NO ) .
b
is
CeIII
Ce
/
Converꢀ Yieldb
sion of 1c of 2c
IV
Entry
Molar
ratio
3
3
2
4 2
3 6
IV
Calculated based on the amount of ketones 1a—f taken for the
1
c : Ce : LiBr : H O : H SO
4
reaction.
2
2
2
%
1
2
1 : 0 : 1 : 0 : 1
1 : 0 : 1 : 10 : 1
—
—
—
—
—
—
erably determined by the purpose to obtain high yields of

ꢀbromoketones with the high conversion of the starting
Procedure A
reagents and simple experimental procedure, i.e., the purꢀ
pose to develop a procedure easily adapted for the use in
the preparative syntheses.
Procedure A (stoichiometric amount of CAN, see Table 1,
entries 3—6). In the absence of CAN, lithium bromide
cannot generate bromine upon the action of only H O or
IV
3
4
5
6
1 : 2.5 : 1 : 0 : 0
1 : 2.5 : 1 : 0 : 0.1
1 : 2.5 : 1 : 0 : 0.2
Ce
50
73
98
90
45
73
95
85
IV
Ce
Ce
Ce
IV
IV
1 : 2.5 : 1 (HBr) : 0 : 0
Procedure B
2
2
IV
7
8
9
1
1
1
1 : 0.3 : 1 : 5 : 0
1 : 0.3 : 1 : 10 : 0
1 : 0.3 : 1 : 10 : 0.1
1 : 0.3 : 1 : 10 : 0.2
1 : 0.3 : 1 : 5 : 0.2
1 : 0.2 : 1 : 10 : 0.2
Ce
Ce
Ce
Ce
Ce
Ce
45
75
75
92
60
56
45
73
75
90
60
56
only H SO , thus failing to cause the bromination reꢀ
2
4
IV
action of ketone 1c (entries 1, 2). At the molar ratio
c : CAN : LiBr = 1 : 2.5 : 1, the conversion of 1c and the
IV
1
IV
IV
IV
0
1
2
yield of bromoketone 2c were 50 and 45%, respectively.
When sulfuric acid was added to the oxidation system in
the amount of 0.2 mol per 1 mol of LiBr, these values
increased almost twofold (entries 3—5). The effect of
sulfuric acid is primarily explained by the increase in
Procedure C
1 : 0.3 : 1 : 10 : 0.2
CeIII
1
3
78
75
1
8
the oxidative efficiency of CAN in the acidic medium.
a
Reaction conditions: 1c (1 mmol), CH CN (10 mL), 65—70 C,
3
III
Moreover, the reaction of sulfuric acid with LiBr leads
to the formation of hydrogen bromide, from which
bromine is generated more readily upon the action of
CAN than from LiBr. In fact, when LiBr was replaced by
5
—6 h (procedure A) or 10—12 h (procedures B and C), Ce is
IV
Ce(NO ) •6H O, Ce is Ce(NH ) (NO ) .
3
3
2
4 2
3 6
b
Calculated based on the amount of ketone 1c taken for the
reaction.

1
216
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 5, May, 2013
Nikishin et al.
HBr, both the conversion 1c and the yield of 2c were
increased (entry 6).
ucts were determined using an internal standard (pentanꢀ2ꢀone
and hexanꢀ2ꢀone) with allowance for the experimentally found
correction coefficients. H and C NMR spectra were recorded
on a Bruker AM 300 spectrometer under standard conditions in
1
13
Procedure B (catalytic amount of CAN, see Table 1,
entries 7—12). At the molar ratio 1c : CAN : LiBr : H O =
2
2
CDCl . Reaction products were isolated by column chromatogꢀ
3
=
1 : 0.3 : 1 : 10, the index conversion of 1c/yield of 2c did
not exceed 75/73%. Like in the procedure A, the introducꢀ
tion of 0.2 mol of H SO per 1 mol of LiBr to the oxidaꢀ
raphy (silica gel L 40/100 m, eluent heptane—ethyl acetate).
The starting ketones (pentanꢀ3ꢀone, heptanꢀ4ꢀone, nonanꢀ5ꢀ
one, undecanꢀ6ꢀone, 2,4ꢀdimethylhexanꢀ3ꢀone, 3,3ꢀdimethylꢀ
butanꢀ2ꢀone), ceric ammonium nitrate (Ce(NH ) (NO ) ),
2
4
tion system leads to the increase in the conversion of keꢀ
tone 1c and the yield of bromoketone 2c to 92 and 90%,
respectively. A decrease in the amount of any of three
components of the oxidation system, either sulfuric acid
to 0.1 mol, or CAN to 0.2 mol, or H O to 5 mol, resulted
4
2
3 6
cerium(III) nitrate hexahydrate (Ce(NO ) •6H O), and hydroꢀ
3
3
2
gen peroxide (35% aqueous solution)) were commercially availꢀ
able from Acros and were used without additional purification.
Acetonitrile (pure grade) was distilled before use. Lithium bromꢀ
ide (pure grade) was calcined before use.
Bromination of ketones 1a—f by the system CAN—LiBr in
MeCN (general procedure). A mixture of ketone 1, CAN,
and LiBr (for ratios of reagents, see Tables 1 and 2) in MeCN
2
2
in the decrease of both the conversion of 1c and the yield
of 2c (see Table 1, entries 9, 11, 12).
Procedure C (catalytic amount of CN, see Table 1,
entry 13). Cerium nitrate as compared to CAN is less efꢀ
ficient in the role of the redox catalyst in the bromꢀ
ination reactions of ketones. At the molar ratio
(
10 mL) was vigorously stirred on a magnetic stirrer at 65—70 C
until the oxidant was completely converted (the change of the
color from orange to light yellow). The reaction time was
5—6 h. The reaction mixture was extracted with diethyl ether
1
c : Ce : LiBr : H O : H SO equal to 1 : 0.3 : 1 : 10 : 0.2,
2 2 2 4
(
3×20 mL), the combined extracts were washed with NaHCO3
the conversion of 1c and the yield of 2c were 78 and 75%,
respectively, that is 15% lower than in procedures A and B.
Ketones 1a,b,d—f were brominated under the optimal
conditions found for ketone 1c (see Table 2). The use of
procedures A and B resulted in the close indices of conꢀ
version of ketones 1a—f (86—98%) and the yields of
and water, and dried with MgSO , the solvent was evaporated.
4
The product yields and the conversion of ketones 1 were deꢀ
termined by GLC using an internal standard (see Tables 1
and 2). The reaction products were isolated by column chromatoꢀ
graphy.
III
Bromination of ketones by the systems H O —LiBr—Ce or
2
2
IV

ꢀbromoketones 2a—f (83—96%). Virtually the same reꢀ
H O —LiBr—Ce in MeCN (general procedure). A solution of
2 2
sults were also obtained for diethyl (1a), dipropyl (1b).
and tertꢀbutyl methyl ketone (1e) in the procedure C. Howꢀ
ever, procedure C has proved less efficient with respect to
the three symmetric ketones 1c,d,f containing butyl, penꢀ
tyl, or isopropyl group sterically more hindered for the
attack by bromine. Ketone 1f was also harder to bromꢀ
inate than other ketones using procedures A and B. The
reason is that bromine not only brominates ketones, but
also facilitates a catalytic decomposition of hydrogen perꢀ
oxide. As a result, the conversion of ketones to ꢀbroꢀ
moketones decreases because of the decreased amount of
H O involved in this process. This is especially proꢀ
nounced in the cases of ketones 1c,d,f. At the same time,
the yield of all the ꢀbromoketones 2a—f (without excepꢀ
tion) calculated based on the consumed in the reaction
ketones 1a—f remained similarly high and reached >95%,
i.e., the reaction proceeded with high selectivity.
35% aqueous H O in MeCN (5 mL) was added in portions (by
2 2
III
IV
0.2—0.3 mL) to a solution of ketone 1, LiBr, and Ce or Ce
salt in MeCN (5 mL) at 65—70 C with vigorous stirring over
0—12 h (for the ratio of reagents, see in Table 2). In the case of
1
IV
Ce , an orange color appeared immediately after mixing ketone 1,
IV
LiBr, and Ce , which disappeared in 20—30 min. In the case of
III
Ce , the color appeared after addition of the first portion of the
H O solution and disappeared also in 20—30 min. Each subseꢀ
2
2
quent portion of H O was added after discoloration of the reacꢀ
2
2
tion mixture . After all peroxide was added, the reaction mixture
was cooled, extracted with diethyl ether (3×20 mL), washed
with aq. NaHCO and water, and dried with MgSO . The yield
3
4
of the products was determined by GLC using an internal stanꢀ
dard (see Table 2). The reaction products were isolated by colꢀ
2
2
umn chromatography.
1
2
ꢀBromopentanꢀ3ꢀone (2a) (cf. Ref. 17). H NMR, : 1.09
(
(
t, 3 H, CH , J = 7.3 Hz); 1.72 (d, 3 H, CH CHBr, J = 7.0); 2.59
m, 2 H, CH ); 4.40 (m, 1 H, CHBr). C NMR, : 8.18 (CH );
2 3
3
3
13
2
0.15 (CH CHBr); 31.96 (CH ); 47.31 (CHBr); 205.07 (CO).
3 2
1
In conclusion, without use of bromine or hydrogen
3ꢀBromoheptanꢀ4ꢀone (2b) (cf. Ref. 17). H NMR, : 0.91
(t, 3 H, CH , J = 7.0 Hz); 1.04 (t, 3 H, CH , J = 7.0 Hz); 1.60
bromide the reaction of ketones with the systems H O —
2
2
3
3
III
IV
(m, 2 H, CH ); 1.97 (m, 2 H, CH Br); 2.35 (t, 2 H, CH CO,
2 2 2
LiBr—Ce
the solution of the problem of preparative synthesis of
-bromoketones.
and H O —LiBr—Ce can be used for
2
2
13
J = 7.3 Hz); 4.16 (t, 1 H, CHBr, J = 6.9 Hz). C NMR, ,: 11.97
(
CH ); 13.68 (CH ); 17.30 (CH ); 26.88 (CH Br); 40.91
3 3 2 2

(
CH CO); 55.47 (CHBr); 204.16 (CO).
2
1
4
ꢀBromononanꢀ5ꢀone (2c) (cf. Ref. 17). H NMR, : 0.87
Experimental
Reaction mixtures were analyzed by GLC on a LKhMꢀ80
chromatograph with the flameꢀionizing detector and analytical
metal columns 2000×3 mm with 5% SEꢀ30 and 5% FFAP on
Chromaton NꢀAWꢀHMDS (0.16—0.20 mm). The yields of prodꢀ
(
(
t, 3 H, CH , J = 6.4 Hz); 0.94 (t, 3 H, CH , J = 6.4 Hz); 1.36
3
3
m, 2 H, CH ); 1.47 (m, 2 H, CH ); 1.59 (m, 2 H, CH ); 1.92
2
2
2
(m, 2 H, CH CHBr); 2.65 (t, 2 H, CH CO, J = 7.0 Hz);
2
2
13
4.24 (t, 1 H, CHBr, J = 7.1 Hz). C NMR, : 13.29 (CH ); 13.77
3
(CH ); 20.61 (CH ); 22.19 (CH ); 25.99 (CH ); 34.58
3
2
2
2
(CH CHBr); 42.70 (CH CO); 53.52 (CHBr); 204.34 (CO).
2
2

Bromination of ketones
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 5, May, 2013
1217
1
5
ꢀBromoundecanꢀ6ꢀone (2d) (cf. Ref. 19). H NMR, : 0.85
6. M. R. Marri, A. K. Macharia, S. Peraka, N. Nama, Tetraꢀ
hedron Lett., 2011, 52, 6554.
(
t, 3 H, CH , J = 6.4 Hz); 0.93 (t, 3 H, CH , J = 6.4 Hz);
3
3
1
.26—1.61 (m, 10 H, 5 CH ); 1.92 (m, 2 H, CH CHBr); 2.51
7. A. K. Macharia, R. C. Nappunni, M. R. Marri, S. Peraka,
N. Nama, Tetrahedron Lett., 2012, 53, 191.
2
2
(
t, 2 H, CH CO, J = 7.1 Hz); 4.2 (t, 1 H, CHBr, J = 7.0 Hz).
3
2
1
C NMR, : 13.71 (CH ), 13.79 (CH ), 22.05 (CH ), 23.55
8. V. Nair, A. Deepthi, Chem. Rev., 2007, 107, 1862.
9. V. Nair, S. B. Panicker, A. Augustine, T. G. George,
S. Thomas, M. Vairamani, Tetrahedron, 2001, 57, 7417.
10. S. C. Roy, C. Guin, G. Maiti, Tetrahedron Lett., 2001,
42, 9253.
11. G. I. Nikishin, L. L. Sokova, V. D. Makhaev, N. I. Kapustiꢀ
na, Russ. Chem. Bull. (Int. Ed.), 2008, 57, 118 [Izv. Akad.
Nauk, Ser. Khim., 2008, 114].
3
3
2
(
(
CH ), 29.40 (CH ), 31.15 (CH ), 34.28 (CH CHBr), 42.65
CH CO), 53.68 (CHBr), 204.19 (CO).
2 2 2 2
2
1
1ꢀBromoꢀ3,3ꢀdimethylbutanꢀ2ꢀone (2e) (cf. Ref. 17). H NMR,
1
3


: 1.23 (s, 9 H, CH ); 4.17 (s, 2 H, CH BrCO). C NMR,
: 26.77 (3 CH ), 31.64 (CH Br), 44.29 (C(CH ) ), 206.19 (CO).
3
2
3
2
3 3
1
2
ꢀBromoꢀ2,4ꢀdimethylpentanꢀ3ꢀone (2f) (cf. Ref. 17). H NMR,

(
: 1.28 (d, 6 H, 2 CH , J = 6.8 Hz); 1.82 (s, 6 H, 2 CH ); 3.40
3
3
m, 1 H, CHCO). 13C NMR, : 18.60 (CH ), 18.67 (CH ), 29.39
12. E. Baciocchi, M. Crescenzi, Tetrahedron, 1988, 44, 6525.
13. S. C. Roy, C. Guin, K. K. Rana, G. Maiti, Tetrahedron Lett.,
2001, 42, 6941.
3
3
(CH ), 29.42 (CH ), 34.63 (CH(CH ) ), 64.65 (CBr(CH ) ),
3
3
3 2
3 2
2
10.02 (CO).
1
1
1
1
4. N. I. Kapustina, L. L. Sokova, G. I. Nikishin, Russ. Chem.
Bull. (Int. Ed.), 2010, 59, 1284 [Izv. Akad. Nauk, Ser. Khim.,
2010, 1255].
5. G. I. Nikishin, L. L. Sokova, N. I. Kapustina, Russ. Chem.
Bull. (Int. Ed.), 2012, 61, 459 [Izv. Akad. Nauk, Ser. Khim.,
This work was financially supported by the Ministry of
Education and Science of the Russian Federation (State
Contract No. 11.519.11.2038).
2
012, 456].
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Received October 3, 2012;
in revised form December 11, 2012