Oxidation of alkanols with a CeIII - LiBr - H2O 2 system

Full text of DOI:10.1007/s11172-009-0334-6

Russian Chemical Bulletin, International Edition, Vol. 58, No. 11, pp. 2402—2403, November, 2009
2402
Letters to the Editor
Oxidation of alkanols with a CeIII—LiBr— H2O2 system
G. I. Nikishin, L. L. Sokova, and N. I. Kapustina
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Eꢀmail: kap@ioc.ac.ru
Among cerium compounds, only cerium(IV) ammoꢀ
nium nitrate (CAN) has found wide application mainly as
a stoichiometric oxidant and as a catalyst for reactions of
different nature. Unlike CeIV, CeIII compounds are virtuꢀ
ally not used in oxidation processes of organic synthesis.
Hydroxylation of βꢀdicarbonyl compounds under the
action of CeCl3•7H2O in combination with molecular
oxygen1 and allylic chlorination of olefins with a
CeCl3•7H2O–NaClO system2 are known. Separate
examples of the application of CeIII in the oxidation of
secondary alkanols3 and ethers4 to ketones, sulfides to
sulfoxides5 with a CAN–NaBrO3 system are documented.
In these reactions, sodium bromate, the stoichiometric
reagent, generates CeIV from produced CeIII.
Scheme 1
The aim was to convert CeIII to CeIV with H2O2 and to
use CeIV as an oxidant to generate bromine from LiBr,
and bromine, in turn, as an oxidant of alkanols according
to the previously proposed6 scheme (Scheme 2).
In the present paper we give the results that can attract
additional attention to CeIII compounds and give a new
impetus to the development of studies on their applicaꢀ
tion in organic chemistry.
An oxidative system Ce(NO3)3•6H2O–LiBr–H2O2
was first proposed and assayed. Using this system, the
oxidation of primary and secondary alkanols to esters and
ketones, respectively, was accomplished (Scheme 1). In
this reaction, hydrogen peroxide is a stoichiometric oxiꢀ
dant, CeIII and LiBr serve as mediators (redox catalysts).
The success of the reaction was not obvious a priori
because of the ability of CeIV to competitively oxidize
both the bromide anion in LiBr and hydrogen peroxide.
Positive results were achieved by maintaining very low
H2O2 concentration in the reaction mixture relative to the
concentration of CeIII. These experimental conditions
became determinant for the transformation of alkanols
into the reaction products. However, even under these
conditions, part of H2O2 was oxidized, therefore its excess
relative to alkanols was required.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2325—2326, November, 2009.
1066ꢀ5285/09/5811ꢀ2402 © 2009 Springer Science+Business Media, Inc.

Oxidation of alkanols
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 11, November, 2009 2403
Scheme 2
bromide anions with water molecules, and therefore
deceleration of their oxidation by CeIV. The excess of
LiBr compensates this effect. In the oxidation of secondary
alkanols to alkanones, a catalytic amount of LiBr suffices;
stoichiometric amount of LiBr leads to αꢀbromo ketones.
At a molar ratio 3 : CeIII : LiBr : H2O2 equal to 1 : 2 : 1 : 10,
2ꢀbromopentanꢀ3ꢀone is formed in a yield of 77 %.
Oxidation of alkanols with a Ce(NO3)3•6H2O—LiBr—H2O2
system (general procedure). To an aqueous solution of an alkanol
(1 mmol), Ce(NO3)3, and LiBr (10 mL), portions (0.5–0.6 mL)
of 35% H2O2 (overall. 10 mL, the reactant ratio is given above)
were added at 65–70 °C and vigorous stirring. After addition of
the first portion, yellow coloration typical of CeIV salts appeared,
only after complete discoloration of the reaction mixture the
next portion of H2O2 was added. Next, the reaction mixture was
cooled, extracted with ether (3×15 mL), washed with aqueous
NaHCO3 solution and water, and dried with MgSO4. The yields
of the reaction products and conversion were determined by
GLC with authentic samples of the internal standards. For the
preparative isolation of the products, column chromatography
on silica gel was used.
R = C5H11 (a), C6H13 (b), C8H17 (c)
i.
; ii. CeIV, ; iii. CeIV—LiBr
By the example of the oxidation of heptanꢀ1ꢀol (1b) in
water, it was established that no reaction occurs in the
absence of one of mediators. At slow uniform addition of
H2O2 to the mixture in 4 h at 65–70 °C at a molar ratio
of reactants 1b : CeIII : LiBr : H2O2 equal to 1 : 0.5 : 5 : 10
the conversion of alkanol 1b was 81 %, the selectivity of
its transformation to heptyl heptanoate (2b) was 98%.
With doubled amounts of CeIII and LiBr, these characterꢀ
istics were almost unchanged, while with halved amounts
the conversion of alkanol 1b noticeably decreased. Subꢀ
stitution of NaBr and KBr for LiBr decreases the converꢀ
sion as well, but the selectivity remained unchanged.
Like compound 1b, hexanꢀ1ꢀol (1a) and nonanꢀ1ꢀol
(1c) oxidize to form esters C5H11COOC6H13 (2a) and
C8H17COOC9H19 (2c), respectively, with the same yield
and selectivity.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 09ꢀ03ꢀ00292a)
and the Council on Grants at the president of the Russian
Federation (Program for State Support of Leading Scienꢀ
tific Schools of the Russian Federation. Grant 2942.2008.3).
References
1. J. Christoffers, T. Werner, S. Unger, W. Frey, Eur. J. Org.
Chem., 2003, 425; J. Christoffers, T. Werner, W. Frey,
A. Baro, Eur. J. Org. Chem., 2003, 4879; J. Christoffers,
T. Kauf, T. Werner, M. Rössle, Eur. J. Org. Chem., 2006,
2601.
Secondary alkanols oxidize more readily than primary
ones. Pentanꢀ3ꢀol (3) is converted to pentanꢀ3ꢀone (4) in
a qualitative yield in 80% aqueous acetonitrile at a molar
ratio 3 : CeIII : LiBr : H2O2 equal to 1 : 0.1: 0.4 : 10. With a
decreased amount of LiBr, the yield of ketone 4 and conꢀ
version of alkanol 3 decrease: these are 75, 65, and 10% in
the case of 0.3, 0.2, and 0.1 mol. equiv. of LiBr, respecꢀ
tively. The selectivity is about 100 %. In the absence of
LiBr or CeIII, no ketone is formed.
In the CeIII–H2O2–alkanol (primary and secondary)
system, only H2O2 undergoes decomposition in the reꢀ
curring cycle CeIII–CeIV–CeIII. In the presence of LiBr,
the bromide anions succeed to intercept a part of proꢀ
duced CeIV ions, which prevents their reduction with
H2O2, and initiates thereby a process of oxidation of
alkanol with bromine that is generated.
2. F. Javier MorenoꢀDorado, F. M. Guerra, F. L. Manzano,
F. Javier Aladro, Z. D. Jorge, G. M. Massanet, Tetrahedron
Lett., 2003, 44, 6691
3. H. Tomioka, K. Oshima, H. Nozaki, Tetrahedron Lett., 1982,
23, 539.
4. G. A. Olah, B. G. Balaram Gupta, A. P. Fung Synth.
Commun., 1980, 897.
5. M. Hashmat Ali, D. Kriedelbaugh, T. Wencewicz, Synthesis,
2007, 3507.
6. N. I. Kapustina, L. L. Sokova, R. G. Gasanov, G. I. Nikishin,
Izv. Akad. Nauk, Ser. Khim., 2007, 1445 [Russ. Chem. Bull.,
Int. Ed., 2007, 56, 1501]; G. I. Nikishin, L. L. Sokova,
N. I. Kapustina, Izv. Akad. Nauk, Ser. Khim., 2009, 303
[Russ. Chem. Bull., Int. Ed., 2009, 58, 303].
In the case of primary alkanols, an excess of LiBr is
required, which probably is caused by solvation of the
Received September 21, 2009