Guanidinium chlorochromate, a new, efficient, and mild oxidizing agent for benzylic and other alcohols to carbonyl compounds in water and organic solvents

Article abstract of DOI:10.1080/00397911.2010.502987

Guanidinium chlorochromate (GCC) has been first reported as a new oxidizing agent for the oxidation of a series of benzylic and a number of other aliphatic and aromatic alcohols to carbonyl compounds and quinones respectively in water in the presence of a phase-transfer catalyst and also in an organic solvent such as methylenechloride. Taylor& Francis Group, LLC.

Full text of DOI:10.1080/00397911.2010.502987

Synthetic Communications1, 41: 2500–2504, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.502987
GUANIDINIUM CHLOROCHROMATE, A NEW,
EFFICIENT, AND MILD OXIDIZING AGENT FOR
BENZYLIC AND OTHER ALCOHOLS TO CARBONYL
COMPOUNDS IN WATER AND ORGANIC SOLVENTS
Shyamaprosad Goswami and Arnab Kar
Department of Chemistry, Bengal Engineering and Science University,
Shibpur, Howrah, India
GRAPHICAL ABSTRACT
Abstract Guanidinium chlorochromate (GCC) has been first reported as a new oxidizing
agent for the oxidation of a series of benzylic and a number of other aliphatic and aromatic
alcohols to carbonyl compounds and quinones respectively in water in the presence of a
phase-transfer catalyst and also in an organic solvent such as methylenechloride.
Keywords Carbonyl compounds; guanidinium chlorochromate (GCC); oxidation
INTRODUCTION
Oxidation reactions are very important in organic synthesis. Many methods
and oxidizing agents have been discovered for oxidation, but development and modi-
fication of known reagents have been studied in recent years.[1] Many important
reviews have highlighted the discovery and use of such oxidizing agents, some of
which are strong and some of which are mild. Manganese- and chromium-based
compounds are classic in nature, and their oxides and different complexes have been
developed for many successful oxidations. Chromium-based oxidizing agents such as
chromium trioxide-pyridine,[2] Jones reagent (CrO3=CH3COCH3=H2SO4),[3]
pyridinium chlorochromate (PCC),[4] pyridinium dichromate (PDC),[5] 1,1,3,3-
tetramethylguanidinium dichromate (TMGDC), pyridinium fluorochromate,[6]
benzyltrimethylammonium fluorochromate, tributylammonium chlorochromate,
Received February 13, 2010.
Address correspondence to Shyamaprosad Goswami, Department of Chemistry, Bengal
Engineering and Science University, Shibpur, Howrah 711 103, India. E-mail: spgoswamical@yahoo.com
2500

GUANIDINIUM CHLOROCHROMATE
2501
methyltriphenylphosphonium halochromates, poly[N-(4-pyridinium dichromate)-p-
styrene sulfonamide],[7] and also ceric ammonium nitrate[8] have been reported and
are widely used. Still the demand of new oxidizing agents that are either soluble in
water or organic solvents is increasing. Co(I) oxidations[9] are also effective in very
mild conditions for oxidation of benzylic alcohols to aldehydes, which we have
developed. The other mild oxidants developed are dimethylsulfoxide–N,N0-dicyclo-
hexylcarbodiimide (DMSO–DCC),[10] DMSO–Ac2O,[11] DMSO–P4O10,[12] DMSO–
oxalyl chloride or trifluoroacetic anhydride (TFAA),[13] hypervalent iodine, and
Oppenauer oxidation.[14]
We herein report the development of another novel oxidizing agent, guanidi-
nium chlorochromate (GCC), whose acidity is somewhat less than that of pyridi-
nium chlorochromate as guanidine is a stronger base than pyridine, and the
solubility of GCC is more in water, although it is soluble in dimethylformamide
(DMF), DMSO, acetone, and acetonitrile. A phase-transfer catalyst like t-butyl-
ammonium bromide increases its applicability for both water-soluble or insoluble
alcohol substrates.
The new oxidizing reagent, GCC, was prepared (Scheme 1) by treatment of
equivalent amounts of guanidinium hydrochloride and chromium trioxide in water
at 0 ꢀC instantaneously by stirring with a glass rod. The reagent is stable at room
temperature, moderately light sensitive in solution state, but fairly light stable
in solid phase. Infrared (IR) spectrum showed peaks at 3454, 1652, 1558, 946, and
902 cmꢁ1
.
This new reagent is more water soluble and versatile for any benzylic-type
alcohols (either water-soluble or insoluble benzylic alcohols by addition of a
phase-transfer catalyst for oxidation to carbonyl compounds) (Scheme 1). GCC in
water is also found to be very effective for secondary alcohols (Table 1). However,
the small-chain primary alcohols like propanol and butanol are converted to the
corresponding acids in aqueous medium. When the oxidation is performed in
Scheme 1. Preparation of GCC and oxidation of alcohols to carbonyl compounds.

2502
S. GOSWAMI AND A. KAR
Table 1. Oxidation of alcohols (1–13) by guanidinium chlorochromate (GCC)a
Mp=bp (ꢀC)
found (reported)
Entry
Substrate
Benzyl alcohol
Isopropanol
Product
Benzaldehyde
Acetone
Yield (%)
1
2
94
93
95
97
98
94
83
95
93
75
92
94
90
178 (178)
56
3
Cyclohexanol
Benzoin
Cyclohexanone
Benzil
155.6 (156)
94 (95)
48 (48)
4
5
1,1-Diphenyl methanol
1-Phenyl ethanol
4-Hydroxy benzyl alcohol
4-Nitrobenzyl alcohol
1-(p-Nitro phenyl) ethanol
9-Fluorinol
Benzophenone
Acetophenone
4-Hydroxy-benzaldehayde
4-Nitro-benzaldehayde
p-Nitroacetophenone
9-Fluorinone
6
200 (202)
116 (116)
104 (103–106)
76 (76)
7
8
9
10
11
12
13
82 (83)
82 (83)
Vanillyl alcohol
Furfuryl alcohol
1-Butanolb
Vanillin
Furfuraldehyde
1-Butanal
164 (162)
74 (75)
aSmall-chain aliphatic alcohols such as propanol and butanol are converted to the acids, and long-chain
alcohols such as palmityl alcohols are almost unreactive.
bReaction is performed in methylenechloride solvent.
methylenechloride as solvent, short-chain primary alcohols (e.g., 1-butanol) is
oxidized to 1-butanal in good yield, but the reagent is not suitable for the oxidation
of primary long-chain saturated alcohols (e.g., palmityl alcohol).
Final confirmation of the structure of the new oxidizing agent GCC was estab-
lished by single-crystal x-ray structure.[15] The single crystal was developed by slow
evaporation of the acetone–water (70:30) solution of GCC. The single-crystal x-ray
structure of GCC is shown below (Fig. 1). The ORTEP diagram shows that the unit
cell contains CðNH2Þþ (symmetrical protonated guanidinium cation) and ClCrO3ꢁ
3
anion as a stable salt. In Fig. 1(b), the short hydrogen bonds between the hydrogen
atoms of the guanidinium cation and the oxygen atoms of the chlorochromate anion
Figure 1. (a) ORTEP diagram (evaluated from single-crystal x-ray study) of GCC; (b) wavelike structure
along crystallographic b axis. Hydrogen bonds are shown as dashed lines.

GUANIDINIUM CHLOROCHROMATE
2503
are shown where an alternate array of the respective cation and anion form a
wavelike network.
Thus the oxidizing reagent, GCC, is found to be very successful in the
oxidation of benzylic and other alcohols to carbonyl compounds.
In conclusion, in this study we have reported the development of a new and
mild reagent for the oxidation of different types of alcohols, mainly in aqueous or
binary phase. The stability, easy preparation, mildness of the reagent, straightfor-
ward workup, mild reaction condition, and good yield of the respective oxidation
product make this reagent useful for oxidization of alcohols to carbonyl compounds.
During the reactions, the color of the oxidant changes from orange to blackish
brown, providing a visual means of ascertaining the progress of the reaction.
ACKNOWLEDGMENTS
We acknowledge the Council of Scientific and Industrial Research (CSIR) and the
Department of Science and Technology (DST), government of India, for financial
assistance. A. K. is grateful to CSIR for a junior research fellowship.
REFERENCES
1. (a) Chinn, L. J. Selection of Oxidants in Synthesis; Marcel Dekker: New York, 1971; (b)
House, H. O. Modern Synthetic Reactions, 2nd ed.; W. A. Benzamin, Inc.: New York,
1972; (c) Piancatelli, G. H.; Trost, B. M. Comprehensive Organic Synthesis–Oxidation;
Pergamon: New York, 1991; (d) Hudlicky, M. M. Oxidation in Organic Chemistry;
American Chemical Society: Washington, DC, 1990; (e) Sheidon, R. A.; Kkochi, J. K.
Metal-Catalysed Oxidation of Organic Compounds; Academic Press: New York, 1981;
(f) Ley, S. V.; Norman, J.; Griffith, W. P.; Marsden, S. P. Tetrapropylammonium per-
ruthenate, Pr4NþRuOꢁ4 , TPAP: A catalytic oxidant for organic synthesis. Synthesis
1994, 639–666; (g) Moffat, J. G. Oxidation; Marcel Dekker: New York, 1971; Vol. 2.
2. (a) Collins, J. C.; Hess, W. W.; Frank, F. J. Dipyridine-chromium(VI) oxide oxidation of
alcohols in dichloromethane. Tetrahedron Lett. 1968, 9, 3363–3366; (b) Collins, J. C.;
Hess, W. W. Org. Synth., Coll. 1988, 6, 644–648.
3. Bowden, K.; Heilbron, I. M.; Jones, E. R. H.; Weedon, B. C. L. Researches on acetylenic
compounds, part I: The preparation of acetylenic ketones by oxidation of acetylenic
carbinols and glycols. J. Chem. Soc. 1946, 39–45.
4. Corey, E. J.; Suggs, J. W. Pyridinium chlorochromate: An efficient reagent for oxidation
of primary and secondary alcohols to carbonyl compounds. Tetrahedron Lett. 1975, 16,
2647–2650.
5. Corey, E. J.; Schmidt, G. Pyridinium chlorochromate: An efficient reagent for oxidation
of primary and secondary alcohols to carbonyl compounds. Tetrahedron Lett. 1979, 20,
399–402.
6. Bhattachharjee, M. N.; Chaudhuri, M. K.; Dasgupta, H. S.; Roy, N.; Khathing, D. T.
Pyridinium fluorochromate: A new and efficient oxidant for organic substrates. Synthesis
1982, 588–589.
7. Khazaei, A.; Mehdipour, E.; Yadegari, S. Poly[N-(4-pyridinium dichromate)-p-styrene
sulphonamide] as an efficient reagent for oxidation of alcohols. Phosphorus, Sulfur Silicon
Relat. Elem. 2004, 179(3), 437–441.
8. Kanemoto, S.; Tomioka, H.; Oshima, K.; Nozaki, H. Cerium- or ruthenium-catalyzed
oxidation of alcohols to carbonyl compounds by means of sodium bromated. Bull. Chem.
Soc. Jpn. 1986, 56, 105–108.

2504
S. GOSWAMI AND A. KAR
9. (a) Goswami, S. P.; Mahapatra, A. K. Aromatic aldehydes from benzylbromides via
cobalt(I)-mediated benzyl radicals in the presence of aerial oxygen: A mild oxidation
reaction in neutral condition. Tetrahedron Lett. 1998, 39, 1981–1984; (b) Goswami, S.
P.; Jana, S.; Dey, S.; Adak, A. K. A simple and convenient manganese dioxide oxidation
of benzyl halides to aromatic aldehydes under neutral condition. Chem. Lett. 2005, 34,
194–195.
10. Pfitzner, K. E.; Moffatt, J. G. Sulfoxide-carbodiimide reactions, I: A facile oxidation of
alcohols. J. Am. chem. Soc. 1965, 87, 5661–5670.
11. Albright, J. D.; Goldman, L. Sulfur trioxide in the oxidation of alcohols by dimethyl
sulfoxide. J. Am. Chem. Soc. 1967, 89, 5505–5507.
12. Onodera, K.; Hirano, S.; Kashimura, N. Oxidation of carbohydrates with dimethyl
sulfoxide containing phosphorus pentoxide. J. Am. Chem. Soc. 1965, 87, 4651–4652.
13. (a) Mancuso, A. J.; Swern, D. Activated dimethyl sulfoxide: Useful reagents for synthesis.
Synthesis 1981, 165–184; (b) Huang, S. L.; Omura, K.; Swern, D. Further studies on
the oxidation of alcohols to carbonyl compounds by dimethyl sulfoxide=trifluoroacetic
anhydride. Synthesis 1978, 297–298.
14. Dess, D. B.; Martin, J. C. Readily accessible 12-I-5 oxidant for the conversion of primary
and secondary alcohols to aldehydes and ketones. J. Org. Chem. 1983, 48, 4155–4156.
15. Fun, H.-K.; Goh, J. H.; Kar, A.; Goswami, S. Guanidinium chloromate. Acta Crystallogr.
E 2010, E66, m203.

Copyright of Synthetic Communications is the property of Taylor & Francis Ltd and its content may not be
copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written
permission. However, users may print, download, or email articles for individual use.