3-carboxypyridinium chlorochromate adsorbed on alumina as a selective oxidant for primary and secondary alcohols

Article abstract of DOI:10.1007/PL00010227

A Simple and efficient method for the oxidation of alcohols to carbonyl compounds under non-aqueous conditions employing 3-carboxypyridinium chlorochromate adsorbed on alumina is described.

Full text of DOI:10.1007/PL00010227

Monatshefte f uÈ r Chemie 130, 481±483 (1999)
3
-Carboxypyridinium Chlorochromate
Adsorbed on Alumina as a Selective Oxidant
for Primary and Secondary Alcohols
Ã
Kourosh Tabar-Hydar, and Mohammad Bolourtchian
Majid M. Heravi , Reza Kiakoojori, Maryam Mirza-Aghayan,
Chemistry and Chemical Engineering Research Center of Iran, Tehran, Iran
Summary. A Simple and ef®cient method for the oxidation of alcohols to carbonyl compounds
under non-aqueous conditions employing 3-carboxypyridinium chlorochromate adsorbed on alumina
is described.
Keywords. Oxidation; Alcohols; Carbonyl compounds; 3-Carboxypyridinium chlorochromate;
Adsorbed reagent; Alumina.
An Aluminiumoxid adsorbiertes 3-Carboxypyridiniumchlorochromat als selektives
Oxidationsmittel f uÈ r prim aÈ re und sekund aÈ re Alkohole
Zusammenfassung. Eine einfache und ef®ziente Methode f uÈ r die Oxidation von Alkoholen zu
Carbonylverbindungen unter nichtw aÈ ûrigen Bedingungen wird beschrieben, welche auf der
Verwendung von an Aluminiumoxid adsorbiertem 3-Carboxypyridiniumchlorochromat beruht.
Introduction
The oxidation of alcohols to carbonyl compounds is an important transformation in
organic chemistry attracting much interest [1±4]. The utility of chromium(VI)
reagents in the oxidative transformation is hampered due to inherent toxicity,
cumbersome preparation, and potential danger (ignition or explosion) as well as by
dif®culties in terms of product isolation and waste disposal [5]. Pyridinium
chlorochromate oxidizes a wide variety of alcohols to carbonyl compounds in
dichloromethane solution with high ef®ciency, but working up of the reaction
mixture is cumbersome.
3
-Carboxypyridinium chlorochromate has been recently introduced as an
ef®cient reagent for the cleavage of carbon-nitrogen double bonds [7] and the
oxidative deprotection of trimethylsilyl ethers and tetrahydropyranyl ethers [8]. In
continuation of our investigations utilizing reagents adsorbed on supports [4, 9, 10 ],
we wish to report a facile oxidation of primary and secondary alcohols to the
à Corresponding author

482
M. M. Heravi et al.
corresponding carbonyl compounds using 3-carboxypyridinium chlorochromate
supported on alumina.
Results and Discussion
3
-Carboxypyridinium chlorochromate (CPCC) is a stable yellow-orange solid. It
can easily and cheaply be prepared by the reaction of nicotinic acid with chromium
trioxide in 6 N hydrochloric acid [7]. Although oxidation of benzyl alcohol to
benzaldehyde smoothly proceeded using this reagent in CH Cl , the oxidation
2
2
of other benzylic alcohols did not occur in good yield. For example, when
4-methylbenzyl alcohol was subjected to oxidation with CPCC, only 20% of
4-methylbenzaldehyde were obtained even after re¯uxing for a long period. Other
primary and secondary alcohols did not give considerable amounts of the
corresponding carbonyl compounds.
Since organic synthesis by solid phase methods is a powerful tool [11] and
chromium oxidants like pyridinium chlorochromate adsorbed on alumina [12],
chromic acid on silica [13], and chromyl chloride on silica-alumina have been
reported to give better yields under milder conditions as compared to the parent
oxidants, we tried to follow this road for CPCC.
Thus, CPCC adsorbed on alumina was prepared by adding alumina to a
solution of CPCC in CH Cl and evaporating to dryness. The yellow-orange solid
2
2
was kept in vacuum at room temperature and stored in the dark before use. A
variety of alcohols dissolved in CH Cl were subjected to oxidation using 1.2±
2
2
2
mmol of the reagent. We found the adsorbed reagent to be remarkably effective in
oxidizing primary and secondary alcohols to aldehydes and ketones in high to
excellent yields. No indications of overoxidation could be observed in the case of
primary alcohols.
Interestingly, cinnamyl alcohol gave only 65% of cinnamaldehyde and 35% of
benzaldehyde, demonstrating carbon-carbon double bonds being prone to cleavage
by the above reagent. The results obtained from the oxidation of 10 alcohols are
reported in Table 1.
Table 1. Oxidation of alcohols to carbonyl compounds by CPCC on alumina in CH Cl
2
2
a
Alcohol
Reaction
time (h)
Product
Yield
(%)
Benzyl
1
Benzaldehyde
98 (92)
95 (90)
92 (85)
90 (86)
65 (60)
88 (80)
80 (70)
85 (72)
90 (82)
95 (90)
4
5
4
-Methylbenzyl
1
4-Methylbenzaldehyde
-Methyl-2-nitrobenzyl
-Nitrobenzyl
2
5-Methyl-2-nitrobenzylaldehyde
4-Nitrobenzaldehyde
Cinnamaldehyde
Cyclohexanone
8
Cinnamyl alcohol
Cyclohexanol
3.5
6
2
1
-Methylcyclohexanol
-Octanol
7
2-Methlcyclohexanone
1-Octanal
7
Benzhydrol
2
Benzophenone
(
� )-Menthol
8
(� )-Menthone
a
Yields determined by GLC numbers in parentheses: yields of isolated products; all compounds
isolated had identical physical data with corresponding authentic samples

3-Carboxypyridinium Chlorochromate on Alumina
483
In conclusion, CPCC adsorbed on alumina can be easily prepared and serves as
an excellent oxidizing agent for various types of alcohols under non-aqueous
conditions at ambient temperature, work-up consisting of a mere ®ltration.
Experimental
Products were characterized by GLC and by direct comparison with authentic samples. Yields are
based on GLC analysis and isolated products.
Carboxypyridinium chlorochromate adsorbed on alumina
To a solution of 10 g chromium trioxide (0.1 mol) in 18 ml 6 N hydrochloric acid, 12.3 g nicotinic
ꢀ
acid (0.1 mol) were added within 5 min at 2±5 C. The mixture was stirred at ambient temperature
ꢀ
until a yellow-orange solid formed. Reheating to 40 C gave a solution. Alumina (60 g) was then
ꢀ
added to the solution with stirring at 40 C. After evaporation in a rotary evaporator, the orange solid
is dried in vacuum for 2 h at room temperature. The reagent could be kept for several weeks under
vaccum in the dark without losing its activity.
Oxidation of alcohols to carbonyl compounds
The above reagent (5 g, 5 mmol) was added to a solution of 2.52 mmol alcohol in 10 ml CH Cl .
2
2
After stirring for the time given in Table 1, the solid was ®ltered and washed with three 10 ml
portions of CH Cl . The combined ®ltrates were evaporated. The residue was passed through a small
2
2
silica gel pad (eluent: petroleum ether:EtOAc ˆ 8:2) to give the pure carbonyl compounds (Table 1).
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Received June 8, 1998. Accepted revised August 17, 1998