Oxidation of alcohols with tetramethylammonium fluorochromate in aceticoi acid

Article abstract of DOI:10.1007/s11176-006-0008-0

A number of alcohols were oxidized to the corresponding carbonyl compounds in excellent yields using tetramethylammonium fluorochromate in acetic acid. The oxidant takes up two electrons, the reaction follows first-order kinetics with respect to the oxidant under pseudofirst-order conditions, and the concentration of alcohols changes according to the Michaelis-Menten dependence.

Full text of DOI:10.1007/s11176-006-0008-0

Russian Journal of General Chemistry, Vol. 75, No. 12, 2005, pp. 1886 1888. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 12, 2005,
pp. 1975 1977.
Original Russian Text Copyright
2005 by Sadeghy, Ghammami.
Oxidation of Alcohols with Tetramethylammonium
Fluorochromate in Aceticoi Acid
B. Sadeghy* and Sh. Ghammami**
* Department of Chemistry, Azad Islamic University, Tonekaboon Campus, Iran
** Department of Chemistry, Faculty of Science, Azad Islamic University, Saveh Campus, Iran
Received January 21, 2005
Abstract A number of alcohols were oxidized to the corresponding carbonyl compounds in excellent
yields using tetramethylammonium fluorochromate in acetic acid. The oxidant takes up two electrons, the
reaction follows first-order kinetics with respect to the oxidant under pseudofirst-order conditions, and the
concentration of alcohols changes according to the Michaelis Menten dependence.
Chromium(VI) reagents are widely used in organic
RR OHOH + (CH3)4N[CrO3F]
chemistry for oxidation of primary and secondary
AcOH
(1)
RR C=O + (CH3)4N[CrO3F] + H2O.
alcohols to carbonyl compounds. In the recent years,
some new chromium(VI)-based reagents were pro-
posed. Such compounds as Collins’ reagent [1],
chromium trioxide 3,5-dimethylpyrazole complex [2],
pyridinium chlorochromate [3], pyridinium dichro-
mate [4], and 2,2 -bipyridinium chlorochromate [5]
have become quite popular and showed high ef-
ficiency as oxidants.
Insofar as the proposed oxidant is stable and so-
luble, the reaction can be carried out at room tempera-
ture, and isolation of the products is facile. During
the process, the reaction mixture changes from orange
to brown; therefore, the progress of oxidation can be
monitored visually. Under pseudofirst-order condi-
tions, the individual kinetic runs are of first order with
respect to TMAFC. The rate constants do not depend
on the initial oxidant concentration. In all cases,
variation of the alcohol concentration conforms to the
Michaelis Menten dependence. The plot of 1/k1
versus 1/[alcohol] is a straight line (r = 0.995) with a
non-zero intercept on the y axis. The apparent rate
constants kap (see table) were determined from the
plots of log[TMAFC] vs. time. The results indicated
the following reaction mechanism:
We recently reported on the synthesis of tetra-
methylammonium fluorochromate(VI) (TMAFC) and
used this reagent for quantitative oxidation of sevaral
organic substrates [6, 7]. The present communication
describes the results of oxidation of several alcohols
with TMAFC in acetic acid medium. The data ob-
tained may be useful for the following reasons:
(1) Information on the kinetics of reactions involving
complex metal ions in strongly acidic media are very
limited, partly due to instability problems and difficult
interpretation of the results; and (2) the reaction under
study may serve as a model of enzymatic oxidation
with alcohol dehydrogenases in acetic acid bacteria
[8, 9].
RCH2OH + (CH3)4N[CrO3F]
K = k1/k ,
Complex,
(2)
1
k2
The use of tetramethylammonium fluorochromate
as oxidant for the transformation of alcohols into the
corresponding carbonyl compounds was quite satisfac-
tory. The results showed that TMAFC is a valuable
addition to the existing oxidants. Figure shows the
data obtained by spectrophotometric monitoring of
the reaction course. The intensities of absorption
maxima corresponding to the initial alcohols gradually
decrease, while no shift of the maximum is observed.
Complex
Reaction products,
(3)
(4)
v = k2K[TMAFC][alcohol]/(1 + K[alcohol]).
Here, v is the reaction rate.
Oxo complexes of transition metals are also used
as general-purpose stoichiometric oxidants in syn-
thetic organic chemistry, and a variety of reaction
pathways including both atom transfer and electron
transfer are involved. The reaction of triphenylphos-
phine with TMAFC at a molar ratio of 1:1.1 in
The overall reaction is described by the following
equation:
1070-3632/05/7512-1886 2005 Pleiades Publishing, Inc.

OXIDATION OF ALCOHOLS WITH TETRAMETHYLAMMONIUM
1887
acetonitrile at room temperature gave triphenylphos-
phine oxide in quantitative yield. This reactions
represents a clear-cut example of oxygen transfer with
participation of TMAFC, in keeping with the results
obtained previously using pyridinium fluorochromate
and chlorochromate [10, 11].
Apparent pseudofirst-order rate constants for the oxidation
of some alcohols to the corresponding carbonyl com-
pounds with tetramethylammonium fluorochromate in
acetic acid
Alcohol
Methanol
kap 104
Alcohol
kap 104
EXPERIMENTAL
251
308
3-Pentanol
4-Methyl-1-
pentanol
268
321
Ethanol
The IR spectra were recorded in KBr on a Shi-
madzu 420 spectrometer. The UV spectra were
measured on a Uvicon 922 spectrophotometer. The
1H, 13C, and 19F NMR spectra were obtained on a
Bruker Avance DRX-500 instrument at 500, 125, and
470.66 MHz, respectively; the chemical shifts were
1-Propanol
2-Propanol
1-Butanol
2-Butanol
2-Methyl-1-
propanol
312
268
326
364
357
1-Hexanol
1-Heptanol
1-Octanol
2-Octanol
Benzyl alcohol
305
297
444
403
433
1
referenced to SiMe4 (external, H, 13C) and CFCl3
(external, 19F).
1-Pentanol
308
Chromium trioxide CrO3 (Merck, analytical grade)
was used without additional purification. The solvents
were purified by standard procedures.
greater) was used in the reaction with TMAFC in
100 ml of acetic acid. The concentration of TMAFC
was determined by spectrophotometry at 350 nm.
The results indicated a 1:1 stoichiometry in reactions
of TMAFC with all alcohols. The reactions were
carried out under pseudofirst-order conditions using a
large excess of alcohol (0.01 0.2 M). The reaction
mixtures were analyzed for the corresponding carbonyl
compounds by the procedures reported previously
[10, 11]. The temperature was maintained constant
within 0.1 C. Spectrophotometric measurements were
performed on a Uvicon-922 instrument equipped with
a temperature control unit using 10-mm quartz cells.
A very small magnetic stirrer was designed at the cell
compartment just in the bottom of a sample cell. The
The concentration of chromium was determined by
iodometric titration. The concentration of Cr in the
reduced oxidant was determined after oxidation with
an acidic solution of potassium peroxodisulfate
(K2S2O8). The elemental analyses for carbon, hydro-
gen, and nitrogen were obtained at the Microanalytical
Laboratories, Department of Chemistry, OIRC
(Tehran, Iran).
Tetramethylammonium
fluorochromate(VI)
(CH3)4N[CrO3F]. The synthesis was carried out
inside a glove box purged with argon. Chromium(VI)
oxide, 1.07 g, was dissolved in 25 ml of anhydrous
acetonitrile in a v polyethylene beaker, and a stoi-
chiometric amount of tetramethylammonium fluoride
(1 g) was added under stirring at room temperature.
After 5 min, a transparent orange solution was formed,
and crystals of tetramethylammonium fluorochromate
separated on cooling. The product was filtered off,
washed with anhydrous isopropyl alcohol and diethyl
ether, dried for 1 h under reduced pressure, and puri-
fied by dissolution in acetonitrile, followed by slow
evaporation of the solvent over a week. IR spectrum,
1.6
1.4
1.2
1
1.0
2
0.8
3
4
0.6
5
0.4
1
6
, cm : 904 (CrO3), 636 (CrF), 940 (CrO3). The
0.2
1
electronic absorption and H, 13C, and 19F NMR spec-
0
tra were consistent with the TMAFC structure [6, 7].
Found, %: C 24.52; H 6.42; N 7.21. C4H12CrFNO3.
Calculated, %: C 24.85; H 6.21; N 7.25.
250
300
350
400
450
, nm
Electronic absorption spectra of the reaction mixture in
the oxidation of 2-propanol with tetramethylammonium
fluorochromate at 30 C in (1) 0.5, (2) 3, (3) 6, (4) 15,
(5) 20, and (6) 25 min after the reaction started. Initial
concentrations of 2-propanol and TMAFC 0.05 and
0.001 M, respectively.
General procedure for oxidation of alcohols
with tetramethylammonium fluorochromate in
acetic acid. The progress of the reaction was moni-
tored by UV/visible spectrophotometry. To determine
the stoichiometry, excess of alcohol (10-fold or
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 12 2005

1888
SADEGHY, GHAMMAMI
reaction mixtures remain homogeneous under the
given conditions.
REFERENCES
1. Collins, J., Hess, W.W., and Franck, F.J., Tetrahedron
Lett., 1968, vol. 9, p. 3363.
Oxidation of triphenylphosphine with tetra-
methylammonium fluorochromate. The reaction
was performed in a dry 100-ml round-bottomed flask
under vigorous stirring in a nitrogen atmosphere. Tri-
phenylphosphine, 1.5 g, was dissolved in 35 ml of
acetonitrile, and 1.21 g of tetramethylammonium
fluorochromate (substrate-to-oxidant ratio 1:1.1) was
added in two portions over a period of 1 min. An exo-
thermic reaction set in instantaneously and was com-
plete in 5 min. The solution was cooled, the reduced
oxidant was separated by centrifugation and washed
with acetonitrile, and the mother liquor and the
washings were passed through a short column charged
with silica gel (7 2 cm). The sorbent was thoroughly
washed with ether (3 35 ml), the filtrates were
combined and evaporated on a water bath, and the
residue was identified as triphenylphosphine oxide by
the elemental analysis and IR spectrum. Yield 1.48 g
(97%), mp 155 C; published data: mp 156 157 C.
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1973, vol. 14, p. 4499.
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ACKNOWLEDGMENTS
vol. 30, p. 257.
10. Bhattacharjee, M.N., Chaudhuri, M.K., Dasgupta, H.S.,
The authors thank Dr. Gh. Rezaei Behbahani for
valuable discussions and also thank the Azad Uni-
versity Saveh Center for performing some spectral
analyses.
and Roy, N., Synthesis, 1982, p. 588.
11. Piancatelli, G., Scettri, A., and D’Auria, M., Synthesis,
1982, p. 245.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 12 2005