696 RESEARCH PAPER
NOVEMBER, 696–698
JOURNAL OF CHEMICAL RESEARCH 2009
Oxidation of alkyl benzenes to corresponding carbonyl compounds with
1,4-dichloro-1,4-diazoniabicyclo [2,2,2] octane bis-chloride in water
Setareh Habibzadeha* and Mahmood Tajbakhshb
aIndustrial Noshiravani University, Babol, Iran
bFaculty of Chemistry, Mazandaran University, Babolsar, Iran
The 1,4-dichloro-1,4-diazoniabicyclo [2,2,2] octane bis-chloride oxidation of various alkylbenzenes gives the
corresponding carbonyl compounds in water as solvent.
Keywords: alkylbenzenes, 1,4-dichloro-1,4-diazoniabicyclo [2,2,2] octane bis-chloride, oxidation, carbonyl compounds
The oxidation of benzylic C–H bonds is a useful transformation
in organic synthesis,1 in the manufacture of various perfumes
and medicines. Transition metal oxidants are commonly used.
In these cases, the initial oxidation products are often more
susceptible to oxidation than the starting material. Once a methyl
group is attacked, it is likely to be oxidised to the carboxylic
acid.2 While such reactions readily give benzoic acids in high
yields, they are rather difficult to stop at the aldehyde and
ketone stage. Previous oxidations of a methylene group attached
to an aromatic ring used stoichiometric quantities of oxidising
agents such as benzeneselenic anhydride,3 2,3-dichloro-5,6-
dicyanobenzoquinone (DDQ),4 Co/Mn/Br-,5 Ag(Py)4S2O8,6
Ce(NH4)2(NO3)6,7 O2/NBS,8 Ce(IV)/methanesulfonic acid,9
RhCl(PPh3),10 KMnO4/Al2O3,11 O2/Laccase/ABTS-(NH4)2,12
CrO3/Me3SiCl,13,14 Mn(III) Salen complex,15 ZnO,16 4-amino-
peroxybenzoic acid,17 copper(II) complex in the presence of
H2O2,18 3,6-bis(triphenylphosphonium)cyclohexene peroxo-
disulfate,19 KMnO4 or K2Cr2O7.20 The Friedel–Crafts acylation
reaction of aromatic rings with an acid halide/anhydride used
stoichiometric amounts of AlCl3 as catalyst21 for the production
of aromatic ketones. However, all of these procedures have
some disadvantages, including drastic reaction conditions,
rather poor yields, long reaction times and an environmentally
unfriendly procedure.
an environmentally benign protocol with the practical
convenience of not having to handle flammable and hazardous
organic solvents.
The reactions can be carried out effectively in high yields
in water (Table 1) without the generation of any toxic
waste by products. In the case of 1,3,5-trimethylbenzene
and xylene, all of methyl groups converted to the aldehyde
groups. Similarly, toluene and p-methoxytoluene under
the reaction conditions gave high yields of benzaldehyde
and p-methoxybenzaldehyde, respectively. Introduction of
electron-withdrawing groups, such as bromine and nitro
groups, on the aromatic ring slowed the oxidation reaction.
In the case of ethylbenzene, acetophenone was obtained.
In order to investigate the applicability of this procedure in
industry, we have carried out the oxidation of p-xylene under
optimum reaction conditions on a large scale (30–35 mmol)
and obtained almost the same yields as in the small-scale
reaction. Note also that, unlike other oxidation methods, the
major drawback of over-oxidation of the aldehyde to the
carboxylic acid was not observed.
In summary, we have reported the efficient and simple
method for the oxidation of alkylarenes to phenyl ketones
or aldehydes using 1,4-dichloro-1,4-diazoniabicyclo [2,2,2]
octane bis-chloride as oxidant. The process exhibited
advantages of mild reaction conditions, good yields, ease of
work up, and reusability of the DABCO and environmental
consciousness because no organic solvent is used in the
reaction and only a small amount was needed for the work up.
Recently there has been an increased interest in the
development of clean and economical processes for the
selective oxidation of alkylarenes to the corresponding
carbonyl compounds. In this context, the use of water as a
solvent and a reusable reagent are very convenient.
Experimental
Results and discussion
All the starting materials were purchased from Fluka and Merck
companies.26 The reaction was monitored by TLC using silica gel plate
and the products were identified by comparison of their spectra and
physical data with those of the authentic samples. 1H NMR spectra were
recorded at 300 MHz on a JEOL spectrometer with tetramethylsilane
(Me4Si) as an internal reference and CDCl3 as solvent. Melting points
were determined using a Mettler FP 5 apparatus and were uncorrected.
IR spectra were recorded on Pye-unicam SP 1100 spectrophotometer.
Elemental analysis was performed on a LECO 250 instrument.
All yields refer to isolated products.
In continuation of our ongoing programme to develop
oxidation reactions involving 1,4-dichloro-1,4-diazonia-
bicyclo [2,2,2] octane bis-chloride in water,22-25 we report
here a novel, convenient and mild approach for the
oxidation of a C–H benzylic to C=O using 1,4-dichloro-1,4-
diazoniabicyclo [2,2,2] octane bis-chloride with water as a
solvent under neutral conditions (Scheme 1). This method has
many advantages over the existing methodologies offering
Cl
Cl
+
O
_
N
water
40 °C
N
+
Ar
+
CH2
R
Ar
C
R
+
N
N
Cl
Cl
R= H, aliphatic or aromatic
Cl2
Scheme 1
* Correspondent. E-mail: habibzadeh@nit.ac.ir