Indi an Journal of Chemistry
Vol. 42B , July 2003 , pp. 1777- 1778
Note
A rapid and efficient method for acetylation
of phenols with acetic anhydride catalysed by
Ti0 2/S0 42-solid superacid
port a rapid 'and efficient method for acetylation of
phenols catalysed by Ti0 2/S0/" solid superacid.
2-
Ti02/804
r.t.or reflux, 1-40 min
Yan-Ran Ma, Tong-Shou Jin* , Zhen-Hua Wang &
Tong-Shuang Li
Department of Chemistry, Hebei Uni versity, Baoding 071002,
Hebei Province, P. R. China
Received 20 March 2001; accepted (revised) 22 March 2002
A rapid and efficient method for acetylati on of phenol s with
acetic anh ydride in the prese nce of TiOiSO/"solid superacid at
room or at reOux temperature in excellen t yield is described.
The protection of hydroxyl group of phenols by the
formation of esters is of great importance in synthetic
organic chemistry I. In addition, some esters have peculiar fragrant which applied as raw materials for
production of perfumery. The routine acylation of
phenols is carried out by acid anhydrides or acid chlorides in the presence of tertiary amines, such as
2
triethylamine and pyridine . Recently , iodine was re3
ported to be used as an acetyl transfer catalyst. In
addition to the above catalysts, protonic acids such as
p-toluenesulfonic acid 4 , Lewi s acids such as zinc
chlorides, cobalt · chloride6 , lithium chloride7 , and
8
scandium trifluoromethanesulfonate were also applied to catalyse the acylation of phenols. Each of the
above methods has its merit and some shortcomings.
Some of these methods were not sati sfactory because
of low yields, long reaction time , problems of corrosivity, tediou s workup , effluent treatment and nonrecoverable catalyst. For example triethylamine and
pyridine have unpleasant odour and not so easy to
remove. Consequently , there is a need to develop an
alternative methods for the acetylation of phenols under mild and environmentally friendly conditions.
More recently, montmorillonite KlO and KSF 9 , exlO
pansive graphite and sulfamjc ac id " were applide as
so lid catalysts for thi s purpose to obtain relatively .
better results .
Ti0 2/S0 4 2 - solid superacid has been used as a cata-
.
.
12- 15 P
.
Iy we h ave d eIyst for orgal11c
reactIOns
. revlOus
veloped a facile and efficient method for the preparati on and cleavage of I, I-diacetates catalysed by
· superac 'd
. h
'
Ti0 2/S0 42- so lJd
l 13.14 . IJ1erem
we WIS
to rc-
ArOH+k~ -----------,.~
1
2.
95-99%
ArOk + HOk
3
As summarized in Table I when phenols 1 were
treated with acetic anhydride 2 in the presence of
Ti0 2/S0/" the corresponding aryl acetates 3 were
obtained in excellent yields.
From above Table I, we found that when 2nitrophenol (If) was treated with acetic anhydride in
the presence of Ti0 2/Sol-, conversion to the COITesponding 2-nitropheny i-acetate (3f) required 4hr at
room temperature. However the reaction is accomplished in refluxing cyclohexane within 20min in the
presence of Ti0 2/S0/" as catalyst. The explanation
for this result may be due to the formation of intramolecular hydrogen bond in If that would reduce
activity of the molecule at room temperature, whereas
heating would destruct this structure.
The catalysts need no regeneration and could be
reu sed ten times for the acetylation of phenols without
significant loss of activity.
In conclusion, we have di scovered a rapid and efficient method for the acetylation of phenols. For its
operational simplicity, short reaction time, high
yields, non-corrosive, non-polluted and employing a
reusable catalyst, this method will be better than many
existing ones.
Experimental Section
General. The Ti0 2/S0/-catalyst was prepared acI3 14
cording to the literature . . Meltin g and boiling
points were uncorrected. IH NMR spectra were determined on a varian YXR-300S spectrometer using
CDCI 3 as solvent and tetramethylsilane (TMS) as internal reference. The products were also characterised
by comparison of their melting or boiling points with
literature values .
General procedure for the acetylation of phenols. A mixture of the phenols l(Smmol) , acetic anhydride 2 (2 equivalent to each hydroxyl group in the
phenols) and finely ground TiOziSO/"OOOmg) was
stirred at roo m temperature or at reflux temperature
INDIAN J. C HEM ., SEC B, JULY 2003
1778
Table I-Acetyl ation of pheno ls catalysed by lri0 2/S0 42SI.
Substrate
No
Phenol 1a
Solvent! T (C)1t
Isolated
(min)
Yield
(0/0 )'
CH 2C1 2/r.t.I20
97
Produc ts
m.p.fC or b .p.itorr
Found
Phe ny l acetate
CH 2C1 2/40/4
97
2
4-Methoxyphe no l Ib
CH 2C1 21r·t.! 1
99
4-Methoxyphenyl acetate
3
3- Meth ylph eno l Ie
Nonc/r.t.I20
98
3-M e thyl phe nyl
CHCI /6113
99
Acetate
4
4-Me thylphenol 1d
CH 2C1 2/r.t.l40
99
4- Methy lpheny l
CHCI/61110
99
Acetate
92-94/20
3 1-32
102-03120
103-05/20
Reported
1961760
16
328
2 121760
16
2 122131760
16
6
5
4-Hydroxybenzoic acid Ie
Cyclohexa ne/8 1/10
98
4-Acetoxybenzoic acid
186-87
18i
6
2-N itropheno l If
Cyclohexane/81/20
95
2-Nirop he nyl acetate
39-40
40-4 116
7
3-Nitropheno l 19
CH 2C1 2/r.t.l20
98
3-Nitro phe nyl acetate
54-55
55-56
CH 2C1 2/40/5
98
8
4-Nitrophenol 1h
CH 2C1 2/r.t.17
98
4-Ni trophenyl acetate
82-83
8 1-8i
16
6
16
9
Phenolphthalein Ii
C H 2C1 2/ r.t.l30
96
Phe no lphthalein-4,4' -di y I
d iacetate
145-46
146
10
Catecho l Ij
CH 2C1 21r.t.I I
99
Be nzene- I ,2-diy l diacetate
64-65
63-64
II
Resorcinol lk
CH 2C1 2/r.t.l20
Benzene- I ,3-diyl diacetate
152-54ILO
2871760
CH 2C1/40/4
98
99
12
Hydroquinone 11
CH 2C1 2/ r.t.l8
99
Benzene- I ,4-diyl diacetate
122-23
123
13
Bcnzene-I,3 ,5-triol 1m
C H 2C1 2/r.t.l30
96
Benzene- I ,3,5-triyltriacetate
104-05
104 16
14
a-Naphtho l In
CH 2C1 2/r.t.l3
98
a-Naphthy l acetate
47-48
47-48
71-72
16
15
p-Naphthol 10
CH 2C1 21r.t.I 1
99
p-Naphthyl acetate
70
16
16
16
16
"Isolated yield
for the length of time indicated in Table I. The progress of reaction was monitored by TLC. After completion of the reaction, Et20 (5mL) was added to the
mixture, the catalyst was filtered off and washed
twi ce with Et 20 ( lOmL ). The filtrate was washed
with 5% HCl (l5mL ), 5%NaHC0 3 (l5mL ) and
twice with brine (10mL ) success ively. After drying
(MgS0 4 ), the so lvent was evaporated under red uced
pressure to give the almost pure products. Further purifi catio n was performed by column chromatography
on silica gel usin g petro leum ether-ether as eluen t or
recrystallization from appropri ate so lvent.
Acknowledgement
The project was supported by NSFC (298720 I I and
29572039), Education Ministry of China, the Education Department of Hebei Province(990 104) and Science and Technology Commission of Hebei Province.
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