Indian Journal of Chem istry
Vol. 4 1B, Deccmber 2002, pp. 2604-2605
Rapid Communication
Table I -
Effect of solvent and ultra 'ound on
esterification of phenol s
Reaction of phenol and acetyl chloride at
reflu x in differcnt solvent:;
K Rama & M A Pasha ';'
SI
No
Department of Studies in Chcm istry, Ce ntral Co ll ege Ca mpus.
Bangalorc Uni vcrsit y. Banga lore 560 00 1, India
I
Tolu ene
60
30
2
Pet. et her
60
26
3
Dichloromelhanc
60
85
4
Tetrah ydrofuran
60
20
Received.5 August 2002; accepted (rel'ised ) .5 NOl'ellliJer 2002
Phcnols are convcni ently ncy lated by acid chl orides in C H ~ CI ~
under thc influence of ultrasound to give csters in sati sfactory
yields.
Esterification, since its discovery i the middle of
eightee nth century by Lauraquai s, who prepared ethyl
acetate by heating strong acetic acid with alcohol is a
very well known reaction among orga ni c chemi sts. t It
has been well esta bli shed th at the reaction attains
eq uilibrium and (a) the presence of a catalyst [such as
pyridine, acti vated alumina, aqueous alkali (SchottenBaumann procedure)l or (b) addition of excess of one
of th e reactants, usually alcohol or (c) removal of ester or water by azeotropic di stillati o or (d) removal
of water by use of a dehydrati ng agent or mol ec ular
sieve, is req uired to drive th e equilibrium to the ri ght.
Though some phenolic esters have been prepared by
th e above meth od, the yields are low . The use of acid
halides with phenols in prese nce of a base like pyridine is rega rded as one of th e be. t method to prepare
phenolic esters,2 other few methods known to give
phenolic esters in vo lve th e use of thallium salts of
phenol with acid chlorides 3 and tetrabutylammoniumhydroge nsulphate(TBAH) as phase transfer catalyst
for steri call y hindered phenols. 4
For the past few years uh rasound has ga ined
prominence as a tool to accelerate chemical reaction s.
The literature) gives informati on about man y reacti ons which have bee n accelerated when subjected to
ultraso und. In continuation of our work on the use of
ultrasound to acce lerate the reactions 6-s we have studied th e esterifi ca ti on of phenol s with acid chlorides in
th e absence of any base or catalyst under the influence
of ultrasound .
To begin with a set of four solvents were chosen
and the reacti on of phenol with acetyl chloride under
normal conditi ons was carried out in these solvents
(Table I) . From Table I, it is lea r that the reacti on
between phenol and acetyl chloride goes to comple-
Solvcnt
Time
(hr)
Yie ld (%) of
Phcny l aectate
tion after refluxin g in CI-IzCi 2 for 60 hI' to give 85 %
ester. In other three sol vents the yield after 60 hI' wa
less than 30%. In order to understand th e effect of
ultraso und on thi s reaction , different substituted phenol s were selected and the reac ti on of th ese phenol s
with acetyl chl oride in CH 2Ci 2 was studi ed at reflu x
temperature of th e solve nt as well as under the influence of ultraso und at 35KH z and the res ults are summari zed in Table II. In a typi ca l ex periment, phenol
(10 mmole) and acetyl chloride ( 15 mmole) and
CH 2C," (15 mL) were sonicated in ;} bath workin g at
35 KH z for 3 hr. The reacti on mi xw re was taken into
ether washed with 20% NaOH so lutio n (to remove
unreacted phenol), 10% Hel , sat. NaI-lC0 3 and water
and th en solvent was removed to get phenyl acetate.
From Table II, one can understand th at, the reaction between phenol and acetyl ch loride in C H2Ci 1
which take abo ut 60 hr for completion, goes to completi on under the influence of ultrm.ouncl within 3 hr
and affords 80% phenyl acetate and different phenoh
react with acety l chloride in CH 2 Cb to give respecti ve
esters in good to satisfactory yields.
In order to ex tend thi s novel reaction to different
acid chl orid es, a set of four different acid chlorides
were prepared and the react ion of these acid chlorides
with different phenols was carried out under the influ ence of ultraso und in CH 2Cb and the results are
summari sed in Table III. From Table III, it is clear
that different acid chlorides react satis fac toril y with
phenols under the influence of ultra so und to give estel's in 50-80% yield. Increase in the so nicati on time
or the acyl chl oride did not improve the yield of the
product.
The results di sc ussed above clearly indi cate th at
this reacti on is general and phenolic esters can be
readily obtained under th e influence of t1traso und and
by simple workup .
RAPID COMMUN ICATIONS
Table II SI
No
2605
Effect of solvent on esterifi ca ti on of phcnols with acctyl chloridc under the influcnce of ultrasound
Phenol
Toluene
Yicld (%)
Pet. ether
CH 2CI 2
THF
C=O stretching
l
(cm· )
1770
I
Phenol
33
37
80
20
2
p-Cresol
30
35
60
14
1769
3
p-Bromophellol
28
30
50
12
1734
4
Resorc inol"
10
12
60
10
1765
5
JI-H ydroxy ace tophenone
12
8
40
8
1766
" Resorc inol: Acety l ch loride: : I : 2.5. to ge t di ace tate
Table 111 SI
No
Esterirication o f phenols with acid chlorides in CH 2C1 2 under th e influence of ultrasound
Phenol
Acid ch loridc
Yi eld
(%)
C=O stretching
(c m· l )
Phenol
Acetyl chloride
80
1770
2
p-Creso l
Benzoy l chlori de
70
1724
3
2-Na phthol
Acetyl chloride
50
1760
4
Phcnol
Oley l chl oride
60
17 19
5
Phenol
Benzoy l chlori de
65
1745
6
Phenol
Phcn y laccty l ch loride
60
1766
7
Van illin
A cety l chloride
Experimental Section
The solve nts were di stilled and dri ed before use.
Phenols were obtained commerciall y from Merck .
Acid ch lorides (except acety l and benzoy l chl oride
which are obtai ned commercially ) were prepared in
the laboratory using SOCh from respectiv e carboxy li c
ac ids. The reacti ons were carried out in so ni c bath (35
KHz, JULABO, USR-3 Germ an make) at 25°C. The
reaction s we re mon itered by TLC [pet. eth er : ethyl
acetate (95 : 5)1. The lR Spectra were reco rded on a
NICOLET-400D ITIR instrument.
Phenol (0.94g, 10mmole) was taken in a fla sk conraining CH2Ci 2 (10 mL). To thi s acety l chl oride
( 1.I Sg, 15 mmole) in CH 2Ci 2 (5 mL) was added
dropw ise and the reacti on mixture was sonicated for 3
hr. After 3 hr of so ni cation the reaction mixtu re was
taken into ether, washed with 20% aOH solution
(2x5 mL), 10% HCI (2x I0 mL), sat.NaHCO,
No react ion
(2x lO mL), water (2x 10 mL) and dried over anh yd.
Na2S04. The solvent CH 2Ci 2 was then evaporated to
get phenyl acetate (SO% yield). The yield and the
properti es of different phenolic esters is given in
Tables II and III .
References
Dyson M alcom. A II/wI/wi oj orgal/ic chelllistry- Th e
cOlllpoli/llls oj carbol/ , hydrogel/ , oxygel/ al/d halugel/.\', Vol. I.
(Longman's Green & Co, London ), 1950.642.
2 March J, Adval/ced orgal/ic chelllistrv (John Wil ey. New
York), 1992.392.
3 Maclay Ta y lor & M cKill op, J Alii Ch elll Soc. 90. 1968.2422.
4 IIli , Tetrah edrol/ Lell , 1979.243 1.
5 Luche Jean Locui s. SYI/th etic orga llic sOl/ochelllistrv (Pl enum
Press, New York and Londo n), 1998.
6 Nagaraja D & Pasha M A , Telrah edron Lell , 40, 1999, 7855.
7 Rama K , Nagendra E & Pasha M A. II/dial/ J Chelll. 39B.
2000,563 .
8 Nagaraj a D & Pasha M A , II/dial/ J Chelll, 4 1B. 2()02. 1747 .