Download Phenyl Acetate Preparation ( from Phenol and

(
M. 6. Hocking'
McGill University
Montreal, QuebecH3A 2A7
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I
Phenyl Acetate Preparation
from Phenol and Acetic Acid
Reassessment of a common textbook misconception
It is often stated (or implied) by authors of textbooks in
organic chemistry t h a t " . . . phenols cannot he esterified directlv"
, I1
. .). Discussion of direct esterification is often dismissed in this way (2) and methods using acid derivati\.es are
outlined. even in the neriodical literature (31.
This paper reportsAthedetermination of the approximate
equilibrium concentrations for the phenol and acetic acid
system, together with an effective method for the direct
preparation of phenyl acetate using a combination of mass
action and azeotropic one pass water removal to drive this
equilibrium to the right to obtain workable ester yields.
Table 1. Approximate Equlllbrlum Phenyl Acetate
Concentratlons from Bolllng Mlxtures of Phenol, Acetic Acld, and
&lfuric Acid
~~~~
Experimental
Equilibration rates and equilibria
Three experiments were run, each using 18.8 g phenol (0.20 mol)
and 12.0 g glacial acetic acid (0.20 mol) in flasks fitted with reflux
condensers. All three were boiled under reflux, one without catalyst,
and the second and third with 23 mg and 250 rng of mnc. sulfuric acid,
respectively. After 22 hr boiling, the first had no phenyl acetate (<I%).
The progression of phenyl acetate content with time for the other two
experiments is given in Table 1.
Phenyl acetate preparation
To a solution of 40 g phenol (0.425 mol) in 300 g glacial acetic acid
(5.0 mol) was added 2 ml cone. sulfuricacid. This solutmn was boiled
while slowly distilling at atmospheric pressure up an efficient column
(100 X 3 cm) fitted with a variable reflux ratio head set at I W l , until
the vapor temperature reached 118O and the distillate began to turn
apale yellow (about 4 hr). The residue was cooled in an ice/salt mixtureand ice cold 50%aqueoussodium hydroxide wasadded dropwise
with stirring until the pH of the aqueous phase reached about 12. The
separated organic phase was promptly washed with chilled water and
2% acetic acid, and then dried (MgSOd. Removal of the solvent by
distillation afforded 32 g (55%)of phenyl acetate (by NMR), h.p.
193-196' (Table 2).
Results
Initial experiments with phenol and acetic acid established
both that the eauilibrium was reached only relatively slowly
and that this c&nprised not more than about 13.5% ester
(Table 1). Water removal via acetic acid azeotroping markedly
raised this, so that preparations employing this technique and
using a four mole excess of acetic acid, achieved 55-60% yields
of ester based on phenol (Table 2 ) .
With less efficient columns (short Vigreux and the like),
equivalent yields were obtained if the molar excess of acetic
acid employed was raised to 7-9 mol per mole of phenol. Use
of benzene for continuous azeotropic water removal in a
modified technique, however, only increased the reaction time
fivefold, and the ternary toluene azeotrope was not amenable
because it would not efficiently phase separate.
Discussion
Ester yields obtained by the method described approximate
those obtained from aliphatic alcohols by the equilibrium
method and lie only about 10%below those attainable with
procedures utilizing azeotropic water removal during formation of the aliphatic esters (4). Employment of molecular
sieves to dehydrate recycled acetic acid, which has been shown
to be effective for dehvdration of aliphatic alcohols ( 5 ) ,did
not demonstrate the Bame enhancement here. Anhydrous
inorganic salts such as copper sulfate (6) or potassium car-
Time
hours
MoI ?4 phenyl acetate contentd
250 mg HISO,
23 mg H.50,
1.7
4.6
3.0
4.5
11.6
22.0
6.3
11.6
13.5
25.0
27.1'
0.1
0.6
2.6
6.0
-
12.4'
-
Initially using020 molofeach ol phew1 andaceticacid. Mol %'s reported represent
relative integrated 'H nmr methyl singlet areas ~alcuiatedthus:
@any1 acetate
X 100.
phenyl acetate + acetic acid
a mir aaqua at= contained 1.9% a-, and 2.4%phydroxyacetopknone. identified
by d i n g experiments using expsnded spsctra. Caocenbatbtianawere determined by dividing
the respective ketone methyl integral by me total methyl Integral (0-, p- ketones. phenyl
acetate,and acetic aca)and multiplying by 100.
~welvegems of acetic acid were aMed a m 22 hrenux p e r i d , and W n exacll~12
g distillsd over dwing the next 3 hr
Table 2. Comparison of Phenyl Acetate Yields Uslng Acetic Acid
Azeotroplng and Variationsa
Reaction
time. hr
Procedure emolaved
Brought to bail and distillation directly
Eight hours reflux prior to distilling
Benzene azeotroping solvent wilh
return of benzene phase
Employing 2009 fresh Molecular
Sieve 3A in a soxhlet, plus acetic
acid return
Yield of
phenyl
acetate
4
12
22-24
55
5
10-12
60
55
a l l experimentsemployed a five to one mot mtio of acetic acid to phenol, and sulfuric
acid catalysis (see Experimental).
bonate (7) may be effective but are less easily regenerated and
hence probably less attractive than the more traditional
phenol esterification methods.
Acknowledgment
Thanks are extended to Professor A. S. Perlin for support
and to Dr. A. Granata for nmr spectra.
Literature Cited
I11 Packer. J., and Vawhn, J.. "A Mudern Approach to Organic Chemirtry,ll Clarendon
Press. Oxbrd. 1958, p. 705.
i 2 ) Nuller,C.R.,"Chemistryof 0rgaganicCumpaundr.ll W. R.Saunder~Co..London,
1965.
p 552. Streilweiser,Jr..A,. Heathcock. C. H.. "lntruductiun toorganic Chemiriry.l.
MacMillan Publishing Cu.. lnc.. New Yurk, 1976, p. YO5 Fiepal, L. F,and Fiessr,
M.. "Advanced O ~ g a n i c C h e m i s t r ~ Reinheld,
,"
New Yurk. 1961.Finar. I. L.."Owanic
Chemistry Vul. 1: The Fundamental Principles." Longman. Landon, 1967, p. 668.
Robem,1. D., and Caseriu. M. C.. "Bade Principles of Organic Chemistry," 2nd Rd.,
W. A. Benjamin.lnc., 0s" Milln,Ontariu, 1977.p. 1294.
(3) Heilrlrin. 6. 152: 1. 87: 11. 151; 111.595:LV.611.
(41 Naff,M. %and Nef1.A. S.,d.CHBM. BDUC. 44,68U (19671.
(5) Fieser. L. P.. and Ficrer, M.,"Reseonts IorOrsanicSynthosis,"Val. I..luhn Wilsy and
&XIS,
New Yurk, 1967, p. 705. Stern. R. L.,and B d a n , E. N., C h e m lnd. (London!
825ILY6il. Harrinm, H. R..Hayer. W. M.. Arthur. P.,snd Eisenbraun,E. J..Chrm.
Ind. ILundonl 156Hl196H1.
(61 Clemmenaen. E., and Heitman, A. H. C.. J. Amrr. Chem. S m 42,519 119091.
(7) Thiolepape, E.. HerVhir 66, ,454 l19:181. Kenyon. J., in "Organic Syntheses, Collective
Vd. I," John Wiloy and Lms. Now Yerk, 1932.p. 261.
1 Present address: Department of Chemistry,University of Victoria,
Victoria, B.C. V8W 2Y2.
Volume 57. Number 7,July 1980 / 527