Pathways of Acetol Formation in the Course of Production of Phenol and Acetone by Cleavage of Cumyl Hydroperoxide

Article abstract of DOI:10.1023/A:1012712420588

The mechanism of acetol formation in two-stage process of sulfuric acid cleavage of cumyl hydroperoxide was studied and confirmed by comparison with related reaction systems.

Full text of DOI:10.1023/A:1012712420588

Russian Journal of Applied Chemistry, Vol. 74, No. 1, 2001, pp. 111 113. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 1,
001, pp. 107 110.
Original Russian Text Copyright
2
2001 by Vasil’eva, Zakoshanskii, Koshelev, Chulkov.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Pathways of Acetol Formation in the Course of Production
of Phenol and Acetone by Cleavage of Cumyl Hydroperoxide
I. I. Vasil’eva, V. M. Zakoshanskii, Yu. N. Koshelev, and V. P. Chulkov
Russian Research Institute of Petrochemical Processes, St. Petersburg, Russia
Received January 28, 2000; in final form, July 2000
Abstract The mechanism of acetol formation in two-stage process of sulfuric acid cleavage of cumyl hydro-
peroxide was studied and confirmed by comparison with related reaction systems.
One of undesirable by-products in production of
phenol and acetone by cleavage of cumyl hydroperox-
ide is hydroxyacetone (acetol). This impurity in com-
mercial phenol dramatically deteriorates its color
index. Acetol is removed from crude phenol cata-
lytically by treatment with sulfonic cation-exchange
resins. On an acid catalyst acetol partially reacts with
phenol to form 2-methylbenzofuran (2-MBF). The
amount of the forming 2-MBF is directly related to
the content of acetol in the product to be catalytically
purified. Separation of 2-methylbenzofuran from
phenol is very difficult and is possible only by frac-
tional azeotropic distillation with water. At the same
time, 2-MBF, even when present in concentrations as
low as 0.001 wt %, also dramatically impairs the color
index of the commercial phenol.
CH C CH=C(CH )
3 3 2
O
+
ROOH + H
R
CH C CH (CH ) COOH,
3
2
3 2
O
CH C CH (CH ) COOH
3
2
3 2
O
+
H
CH C CH OH.
2
3
(
CH ) CO
3 2
O
It was also suggested [2] that acetol can form by
reaction of acetone with hydrogen peroxide present in
a small amount in the reaction mixture from cleavage
of CHP.
The simplest way to improve the color index of
commercial phenol is to prevent formation of acetol
or sharply decrease its content in products fed to
distillation. It is known that acetol is formed in the
stage of sulfuric acid decomposition of cumyl hydro-
peroxide (CHP) into phenol and acetone; its concen-
tration in the reaction mixture reaches 0.2 wt %. The
mechanism of acetol formation and ways to decrease
its concentration in CHP decomposition products were
not elucidated. It was suggested that acetol forms with
participation of acetone and CHP [1]. It was assumed
that CHP directly reacts with acetone, or that CHP
reacts with mesityl oxide formed by condensation of
two acetone molecules in the presence of sulfuric acid.
The mechanism of the direct reeaction was not de-
scribed, and the second pathway was presented as a
series of consecutive reactions:
EXPERIMENTAL
Acetol formation was studied under conditions of
two-stage CHP decomposition into phenol and ace-
tone in the presence of catalytic amounts of sulfuric
acid [3]. The first stage, according to the adopted
process scheme, was performed under conditions of
almost complete decomposition of technical-grade
CHP into target products, phenol and acetone, with
simultaneous transformation of dimethylphenylcarbi-
nol (DMPC) impurity into dicumyl peroxide (DCP).
The experiment was performed in a glass flow-circula-
tion system. The second stage, in which decomposi-
tion of CHP was completed and DCP was converted
into -methylstyrene, was performed in an autoclave
equipped with a stirrer and a sampler. The composi-
tion of the products was determined by GLC [4].
2
CH C CH3
CH C CH C(OH)(CH )
3 2 3 2
3
O
O
CH3 C CH C(CH3)2,
The elucidate the mechanism of acetol formation in
the first stage of CHP decomposition at various initial
O
1
070-4272/01/7401-0111$25.00 2001 MAIK Nauka/Interperiodica

112
VASIL’EVA et al.
Table 1. Concentration of acetol in the first stage of CHP
decomposition
We found that the acid concentration has no appre-
ciable efect on the rate of acetol accumulation, and the
decisive factor affecting the reaction rate is the tem-
perature. Data on variation of the acetol concentration
in the reaction mixture with time at various tempera-
tures are given in Tables 1 and 2.
Cacid
CCHP
T,
C
, s
CA, wt %
M
4
6
8
9
3
80
80
80
80
70
70
80
80
80
80
80
80
80
0.0034
0.0030
0.0029
0.0032
0.0032
0.0010
0.0011
0.0021
0.0022
0.0038
0.0035
0.0034
0.0032
0.258
0.188
0.198
0.544
0.356
0.197
0.243
0.227
0.205
0.178
0.258
0.246
0.202
0.070
0.067
0.076
0.115
0.080
0.051
0.058
0.078
0.071
0.091
0.080
0.099
0.160
In the course of studying accumulation of acetol in
the second stage of CHP decomposition, we revealed
some experimental trends. First, when we used as the
feed the products obtained in the circulation unit, the
acetol concentration in the reaction mixture consider-
ably increased. Second, when the feed for the second
stage was prepared in the first stage at the same sul-
furic acid concentrations, temperatures, and circula-
tion multiplicities, the final acetol concentrations after
completion of the second stage were equal irrespective
of its conditions. Third, when we used as the feed for
the second stage a model mixture identical in the
composition (according to GLC analysis) to the prod-
uct of the first stage, the increase in the acetol con-
centration in the reaction mixture did not exceed
0.005 wt %.
4
4
4
4
5
5
4
4
4
4
5
6
5.8
1.5
1.5
9
8.1
7.5
0
0
4.5
Table 2. Concentration of acetol in the second stage of
CHP decomposition
These facts give some insight into possible path-
ways of acetol formation in the course of sulfuric acid
decomposition of CHP. Apparently, the necessary
condiiton for acetol formation is simultaneous pres-
ence in solution of acetone, hydroperoxide (HP), and
catalytic amounts of sulfuric acid. The nature of HP
and the presence of phenol are of no significance;
additional experiments showed that acetol is efficient-
ly formed in acetone solution in the presence of other
HPs, in particular, hydrogen peroxide and tert-butyl
hydroperoxide (TBHP). Data on acetol accumulation
in the second stage of CHP decomposition are con-
sistent with this conclusion; the only specific feature
is that with the products from the first stage used as
the feed the amount of the forming acetol, according
to GLC data, exceeds several times that obtained with
the model mixture of the same composition. This fact
can be explained only by assuming that formation of
acetol from acetone in the presence of CHP and acid
occurs via formation of intermediate(s) undetectable
by GLC. It is assumed that in the first stage of CHP
decomposition this intermediate transforms into acetol
only partially, and the reaction is completed in the
second stage.
C , wt %, at indicated T,
C
A
,
min
1
00
110
120
130
0
5
7
9
0
2
5
8
0
5
0
0.077
0.087
0.079
0.087
0.093
0.085
0.102
0.110
0.087
0.120
0.120
0.120
1
1
1
1
2
2
3
0.091
0.100
0.105
0.107
0.119
0.123
0.127
0.112
0.113
0.119
0.123
0.127
concentrations CCHP, we studied the dependence of
the acetol concentration C in the reaction mixture on
A
the main process parameters: temperature T, sulfuric
acid concentration Cacid, and residence time .
The results show that the concentration of acetol in
the reaction mixture in the circulation conduit depends
on all the above-mentioned parameters; the concentra-
tion decreases with decreasing temperature, sulfuric
acid concentration, and residence time.
Possible intermediates that cannot be isolated and
identified are 2-hydroxy-2-cumylperoxypropane I and
2,2-bis(cumylperoxy)propane II. It is known that
compound I and related -hydroxy peroxides derived
from other HPs are formed reversibly in reactions of
ketones with HPs at low temperatures [5]. These com-
pounds are extremely labile, and their formation was
To elucidate the specific features of acetol accum-
ulation in the second stage of the process, we studied
the dependence of its concentration in the reaction
mixture on the sulfuric acid concentration and temper-
ature at various residence times.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 1 2001

PATHWAYS OF ACETOL FORMATION
confirmed only by IR spectroscopy. Compound II was
not described in the literature, but data are available
on its analog prepared from acetone and TBHP [6].
113
HO CH C CH .
2
3
ROH
O
Based on the above assumption and taking into
account published data, we suggest the following
scheme of acetol formation from acetone and CHP:
Since it is extremely difficult to confirm experi-
mentally formation of acetol by pathway (1) because
of the low stability of -hydroxy peroxides, we exam-
ined the possibility of occurrence of reaction (2). An
evidence in favor of this process could be formation
of CHP, DMPC, and acetol in a stoichiometric ratio
from specially prepared compound II. Since this com-
pound does not exist in the neat form and since CHP
formed from II by reaction (2) rapidly decomposes
into phenol and acetone under conditions of acid
catalysis, our proof of this mechanism was based on
chemical analogies. To simulate formation of acetol
in the second stage of CHP decomposition, we used
an analog of II, which was specially prepared from
acetone and TBHP according to [6]. This compound
was subjected to decomposition in the presence of
sulfuric acid in a solution of phenol in acetone. The
GLC analysis showed that decomposition of this di-
peroxide yields equimolar amounts of TBHP, trimeth-
ylcarbinol, and acetol, which is an indirect evidence
in favor of the suggested mechanism. In this process,
acetol is formed via intermediate carbocations, as
indicated by the absence of acetol in the products of
thermal decomposition of the model hydroperoxide
CH3
CH3
CH3
+
H
+ ROOH
O=C
CH3
HO C
CH3
HO C O O R
+
H
CH2
H
I
_
_
CH3
HO C O
CH _
CH3
C=O,
OH
+
H
(1)
ROH
_
2
CH2
where R is the cumyl radical.
Decomposition of I with intermediate formation of
the oxide is shown arbitrarily; most probably, decom-
position with carbinol elimination and intramolecular
rearrangement occur simultaneously.
The above hypothetical scheme can explain the
pathway of acetol formation in the first stage of CHP
decomposition, but, because of the low stability of
-hydroxy peroxides, in the second stage this pathway
is improbable. The acetol precursor in the second
stage should be a relatively stable compound. Presu-
mably, along with the reactions shown in scheme (1),
compound I reacts with CHP with formation of more
stable compound II by the scheme
in aprotic CCl without acid.
4
CONCLUSIONS
Formation of acetol in the course of sulfuric acid
decomposition of cumyl hydroperoxide into phenol
and acetone occurs by the carbocationic mechanism
via intermediate formation of 2-hydroxy-2-cumylper-
oxypropane and 2,2-bis(cumylperoxy)propane.
CH3
CH3
+
H
R O O C OH
R O O C+
CH3
H O
2
CH3
REFERENCES
CH3
1. Messina, G., Lorezoni, L., Cappellazzo, O., and Gam-
+
ROOH
ba, A., Chim. Ind. (Milan), 1983, vol. 65, no. 1, pp. 10
R O O C O O R.
(2)
1
7.
+
H
2
. Pasterean, M., C. R. Acad. Sci. Paris, 1907, vol. 144,
pp. 90 93.
CH3
II
3
4
. USSR Patent 1361937.
. Tsypysheva, L.G., Mishchenko, L.Ya., and Portno-
va, T.V., Zh. Anal. Khim., 1987, vol. 42, no. 2,
pp. 347 351.
Compound II, presumably formed in the course of
CHP decomposition in the first stage, in the second
stage at elevated temperature decomposes to form
CHP, DMPC, and acetol:
5
. Antonovskii, V.L. and Terent’ev, V.A., in Uspekhi
khimii organicheskikh perekisnykh soedinenii i auto-
okisleniya (Advances in Chemistry of Organic Perox-
ides and Autooxidation), Moscow: Khimiya, 1969,
pp. 442 450.
CH3
R O O C O O R
CH3
CH3
R O O C OH
CH3
+
H O
2
ROOH
6. Dickey, F.H., Rust, F., and Vaughan, W.E., J. Am.
Chem. Soc., 1949, vol. 71, pp. 1432 1434.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 1 2001