Base-catalyzed autocondensation of cyclohexanone

Article abstract of DOI:10.1023/B:RJAC.0000022446.21411.4d

Autocondensation of cyclohexanone in air at 119-137°C, catalyzed with a solid alkali, was studied.

Full text of DOI:10.1023/B:RJAC.0000022446.21411.4d

Russian Journal of Applied Chemistry, Vol. 76, No. 12, 2003, pp. 1955 1957. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 12, 2003,
pp. 2004 2007.
Original Russian Text Copyright
2003 by Trakhanov, Kruk, Maksimuk.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Base-Catalyzed Autocondensation of Cyclohexanone
P. K. Trakhanov, V. S. Kruk, and Yu. V. Maksimuk
Research Institute of Physicochemical Problems, Belarussian State University, Minsk, Belarus
Received May 6, 2003
Abstract Autocondensation of cyclohexanone in air at 119 137 C, catalyzed with a solid alkali, was studied.
Cyclohexanone is an intermediate in industrial
organic synthesis. Its characteristic feature is tendency
to undergo autotransformations yielding a series of
products [1]. In synthesis of caprolactam [2] and adip-
ic acid [3], autocondensation is a side reaction, where-
as in the first step of industrial synthesis of 2-phenyl-
phenol (a bactericide) [4 6] or 2-cyclohexylcyclohex-
anol (a fragrance) [7], this is the principal process.
To improve the existing processes involving cyclo-
hexanone and develop new ones, it is appropriate to
study the kinetic features of its autocondensation,
primarily with the aim to obtain input data for simu-
lation of flowsheets and process equipment.
Formation of condensation products containing
three and more rings was considered in [11 13]. The
autocondensation is reversible, and, at elevated tem-
peratures, compounds II and III are hydrolyzed back
to cyclohexanone in the presence of water. The ki-
netic (in the range 180 290 C) and thermodynamic
characteristics of this reaction, which is very important
for processing by-products from caprolactam produc-
tion [14], have been considered previously [15 17].
Data on liquid-phase autooxidation of cyclohex-
anone under various conditions are summarized in
Table 1. It is seen that the major influence on the
reaction rate is exerted by the temperature and cata-
lyst. Virtually no data are available for the interval
from 80 to 210 C in which the majority of industrial
processes are performed. In this study, we examined
the kinetics of cyclohexanone autocondensation in air
at 119 137 C, catalyzed with a solid alkali.
The condensation is nonselective and yields a mix-
ture of isomers; the resulting compounds with double
bonds are not quite stable. Therefore, not all of the
products of deep autocondensation of cyclohexanone
have been identified. Compounds I III have been
studied in most detail [1, 8 10].
EXPERIMENTAL
O
O
O
OH
The kinetics of liquid-phase aldol condensation of
cyclohexanone was studied in a laboratory installation
consisting of a round-bottomed three-necked glass
flask fully immersed in a thermostat with silicone oil.
I
II
III
Table 1. Kinetics of liquid-phase autocondensation of cyclohexanone
T,
C
Catalyst/solvent
Other conditions
Analytical method References
25
Aqueous NaOH
Analysis of aqueous and organic layers
IR
[8]
[9]
[18]
30 70 Alcoholic or aqueous-alcoholic KOH Preliminary purging with argon
80
1H NMR
GLC
/
Under N2,
in the dark,
with removal of water
In air, with removal of water
Under N2, without removal of water
/CCl4
/CCl4 + DPPH*
119 137
210 0.5
(0.6 MPa)
KOH(cr.)/
Al, Fe oxides/decalin
GLC
GLC
This work
[19]
*
DPPH is 1,1-diphenyl-2-picrylhydrazyl (inhibitor of radical reactions).
1070-4272/03/7612-1955 $25.00 2003 MAIK Nauka/Interperiodica

1956
TRAKHANOV et al.
Table 2. Kinetic study of base-catalyzed autocondensation
Five experiments were performed at 119, 125, 129,
133, and 137 C. The flask was charged with 240 ml
of purified cyclohexanone (main substance content
>99.5%), which was preliminarily kept at the experi-
mental temperature for 40 min. Granulated KOH
(chemically pure grade), 2.4 g, was added with vigor-
ous stirring. The time of mixing of the alkali with
cyclohexanone was considered to be the start of the
process. Samples of the reaction mixture (2 3 ml)
were taken with a glass syringe 5, 10, 20, 40, 80, and
160 min after the start of the reaction. The samples
were transferred into glass test tubes containing 1-tet-
radecene (pure grade, distilled). The reaction in a
withdrawn sample was stopped by rapid cooling. Pre-
liminary experiments showed that change in the re-
actant concentrations after rapid cooling to 20 C
was negligible.
of cyclohexanone
Cyclo- Condensation products, wt %
T,
C
,
hexanone,
wt %
min
II + III
IV
V
119
125
129
133
137
5
10
20
40
80
160
5
10
20
42
84
160
5
10
20
40
80
160
5
10
20
40
80
160
5
98.7
96.9
93.6
90.9
87.6
84.2
98.1
96.0
92.1
88.4
85.0
81.4
95.9
92.7
89.4
85.8
81.7
76.7
95.0
92.0
88.5
84.4
79.0
72.3
92.4
90.2
86.0
79.6
68.0
56.0
1.2
2.9
6.0
0.1
0.1
0.1
0.2
0.2
0.5
0.1
0.1
0.2
0.3
0.5
0.6
0.2
0.2
0.3
0.5
0.6
0.9
0.2
0.2
0.3
0.4
0.6
1.4
0.3
0.2
0.4
0.8
1.7
3.5
0.1
0.1
0.3
0.3
0.5
0.6
0.1
0.1
0.2
0.3
0.5
0.7
0.1
0.3
0.4
0.5
0.7
0.9
0.1
0.2
0.3
0.2
0.5
1.0
0.2
0.3
0.5
0.8
1.5
2.4
8.6
11.6
14.7
1.8
3.8
7.5
11.0
14.5
17.3
3.7
The amount of water collected in the Dean Stark
trap was insignificant. The maximum amount was
about 5 ml at the highest experimental temperature
(137 C). Therefore, despite the fact that the distillate
was an azeotropic mixture of water and cyclohexan-
one, changes in the amount of cyclohexanone in the
flask were negligible.
6.9
10.0
13.0
17.0
21.4
4.0
6.9
11.3
14.4
18.2
25.3
7.1
Samples were analyzed by gas liquid chromatog-
raphy (GLC) on a Tsvet-800 device (flame ionization
detector; 2000 3-mm steel column packed with
Chromaton N-Super + 3% OV-1; column temperature
schedule: 140 C, 25 min; heating to 190 C at a rate of
10
20
40
80
160
9.3
1
13.2
18.7
28.7
38.2
25 deg min ; 190 C, 35 min; vaporizer and detector
temperatures 200 C; carrier gas nitrogen).
According to our results and those of Kim et al.
[11], GLC makes it possible to determine the ratios of
condensation products differing in the number of cy-
clohexane rings, but not the ratios of particular iso-
mers, because the products undergo isomerization in
the chromatographic column in the course of the anal-
ysis. Thus, we determined the total amount of prod-
ucts with two (II + III, retention time 10 min), three
(IV, 35 min), and more (V, 52 min) cyclohexane
rings. This assignment was based on the retention
times of authentic samples of II [16], III [20], cis-2,6-
di(1-cyclohexen-1-yl)cyclohexanone (a representative
of compounds IV) [13], 2,6-dicyclohexylidencyclo-
hexanone [21], and dodecatriphenylene (a representa-
tive of compounds V) [22]. Compound I is thermally
unstable [10] and decomposes in the course of the ki-
netic experiment.
The flask was equipped with a reflux condenser with
a Dean Stark trap, a high-speed glass stirrer with
a glass hydroseal, and a control thermometer. The
temperature in the flask was maintained with an accu-
racy of 0.2 C.
The concentrations of cyclohexanone and its con-
densation products (Table 2) were calculated from the
chromatograms using 1-tetradecene (retention time
5 min) as internal reference [23].
Fig. 1. Variation of the concentrations c of (1) cyclo-
hexanone and of its condensation products (2) II + III
and (3) IV with time
at 137 C.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 12 2003

BASE-CATALYZED AUTOCONDENSATION OF CYCLOHEXANONE
1957
Fig. 2. Variation of the concentrations c of (a) cyclohexanone and (b) II + III with time of autocondensation at (1) 119,
(2) 125, (3) 129, (4) 133, and (5) 137 C.
The kinetic curves of consumption of cyclohexan-
one and accumulation of condensation products are
shown in Figs. 1 and 2. The reaction order evaluated
from these curves is abnormally high for all the tem-
peratures except 137 C. We failed to interpret the
kinetic curves in terms of formal kinetics and to sug-
gest the condensation mechanism; apparently, several
reactions occur simultaneously.
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CONCLUSIONS
(1) A procedure was developed for GLC analysis
of products of cyclohexanone autocondensation, which
differ in the number of cyclohexanone rings.
(2) The temperature dependences of the concentra-
tions of the starting cyclohexanone and reaction prod-
ucts in autocondensation in air were obtained. The
reaction is accompanied by formation of heavy con-
densation products in the entire temperature range
studied (119 137 C); at 137 C, their amount reaches
4.5% in 2 h.
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 12 2003