A highly selective aldol condensation of cyclopentanone with valeraldehyde over hydrotalcite-type catalysts

Article abstract of DOI:10.14233/ajchem.2013.13814

The aldol condensation using cyclopentanone with valeraldehyde was conducted at hydrotalcites catalysis. The catalyst was obtained by calcining the hydrotalcite precursor (Mg/Al = 3:1) at 773 K. Its reaction performance was evaluated on the various molar ratios of cyclopentanone to n-valeraldehyde. A good catalytic selectivity of 90 % and a high conversion of 93 % were achieved under mild conditions.

Full text of DOI:10.14233/ajchem.2013.13814

Asian Journal of Chemistry; Vol. 25, No. 7 (2013), 3847-3849
http://dx.doi.org/10.14233/ajchem.2013.13814
A Highly Selective Aldol Condensation of Cyclopentanone
with Valeraldehyde Over Hydrotalcite-type Catalysts
*
J. XU, Y. CAO, Q. MA and X. PENG
Department of Chemistry, School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, P.R. China
*Corresponding author: Tel/Fax: +86 25 84315520; E-mail: xhpeng@njust.edu.cn
(Received: 2 April 2012;
Accepted: 14 January 2013)
AJC-12708
The aldol condensation using cyclopentanone with valeraldehyde was conducted at hydrotalcites catalysis. The catalyst was obtained by
calcining the hydrotalcite precursor (Mg/Al = 3:1) at 773 K. Its reaction performance was evaluated on the various molar ratios of
cyclopentanone to n-valeraldehyde. A good catalytic selectivity of 90 % and a high conversion of 93 % were achieved under mild
conditions.
Key Words: 2-Pentylidene-cyclopentanone, Aldol condensation, hydrotalcite, Cyclopentanone, n-Valeraldehyde.
valeraldehyde3. Similarly, Wilson et al.4, improved the selec-
tivity of the aldol condensation reaction by controling the title
reactants molar ratio to 1.8. The hydrotalcites (HTc) and their
INTRODUCTION
Aldol condensation reactions are of fundamental impor-
tance in the synthesis of numerous large-volume organic
mixed oxides as heterogeneous catalyst with finely tunable
chemicals and fine chemicals which are extensively used in
basicities are developed recently. As their good basicity and
rubber, plastic, coating, pharmaceutical, pesticide and feed
stable lamellar structure, these materials have already been
additive industries. We successfully obtained 2-pentylidene-
cyclopentanone (e) through the aldol condensation between
used as catalysts for many organic preparations involving aldol
condensation reaction5-9. The present work deals with the aldol
condensation of cyclopentanone (a) with valeraldehyde (b) to
the reactants in the title (Scheme-I).The target substance is
used for some intermediates of biologically active substances
or perfumes such as methyl dihydrojasmonate1,2.
produce 2-pentylidene-cyclopentanone (e) with the hydrotalcites
(HTc) participated.
O
O
O
EXPERIMENTAL
CHO
Preparation of hydrotalcites: Hydrotalcites of 3:1
Mg/Al molar ratios were prepared by coprecipitation at high
supersaturation. Solution A was prepared by dissolving 25.6
g (0.10 mol) of Mg(NO3)2·6H2O and 12.1 g (0.033 mol) of
Al(NO3)3·9H2O in 100 mL deionized water. Solution B was
prepared by dissolving 10.7 g (0.2675 mol) NaOH and 7.4 g
(0.0698 mol) Na2CO3 in 100 mL deionized water. Put A into a
250 mL flask, solution B was then added dropwise with vigo-
rous stirring over a 2 h period while keeping the temperature
at 60 ºC and the pH value of the solution in the range of 8-10.
Then keep the precipitates at 60 ºC for 24 h in a thermostatic
bath. The solid was washed several times with deionized water
until the filtrate showed no presence of free base and subse-
quently dried at 90 ºC for 24 h. The hydrotalcites of 3:1 Mg/Al
molar ratio was calcined at 773 K for 6 h in a muffle furnace
prior for using.
g
f
c
d
O
Self-condensation
e
O
O
Cross-condensation
O
and
H
H
b
a
h
Scheme-I: Aldol condensation reaction between cyclopentanone and
valeraldehyde
The aldol condensation reaction of valeraldehyde with
cyclopentanone has already been paid much attention. A new
catalytic system"AlPON" and "ZrPON" exhibited good perfor-
mance for the aldol condensation of cyclopentanone with

3848 Xu et al.
Asian J. Chem.
Catalytic condensation: A 250 mL four-neck round-
Lewis acid sites. The former is due to the presence of oxygen
atoms with low cordination, while the latter toAl3+ cation3,7,14
.
bottom flask equipped with mechanical stirrer and reflux
condenser are charged. 10.5 g (0.125 mol) of cyclopentanone
and 0.4 g of the HTc were added in the round-bottom flask
and 4.3 g (0.05 mol) of n-valeraldehyde was then added
dropwise with stirring slowly while keeping the reaction tempe-
rature at 80 ºC for 11 h. Then, the Mg-Al mixed oxides was
separated by filtration, the filtrate was dried over anhydrous
sodium sulfate and analyzed by gas chromatography on an
Angilent 6890A chromatograph with FID detector and equipped
with a SE-30 column. The desired product of 2-pentylidene-
cyclopentanone (e) was separated by column chromatography
(n-hexane:ethyl acetate = 12:1) and its structure was identified
by 1H NMR spectrum and MS (Trace DSQ-GC-MS). The 1H
NMR spectra were recorded on a Bruker ARX300 instrument
with TMS as the interior standard. The 1H NMR (CDCl3) of
2-pentylidene-cyclopentanone (e): δ 0.866-0.914 (t, 3H, CH3),
1.311-1.455 (m, 8H, 4CH2), 1.890-1.965 (m, 2H, CH2), 2.099-
2.171 (m, 2H, CH2), 2.286-2.338 (t, 2H, CH2), 2.544-2.605 (t,
2H, CH2), 6.533 (t, 1H, -C=C-H). MS (EI, 70 eV): m/z = 151.94
(M+).
The reaction procedure of the aldol condensation
(Scheme-II) is nearly the same as the traditional procedure.
The aldol condensation was carried out on basic sites firstly
by capturing an α-H atom from cyclopentanone. Then the
generated carbanion species will attack the carbonyl group of
valeraldehyde. Finally, the ultimate product (e) was achieved
by dehydrating on the weak acid sites of the HTc (773 K).
Although it is easier to form a carbanion on the cyclopentanone
in the presence of base properties, the weak acid properties
can promote the formation of the protonated carbonyl compound
on valeraldehyde to be attacted by the generated carbanion.
As a result, the catalyst which has acid-base properties is benefit
for the cross-condensation3,15
.
O
O
O
Valeraldehyde
B
+
-BH
O
O
O
O
OH
+BH
_
B
-H O
2
RESULTS AND DISCUSSION
Scheme-II: Procedure of the cross-condensation between cyclopentanone
and valeraldehyde
The catalyst of HTc (773 K) used in the aldol condensation
between valeraldehyde and cyclopentanone was achieved by
calcinating hydrotalcite precursor HT (Mg/Al = 3) at 773 K.
The XRD powder patterns of HT (a) and HTc (773 K) (b)
were shown in Fig. 1. The XRD patterns indicated that the
lamellar structure of the HT (a) was changed. Moreover, the
obvious characteristic peaks of MgO (200) and Al2O3 (135)
appeared in the XRD patterns.
In order to get a better catalytic performance, reaction
temperature was taken into account firstly in our experiments.
Varying temperature of 60, 80 and 100 ºC, respectively were
carried out with a valeraldehyde/cyclopentanone molar ratio
of 1/5 and without solvent. Entries 4, 7, 8 (Table-1) indicated
that with the temperature up to 100 ºC, the valeraldehyde
conversion was increased. However, the selectivity of e was
the best when the temperature at 80 ºC. Due to low temperature
couldn't activate the carbonyl of cyclopentanone and the
catalysts efficiently, the lower temperature could result in low
valeraldehyde conversion and selectivity to e. On the contray,
a product g appeared that isomerizing from e when the reaction
temperature reached 100 ºC. 2-Cyclopenten-1-one (g) was
more thermodynamically stabler than 2-pentylidene-cyclo-
pentanone (e) because the conjugate between the carbonyl and
cyclic olefinic bond was more easier and stabler. Higher
temperature could favour to activate the catalyst and the
procedure of isomerization.
(003)
(a)
(006)
(012)
(015)
(110)
(018)
(112)
(200)
(135)
(b)
The reaction was also carried out over the different amount
of catalyst. From the entries 4, 9, 10, we could see that the
valeraldehyde conversion wouldn't increase with the HTc (773
K) used from 0.4-0.6 g. However, the side product g also
appeared when 0.6 g catalyst was used. 0.4 g HTc (773 K)
was enough for the procedure of the reaction under this
reaction condition. While increasing HTc (773 K) would
decrease the selectivity for producing g as a side product. Less
catalyst couldn't activate the substance efficiently and result
in low valeraldehyde conversion and poor selectivity to the
major product e.
0.
10
20
30
40
2θ (º)
50
60
70
80
90
Fig. 1. XRD powder patterns of HT (a), HTc (773 K) (b)
It is well known that the aldol condensation can be
catalyzed by both acid and base10-13. The base catalyst is favour
to the formation of carbanion on the cyclopentanone. However,
the acid catalyst can active the carbonyl group on the
valeralderhyde easily and strengthen the carbocation of the
carbonyl to be attacted by the carbanion species. The catalyst
of HTc (773 K) owned both the acid and base catalyst
excellences simultaneously for its both strong Lewis basic and
The molar ratio between valeraldehyde and cyclopen-
tanone also played an important role in the selectivity between
cross- and self-condensation3,7,9,16. Entries 1-6 (Table-1) showed
that valeraldehyde/cyclopentanone molar ratio of 1/5 was the

Vol. 25, No. 7 (2013)
A Highly Selective Aldol Condensation of Cyclopentanone with Valeraldehyde 3849
TABLE-1
ALDOL CONDENSATION BETWEEN VALERALDEHYDE AND CYCLOPENTANONE WITH HTc (773 K) CATALYZED
Product distribution (%)i
Catalyst
(m)
T
(ºC)
Valeraldehyde
conversion (%)b
Entry
n1:n2a
(c)
39
34
12
6
(d)
0
(e)
49
58
80
90
88
88
41
76
79
86
(f)
12
8
(g)
0
(h)
0
1
2
1:1
1:3
1:4
1:5
1:6
1:7
1:5
1:5
1:5
1:5
0.4 g
0.4 g
0.4 g
0.4 g
0.4 g
0.4 g
0.4 g
0.4 g
0.2 g
0.6 g
80
80
80
80
80
80
60
100
80
80
83
89
90
93
83
78
34
97
52
93
0
0
0
3
0
8
0
0
4
0
4
0
0
5
5
0
7
0
0
6
0
0
12
19
11
6
0
0
7
40
3
0
0
0
8
0
10
0
0
9
15
0
0
10
5
0
3
6
0
an1:n2 = The molar ratio of valeraldehyde:cyclopentanone, the amount of valeraldehyde was 0.025 mol. bDetected by GC,GC yield. iDetected by
GC,GC conversion. (d), (e), (f) were identified by GC-MS, the structure of (c) and (g) were identified by 1H NMR. (c): 2-Propyl-2-heptenal, (d): 2-
cyclopentylidene-cyclopentanone; (e): 2-pentylidene-cyclopentanone; (f): 2,5-dipentlidene-cyclopentanone; (g): 2-cyclopenten-1-one; (h): 2-
cyclopentylidenepentanal.
optimal reaction condition. The selectivity to e was 90 % and
valeraldehyde conversion was 93 % at the optimal reaction
condition. Decreasing the valeraldehyde/cyclopentanone molar
ratio could reduce the selectivity to c that was yielded by the
valeraldehyde self-condensation and product c disappeared
when the molar ratio down to 1:7. The low percentages of
valeraldehyde decreased the reaction rate and the opportunity
of self-condensation. However, according to Table-1 we could
also find that valeraldehyde conversion decreased when the
molar ratio was in the range of 1/5-1/7. For the reason of steric
hindrance, valeraldehyde is a bit activer than cyclopentanone.
It is difficult for carbanion gained on the cyclopentanone to
attack the carbonyl of the cyclopentanone. Product d and h
didn't appear via GC detected, whatever the valeraldehyde/
cyclopentanone molar ratio was with 0.4 g HTc (773 K) used
at 80 ºC.
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