Published on the web November 20, 2010
1329
Synthesis and Gelation Behavior of 4¤-Propyl-1,1¤-bi(cyclohexyl)-4-one
-Alkoxybenzoylhydrazone
4
Juan Li, Pei Chen,* Xinbing Chen, Zhongwei An, and Yan Li
Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education,
School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an 710062, P. R. China
(
Received September 17, 2010; CL-100797; E-mail: chenpei@snnu.edu.cn)
A series of new alkoxybenzoylhydrazones of 4¤-propyl-1,1¤-
bi(cyclohexyl)-4-one were prepared as novel low molecular weight
organogelators (LMOGs). Their gelation behaviors in 10 solvents
were tested. Some of the compounds could form stable gels in bulk
organic solvents and self-assemble into fibrous microstructures in
organogel phase. FTIR and H NMR spectroscopy studies revealed
that hydrogen bonding between the gelator molecules was one of
the main driving forces for the formation of the gels.
O
RBr
O
N2H4
.
H2O
O
HO
RO
RO
OEt K2CO3
OEt
O
NHNH2
H
N
O
RO
N
1
O
(3HHB-n)
(FPB-n)
H
N
OHC
F
RO
N
F
R = CnH2n+1 ; n = 4, 5, 6, 7, 8, 12
Low molecular weight organogelators (LMOGs) have been
an active research field in materials science and supramolecular
chemistry due to their potential applications, involving optoelec-
Scheme 1. Synthetic routes of 3HHB-n and FPB-n.
1
tronic devices, sensors, nanomaterials, and delivery or modifi-
corresponding bromoalkanes with ethyl p-hydroxybenzoate.
3HHB-n was purified through recrystallization from alcohol to
give a purity more than 99% for HPLC measurement with
2
cation agents for drugs. Generally, LMOGs can self-assemble
into fibrous super-structures driven by multiple and weak non-
covalent interactions such as hydrogen bonding, dipoledipole,
van der Waals interaction, ³-stacking, and ionic interactions.3
Hydrogen-bonding interaction is thought to be the major driving
force of gelation for amide compounds such as amino acids,
peptides, ureas, carbamates, and thioureas. These LMOGs are
generally composed of alkyl chains and one amide group
¹
1
methanol as eluent at 1 mL min flow rate. The structures of the
intermediates and the products 3HHB-n and FPB-n were
1
confirmed by H NMR and FTIR measurements.
Gel samples were prepared according to the following
procedure. A weighed powder sample was mixed with an organic
solvent in a sealed test tube and the mixture was heated until the
solid dissolved, and the resulting solution was cooled to room
temperature in air. Then, the gelation was checked visually. If a
test tube containing the solution was inverted and no liquid was
observed running down the wall of the tube, it was judged to be a
gel. As shown in Table 1, 3HHB-n showed gelation ability in
(CONH) or two, together with acid moiety, hydroxy moiety, or
amino groups to ensure the formation of multiple intermolecular
hydrogen bonding between neighboring molecules. On the other
hand, cholesterol derivatives are nonhydrogen-bond-based gela-
tors, where van der Waals interaction is responsible for gelation.
Some LMOGs consisting of an amide group and a cholesteryl
¹
1
different solvents at a gel concentration of 25 mg mL
.
4
moiety have been developed in recent years. To the best of our
Moreover, the obtained gels were stable for a long time at
room temperature. Noted that length of alkyl chain of the
compounds showed obvious effect on their gelation abilities. The
suitable length of alkyl chain of the compounds was in favor
of the hydrophilelypophile balance in different organic liquids.
Compared with 3HHB-n, FPB-n exhibited no gelation ability,
indicating that bi(cyclohexyl) moiety could help to enforce van
der Waals interaction. These results demonstrated that a benzoyl-
hydrazone moiety, a bi(cyclohexyl) group, and a suitable length
alkyl chain were essential groups for gelation.
knowledge, compounds containing only one amide group
reported as LMOGs are few.5 Herein, a new LMOG with an
amide group has been designed and synthesized. The gelator
consists of three parts: an alkoxybenzoyl group, a bi(cyclohexyl)
moiety, and a hydrazone group functioning as a linker (Scheme 1,
3
HHB-n). The main ideas behind this design are as follows: (1)
benzoylhydrazone moiety bearing an amide group has a strong
tendency to form hydrogen bonds; (2) bi(cyclohexyl) moiety,
exhibiting specific spatial configuration, is introduced into the
structure to enforce van der Waals interaction. The obtained
compounds 3HHB-n are able to self-assemble into ordered
aggregates in a number of organic liquids and finally gelatinize
the liquids. For comparison, analogous compound 4-fluorobenz-
aldehyde 4-alkoxybenzoylhydrazone (FPB-n, Scheme 1) has also
been prepared and studied.
Concentration dependence of 2-propanol gels with 3HHB-6
were also conducted, as shown in Figure 1. The gel to sol
transition temperature (Tgel) increased with increasing concen-
tration of 3HHB-6 and then remained at 65 °C when the
¹
1
concentration was over 120 mg mL . In the lower concentration
¹
1
range (below than 15 mg mL ), not enough fibrils were formed
and the association interactions among fibrils related to the gelator
network were not complete.
4
¤-Propyl-1,1¤-bi(cyclohexyl)-4-one 4-alkoxybenzoylhydra-
zone, coded as 3HHB-n (n = 4, 5, 6, 7, 8, and 12), was prepared
by a condensation reaction between 4¤-propyl-1,1¤-bi(cyclohexyl)-
In order to investigate the aggregation morphology, xerogels
of 3HHB-n from ethanol or 2-propanol were obtained through
slowly evaporating the solvent in vacuum. The SEM pictures
were taken using FEI Quanta 200. Typical SEM images of
3HHB-n xerogels are shown in Figure 2. The SEM images
4
-one and 4-alkoxybenzoylhydrazine in absolute ethanol at reflux
for 6 h, as shown in Scheme 1, where 4-alkoxybenzoylhydrazine
was prepared by a reaction between hydrazine monohydrate and
ethyl 4-alkoxybenzoate obtained from etherification of the
Chem. Lett. 2010, 39, 13291330
© 2010 The Chemical Society of Japan
Li, Juan
