Thermal stability of some ferrocene containing schiff bases

Article abstract of DOI:10.1007/s10973-007-8450-8

Taking into account the importance of thermal stability in the liquid crystals field, the study presents the thermal behavior of some ferrocene containing Schiff bases. Some other kinetic characteristics, such as reaction order (n), activation energy (E _a) and pre-exponential factor (lnA) have been also evaluated. The thermal stability series of Schiff bases was established analysis associated with three parameters (T _d, T _max, E _a) is: S₆43512.

Full text of DOI:10.1007/s10973-007-8450-8

Journal of Thermal Analysis and Calorimetry, Vol. 91 (2008) 2, 535–540
THERMAL STABILITY OF SOME FERROCENE CONTAINING
SCHIFF BASES
Irina C-rlescu, Gabriela Lisa* and D. Scutaru
‘Gh. Asachi’ Technical University Iasi, Faculty of Chemical Engineering, Bd. D. Mangeron, No. 71, 700050 Iasi, Romania
Taking into account the importance of thermal stability in the liquid crystals field, the study presents the thermal behavior of some
ferrocene containing Schiff bases. Some other kinetic characteristics, such as reaction order (n), activation energy (Ea) and pre-ex-
ponential factor (lnA) have been also evaluated. The thermal stability series of Schiff bases was established analysis associated with
three parameters (Td, Tmax, Ea) is: S6<S4<S3<S5<S1<S2.
Keywords: ferrocene containing Schiff bases, kinetic characteristics, thermal degradation
Introduction
OR
N
CH
Fe
Liquid crystal phases are often referred to as a fourth
state of matter. Various applications based on liquid
crystal phases are of importance in every day life.
They are indispensable in biological systems
(e.g. membranes) and are becoming an increasing part
of high-tech processes.
Although thermal stability of polymeric liquid
crystals has been extensively studied [1–4], only a mi-
nor attention has been paid to the small molecular liq-
uid crystals [5–10].
S1, R= –C18H37
S2, R= –OC–C17H35
O
N
CH
OR
O
Fe
S3, R= –C18H37
S4, R= –OC–C17H35
O
OR
N
CH
O
Fe
S5, R= –C18H37
S6, R= –OC–C17H35
Liquid crystalline materials containing ferrocene
are attracting special attention because of the ability
of the transition metal center to impart unique optical,
magnetic and electrical properties [11]. More than
that, ferrocene exhibits the properties of a typical aro-
matic molecule and is stable to more than 500°C. The
presence of the ferrocene into liquid crystalline com-
pounds induces a monotropic or enantiotropic
behavior [12].
Thermal stability represents an important param-
eter that may affect the use of new compounds, espe-
cially into domains that require treatment at elevated
temperatures [9, 10]. In the case of liquid crystals,
alongside to the especially properties: fluidity, optical
birefringence, compounds must be thermally stable in
the temperature range of the mesophase domain.
The paper presents the study of the thermal sta-
bility of some ferrocene derivatives presented in
Scheme 1. Ferrocene derivatives S3–S6 presented
broad enantiotropic liquid crystalline phases. The
degradation process is complex and depends on the
mesogenic units attached to the ferrocene.
Scheme 1 The chemical structure of the target compounds
Experimental
Materials
Silica gel 60 (Merck) was used for column chroma-
tography. TLC was performed on Silicagel F254 plates
(Merck). The used amino and aldehydic compounds
were previously prepared in our laboratory.
General procedure for sample preparation
To a stirred solution containing the amino and aldehy-
dic compounds in ethanol a few drops of glacial acetic
acid were added. The solution was refluxed with stir-
ring for 6 h. The mixture was filtered while hot and
the solid was washed on filter with hot ethanol. The
resulting solid was recrystallised from ethanol or pu-
rified by column chromatography (CC).
*
Author for correspondence: gapreot@ch.tuiasi.ro
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2007 Akadémiai Kiadó, Budapest

C„RLESCU et al.
4-Octadecyloxybenzylidene-4-ferrocenylphenylamine (S1)
4-Ferrocenylbenzoic acid 4-[(4-octadecanoyl-
oxybenzylidene)amino]phenyl ester (S4)
Quantities: 0.3 g (1.08 mmol) 4-ferrocenylaniline in
30 mL ethanol, 0.405 g (1.08 mmol) 4-octadecyl-
oxybenzaldehyde, glacial acetic acid (catalytic). The
product was recrystallised from ethanol. Yield: 74.4%
(0.51 g), m.p.: 109–112°C. IR (KBr, cm–1): 2918,
2848, 1606, 1570, 1516, 1469, 1309, 1247, 1168,
Quantities: 0.35 g (0.881 mmol) 4-aminophenyl-
4-ferrocenylbenzoate in 30 mL ethanol, 0.342 g
(0.881 mmol) 4-octadecanoyloxybenzaldehyde, gla-
cial acetic acid (1–2 drops). Purification: CC/silica
gel/CH2Cl2:petroleum ether: TEA=1:4:3%. Yield:
53.2% (0.36 g), m.p. (liquid crystal): 114°C (K1/K2),
126°C (K2/CL), 153°C (CL/I), 151°C (I/CL), 104°C
(CL/K2), 82°C (K2/K1). IR (KBr, cm–1): 2920, 2848,
1
1029, 842. H-NMR dH (CDCl3): 8.38 (s, 1H, CH),
7.78 (d, 2H, ArH), 7.43 (d, 2H, ArH), 7.09 (d, 2H,
ArH), 6.91 (d, 2H, ArH), 4.58 (t, 2H, C5H4), 4.25 (t,
2H, C5H4), 3.98 (s, 5H, C5H5), 3.95 (t, 2H, –OCH2–),
1.74 (m, 2H, –CH2–), 1.40–1.19 (m, 30H, 15CH2),
0.81 (t, 3H, –CH3). m/z: 631 [M-2]+.
1
1761, 1724, 1602, 1504, 1265, 1178, 815. H-NMR
dH (CDCl3): 8.47 (s, 1H, CH), 8.13 (d, 2H, ArH), 7.95
(d, 2H, ArH), 7.59 (d, 2H, ArH), 7.26 (m, 4H, ArH),
7.22 (d, 2H, ArH), 4.75 (t, 2H, C5H4), 4.43 (t, 2H,
C5H4), 4.06 (s, 5H, C5H5), 2.58 (t, 2H, –OC–CH2–),
1.77 (m, 2H, –CH2–), 1.43–1.26 (m, 28H, 14CH2),
0.88 (t, 2H, –CH3). 13C–NMR dC (CDCl3): 172.3
(>C=O), 165.7 (>C=O), 159.6 (–CH=N–), 153.6,
149.9, 149.6, 146.5, 134.1, 130.1, 130.4, 126.9,
126.1, 122.8, 122.5, 122.2 (12 C aromatic), 83.4,
70.4, 70.3, 67.4 (4 C, C5H4 and C5H5), 34.8–14.5
(17 C aliphatic). m/z: 766 [M-1]+.
4-(4-Ferrocenylphenyliminomethyl)benzoic acid
heptadecyl ester (S2)
Quantities: 0.25 g (0.90 mmol) 4-ferrocenylaniline in
30 mL ethanol, 0.35 g (0.90 mmol) 4-octadeca-
noyloxybenzaldehyde, glacial acetic acid (catalytic).
The product was recrystallised from ethanol. Yield:
46% (0.269 g), m.p.: 115°C. IR (KBr, cm–1): 2914,
2848, 1751, 1685, 1656, 1598, 1465, 1384, 1219,
1
1157, 925, 840. H–NMR dH (CDCl3): 8.49 (s, 1H,
4-[(4-Octadecyloxybenzylidene)amino]benzoic acid
4-ferrocenylphenyl ester (S5)
CH), 7.92 (d, 2H, ArH), 7.49 (d, 2H, ArH), 7.18 (m,
4H, ArH), 4.64 (t, 2H, C5H4), 4.31 (t, 2H, C5H4), 4.03
(s, 5H, C5H5), 2.56 (t, 2H, –OC–CH2–), 1.75 (m, 2H,
–CH2–), 1.57–1.24 (m, 28H, 14CH2), 0.86 (t, 3H,
–CH3). m/z: 645 [M-2]+.
Quantities: 0.2 g (0.503 mmol) 4-ferrocenylphenyl-
4-aminobenzoate in 20 mL ethanol, 0.188
g
(0.503 mmol) 4-octadecyloxy-benzaldehyde, glacial
acetic acid (1–2 drops). Purification: CC/silica
gel/CH2Cl2: petroleum ether:TEA=1:4:3%. Yield: 63%
(0.425 g), m.p. (liquid crystal): 97°C (K1/K2), 114°C
(K2/CL), 145°C (CL/I), 143°C (I/CL), 76°C (CL/K2),
32°C (K2/K1). IR (KBr, cm–1): 2918, 2848, 1753, 1593,
4-Ferrocenylbenzoic acid 4-[(4-octadecyloxy-
benzylidene)amino]phenyl ester (S3)
Quantities: 0.3 g (0.755 mmol) 4-aminophenyl-
4-ferrocenylbenzoate in 30 mL ethanol, 0.282 g
(0.755 mmol) 4-octadecyloxy-benzaldehyde, glacial
acetic acid (1–2 drops). Purification: CC/silica
gel/CH2Cl2: petroleum ether: TEA=1:4:3%, Yield:
43.9% (0.25 g), m.p. (liquid crystal): 79°C (K1/K2),
133°C (K2/CL), 144°C (CL/I), 143°C (I/CL), 118°C
(CL/K2), 34°C (K2/K1). IR (KBr, cm–1): 2918, 2848,
1726 (>C=O), 1604, 1570, 1508, 1255, 1180, 813.
1H-NMR dH (CDCl3): 8.41 (s, 1H, CH), 8.13 (d, 2H,
ArH), 7.85 (d, 2H, ArH), 7.59 (d, 2H, ArH), 7.25 (m,
4H, ArH), 6.99 (d, 2H, ArH), 4.75 (t, 2H, C5H4), 4.42
(t, 2H, C5H4), 4.06 (s, 5H, C5H5), 4.02 (t, 2H,
–O–CH2–), 1.79 (m, 2H, –CH2–), 1.51–1.26 (m, 30H,
15CH2), 0.88 (t, 3H, –CH3). 13C–NMR dC (CDCl3):
163.2 (>C=O), 159.9 (–CH=N–), 157.8, 147.9, 146.7,
144.0, 128.4, 128.2, 126.8, 124.7, 123.7, 120.26,
119.7, 112.6, (12 C aromatic), 81.3, 67.9, 67.8, 66.2,
64.9 (5 C, C5H5, C5H4 and –O–CH2–), 29.8, –12.0
(17 C, aliphatic). m/z: 752 [M-1]+.
1
1571, 1251, 1165, 812. H-NMR dH (CDCl3): 8.43 (s,
1H, CH), 8.25 (d, 2H, ArH), 7.87 (d, 2H, ArH), 7.49 (d,
2H, ArH), 7.26 (m, 4H, ArH), 7.13 (d, 2H, ArH), 4.72 (t,
2H, C5H4), 4.39 (t, 2H, C5H4), 4.14 (s, 5H, C5H5), 4.03
(t, 2H, –O–CH2–), 1.79 (m, 2H, –CH2–), 1.44–1.26 (m,
30H, 15CH2), 0.88 (t, 2H, –CH3). 13C-NMR dC (CDCl3):
163.05 (>C=O), 160.05 (–CH=N–), 156.8, 153.7,
148.28, 137.1, 133.4, 131.6, 128.4, 125.2, 124.8, 121.5,
118.6, 120.6 (12 C aromatic), 69.8, 67.9, 67.3, 66.7,
65.0 (C5H4, C5H5 and –OCH2), 29.5–11.7 (17 C,
aliphatic). m/z: 752 [M-1]+.
4-[(4-Octadecanoyloxybenzylidene)amino]
benzoic acid 4-ferrocenylphenyl ester (S6)
Quantities: 0.35 g (0.88 mmol) 4-ferrocenylphenyl-
4-aminobenzoate in 25 mL ethanol, 0.342
g
(0.88 mmol) 4-octadecanoyloxy-benzaldehyde, glacial
acetic acid (1–2 drops). Purification: CC/silica
gel/CH2Cl2: petroleum ether:TEA=1:4:3%. Yield: 63%
(0.425 g), m.p. (liquid crystal): 66°C (K1/K2), 129°C
(K2/CL), 155°C (CL/I), 151°C (I/CL), 67°C (CL/K2),
536
J. Therm. Anal. Cal., 91, 2008

FERROCENE CONTAINING SCHIFF BASES
55°C (K2/K1). IR (KBr, cm–1): 2918, 2848, 1751, 1723,
The obtained curves for the S1 and S2 samples are
presented in Figs 1–3 and in Figs 4–6 for compounds
S3, S4, S5, S6.
The curves revealed that the initial temperature
at which the thermal degradation for the first stage be-
gins is more than 400°C, which proves a better ther-
mal stability for the analyzed Schiff bases.
For all samples, the degradation took place in
two stages, with different mass loss (Table 2).
Table 2 reveals the TG data such as: Td – the on-
set temperatures, Tmax – temperature of maximum de-
gree rate, mass loss (m, %) corresponding for each
stage and DTA characteristics.
1627, 1595, 1278, 1211, 1161, 825. 1H-NMR dH
(CDCl3): 8.45 (s, 1H, –CH–), 8.25 (d, 2H, ArH), 7.97 (d,
2H, ArH), 7.49 (d, 2H, ArH), 7.28 (m, 2H, ArH), 7.25
(d, 2H, ArH), 7.16 (d, 2H, ArH), 4.72 (t, 2H, C5H4), 4.40
(t, 2H, C5H4), 4.14 (s, 5H, C5H5), 2.59 (t, 2H,
–O–CO–CH2–), 1.77 (m, 2H, –CH2–), 1.43–1.26 (m,
28H, 14CH2), 0.88 (t, 3H, –CH3). 13C-NMR dC (CDCl3):
172.03 (>C=O), 165.05 (>C=O), 160.07 (–CH=N–),
156.8, 153.7, 149.28, 137.1, 133.4, 131.6, 130.4, 127.2,
126.8, 122.3, 121.6, 120.9 (12 C aromatic), 70.32,
69.61, 68.03, 67.05 (4 C, C5H4, C5H5), 34.5–14.2 (17 C
aliphatic). m/z: 766 [M-1]+.
The most important mass loss for S1, S3, S4, S5,
S6 has been recorded in the first stage of the thermal
degradation, at temperatures onset over 400°C. In
contrast, S2 have a special behavior, the most impor-
tant mass loss being recorded in the second stage of
the thermal degradation, at temperatures onset be-
Methods
Confirmation of the structures of the products was ob-
tained by 1H-NMR and 13C-NMR spectroscopy, using
a Jeol ECA 600 MHz spectrometer with tetra-
methylsilane as internal standard. IR spectra were re-
corded using a Nicolet Magna 550 FT-IR spectrome-
ter (NaCl crystal window). Mass spectra were
recorded on a Jeol JMS-AX 505 mass spectrometer
using the FAB+ method for ionization.
Thermogravimetric experiments were recorded on
Paulik–Paulik–Erdey type Derivatograph MOM Hun-
gary in the following conditions: samples mw=35±5 mg,
Al2O3 as reference material, heating rate 10°C min–1,
stating conditions, temperature range 10–900°C.
The processing of the thermogravimetric data
was performed using the integrable methods
Coats–Redfern [13] and Reich–Lewi [14].
S1
S2
0
200
400
600
800
1000
Temperature/°C
Fig. 1 TG curves for samples S1 and S2
Results and discussion
The performed reactions are presented in Scheme 2.
Table 1 contains the structure of the investigated
products.
S1
Table 1 Structure of compounds
Sample
Z
R
S2
S1
S2
S3
S4
S5
S6
–C6H4–
–C18H37
–OC–C17H35
–C18H37
–C6H4–
–C6H4–COO–C6H4–
–C6H4–COO–C6H4–
–C6H4–OCO–C6H4–
–C6H4–OCO–C6H4–
–OC–C17H35
–C18H37
0
200
400
600
800
1000
Temperature/°C
–OC–C17H35
Fig. 2 DTA curves for samples S1 and S2
EtOH
H
C
Z
OR
Z
NH2
+
N
CH
OR
O
acetic
acid
Fe
Fe
Scheme 2 Synthesis of Schiff bases
J. Therm. Anal. Cal., 91, 2008
537

C„RLESCU et al.
S1
S3
S4
S2
S5
S6
0
200
400
600
800
1000
0
200
400
600
800
1000
Temperature/°C
Temperature/°C
Fig. 3 DTG curves for samples S1 and S2
Fig. 5 DTA curves for samples S3, S4, S5 and S6
S3
S4
S3
S4
S5
S5
S6
S6
0
200
400
600
800
1000
0
200
400
600
800
1000
Temperature/°C
Temperature/°C
Fig. 4 TG curves for samples S3, S4, S5 and S6
Fig. 6 DTG curves for samples S3, S4, S5 and S6
tween 580 and 805°C. For all the samples, the degra-
dation processes are not complete, for each case a
residue being left.
Using as thermal stability criteria the onset tem-
peratures (Td) for the first stage, the thermal stability
series was established as being the following:
the values of activation energy for the first stage of
thermal degradation, the following series of thermal
stability of some ferrocene derivatives are obtained.
The observed results are in agreement with thermal
stability series obtained previously by considering Td
or Tmax as thermal stability criteria.
S6<S4<S3<S5<S1<S2
S4@S6<S3<S5<S1<S2
The same conclusions regarding the thermal sta-
bility are obtained even if is considered the tempera-
ture of degradation at maximum degree rate (Tmax) as
criteria of stability.
In order to obtain information regarding the deg-
radation mechanism, a kinetic processing of the data,
by using the Coats–Redfern integral method, has been
made [4]. The obtained results: reaction order (n), ac-
tivation energy (Ea), pre-exponential factor (lnA),
compensation parameter (Sp=Ea/lnA) and correlation
coefficients (r2) are presented in Table 3.
For all the thermal degradation stages the found
reaction order was 1. The activation energy for S2
sample from first stage is bigger than those corre-
sponding to the other sample, fact that demonstrate
the higher thermostability, which correspond with the
thermogravimetric data from Table 2. By comparing
For getting supplementary evidences regarding
the degradation mechanism of the analyzed com-
pounds, a study of the compensation effect has been
effectuated. Accordingly, a graphical representation
of lnA as function of Ea has been carried out, the com-
pensation equations being represented in Fig. 7.
The linear dependence confirms the similar degra-
dation mechanism of the analyzed compounds in the
first stages, the slope of the lines being around 0.15.
In order to obtain supplementary information about
the degradation mechanism, the influence of the conver-
sion degree on the activation energy value was evalu-
ated by Reich–Lewi methods. The calculated
Reich–Lewi diagrams for analyzed ferrocene deriva-
tives are presented in Figs 8 and 9. The values of the ac-
tivation energy are grouped according to the two main
538
J. Therm. Anal. Cal., 91, 2008

FERROCENE CONTAINING SCHIFF BASES
Table 2 Thermogravimetric data
Stage of thermal
degradation
DTA
characteristic data
Td/
°C
Tmax
°C
/
Mass loss/
%
Sample
S1
I
exo
exo
492
552
519
671
52.79
37.14
10.07
46.24
48.33
5.43
II
residue
I
exo
exo
505
580
567
758
S2
S3
S4
S5
S6
II
residue
I
exo
exo
472
568
503
661
48.42
34.12
17.46
56.18
37.46
6.36
II
residue
I
exo
exo
470
550
490
643
II
residue
I
exo
exo
484
585
517
744
51.30
31.15
17.55
50.85
29.91
19.24
II
residue
I
exo
exo
409
575
486
733
II
residue
Table 3 Kinetic characteristics in non-isotherm conditions
Table 4 Characteristic temperatures and apparent activation
energies obtained by the Reich–Levi method at con-
version degree a=0.5
Ea/
kJ mol–1
Sp
Sample
n
lnA
Stage I
r2
T0.5 at 50%
conversion
Ea at 50% conversion/
kJ mol–1
Sample
S1
S2
S3
S4
S5
S6
1
1
1
1
1
1
178.84
200.33
126.98
91.29
29.34
32.14
22.22
15.49
25.55
14.62
6.09
6.23
5.71
5.89
5.97
6.22
0.999
0.999
0.999
0.996
0.998
0.998
S1
S2
S3
S4
S5
S6
568
607
560
548
577
551
109
148
100
95
152.60
91.38
107
87
Stage II
S1
S2
S3
S4
S5
S6
1
1
1
1
1
1
98.24
101.92
112.21
100.46
90.60
13.60
12.50
15.41
13.93
11.58
11.76
7.22
8.15
7.28
7.21
7.82
8.07
0.998
0.999
0.997
0.996
0.999
0.999
35
30
25
20
15
10
5
S2
S1
S5
S3
S4
S6
95.00
lnA(stage I)=0.1579Ea+1.0795
R2=0.9905
degradation steps. In addition, similar values at conver-
sion values higher than 0.7 were observed.
stage I
0
0
The results for activation energy obtained by us-
ing the Reich–Levi method and the temperature cor-
responded to the 50% transformation degree are pre-
sented in Table 4. By analyzing the calculated values,
an agreement with the thermal stability series ob-
tained previously was observed.
50
100
150
200
250
Ea/kJ mol–1
Fig. 7 The pre-exponential factor dependence as function of
the activation energy
J. Therm. Anal. Cal., 91, 2008
539

C„RLESCU et al.
Acknowledgements
D. S., G. L. and I. C. gratefully acknowledges for financial
support from Ministry of Education of Romania (grant
33371/2004, code CNCSIS 554/40).
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Conclusions
Received: February 8, 2007
Accepted: April 18, 2007
OnlineFirst: June 28, 2007
The thermal stability and degradation kinetics of
ferrocene containing Schiff bases have been reported in
this research. Kinetic parameters of degradation were
evaluated by using the Coats–Redfern and Reich–Levi
methods. The thermal stability series of Schiff bases was
established analysis associated with three parameters
(Td, Tmax, Ea) is: S6<S4<S3<S5<S1<S2.
DOI: 10.1007/s10973-007-8450-8
540
J. Therm. Anal. Cal., 91, 2008