Structural and electrical conductivity studies on 1,4 bis (P-methoxybenzilidine) (SB) and its diphenyl phosphine derivative (OPSB)

Article abstract of DOI:10.1080/10426500490466904

Schiff base "1,4 bis (p-methoxybenzilidine) benzene" (SB) and its diphenyl phosphine derivative (OPSB) have been isolated in solid state and characterized on the bases of macroanalytical, infrared IR, electronic and ¹H NMR spectral data, and th

Full text of DOI:10.1080/10426500490466904

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Phosphorus, Sulfur, and Silicon and the Related
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STRUCTURAL AND ELECTRICAL CONDUCTIVITY STUDIES
ON 1,4 BIS (P-METHOXYBENZILIDINE) (SB) AND ITS
DIPHENYL PHOSPHINE DERIVATIVE (OPSB)
R. S. Farag a , B. A. El-Sayed a , M. A. El-Nawawy a & S. M. Shaaban a
a Chemistry Department, Faculty of Science, Al-Azhar University , Cairo, Egypt
Published online: 16 Aug 2010.
To cite this article: R. S. Farag , B. A. El-Sayed , M. A. El-Nawawy & S. M. Shaaban (2004) STRUCTURAL AND ELECTRICAL
CONDUCTIVITY STUDIES ON 1,4 BIS (P-METHOXYBENZILIDINE) (SB) AND ITS DIPHENYL PHOSPHINE DERIVATIVE (OPSB),
Phosphorus, Sulfur, and Silicon and the Related Elements, 179:10, 1923-1931, DOI: 10.1080/10426500490466904
To link to this article: http://dx.doi.org/10.1080/10426500490466904
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Phosphorus, Sulfur, and Silicon, 179:1923–1931, 2004
ꢀC
Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490466904
STRUCTURAL AND ELECTRICAL CONDUCTIVITY
STUDIES ON 1,4 BIS (P-METHOXYBENZILIDINE)
(SB) AND ITS DIPHENYL PHOSPHINE DERIVATIVE
(OPSB)
R. S. Farag, B. A. El-Sayed, M. A. El-Nawawy,
and S. M. Shaaban
Chemistry Department, Faculty of Science,
Al-Azhar University, Cairo, Egypt
(Received June 20, 2003; accepted February 11, 2004)
Schiff base “1,4 bis (p-methoxybenzilidine) benzene” (SB) and its
diphenyl phosphine derivative (OPSB) have been isolated in solid state
and characterized on the bases of macroanalytical, infrared IR, elec-
tronic and 1H NMR spectral data, and thermal gravimetric analysis
(TGA).
The electrical conductivity as a function of temperature for the two
compounds under investigation (SB and OPSB) have been measured.
The results of the electrical conductivity (σ), thermal activation ener-
gies associated with the electrical conductivity, as well as energy gaps
calculated from the electronic absorption spectra in the solid state were
consistent with those of the traditional semiconductors.
Keywords: Electrical conductivity; electronic; 1H NMR; IR; organopho-
sphorus compounds
INTRODUCTION
The synthesis of Schiff bases has been reported, and its coordination
chemistry has been a subject of intensive study.1–7 Little is known
about the reaction of Schiff bases with halogenated organophospho-
rus compounds.8,9 Also, recent work has produced useful study on the
synthesis of phosphate and phosphine Schiff-base complexes.10,11
Attempts have been devoted to relating the electrical conductiv-
ity, as well as dielectric constants of a number of important classes
of compounds involved the azomethine linkage (\/C N ), the oximes
Address correspondence to B. A. El-Sayed, Chemistry Department, Faculty of Science,
Al-Azhar University, Cairo, Egypt. E-mail: badr elsayed@hotmail.com
1923

1924
R. S. Farag et al.
(\C N OH), the hydrazones (\C NNH2) and the azines (\C N)2, to
/
/
/
their chemical structures, where the electron system of these com-
pounds is highly conjugated and considered to be delocalized to some
extent. Thus, they show semiconducting properties.12–17 El-Sayed et al.
investigated the dependencies of the electrical conductivity (σ), in-
frared, ultraviolet, and visible absorption spectra of some Schiff-base
compounds and their diphenyl phosphinyl derivatives on chemical
constitution.18,19 In the present work 1,4 bis (p-methoybenzilidine)-
benzene (SB) and its diphenylphosphine derivative (OPSB) have been
isolated in solid state and characterized. The electrical conductivity (σ)
as a function of temperature for SB and OPSB showed semiconducting
properties.
EXPERIMENTAL
The chemicals used in this study were provided in a high-purity grade
by Aldrich & BDH.
1,4 bis (p-methoxy denzilidine) benzene (SB) was prepared and pu-
rified as follows:
A
mixture of p methoxy benzaldehyde (0.2 mole) and p-
phenylenediamine (0.1 mole) were heated in about 100 ml of ethanol
till boiling for a half hour. The residue was cooled and the product was
recrystallized from ethanol to give a yellow crystalline compound SB
with m.p. 130◦C.
1,4, bis p-methoxy benzilidine diphenylphosphine methylene amino
phenyl (OPSB) was prepared and purified as follows:
A solution of diphenyl chlorophosphine (0.2 mole) was added to a
well-stirred mixture of 1,4 bis (p-methoxybenzilidine) benzene (SB; 0.1
mole) and triethylamine (0.2 mole) as a base in 100 ml of dry dioxane.
After completing the addition, the reaction mixture was heated under
reflux for 3 h. The solid formed (triethylamine hydrochloride) was fil-
tered off, and the filterate was evaporated under vacuum to give a solid
compound that was recrystallized from DMF to obtain a yellow crys-
talline compound OPSB (m.p. 210◦C).
The prepared compounds SB and OPSB were checked by thin layer
chromatography (TLC). Microanalyses of carbon, hydrogen, and nitro-
gen were carried using the Perkin-Elmer 2400 CHN elemental analyzer.
IR spectra were measured as a KBr pellets at 28 0.1◦C using a
Shimadzu IR 440, and the data were reported in cm−1. The electronic
spectra were recorded using Perkin-Elmer lambda 3B spectrophotome-
1
ter. H-NMR spectra were recorded on a Varian EM 360 L-90 MHz
spectrometer using DMSO d6 as a solvent.

Benzilidine and Its Diphenyl Phosphine Derivative
1925
The dc electrical conductivity was measured at different tempera-
tures from room temperature up to near the melting point of each sam-
ple in the ohmic region by using the potential probe method.20 The
samples were prepared as compressed disks at ∼4 ton cm−2, diame-
ter 10 mm, and thickness 1–2 mm, coated with silver paste BDH, and
checked several times for good contact.
TGA was measured from room temperature up to 600◦C under
heating rate 10◦C/min. the data were performed using Shimadzu
TGA-50 H.
RESULTS AND DISCUSSION
SB and OPSB were checked by TLC and identified on the bases of their
elemental analysis (Table I).
IR spectra of compound SB (Figure 1) showed the characteristic
v CH N stretching vibration at 1566 cm−1 and a characteristic
stretching frequency for paradisubstituted aromatic ring at 783 cm−1
,
but the IR spectra of compound OPSB (Figure 1) showed the character-
istic v CH N stretching vibration at 1600 cm−1. A band at 700 cm−1
characterized stretching frequency for phenyl rings that attached to
the phosphorus atom.21 The band at 1100 cm−1 is investigated to be
stretching vibration of v P C, and a band at 2708 cm−1 is due to the
stretching vibration of v CH aromatic.
The electronic spectra of SB showed two characteristic bands: one at
325 nm is corresponding to n–π∗, and the other one at 260 nm is due to
the π–π∗ transition. On the other hand the spectra of OPSB showed two
characteristic bands: one at 325 corresponds to n–π∗, and one at 262 nm
corresponds to π–π∗ transition of the π electron system of phenyl
rings.
1H NMR spectra of SB indicate the presence of the azomethine proton
at δ = 8.3 ppm (1 H,S), methoxy protons at δ = 3.9 ppm (OCHs, 3 H,S),
and para disubstitution aromatic protons as AB system at δ = 7.2–
1
7.8, J = 0.7 ppm. The H NMR spectra of compound OPSB indicated
TABLE I Chemical Analysis and Melting Points of SB and the OPSB
Chemical analysis
Solvent
% Calculated
% Found
used for
m.p.
Compound
Color
crystallization (◦C)
C
H
N
P
C
H
N
P
SB
OPSB
Deep yellow
Yellow
EtOH
D.M.F
130 77.2 6.1 10.6
210 62.1 4.5 5.8 5.5 62.4 4.8 5.5 5.8
—
77.4 5.8 11.5
—

1926
R. S. Farag et al.
FIGURE 1 IR spectra of compounds (SB) and (OPSB).
the disappearance of the azomethine proton due to the replacement of
the hydrogen atom by the diphenylphosphine group, the methoxy pro-
tons appeared at δ = 3.7 ppm (OCHs, 3 H,S), and para disubstituted
aromatic protons as AB system associated with the phenyl protons of
diphenylphosphine group at δ = 6.7–8.2 ppm.
The obtained data are in good agreement with those calculated for
the suggested structure of the prepared compounds SB and OPSB.
The TGA thermograms of SB and OPSB compounds indicate two
transition steps and residue due to decomposed products, where the

Benzilidine and Its Diphenyl Phosphine Derivative
1927
TABLE II Transitions of the TGA of SB and OPSB Compounds
Compound
SB
Mol. wt.
344
m.p.
130
Transition, weighty, temperature Residue %
92.44%
290–400◦C
33.45%
6.63%
0.93
400–600◦C
37.50%
OPSB
712
210
29.05
200–350◦C
350–600◦C
residue is thermally stable up to 600◦C as indicated in Table II and
Figure 2.
The electrical conductivity (σ) of the SB and OPSB is measured up
to a temperature near the melting point of each compound from room
temperature. The variation of conductivity with temperature for the
compounds is shown in Figures 3 and 4. The electrical conductivity
FIGURE 2 TGA diagram of (SP) and (OPSB).

1928
R. S. Farag et al.
FIGURE 3 The relation between ln a and 1/T of (SB) at 20 V and 70 V.
values and the thermal activation energies for both compounds are
given in Table III. In general, it has been well established from these
values that they behaved as the traditional semiconductor materials,
i.e., with (a) varying exponentially with temperature according to the
following equation:
σ = (σo exp (−E/kT))
(1)
where σo is the pre-exponential factor and Ec is the activation en-
ergy of conduction. Equation (1) is illustrated by the Arrhenius plots of
Figures 3 and 4, whose slopes give the different activation energies Ec
listed in Table III. The different straight lines associated with different

Benzilidine and Its Diphenyl Phosphine Derivative
1929
FIGURE 4 The relation between ln a and 1/T of (OPSB) at 10 V, 20 V, and
70 V.
activation energies indicated the simultaneous existence of intrinsic
and extrinsic conductivity (Equation (1)). The conductivity of the SB
and OPSB at room temperature is in the range of 0.79–1.39 × 10−9 ꢀ−1
.
The variation of conductivity with temperature for both SB and OPSB
can be divided into two regions. These two regions of conduction pro-
cesses could be explained on the basis of their electronic transition en-
ergies within the molecules in the solid state. Through the first region
of conduction at low temperature range the generation of charges of all
allowed n–π∗ electronic transitions of the lowest excited states, which

1930
R. S. Farag et al.
TABLE III Values of the Electrical Conductivity (σ) and the Activation
Energies EI and EII
Applied
Tac (K)
σlow × 10−9 at
σhigh × 10−8 at
373 K(ꢀ−1cm−1
)
voltage
(Volt)
EbI (eV) EbII(eV)
low high
Sample
SB
I
II
303 K(ꢀ−1cm−1
)
10
20
70
10
20
70
361
361
361
403
—
—
—
—
0.0255 0.05
0.0255 0.05
0.0210 0.035
0.0420 0.0765
1.37
1.39
1.11
1.07
0.799
0.801
0.171
0.170
0.128
0.131
0.0930
0.0935
OPSB
361 392 0.0420 0.079
388 362 0.0475 0.085
Tac , transition temperature; Eb and EIbI, activation energies at the low and high
temperature ranges, respectivelIy.
absorb at (λmax: 325 nm) for both SB and OPSB, were associated with
less activation energy (ꢁE: 3.85 eV) and thus were able to participate
in this region of conduction process. The second region of conduction
at higher temperature range could be attributed to the admixed elec-
tron of the n–π∗ and π–π∗ transitions that absorb at (λmax: 260 nm and
262 nm), which were associated with higher activation energies (ꢁE:
4.80 eV and 4.77 eV) for SB and OPSB, respectively.
The higher conductivity of the SB (of the order l0−9
pared to those of the published Schiff bases of the order 10−11 and
10−12 ꢀ−1 cm−1 22
and ordinary materials such as naphthalene and
ꢀ
−1 cm−1) com-
,
anthracene (of the order 10−20 ꢀ−1 cm−1),23 is attributed to the high
conjugation within the molecular system that increases the delocal-
ization of π electrons participating in the conduction process. Infrared
spectral studies (Figure 2) indicate unsaturated C N bonds in conju-
gation with C C bonds of benzene rings at 1566 cm−1 and 1600 cm−1
for SB and OPSB, respectively. This lowers the energy gap between the
valence state and the next allowed energy state and might explain the
relatively high conductivity of SB and OPSB. The greater decrease of
conductivity of OPSB, as compared to SB, with elevated temperature
can probably be ascribed to the free rotation of the phenyl groups of
diphenylphosphinyl group, which is opposing a delocalization of the π
electrons, as to the influence of the electrode materials.14
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Benzilidine and Its Diphenyl Phosphine Derivative
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