Journal of Chemistry

Volume 2013 (2013), Article ID 298205, 6 pages

http://dx.doi.org/10.1155/2013/298205

Research Article

Structural and Surface Characterization of Newly Synthesized D-π-D Type Schiff Base Ligand: (1E,2E)-3-[4-(Dimethylamino)phenyl]prop-2-en-1-ylidene)phenylamine

Gulsah Gumrukcu, Serkis Garikyan, Gulnur Keser Karaoglan, and Dolunay Sakar

Department of Chemistry, Yildiz Technical University, Davutpasa Campus, Esenler, 34220 Istanbul, Turkey

Received 31 May 2013; Accepted 2 July 2013

Academic Editor: Antonio J. Melendez-Martinez

Copyright © 2013 Gulsah Gumrukcu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

A new Schiff base with D-π-D type, (1E,2E)-3-[4-(dimethylamino)phenyl]prop-2-en-1-ylidene)phenylamine, has been successfully synthesized using the reaction of (2E)-3-[4-(dimethylamino)phenyl]acrylaldehyde with aniline. The Schiff base ligand has been characterized by FTIR, UV-visible, and ¹H NMR as well as TG/DTA, SEM, BET, and elemental analyses and mass spectra. Surface properties and acid-base constants of Schiff base ligand were determined by IGC measurements.

1. Introduction

The coordination compounds including the Schiff base ligands are of significantly important and play a pivotal role in industry, technology, and life processes. Due to their potential applications in various fields, it has always fascinated and inspired chemists in the world. This can be evidenced by the vast prolificity and scope of research papers on the subject in recent times and also by the diversity in which it has found applications. Some Schiff bases and their derivatives represent an interesting class of compounds possessing a wide spectrum of biological activities, such as analgesic, antiviral, antifungal, and anticancer activities. The Schiff base ligands and their complexes have been a fascinating area of research, due to their biological relevance. These compounds can act as pro- or antioxidants. The published opinions on the structure and antioxidant activity relationships are, however, quite inconsistent. It can be assumed from several scientific works that the quality of antioxidant action depends on the type of ligands forming the bioactive complexes [1, 2].

In the past few decades, very fast development in the field of organic-based conjugated materials was observed [3, 4]. Schiff bases and their metal complexes have many applications in medicinal, industrial, pharmaceutical, biological, and chemical fields. For example, they are industrially used as dyes and pigments in textile besides their application in pharmacology for the synthesis of antibiotics, antiallergic, and antitumor substances. The Schiff bases can also exhibit thermochromic and photochromic properties [5–7]. Moreover, the Schiff base compounds have been regarded as excellent fluorescent materials because of their ability to achieve high thermal stability as well as high photoluminescent efficiency. The conjugated Schiff base systems that contain electronically coupled photo- and/or redox-active sites across an unsaturated organic bridge are of considerable current interest [8–13].

Many complicated factors can affect the two-photon excitation (TPE) properties of organic materials. So it is important to investigate the structure and the TPE effect relationships of organic materials. However, most of these compounds employ C=C bonds as the conjugation bridge; the compounds with C=N structure such as the Schiff bases are less studied to our knowledge [14, 15].

In the present work, a new Schiff base ligand with D-π-D type which is N,N-dimethyl-4-[(1E,3E)-3-phenylimino)prop-1-en-1-yl]aniline{(1E,2E)-3-[4-(dimethylamino) phenyl]prop-2-en-1-ylidene) phenylamine (SBL) has been successfully synthesized using the reaction of (2E)-3-[4-(dimethylamino)phenyl]acrylaldehyde with aniline. It can be used as a pigment in some applications because of excellent yellow colour. The structure of the SBL was determined by elemental analysis, FTIR, UV-visible, ¹H NMR, TG/DTA, and LC-MS spectrometry. In addition, IGC was applied to the investigation of adsorption properties of the SBL. The relation of SBL with used polar and nonpolar solvents was tested at temperatures between 30°C and 60°C under melting point of SBL. The goals of this paper were (1) to synthesize ad characterize new D-π-D type Schiff base ligand, (2) to figure out the surface free energy of SBL, (2) to calculate adsorption thermodynamic parameters of SBL, (3) to determine the acid-base quantity of SBL.

2. Experimental

2.1. Materials

All reagents and solvents were of reagent grade quality, obtained from commercial suppliers (Merck, USA). Aniline and (2E)-3-[4-(dimethylamino) phenyl]acrylaldehyde were used as supplied commercially from Merck. The progress of the reaction was monitored by TLC (SiO₂). IR spectra were recorded on a Perkin Elmer Spectrum One FTIR (ATR sampling accessory) spectrophotometer; electronic spectra in the UV-Vis region were recorded with an Agilent 8453 UV/Vis spectrophotometer. ¹H NMR spectrum was recorded in CDCl₃- on a Varian UNITY INOVA 500 MHz spectrophotometer using TMS as internal reference. Mass spectra were performed on a Thermo Finnigan LCQ Advantage Max LC/MS/MS. Melting point was determined on Perkin Elmer model: TG/DTA 6300 under nitrogen atmosphere. Elemental analysis was performed on a Thermo Flash EA 1112.

2.2. Synthesis of (1E,2E)-3-[4-(Dimethylamino)phenyl]prop-2-en-1-ylidene)phenylamine (SBL)

A solution of aniline (1) (0.79 g, 8.56 mmol) in 20 mL dry ethanol was added dropwise to a solution of (2E)-3-[4-(dimethylamino) phenyl]acrylaldehyde and (2) (1.50 g, 8.56 mmol) in 10 mL dry ethanol, and the mixture was stirred under argon for 12 h at 90°C. The solvent was evaporated to 1/2 of the initial volume, and petroleum ether was added at room temperature. A yellow precipitate was obtained when the solution was cooled to room temperature. It was filtered off and then recrystallized from 2 : 1 n-hexane/ethylacetate (Figure 1). Yield 81%, m.p. 138.8°C, FTIR /cm⁻¹: 3033 (Ar, w), 2899–2809 (–CH₃–, m), 1662 (HC=N, s). ¹H NMR (CDCl₃-) δ, ppm: 8.1 (d, H, HC=N) (disappeared with D₂O), 6.6–7.6 (m, 4H, Ar–H), 7.0 (m, 2H, –CH=CH–), 2.92 (s, 6H, N–(CH₃)₂). LC-MS (APCI) m/z (100%): 250.937 [M]⁺. Anal. Calc. for C₁₇H₁₈N₂ (%): C, 81.56; H, 7.25; N, 11.19. Found (%): C, 81.59; H, 7.23; N, 11.18.

Figure 1: The UV-Vis spectra of (2E)-3-[4-(dimethylamino) phenyl]acrylaldehyde (line) and the Schiff base ligand (dashed line) in ethanol at room temperature.

2.3. BET and SEM Analyses

BET analysis was carried out to determine the BET surface area and pore size of SBL. The surface area and pore size are very important application parameters as the surface contributes to the potential for interaction between the pigment and the polymer matrix [16]. Quantachrome Ins. Quadrasorb SI model BET was used in this study. The measurements were carried out under nitrogen atmosphere. SEM analysis was carried out to determine the shape of SBL with Zeiss model: EVO LS 10.

2.4. Inverse Gas Chromatography (IGC) Measurements

A Hewlett-Packard 6890 Model, series II, gas chromatograph with a thermal conductivity detector was used to measure the retention time of the solvents in this study. The column was stainless steel tubing with 3.2 mm o.d. and 0.5 m in length. The SBL was coated on the support by slow evaporation of chloroform as stirring the Chromosorb W in the SBL solution. Trace amount of solvent was injected into the chromatograph. The column was conditioned at 110°C for 24 h under helium atmosphere. The probes were of high purity grade n-alkanes such as n-hexane (Hx), n-heptane (Hp), n-octane (O), n-nonane (N), and other acidic, basic, and amphoteric probes such as tetrahydrofurane (THF, basic), dichloromethane (DCM, acidic), chloroform (TCM, acidic), acetone (AC, amphoteric), and ethyl acetate (EA, amphoteric) were used without further purification. The all studied solvents and support materials being Chromosorb W (AW-DMCS-treated, 80/100 mesh) were supplied from Merck AG. Inc. Silane treated glass wool used to plug the ends of the column was obtained from Alltech Associates, Inc.

2.5. IGC Theory

The IGC technique provides a means of gaining information concerning the surface polarity of particulates and the acid-base nature of particulates. It provides a basis for determining the potential for chemical interaction between the pigment and its medium (polymer matrix or paint solutions, etc.). The material to be investigated is immobilised within a chromatographic colomn which is flushed through with inert gas such as helium or nitrogen. The stationary phase characterisation is achieved by utilising the partitioning of the sample between the mobile phase and the stationary phase, indicated by the time taken to elute the sample. The probe-probe interactions in IGC experiments are negligible because of being carried out in infinite dilution. The theory and the technique are now quite well described in the literature [16, 17].

The adsorbate net retention volumes were calculated from the following expression:

where is the adsorbate retention time, is the retention time of air, is volumetric flow rate measured at column outlet and at ambient temperature (K), is the column temperature (K), and the is James-Martin gas compressibility correction factor [18].

The dispersive component of surface energy was determined using both the Dorris-Gray and the Fowkes methods. The adsorption energy for the n-alkanes increases with the number of carbon atoms in the chain. According to Dorris & Gray (1980), the increment, corresponding to the adsorption energy of a methylene group, is given by [19]

where and are the retention volumes of two n-alkanes having and carbon atoms in their chain. This parameter is independent of the chosen state of the adsorbed molecule. Thus, at constant temperature, for a series of alkane probes, a plot versus the number of carbon atoms should give a straight line from which can be found.

The methylene adsorption energy can also be defined as [19]

where is Avagodro’s number, is the surface area covered by one methylene group (0.06 nm²), and is the surface free energy of a surface consisting of methylene groups, that is, polyethylene, given by

Thus, using (2)–(4) and the experimentally determined values of and , the dispersion component of the surface free energy, may be calculated.

The free energy of adsorption may also be defined in terms of the retention volume of the probes [20]:

is the column temperature and is a constant for a given column.

Consequently, the equations may be combined to give the Fowkes equation [21]:

Thus, for a series of n-alkane probes, a plot of against will give a slope of . Values of and boiling point (°C) of apolar solvents are found in the literature [22, 23].

The specific component of the free energy is determined from the n-alkane plot of against . The distance between the ordinate values of the polar probe datum point and the n-alkane reference line gives the specific component of the surface free energy, .

An equation may be written for this procedure,

where and are the retention volume for the polar probe and the retention volume for the n-alkanes’ reference line, respectively.

The adsorption of a polar probe onto the adsorbent surface leads to a change in the enthalpy of the system and the entropy of the system. These factors are related to the energy of adsorption by the following:

Here, is the adsorption enthalpy by the Lewis acid-base interactions, is the adsorption entropy the Lewis acid-base interactions, and is the column temperature. For each polar probe, and can be determined from a plot of against .

The surface Lewis acidity and basicity constants, and , may be calculated from the follwoing,

Here, and are Gutmann’s donor and modified acceptor numbers, respectively. Values of , boiling point, (°C), Gutmann’s modified acceptor number, , and donor number, , of the polar probes used in this study are taken from [23, 24].

and are obtained from a plot of versus with as the slope and as the intercept. Parameters and reflect the ability of the examined surface to act as an electron acceptor and electron donor, respectively [20].

3. Results and Discussion

The new Schiff base ligand was synthesized from the reaction of (2E)-3-[4-(dimethylamino) phenyl]acrylaldehyde with aniline, in a good yield, as shown in Scheme 1. The IR spectrum of the SBL shows the characteristic Schiff base stretching band at 1662 cm⁻¹. This intense band is assigned to the –C=N stretching frequency of the ligand and is characterized for the azomethine moiety of most of the Schiff base compounds. The absorption band of the C=O in (2E)-3-[4-(dimethylamino) phenyl]acrylaldehyde disappeared in the infrared spectrum of the ligands, which indicates that the condensation has occurred. The alkyl and aryl bands of the ligand are observed at 2809–2899, 1364–1448, and 1149–1151 cm⁻¹, respectively.

Scheme 1: Synthesis of the Schiff base ligand (SBL).

Elemental analysis of the Schiff base ligand shows good agreement with the proposed structures. The ¹H NMR spectrum of the SBL in CDCl₃- confirmed the proposed structure showing one D₂O-exchangeble proton at 8.1 ppm for the HC=N group. The assignments of the protons are highly complicated in the regions of 2.92 and 6.6–7.6 ppm, where the signals are due to the protons of the alkyl and aromatic groups.

The SBL is stable at room temperature but hygroscopic. The SBL is soluble in common polar organic solvents, such as ethanol, methanol, and chloroform but partially soluble in nonpolar organic solvents, such as benzene and hexane.

The UV-Vis spectral data for the SBL ligand show low-energy band at approximately 249 nm and high energy band at approximately 389 nm, due to n-π* and π-π* transitions of the azomethine group in the ligands [25, 26] (Figure 1).

According to UV spectra, the peaks recorded in the spectrum are broadened and slightly red shifted (Figure 1).

In the mass spectra, the molecular ion peak of the L appeared at m/z (100%): 250.937 [M]⁺. Mass spectral data confirmed the proposed structure of the Schiff base ligand (Figure 2).

Figure 2: Mass spectrum of SBL.

According to BET results, the surface area and pore size of SBL were determined as 32.4 m²·g⁻¹ and 3.056 nm, respectively. This ligand has a potential to be used in nanotechnology paint applications. The SEM micrograph of SBL was given in Figure 3.

Figure 3: The SEM micrograph of SBL.

The shape of SBL was determined as a rod-like structure from SEM micrograph. The retention diagrams of nonpolar and polar solvents on SBL were plotted net retention volumes, , of solvents on SBL which were calculated from IGC measurements between 30°C and 60°C by using (1) versus inverse temperature. According to (2), is independent of the chosen reference state of adsorbed molecule. The versus carbon number of n-alkanes were plotted in Figure 4.

Figure 4: The plot of versus carbon number of n-alkanes.

The slope of the fitted line is equal to . The variation of according to the Dorris-Gray approach and with temperature were calculated from (3) and (4), respectively. According to Fowkes, calculated values of were plotted against . An example of the pattern of results obtained was given in Figure 5 for the isotherm at 303 K.

Figure 5: A plot of versus for n-alkanes and polar probes on SBL at 303 K.

The results of , and according to the Dorris-Gray and the Fowkes approaches were given in Table 1.

Table 1: The adsorption energy of a methylene group, , the surface free energy of a surface consisting of methylene groups, and dispersion component of surface free energy, , values calculated by the Dorris-Gray and the Fowkes approaches for determined at studied temperatures.

(K)

(mJ/m²)

(10⁶ mJ/mol)
Dorris-Gray (mJ/m²)
Slope (10²⁴)
Fowkes  

(mJ/m²)

303
35.02
2.25
27.80
6.33
27.65

313
34.44
2.12
24.95
6.17
26.23

323
33.86
2.02
23.19
6.06
25.36

333
33.28
1.87
20.09
5.78
23.08

The values of calculated according to the Dorris-Gray and the Fowkes approaches are very close each to other at the studied temperature ranges. Compared to the values with the before published other Schiff base ligand values, the of (E)-N-((E)-3-(4-(dimethylamino)phenyl)allylidene)-4-(4-((E)-((E))-3-(4(dimethylamino)phenyl)allylidene) amino)-3-methylnaphthalen-1-yl)-2-ethylnaphthalen-1-amine as determined as 33.93 (mJ/m²) at 303 K according to the Dorris-Gray approach [7]. The values are different due to chemical nature difference between the two ligands. It can be said that when the phenyl ring is added to the Schiff base structure, of ligand is increasing.

The specific component of the surface free energy, , is calculated using the difference between the calculated value of and that which was derived using the equation of the linear fit of the n-alkane reference line. By plotting the values of against , the adsorption enthalpy, and the adsorption entropy, were determined for each studied polar probe. The values of and were calculated using (9). The plotting versus with as the slope and as the intercept (Figure 6).

Figure 6: The plot of versus .

The values of and are found to be 0.1 and 0.6, respectively. According to the values obtained for and , the surface of SBL is the basic character between 30–60°C.

4. Conclusions

In this study, a new Schiff base ligand with D-π-D type has been successfully synthesized using the reaction of (2E)-3-[4-(dimethylamino) phenyl]acrylaldehyde with aniline and characterized by FTIR, UV-visible, ¹H NMR, elemental analysis, and mass spectrum for structural characterization and BET, SEM, and IGC for surface characterization. The big surface area and small pore size of SBL were determined from the BET result. It can be used in nanotechnology paint applications. In addition, IGC was applied to the investigation of adsorption properties of the SBL. The relation of SBL with used polar and nonpolar solvents was tested at temperatures between 30°C and 60°C in which SBL does not show any thermal transition. The base constant of newly synthesized SBL was determined as 0.64, while acid constant is 0.1.

Conflict of Interests

All the authors declare no financial relationships with Merck or any companies.

Acknowledgments

This research has been supported by Yıldız Technical University Scientific Research Projects Coordination Department. Project nos.: 2011-01-02-GEP03, 28-01-02-12, and 28-01-02-14.

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