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Short Note

1,3-Bis[(E)-(3-bromobenzylidene)amino]propan-2-ol

1
Department of Chemistry, An-Najah National University, P.O. Box 7, Nablus, Palestine
2
Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
3
Department of Basic Sciences, School of Engineering and Technology, Jain University, Bangalore 562 112, India
*
Author to whom correspondence should be addressed.
Molbank 2017, 2017(4), M971; https://doi.org/10.3390/M971
Submission received: 26 November 2017 / Revised: 12 December 2017 / Accepted: 15 December 2017 / Published: 19 December 2017
(This article belongs to the Special Issue Heterocycles)

Abstract

:
1,3-Bis[(E)-(3-bromobenzylidene)amino]propan-2-ol Schiff base was synthesized in an acceptable yield by condensation of 3-bromobenzaldehyde with 1,3-diaminopropan-2-ol in methanol. The structure of the desired Schiff base compound was spectroscopically analyzed by EI-MS, CHN-elemental analysis, FT-IR, UV-visible, and 1H and 13C-NMR. The structure was also computed by DFT-optimization, MEP, Mulliken, NPA, IR- B3LYP/6-311++G(d), and SCF-TD-DFT.

Graphical Abstract

1. Introduction

Schiff bases as azomethine compounds are well-known versatile molecules that have recently received great attention in different fields [1,2,3]. Such compounds have been used as dyes and pigments, corrosion inhibitors, thermo-stable materials, and catalysts [3,4,5,6] and in medical applications as antifungal, anticancer, and antibacterial agents [7,8,9,10,11,12].
The presence of the unsaturated nitrogen atom (>C=N) together with its lone pair of electrons makes the Schiff base an attractive e-donor ligand [11,12,13,14]. Such donation ability plays a critical role in the complexation with several metal ions centers [10,11,12,13,14,15,16,17].
Metal-Schiff based drugs are highly promising and of great interest in biology and chemistry. Biologically active nitrogen of (>C=N-) upon coordination with a transition metal center lead to complexes with improved pharmacological and physicochemical properties [7,8,9,10,11,12,13,14,15]. Despite the large number of the prepared Schiff base ligands together with their complexes, there remains an urgent need for novel ligands with new applications and properties.
In connection with previous work [12,13,14,15,16,17,18], we report the preparation of 1,3-bis[(E)-(3-bromobenzylidene)amino]propan-2-ol, its spectroscopic characterization, and computational studies using DFT techniques.

2. Results

1,3-Bis[(E)-(3-bromobenzylidene)amino]propan-2-ol was synthesized by condensing 2.1 equiv of 3-bromobenzaldehyde with 1 equiv 1,3-diaminopropan-2-ol in absolute methanol under reflux conditions, as shown in Scheme 1. The compound was a white powder with m.p. = 145.2 °C as a final product. The product was soluble in chloroform at RT, soluble in EtOH at 50 °C, and insoluble in n-hexane (non-polar) or water even at high temperature.
The elemental analysis of the 1,3-bis[(E)-(3-bromobenzylidene)amino]propan-2-ol is consistent with its proposed molecular formula (Calcd. for C17H16Br2N2O: C, 48.14; H, 3.80 and N, 6.60. Found: C, 48.02; H, 3.71 and N, 6.53). EI-MS reflected an excellent agreement with the expected structure, the experimental molecular ion [M+] m/z = 424.1 (424.9 theoretical).

2.1. Optimization, MEP, Mulliken, and NPA Analysis

The B3LYP/6-311++G(d)-optimized molecular structure (bonds and angles lengths) of 1,3-bis[(E)-(3-bromobenzylidene)amino]propan-2-ol ligand is shown in Figure 1a and Table 1. The compound exists as E,E-conformation with respect to the imine functions. The bond lengths of N2=C and N5=C are found to be 1.2733 and 1.2739 Å, respectively, which is clearly consistent with C=N. The C–N=C bond angle of 117.82 and 118.87 (o) confirms the sp2 hybridization character of both N atoms, as seen in Table 1. The calculation indicated a short intramolecular hydrogen bond of the type O–H…N (2.233 Å) with a pseudo S5-heterocyclic formation (in Figure 1a). Moreover, the phenyl rings are oriented in perpendicular planes, which minimized the internal repulsion energy in the desired molecule.
The nucleophilic and electrophilic positions of one molecule are represented here by an MEP map (Figure 1b). The O and one of the N atoms are indicated as nucleophilic centers, since it appears in red (electron-rich). The H of hydroxyl group together with its phenyl rings, indicated by the blue color, exhibit electrophilic behavior. The second N atom was not red since it was bonded to the H of the hydroxyl through the intramolecular hydrogen bond. The other functional groups in green were found to lack a nucleophilic or electrophilic character.
The Mulliken and neutral population charge analysis (NPA) of the compound along with the MPE result are shown in Figure 1c. The analysis revealed the presence of a negative charge on the donor atoms (nucleophilic positions) such as O, 2N, 2Br, and most of the C atoms. The hydrogen atoms together with the other C atoms reflected a positive character as electrophilic positions (acceptor atoms).
The condensation reaction was monitored by FT-IR, by measuring the IR of the starting materials before and after dehydration, as seen in Figure 2. The formation of the product mainly can be confirmed by the N–H amine disappearing at 3245 cm−1 (Figure 2a) and aldehyde C=O at 1685 cm−1 (Figure 2b) shifting to C=N at 1625 cm−1 (Figure 2c).
Theoretical-DFT-IR calculation was performed at the B3LYP/6-311++G(d) level of theory, as shown in Figure 2d. Experimental and theoretical FT-IR spectra showed acceptable agreement. There was a small expected discrepancy: DFT-calculation reflected higher functional-group frequencies compared to the experimental one [16].

2.2. Electronic Transfer and TD-SCF Analysis

TD-SCF theoretical and experimental electron transfer spectral analysis was performed in an MeOH solvent. The experimental and TD-SCF/DFT analysis revealed no bands in the visible area. The λmax = 260 nm (π→π*) and 295 nm (n→π*) electronic transition were detected experimentally (Figure 3a). In the DFT calculation, a broad peak mainly at λmax = 270 nm was predicted (Figure 3b).
1H-NMR spectrum of the 1,3-bis[(E)-(3-bromobenzylidene)amino]propan-2-ol is simple and appeared in good agreement with its assigned structure: five aliphatic protons (δH 3.4, 3.5 and 4.2 ppm), one alcohol (δH δ 4.6 ppm), eight aromatic protons (δH 7.1–7.8 ppm), and two aldimine protons (δH 8.3 ppm) were observed as shown in Figure 4a.
13C-NMR spectrum revealed nine carbon signals. Two of them arose from aliphatic carbons at 50–70 ppm, six were aromatic carbons at 120–142 ppm, and aldimine carbons were noted at 165.5 ppm, as seen in Figure 4a.

3. Materials and Methods

NMR was performed on a DRX 250 Bruker spectrometer (Bruker, Mainz, Germany). The UV-Visible spectrum was recorded on a double beam TU-1901 spectrophotometer (Purkinje General Instrument Co., Ltd., Beijing, China). The FT-IR spectra were measured with a PerkinElmer-1000 FT-IR Spectrometer (PerkinElmer Inc., Waltham, MA, USA). EI-MS were recorded on a Finnigan 711A (8 kV) (PerkinElmer Inc., Waltham, MA, USA).
A solution of 1,3-diaminopropan-2-ol (1 mmol) and 3-bromobenzaldehyde (2.1 mmol) in MeOH (20 mL) was subjected to reflux for 4 h. The mixture volume was reduced under vacuum (2 mL) until the white precipitate product appeared. The product was filtered, washed several times with distilled water and several times with n-hexane and ethers, and then dried.
Yield: 81% as a white powder, mp = 145.2 °C, was collected; molecular formula C17H16Br2N2O; 1H-NMR (250 MHz, CDCl3): (ppm) 3.4, 3.5 (2m, 4H, =NCH2CH(OH)CH2N=), 4.2 (m, 1H, =NCH2CH(OH)CH2N=), 4.6 (br, 1H, =NCH2CH(OH)CH2N=) 7.1–7.8 (8H, Ph), 8.3 (s, 2H, –HC=N-). 13C-NMR (62.5 MHz, CDCl3): (ppm) 49.8 (2C, =NCH2CH(OH)CH2N=), 70.1 (C, =NCH2CH(OH)CH2N=), 124.8, 127.2, 130.4, 131.8, 138.1, 141.8 (12C, Ph), 165.5 (2C, –HC=N-). [M+] = 424.1 m/z. IR: 3240 cm−1 (O–H), 3040 cm−1 (ArC–H), 2985-2765 cm−1 (Aliphatic C–H), 1625 cm−1 (C=N).

Acknowledgments

The authors are thankful to DST-FIST for providing financial support under research grant scheme Project No. SR/FST/ETT-378/2014.

Author Contributions

H.A., N.A., and A.A.A. performed the experiments; N.A.-Z. measured and analyzed the NMR; N.S. measured and analyzed the MS; M.A.-N. and I.W. wrote the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

References

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Scheme 1. Synthesis of the 1,3-bis[(E)-(3-bromobenzylidene)amino]propan-2-ol ligand.
Scheme 1. Synthesis of the 1,3-bis[(E)-(3-bromobenzylidene)amino]propan-2-ol ligand.
Molbank 2017 m971 sch001
Figure 1. (a) DFT-optimized structure; (b) MEP; and (c) Mulliken and NPA analysis.
Figure 1. (a) DFT-optimized structure; (b) MEP; and (c) Mulliken and NPA analysis.
Molbank 2017 m971 g001
Figure 2. IR spectra of (a) 1,3-diaminopropan-2-ol; (b) 3-bromobenzaldehyde; (c) 1,3-bis[(E)-(3-bromobenzylidene)amino]propan-2-ol; and (d) the B3LYP/6-311++G(d)-IR of the product.
Figure 2. IR spectra of (a) 1,3-diaminopropan-2-ol; (b) 3-bromobenzaldehyde; (c) 1,3-bis[(E)-(3-bromobenzylidene)amino]propan-2-ol; and (d) the B3LYP/6-311++G(d)-IR of the product.
Molbank 2017 m971 g002
Figure 3. (a) UV-Visible spectrum and (b) TD-SCF-DFT of the compound in MeOH at RT.
Figure 3. (a) UV-Visible spectrum and (b) TD-SCF-DFT of the compound in MeOH at RT.
Molbank 2017 m971 g003
Figure 4. (a) 250 MHz 1H-NMR and (b) 62.5 MHz 13C-NMR of 1,3-bis[(E)-(3-bromobenzylidene)amino]propan-2-ol in CDCl3.
Figure 4. (a) 250 MHz 1H-NMR and (b) 62.5 MHz 13C-NMR of 1,3-bis[(E)-(3-bromobenzylidene)amino]propan-2-ol in CDCl3.
Molbank 2017 m971 g004
Table 1. Structure parameters (bond length and bond angle) of the compound.
Table 1. Structure parameters (bond length and bond angle) of the compound.
Bond No.Bond TypeÅAngle No.Angle Type(o)
1C1N21.471N2C1C3109.47
2C1C31.542C1N2C6120
3N2C61.29363C1C3C487.9
4C3C41.544C1C3O7138.96
5C3O71.42995C4C3O785.01
6C4N51.46996C3C4N5109.47
7N5C151.29367C4N5C15120
8C6C271.548N2C6C27120
9C15C211.549N5C15C21120
10C16C171.401410C17C16C21120
11C16C211.401411C16C17C18120
12C17C181.401412C16C17Br37120
13C17Br371.9113C18C17Br37120
14C18C191.401514C17C18C19120
15C19C201.401415C18C19C20120
16C20C211.401516C19C20C21120
17C27C281.401417C15C21C16120
18C27C291.401418C15C21C20120
19C28C301.401419C16C21C20120
20C29C321.401420C6C27C28120
21C30C341.401421C6C27C29120
22C30Br381.9122C28C27C29120
23C32C341.401423C27C28C30120
24C27C29C32120
25C28C30C34120
26C28C30Br38120
27C34C30Br38120
28C29C32C34120
29C30C34C32120

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MDPI and ACS Style

Warad, I.; Abedalrazeq, H.; Amer, N.; Al-Nuri, M.; Al Ali, A.; Al-Zaqri, N.; Shivalingegowda, N. 1,3-Bis[(E)-(3-bromobenzylidene)amino]propan-2-ol. Molbank 2017, 2017, M971. https://doi.org/10.3390/M971

AMA Style

Warad I, Abedalrazeq H, Amer N, Al-Nuri M, Al Ali A, Al-Zaqri N, Shivalingegowda N. 1,3-Bis[(E)-(3-bromobenzylidene)amino]propan-2-ol. Molbank. 2017; 2017(4):M971. https://doi.org/10.3390/M971

Chicago/Turabian Style

Warad, Ismail, Huda Abedalrazeq, Nisreen Amer, Mohammmed Al-Nuri, Anas Al Ali, Nabil Al-Zaqri, and Naveen Shivalingegowda. 2017. "1,3-Bis[(E)-(3-bromobenzylidene)amino]propan-2-ol" Molbank 2017, no. 4: M971. https://doi.org/10.3390/M971

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