Polyethylene Glycol and Montmorillonite Clay Anchored Schiff Base

Article pubs.acs.org/IECR

Polyethylene Glycol and Montmorillonite Clay Anchored Schiff Base Ligand−Metal Complexes Shilpa Narang,† Rajeev Mehta,*,‡ and S. N. Upadhyay§ †

School of Chemistry and Biochemistry, and ‡Department of Chemical Engineering, Thapar University, Patiala, Punjab, India Department of Chemical Engineering, IIT BHU, Varanasi, UP, India

§

ABSTRACT: Three ligands were synthesized through condensation of o-phenylenediamine with salicylaldehyde (ligand 1) and 2-hydroxy-1-naphthaldehyde (ligand 2) and of 1,8-diaminonaphthalene with 2-hydroxy-1-naphthaldehyde (ligand 3) in 1:2 molar ratio; the ligands were characterized using NMR and FTIR techniques. The 1:1 complexes of ligand 1 with FeCl3 and CoSO4; ligand 2 with FeCl3, CoSO4·6H2O, and CoCl2·6H2O; and ligand 3 with FeCl3 were prepared and characterized using FTIR and XRD techniques. These ligand−metal complexes were then anchored on polyethylene glycol (PEG, MW = 6000), montmorilonite (MMT), and organically modified montmorillonite (OMMT, Closite30B) clays and characterized by FTIR. The spectral data of the ligands and their complexes have been explained in terms of structural changes occurring due to complexation. The XRD data indicated that anchoring on the three supports resulted in the reduction the crystal size providing higher surface area to volume ratio and, hence, potentially enhanced catalytic activity. Additionally, catalytic activity of the complexes has been proven by chemically fixing carbon-dioxide to propylene carbonate using propylene oxide.

1. INTRODUCTION

2. EXPERIMENTAL SECTION 2.1. Materials. Laboratory reagent grade o-phenylenediamine and salicylaldehyde were obtained from Loba Chemical (India); 1,8-diaminonapthalene and 2-hydroxy-1-naphthaldehyde were from Aldrich. Absolute alcohol was obtained from E Merck (Germany) and analytical reagent grade metallic salts CoCl2·6H2O, CoSO4, FeCl3, polyethylene glycol (PEG-6000), and methanol were from Sd-Fine Chemicals (India). Montmorillonite (MMT) and montmorrilonite (Closite 30B) modified with methyl tallow, bis-hydroxyethyl, and quaternary cations (OMMT) were obtained from Southern Clay Products (USA). Double distilled water was used when required. All chemicals were used as received. 1 H NMR spectra were recorded with a Bruker Advance II spectrometer operating at 400 MHz using CDCl3 as internal standard for N,N′-bis-(salicylaldehyde)-o-phenylenediamine (salen) and DMSO for N,N′-bis-(2-hydroxy-1-napthaldehyde)-o-phenylenediamine (napthen) and N,N′-bis-(2-hydroxy-1-napthaldehyde)-1,8-diaminonapthalene (dapthen). FTIR spectra were recorded on Perkin-Elmer FTIR spectrometer, using KBr pellets. XRD data was recorded on the Xpert Pro-instrument with 2θ value in the range of 5° to 60°. 2.2. Preparation of Schiff’s Bases. The Schiff’s bases, [N,N′-bis-(salicylaldehyde)-o-phenylenediamine] (salen) and [N,N′-bis-(2-hydroxy-1-naphthyldehyde)-o-phenyleneldiamine] (naphthen), were prepared by refluxing with continuous stirring o-phenylenediamine separately with salicylaldehyde and 2-hydroxy-1-naphthaldehyde in 1:2 molar ratios using ethanol as solvent. The procedure was as described by Mokhles et al.14 The reactions were carried out for 3 h. At the end of the

Schiff bases having an N2O2 donor group are well-known to coordinate with number of metal ions.1−5 They have also gained importance because of their preparative accessibility, diversity, and structural variability.6,7 Since these complexes carry a metal ion along with the nucleophilic group attached to them, they can exhibit good catalytic activity in a number of reactions. Schiff bases of o-phenylenediamine and 1,8diaminonaphthalene and their complexes have several biological,8,9 clinical,10 and analytical5 applications. The present work focused on the preparation and characterization of Schiff base complexes with FeCl3, CoSO4, and CoCl2·7H2O. These complexes were anchored on to PEG6000, MMT, and OMMT. It was observed that the Schiff base−metal complexes remained on the surface of PEG skeleton.11 MMT is a soft silicate mineral typically comprising microscopic crystals forming clay. It is used extensively in catalytic processes requiring adsorption of heavy metals and as a support for several catalysts.12 Further, MMT is hydrophilic in nature in contrast to OMMT which repels water molecules and may be useful for carrying out reactions that are terminated by water. In view of the above inherent characteristics, the anchored ligand−metal complexes are expected to exhibit enhanced heterogeneous catalytic activity, reactivity, and selectivity due to changed nature. In the present study, the ligand metal complexes have been used as catalysts for the fixation of CO2 to cyclic carbonates using propylene oxide. The cyclic carbonates thus synthesized have a number of applications, such as electrolytes in lithium ion batteries, polar aprotic solvents, monomers for synthesizing polycarbonates, chemical ingredients for preparing medicines or agricultural chemicals.13 The methodology is a promising avenue in the field of green chemistry as it involves fixing CO2 to cyclic carbonates which is a value added product. © XXXX American Chemical Society

Received: December 9, 2012 Revised: February 8, 2013 Accepted: February 24, 2013

A

dx.doi.org/10.1021/ie3033697 | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Industrial & Engineering Chemistry Research

Article

Figure 1. Reaction scheme for preparation of N,N′-bis-(salicylaldehyde)-o-phenylenediamine] (salen).

Figure 2. Reaction scheme for preparation of N,N′-bis-(2-hydroxy-1-naphthyldehyde)-o-phenyleneldiamine] (naphthen).

Figure 3. Reaction scheme for preparation of N,N′-bis-(2-hydroxy-naphthaldehyde)-1,8-diaminonaphthalene (daphthen).

single spot. Further characterization of crystalline products was done with the help of FTIR and 1H NMR. The Schiff’s base ligand [N,N′-bis-(2-hydroxy-naphthaldehyde)-1,8-diaminonaphthalene] (daphthen) was prepared by refluxing with continuous stirring 2-hydroxy-naphthaldehyde and 1,8-diaminonaphthalene in molar ratio of 1:2 using ethanol as solvent. The reaction was carried out for 6 h, and the solid product obtained was filtered using vacuum filtration and further crystallized using methanol. The reaction scheme is given in Figure 3. Here also the completion of reaction was confirmed using TLC, and further characterization of the product was done using FTIR and 1H NMR techniques. 2.3. Preparation of Ligand−Metal Complexes. Complexation of salen was carried out separately with CoSO4 and FeCl3 by refluxing with continuous stirring a 1:1 molar mixture of salen and salt dissolved in methanol for 3 h. The solid products thus obtained were filtered using vacuum filtration. The color of the salen−CoSO4 complex was brown and that of the salen−FeCl3 complex was black. A similar procedure was followed for complexing naphthen separately with CoCl2·6H2O, CoSO4, and FeCl3. In these cases refluxing with stirring was done for 3−4 h. The complexes with first two salts were brown in color and that with FeCl3 was black.

Figure 4. Anchoring of Schiff base ligand metal complexes.

Figure 5. Reaction scheme for preparation of propylene carbonate.

reaction, Salen was obtained as bright orange crystals and naphthen as bright yellow crystals. The corresponding reaction schemes are given in Figures 1 and 2, respectively. Crystalline products thus obtained were recrystallized in methanol. The confirmation of the completion of reaction was done with the help of thin layer chromatography (TLC) which gave only a B



Article

Figure 6. 1H NMR of N,N′-bis(salicylaldehyde)-o-phenylenedimine.

Figure 7. 1H NMR of N,N′-bis(2-hydroxy-1-napthaldehyde)-o-phenylenediamine.

probe for about 15 min. The cavitation created by sonic waves causes the clay layers to separate out (exfoliate) leading to tremendous increase in surface area and thus resulting in improved anchoring of complexes. The required amount of ligand−metal complex was then added. The resultant mixture was sonicated again for 10 min and the solvent was then evaporated to obtain the product. Using a similar procedure, salen−CoSO4, salen−FeCl3, and daphthen−FeCl3 complexes were anchored on to OMMT (Closite30B, ion exchange capacity = 90 meq/100 g). A schematic representation of anchoring of Schiff’s bases onto supports is shown in Figure 4 2.5. Synthesis of Cyclic Carbonates. A 100 mL autoclave reactor was heated to 80 °C under vacuum for 3 h and then cooled to room temperature. A mixture of catalyst (salenCoSO4/napthenCoSO4) and cocatalyst (tetradecyltrimethyl ammonium bromide) was dispersed in propylene oxide with

The daphthen−FeCl3 complex was prepared by refluxing with stirring a 1:1 molar mixture dissolved in ethanol, and the color of the complex so obtained was dark green. All complexes thus formed were characterized by FTIR, and of these, a selected few were also characterized by XRD techniques. 2.4. Anchoring of Complexes on Supports. The naphthen−COSO4, naphthen−FeCl3, and salen−CoSO4 complexes were anchored onto PEG-6000. The polymer and ligand−metal salt complexes were taken in the ratio of 1:20 by weight, dissolved in dichloromethane (DCM), heated to 60 °C, and stirred for 2 h. A solid product was obtained by evaporating the solvent in a rotary evaporator. These complexes were also anchored onto MMT. The amount of clay used was determined on the basis of the cation exchange capacity of MMT (120 meq/100 g). The clay was suspended in acetone and was sonicated using ultrasonication C



Article

Figure 8. 1H NMR of N,N′-bis(2-hydroxy-1-napthaldehyde)-1,8-diamminonapthalene.

Figure 9. 1H NMR for propylene carbonate formed by chemical fixation of CO2 and propylene oxide.

CO2 using propylene oxide to cyclic carbonates was confirmed using 1H NMR and FTIR. The results are discussed below. 3.1. 1H NMR Spectra. The 1H NMR spectra of salen, naphthen, and daphthen together with their structures are shown in Figures 6−8. The presence of sharp singlet for the −C(H)N proton at 8.6 ppm in salen, 9.5 ppm in naphthen, and 8.7 ppm in dapthen clearly indicates similar environment for all such protons and hence a planar structure. The signals for OH protons in the ligands are observed at 13.1, 15.1, and 10.09 ppm in salen, naphthen, and daphthen, respectively. The multiplets of the aromatic protons appear within 6.89−7.37 ppm for salen, 6.86−8.9 for naphthen, and 6.2−7.8 for daphthen. These results confirm formation of ligands.

monomer to initiator ratio of 2000:1 and added to the autoclave. The reaction was then carried out at a constant temperature of 60 °C and CO2 pressure of 30 bar. The mixture was stirred (with an overhead mechanical stirrer) for about 6 h, after which it was cooled to room temperature and the remaining CO2 was vented in a fume hood. The corresponding reaction scheme for the synthesis of propylene carbonate has been given in Figure 5. Finally, a small aliquot of the resultant product was removed from the reactor for 1H NMR analysis.

3. RESULTS AND DISCUSSION Anchored and unanchored ligand−metal complexes were characterized in terms of their structure and catalytic activity using 1H NMR, FTIR, and XRD techniques. The fixation of D



Article

Figure 12. FTIR of napthen metal complexes and complexes supported on polyethylene glycol (PEG).

Figure 10. FTIR of salen and salen metal complexes.

Figure 11. FTIR of salen metal complexes supported on Closite30B.

Figure 13. FTIR of dapthen−FeCl3 complexes and complexes supported on Closite 30B.

1

H NMR spectra of propylene carbonate formed during chemical fixation of CO2 using propylene oxide is given in Figure 9. The presence of a doublet at 1.49 ppm for CH3, a triplet at 4.0 and 4.5 ppm for CH2, and a multiplet for CH at 4.8 ppm confirms the formation of propylene carbonate. The multiplet at 4.8 ppm confirms the coupling of CH with both methyl as well as methylene hydrogens. 3.2. FTIR Spectra of Ligand−Metal Complexes (Anchored and Unanchored) and Propylene Carbonate. The FTIR spectra of ligand−metal complexes are shown in Figures 10−13, and the relevant data are summarized in Table 1. From Figure 10 it is seen that the band at 1274 cm−1 in salen attributed to C−O has shifted to higher frequency of about 30−40 cm−1 in case of complexes confirming the participation of oxygen in the C−O−M bond. The band for the ligand at 1613 cm−1 due to CN stretching has shifted to a lower frequency of 1604 cm−1 in the case of the salen−CoSO4 complex and of 1608 cm−1 in case of the salen−FeCl3 complex. The weak broad band seen in the ligand at around 2500−3000

Table 1. FTIR Data of Synthesized Metal Complexes s. no.

metal complexes

C−O (cm‑1)

C−N (cm‑1)

CN (cm‑1)

1. 2.

salen salen CoSO4

1274 1320

1479 1459

1613 1604

3.

salen FeCl3

1314

1461

1608

4. 5.

napthen napthen CoSO4

1325 1360

1470 1486

1622 1614

6.

napthen FeCl3

1360

1484

1613

8.

napthen CoCl6·6H2O dapthen dapthen FeCl3

1366

1452

1603

1328 1347

1407 1437

1624 1623

9. 10.

E

OH (cm‑1) 2500−3000 disappearance band disappearance band 3434 disappearance band disappearance band disappearance band 3245 disappearence band

of of

of of of

of



Article

Figure 17. X-ray diffractogram of salen−CoSO4 anchored on montmorillonite clay. Figure 14. FTIR spectra of propylene carbonate.

Table 2. Crystal Sizes of the Various Complexes s. no.

complex

fwhm

2θ

crystal size (Å)

1. 2. 3. 4.

salen salen−CoSO4 salen−CoSO4 PEG salen−CoSO4 MMT

0.2 0.3 0.38 0.5

15.2 18.1 19.1 26.7

411.3 270.3 212.9 163.8

metal ion through charged phenolic oxygen and nitrogen atoms. The sharp signal observed for Dapthen at 3245 cm−1 due to OH has disappeared in the ligand−FeCl3 complex, but on the other hand, the CC vibrations of the ring have remained unaffected. The band due to C−O at 1328 cm−1 has shifted to 1347 cm−1 and confirms the participation of oxygen in the formation of C−O−M bonds. The peaks observed in the spectra of salen and daphen at 3400 and 3200 cm−1 are the characteristic peaks attributed to FeCl3 and CoSO4, respectively. Figure 12 shows the FTIR spectra of napthen, napthen− CoCl2·6H20, napthen−COSO4, naphthen−FeCl3, naphen− FeCl3, and naphen−CoSO4 anchored onto PEG. In the FTIR spectra of the ligand−metal complex anchored to PEG-6000, the presence Schiff’s base−metal complex and PEG-6000 as additional peaks due to OH and CC groups of PEG are observed at 3434 and 2888 cm−1, respectively. The bands due to Closite30 B and MMT and salen−metal complexes are observed in the FTIR spectra of salen−metal complexes anchored onto Closite30 B and MMT. Figure 13 shows the FTIR spectra of dapthen, daphthen−FeCl3 complex, Closite, and dapthen−FeCl3 complex anchored on to Closite. Figure 14 shows the FTIR spectra of propylene carbonate. The bands due to CO at around 1790 cm−1 and C−O stretching at about 1180 cm−1 are the characteristic bands of propylene carbonate and thereby confirm the formation of the cyclic product in both reactions. 3.3. X-ray Diffraction. The X-ray diffraction patterns of ligands, ligand−metal complexes, and anchored ligand−metal complexes were obtained to know the nature of the solid phase (crystalline or amorphous) and particle size. The X-ray diffraction patterns of salen−COSO4, salen−COSO4 anchored onto MMT, and salen−COSO4 anchored onto PEG are shown in Figures 15−17 as typical examples. Peaks of maximum intensity were selected to calculate fwhm (full wave half maxima) and crystal size. The results for salen, salen−CoSO4 complexes, and salen−CoSO4 complexes anchored on to MMT

Figure 15. X-ray diffractogram of salen−CoSO4.

Figure 16. X-ray diffractogram of salen−CoSO4 anchored on polyethylene glycol.

cm−1 attributed to the OH group has disappeared in the case of the complexes. The ring skeletal vibrations attributed to CC bonds are consistent in all derivatives and remain unaffected due to complexation. The disappearance of the band at 3434 cm−1 due to the OH group indicates protonation of the OH group and a subsequent formation of a bond between O and the metal ion. The peaks, due to M−O and M−N observed in the range of 435−470 cm−1, are not present in the spectra of ligand. These, therefore, permit us to infer that the ligand coordinates with the F



Article

(7) Lloyd, L.; Handbook of Industrial Catalysts; Springer: New York, 2011; pp 181−182. (8) Sari, M.; Atakol, O.; Yilmaz, N.; Ulku, D. Crystal structure of {2[(2-hydroxyphenyl)iminomethyl]-4,6-dinitrophenolato-O,N,O′}tris(3-ethylpyridine-N)}nickel(II). Anal. Sci. 1999, 15 (4), 401. (9) Kulkarni, P. A.; Habib, S. I.; Saraf, D. V.; Deshpande, M. M. Synthesis, spectral analysis and antimicrobial activity of some new transition metal complexes derived from 2, 4-dihyroxy acetophenones. Res. J. Pharm., Biol. Chem. Sci. 2012, 3 (4), 108. (10) Raman, N.; Pitchaikani, R., Y.; Kulandaisamy, A. Synthesis and characterisation of Cu(II), Ni(II), Mn(II), Zn(II) and VO(II) schiff base complexes derived from o-phenylenediamine and acetoacetanilide. Proc. Indian Acad. Sci. 2001, 113 (3), 183. (11) Alvaro, M.; Baleizao, C.; Carbonell, E.; Ghoul, M. E.; Garci, H.; Gigante, B. Polymer-bound aluminium salen complex as reusable catalysts for CO2 insertion into epoxides. Tetrahedron. 2005, 61 (51), 12131−12139. (12) Bhattacharyya, K. G.; Gupta, S. S. Adsorption of a few heavy metals on natural and modified kaolinite and montmorillonite: a review. Adv. Colloid Interface Sci. 2008, 140 (2), 114. (13) Wang, J. Q.; Kong, D. L.; Chen, J. Y.; Cai, F.; He, L. N. Synthesis of cyclic carbonates from epoxides and carbon dioxide over silica-supported quaternary ammonium salts under supercritical conditions. J. Mol. Catal. A: Chem. 2006, 249 (1−2), 143−148. (14) Mokhles, M.; Elzaher, A. Synthesis and spectroscopic characterization of some tetradentate schiff bases and their Nickel, Copper And Zinc Complexes. Synth React. Inorg. Met Org Chem. 2000, 30 (9), 1805−1816.

and PEG are given in Table 2. Comparison of the fwhm and D values obtained from the peaks indicated that the crystals of complexes attached to the support have a higher surface area to volume ratio than the unanchored ligand−metal complexes. This is due to the smaller crystallite size in the former case. The crystal size of the salen−CoSO4 complex was found to be 270.3 Å, and those of the complexes anchored on to MMT and PEG were 163.8 and 212.3 Å, respectively.

4. CONCLUSION Several Schiff’s base ligands, salen, dapthen, and napthen, were synthesized and complexed with metallic salts like CoCl2·6H2O, CoNO3·7H2O, CoSO4, and FeCl3. It was found that salen forms complexes with CoSO4 and FeCl3 and daphen complexes efficiently with FeCl3. The ligand−metal complexes have been successfully anchored onto MMT, OMMT (Closite30B), and PEG-6000. Anchoring has been found to reduce the crystallite size and increase the surface area. Due to the presence of metal ions along with the nucleophilic groups, the Schiff’s base−metal complexes have exhibited good catalytic activity. Some of the synthesized metal complexes (salen− CoSO4 and napthen−CoSO4) were used as catalysts along with cocatalyst (tetradecyltrimethyl ammonium bromide) for the chemical fixation of carbon dioxide through its reaction with propylene oxide to give propylene carbonate.

■

AUTHOR INFORMATION

Corresponding Author

*Tel: 911752393063. Fax: 911752393005. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported in part by All India Council of Technical Education, New Delhi (India) under Project No. 8023/RID/RPS/068/11/12.

■

REFERENCES

(1) Fakhari, A. R.; Khorrami, A. R.; Naeimi, H. Synthesis and analytical application of a novel tetradentate N2O2 Schiff base as a chouromogenic reagent for determination of nickel in some natural food samples. Talanta 2005, 66 (5), 813−817. (2) Teleb, S. M.; Sadeek, S. A.; Nour, E. M. Synthesis and vibrational studies of oxovanadium(IV)-tetradentate schiff base complexes. Spectrosc. Lett. 1993, 26 (1), 169. (3) Nour, E. M.; Al Kority, A. M.; Sadeek, S. A.; Teleb, S. M. Synthesis and spectroscopic studies of N,N′-O-phenylenebis(salicylideneiminato)dioxouranium(Vi)solvents(L) (L=Dmf& Py). Synth. React. Inorg. Met.-Org.Chem. 1993, 23 (1), 39. (4) Jamaluddin, A. M.; Reazul, H. M. A rapid spectrophotometric method for the determination of chouromium in environmental samples using bis(salicylaldehyde) orthophenylenediamine. Res. J. Chem. Sci. 2011, 1 (1), 1. (5) Munde, A. S.; Shelke, V. A.; Jadhav, S. M.; Kirdant, A. S.; Vaidya, S. R.; Shankarwar, S. G.; Chondhekar, T. K. Synthesis, characterization and antimicrobial activities of some transition metal complexes of biologically active asymmetrical tetradentate ligands. Adv. Appl. Sci. Res. 2012, 3 (1), 75−182. (6) Boghaei, D. M.; Mohebi, S. Synthesis, characterization and study of vanadyl tetradentate schiff base complexes as catalyst in aerobic selective oxidation of olefins. J. Mol. Catal A: Chem. 2002, 179 (1−2), 41−51. G


Polyethylene Glycol and Montmorillonite Clay Anchored Schiff Base

Recommend Documents