Elsevier

Journal of Molecular Liquids

Volume 240, August 2017, Pages 486-496
Journal of Molecular Liquids

Synthesis, characterisation and catalytic activity of dithiocarbazate Schiff base complexes in oxidation of cyclohexane

https://doi.org/10.1016/j.molliq.2017.05.081Get rights and content

Highlights

  • A series of metal complexes of dithiocarbazate Schiff bases were synthesized.

  • They were characterized and evaluated for the oxidation of cyclohexane.

  • The selectivity of the reaction was 98%.

Abstract

Schiff base complexes of transition metals can be used for catalytic oxidation of hydrocarbons in the presence of tert-butyl hydroperoxide (TBHP). In this work, metal complexes of dithiocarbazate Schiff bases (abbreviated as NiSBdiAP, CuSBdiAP, CoSBdiAP, FeSBdiAP, MnSBdiAP and ZnSBdiAP, in which SBdiAP represents the Schiff base) were synthesized and characterized using several techniques; Fourier transforms infrared spectroscopy, nuclear magnetic resonance, 1H NMR and 13C NMR, magnetic susceptibility measurements, molar conductivity, ultraviolet-visible spectroscopy, and inductively coupled plasma spectrometry. The oxidation of cyclohexane by the prepared metal complexes as catalysts was investigated in the presence of TBHP as an oxidative source under mild conditions. The product was analyzed using gas chromatography. It was found that cyclohexanol and cyclohexanone were the main products of the oxidation reaction. The iron complex of Schiff base derived from 2,6-diacetyl pyridine and S-benzyldithiocarbazate showed the highest activity during the screening studies towards cyclohexane oxidation. The results showed that the time of the reaction, temperature, and the concentration of TBHP and the catalyst type influenced the selectivity and conversion of cyclohexane oxidation. The selectivity of the reaction was 96% indicating the significance of the work toward industrial oxidation of cyclohexane.

Introduction

The reaction of an amine with an aldehyde or a ketone in suitable conditions produces Schiff base compounds. Basically, Schiff base can be synthesised by the replacement of a carbonyl group with an imine or azomethine in the nitrogen analogue of an aldehyde or ketone. Schiff base can interact with most of the metal ions to produce various complexes [1], [2], [3]. Schiff base compounds have several unique physical and chemical properties. Most Schiff base ligands have an important role in many reactions due to their high catalytic activity that increase the yield and selectivity. In general, the catalytic application of Schiff bases as metal complexes depends on the method that has been used for synthesis and thermal stability of these ligands [4]. Schiff base complexes of transition metal ions work as active catalysts in homogeneous and heterogeneous reactions and their activity differs according to the metal ions, kind of ligands and coordination sites [5], [6]. The metal complexes of Schiff bases have been used as catalysts during the last decades in many reactions such as; thionyl chloride reduction polymerization reaction, ketones reduction, reaction of aldol, Henry reaction, alkenes epoxidation, ketones hydrosilylation, reaction of Dielss Alder and oxidation of organic compound that has attracted a huge attention in the field of academic and industrial study [7]. There are a lot of hydrocarbons in the constituents of the natural gas and oil, thus, the usage of the hydrocarbons in reactions was the way for several economic industries. Selective oxidation is the most significant functionalization of hydrocarbons. In the liquid phase, different oxidants such as; hydrogen peroxide, tert-butyl hydroperoxide (TBHP) and others have been used for oxidation of cycloaliphatic and aliphatic compounds by using oxygen to produce suitable alcohol and ketones under tough conditions like high temperature and pressure due to the difficulty of making the activation of Csingle bondH bonds [8], [9].

Annually, more than one billion tons of cyclohexanone and cyclohexanol are formed widely around the world, for the industrialization of the polymers Nylon-6 and Nylon-6,6, that have been used in the manufacture of adipic acid, polyamide-6, acidulant in baking powder and caprolactam [10], [11], [12]. The oxidation reaction of cyclohexane to cyclohexanone and cyclohexanol (also known as KA oil) has a significant importance in the industry field. In the last few decades, the oxidation of cyclohexane using Schiff base metal complexes has attracted scientists to conduct research in this area. Schuchardt et al. discussed an alternate method on how to develop the industrial method of the oxidation of cyclohexane, that focused on the improvement of new catalysts to oxidize cyclohexane under a suitable condition [13]. The use of metal complexes as catalysts to activate hydrocarbons was improved by applying Schiff base transition metal complexes as catalysts because of their cheap and easy synthesis and their chemical and thermal stability [14], [15], [16], [17]. The use of Schiff base metal complexes in the cyclohexane oxidation has a great interest due to their potential catalytic activity [18], [19], [20].

In the present work, we have synthesised new metal complexes containing a bis-dithiocarbazate ligand. The synthesised complexes were investigated as catalysts for cyclohexane oxidation and tert-butyl hydroperoxide was used as an oxidant. The prepared metal complexes as catalysts were cobalt(II), copper(II), iron(II) manganese(II), nickel(II), cobalt(II) and zinc complexes derived from the Schiff base (2E,2′E)-dibenzyl 2,2′-(1,3-phenylenebis(ethan-1-yl-1-ylidene))bis (hydrazine carbo dithioate) [SBdiAP]. The catalytic activity of the prepared metal complexes was screened for cyclohexane oxidation. These catalysts showed high yield and good products quality under mild conditions.

Section snippets

Materials

The chemicals and solvents used in the present work were used as received without any additional purification. Manganese(II) chloride tetrahydrate (Merk), ferrous chloride tetrahydrate (Aldrich), cobalt(II) chloride hexahydrate (Merk), nickel(II) chloride hexahydrate (Merk), copper(II) chloride dehydrate (Merk), zinc chloride (Merk), tert-butyl hydroperoxide (70%w/v, Aldrich), cyclohexane (99.7%, Merck), 2,6-diacetylpyridine (Fluka), dichloromethane (Analar), ethanol (99.8%, Scharlau),

Physico-chemical data

The physical characteristics of the Schiff base and all the metal complexes are as shown in Table 1. All compounds were characterised according to yields, melting point, and colour. In general, the metal complexes have different colours compared to Schiff base indicating an initial successful reaction between the Schiff base and metal salt. The melting points of the prepared metal complexes were higher than the melting point of the of Schiff base.

CHNS elemental analysis

CHNS analysis was used to calculate the

Conclusions

The catalytic activities of the synthesised metal complexes of Schiff base were investigated for the oxidation of cyclohexane using TBHP as an oxidant under mild conditions. The main products of the oxidation were cyclohexanone and cyclohexanol and no conversion of the cyclohexane in the absence of the catalyst was obtained. The selectivity of cyclohexanone was found to be greater. The catalytic activity of iron complex (FeSBdiAP) that gave the highest conversion in the screening study of the

Acknowledgement

This research was funded by Ministry of Education Malaysia under the Fundamental Research Grant Scheme (FRGS No. 01-02-13-1342FR) and Universiti Putra Malaysia (UPM) under the Putra Grant (IPS No. 9462800). Ali Ahmed Alshaheri would like to thank Albaida University for the study financial support.

References (48)

  • W.J. Geary

    The use of conductivity measurements in organic solvents for the characterisation of coordination compounds

    Coord. Chem. Rev.

    (1971)
  • K.-B. Chew et al.

    Synthesis, characterization and bio-activity of metal complexes of bidentate N–S isomeric Schiff bases derived from S-methyldithiocarbazate (SMDTC) and the X-ray structure of the bis[S-methyl-β-N-(2-furyl-methylketone)dithiocarbazato]cadmium(II) complex

    Polyhedron

    (2004)
  • M. Mohan et al.

    Some metal(II) chelates of 4-(m-aminophenyl)-2-formylpyridine thiosemicarbazone: their preparation, characterization and antitumour activity

    Inorg. Chim. Acta

    (1985)
  • C. Adhikary et al.

    Catalytic efficacy of Schiff-base copper(II) complexes: synthesis, X-ray structure and olefin oxidation

    Polyhedron

    (2008)
  • A.A. Leontiou et al.

    Kinetics investigation of NO + CO reaction on La-Sr-Mn-O perovskite-type mixed oxides

    Appl. Catal. A Gen.

    (2004)
  • R.R. Fernandes et al.

    Bis- and tris-pyridyl amino and imino thioether Cu and Fe complexes. Thermal and microwave-assisted peroxidative oxidations of 1-phenylethanol and cyclohexane in the presence of various N-based additives

    J. Mol. Catal. A Chem.

    (2011)
  • R.R. Fernandes et al.

    Oxidations of cycloalkanes and benzene by hydrogen peroxide catalyzed by an {FeIIIN2S2} centre

    Appl. Catal. A Gen.

    (2009)
  • M.C. Esmelindro et al.

    Catalytic oxidation of cyclohexane by a binuclear Fe(III) complex biomimetic to methane monooxygenase

    J. Inorg. Biochem.

    (2005)
  • Y.P. Tian et al.

    Synthesis, crystal structure, and second-order optical nonlinearity of bis(2-chlorobenzaldehyde thiosemicarbazone)cadmium halides (CdL(2)X(2); X = Br, I)

    Inorg. Chem.

    (1997)
  • M.P. de Almeida et al.

    Homogeneous and heterogenised new gold C-scorpionate complexes as catalysts for cyclohexane oxidation

    Catal. Sci. Technol.

    (2013)
  • Z.-H. Liu et al.

    Design, synthesis, and crystal structure of a cis-configuration N(2)S(2)-coordinated palladium(II) complex: role of the intra- and intermolecular aromatic-ring stacking interaction

    Inorg. Chem.

    (1999)
  • R.H. Crabtree

    Aspects of methane Chemistry

    Chem. Rev.

    (1995)
  • G. Shul'pin

    New trends in oxidative functionalization of carbon–hydrogen bonds: a review

    Catalysts

    (2016)
  • R. Antony et al.

    Highly dispersed Cu(II), Co(II) and Ni(II) catalysts covalently immobilized on imine-modified silica for cyclohexane oxidation with hydrogen peroxide

    RSC Adv.

    (2014)
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