Selection of Promoter and Micellar Catalyst for ...

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Germany www.TSD-journal.com. Not for use in internet or intranet sites. Not for electronic .... Seo, S. H., Chang, J. Y. and Tew, G. N.: Angew Chem. Int. Edn. 45 (2006) 7526 ... in my lab in “Inorganic Reaction Mechanism and Catalysis” division.
PHYSICAL CHEMISTRY

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y

Kakali Mukherjee, Sumanta K. Ghosh, Rumki Nandi, Aniruddha Ghosh, Indrajit Saha, Rumpa Saha and Bidyut Saha

Selection of Promoter and Micellar Catalyst for Chromic Acid Oxidation of Tartaric Acid in Aqueous Medium at Room Temperature Chromic acid oxidation of tartaric acid in aqueous acid media produces glycolaldehyde very sluggishly at room temperature. Suitable combination of promoter (2,2’-bipyridine and 1,10-phenanthroline) and micellar catalyst (sodium dodecyl sulphate, cetylpyridinium chloride, triton X-100) enhances the rate of reaction to almost 14-fold. Observation showed that anionic surfactant (SDS) and nonionic surfactant (TX-100) accelerates the process but cationic surfactant (CPC) retards the reaction. The efficient combination for the production of glycolaldehyde from tartaric acid is found to be 1,10-phenanthroline and SDS. Key words: Promoter, micellar catalyst, chromic acid, oxidation, tartaric acid, aqueous medium

Auswahl eines Promotors und mizellaren Katalysators für die Chromsäureoxidation von Weinsäure im wässrigen Medium bei Raumtemperatur. Die Chromsäureoxidation von Weinsäure im sauren, wässrigen Medium bei Raumtemperatur erzeugt sehr langsam Glycolaldehyd. Geeignete Kombinationen aus einem Promotor (2,2’-Bipyridin and 1,10-Phenanthrolin) und einem mizellaren Katalysator (Natriumdodecylsulfat, Cetylpyridiniumchlorid, Triton X-100) erhöht die Reaktionsgeschwindigkeit um nahezu das 14-fache. Es wurde festgestellt, dass anionische (SDS) und nichtionische Tenside (TX-100) den Prozess beschleunigen, kationische Tenside (CPC) dagegen die Reaktion hemmen. Die effektive Kombination für die Erzeugung von Glycolaldehyd aus Weinsäure ist 1,10-Phenanthrolin und SDS. Stichwörter: Promotor, mizellarer Katalysator, Chromsäure, Oxidation, Weinsäure wässriges Medium

1 Introduction

Amphiphiles are molecules consisting of a hydrophilic head group and a hydrophobic tail and are thus able to interact with both polar and non polar compounds. When the hydrophobic tail reaches a certain chain length, the amphiphiles reduce the unusually high surface tension of water and are referred to as surfactants [1]. Surfactants dissolve completely in water at very low concentrations, but above a certain level, the critical micelle concentration (CMC), the molecules form globular aggregates, called micelles. The hydrophobic tails group together to create a non polar interior with the head groups located at the surface of the glob in contact with the aqueous micelles varies in size and shape, but is commonly rough surfaced sphere with an aggregation number in the order of 50 – 100. Any reactive species added to the solution containing micelle will distribute itself between mi-

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celle and aqueous phase. If these two environments result in different reaction rates, the micelles will act as either catalysts or inhibitors [2 – 4]. The physical basis for micellar catalysis involves localizing of the reacting species in the relatively small volume of the micelles compared to the bulk solution. This leads to a large increase in the effective concentration (in terms of moles per unit time per liter of the entire solution) of the reactants. The catalytic efficiency will be governed both by the affinity of the reagents for the micelles and by the reactivity of the bound reagent molecules. Oxidation is a key reaction for organic synthesis [5]. Chromic acid is a widely used oxidizing agent [6 – 8]. 2,2’-bipyridine (bpy) and 1, 10-phenanthroline (phen) are well known to act as a promoter for Cr(VI) oxidation of organic substances [9 – 17]. Present work will find out best catalyst (among anionic, cationic and non ionic surfactant) and best promoter (among bpy and phen) for chromic acid oxidation of tartaric acid. 2 Experimental 2.1

Materials and methods

1,10-phenanthroline (AR, Merck), 2,2’-bipyridine (AR, Spectrochem, India), L-tartaric acid (AR, Merck), K2Cr2O7 (AR, BDH), sodium dodecyl sulphate (AR, SRL), N-cetylpyridinium chloride (AR, SRL), TX-100 (AR, SRL) and all other chemicals used were of highest purity available commercially. The surfactants were used without further treatment in order to achieve the investigation from an application point of view. The solutions were prepared in double distilled water. Solutions of the oxidant and reaction mixtures containing the known quantities of the substrate(s) (i. e. tartaric acid), promoter (2,2’-bipyridine and 1,10-phenanthroline) under the kinetic conditions [tartaric acid]T 4 [Cr(VI)]T and [promoter]T 4 [Cr(VI)]T acid and other necessary chemicals were separately thermostated (€ 0.1 8C). The reaction was initiated by the requisite amounts of the oxidant with the reaction mixture. Progress of the reaction is monitored by following the rate of disappearance of Cr(VI). The concentration of Cr(VI) at different time intervals was measured by a titrimetric quenching technique using excess of standard Mohr’s solution and unreacted Fe(II) was estimated by a standard Ce(IV) solution using ferroin indicator. The pseudo first order rate constants were calculated from the slopes of the plot of log[Cr(VI)]T versus time t, which were linear at least for three half lives. The scanned spectra and spectrum after completion of the reaction were recorded with a UV-VIS spectrophotometer [UV-2450 (SHIMADZU)]. Quartz cuvettes of path length 1 cm were used. Under the experimental conditions, the possibility of decomposition of

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Kakali Mukherjee et al.: Selection of promoter and micellar catalyst for chromic acid oxidation of tartaric acid

2.2

Product analysis and stoichiometry

Under the kinetic conditions [TA]T 4 [Cr(VI)]T, the acid was quantitatively oxidized to glycolaldehyde. Grass green colour is produced on heating the solution with naphtharesorcinol in 23 N sulphuric acid indicates the formation of glycolaldehyde [18]. CHðOHÞðCOOHÞ 2j þ 3HCrO4 þ 17Hþ ! 2CHO þ 3CrIII þ 12H2 O þ 4CO2 CHðOHÞðCOOHÞ j CH2 OH 2.3

Reaction mechanism

phen) under the identical conditions is pale violet [kmax = 550 nm, for 4A2 g (F) ? 4T2 g (F) of Cr(III)-species]. The spectra of the final solution of without promoter reaction and pure chromic sulphate solution in aqueous sulphuric acid media are identical. It proves that the final Cr(III)-species is simply Cr(III)-species for the without promoter reaction while for the promoted reaction (phen); the final Cr(III)-species is a different species, which is Cr(III)-promoter complex. For promoted reaction (phen), there is a blue shift (Fig. 1) for the peak due to the transition 4A2 g (F) ? 4T2 g (F) compared to the final solution of the without promoter path. This blue shift is due to the presence of the strong field donor site, i. e. heteroaromatic N-donor site of promoter. For the Cr(III)-promoter complex, the peak due the transition 4A2 g (F) ? 4T2 g (F) merges with a charge transfer band (Fig. 1). For Cr(III)-aqueous species, the band at 270 nm due to 4A2 g (F) ? 4T1 g (P) transition appears as a shoulder on high energy charge transfer band [12]. For

Scheme 1 is drawn on the basis that the reaction follows first order dependency on [Cr(VI)]T and [TA]T but second order dependency on [H+] (not shown in the paper). Scheme 2 is drawn on the basis that the reaction follows first order dependency on [TA]T, [Cr(VI)]T, [Phen]T and [H+] (not shown in the paper). Scheme 3 is drawn on the basis that the reaction follows first order dependency on [TA]T, [Cr(VI)]T, [bpy]T and [H+] (not shown in the paper). 3 Results and Discussion 3.1

Spectrophotometric analysis

The colours of the final solutions in the absence of the promoter and in the presence of the promoter are different due to the presence of different types of Cr(III)-species. The colour of the final solution in the absence of the promoter under the experimental condition is pale blue (kmax = 416 nm and 580 nm) and the corresponding transitions [12] are 580 nm for 4A2 g (F) ? 4T2 g (F) and 416 nm for 4A2 g (F) ? 4 T1 g (F) of Cr(III)-species. On the other hand, the colour of the final solution of the promoted reaction (in presence of

Scheme 2 dine

Chromic acid oxidation of tartaric acid in presence of 2,2’-bipyri-

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the surfactants by Cr(VI) was investigated and the rate of decomposition in this path was kinetically negligible.

Scheme 1 Chromic acid oxidation of tartaric acid in absence of promoter

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Cr(III)-promoter complex, the appearance of the charge transfer band at much lower energy for the proposed Cr(III)-promoter complex is quite reasonable because of the favoured metal to ligand charge transfer. The vacant p* of the phen favours the metal to ligand charge transfer. The existence of the charge transfer band (metal to ligand) at lower energy for the promoted reaction may be the cause of rate enhancement. For the phen promoted reaction the charge transfer band at higher wave length than the bpy promoted path (Fig. 1).

The scanned spectrum (Fig. 2a) indicates the gradual disappearance of Cr(VI) species and appearance of Cr(III) species with an isobestic point at k = 510 nm for the without promoter reaction. Whereas in presence of promoter isobestic point (Fig. 2b) appears at k = 527 nm (only phen promoted scan is shown). Observations of this single isobestic point indicate the very low concentration of Cr(V) and Cr(VI) intermediates under the present experimental condition. In presence of promoter, Cr(VI)-phen and Cr(VI)-bpy are the active oxidants [13] (Figure 3). 3.2

Effect of micellar catalysts

Partition of neutral tartaric acid is equally probable to all types of surfactants (Fig. 4). Partitioning of proton is maximum in SDS due to electrostatic attraction less in CPC due to electrostatic repulsion. Rate is maximum in SDS, minimum in CPC and TX-100 has effect in between them (Table 1). Active oxidant Cr(VI)-bpy (Scheme 2) or Cr(VI)-phen (Scheme 3) complex react with the substrate to form a ternary complex which experience a redox decompositions in a rate limiting step [13] giving rise to organic product. Positively charged active oxidants are preferably accumulated in the anionic micellar phase of SDS due to electronic attraction. In fact, in the presence of SDS, the reaction simultaneously goes on in both in the micellar phase and aqueous phase and the rate is accelerated in the micellar phase because of the preferential accumulation of the reactants in the micellar phase. In the presence of CPC, although the substrate is partitioned in the micellar phase, the approach of the active oxidants Cr(VI)-bpy (Scheme 2) or Cr(VI)-phen (Scheme 3) complexes are repelled. Thus in the presence of CPC, the reaction is restricted to the aqueous phase which is depleted in the concentration of the substrate. This leads to the rate retardations. As the micellar head groups of TX-100 are neutral it produces rate enhancement more than water and less than SDS (Table 1). 4 Conclusion Scheme 3 Chromic acid oxidation of tartaric acid in presence of 1,10-phenanthroline

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Kakali Mukherjee et al.: Selection of promoter and micellar catalyst for chromic acid oxidation of tartaric acid

Combination of 1,10-phenanthroline and SDS is suitable for the production of glycolaldehyde from tartaric acid.

Figure 1 (A) Absorption spectrum of unpromoted reaction mixture (after completion of reaction): [tartaric acid]T = 0.01 mol dm–3, [Cr(VI)]T = 5 · 10–4 mol dm–3, [H2SO4]T = 1 mol dm–3. (The spectrum of the chromic sulfate is identical with this under the experimental condition.) (B) Absorption spectrum of the promoted reaction mixture (after completion of reaction): [tartaric acid]T = 0.01 mol dm–3, [Cr(VI)]T = 5 · 10–4 mol dm–3, [H2SO4]T = 1 mol dm–3. [bpy]T = 50 · 10–4 mol dm–3. (C) Absorption spectrum of the promoted reaction mixture (after completion of reaction): [tartaric acid]T = 0.01 mol dm–3, [Cr(VI)]T = 5 · 10–4 mol dm–3, [H2SO4]T = 1 mol dm–3. [phen]T = 50 · 10–4 mol dm–3

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Kakali Mukherjee et al.: Selection of promoter and micellar catalyst for chromic acid oxidation of tartaric acid

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Figure 2(a) Scanned absorption spectra of the reaction mixture at regular time intervals (5 min). [tartaric acid]T = 0.01 mol dm–3, [Cr(VI)]T = 5 · 10–4 mol dm–3, [H2SO4]T = 1 mol dm–3. [promoter]T = 0 mol dm–3

2013 Carl Hanser Verlag, Munich, Germany

Figure 2(b) Scanned absorption spectra of the reaction mixture at regular time intervals (3 min). [tartaric acid]T = 0.01 mol dm–3, [Cr(VI)]T = 5 · 10–4 mol dm–3, [H2SO4]T = 1 mol dm–3. [phen]T = 0.005 mol dm–3

Figure 3 Absorption spectrum of reaction mixture with and without promoter (in absence of substrate): (a) [Cr(VI)]T = 5 · 10–4 mol dm–3, [H2SO4]T = 1 mol dm–3. (b) [Cr(VI)]T = 5 · 10–4 mol dm–3, [H2SO4]T = 1 mol dm–3, [bpy]T = 0.005 mol dm–3, (c) [Cr(VI)]T = 5 · 10–4 mol dm–3, [H2SO4]T = 1 mol dm–3, [phen]T = 0.005 mol dm–3

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2013 Carl Hanser Verlag, Munich, Germany

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Kakali Mukherjee et al.: Selection of promoter and micellar catalyst for chromic acid oxidation of tartaric acid

Figure 4 Schematic representation of partitioning of substrate and neutral ester and H+ in (a) cationic surfactant, (b) anionic surfactant and (c) neutral surfactant

Figure 5 Schematic representation of partitioning of substrate and active oxidant [AO+ = Cr(VI)Phen complex] in (a) Cationic surfactant, (b) Anionic surfactant and (c) Neutral surfactant Tcom (min)

Promoter

Micellar catalyst

536.37

Absent

Absent

69.15

Absent

SDS (2 · 10–2 mol dm–3)

158.73

Absent

TX-100 (2 · 10–2 mol dm–3)

737.2

Absent

CPC (8 · 10–3 mol dm–3)

154

Phen (0.005 mol dm–3)

Absent

219.30

Bpy (0.005 mol dm–3)

Absent

38.04

Phen (0.005 mol dm–3)

SDS (2 · 10–2 mol dm–3)

[Cr(VI)]T = 5 · 10–4 mol dm–3, [tartaric acid]T = 0.01 mol dm–3

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Correspondence address Dr. B. Saha Homogeneous Catalysis Laboratory, Department of Chemistry The University of Burdwan, Golapbag, Burdwan Pin 713104, WB India E-Mail: [email protected] (B. Saha), [email protected] (R. Saha)

The authors of this paper Kakali Mukherjee: She was born in Bankura, in 1988. She passed her M.Sc degree from the University of Burdwan in 2011 and got NET-LS fellowship on the year 2010. She is working in my lab in \Bio-remediation" division.

Table 1 Reaction completion time (87.5 %) in presence and absence of promoter and catalyst

Sumanta Kr. Ghosh: He was born in Burdwan, in 1974. He passed his M.Sc degree from the Visva-Bharati and got NET-CSIR fellowship on the year 1999. He is working in my lab in \Inorganic Reaction Mechanism and Catalysis" division.

Acknowledgements

Rumki Nandi: She was born in Chandannagore, in 1988. She passed her M.Sc degree from the University of Burdwan in 2010 and got NET-CSIR fellowship on the year 2010. She is working in my lab in \Bio-remediation" division.

Thanks are due to CSIR, New Delhi for financial support. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Ghosh, S. K., Basu, A., Paul, K. K. and Saha, B.: Mol. Phys. 107 (2009) 615. Dwars, T., Paetzold, E. and Oehme, G.: Angew Chem. Int. Edn. 44 (2005) 7174. Ryu, J. H., Hong, D. J. and Lee, M.: Chem. Commun. (2008) 1043. Seo, S. H., Chang, J. Y. and Tew, G. N.: Angew Chem. Int. Edn. 45 (2006) 7526. Sundaram, S. and Raghavan, P. S.: Chromium-VI Reagents: Synthetic Applications. Springer. 2011. Saha, R., Nandi, R. and Saha, B.: J. Coord. Chem. 64 (2011) 1782. Saha, B. and Orvig, C.: Coord. Chem. Rev. 254 (2010) 2959. Meenakshisundaram, S. P., Gopalkrishnan, M., Nagarajan, S. and Sarathi, N.: Catal. Commun. 8 (2007) 713. Saha, R., Ghosh, A. and Saha, B.: J. Coord. Chem. 64 (2011) 3729. Mandal, J., Chowdhuri, K. M., Paul, K. and Saha, B.: J. Coord. Chem. 63 (2010) 99. Chowdhuri, K. M., Mandal, J. and Saha, B.: J. Coord. Chem. 62 (2009) 1871. Islam, M., Saha, B. and Das, A. K.: J. Mol. Catal A: Chem. 266 (2007) 21. Islam, M., Saha, B. and Das, A. K.: J. Mol. Catal A: Chem. 236 (2005) 260. Bayen, R., Islam, M., Saha, B. and Das, A. K.: Carbohydr. Res. 340 (2005) 2163. Meenakshisundaram, S. and Sarathi, N.: Trans. Met. Chem. 31 (2006) 569. Meenakshisundaram, S. and Markkandan, R.: Trans. Met. Chem. 29 (2004) 308. Khan, Z., Masan, S., Raju, and Kabir-ud-Din: Trans. Met. Chem. 28 (2003) 881. Dickens, F. and Williamson, D. H.: Nature. 178 (1956) 1118.

Received: 14. 09. 2012 Revised: 05. 01. 2013

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Aniruddha Ghosh: He was born in Raniganj, in 1988. He passed his M.Sc degree from the University of Burdwan in 2010 and got NET-UGC fellowship on the year 2010. He is working in my lab in \Bio-remediation" division. Indrajit Saha: He was born in Howrah, in 1981. He passed his M.Sc degree from IIT Kanpur in 2007 and got NET-CSIR fellowship on the year 2006. He is working in my lab in \Inorganic Reaction Mechanism and Catalysis" division. Rumpa Saha: She was born in Burdwan, in 1987. She passed her M.Sc degree from the University of Burdwan in 2009 and got NET-CSIR fellowship on the year 2008. She is working in my lab in \Bio-remediation" division. Dr. Bidyut Saha: He was born in Birbhum, WB, India in 1975. He obtained his Ph.D degree from Visva Bharati University, India in 2007. He was a visiting scientist for the year 2009 – 2010 in the Department of Chemistry, UBC, Canada. Dr. Saha is presently working as an Assistant Professor in the Department of Chemistry, Burdwan University, India His area of interests is bioremediation of toxic metal, micellar catalysis and inorganic reaction mechanism. He has already published forty papers in international journals.

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