Novel synthesis of coordination biopolymer precursor from oxidation of methyl cellulose by alkaline potassium permanganate

Purpose of the study: Synthesis of diketomethyl cellulose. Materials and method: Diketomethyl cellulose was quantitatively prepared by the oxidation of methyl cellulose by potassium permanganate in alkaline medium at pH`s > 12. Results: The dike to-derivative was characterized by formation of 2,4-dinitrophenyl hydrazone and dioxime derivatives when reacting with dinitrophenyl haydrazine and hydroxyl amine, respectively, as well as by the FTIR spectral bands observed at 1760-1730 cm-1 that characterize to the carbonyl group of α-diketones. Conclusion: This oxidation product can be used as a dietary fiber and a functional fiber when added to food. In addition, it found that the product has a high affinity for chelation with most of divalent and polyvalent metal ions forming stable coordination biopolymer complexes of methyl cellulose. The product is characterized by its non-toxicity, low cost and high performance. Diketomethyl cellulose can be used effectively for removal of poisonous heavy metal ions such as Sn2+, Cd2+, Hg2+ and Pb2+, Ca2+ along with other divalent and polyvalent metal ions which are contaminated in wastewater and environment. Introduction Cellulose is the major component of cell walls in plant. It is considered as a dietary fiber as well as a functional fiber when added to food [1]. Methyl cellulose (MC) is a cellulose ether derivative. It is a water-soluble due to the presence of hydroxyl moieties at C-2 and C-3 positions which prevent extensive hydrogen bonding. It is a hydrophilic macromolecule unless the temperature exceeds that of the lower critical temperature of solution (LCST) of the approximate range 40-70 οC [2]. Therefore, this natural polymer is expected to have advantageous as a dietary fiber in food industry. The kinetics and mechanisms of oxidation of polysaccharides such as alginates [3], pectates [4], methyl cellulose [5,6], carboxymethyl cellulose [7], carrageenan [8,9] and chondroitin-4-sulfate [10] by alkaline permanganate have been investigated in more details as reported elsewhere. However, the synthesis of the keto-derivatives for the oxidation of products of the studied polysaccharides was reported elsewhere [11,12], it seems that no mention on the synthesis of the methyl cellulose keto-derivatives. Moreover, it was reported that the high tendency of alginate polysaccharide to form coordination biopolymers with polyvalent metal cations was attributed to the presence of both carboxylate and hydroxyl groups within the monomers [13]. This means that the presence of such groups in particularly the carboxylate groups within the monomers is essential for formation of such coordination biopolymer complexes. Despite the absence of carboxylate groups within the skeleton of the synthesized diketo-methyl cellulose, preliminary experiments indicated *Correspondence to: Hassan RM, Chemistry Department, Faculty of Science, Assiut University, Assiut 71516 Egypt, Tel: 01116770589; E-mail: rmhassan2002@yahoo.com


Introduction
Cellulose is the major component of cell walls in plant. It is considered as a dietary fiber as well as a functional fiber when added to food [1]. Methyl cellulose (MC) is a cellulose ether derivative. It is a water-soluble due to the presence of hydroxyl moieties at C-2 and C-3 positions which prevent extensive hydrogen bonding. It is a hydrophilic macromolecule unless the temperature exceeds that of the lower critical temperature of solution (LCST) of the approximate range 40-70 ο C [2]. Therefore, this natural polymer is expected to have advantageous as a dietary fiber in food industry.
The kinetics and mechanisms of oxidation of polysaccharides such as alginates [3], pectates [4], methyl cellulose [5,6], carboxymethyl cellulose [7], carrageenan [8,9] and chondroitin-4-sulfate [10] by alkaline permanganate have been investigated in more details as reported elsewhere. However, the synthesis of the keto-derivatives for the oxidation of products of the studied polysaccharides was reported elsewhere [11,12], it seems that no mention on the synthesis of the methyl cellulose keto-derivatives.
Moreover, it was reported that the high tendency of alginate polysaccharide to form coordination biopolymers with polyvalent metal cations was attributed to the presence of both carboxylate and hydroxyl groups within the monomers [13]. This means that the presence of such groups in particularly the carboxylate groups within the monomers is essential for formation of such coordination biopolymer complexes. Despite the absence of carboxylate groups within the skeleton of the synthesized diketo-methyl cellulose, preliminary experiments indicated by permanganate ion oxidant rather than by the dissolved oxygen. The oxidation product was identified by the spectral data and elemental analysis [18]. The diketo-derivative was characterized by the formation of 2,4-dinitrophenyl hydrazone and dioxime derivatives as well as by the FTIR spectral bands observed at 1760-1730 cm -1 that characterize to the carbonyl group of α-diketones [17] as shown in Figure 1.

Kinetics and mechanism
The kinetics and mechanism for oxidation of MC substrate by alkaline [5,6] and acidic [20] permanganate have been discussed in more details earlier. In case of oxidation of MC by alkaline permanganate [5,6], it was found that the oxidation process was proceeding through two distinct separate stages. The naked-eye observations indicated the change in color of the solution mixture from purple (Mn (VII)) to blue (Mn(V)) to green (Mn (VI)) to yellow (Mn (IV)). The first stage was relatively fast with formation of 1:1 intermediate transient coordination biopolymer complexes involving blue hypomamanganate (V) and/ or green manganate (VI) transient species. This stage was followed by slow decomposition of these intermediates to give rise to the final oxidation products as monoketo-or diketo -methyl cellulose precursor derivatives in the final slow stage depending on the initial concentration molar ratio of reactants. Inner-sphere type of the electron transfer mechanism without free-radical intervention was suggested. On the other hand in case of oxidation of MC by acidic permanganate, the oxidation process was found also to proceed via two distinct stage of sigmoidal S-shape nature for pseudo first-order plots. The first stage was found to be relatively slow via formation of 1:2 intermediate complexes prior to the rate-determining step. It corresponds to the formation of substrate radical and Mn 3+ and/or Mn 4+ transient species as initial oxidation products. This stage was followed by a fast reaction to give rise to keto-derivatives of methyl cellulose in the second fast stage. The mechanisms of oxidation of methyl cellulose by acidic [5,6] and alkaline [20] permanganate are illustrated in Figures 2 and 3, respectively. difficult. A stock solution of permanganate was prepared, stored and standardized as described elsewhere [15,16]. All other reagents were prepared by dissolving the requisite amounts of the sample in doubly distilled water.

Preparation of diketomethy cellulose (DKMC)
Methyl cellulose powder (5 g) was dissolved in 350 cm 3 of deionized water whose pH was previously ad justed to pH ≥ 12 using sodium hydroxide. This process was performed by stepwise addition of the powder MC to the solution while stirring rapidly and continuously to avoid the formation of aggregates. A 150 cm 3 solution containing 3.87 g of potassium permanganate and 4.07 g of sodium fluoride was then added stepwise over 2 h to the MC solution. The reaction mixture was stirred for 48 h at room temperature, the formed MnF 4 was filtered off, and the solution was concentrated to one-fifth of the original solution us ing a rotary evaporator. A portion of this concen trated solution was acidified using dilute acetic acid to a pH of ca. 5-6. The resultant solution dried under vacuum, and then subjected to elemental analysis and IR spectroscopy.
The diketo-derivative was characterized by formation of 2,4-dinitrophenyl hydrazone and dioxime derivatives when reacting with dinitrophenyl haydrazine and hydroxyl amine, respectively, as well as by the FTIR spectral bands observed at 1760-1730 cm -1 that characterize to the carbonyl group of α-diketones.

IR-spectra
The IR-spectra were scanned on a Pyc Unicum Sp 3100 spectrophotometer using the KBr disc technique (4000-200 cm -1 ). The diketo-derivative was also identified by elemental analysis and IR spectral data as described elsewhere [18,19].

Results and discussion
where C 7 H 12 O 5 and C 7 H 8 NO 5 represent the MC and its corresponding diketo-derivative, respectively. The oxidation product was found to be the same in either the presence or absence of nitrogen atmosphere indicating that the oxidation of the formed aldehyde occurs

Chelation geometry with metal ions
It was found that the oxidation product under our experimental conditions (diketo-methyl cellulose derivative) possesses a high tendency to chelate with many metal cations such as silver (I), di-, triand tetravalent metal ions, whereas the MC itself does not chelate with these metal ions. The characteristics and geometrical configuration of these complexes are in progress in our laboratory.

Conclusion
Diketomethyl cellulose can be used as a dietary fiber and a functional fiber when added to food. In addition, it found that the product has a high affinity for chelation with most of divalent and polyvalent metal ions forming stable coordination biopolymer complexes of methyl cellulose. The product is characterized by its non-toxicity, low cost and high performance. Diketomethyl cellulose can be used effectively for removal of poisonous heavy metal ions such as Sn 2+ , Cd 2+ , Hg 2+ and Pb 2+ , Ca 2+ along with other divalent and polyvalent metal ions which are contaminated in wastewater and environment.

Conflicts of interest
No.