INTRODUCTION:

EDTA (ethylenediaminetetraacetic acid) is versatile chelating agent. This compound has massive uses in world wide with household and industrial applications. It is a colourless chelating agent with a molecular formula C₁₀H₁₆N₂ fig 1.

It can form four or six bonds with metal ions. EDTA is a chelate ligand with a high affinity constant to form metal-EDTA complexes, being deliberately added to sequester metal ions. [1]

EDTA usually binds a metal cation through its two amines and four carboxylates groups. [2]

Zinc is an essential micronutrient for plant. It plays important role in plant metabolism by stabilization of ribosomal fractions, controlling activities of hydrogenase and carbonic anhydrase enzyme, regulation of gene expression and synthesis of cytochrome. [3] [4]

chelates are an important group of natural and synthetic organic compounds, which are used as a source of micronutrients. The best known synthetic chelating compound is Zinc EDTA, which is used as a fertilizer [5]. Zinc is absorbed by plant roots as divalent Zn²⁺ or as Chelated zinc [6]. chelated forms are well absorbed by the plants, which will improve zinc deficiencies [7].

Zinc EDTA play major role hydroponics agriculture.it suppresses the gene causing root tomato disease in hydroponic culture [8][9]. This complex is stable in alkaline and acidic conditions which implies that it is available for plants at wide range of P_H levels [10].

Chelated Zinc EDTA releases cations and has a high affinity with lead which plays an essential role in detoxification of lead in plants. This prevents plants from the toxic effects of lead. [11][12]

It was reported by the x-ray studies that Zinc EDTA taken up in chelated form more readily than in ionic form Zn²⁺in wheat plant (triticum aestivum) [13]

In our present study synthesis of Zinc EDTA complex is carried out in electrochemical cell in which there are two electrodes, the sacrificial anode (positive) and the cathode (negative). The electrodes are submerged in an organic solvent with supporting electrolyte dissolved in it to assist in carrying the current through the cell.

Cell reaction:

Anode reaction:

nL^- + M [ML_n] + ne^-

cathode reaction:

nHL^-+ ne- nL^- + H₂

_{overall reaction:}

nHL + M [ML_n] +H₂

Above electrosynthesis process can be summarized: EDTA reacts with zinc metal ion to form Zn EDTA coordination complex. In eq :1 shown that EDTA has two binding site through which it coordinate to zinc metal to form chelate.

Equation:1

MATERIALS:

Metals (Cu, Zn) rod, methanol and LiClO_4.3H₂O (Aldrich) were used as supplied. The electrosynthesis were carried out using a power supply 3.5 dc volt (rectifier).

INSTRUMENTATIONS:

Metal percentage were determined by Thermo Scientific ICE 3000 series Flame Mode atomic absorption spectrophtometery. C, H, N contents were determined by standard methods of organic analysis on a Carlo-Erba 1108 microanalyzer. IR spectra were recorded on a Shimadu-8201PC spectrophotometer. Perkin Elmer diamond TG/DT instrument was used for thermal analysis.

Procedure:

Electrochemical cell consisted of a 100 ml tall form beaker in which two electrode: platinum as cathode and zinc as anode are suspended in a liquid phase containing ligand: ethylenediaminetetraacetic acid (2gm); solvent: water (30ml); and supporting electrolyte: LiClO₄.3H₂O (0.05gm dissolved in 5ml of methanol). The electrolysis was conducted at current strength of 20 mA and voltage 3.5 v for 8 hours at room temperature. As the electrolysis proceeded, gas evolved at the cathode and a white colour product is formed at the anode. This material gradually gets deposited at the bottom of the cell. At the end of the experiment it was collected by filtration, washed with acetone (5ml) and dried in a vacuo. White colour amorphous product was obtained and named as EDZN. The complex obtained in pure state was subjected to elemental, spectral and thermogravimetric analysis

The electrochemical cell can be represented as:

Zn ₍₊₎| H₂O + ethylenediaminetetraacetic acid +LiClO_4. 3H₂O + methanol | Pt _(-)

FTIR SPECTRAL ANALYSIS:

The FTIR spectrum zinc complex with ethylenediaminetetraacetic as a ligand, is given in the Graph: 1

Graph:1

The spectrum exhibit the following characteristic absorption

Table 1: IR absorption peaks. EDZN

PEAKS (cm^-1)	NATURE OF PEAKS	group assignment
3332.99	Broad	n(O-H) stretching of COOH
2900.94	Broad	n(C-H )of CH₂ group
1504.48	Sharp	n _asymCOO^-
1384.89	Sharp	n _symCOO^-
1091.71	Sharp	n C-N stretching
945.12	Medium	n C-N stretching
698.23	Sharp	-C-H wagging
628.79	Sharp	nM-O stretching
466.77	Sharp	nM-N stretching

THERMOGRAVIMETRIC ANALYSIS:

Thermogravimetric loss pattern of EDZN

Fig: 2 TGA CURVE

Fig: 3 DTA CURVE

The sequence of decomposition reactions as deduced from TGA and DTA studies in.

Graph: 2 and 3 are summarized below:

Temperature

Formulation Sequence

Experimental Loss %

Theoretical Loss %

50⁰C-100⁰C

200⁰C-450⁰C

Zn (CH₂CH₂) N₂ (CH₂COO) ₄.

- (CH₂COO)

Zn (CH₂CH₂) N₂(CH₂COO)₃

-CO₂

Zn(CH₂CH₂)N₂(CH₂)(CH₂COO)₂

16.05%

9.34%

16.65%

12.41%

DISCUSSION:

FTIR ANALYSIS:

The most interesting features in the EDZN complex spectrum are the bands at 1384 cm^-1and 1504 cm⁻¹ attributed to the symmetrical and asymmetrical vibration of COO−; the band at 1681 cm−1 corresponding to the stretching vibration of un-ionized COOH [14]. Broad band at 3520 cm^-1 corresponds to OH stretching vibration of carboxylic acid group, after deprotonation, the band somewhat move to lower energies 3332.99 cm^-1 in the complexes which probably indicate the formation of covalent bond between oxygen atom of carboxylate ion acid and metal ion[15]. Band at 628 cm-1 was attributed to nM-O. The band at 2900 cm⁻¹ attributed to ν C–H of alkyl groups (Bellamy, 1975). The Bidentate coordination of carboxylate groups of EDTA is suggested by the difference in wave number (Δν≤200 cm⁻¹) between n_asand ν_s of COO− (Deacon and Philips, 1980). This value is Δ ν=120 cm⁻¹ which confirms bidentate coordination of COO^- group in complex formation. The band due to n(C- N) in ligands were shifted to a lower wavenumbers in complexes which indicated the involvement of nitrogen atom in the Coordination to the metal center^{[16], [17] ,[18], [19]}Appearance of band at 466 cm^-1 supports to n M-N bonding.

Above spectral data analysis supports the proposed formulation shown in fig :1

Fig: 1

THERMAL ANALYSIS:

TG curves of Zn (CH₂CH₂) N₂ (CH₂COO) ₄. H₂ O in a N₂ atmosphere, show mass losses in two steps. The first step occurs in the range 50⁰c-100⁰c and it is attributed to loss of acetate group of coordinated ligand. The second steps occurs in the range 200⁰C-400⁰C with mass loss at 9.34% (theoretical 12.41 %), corresponds to decarbonylation. DTA curve, three endothermic peaks at 208⁰c, 275⁰c and 375⁰c. Observed and theoretical mass loss are found to be almost equal. The proposed formulation Fig: 1 is supported by thermogravimetric loss pattern ^{[20], [21]}

ACKNOWLEDGEMENT:

The authors are thankful to the head of the university department of chemistry, Ranchi University Professor Dr. Hari Om Pandey for providing necessary facilities and encouragement. We are grateful to acknowledge IIT Mumbai, CIF, Bit Meshra Ranchi and SAIF Tezpur University for providing the facility to carry out thermal, elemental and FTIR analysis.

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Received on 14.11.2018 Modified on 11.12.2018

Asian J. Research Chem. 2019; 12(1): 21-24.

DOI: 10.5958/0974-4150.2019.00005.1

sample	colour	C%	H%	N%	O%	M%	Empirical Formula
EDZN	white	O: 33.86%	O:3.76%	O:7.90%	O:36.12%	O:18.43%	C₁₀H₁₃N₂O₈Zn
		E:32.06%	E:3.12%	O: 7.50	E: 28.00%	O:17.02%	C₁₀H₁₃N₂O₈Zn