Novel cyclic voltammetry behavior of 3-( ( benzothiazol-2-diazenylnaphthalene-2 , 7-diol and use it for spectrophotometric determination of copper ( II ) in honey sample

The azo reagent 3-((benzothiazol-2-diazenylnaphthalene-2,7-diol] was synthesized and characterized by FT-IR , 1 H-NMR and 13 CNMR spectral techniques. The electrochemical behavior of the azo reagent and its complex with Cu (II) has been studied at glassy carbon disk GCE electrode in different supporting electrolyte at concentration (1M) and scan rate (100mv.s -1 ). Spectrophotometric determination of copper (II ) is based on the formation of a 2:1 complex with above reagent. The complex has λmax at(588) nm and Ԑmax of( 1.436x10 4) L.mol -1 .cm -1 .

In this study the FT-IR spectra of azo compound was recorded on Schimadzu FT-IR spectrophotometer model in KBr wafer and the NMR spectra was obtained on BRUKER AV 400 AvanceIII 400MHz instrument using DMSO as solvent and reported relative to TMS as internal standard , CE440CHN/O/S Elemental Analyser was made by EAI while voltammetric experimentas were carried out using a computercontrolled electroanalysis system using an( EZ-State by NuVant) system .A three-electrod compination system was an Ag /AgCl reference electrode,a Pt wire auxiliary electrode and glassy carbone electrode as working electrode, the potential range selected was in the Range(1-1.25) mV. All measurements were carried out at room temperature. 2-amino Benzothaizole(0.0066mole) 1.0000g was diazotized by dissolving it in (5ml) ethanol then (15ml) of HCl(4M) was added keeping the temperature at (0-5Cº) then adding NaNO2 solution gradually and left it about (15min) to cool well.The coupling material (2,7-dihydroxy naphthalen)(0.0066mole)(1.0650g) was dissolved in 15ml of NaOH(4M) and leave to cool well , then this solution was added to diazonium salt solution slowly drop by drop to maintain temperature (0-5Cº)The mixture was allowed precipitate was filtered off and washed several times with
Other ions (foreign) solution: All of ions were prepared by using a suitable amount of the compound in deionized water in a calibrated flask.

Results and Discussion:
Absorption Spectra: The reagent (BTHN) )nm possess a maximum absorption at 440 nm ( Fig .1) reacts with ( CuCl2.2H2O) at room temperature to give a (BTHN-Cu(II) colored complex at pH 7. . The absorption spectrum shows a maximum at 588 nm, whereas the reagent blank give no absorption at this wavelength ( Figure. The effect of various parameters on the absorption intensity of the formed products was studied and the reactions condition were optimized. The reaction of(BTHN) with Cu(II) was studied at different pH by using HCl or NaOH( 0.05N)in the range (2-10). It was found that the chelating complex was formed at pH 7. (Fig. 3) . It was found that absorbance rises with increasing reagent concentration and got its maximum value on using (1.5 ml of 1x10 -3 M ) in supsequent experiment.

Quantification:
In order to study the range in which the colored complex adhere to Beer's law the absorbance of the complex was measured at λmax for sequence of solutions containing increasing amounts of Cu(II) at optimum conditions. The validity of Beers law , molar absorptivity and Sandells sensitivity values were estimated and are given in Table .1 , showed that the method is sensitive . The proposed method showed a good linearity for the determination of Cu(II) with a good correlation coefficient (0.9588) . The relative standard devaiation %(RSD) for the analysis of six replicates of Cu(II)is equal to(0.464)showed that the method is precise and accurate, while detection limit is equal to (0.0139) . The stiochiometric ratio of (BTHN) and Cu(II) was studied applying the continuous variation(Job , s) and mole ratio methods [20,21] using equimolar solutions of the new ligand and Cu(II) (1*10 -4 ).It was found that (BTHN) forms a dye coupled product with Cu(II) in the ratio 2:1 as in (Figure.   The FT-IR spectra of the free ligand have abroad band about(3421-3176)cm -1 which could be attributed to(-OH)stretching vibration ,the shape and intensity of band were changed that led to expect coordination wasaccurein complex(Cu-BTHN), likewise the stretching frequency of (N=N) at (1561)cm -1 was shifted to a lower frequency (1531) cm -1 in complexes. The bands at frequency (1651-1593)of(C=N)also was changed as well as the band at(1305-1201) which corresponding with (C-N=N-C) and (C=N-N=C) were shifted towards lower frequency [22][23][24]. The FT-IR spectra of copper complex also shows additional bands in (495) The 1 H-NMR and 13 C-NMR spectra of the prepared azocompound was made ligand in DMSO solution with tetra methylsaline as an internal standard indications the following signals as in Table. 2 and Table .3. ( Fig.7-10    According to the results of the FT-IR, 1 H-NMR , 13 C-NMR, stoichiometric and elemental analysis the structure of complex can be suggested as the following:

Interferences
The effect of different ions in the determination of copper (II)was studied . Cu(II) can be determined in presence of 10 or more fold excess of cation and the interference via the various ions were removed by using suitable masking agent Table( Table 5, indicate that satisfactory precision and accuracy could be attained with proposed method

Electrochemical behavior of azo dye(BTHN)and redox mechanisum in aqueous solution:
The cyclic voltammogrames of investigated azo dyes shown one to three irreversible cathodic peaks [26 ,27] .The number of peaks depends on pH and nature of compounds. The peaks observed are due to the reduction of azo -N=Ncenter . The reduction mechanism includes the formation of hydrazo derivatives followed by the cleavage of the -N=Nbond and the final formation of amines [28,29] according to the following ) for all cyclic voltammogrames .All voltammogrames are shows reduction peak of azo group (-N=N-) at potential ranged (-500mv -750mv). The choice of the better supporting electrolyte depends on the higher current for oxidation peak and clarity of peak (Fig.12-14) Table .6 .

Redox behavior of(Cu-BTHN) complex
Cyclic voltammograms of copper complex was recorded in different supporting electrolyte ,the results are summarized in Table.8 (Fig . 15-18), NaH 2 PO 4 1M as supporting electrolyte was proposed the best electrolyte depending on the clarity of redox peaks (Fig . 23) .It clearly reveals that the redox process of the copper (II) complex at the scane rate (0.1Vs -1 ) involves one reduction cathodic peak (Epc=-48.6 mv) . In the anodic side the direct oxidation of complex is observed with a strong peak at( Epa= 90.2 mv) .It is observed that ∆Ep values was found equal to (138.8 mv) and the ratio of anodic to cathodic peak currents(Ipa/Ipc≠1) corresponds to more than one electron transfer process. The difference in the value of (Epc-Epa is ∆Ep) which is smaller than the value required for a reversible process ( 59 mv) indicating that , reduction of copper complex at silver electrode is irreversible

Conclusion:
This work azo employing 3-((benzothiazol-2-diazenylnaphthalene-2,7-diol(BTHN) was successfully applied for the estimation of copper(II) ion .Due to of the sensitivity ,rapidly and selectivity of the method , its application canbe estimation of this ion in biological sample. The cyclic voltammetric system of (BTHN) led to the formation of same hydrazine derivative which remains at the electrode surface according to equations :