Polarographic Study of 3-Hydroxy-3-Phenyl-1-(2,5-ichlorophenyl)Triazene

 

Krishan Kant Kodli, Pooja Joshi, R.S. Chauhan, A.K. Goswami*

Department of Chemistry Mohan Lal  Sukhadia University, Udaipur (Raj.), India

*Corresponding Author E-mail: akumargoswami@rediffmail.com

 

Electrochemical Study of 3-hydroxy-3-phenyl-1-(2,5-dichlorophenyl)triazene has been done  at D.M.E  in the Britton-Robinson Buffer solution between the pH range  3.5 – 8.0. The electrochemical reduction of the 3-Hydroxy-3-phenyl-1-(2,5-dichlorophenyl)triazene (HPDCT) is diffusion controlled in nature. Well defined polarographic waves are obtained. The reduction mechanism indicates six electron reversible reduction process.

 

 

INTRODUCTION:

Hydroxytriazenes are well known organic chelating reagents which have played an important role in inorganic analysis. These compounds are widely used in determination of various transition and non-transition metal ions due to their high sensitivity and ability to form stable complexes over a wide pH range. These compounds have a variety of applications in complexometric, spectrometric and polarographic determination of transition and non-transition metal ions^i-vi   These compounds and their complexes with various metals also showed very good biological activities ^vii-xv.

 

MATERIALS AND METHOD:

Synthesis of 3-hydroxy-3-phenyl-1-(2, 5-dichloro phenyl)  triazene:

Step (a): Preparation of phenylhydroxylamine:

In one liter beaker 0.1M of nitrobenzene, 7.5g of NH₄Cl, 100ml of water along with 50ml of rectified spirit were taken and stirred mechanically. The temperature of the reaction mixture was maintained between 50 to 60^oC. A 20g of zinc dust was added in small portions with continuous stirring and after complete addition of zinc dust, the reaction mixture was further stirred mechanically for another 15 minutes. The resulting mixture was filtered under suction and the residue was washed with ice cold water. The filtrate was taken in another beaker and kept in fridge to cool.

 

Step (b): Diazotisation of aniline:

In a 500ml beaker 2, 5-dichloro aniline 0.1M was dissolved in warm mixture of 25ml hydrochloric acid and 25ml of distilled water. After stirring vigourously this mixture was put in an ice bath to maintain temperature between 0 to 5^oC. In another beaker 6.9g of sodium nitrite was dissolved in distilled water (20ml) and it was cooled below 5^oC. Sodium nitrite solution was added to aniline solution drop by drop with continuous stirring. The diazotized product so obtained was directly used for coupling.

 

Step (c): Coupling:

The beaker containing phenyl hydroxylamine solution obtained in step (a) was placed in an ice bath to maintain temperature between 0 to 5^oC and it was stirred mechanically. The beaker containing diazonium salt obtained in step (b) was also placed in ice bath and this solution was added to phenylhydroxylamine solution drop by drop.The pH of the reaction mixture was maintained close to 6 by adding 10% sodium acetate solution. After complete addition of diazonium salt brownish yellow crude product formed was filtered under suction and washed with ice cold water. It was treated with activated charcoal and recrystallised with alcohol. The final product was obtained as light yellow needle shape crystals. Melting points of the compound was taken in open capillary and were uncorrected. C H N analysis corroborated the purity of compound. The results have been showed in Table I.

 

 

Table I.  Physical Characteristics, M.P., CHN values of the Reagent

Molecular formula	Colour and shape of the crystals	Solvent used	Elemental analysis				M.P. (°C)
				% Carbon	% Hydrogen	% Nitrogen
C12H8N3OCl2	Yellow coloured micro crystals	Ethanol	Th. Exp.	41.86 41.90	4.65 4.61	24.41 24.40	81

 

 

The compound was subjected to IR spectral analysis and following bands were observed 3480 cm^- 3570 (ν_N-H), 3070 cm^- , 3050, 3060 cm^- (ν_Ar-H), 2850 (m) cm^-_,1600 cm^- (δ_N-H), 1500-1450cm^- (ν_c=c), 1620 cm^- (ν_C-N), 1090 (vs) cm^-1260 cm^-, 1230 cm^- (δ_C-H mono-substitution). The general reaction scheme for synthesis of hydroxytriazene has been given in scheme I:

 

Electrochemical study of 3-hydroxy-3-phenyl-1-(2,5-dichlorophenyl) triazene:

HDPTDC was synthesized by using the method reported above. Weighed amount of compound was dissolved in pure ethanol to prepare a 0.01 M solution. The studies were performed with Britton-Robinson buffer which was prepared by standard method. The studies were carried out generally from pH range 3.5 to 8.5. The pH was measured by Systronics pH meter. All the experiments were performed at room temperature. The solutions were deoxygenated by purging high purity nitrogen gas for at least 15 minutes . Drop time was 1drop/1 sec. Polarograms were recorded on an automatic set of polarograph.

 

 

Scheme I

(a) Synthesis of phenyl hydroxylamine

 

(b) Diazotisation

 

(c) Coupling

 

RESULTS AND DICSUSSION:

The polarographic reduction of 1x10^-4M solution was studied at 3.5 to 8.5 pH range in Britton Robinson buffer solution used as supporting electrolyte. At each pH, a well defined single wave appeared.  A  plot has been drawn between i_d vs.  (Figure I).  This plot showed a straight line which verified  the diffusion controlled nature of each wave.

 

Figure I

 

The data have been given in Table II .Gelatin solution was used as maxima suppressor. However, below pH 3.5 and above pH 8.5, the waves were not found to be well defined.

 

Table-II Effect of varying height of mercury column

 

It is evident from the table III, that i_d first increases with increasing pH 7, where it attains a maximum value. A further increase in pH decreases the i_d and it goes on gradual decrease, reaching small value at high pH viz., pH 8.5.

 

E_1/2 on the other hand gradually increases with increasing pH towards a more negative side. It may be observed from Table III that at higher pH values, the E_1/2  attains maximum values, but within this pH range (8.0 to 9.5) the change in E_1/2  is relatively very small.

 

Table– III-Dependence of diffusion current over pH of HDPTDC (1x10^-4M) in B.R. buffer at room temperature

S. No.	pH	id (μA)	(-V vs. SCE)
1.	3.5	1.10	0.980
2.	4.0	2.05	1.020
3.	4.5	2.97	1.030
4.	5.0	2.99	1.040
5.	5.5	3.01	1.050
6.	6.0	3.05	1.060
7.	6.5	3.05	1.070
8.	7.0	3.10	1.075
9.	7.5	3.0	1.078
10.	8.0	2.98	1.080
11.	8.5	2.96	1.081

 

The above observation may be understood with the help of, effect of protonation on the depolarizer. It appears that in acidic medium, the E_1/2 has lower negative values than in alkaline medium which indicates that, in the acidic pH region, the protonation of the depolarizer is to a larger extent than in higher value which, makes the depolarizer reduce at lower negative potential; as in this pH region the depolarizer shall be overall electrophilic in nature.

 

The shape of wave and the slope analysis indicates a six electrons irreversible process. The compound HDPTDC was reduced to phenyl hydrazine and aniline, through 6 electron reduction mechanism. Further, on the basis of product analysis using TLC, it is supported since a single spot for aniline which is the end product, is obtained. The final product was also tested qualitatively for amino group which proves the proposed mechanism.

 

Since all steps involved in above reaction mechanism take place at the same potential, there occurs a single reduction peak corresponding to transfer of 6 electrons (scheme II) ^xvi.

 

Scheme II: Proposed  scheme for reduction  of HDPTDC at D.M.E

 

 

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Received on 19.07.2013          Modified on 02.08.2013

Accepted on 23.08.2013          © AJRC All right reserved