The performance of mono-chloro-substituted m-dinitrobenzene compounds in magnesium battery is reported here. While the

operating voltage is improved, the current efficiency is lowered by the chloro-substituents. The influence is explained taking

into account inductive and mesomeric effects of the substituent

Dakshinamurthy, K.

Rajeswari, S.

Sivasamy, K.

IR@CECRI

B. Electrochem 4(4) April 1988, pp 347-350 MONO-CHLORO-SUBSTITUTED m-DINITROBENZENE COMPOUNDS AS CATHODE MATERIALS IN MAGNESIUM BATTERY K SIVASAMY, S RAJESWARI Department of Analytical Chemistry, University of Madras, Madras 600 025, INDIA and K DAKSHINAMUR THr CECRI Unit, CSIR Complex, Taramani, Madras-600 113, INDIA peceived: 1987 November; Accepted: 1988 January] The performance of mono-chloro-substituted m-dinitrobenzene compounds in magnesium battery is reported here. While the operating voltage is improved, the current efficiency is lowered by the chloro-substituents. The influence is explained taking into account inductive and mesomeric effects of the substituents. Key words: Magnesium battery. chloro-substituted m-dinitrobenzene compounds, cathode material, watt hour per gram INTRODUCTION A monk the organic compounds m-di'nitrobenzene (m-DNB) has long been considered as possible cathode material for primary magnesium batteries [I-43. The influence of substituted groups in m-DNB was studied [l-21 and showed that electron withdrawing groups increase the operating potential of m-DNB and electron donating substituents decrease the operating potential. However the influence of substituents of m-DNB at different possible posi- tions have not been studied. There is also no detailed account of coulombic efficiency, when such groups are attached to the ring, at different current densities and at different temperatures. The present study involves the effect of mono-chloro-substitution on m-DNB at the three possible positions. Chloro-2,4-dinitrobenzene has been investigated [g to some extent. The following compounds are studied (i) m-Dinitrobenzene (m-DNB) (ii) 1-Chloro 2,4-dinitrobenzene (CI-2,4 DNB) (iii) I-Chloro 2,6-dinitrobenzene (CI-2,6 DNB) (iv) 1Chloro 3.5-dinitrobenzene (Cl-3,5 DNB) EXPERIMENTAL Fabrication of cell and discharge study Magnesium alloy AZ3 1 of area 3 x 3 cm is used as anode. Circular type cathode of area 6.3 cm2 has been used. The cathodes are prepared by pressing the cathode mix containing m-DNB or Chloro- ubstituted m-DNB (0.4 gm), acetylene black for conductance (0.2 3m), barium chromate for inhibition of magnesium corrosion :0.012 gm) and 3% carboxy methyl cellulose as binder (0.25 ml) In a 20 mesh copper grid at an optimised pressure. The cathode s closely packed between two anodes interposed by polyester cloth ieparator. Magnesium perchlorate (2 M) is used as electrolyte. The cells are discharged at different current densities (0.8 to 8 nA cm-2) through a constant current discharge unit at 303K, 293K md 273K. Polarographic study Stock solution and supporting electrolyte Saturated solutions (4 10-3 M) of these compounds are prepared in water and magnesium perchlorate (10-1 M) as supporting elec- trolyte, the pH being 7 & 0.2. Polarograms are run by using Tacussel electronic polaroprocessor. RESULTS AND DISCUSSION Cell voltage Room temperature studies (303K) Fig ( 1 )  shows the discharge curves of these four compounds at 0.8mA cm-2 current density. Here almost all the compounds show Fig. I: Discharge curves at 0.8mA.cm-2 current density at 3X3K twin discharge plateau. The chloro-substituted compounds show higher mean operating potential than m-DNB and the order of the operating potential is C1-2,4 DNB )CI-2.6 DNB > C1-3,5 DNB > Sivasamy eta1 - Mono-chloro-substituted m-dinitrobenzene compounds as cathode materials in magnesium battery m-DNB. When current density increases the operating voltage of these compounds are slightly lowered as seen from Figs. (2) and (3). TABLE-II: Half wave potentials of m-DNB and chlora substituted m-DNB compounds 0 2 4 6 8 DISCHAROE TIME (Hours I Fig.2: Discharge curves at 8mA.cm-2 current density at 303K 0.8 2.4 4.8 8-0 CURRENT DENSITY ( m ~ / c m '  I ? 0.8- 3 : Fig.3: Current density vs operating voltage curves at 303K 0 C 1 - 2 , S r n I  9 C I -  3.5WeI [t is also seen that there is a single discharge plateau at higher drain rates. From Fig (3), the internal resistance values computed in- dicated slightly higher value for the C1-2,6 DNB (vide Table I). 0.7- 1 I I TABLE-I: lnternal resistance values of m-DNB and chloro- substituted m-DNB compounds Compound Internal resistance of cell (-n-) n-DNB 21-2,4 DNB 3-2.6 DNB 31-3.5 DNB rhis reduces its operating potential. Polarographic studies also con- irm the two-stage reduction observed at low current drain (nble 11). Compounds E l l 2  values (V) I Wave I1 Wave m-DNB -0.460 -0.597 CI-2.4 DNB -0.379 -0.325 CI-2,6 DNB -0.41 3 -0.502 CI-3.5 DNB -0.437 -0.516 The E l l z  values of these chloro-substituted compounds are more positive than m-DNB. This explains the higher operating voltage of these compounds. The nitro groups are reduced polamgraphically at more positive potential in the following order C1-2,4 DNB) C1-2.6 DNB > C1-3,s DNB > m-DNB as seen in the first wave. The order is different for the second wave. In the performances of the cell, the same behaviour is observed. Low temperature studies Figs.(4) and (5) show the discharge curves of these compounds at 8 mA crn-2 current density at 293K and 273K. At lower temperatures, 0 0 2 4 6 DISCHARGE ' TIYE (Hoar* ) Fig.4: Discharge curves at 8mA.cm-2 current density at 303K when the cells are discharged at different current densities, the operating voltages of these compounds are lowered considerably. AMPERE HOUR AND WATT HOUR EFFICIENCY Ampere hour and watt hour per gram efficiency Room temperature studies Tables 111 and IV illustrate ampere hour per gram and watt hour per gram of these compounds at 303K. 348 B. Electrochem 4(4) Apr 1988 Sivasamy eta1 - Mono-chloro-substituted m-dinitrobenzene compounds as cathode materials in magnesium battery 7g.5: Discharge curves at 8mA.cms current density at 273K TABLE-Ill: Ampere hour per gram at different current densities It 303K - Ampere hour per gram Compounds 0.8 mA. 2.4 mA. 4.8 mA. 8 mA. cm-2 cm-2 cm-2 cm-2 m-DNB 1.12 (0.9) 0.96 (0.9) 0.94 (0.85) 0.83 (0.8) Cl-2.4 DNB 0.83 (0.9) 0.59 (0.9) 0.53 (0.85) 0.49 (0.85) Cl-2,6 DNB 1.00 (0.9) 0.93 (0.9) 0.73 (0.85) 0.69 (0.8) Cl-3,s DNB 1.03 (0.9) 0.85 (0.9) ... 0.54 (0.8) Parenthesis shows cut off voltage of the cell TABLE-IV: Wan hour per gram at different current densities at 303K Compounds Watt hour per gram 0.8 mA. 2.4 mA. 4.8mA. 8 mA. cm-= cm-2 cm-2 cm-2 n - D N B  1.1 0.93 0.89 0.75 3-2,4 DNB 0.87 0.63 0.55 0.49 3-2,6 DNB 1.04 0.93 0.71 0.65 31-3,s DNB 1.06 0.86 ... 0.52 Even though chloro-substituted compounds have higher )prating potential than m-DNB, the coulombic performance is ower than m-DNB. The order of ampere hour efficiency is as ollows: m-DNB > C1-2.6 DNB > CI-3,5 DNB > C1-2,4 DNB The C1-3,5 DNB is better than C1-2,6 DNB at lower current density only. There is no improvement in watt hour output per gram for the chloro- substituted compound as the ampere hour efficiency is low compared to m-DNB. The order of watt hour out- put is m-DNB >C1-2.6 DNB > CI-3.5 DNB > C1-2'4 DNB, same as above. Low temperature studies Tables V and VI illustrate the ampere hour per gram and watt hour per gram at 303K. 273K temperatures. When temperature is lowered TABLE-V: Ampere hour per gram at 293K and 273K at different current densities Ampere hour per gram Compound 293K temperature 273K temperature m-DNB 0.73 (0.8) 0.63 (0.75) 0.30 (0.75) 0.15 (0.6) C1-2,4DNB 0.46(0.8) 0.38(0.8) 0.42(0.8) 0.24(0.7) Cl-2.6 DNB 0.65 (0.85) 0.41 (0.75) 0.29 (0.7) 0.13 (0.7) CI-3.5 DNB 0.38 (0.8) 0.17 (0.75) 0.21 (0.7) 0.08 (0.7) Paranthesis shows cut off voltage of the cell TABLE-VI: Watt hour per gram efficiency at different current den- sities at  292K and 273K temperatures Watt hour per gram Compound 293K temperature 273K temperature m-DNB 0.66 0.54 0.26 0.13 C1-2,4 DNB 0.45 0.36 0.39 0.20 CI-2.6 DNB 0.64 0.36 0.25 0.10 C1-3.5 DNB 0.36 0.16 0.18 0.07 there is a marked improvement in the performance of CI-2,4 DNB. At 273K it is better than even m-DNB. The general mechanism for electro-reduction in aromatic nitro group is given in Fig. (6). Increased availability of electrons at the -C-NO2 (carbon atom carrying the nitro group) assists the initial protonation step thereby improving the overall current density. In the case of chloro- substituted m-DNB, increased electron availability at the -C-NO2 is possible only in the case of CI-2,4 DNB due to - I  (by the theory of alternating polarity [6] and + T effect. This in effect means that the current efficiency should be greater for these compounds than B. Electrochem 4(4) Apr 1988 349 Sivasamy eta1 - Mono-chloro-substituted m-dinitrobenzene compounds as cathode materials in magnesium battery m-DNB. However it is seen that it is lower than m-DNB. The high activity of the -C-NO2 position is responsible for the alteration in electron availability probably renders the compounds active, current efficiency is borne by the fact that at lower temperatures, thereby facilitating side reaction. This has in fact been observed there is a change in the trend. At 273K Cl-2,4 DNB shows the best in the case o f  chloro-substituted compounds. The condensation performance and is better than m-DNB. Due to lowering of  temperature, moderation in the activity of the -C-NO2 position reduces the side reaction (nitroso hydroxylamine condensation) thereby improving ampere hour per gram efficiency. CONCLUSION 1. The operating voltage is increased by chloro substituents in m- DNB in all three positions. 2. There are two stages in electro-reduction of the compounds + especially at low current drain. 3. There are two competing reactions viz. electro-reduction of - 2,,; 26 NO2 group and chemical condensation of -NO and -NHOH to azoxy compound. Because of this, the current efficiency of the * 2  mono-chloro-substituted m-DNB is reduced especially for or- tho/para and dual ortho substituents. 4. -1 and + T effect of the substituents reinforce to affect the course of the reaction. NHOH NHOH NH, 0 4 H ' . 4 %  0 4 # , 4 5  0 ' 4 ' NHOH NH2 Fig.6: Mechanism of electrochemical reaction of m-DNB Acknowledgement: The authors are thankful t o  Prof. K 1 Vasu, Director, CECRl Karaikudi and Dr. N V Parthasaradhy, Scientist- in-charge, CECRl Madras for their help in carrying out the work. K S is thankful t o  UGC for the S.R.Fellowship and Prof. Agnes Paul, Head of the Department of Analytical Chemistry, Universi- ty of Madras, for all the facilities extended towards the conduct of the work. between nitroso-and hydroxylamine is sufficiently rapid to permit the formation of considerable quantities of azoxy compounds. Thus there is a competition between electro-reduction of nitroso in- termediate and its chemical condensation with already formed hydroxylamine derivative to form azoxy compound. This in ef- fect reduces the current efficiency of Cl-2,6 DNB and Clc2,4 DNB. In the case of chloro-2,4 DNB,.the chloro group is ortho to one nitro group and para to other nitro group. The presence of p-nitro group influences the formation of azoxy compounds more readi- ly. This effect was observed in p-chloro nitrobenzene [7] when p- chloro nitrobenzene undergoes reduction; the speed of the con- densation between p-chloro nitrosobenzene and p-chloro phenyl hydroxylamine even in acid solution is sufficiently rapid to permit the formation of considerable quantity of p-chloro azoxy benzene. This explains the lower efficiency observed for the ortho/para jubstituent. In the case of CI-3,5 DNB, both -I and + T  effect render the -C-NO2 position more electron deficient comparative- ly than the ortho/para or dual ortho (Cl-2.6 DNB) substituents. This decreases the tendency for azoxy compound formation and improves the efficiency compared to 1-CI-2,4 DNB. It is to  be noted :hat the efficiency is still lower than that of m-DNB due to elec- tron deficiency at  -C-NO2 position. That the variation in the REFERENCES 1. R Glicksman and C K Morehouse, J Electrochem Soc, 105 (1958) 299 2. C K Morehouse and R Glicksman, JElectrochem Soc. 105 (1958) 306 3. H Comyn Raymond, Nelson Jaffrey Tollin and F McMillen Donald, Steuernagel, Werner H,  Proc Annu Power Sources Conf. 23 (1969) 153; CA 72 (1970) 8727 z 4. D P Bhatt, N Muniyandi and P B Mathur, Trans SAEST, 22 (1987) 13 5. Berardelli, L Maria, Pecci, Gianfran Co., Polcaro, Anna M Ric Sci. 39 (7-9) (1969) 735 6. I L Finar, Ed, Organic Chemktry, Vol. 1, 3rd Edition, Longman Group Ltd., London, (1957) p 490 7. C J Brockman, Ed, Electro-organic chemistry, John Wiley and Sons (1926) p 214 / 360 B. Electrochem 4(4) April 1988 

Mono-chloro-substituted m-dinitrobenzene compound as cathode materials magnesium battery

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