The electrochemical reduction of several 2,5- and 5,6- dihalonicotinic acids have been studied in dimethyl sulfoxide as well as in aqueous buffers of different pH. The polarographic half-wave potentials for the reduction of these compounds in both media are reported here. The compounds appear to reduce at the carboxyl group. The presence of halogen atoms on the pyridine ring facilitates reduction

Battles, Lourie A.

Dixon, Tappi A.

Setliff, Frank L.

Shaikh, Ali U.

English

ScholarWorks@UARK

Journal of the Arkansas Academy of ScienceVolume 40 Article 201986Electrochemistry of Dihalogenated NicotonicAcids in Aqueous and Aprotic MediaAli U. ShaikhUniversity of Arkansas at Little RockTappi A. DixonUniversity of Arkansas at Little RockLourie A. BattlesUniversity of Arkansas at Little RockFrank L. SetliffUniversity of Arkansas at Little RockFollow this and additional works at: http://scholarworks.uark.edu/jaasPart of the Physical Chemistry CommonsThis article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able toread, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking priorpermission from the publisher or the author.This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academyof Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu, ccmiddle@uark.edu.Recommended CitationShaikh, Ali U.; Dixon, Tappi A.; Battles, Lourie A.; and Setliff, Frank L. (1986) "Electrochemistry of Dihalogenated Nicotonic Acids inAqueous and Aprotic Media," Journal of the Arkansas Academy of Science: Vol. 40 , Article 20.Available at: http://scholarworks.uark.edu/jaas/vol40/iss1/20ELECTROCHEMISTRY OF DIHALOGENATEDNICOTINIC ACIDS IN AQUEOUSAND APROTIC MEDIAALIU. SHAIKH, TAPPI A. DIXON, LOURIE A. BATTLESand FRANK L. SETLIFFDepartment of ChemistryUniversity of Arkansas at Little RockLittleRock, AR 72204ABSTRACTThe electrochemical reduction ofseveral 2,5- and 5,6- dihalonicotinic acids have been studied in dimethylsulfoxide as well as in aqueous buffers of different pH. The polarographic half-wave potentials for thereduction of these compounds in both media are reported here. The compounds appear to reduce atthe carboxyl group. The presence of halogen atoms on the pyridine ring facilitates reduction.INTRODUCTIONIfhesynthesis and spectroscopic (IR and NMR) characterization oferal 2,5- and 5,6- dihalonicotinic acids have been reported earliertliff, 1970, 1972, 1973, 1976 and 1978). Because of the chemicallilarity with vitamin B(niacin), these compounds are of importantlogical significance. Since biological activities ofchemical agents areerally believed to occur via oxidation-reduction mechanism, it isjntialthat the redox properties of these compounds be determined>rder to understand the molecular basis ofsuch activities. No electro-mical studies ofnicotinic acid and its halogen derivatives have yetn reported. We have therefore undertaken the task of determiningpolarographic half-wave potentials for the reduction of these com-mds in both protic and aprotic media. In this report, the results ob-led in dimethyl sulfoxide and in aqueous buffers are presented.EXPERIMENTALIgents: Dimethyl sulfoxide(DMSO) and tetrabutylammonium:hlorate (TBAP) were of analytical grade (Fisher Chemicals) and;used without further purification. Aqueous buffers of various pH:prepared (Carmody, 1961) fromanalytical grade boric acid, citric!and trisodium phosphate (Fisher Chemicals). The aqueous reac-media were 0.1M buffer solutions, whereas the aprotic mediuma solution of 0.1M TBAP in DMSO, which was dehydrated (com-cial TBAP and DMSO contain water) prior to use by passing overc alumnia (Woelm).IparaUis: The half-wave potentials were determined by Differen-Pulse Polarography using a three-electrode polarographic analyzerodel PAR 174A; Princeton Applied Research Corporation,nceton, NJ). The cathode, the counter-electrode and the referencectrode were dropping mercury electrode (DME),platinum foilandurated calomel electrode (SCE) respectively. In aprotic medium,,vever, a low-porosity calomel, filled with 0.40M tetraethylammoniumoride to adjust voltage to 0.00 volt vs. SCE, was used as referenceminimize water-leakage into the medium. The polarograms wereorded on an X-Y recorder (Model 2200 Omnigraphic; Houston In-jments, Austin, TX).The mercury drop-rate of the DME was con-lied by a mechanical drop-timer (Princeton Applied Research Cor-ation). The temperature ofthe reaction medium was maintained atP:edure: Twenty ml of the solution was poured into the reaction;1, purged withultra-high purity argon for thirty minutes to remove)lved oxygen and a differential pulse polarogram of the mediumkground) was taken using the followingconditions: Initial Poten-= 0.00 volt vs. SCE, Potential Scan Rate = 5 mV/sec, PulseAmplitude = 25m V and Drop Time ¦ 1.0 sec. During potential scanin the negative direction (reduction), the solution was quiescent andthe argon flow was diverted above the solution to keep atmosphericoxygen and moisture away. To the solution, about fivemg of a par-ticular compound was then added, stirred to dissolve completely, andthe polarogram was taken under the same condition as above. The pro-cedure was repeated for other compounds.RESULTS ANDDISCUSSIONThe technique ofDifferential Pulse Polarography (DPP) is superiorto that of Direct Current Polarography (DCP) for the determinationof half-wave potentials due to improvement of signal to noise ratio asa result of discrimination against capacitative current (Bond, 1984).Moreover, polarograms obtained by DPP show Gaussian peaks dueto charge-transfer process, compared to sigmoidal curves in DCP, andcan be evaluated more precisely. In DPP, the half-wave potential(E1/2), which is characteristic of a particular electroactive compoundand is a measure of its ability to be either oxidized or reduced, can berelated to the peak potential (Ep) of the polarogram by the equation:E1/2 = Ep ± AE/2where AE =pulse amplitude and'+'and'-'signs refer to reductionand oxidation processes respectively.Figure 1 shows typical polarograms obtained by DPP in DMSO fornicotinic acid and two of its dihalogenated derivatives, namely,5-chloro-6-iodo- and 6-chloro-5-iodo- nicotinic acids. Each polarogramdisplays two distinct peaks, indicating that the compounds are undergo-ing reduction in two steps. A previous report (Lund, 1983) showed thatin acetonitrile, an aprotic medium, the electrochemical reduction ofpyridine ring is very difficult.The two peaks, therefore, can be attributedto reduction of the carboxyl group.The half-wave potentials obtained for a number of dihalonicotinacids in both protic and aprotic media are shown in Table 1. Whieach compound showed two peaks in DMSO, additional peaks weobserved in aqueous media, especially at a lower pH. This may indicathat in aqueous media either the protonated nitrogen of the pyridiring or halogen atoms on the ring are also reduced. The presencehalogen atoms on the ring also have profound effect on the half-wapotential for the reduction of carboxyl group (see Figure 1 and Tab1). Both in aqueous and aprotic media, the first E, /2 is shifted tomore positive value, as compared to that of the unsubstituted nicotinacid, indicating that halogen atoms facilitate reduction. This positishift of E1/2 can be explained in terms ofcounter-balancing inductieffect (-1) and resonance effect (+R) of aryl halogen substituen(Gould, 1959). Because of this opposing action, the net electrowithdrawing capacity of halogens is in the order: I> Br > Cl >Proceedings Arkansas Academy of Science, Vol.XXXX,1986 59Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 20Published by Arkansas Academy of Science, 1986Electrochemistry off Dihalogenated Nicotinic Acids in Aqueous and Aprotic MediaTable 1.Half-Wave Potentials forReduction of Some DihalonicotinicAcids in DMSO and in Aqueous BuffersCompound *E1/2 In DMSO EJ/2 In Water (Volt vs. SCE!(Nicotinic Add) (Volt vs. SCE) pH 2.0 pH 4.0 pH 6.0Unsubstituted -1.92 '-1.05 -1.05-1.05-2.36 -1.14 -1.13-1.225-chloro-6-1odo- -1.38 -0.32 -0.44 -0.61-2.51 -0.86 -1.21 -1.37-1.09 N.D. N.D.6-ch1oro-5-iodo- -1.14 -0.69 -0.80 -1.01-2.62 -1.07 -0.90 -1.09-1.16 -1.24 N.D.2-chloro-5-1odo- -1.57 -0.83 -1.11-1.33-2.43 -1.12 -1.37 -1.452-bromo-5-1odo- -1.35 -0.75 -0.93 -1.26-2.43 -1.08 -1.25 -1.61-1.15 N.D. N.D.5-bromo-6-1odo- -1.34 -0.31 -0.43 -0.57-2.47 -0.85 -0.99 -1.38-1.09 -1.19 N.D.6-bromo-5-1odo- -1.09 -0.59 -0.72 -0.92-2.53 -0.66 -1.23 -1.14-1.13 N.D. N.D.5,6-dibromo--1.50 -0.60 -0.73 -1.03-2.47 -0.85 -0.99 -1.38-1.09 -1.19 N.D.2,5-d1brotno- -1.49 -0.81 -1.01 -1.36-2.49 -0.93 -1.23 N.D.-1.13 N.D. N.D.2,5-dichloro--1.59 -0.94 -1.29 -1.42-2.44 -1.11 -1.51 N.D.5,6-d1chloro--1.57 -0.68 -0.86 -1.13-2.41 -0.85 -1.10 -1.23-1.11 -1.23 -1.35* Half -wave potentials are given in each column in sequence of First E. ,?,Second E1/2 etc.'N.D.= The peak corresponding to the half-wave potential is in existence butis not clearly detectable.E1/2 was generally observed (see Table 1), indicating greater difficultyof further reduction of the compounds. The reason for such a shift isnot clearly understood, although it appears that solvent (DMSO)molecules may play an important role.Figure 2 shows typical cyclic voltammograms obtained forhalogenated nicotinic acids in DMSO at various potential scan rates.The initialreduction of the compound is followed by a rapid chemicalreaction (EC mechanism) of the product with solvent molecules. Asa result, the product cannot be reoxidized back to the original com-pound during reverse scan. Similar behavior was also observed inaqueous media.From Table 1, it is also obvious that the pH ofthe aqueous mediahas a profound effect on the relative ease of reduction of the carboxylgroup. Atlower pH, the half-wave potential shifts to the positive direc-tion, showing the protons are involved in the reduction process. Similarproton-mediated reduction ofisonicotinic acid has been reported earlier(Lund, 1963). Indry DMSO, however, the absence ofprotons dictatesthat the mechanism ofreduction may be totally different from that inaqueous medium and most likely the reduction proceeds through a free-radical mechanism. The reaction products in two solvents may thereforebe quite different. Caulometric analysis of the reduction processes inboth media, followed by isolation and gas-chromatographic identifica-tion of the products, are now in progress in our laboratory to fullyunderstand the mechanism of reduction of these biologically impor-tant compounds.Figure 1. Differential Pulse Polarograms of nicotinic acid and itsdihalogenated derivatives in 0.10M TBAP/DMSO. Conditions: scanrate = 5mV/sec, pulse amplitude = 25 mV, drop time = 1.0 sec. Thebottom curve (flat) represents the background.Igure 2. Cyclic Voltammograms of 5-Chloro-6-iodo- nicotinic acid in10M TBAP/DMSO at potential scan rates of10, 20, 50, 100 and 200Vsec. The peak height increases with scan rate,nd Br at 5- and 6-positions ofthe pyridine ring therefore favor reduc-tn of the carboxyl group. InDMSO, a negative shift of the second60 Proceedings Arkansas Academy of Science, Vol. XXXX,1986 60Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 20http://scholarworks.uark.edu/jaas/vol40/iss1/20Proceedings Arkansas Academy of Science, Vol. XXXX,1986 61AM U. Shaikh, Tappi A.Dixon, Lourie A. Battles, and Frank L.SetliffACKNOWLEDGEMENTThe financial support from an Institutional FacultyResearch Grant and the Office ofResearch in Science andTechnology at the University ofArkansas at Little Rockis gratefully acknowledged.LITERATURE CITEDBOND, A. M. 1984. InPolarographic Methods of Analysis. Marcel-Dekkar, New York.CARMODY, W. R. 1961. An Easily Prepared Wide Range BufferSeries. J. Chem. Ed. 38:559-560.GOULD, E. S. 1959. InMechanism and Structure in Organic Chemistry.Holt, Reinhart and Winston, NY. p 219.LUND, H. 1963. Electroorganic Preparations XI. Reduction ofIsonicotinic Acids in Acid Solution. Acta Chem. Scand. 17:972-978.LUND, H. 1983. In Organic Electrochemistry, Baizer, M. M. andLund, H. Eds., Marcel-Dekkar, NY. p 553.SETLIFF, F. L. 1970. Some 2,5- and 5,6- Dihalonicotinic Acids andTheir Precursors. J. Chem. Eng. Data 15:590-591.SETLIFF, F L. 1972. Some 2,5- and 5,6- Dihalonicotinic Acids andTheir Precursors. II.J. Chem. Eng. Data 17:515-516.SETLIFF, F. L. 1973. Some 2,5- and 5,6- Dihalonicotinic Acidsand Their Precursors. III.J. Chem. Eng. Data 18:449-450.SETLIFF, F. L.1976. Some 2,5- and 5,6- Dihalonicotinic Acids andTheir Precursors. IV. J. Chem. Eng. Data 21:246-247.SETLIFF, F. L. 1978. Some 2,5- and 5,6- Dihalonicotinic Acids andTheir Precursors. 5. J. Chem. Eng. Data 23:96-97.61Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 20Published by Arkansas Academy of Science, 1986

Electrochemistry of Dihalogenated Nicotonic Acids in Aqueous and Aprotic Media

UARK (University of Arkansas )

Journal of the Arkansas Academy of Science Volume 40 Article 20 1986 Electrochemistry of Dihalogenated Nicotonic Acids in Aqueous and Aprotic Media Ali U. Shaikh University of Arkansas at Little Rock Tappi A. Dixon University of Arkansas at Little Rock Lourie A. Battles University of Arkansas at Little Rock Frank L. Setliff University of Arkansas at Little Rock Follow this and additional works at: https://scholarworks.uark.edu/jaas  Part of the Physical Chemistry Commons Recommended Citation Shaikh, Ali U.; Dixon, Tappi A.; Battles, Lourie A.; and Setliff, Frank L. (1986) "Electrochemistry of Dihalogenated Nicotonic Acids in Aqueous and Aprotic Media," Journal of the Arkansas Academy of Science: Vol. 40 , Article 20. Available at: https://scholarworks.uark.edu/jaas/vol40/iss1/20 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu. ELECTROCHEMISTRY OF DIHALOGENATEDNICOTINIC ACIDS IN AQUEOUSAND APROTIC MEDIAALIU. SHAIKH, TAPPI A. DIXON, LOURIE A. BATTLESand FRANK L. SETLIFFDepartment of ChemistryUniversity of Arkansas at Little RockLittleRock, AR 72204ABSTRACTThe electrochemical reduction ofseveral 2,5- and 5,6- dihalonicotinic acids have been studied in dimethylsulfoxide as well as in aqueous buffers of different pH. The polarographic half-wave potentials for thereduction of these compounds in both media are reported here. The compounds appear to reduce atthe carboxyl group. The presence of halogen atoms on the pyridine ring facilitates reduction.INTRODUCTIONIfhesynthesis and spectroscopic (IR and NMR) characterization oferal 2,5- and 5,6- dihalonicotinic acids have been reported earliertliff, 1970, 1972, 1973, 1976 and 1978). Because of the chemicallilarity with vitamin B(niacin), these compounds are of importantlogical significance. Since biological activities ofchemical agents areerally believed to occur via oxidation-reduction mechanism, it isjntialthat the redox properties of these compounds be determined>rder to understand the molecular basis ofsuch activities. No electro-mical studies ofnicotinic acid and its halogen derivatives have yetn reported. We have therefore undertaken the task of determiningpolarographic half-wave potentials for the reduction of these com-mds in both protic and aprotic media. In this report, the results ob-led in dimethyl sulfoxide and in aqueous buffers are presented.EXPERIMENTALIgents: Dimethyl sulfoxide (DMSO) and tetrabutylammonium:hlorate (TBAP) were of analytical grade (Fisher Chemicals) and;used without further purification. Aqueous buffers of various pH:prepared (Carmody, 1961) fromanalytical grade boric acid, citric!and trisodium phosphate (Fisher Chemicals). The aqueous reac-media were 0.1M buffer solutions, whereas the aprotic mediuma solution of 0.1M TBAP in DMSO, which was dehydrated (com-cial TBAP and DMSO contain water) prior to use by passing overc alumnia (Woelm).IparaUis:The half-wave potentials were determined by Differen-Pulse Polarography using a three-electrode polarographic analyzerodel PAR 174A; Princeton Applied Research Corporation,nceton, NJ). The cathode, the counter-electrode and the referencectrode were dropping mercury electrode (DME),platinum foilandurated calomel electrode (SCE) respectively. In aprotic medium,,vever, a low-porosity calomel, filled with 0.40M tetraethylammoniumoride to adjust voltage to 0.00 volt vs. SCE, was used as referenceminimize water-leakage into the medium. The polarograms wereorded on an X-Y recorder (Model 2200 Omnigraphic; Houston In-jments, Austin, TX).The mercury drop-rate of the DME was con-lied by a mechanical drop-timer (Princeton Applied Research Cor-ation). The temperature ofthe reaction medium was maintained atP:edure:Twenty ml of the solution was poured into the reaction;1, purged withultra-high purity argon for thirty minutes to remove)lved oxygen and a differential pulse polarogram of the mediumkground) was taken using the followingconditions: Initial Poten-= 0.00 volt vs. SCE, Potential Scan Rate = 5 mV/sec, PulseAmplitude = 25m V and Drop Time ¦ 1.0 sec. During potential scanin the negative direction (reduction), the solution was quiescent andthe argon flow was diverted above the solution to keep atmosphericoxygen and moisture away. To the solution, about fivemg of a par-ticular compound was then added, stirred to dissolve completely, andthe polarogram was taken under the same condition as above. The pro-cedure was repeated for other compounds.RESULTS ANDDISCUSSIONThe technique ofDifferential Pulse Polarography (DPP) is superiorto that of Direct Current Polarography (DCP) for the determinationof half-wave potentials due to improvement of signal to noise ratio asa result of discrimination against capacitative current (Bond, 1984).Moreover, polarograms obtained by DPP show Gaussian peaks dueto charge-transfer process, compared to sigmoidal curves in DCP, andcan be evaluated more precisely. In DPP, the half-wave potential(E1/2), which is characteristic of a particular electroactive compoundand is a measure of its ability to be either oxidized or reduced, can berelated to the peak potential (Ep) of the polarogram by the equation:E1/2= Ep ± AE/2where AE =pulse amplitude and'+'and '-' signs refer to reductionand oxidation processes respectively.Figure 1 shows typical polarograms obtained by DPP in DMSO fornicotinic acid and two of its dihalogenated derivatives, namely,5-chloro-6-iodo- and 6-chloro-5-iodo- nicotinic acids. Each polarogramdisplays two distinct peaks, indicating that the compounds are undergo-ing reduction in two steps. A previous report (Lund, 1983) showed thatin acetonitrile, an aprotic medium, the electrochemical reduction ofpyridine ring is very difficult.The two peaks, therefore, can be attributedto reduction of the carboxyl group.The half-wave potentials obtained for a number of dihalonicotinacids in both protic and aprotic media are shown in Table 1. Whieach compound showed two peaks in DMSO, additional peaks weobserved in aqueous media, especially at a lower pH. This may indicathat in aqueous media either the protonated nitrogen of the pyridiring or halogen atoms on the ring are also reduced. The presencehalogen atoms on the ring also have profound effect on the half-wapotential for the reduction of carboxyl group (see Figure 1 and Tab1). Both in aqueous and aprotic media, the first E, /2 is shifted tomore positive value, as compared to that of the unsubstituted nicotinacid, indicating that halogen atoms facilitate reduction. This positishift of E1/2 can be explained in terms ofcounter-balancing inductieffect (-1) and resonance effect (+R) of aryl halogen substituen(Gould, 1959). Because of this opposing action, the net electrowithdrawing capacity of halogens is in the order: I> Br > Cl >Proceedings Arkansas Academy of Science, Vol.XXXX,1986 59Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 20Published by Arkansas Academy of Science, 1986Electrochemistry off Dihalogenated Nicotinic Acids in Aqueous and Aprotic MediaTable 1.Half-Wave Potentials forReduction of Some DihalonicotinicAcids in DMSO and in Aqueous BuffersCompound *E1/2 In DMSO EJ/2 In Water (Volt vs. SCE!(Nicotinic Add) (Volt vs. SCE) pH 2.0 pH 4.0 pH 6.0Unsubstituted -1.92 '-1.05 -1.05 -1.05-2.36 -1.14 -1.13 -1.225-chloro-6-1odo- -1.38 -0.32 -0.44 -0.61-2.51 -0.86 -1.21 -1.37-1.09 N.D. N.D.6-ch1oro-5-iodo- -1.14 -0.69 -0.80 -1.01-2.62 -1.07 -0.90 -1.09-1.16 -1.24 N.D.2-chloro-5-1odo- -1.57 -0.83 -1.11 -1.33-2.43 -1.12 -1.37 -1.452-bromo-5-1odo- -1.35 -0.75 -0.93 -1.26-2.43 -1.08 -1.25 -1.61-1.15 N.D. N.D.5-bromo-6-1odo- -1.34 -0.31 -0.43 -0.57-2.47 -0.85 -0.99 -1.38-1.09 -1.19 N.D.6-bromo-5-1odo- -1.09 -0.59 -0.72 -0.92-2.53 -0.66 -1.23 -1.14-1.13 N.D. N.D.5,6-dibromo- -1.50 -0.60 -0.73 -1.03-2.47 -0.85 -0.99 -1.38-1.09 -1.19 N.D.2,5-d1brotno- -1.49 -0.81 -1.01 -1.36-2.49 -0.93 -1.23 N.D.-1.13 N.D. N.D.2,5-dichloro- -1.59 -0.94 -1.29 -1.42-2.44 -1.11 -1.51 N.D.5,6-d1chloro- -1.57 -0.68 -0.86 -1.13-2.41 -0.85 -1.10 -1.23-1.11 -1.23 -1.35*Half -wave potentials are given in each column in sequence of First E. ,?,Second E1/2 etc.'N.D.= The peak corresponding to the half-wave potential is in existence butis not clearly detectable.E1/2 was generally observed (see Table 1), indicating greater difficultyof further reduction of the compounds. The reason for such a shift isnot clearly understood, although it appears that solvent (DMSO)molecules may play an important role.Figure 2 shows typical cyclic voltammograms obtained forhalogenated nicotinic acids in DMSO at various potential scan rates.The initialreduction of the compound is followed by a rapid chemicalreaction (EC mechanism) of the product with solvent molecules. Asa result, the product cannot be reoxidized back to the original com-pound during reverse scan. Similar behavior was also observed inaqueous media.From Table 1, it is also obvious that the pH ofthe aqueous mediahas a profound effect on the relative ease of reduction of the carboxylgroup. Atlower pH, the half-wave potential shifts to the positive direc-tion, showing the protons are involved in the reduction process. Similarproton-mediated reduction ofisonicotinic acid has been reported earlier(Lund, 1963). Indry DMSO, however, the absence ofprotons dictatesthat the mechanism ofreduction may be totally different from that inaqueous medium and most likely the reduction proceeds through a free-radical mechanism. The reaction products in two solvents may thereforebe quite different. Caulometric analysis of the reduction processes inboth media, followed by isolation and gas-chromatographic identifica-tion of the products, are now in progress in our laboratory to fullyunderstand the mechanism of reduction of these biologically impor-tant compounds.Figure 1. Differential Pulse Polarograms of nicotinic acid and itsdihalogenated derivatives in 0.10M TBAP/DMSO. Conditions: scanrate = 5mV/sec, pulse amplitude = 25 mV, drop time = 1.0 sec. Thebottom curve (flat) represents the background.Igure 2. Cyclic Voltammograms of 5-Chloro-6-iodo- nicotinic acid in10M TBAP/DMSO at potential scan rates of10, 20, 50, 100 and 200Vsec. The peak height increases with scan rate,nd Br at 5- and 6-positions ofthe pyridine ring therefore favor reduc-tn of the carboxyl group. InDMSO, a negative shift of the second60 Proceedings Arkansas Academy of Science, Vol. XXXX,1986 60Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 20https://scholarworks.uark.edu/jaas/vol40/iss1/20Proceedings Arkansas Academy of Science, Vol. XXXX,1986 61AM U. Shaikh, Tappi A.Dixon, Lourie A. Battles, and Frank L.SetliffACKNOWLEDGEMENTThe financial support from an Institutional FacultyResearch Grant and the Office ofResearch in Science andTechnology at the University ofArkansas at Little Rockis gratefully acknowledged.LITERATURE CITEDBOND, A. M. 1984. InPolarographic Methods of Analysis. Marcel-Dekkar, New York.CARMODY, W. R. 1961. An Easily Prepared Wide Range BufferSeries. J. Chem. Ed. 38:559-560.GOULD, E. S. 1959. InMechanism and Structure in Organic Chemistry.Holt, Reinhart and Winston, NY. p 219.LUND, H. 1963. Electroorganic Preparations XI. Reduction ofIsonicotinic Acids in Acid Solution. Acta Chem. Scand. 17:972-978.LUND, H. 1983. In Organic Electrochemistry, Baizer, M. M. andLund, H. Eds., Marcel-Dekkar, NY. p 553.SETLIFF, F. L. 1970. Some 2,5- and 5,6- Dihalonicotinic Acids andTheir Precursors. J. Chem. Eng. Data 15:590-591.SETLIFF, F L. 1972. Some 2,5- and 5,6- Dihalonicotinic Acids andTheir Precursors. II.J. Chem. Eng. Data 17:515-516.SETLIFF, F. L. 1973. Some 2,5- and 5,6- Dihalonicotinic Acidsand Their Precursors. III.J. Chem. Eng. Data 18:449-450.SETLIFF, F. L.1976. Some 2,5- and 5,6- Dihalonicotinic Acids andTheir Precursors. IV. J. Chem. Eng. Data 21:246-247.SETLIFF, F. L. 1978. Some 2,5- and 5,6- Dihalonicotinic Acids andTheir Precursors. 5. J. Chem. Eng. Data 23:96-97.61Journal of the Arkansas Academy of Science, Vol. 40 [1986], Art. 20Published by Arkansas Academy of Science, 1986

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Electrochemistry of Dihalogenated Nicotonic Acids in Aqueous and Aprotic Media

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