Publication: Kumarin ve Kumestan benzeri bileşiklerin elektrokimyasal indirgenmesinin incelenmesi
Abstract
KUMARİN VE KUMESTAN BENZERİ BİLEŞİKLERİN ELEKTROKİMYASAL İNDİRGENMESİNİN İNCELENMESİ Bu çalışmada kumarin türevlerinden olan 3-(3'-4'-Dihidroksifenil) kumarin bileşiğinin ve kumestan benzeri bileşiklerden olan 6,7-Dihidroksi-3,3-dimetil 3,4-dihidro-2H-dibenzofuran-1-on ve 6,7-Dimetoksi-3,3-dimetil-3,4-dihidro-2H-dibenzofuran-1-on bileşiklerinin sentezleri yapılmış ve saflaştırılmıştır. Bu bile-şiklerin dönüşümlü voltametri (Cyclic Voltammetry) yöntemini kullanarak, elektrokimyasal indirgenme mekanizması incelenmiştir. Dönüşümlü voltametri çalışmalarında 3 elektrotlu bir sistem kullanılmıştır. Referans elektrot olarak doymuş kalomel elektrot ve yardımcı elektrot olarak bir platin elektrot kullanılmıştır. Dönüşümlü voltametrik çalışmalarda çalışma elektrodu olarak, yüzey alanı 0,0445 cm2 olan bir asılı cıva damla elektrodu kul-lanılmıştır. Çalışmalarda kullanılan cıva elektrokimyasal bir yöntemle temizlen-miştir. Deneysel çalışmalar metil alkol-su karışımında (farklı yüzdelerde) ve 0.1 M. LiCl kullanılarak gerçekleştirilmiştir. Tüm çalışmalar oda sıcaklığında yapıl-mıştır. Çalışma çözeltilerinin tamponlanmasında, 0.04 M. CH3COOH + 0.04 M. H3PO4 + 0.04 M. H3BO3 den oluşmuş Britton-Robinson tampon sistemi kulla-nılmıştır. Tampon çözeltilerin pH değerleri (2,50-10.50) katı NaOH ile ayarlan-mıştır. %100 metil alkol ortamındaki çalışmalarda Na3PO4 çökmesi sebebiyle, Britton-Robinson tamponunun H3PO4 bileşeni kullanılmamıştır. Sentezlenen bileşiklerin asılı cıva damla elektrodu kullanılarak siklik voltamogramları alınmıştır. Elde edilen voltamogramlardan, doymuş kalomel elektroda karşı pik potansiyelleri ve pik akımları saptanmıştır. Çalışma çözeltisi içerisinde çözünmüş halde bulunan oksijeni uzaklaştırmak için, her voltamogram alınmadan önce yaklaşık 20 dakika süreyle argon gazı ge-çirilmiştir. Gaz geçirme işleminden sonra çözelti, 0-(-2000) mV potansiyel de-ğerleri arasında, farklı tarama hızlarında, önce katodik ve sonra da anodik olarak taranmıştır. Voltametrik çalışmalarda, katodik taramalarda pik elde edilirken, anodik yöndeki taramalarda önemli sayılabilecek hiç bir pik gözlenmemiştir. 0-(-2000) mV potansiyelleri arasında bu bileşiklerin tamamen irreversibl bir reaksiyonla indirgendikleri görülmüştür. Voltametrik verilerin değerlendirilmesinden kumarin bileşiğinin bir elektronlu işlemle redüksiyona uğradığı, kumestan benze-ri bileşikler içinse iki elektronlu bir işlemle redüksiyona uğradığı, bu işlemlerin aynı anda elektron ve proton katılımıyla irreversibl olarak gerçekleştiği bulun-muştur.
The Investigation of Electrochemical Reduction of the Some Coumarin Compounds and Coumestane Analogs. In this study, 3-(3'-4'- dihydroxyphenyl) coumarin (one of the coumarin de-rivatives) and 6,7-dihydroxy-3,3-dimethyl-3,4-dihydro-2H-dibenzofurane-1-one and 6,7-dimethoxy-3,3-dimethyl-3,4-dihydro-2H-dibenzofurane-1-one (cou-mestane analogs) were synthesised and purified. The mechanism of electro-chemical reduction of these compounds were investigated by using cyclic volt-ammetry. The cyclic voltammetric experiments were used with a 3-electrode cell system. In this study saturated calomel electrode (SCE) as the reference and platinum as the counter electrode were used. In the cyclic voltammetric experi-ments, the hanging mercury drop electrode was used as the working electrode whose surface area was 0.0445 cm2. The mercury was purified electrochemically. The experiments were carried out in a methanol-water mixture (different percent) solvent medium and in a 0.1 M. LiCl. All measurements were performed at room temperature. Britton-Robinson solutions (made up from acetic acid, orthophosphoric acid, and boric acid, 0.04 M. in each) were used for buffering the working solu-tions. pH values of the buffer solutions which varied (2.50-10.50) were adjusted by using solid NaOH. In the 100% methanol medium, orthophosphoric acid was left out of the Britton-Robinson buffer in these cases in which Na3PO4 precipi-tates. The cyclic voltammograms of this compounds were taken using hanging mercury drop electrode. Peak currents and peak potentials were determined against a saturated calomel reference electrode from the voltammograms. To remove dissolved oxygen from the working solution was purged for 10-20 minutes with argon prior to recording the cyclic voltammogram. The solution was then scanned between 0-(-2000) mV first in a cathodic direction and then in a anodic direction using scan different rates. Many reduction peaks were obtained during cathodic stripping, however, no oxidation peaks which might be considered important were obtained during ano-dic stripping. It was observed that these compounds were totaly reduced in an irreversible reaction between potentials from O mV to -2000 mV. The assesment of voltammetric indicated the following results. 3,(3'-4'-dihydroxyphenyl) coumarin were subjected to reduction by one-electron and the simultaneous electronic and protonic processes were irreversible. 6,7-dihydroxy-3,3-dimethyl-3,4-dihydro-2H-dibenzofurane-1-one and 6,7 dimethoxy-3,3-dimethyl-3,4-dihydro-2H-dibenzofurane-1-one were subjected to reduction by two-electron and the simultaneous electronic and protonic processes were irre-versible.
The Investigation of Electrochemical Reduction of the Some Coumarin Compounds and Coumestane Analogs. In this study, 3-(3'-4'- dihydroxyphenyl) coumarin (one of the coumarin de-rivatives) and 6,7-dihydroxy-3,3-dimethyl-3,4-dihydro-2H-dibenzofurane-1-one and 6,7-dimethoxy-3,3-dimethyl-3,4-dihydro-2H-dibenzofurane-1-one (cou-mestane analogs) were synthesised and purified. The mechanism of electro-chemical reduction of these compounds were investigated by using cyclic volt-ammetry. The cyclic voltammetric experiments were used with a 3-electrode cell system. In this study saturated calomel electrode (SCE) as the reference and platinum as the counter electrode were used. In the cyclic voltammetric experi-ments, the hanging mercury drop electrode was used as the working electrode whose surface area was 0.0445 cm2. The mercury was purified electrochemically. The experiments were carried out in a methanol-water mixture (different percent) solvent medium and in a 0.1 M. LiCl. All measurements were performed at room temperature. Britton-Robinson solutions (made up from acetic acid, orthophosphoric acid, and boric acid, 0.04 M. in each) were used for buffering the working solu-tions. pH values of the buffer solutions which varied (2.50-10.50) were adjusted by using solid NaOH. In the 100% methanol medium, orthophosphoric acid was left out of the Britton-Robinson buffer in these cases in which Na3PO4 precipi-tates. The cyclic voltammograms of this compounds were taken using hanging mercury drop electrode. Peak currents and peak potentials were determined against a saturated calomel reference electrode from the voltammograms. To remove dissolved oxygen from the working solution was purged for 10-20 minutes with argon prior to recording the cyclic voltammogram. The solution was then scanned between 0-(-2000) mV first in a cathodic direction and then in a anodic direction using scan different rates. Many reduction peaks were obtained during cathodic stripping, however, no oxidation peaks which might be considered important were obtained during ano-dic stripping. It was observed that these compounds were totaly reduced in an irreversible reaction between potentials from O mV to -2000 mV. The assesment of voltammetric indicated the following results. 3,(3'-4'-dihydroxyphenyl) coumarin were subjected to reduction by one-electron and the simultaneous electronic and protonic processes were irreversible. 6,7-dihydroxy-3,3-dimethyl-3,4-dihydro-2H-dibenzofurane-1-one and 6,7 dimethoxy-3,3-dimethyl-3,4-dihydro-2H-dibenzofurane-1-one were subjected to reduction by two-electron and the simultaneous electronic and protonic processes were irre-versible.