218 



REDUCTION OF CARBON DIOXIDE 



CHAP. 9 



Table 9.IV 



Total Energies, A/T, and Free Energies, AF, of Hydrogenation " of C- 

 AND C— O Bonds and the Corresponding Oxidation-Reduction 

 Potentials, Eo (at pH 0) and Eo' (at pH 7) '' 



Example 

 no. 



A 



(oxidant) 



A Hz 



(reductant) 



AH 

 kcal 



AF, 



kcal 



(298° K.) 



Eo, 

 volt 



Eo' 



(pH 7), 



volt 



la 

 lb 



Succinic acid (s.) 

 Succinate (aq.) 



I. C— C Bond 



2 Acetic acid (I.) 

 2 Acetate" (aq.) 



- 8.2 



-10.2 

 -14.4 



(-0.22) 

 ( -0.30) 



(+0.20) 

 (+0.12) 



2 

 3a 

 3b 

 4 



Ethylene (g.) 

 Fumaric acid (s.) 

 Fumarate (aq.) 

 Cyclohexene (g.) 



Cyclohexadiene (g.) 

 Furan (g.) 

 Benzene (g.) 



IIA. C=C Bonds 



Ethane (g.) 

 Succinic acid (s.) 

 Succinate (aq.) 

 Cyclohexane (g.) 



JIB. C=C— C = C Group 



Cyclohexene (g.) 

 Dihydrofuran (g.) 

 Cj'clohexadiene (g.) 



(-0.53) 



(-0.48) 



-0.45 



(-0.40) 



(-0.10) 

 (-0.06) 

 -0.03 

 (+0.02) 



(+0.03) 

 (+0.36) 

 (+0.72) 



8a 

 8b 

 9a 

 9b 



Formaldehyde (g.) 

 Formaldehyde (aq.) 

 Acetaldehyde (g.) 

 Acetaldehyde (aq.) 



IIIA. 0=0 Bonds 



Methanol (g.) 

 Methanol (aq.) 

 Ethanol (g.) 

 Ethanol (aq.) 



C=0 

 IIIB. I Geoup 



HO— 6=0 



(+0.14) 

 (+0.23) 

 (+0.27) 

 (+0.22) 



14a 



14b 



14c 



15a 

 15b 



15c 



16a 

 16b 

 16c 

 16d 

 16e 



Formic acid (g.) 



Formic acid (aq.) 



Formate" (aq.) + 



Acetic acid (g.) 

 Acetic acid (aq.) 



Acetate" (aq.) + 



H+ 



aq. 



Carbon dioxide (g.) 

 Carbon dioxide (aq.) 

 Carbon dioxide (aq.) 

 Bicarbonate" (aq.) 

 Carbonate (aq.) + 

 H+aq. 



HID. C— OH Group 



Formaldehyde (g.) + 



water (g.) 

 Formaldehyde (aq.) + 



water (1.) 

 Formaldehyde (aq.) + 



water (1.) 

 Acetaldehyde (g.) + water (g.) 

 Acetaldehyde (aq.) + 



water (1.) 

 Acetaldehyde (aq.) + 



water (1.) 



HIE. 0=C=0 Group 



Formic acid (g.) 

 Formic acid (aq.) 

 Formate" (aq.) + H'''aq. 

 Formate" (aq.) + water (1.) 

 Formate" (aq.) + water (1.) 



-11.0 

 -15.5 



-0.24 

 -0.33 



+0.18 

 +0.10 



(+0.46) 



(+0.43) 



(+0.53) 



(+0.52) 

 (+0.54) 



(+0.62) 



(+0.68) 

 (+0.56) 

 (+0.46) 

 (+0.44) 

 (+0.33) 



" Cf. bibliography on page 245. 



' The sign of the potential is chosen here to coincide with the sign of the change in free energy upon 

 reduction. In European literature, a reverse convention prevails, with positive potentials assigned to 

 strong oxidants, rather than, as here, to strong reductants, 



