OXIDATION AND REDUCTION 



conditions possible, even in extremely acid solution, V changes its 

 acidic ionization level by expelling the two protons and forming acet- 

 aldehyde (VI). • Here again we do not claim that V is formed first 

 and VI subsequently. It is, however, emphasized that the process 

 of oxidation proper is the detachment of electrons, and that the simul- 

 taneous loss of the two protons, although it may be a necessary con- 

 sequence, does not belong to the process of oxidation itself. Dehy- 

 drogenation is thus a special case of oxidation. 



The term dehydrogenation need not be discarded but may be 

 used advantageously for those cases in which the release of an electron 

 involves the simultaneous release of a proton. Whether or not this 

 simultaneous release of the proton occurs depends on the pH of the 

 solution. The term dehydrogenation can be reserved for the cases in 

 which even in extremely alkaline solution the release of an electron is 

 accompanied by a release of a proton. The conversion of succinic acid 

 (VII) to fumaric acid (VIII) may be called a dehydrogenation because 

 the intermediate stage (IX) is not capable of permanent existence. 

 Molecular species VIII may be considered as an infinitely strong acid, 

 which even in an acid solution is not capable of holding on to protons. 

 Therefore the enzyme which catalyzes the reaction VII -^ VIII may 



COOH COOH COOH 



I I I 



CH2 CH CH-H + 



I II I 



CH2 CH CHH+ 



I I I 



COOH COOH COOH 



VII VIII IX 



be justly termed a dehydrogenase. When quinone (I) is reduced in 

 an acid solution, we may speak also of dehydrogenation, whereas in 

 the reduction of quinone in a more alkaline solution (IX and VIII) 

 the synonymous use of the terms oxidation and dehydrogenation would 

 involve a more generalized definition of dehydrogenation. 



Analogously, if we define oxidation as the loss of an electron, 

 we are compelled to generalize the definition by the amendment that 

 this definition holds whether or not a proton is also released; so 

 whether one uses "oxidation" or "dehydrogenation" is a matter of 

 nomenclature only. In this essay, we shall use "oxidation" and 

 "reduction," and not "dehydrogenation" and "hydrogenation." For 



21 I 



