OXIDATION AND REDUCTION 



chlorine, can also accept :\n electron and thus "oxidize'' other sub- 

 stances. Oxygen, therefore, is only one among many molecular species 

 which can withdraw an electron from other molecules and so "oxidize" 

 them. 



One must remember that the transition of the original definition 

 of oxidation to the modern one has been gradual. Historically, there 

 has been a transition stage inaugurated by Wieland, who developed 

 his concept mainly with respect to oxidation of organic molecules. 



/H /H 



When alcohol, CH3C— H, is oxidized to aldehyde, CH3C , the over- 



\OH ^O 



all eflfect is the loss of two hydrogen atoms. According to the original 

 definition of oxidation, one may say that the primary process is the 



addition of one oxygen atom to alcohol in order to form CH3C — OH 



\0H 



which, by splitting off one molecule of water, becomes CH3C 



^O 

 Wieland's suggestion is that the process does not pass through the stage 

 of an addition of oxygen, but that what had been designated as oxida- 

 tion is in fact a withdrawal of two hydrogen atoms. The oxidizing 

 agent is the acceptor for the hydrogen atoms; for such cases, he re- 

 places the term "oxidation" by "dehydrogenation." 



The reconciliation of this idea with the more modern one can 

 be based on the fact that a hydrogen atom consists of a positively 

 charged proton and a negatively charged electron. Then, one may 

 say that the withdrawal of two electrons is essential for oxidation of 

 alcohol. Since the two protons, which should remain, are no longer 

 held by any noticeable force, they are detached also, and become 

 bound to some proton acceptor, such as water, with which they form 

 the hydrogen ion, OH3+, as it exists in the presence of water (called 

 also the oxonium ion); or they may be bound to some anion that 

 may be present, such as the acetate ion, GH3GOO~, with which they 

 form an "acid," CH3COOH. This hypothesis should not involve the 

 idea that the expulsion of the electron occurs first and the expulsion of 

 the proton thereafter. The sequence is undecided. The principle is, 

 rather, that the withdrawal of each hydrogen atom is the same as the 



209 



