Mechanisms in the Microbial Oxidation of Alkanes 455 



R — CH2 — CH3 



Alkane 



f — . ♦ 



R-CH-CH3 ., R-CHz-CHz* 



I O2 ^^^^ radical equilibrium q 



OOH 

 I 

 R-CH-CH3 Hydroperoxide R-CH2— CH2-OOH 



Secondary alcohol Primary alcohol 



Methyl ketone Fatty acid 



Fig. 2. Formation of n-alcohols and methyl ketones from alkyl free radicals 

 [Leadbetter and Foster (9)]. 



proposed. Independently, Leadbetter and Foster (8, 9) arrived at 

 the same conclusion after investigating the oxidation of alkanes 

 by Pseudomonas methanica and other alkane utilizing bacteria. 

 Incorporation of O^^ into cell material of organisms grown in 

 various n-paraffins was found to decrease markedly as the length 

 of tlie paraffin increased. The results were taken as evidence that 

 the first reaction involved in alkane oxidation was one requiring 

 participation of molecular oxygen and subsequent reactions in- 

 volved the oxygen of water. Thus, oxidation and assimilation of 

 intermediates with long alkyl chains would necessarily involve a 

 larger number of reactions, thereby diluting the original O^® in- 

 corporation levels of cells utilizing long chain paraffins. 



The formation of methyl ketones observed by Leadbetter and 

 Foster ( 9 ) , acetone from propane, for example, does not necessar- 

 ily mitigate against either the terminal carbon attack or the 

 hydroperoxidation hypothesis. Hydroperoxidation very likely in- 

 volves a free radical mechanism and one factor involving the 

 nature of the products formed may lie in the relative stabilities 

 associated with free radical intermediates. Stabilities of alkyl 

 radicals increase in the order 1° < 11° < 111° and also increase 



