General Considerations of Transformation Options

We discussed, in the Introduction, an attractive but nevertheless totally unrealistic route to the synthesis of acetic acid from methane and carbon dioxide  

Is this route actually unrealistic Both the elemental composition and the structure of the final compound suggest that this is the shortest and most direct synthetic pathway. Yet if you mix methane and carbon dioxide you will see that absolutely nothing happens, regardless of reaction conditions. The necessity to discard this simple and appealing route can be explained by at least two reasons. 

The first reason is analogous to a simple observation a sled goes downhill on its own volition but under no circumstances will it go uphill by itself. Acetic acid 

Secondly, even if a reaction looks good on paper and even if thermodynamic factors are favorable (going downhill in free energy), there still must exist a realistic mechanism by which the reaction can occur. No such reaction channel is available for the direct conversion of methane and carbon dioxide into acetic acid. Yet there are ways of going around these apparently insurmountable obstacles. For example, in the present case the following stepwise detour can be proposed  

CH4 + Br2 - CH3Br + HBr CHjBr + Mg CHjMgBr CHjMgBr + CO2 - CHjCOOMgBr CHjCOOMgBr + HBr - CH3COOH + MgBrj 

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