Reactions of Oxygen-Containing Functional Groups

Oxygen functions in coal have been studied in terms of their reduction behavior. Thus, the most likely fate of the carbonyl groups during coal hydrogenation is reduction to the hydroxyl groups  

On the other hand, carbonyl oxygen occurring as aldehyde functions is very susceptible to oxidation whereas ketone functions are much less susceptible. The oxidation of aldehydes in air (autooxidation) occurs readily by way of a free-radical mechanism  

Hydroxyl oxygen, especially in the higher-rank coals, occurs predominantly as phenolic oxygen and carbonyl oxygen. Most of the chanical reactions used for hydroxyl oxygen have been used with the object of estimating the proportion present. However, phenoUc hydroxyl has a limited reactivity but the function is acidic and the reaction has been used as a means of determining the phenolic hydroxyl content of coal by titration of the excess barium hydroxide  

In addition, phenolic hydroxyl adjacent to a carboxyl group on an aromatic ring constitutes the major entity responsible for the chelation of metals in coal, particularly in the lower-rank coals. Phenolic hydroxyl is also determined by reaction with diazomethane (CH2N2) to form the methoxyl group (-OCH3) with the release of elemental nitrogen. 

Total hydroxyl can be determined by reaction with acetic anhydride in pyridine this process may require prolonged periods (several days) at 90°C (195°F). Alcoholic hydroxyl can be determined by esterification with phthalic anhydride and this reaction also requires several days at 90°C (195°F) to ensure completion. 

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