Hydrotreating chemistry of model products from bioprocessing of carbazoles

Carbazoles are among the most difficult heterocyles to remove by conventional hydrotreating, due to their low basicity and the stability of the carbon-nitrogen bonds. An alternative approach to hydrotreating may be biological catalysts which have the ability to open the central ring of carbazole to give a free amine. The resulting compound would then be more amenable to catalytic hydrotreating. The purpose of this study was to assess the behavior of functional groups that are typical of biological oxidation under hydrotreating conditions. This information can be used to define the best possible pathways for screening of potential biocatalysts. A series of monofunctional and bifunctional aromatic compounds were reacted, included amines, phenols, alcohols, and carboxylic acids. All of the amines were more reactive than carbazole, but some bifunctional compounds, such as amino-alcohols and phenol-alcohols, tended to give polymerization or ring-closure reactions. The most desirable pathways for biological treatment of carbazole, therefore, are either complete deamination or ring opening without leaving active leaving groups proximate to a free amine.