Production of hydroxylaminobenzene (HAB) via zinc reduction of nitrobenzene (NB) is an established batch
process based on aqueous electrolytic reactions involving an electrolyte as the promoter. This experimental
study explored continuous production of HAB that is needed as an intermediate in a novel zinc/biocatalyst
processing train, recently demonstrated by Luckarift et al. to obtain aminophenols. Experiments were conducted
using a Zn packed bed to probe the role of promoters under continuous-flow conditions at a temperature of
60 °C and promoter/NB molar ratios of 0.75, 1.15, and 1.5. In addition to the conventional NH4Cl, ammonium
formate and acetate were used as promoters. The best HAB yield was 95%, as compared to the batch yield
of 68%. The formation of oxidized zinc species caused the packed bed to build back pressure, which appeared
to enhance the selectivity of HAB/aniline. The formation of NB and ammonium/zinc complexes, as supported
by voltammetric evidence, appears to be one of the key roles of promoters. These findings demonstrated
efficacy and advantages of the continuous HAB production process.
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