Reduction of nitrobenzene with alkaline ascorbic acid: Kinetics and pathways

Area of Science:

• Environmental Chemistry
• Green Chemistry

Background:

• Nitroaromatic compounds like nitrobenzene (NB) are common environmental pollutants.
• Ascorbic acid (AA) is a readily available reducing agent with potential for pollutant degradation.

Purpose of the Study:

• To investigate the reductive degradation of nitrobenzene (NB) using alkaline ascorbic acid (AA).
• To determine the optimal alkaline pH for NB degradation and identify reaction intermediates and products.

Main Methods:

• Assessing the effect of alkaline pH (9-13) on NB degradation by AA.
• Kinetic analysis of the reaction at pH 12.
• Identification of intermediates and products using Gas Chromatography/Mass Spectrometry (GC/MS).
• Preliminary soil remediation experiments.

Main Results:

• Degradation rate increases significantly as pH approaches or exceeds the pKa2 of AA (11.79).
• The reaction kinetics at pH 12 were determined: r=((0.89±0.11)×10(-4) mM(1-(a+b))h(-1))×[NB](a=1.35±0.10)[AA](b=0.89±0.01).
• Intermediates identified include nitrosobenzene, azoxybenzene, and azobenzene, with aniline (AN) as the final product.
• Soil remediation requires alkaline pH and a high water-to-soil ratio.

Conclusions:

• Alkaline AA efficiently reduces NB to AN, primarily through direct electron transfer pathways.
• The process is pH-dependent, with higher alkalinity favoring degradation.
• Alkaline AA shows promise for remediating NB-contaminated soils.