Effect of Chloroaniline Isomerism on Inhibition of Methane Biosynthesis by the Methanogenic Bacteria

Aims: The present work aims to determine the toxicity of Chloroanilines isomers and evaluate the effect of Chloroanilines isomerism and intramolecular hydrogen bonds on inhibition of methane biosynthesis by the acetoclastic methanogenic bacteria.
Study Design: Anaerobic digestion of pig manure, anaerobic toxicity essay, Effect of the isomerism (functional groups position) on inhibition of methane biosynthesis by the methanogenic bacteria), Correlation of the methanogenic toxicity (IC50) with Chloroanilines boiling point.
Place and Duration of Study: Department of Chemistry, University of Kinshasa, DR Congo, between April 2011 and March 2012.
Methodology: The toxicity to acetoclastic methanogenic bacteria was performed with the standard method of serum bottles; digested pig manure was utilized as inoculums and acetate as substrate. The methane gas volume produced was measured by serum bottles liquid displacement systems (Mariotte flask system).
Results: The obtained results indicate there are relationships between the isomerism of Chloroanilines and their inhibitory effects on methanogenic bacteria. The various isomers of Chloroaniline have toxicities which are different from 51.00; 539.78 and 787.47 mg / l respectively for the ortho, meta and para-Chloroaniline. One can notice that the o-Chloroaniline IC50 value is 10.43 and 15.44 times more toxic than meta and para Chloroaniline respectively. Contrary to all predictions, it is more toxic than benzene. This behavior can be explained by the formation of a strong hydrogen bond between the electronegative chlorine atom (-Cl) and amino group (-NH2) in o-Chloroaniline in ortho position of aromatic ring. The formation of this intramolecular bond decreases the steric hindrance of this isomer and increases its mobility (diffusion coefficient) to the cell membrane). A significant linear correlation was found between the IC50 values of Chloroanilines isomers and their boiling temperatures.
Conclusion: The results obtained in this paper indicate that some relationships exist between the isomerism (functional groups position) of Chloroanilines and their inhibitory effects on methane biosynthesis by the methanogenic bacteria. The formation of a very strong intramolecular hydrogen bonds between chlorine atom and amine group renders ortho Chloroaniline very toxic than the others tested Chloroaniline isomers.