TY - JOUR
T1 - Computational study of mechanistic pathway and effect of zero valent metals on reductive debromination of some polybrominated biphenyls
AU - Olasunkanmi, Lukman O.
AU - Wahab, Olaide O.
AU - Oladokun, Adebukola H.
AU - Adepoju, Adedolapo O.
AU - Govender, Penny P.
N1 - Publisher Copyright:
© 2023 Elsevier B.V.
PY - 2023/9
Y1 - 2023/9
N2 - Complete debromination of three polybrominated biphenyls (PBBs), namely 2,2′,3,3′,4,4′-hexabromobiphenyl (PBB-128), 2,2′,3,3′,4,5- hexabromobiphenyl (PBB-129) and 2,2′,3,3′,4,5′- hexabromobiphenyl (PBB-130) aided by zero valent magnesium (Mg0) and zinc (Zn0) in the presence of methanol was studied computationally using dispersion corrected ωB97XD functional with cc-pVTZ basis set. All possible debromination pathways were explored for each parent PBB and the most energetically favoured pathway was identified. Mono-debromination of each PBB afforded a two-step mechanism, viz, formation of a highly charged covalent intermediate that involves a phenyl-metal-bromine connectivity and protonation by methanol molecule. Total activation energy for the step-wise removal of one bromine substituent increased along the debromination pathway. Using substituent positions, favourable sequence of stepwise debromination was found to follow the order 3 or 3′ 2 or 2′ 4 or 4′, while Mg0 catalyzed the debromination reaction better than Zn0. The order of ease of debromination was found to be PBB-128PBB-130 PBB-129.
AB - Complete debromination of three polybrominated biphenyls (PBBs), namely 2,2′,3,3′,4,4′-hexabromobiphenyl (PBB-128), 2,2′,3,3′,4,5- hexabromobiphenyl (PBB-129) and 2,2′,3,3′,4,5′- hexabromobiphenyl (PBB-130) aided by zero valent magnesium (Mg0) and zinc (Zn0) in the presence of methanol was studied computationally using dispersion corrected ωB97XD functional with cc-pVTZ basis set. All possible debromination pathways were explored for each parent PBB and the most energetically favoured pathway was identified. Mono-debromination of each PBB afforded a two-step mechanism, viz, formation of a highly charged covalent intermediate that involves a phenyl-metal-bromine connectivity and protonation by methanol molecule. Total activation energy for the step-wise removal of one bromine substituent increased along the debromination pathway. Using substituent positions, favourable sequence of stepwise debromination was found to follow the order 3 or 3′ 2 or 2′ 4 or 4′, while Mg0 catalyzed the debromination reaction better than Zn0. The order of ease of debromination was found to be PBB-128PBB-130 PBB-129.
KW - Activation energy
KW - DFT
KW - Debromination pathway
KW - Polybrominated biphenyls
KW - Potential energy surface
KW - Zero valent Metals
UR - http://www.scopus.com/inward/record.url?scp=85164411538&partnerID=8YFLogxK
U2 - 10.1016/j.comptc.2023.114238
DO - 10.1016/j.comptc.2023.114238
M3 - Article
AN - SCOPUS:85164411538
SN - 2210-271X
VL - 1227
JO - Computational and Theoretical Chemistry
JF - Computational and Theoretical Chemistry
M1 - 114238
ER -