Abstract
Activated carbon (AC) is widely used as an adsorbent in water and air purification, but recent studies show that AC can also mediate chemical reactions at ambient temperature, including electron-transfer, redox, free radical, and dehydrohalogenation. Here, we expand the repertoire of such reactions to SN2 base hydrolysis of alkyl bromides. Detailed studies were carried out on the quarantine and pre-shipment fumigant, methyl bromide (MeBr), whose removal from fumigation vent streams is sought due to its ozone-depleting potential. Mixed with a 1M solution of NaOH, ACs are effective adsorbents, but also participate in hydrolysis of MeBr to bromide, methanol, and dimethyl ether. MeBr decay is first order in MeBr and obeys a two-term rate law corresponding to aqueous- and adsorbed-state reactions. The adsorbed-state reaction is, i) unassisted by surface groups, as shown by cycling experiments; ii) 0.83 order in aqueous hydroxide concentration suggesting participation of adsorbed hydroxide; iii) accelerated by pre-adsorption of quaternary ammonium surfactants, which also shift the zeta potential into the positive region; and iv) inhibited by competing inert anions in the order of their chromatographic retention time on ion-exchange resins: Br−<NO3−<ClO4−. The results support an anion exchange mechanism in which hydroxide is attracted to positive sites on the carbon. Normalized to aqueous-phase rate constants, adsorbed-state rate constants for RBr followed the order, R=methyl>ethyl>propyl.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.