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Reactions of N 2 O 5 with Salty and Surfactant-Coated Glycerol: Interfacial Conversion of Br - to Br 2 Mediated by Alkylammonium Cations

Reactions of N 2 O 5 with Salty and Surfactant-Coated Glycerol: Interfacial Conversion of Br - to Br 2 Mediated by Alkylammonium Cations

Michael A Shaloski, Joseph R Gord, Sean Staudt, Sarah L Quinn, Timothy H Bertram, Gilbert M Nathanson

J Phys Chem A. 2017 May 18;121(19):3708-3719.

PMID: 28425716

Abstract:

Gas-liquid scattering and product-yield experiments are used to investigate reactions of N2O5 with glycerol containing Br- and surfactant ions. N2O5 oxidizes Br- to Br2 for every solution tested: 2.7 M NaBr, 0.03 M tetrahexylammonium bromide (THABr), 0.03 M THABr + 0.5 M NaBr, 0.03 M THABr + 0.5 M NaCl, 0.03 M THABr + 0.01 M sodium dodecyl sulfate (SDS), and 0.01 M cetyltrimethylammonium bromide (CTABr). N2O5 also reacts with glycerol itself to produce mono- and dinitroglycerin. Surface tension measurements indicate that 0.03 M THABr and 2.7 M NaBr have similar interfacial Br- concentrations, though their bulk Br- concentrations differ by 90-fold. We find that twice as much Br2 is produced in the presence of THA+, implying that the conversion of Br- to Br2 is initiated at the interface, perhaps mediated by the charged, hydrophobic pocket within the surface THA+ cation. The addition of 0.5 M NaBr, 0.5 M NaCl, or 0.01 M SDS to 0.03 M THABr lowers the Br2 production rate by 23%, 63%, and 67% of the THABr value, respectively. When CTA+ is substituted for THA+, Br2 production drops to 12% of the THABr value. The generation of Br2 under such different conditions implies that trace amounts of surface-active alkylammonium ions can catalyze interfacial N2O5 reactions, even when salts and other surfactants are present.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP4328136	Tetrahexylammonium bromide		4328-13-6	Price

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