A Rearrangement Reaction to Yield a NH₄⁺ Ion Driven by Polyoxometalate Formation

Abstract

Triethylamine is a volatile liquid and exists in the atmosphere in the gas phase. It is a hazardous air pollutant and identified as a toxic air contaminant. Thus, producing ammonia (a vital chemical for fertilizer production) from the vapor state of this toxic substance is a challenging task. Diffusion of the vapor of triethylamine, (C 2 H 5 ) 3 N, into an acidified aqueous solution of sodium molybdate results in the formation of single crystals of compound [(C 2 H 5 ) 3 NH] 2 [(C 2 H 5 ) 4 N][NaMo 8 O 26 ] ( 1 ). Notably, compound 1 includes a [(C 2 H 5 ) 4 N] + cation, even though the concerned reaction mixture was not treated with any tetraethylammonium salt. The formation of the [(C 2 H 5 ) 4 N] + cation from (C 2 H 5 ) 3 N in an acidic aqueous medium is logically possible only when an ammonium cation (NH 4 + ) is formed in the overall reaction: 4(C 2 H 5 ) 3 N + 4H + = 3[(C 2 H 5 ) 4 N] + + [NH 4 ] + . Although the resulting NH 4 + cation (identified by Nessler’s reagent test) is not included in the crystals of compound 1 as a cation, it can be made associated with a crown ether in the isolation of single crystals of compound [NH 4 ⊂B15C5] 3 [PMo 12 O 40 ]·B15C5 ( 2 ), (B15C5 = benzo-15-crown-5). Crystal structure analysis and 1 H NMR studies of compound 2 have established the presence of an H-bonded NH 4 + ion in compound 2 , thereby established the rearrangement reaction.