Atmospheric pressure Eberlin transacetalization reactions in the heterogeneous liquid/gas phase

The Eberlin reaction, the ionic transacetalization of cyclic acetals and analogues with acylium and related ions. is demonstrated in the course of ion/molecule reactions at atmospheric pressure. Selected gaseous acetals ( 1.3-dioxolane, 2-methyl- 1.3-dioxolane. 2.2-dimethyl-1,3-dioxolane. 4-methyl- 1,3-dioxolane, 2-phenyl-1,3-dioxolane. 1.3-dioxane. and 1.3.5-trioxane) react efficiently with the (CH3)(2)NCO+ acylium ion. generated by electrosonic spray ionization (ESSI) of an aqueous/methanol solution of tetramethylurea (TMU), to furnish the characteristic cyclic ionic acetals, the Eberlin products, in moderate to high yields. It is proposed that acylium ions Oil the surface of the ESSI-generated droplets interact with gaseous neutral reagents. The Eberlin products dissociate exclusively to re-form the reactant (CH2)(2)NCO+ acylium ion upon collision-induced dissociation (CID), confirming their structures. The intact adduct. i.e., acylium ion Plus neutral reagent (the stable precursor of the Eberlin product), is observed in these experiments whereas it is not observed in studies of the same Eberlin reactions under conventional reduced pressure ion/molecule reaction conditions. It is suggested that under atmospheric pressure conditions these intact adducts are likely stabilized through deactivation via collision with buffer gas. (C) 2006 Elsevier B.V. All rights reserved.253328128

High production of small organic dicarboxylate dianions by DESI and ESI

A significant production of gas-phase dicarboxylate dianions has been observed in standard ESI and DESI during the analysis of small organic dicarboxylic acids under moderate or highly alkaline conditions. In ESI, this can be attributed to an excess of hydroxyl ions (OH–) which favor the formation of an high amount of dianions in solution, contemporarily trapping the potential counter ions during the ESI process. The results obtained in DESI highlight the role of the surface in trapping the counterions during desorption process and determining the ultimate nature of the observed gas-phase ion