title: Investigating the formation and the properties of monoalkyl carbonates in aqueous medium using capillary electrophoresis with capacitively coupled contactless conductivity detection.
abstract: Although alkyl carbonic acids (ACAs) and their salts are referred to as instable species in aqueous medium, we demonstrate that a monoalkyl carbonate (MAC) can in fact be easily formed from bicarbonate and an alcohol even in the presence of a high amount of water. A CE system with two capacitively coupled contactless conductivity detectors (C⁴Ds) was used to obtain different parameters about these species and their reactions. Based on the mobilities obtained for a series of alcohols ranging from 1 to 5 carbons, the coefficients of diffusion and the hydrodynamic radii were calculated. When compared with the equivalent carboxylates, MACs have radii systematically smaller. Although the precise pK(a) values of the ACAs could not be obtained, because of the fast decomposition in acid medium, it was possible, for the first time, to show that they are below 4.0. This result suggests that the acidity of an ACA is quite similar to the first hydrogen of H₂CO₃. Using a new approach to indirectly calibrate the C⁴D, the kinetic constants and the equilibrium constants of formation were also obtained. The results suggest that the increase in the chain length makes the MACs less stable and more inert.
authors.affiliation: Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Denis Tadeu Rajh
authors.initials: DT
authors.lastname: Vidal
authors.forename: Thiago
authors.initials: T
authors.lastname: Nogueira
authors.forename: Renata Mayumi
authors.initials: RM
authors.lastname: Saito
authors.forename: Claudimir Lucio
authors.initials: CL
authors.lastname: do Lago
mesh_terms: D002254:Carbonates / Q000737:chemistry*; D004058:Diffusion; D004553:Electric Conductivity; D019075:Electrophoresis, Capillary / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D014867:Water / Q000737:chemistry*
chemical_list: D002254:Carbonates; D014867:Water