A novel countercurrent chromatographic technique is described for the preparative separation-with excellent resolution-of up to multigram quantities of organic acids. This separation is accomplished by addition of a simple acid (e.g., trifluoroacetic acid) to the sample solution or stationary phase, followed by isocratic elution with a basic mobile phase. The acids elute as well-resolved rectangularly shaped peaks. This technique should find widespread application in any organic chemistry laboratory for the separation of crude mixtures and for the purification of isolated acids.
The isomeric 3- and 4-dehydrobenzenesulfonic acid anions b and c were prepared by collision induced dissociation (CID) of the [M - H](-) ions of isomeric sulfobenzoic acids obtained by negative electrospray ionization (ESI). The CID spectra (MS(3)) of anions b and c are different from each other, and both are different from that of the isomeric benzenesulfonate anion a, obtained from benzenesulfonic acid. The stability of ions b and c shows that 1,2-proton transfer does not take place in this system under the conditions of the CID experiment. Density functional (DFT) calculations at B3LYP/6-31+G(2d,p) level of theory show that benzenesulfonate anion a is the most stable isomer, and the energies of isomers b and c are higher by more than 65 kcal mol(-1). The calculated energies of the transition states involved in the 1,2-hydrogen migration leading to the interconversion of the isomeric anions are very high (>120 kcal mol(-1)relative to ion a, barrier energies >55 kcal mol(-1)), much higher than those of transition structures leading to fragmentation. This situation does not allow isomerization of ions b and c to a, under the conditions of the CID experiments. The isomeric 2-dehydrobenzenesulfonic acid anion isomerizes to the benzenesulfonate anion a by a facile proton transfer from the SO(3)H group to the adjacent position 2. The results of this work indicate that the gas phase deprotonation of meta- and para-sulfobenzoic acids is a kinetically controlled process.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.