NMR Investigation of the Thermolysis of Citric Acid

The thermolytic decomposition of citric acid in the presence of tin/lead solder has been investigated. The solid reaction products were first examined by solid-state 13 C NMR. The samples were then dissolved in D 2 O, and 1 H and 13 C 1D and 2D (HMQC, TOCSY) spectra were obtained. Results indicate the presence of a series of compounds including 3-hydroxyglutaric, citraconic, itaconic and aconitic acids, and anhydrides. Solution- and solid-state NMR data are provided for citric acid and a number of metal and alkali metal citrate salts. Results of this work are related to the use of citric acid as a solder flux and to the elimination of chlorofluorocarbon cleaning processes in the electronics industry.