A note on the composition of cerium-TTA complexes and the oxidation of cerium (III) ion

Abstract

Spectrophotometric methods for the determination of cerium with thenoyltrifluoroacetone (TTA) were developed by Khopkar and De, and Onishi and Banks. The composition of the cerium-TTA complex extracted with xylene from 1N sulfuric acid solution containing bromate (the conditions of Onishi and Banks) is probably CeT4, where HT is the enol form of TTA. The extraction constant of this system is calculated to be 2×103. An attempt to obtain a precipitate of the complex under similar conditions was not successful.The composition of the cerium-TTA complex extracted under Khopkar and De's conditions could not be determined, because the plot of log DCe versus log [TTA] was not a straight line (DCe : distribution ratio of cerium). Apparent molar absorptivities for cerium (IV) in benzene are 4.1×103 and 3.6×103 at 440 and 450mμ, respectively. Although Khopkar and De suggested the oxidation of cerium(III) by bromate and dichromate in slightly acid solution, this oxidation is incomplete. The oxidation of cerium(III) (1020mg) is almost complete when 10ml of a solution that is 1N in sulfuric acid and 0.3M in sodium bromate is heated at 70°C for 1 hour.