Photo‐degradation of hydrophobic esters of pyridinecarboxylic acids as copper extractants from chloride media and their copper complexes

Abstract

The photo-stability of hydrophobic esters of pyridine-3-carboxylic acid and pyridine-3,5-dicarboxylic acid containing 2-ethylhexyl-, octyl-, and dodecyl-substituents which are model extractants of copper from chloride media were studied together with the photo-degradation of their copper complexes. The results indicate that UV light degraded the esters of both pyridine-3,5-dicarboxylic acid and pyridine-3-carboxylic acid. The degree of degradation depended on the structure of the ester, the type of solvent, and the presence of oxygen, water or hydrochloric acid in the solution during exposure to visible or UV-visible light. Photo-reactions between the solvent and the esters were also observed. Copper has a considerable influence on the photo-stability of the esters.

Photodegradation of Hydrophobic Pyridineketoximes in Toluene and Heptane

“…The first stage of the reaction is a hydrogen‐atom abstraction from a solvent by the pyridine nitrogen atom. The second stage is a replacement of a ring hydrogen by strong nucleophilic alkyl radicals (Scheme ) .…”

“…1‐(2‐pyridyl)tridecan‐1‐one oxime and 1‐(3‐pyridyl)tridecan‐1‐one oxime dissolved in toluene or heptane and their complexes with copper(II) chloride (1 × 10 −3 mol oxime L −1 ) dissolved in toluene were irradiated in a Heraeus photoreactor of 120 mL volume containing a medium pressure mercury lamp TQ 150 W (Heraeus) and quartz filter (1 mL optical length) . The lamp was positioned within the inner part of the photoreactor, and cooling water was circulated through a Pyrex jacket surrounding the tube.…”

Degradation of organothiophosphorous extractant Cyanex 301

“…There was no definite effect of metal on the photostability compounds but the reduction of Cu(II) ions to the copper mirror Cu(0) was detected as the result of the photochemical decarboxylation of mono-and di-esters. The survey also found out that pyridinecarboxamides are more stable to UV-vis light than esters of pyridinecarboxylic acid, but both tested derivatives of pyridinecarboxylic acid were more stable than hydroxyoximes extractant [20][21][22]. The influence of the presence of metal ions on the stability of other ligands was also noted [14,23] but only for derivatives of phosphoric acids the mechanism of the reaction was studied.…”

“…Photo-degradation was carried out in the same way as previous studies of other pyridine derivatives and individual model hydroxyoximes, and commercial hydroxyoxime extractants [19][20][21][22]. Extractant samples (0.001 M) in hexane or toluene were irradiated in a Heraeus photoreactor of 120 cm 3 volume containing medium pressure mercury lamp TQ 150 W (Heraeus) and a quartz filter ( = 0.6 and 4.7 W for = 270 and 579 nm, respectively).…”