RESUMO
RATIONALE: Ionic liquids (ILs) are a subject of active research in the field of alternative solvents. We studied the behaviour of a piperidine IL, 1-butyl-1-methylpiperidinium tetrafluoroborate (BMPA), through the elucidation of its transformation products (TPs) in water. METHODS: The transformation pathways of BMPA were investigated using high-performance liquid chromatography (HPLC) combined with a hybrid LTQ-Orbitrap instrument on the basis of mass defect filtering. TPs of BMPA were identified by fragmentation patterns and accurate mass measurements. RESULTS: The separation and identification of 32 TPs was achieved. BMPA can be oxidized at different positions in the alkyl chains. The ultimate products corresponds to N-methyl-piperidinium and some byproducts involving ring-opening. Tests of acute toxicity, evaluated with Vibrio Fischeri bacteria, show that BMPA transformation proceeds through the formation of slightly harmful compounds. CONCLUSIONS: Results showed that the main transformation pathways of BMPA were alkyl chain hydroxylation/shortening and de-alkylation, and that HPLC/LTQ-Orbitrap can serve as an important analytical platform to gather the unknown TPs of ILs.
RESUMO
We studied some ionic liquids (ILs) belonging to the pyridinium class under photocatalytic treatment. In particularly, we analysed how the length of the alkyl chain, the kind of inorganic ion and the type of substituents could influence the disappearance rate, the mineralization extent, the acute toxicity and the transformation mechanism. For such, we selected some pyridinium derivatives with different alkyl chain but the same anion, namely tetrafluoroborate (1-ethylpyridinium, 1-butylpyridinium, 1-hexylpyridinium), with two alkyl substituents (4-methyl-1-butylpyridinium) and with a different substituent (1-cyanopropylpyridinium). Then, on a selected IL (1-butylpyridinium), we evaluate the role of different inorganic anions (bromine and chlorine). The results show that irrespective to the alkyl chain or the number of substituents, the transformation involved an attack to the alkyl chain, proceeded through the formation of harmless compounds and the mineralization was easily achieved within 4h. Nitrogen was mainly released as ammonium ion. When introducing a cyano group, the extent of nitrate ions and the number of possible transformation route increased. Conversely, the type of inorganic ion deeply affected the transformation pathways and the extent of mineralization. Actually, in the presence of bromide as anion, IL was only partially mineralized and the formation of highly persistent transformation products occurred.
RESUMO
The photochemical reactivity of three ionic liquids (1-ethylpyridinium tetrafluoroborate, 1-butyl-4-methylpyridinium tetrafluoroborate, and 1-(3-cyanopropyl)pyridinium chloride) was studied by combining laboratory experiments and photochemical modeling, to get insight into the possible behavior in surface-water environments. Among the studied compounds, phototransformation in sunlit surface waters could be an important attenuation pathway for 1-butyl-4-methylpyridinium tetrafluoroborate (BMPOTFB). In this case the reaction with the carbonate radicals (CO3-) would prevail at low values of the dissolved organic carbon (DOC), while the direct photolysis would be important at intermediate to high DOC values. The sensitization by the triplet states of chromophoric dissolved organic matter could play a significant role at high DOC, especially in the presence of a considerable fraction of highly photoreactive pedogenic organic matter derived from soil runoff. The main processes that account for the phototransformation of BMPOTFB and produce the main detected transformation products (TPs) are hydroxylation, detachment/shortening of the butyl chain and double bond formation. Interestingly, there is a considerable overlap between the TPs formed by direct photolysis and those produced by indirect photochemistry. Some of the TPs formed from BMPOTFB are more toxic than the parent compound towards Vibrio fischeri bacteria, and account for the increase in toxicity of the irradiated mixtures. Differently from BMPOTFB, in the case of the other two studied ionic liquids the photodegradation would play a negligible role in environmental attenuation, with the possible exception of very shallow waters with low DOC.