Photo-fragmentation of alkyl phosphates in the gas-phase

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Vol. 365; pp. 13 - 22
• Main Authors: Chiarinelli, J., Markus, P., Bolognesi, P., Avaldi, L., Turco Liveri, V., Calandra, P.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01-10-2018; Elsevier BV
• Subjects: Alkyl phosphates; Atoms & subatomic particles; Biodegradation; Chains; Chemical industry; Dimers; Esters; Flame retardants; Fragmentation; Ionization; Mass spectra; Mass spectrometry; Phosphates; Photo-fragmentation; Photons; Spectrometry; Ultraviolet radiation; Vacuum; Alkyl phosphates; Mass spectra; Photo-fragmentation
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2018.07.017

The finding of fragments at m/z = 211 is a signature of DBP ionized dimer presence in the gas phase.
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•Acidic alkylphosphates (bis-2-ethylhexyl phosphate and dibutylphosphate) can unergo evaporation as dimers.•All alkylphosphates have the tendency to saturate all the oxygen bonds.•The VUV radiation-induced chemistry represents an accelerated alternative to the bacteria-induced alkylphosphate degradation.
Alkyl phosphates are experiencing an ever increasing use due to the current arising of new applications. This implies their increasing presence in the environment so their stability and reactivity under high-energy photons, which are still unknown, need to be clarified.
In this study, a mass spectrometric investigation of the ionization and fragmentation processes of four representative alkyl phosphates (dibutyl, tributyl, bis-2-ethylhexyl, and tris-2-ethylhexyl phosphate) induced by vacuum ultraviolet (VUV) radiation has been carried out. The experimental data show that fragmentation occurs through a stepwise cleavage of the bonds between the phosphate group and the alkyl chains leading to the formation of esters with a lower number of alkyl chains and the protonated orthophosphoric acid as ending product. Interestingly, the presence of charged species with mass-over-charge (m/z) values larger than the parent ion is also observed in dibutyl and bis-2-ethylhexyl phosphate, suggesting the existence of their dimers in the gas phase. This has been rationalized, with the aid of ab-initio DFT calculations, in terms of the capability of these molecules to form H-bonds. The photo-induced reactivity in the gas phase has been clarified, and its similarity with the natural bacterial degradation has been pointed out.