Elucidating the Reaction Mechanisms between Triazine and Hydrogen Sulfide with pH Variation Using Mass Spectrometry

Abstract

Triazine is one of the most economical and effective scavengers for hydrogen sulfide (HS) removal, but the reaction mechanisms between triazine and HS with pH variation in solution are still poorly understood. Herein, we show that the reaction process can be directly probed by means of paper spray mass spectrometry, in which an aprotic solvent (e.g., acetonitrile) is more favorable to the observation of reaction intermediates than a protic solvent (e.g., methanol), because of hydrogen bond interaction. Varying the pH of the reaction leads to completely different reaction pathways. With the pH in the range of 5.58 to 7.73, the major product was thiadiazine. With a pH of 3.02-3.69, thiadiazine is converted to 2-(5-(2-hydroxyethyl)-1,3,5-thiadiazinan-3-yl)acetaldehyde, which differs from the traditional pathway of analogous reactions. However, as ammonia was added into the reaction and the pH was adjusted to the range 8.45-9.43, triazine readily undergoes hydrolysis, and the formed intermediate reacts with ammonia and formaldehyde generated in situ from triazine to produce 1-(2-hydroxyethyl)-3,5,7-triaza-1-azoniatricyclo [3.3.1.1]decane (HTAD). Further increasing the pH up to 10.27-11.21 leads to the decomposition of HTAD. Based on the experimental observation and evidence from high-resolution and tandem mass spectrometry, we propose the plausible reaction mechanisms between triazine and HS, as well as the derived reaction from triazine under different pH conditions.

Raman and DFT Study of the H2S Scavenger Reaction of HET-TRZ under Simulated Contactor Tower Conditions

“…This issue could be associated with the type of analytical technique used in each study. This compound has been successfully identified using low invasive solution-state NMR or softer MS ionization methods, such as electron spray ionization (ESI) or collision-induced dissociation (CID) . In contrast, it has remained elusive when high energy electron-impact ionization (EI) MS has been the detection method of choice.…”

“…This compound has been successfully identified using low invasive solution-state NMR or softer MS ionization methods, such as electron spray ionization (ESI) 10 or collision-induced dissociation (CID). 11 In contrast, it has remained elusive when high energy electronimpact ionization (EI) MS 17 has been the detection method of choice. For some molecules, high collision energies cause extensive fragmentation and the loss of the parent peak, which might be the case for TDZ.…”

“…Density functional theory (DFT) calculations have shown that the addition of a third H 2 S molecule is energetically disfavored due to the lower electrophilicity of the carbon atoms bonded to the nitrogen and sulfur atoms in the DTZ heterocycle . The presence of TDZ and DTZ has also been corroborated by electrospray ionization mass spectrometry (ESI-MS) and paper spray mass spectroscopy (PS-MS) …”

“…9 The presence of TDZ and DTZ has also been corroborated by electrospray ionization mass spectrometry (ESI-MS) 10 and paper spray mass spectroscopy (PS-MS). 11 Despite being an effective H 2 S scavenger, HET-TRZ has a significant drawback. It is known that under unoptimized reaction conditions, the H 2 S removal process leads to the formation of a heavily insoluble and intractable solid deposit, which is the leading cause of equipment fouling in bubble tower contactors for gas treating.…”

Water coordinated on Cu(I)-based catalysts is the oxygen source in CO2 reduction to CO

“…Mass spectrometry (MS) is a formidable tool for chemical analysis and has also been used to explore the mechanisms of various chemical reactions 27 – 31 . Nevertheless, there have been few reports on the use of MS to study CO 2 RR mechanisms in operando 32 .…”