Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry Analysis of Eutectic Bis(2,2-dinitropropyl) Acetal/Formal Degradation Profile: Nontargeted Identification of Antioxidant Derivatives

In the eutectic mixture of bis(2,2-dinitropropyl) acetal (BDNPA) and bis(2,2-dinitropropyl) formal (BDNPF), also known as nitroplasticizer (NP), n-phenyl-beta-naphthylamine (PBNA), an antioxidant, is used to improve the long-term storage of NP. PBNA scavenges nitrogen oxides (e.g., NOx radicals) that are evolved from NP decomposition, hence slowing down the degradation of NP. Yet, little is known about the associated chemical reaction between NP and PBNA. Herein, using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF), we thoroughly characterize nitrated PBNA derivatives with up to five NO2 moieties in terms of retention time, mass verification, fragmentation pattern, and correlation with NP degradation. The propagation of PBNA nitration is found to depend on the temperature and acidity of the NP system and can be utilized as an indirect, yet reliable, means of determining the extent of NP degradation. At low temperatures (< 55?), we find that the scavenging efficiency of PBNA is nullified when three NO2 moieties are added to PBNA. Hence, the dinitro derivative can be used as a reliable indicator for the onset of hydrolytic NP degradation. At elevated temperatures (>= 55 ?) and especially in the dry environment, the trace amount of water in the condensed NP (< 700 ppm) is essentially removed, which accelerates the production of reactive species (e.g., HONO, HNO3 and NOx). In return, the increased acidity due to HNO3 formation catalyzes the hydrolysis of NP and PBNA nitro derivatives into 2,2-dinitropropanol (DNPOH) and nitrophenol/dinitrophenol, respectively.

Automated summary

In this study, PBNA nitrated derivatives were thoroughly characterized using liquid chromatography quadrupole time-of-flight mass spectrometry. The propagation of PBNA nitration was found to depend on temperature and acidity, providing a reliable means of determining the extent of NP degradation.