Abstract
ABSTRACT
Rationale
Diphenylamine (DPAH) derivatives, widely used as antioxidants, interact with oxygen molecules (or ozone) to form radicals at the amine group. Although the antioxidation mechanism involves radical processes, separating these radicals using chromatography is challenging.
Methods
Rapid oxidation of DPAH was achieved through ozonation in an acetone solution, and the oxidation products, including radical and neutral species, were analyzed using direct APCI‐MS. The analysis was performed using a single quadrupole mass spectrometer in both positive‐ and negative‐ion modes. The types and yields of the oxidation products were analyzed according to the ozonation time. Energy differences based on the oxidation product size were compared to explain their favorability for formation.
Results
The major oxidation products included (DPA
•
+
n
O) and (DPA
•
+
n
O − H). They were detected as [DPA
•
+
n
O + H]
+
and [DPA
•
+
n
O]
+
in the positive‐ion mode, respectively, and observed as [DPA
•
+
n
O − H]
−
and [DPA
•
+
n
O − 2H]
−
in the negative‐ion mode, respectively. The abundance of oxidized DPAH products increased significantly until (DPA
•
+ 2O) and (DPA
•
+ 2O − H) and then notably decreased as the number of oxygen atoms increased.
Conclusion
No significant differences in energies were observed for the consecutive addition of oxygen atoms to (DPA
•
+
n
O) and (DPA
•
+
n
O − H) with
n
= 1–6. Steric hindrance significantly influenced the number of oxygen atoms adducted to DPAH. The reasonable maximum number of oxygen atoms adducted to DPAH is five, considering thermodynamic favorability and steric hindrance.