1038
JIAN-QIANG HU et al.
H
H
Lewis acid
N
+
+ HCHO
N
Lewis acid
H
H
H
N
CH2
N
CH2
N
n
(n = 2)
Scheme 1. Reaction pathway of PDPA.
was observed at 2965 and 2902 cm–1, respectively.
These results indicated the existence of methyl in the
product. The same C-H bands were observed at 2929
and 2872 cm–1, which were the characteristic peak of
methene. A strong band from 3000–3100 cm–1, a band
that includes 1597, 1513, and 1450 cm–1, and a charac-
teristic band for benzene were observed in the spec-
trum. In addition, the absorption band of C−C bonds
belonging to 1,4-substituted benzene was confirmed
by the peak at 826 cm–1. The absorption spectrum of
the frequency zone at 1650–2000 cm–1 was a typical
characteristic of the substituent counterpoint in ben-
zene. The analysis of infrared spectra revealed the
presence of methyl, methylene, and substituted ben-
zene in the molecules, and the benzene substituents
were likely alkyl and amino which had obvious align-
ment characteristics.
The ideal mass and optimum proportions were
optimized through the orthogonal array testing, the
steps were as follows. First, diphenylamine (16.9 g,
0.1 mol) was placed in a round-bottom flask and
heated to melt. Activated clay treated by alkali was
combined with diphenylamine in the flask. The mix-
ture was immediately heated to 220°C. Afterward, sty-
rene (43.2 g, 0.41 mol) was added to the content drop
by drop in a period of 2 h, and the reaction mixture was
refluxed for 2 h at 220°C. Intermediate products were
obtained after hot filtration (yield of 80.1%). Second,
toluene (200 ml), potassium hydroxide (14 g, 0.25 mol),
and the intermediate products (37.7 g, 0.10 mol) were
added to a 500 ml three-necked bottle and stirred at
70°C. Then formaldehyde (2.25 g, 0.075 mol) was
added and the mixtures were stirred for 1.5 h. After
complete reaction, the reaction mixtures were washed
with water, distilled, and dried over anhydrous sodium
sulphate. The brown viscous product PDPA was
1
The H NMR spectrum showed peaks at 6.82–
finally obtained (yield of 98.4%). The typical proper- 7.57 ppm, which indicated benzene formation. The
ties of antioxidant PDPA are listed in Table 1.
appearance of peaks at 4.20–4.24 ppm correspond-
ing to hydrogen atoms in amino and peaks at 4.30–
4.38 ppm corresponding to methylene groups between
singlet-connected benzene was detected. The protons
of the methyl groups were observed at 0.88 ppm adja-
cent to alkyl. These protons belonging to aminoben-
zene, benzyl and benzene were all detected. Further-
more, the ratio of hydrogen in benzene to hydrogen in
methyl and methylene was about 9 : 4 according to the
values of the peaks in the spectrum. We can obtain
Characterization of PDPA. The structure of PDPA
was confirmed through infrared spectroscopy spec-
trum (IR) with a PerkinElmer Fourier Transform
Spectrum BX instrument, proton nuclear magnetic
resonance spectroscopy (NMR) with FX-90Q, mass
spectrum (MS) with a MALDI-TOF mass spectrom-
eter, and elementary analysis with JB-750. The syn-
thesized compounds of PDPA were isolated through
chromatography and its structure was identified
through the methods described.
The stretching vibration absorption band of N-H
bonds during FTIR at 3400 cm–1 was observed in the
product. The bending vibration absorption band of C-N
bonds was detected at 1513 cm–1 and confirmed the
formation of amidogen in the aromatic secondary
amine compound. The formation of asymmetric and
symmetric stretching vibration absorption bands of C-H
13
additional information from the C NMR spectrum.
The peaks at 117.1–147.1 ppm indicated the presence
of benzene carbon. The peaks at 22.0–22.5 ppm and
those at around 39.8–44.8 ppm suggested the pres-
ence of methyl and methylene, respectively.
The proportion of each element in the elementary
analysis was (wt %): C—87.58 (87.26); H—7.16 (7.24)
and N—4.09 (4.16). Furthermore, the mass spectrum
data showed that molecular weights were about 1516,
which confirmed the product structures.
Oxidation–corrosion tests. Oxidation degradation
of lubricants usually results in chemical composition
changes in oils and further affects physical and chem-
ical properties. The thermal oxidation stability of
PDPA added to 500 SN and PE was evaluated by kine-
matic viscosity (KV) according to ASTM D445-06
and total acid number (TAN) according to ASTM
D664-06 after the oxidation–corrosion tests. All
experiments were repeated in triplicate. Oxidation–
Table 1. Typical properties of PDPA
Item
PDPA
Color
Brown liquid
Nitrogen content
Kinematic KV (40°C)
4.1%
650 mm2/s
1.09 g/mL
230°C
Density (20°C)
Flash point (opening)
PETROLEUM CHEMISTRY
Vol. 59
No. 9
2019