J Am Oil Chem Soc (2013) 90:563–570
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relaxation delay. The H-NMR spectra were referenced to
ground and dried in vacuo to afford purified pale blue DPAS
in 65 % yield. 1H NMR ((CD3)2SO, d ppm, Fig. 1b): 11.09
(s, –NH2?–), 7.20 (t, –CHb=), 7.07 (d, =CHa–C–N), and
6.79 (t, =CHc–). 13C NMR ((CD3)2SO, d ppm, Fig. 1b):
143.54 (=C–N), 129.34 (–CHb=), 119.82 (=CHc–), and
116.87 (=CHa–C–N).
the proton resonance resulting from incomplete deuteration
of (CD3)2SO (d 2.50) with TMS (d 0.00), while the
13C-NMR spectra were similarly referenced to (CD3)2SO
(d 39.51). The assignments of the exchangeable protons of
?
the NH and [NH2 groups were determined and assigned
by addition of small quantities of D2O. NMR samples were
prepared using a freeze–pump–thaw procedure. The liquid
was frozen in an acetone/dry ice bath, the air was removed
under vacuum, nitrogen was introduced, and the sample was
brought to room temperature (RT). This freeze–pump–thaw
process was repeated a total of three times for each sample.
Infrared spectroscopic analysis was conducted with a Bru-
ker IR equipped with an ATR platinum diamond crystal.
The absorbance of each sample (10 mg) was taken at
wavelength ranges of 4,000–500 cm-1. Twenty-four scans
Synthesis of Diphenylamine Hydrochloride
DPA (1 g, 5.9 mmol) was dissolved in hexanes (20 mL) in
a round-bottom flask fitted with an addition funnel con-
taining 12 M aqueous HCl (0.65 mL, 7.8 mmol). At RT,
the HCl was added dropwise from the addition funnel to
the DPA solution while stirring. The mixture was stirred
under nitrogen at RT for *48 h. As the reaction pro-
ceeded, solids precipitated from the hexanes solvent. The
solids were then vacuum filtered to remove the liquid and
provided 88 % yield of light pink solid, crude DPACl.
Crude DPACl was then purified by recrystallization:
DPACl (2 g, 9.7 mmol) was dissolved in ethanol (30 mL)
in a 60 °C oil bath and, after cooling, EA was slowly
added. White solids were formed after chilling for 4 days at
-15 °C. The solids were gravity filtered and washed with
cold ethanol to afford pale light green pure DPACl in 50 %
yield. 1H-NMR ((CD3)2SO, d ppm, Fig. 1c): 11.06 (s,
–NH2?–), 7.20 (t, –CHb=), 7.09 (d,=CHa–), and 6.80
(t,=CHc–). 13C NMR ((CD3)2SO, d ppm, Fig. 1c): 143.38
(=C–), 129.19 (–CHb=), 119.83 (=CHc–), and 116.90
(=CHa–C–N).
were collected at a resolution of 4 cm-1
.
Synthesis of Diphenylamine Sulfate
In a nitrogen atmosphere, DPA (10 g, 59 mmol) was dis-
solved in hexanes (200 mL) in a three-neck round-bottom
flask fitted with an addition funnel containing H2SO4
(6.5 mL, 115 mmol). At RT, H2SO4 was added dropwise
from the addition funnel to the DPA solution while stirring.
The mixture was allowed to react at RT for 48 h. Upon
completion, the hexanes were decanted off, and the
remaining yellow emulsion was rinsed with EA
(*125 mL) to produce a fine off-white solid crude product
(DPAS). The solid was vacuum filtered using a Bu¨chner
funnel with a 90-mm Grade 2 Whatman filter paper
(Maidstone, England) to remove EA. The solid was ground
using a mortar and pestle and dried in vacuo, resulting in a
91 % yield of crude off-white DPAS. Since the H2SO4 used
to make this salt complex could also catalyze FFA esteri-
fication, the crude DPAS salt was thoroughly purified to
ensure that it was free from liquid acid. Crude DPAS was
transferred to a 125-mL centrifuge flask with 80 mL EA and
stirred for 30 min. The suspension was centrifuged at RT at
4,0009g for 10 min, and the liquid phase was decanted.
The solid was then mixed for 30 min with 80 mL EA,
centrifuged, and drained. This washing process was repe-
ated eight more times followed by one final vacuum filtra-
tion with EA wash. This procedure resulted in grey DPAS in
52 % yield. While this method probably removed residual
liquid H2SO4, we were still concerned that there could be
residual acid trapped in the salt. Thus, we developed a
recrystallization procedure to purify the crude DPAS. We
first dissolved the salt (300 mg, 1.12 mmol) in methanol
(0.6 mL) in an 85 °C oil bath. The solution was allowed to
cool to RT, after which EA (10 mL) was slowly added
to form two distinct layers. The mixture was then placed in a
-15 °C freezer for 5 days. The crystals which formed were
Transesterification and/or Esterification of Fatty Acids
A typical reaction was performed as follows. Pure oil (oleic
acid, 2 g, 6.4 mmol) or used grease (yellow and brown
greases, 2 g, 0.6 mmol or trap grease, 0.5 g, 1.6 mmol)
was reacted with methanol (20 equiv. to FFA in the oil) and
catalyst (0.5 mol% to FFA in the oil) in a tightly capped
conical vial sealed with Teflon tape with heating and stir-
ring at 125 °C for 1 h. After the reaction, the solution was
transferred with hexanes (*2 mL) and dried in vacuo at
RT. The resultant oil was filtered with a glass syringe fitted
with a 0.45 lm Millipore PTFE filter (Billerica, MA,
USA). A small aliquot was diluted with hexanes (1.5 mL)
and analyzed by HPLC.
Results and Discussion
Two homogeneous diphenylammonium salts, DPAS and
DPACl, were investigated for FAME synthesis. The
structures of the salts are shown in Fig. 1b, c. Although the
salts are commercially available, there is very little
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