PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
3
corresponding H-phosphonate diesters and benzaldehyde Synthesis
was also known,[12] however, the C–P bond cleavage of
a-HDPO was not reported. Therefore, we started to explore
the stability of a-HDPO. As shown in Table 2, when
a-HDPO was dissolved in CH2Cl2, as time went by, it was
gradually converted to MesCHO and Ph2P(O)H (runs 1–3).
Addition of a base or an acid accelerated this transformation
(runs 4 and 6), while addition of water did not affect the
result (run 5). Interestingly, when the temperature was
reduced to 0 ꢀC, a-HDPO became so stable that it remained
intact even in 16 h (runs 7–8). On the contrary, at an ele-
vated temperature, a-HDPO rapidly decomposed and gener-
ated quantitative yield of Ph2P(O)H and MesCHO (runs
9–10). Other solvents were also screened, it was shown that,
Experimental procedures for the preparation of a-HDPO
To a Schleck tube was charged with diphenylphosphine oxide
(20.0 mmol, 4.04 g), 2,4,6-trimethylbenzaldehyde (40.0 mmol,
5.9 mL), and toluene (30.0 mL), then the mixture was stirred at
room temperature for 16 h, the residue was washed with
EtOAc (50 mL ꢂ 5) and recrystallization, affording a-HDPO
with 6.3 g (white solid, 18.1 mmol, 90% yield); 1H NMR
(400 MHz, CDCl3): d 7.79–7.84 (m, 2H), 7.53–7.55 (m, 1H),
7.40–7.48 (m, 5H), 7.23–7.27 (m, 2H), 6.67 (s, 2H), 5.90 (t, 1H,
J ¼ 6 Hz) , 4.18 (q, 1H, J ¼ 12.8, 5.6 Hz), 2.19 (s, 3H), 1.97–2.15
(br, 6H); 13C NMR (100 MHz, CDCl3): d 137.47, 132.21 (d,
JP–C ¼ 8.6 Hz), 131.93, 131.84, 131.32 (d, JP–C ¼ 42 Hz), 130.39
(d, JP–C ¼ 43.8 Hz), 129.61, 128.67 (d, JP–C ¼ 11.2 Hz), 128.09
in MeOH, the conversion of a-HDPO was the lowest (runs (d, JP–C ¼ 11.4 Hz), 71.73 (d, JP–C ¼ 77.3 Hz), 21.15, 20.90; 31P
11–13) at 70 ꢀC. The above results would help for investigat-
ing the reactions involving a-HDPO.
NMR (162 MHz, CDCl3): d 31.65.
Experimental procedures of investigation on the reaction
conditions of oxidizing a-HDPO to TPO
A mixture of a-HDPO (0.05 mmol, 17.5 mg) in CH2Cl2
(2.0 mL) and MnO2 (1.0 mmol, 89.6 mg) was stirred at room
Conclusions
In summary, we have fixed the optimized oxidation condi- temperature for 1 h. After removal of MnO2 (via centrifiga-
tion) and the solvent (vacuumed under reduced pressure),
tions of a-HDPO to (2,4,6-trimethylbenzoyl)diphenylphos-
phine oxide (TPO) by magnesium dioxide provided by Japan
Metals & Chemicals Co. Ltd. Toluene is better than CH2Cl2.
The used MnO2 showed good oxidation efficiency after recov-
ering by O2. On the other hand, the study on decomposition
of the a-HDPO revealed that low temperature contribute to
the stability of a-HDPO, and MeOH was a better solvent for
slowing down the decomposition of the a-HDPO.
1
the crude product was diluted in CDCl3 and detected by H
1
NMR. The H NMR yield was calculated by integrating the
single peaks at dH ¼ 6.798 ppm (TPO), dH ¼ 6.687 ppm
(a-HDPO) and dH ¼ 6.689 ppm (MesCHO) based on
a-HDPO used. TPO prepared by the scaled-up reaction
(0.5 mmol) was purified through a silica gel column with
EtOAc/Hexane ¼ 1/2 as eluent. 1H NMR (400 MHz,
CDCl3): d 7.96–7.99 (m, 4H), 7.48–7.54 (m, 6H), 6.79 (s,
2H), 2.25 (s, 3H), 2.02 (s, 6H); 13C NMR (100 MHz, CDCl3):
d
220.13 (d, JP–C ¼ 72.2 Hz), 140.69, 136.34 (d,
JP–C ¼ 39.6 Hz), 134.99, 132.52 (d, JP–C ¼ 2.5 Hz), 131.98 (d,
Experimental
JP–C ¼ 8.7 Hz), 129.76 (d, JP–C ¼ 92.8 Hz), 128.99, 128.84 (d, J
¼ 11.8 Hz), 21.31, 19.79; 31P NMR (162 MHz, CDCl3):
Materials
P–C
d 13.80.
Common solvents and reagents including 2,4,6-trimethyl-
benzaldehyde were purchased from TCI. Diphenylphosphine
oxide was provided by Katayama Co., Ltd. MnO2-A was
purchased from Kishida Chemistry Ltd. MnO2-B was pur-
chased from SIGMA-ALDRICH. MnO2-C was purchased
Experimental procedures of investigation on the equilib-
rium of a-HDPO and Ph2P(O)H
A mixture of a-HDPO (0.05 mmol) and solvent (2.0 mL)
from Merck KGaA. MnO2-D (D1, D2, D3) were purchased was placed at 25 ꢀC for 1 h. Yield was detected by 31P NMR
of the crude mixture (1: 30 ppm; 2: 21 ppm).
from Japan Metals & Chemicals Co. Ltd.
Disclosure statement
Instrumentation
No potential conflict of interest was reported by the authors.
1H, 13C, and 31P NMR were recorded on a JEOL JNM-
ECS400 (400 MHz for 1H NMR, 100 MHz for 13C NMR, Funding
and 162 MHz for 31P NMR spectroscopy). Chemical shifts
This work was primarily supported by joint research between AIST
and Maruzen Petrochemical Co., Ltd.
for 1H NMR are referred to internal Me4Si (0 ppm) and
reported as follows: chemical shift (d ppm), multiplicity,
coupling constant (Hz), and integration. Chemical shifts for
31P NMR were relative to H3PO4 (85% solution in D2O,
ORCID
1
0 ppm). The Supplemental Materials contain sample H, 13C,
and 31P NMR spectra for the products (Figures S1–S6).
Jian-Qiu Zhang