T. Wang et al.
of acyl chloride and alkoxyphosphine. Method II is two-
step reaction: (1) aldehyde reacts with diphenylphosphine
oxide to form α-hydroxyphosphine oxide; (2) followed by
oxidation of α-hydroxyphosphine oxide to MAPOs. Com-
paratively, Method I has limited substrate tolerance and
forms by-product of alkyl chloride (difficult to handle) [15];
Method II has the advantage of mild reaction condition and
broad substrate scope. Thus, Method II is commonly used
in MAPOs synthesis.
for catalyst preparation. For comparison, the performance
of VO(acac) + TBHP system was tested.
2
2 Experimental
2.1 Catalyst Preparation
MCM-41 supported vanadium (V/MCM-41) catalysts
were prepared by solid state impregnation, similar as the
procedure in literature [23]. Typically, vanadium precur-
sor (NH VO or V O , Aladdin) and MCM-41 (JCNANO
It is known that the oxidation of alcohols to the corre-
sponding carbonyl compounds is of great importance both in
academia and in industry. Thus, plenty of studies were car-
ried out to obtain the optimized and environmental friendly
oxidation system [16–19]. Based on these, many oxidants
4
3
2
5
Tech Co., Ltd) were added to an agate mortar and manually
ground for 0.5 h. The ground mixture was then transferred
to a crucible and calcined in air at 550 °C for 4 h. The theo-
retical V loading was set as 7 wt%, which was then analyzed
(
such as chromium trioxide, potassium permanganate,
iodobenzenediaceate, vanadyl acetylacetonate, manganese
dioxide, pyridinium dichromate, etc.) have been used for the
oxidation of α-hydroxyphosphine oxide [20]. However, the
instability of α-hydroxyphosphine oxide under common oxi-
dation conditions makes all the aforementioned experiments
fail [20, 21]. Up to now, only two oxidation systems could
by ICP (Table S2). Obtained samples were denoted as V /M
1
(NH VO as precursor) and V /M (V O as precursor).
4
3
2
2
5
2.2 Catalyst Characterization
give satisfactory yield of MAPOs: (1) active MnO [20];
Crystalline structures of the catalysts were investigated by
X-ray diffraction (XRD) measurements (D/Max250pc). The
morphologies of samples were recorded using SEM (Nova
Nano SEM450) and TEM (Tecnai G2 20). The textural
2
(
2) combination of vanadyl acetylacetonate (VO(acac) ) and
2
tert-butylhydroperoxide (TBHP) [22]. For the first oxidation
system, huge amounts (20 times to the substrate) of active
MnO are needed [20]. For the second system, large usage
properties of samples were analyzed by low temperature N
2
2
(
ca. 35 times to the substrate) of VO(acac) causes environ-
adsorption/desorption using an Autosorb-IQ gas absorp-
tion analyzer and the specific surface areas were calculated
using the BET equation. The vanadium loading was deter-
mined by ICP analysis (Optima 7300 DV). Chemical states
of vanadium in the catalysts were determined by UV–Vis
(UV-3031, Shimadzu).
2
mental pollution [22]. Taking account of the importance of
MAPOs in light-curing and the drawbacks of the two oxi-
dation systems, we decided to explore highly effective and
environmental friendly synthesis using Method II method
for MAPOs. 2,4,6-trimethylbenzoyldipenylphosphine oxide
(
TPO, Fig. 1) is chosen as the target MAPOs in this study
and Method II is used in the synthesis. Initially, Mn, Mo, W
and Fe were chosen as active metal for the oxidation syn-
thesis of TPO. Both zeolites and metal oxides were used as
support. However, the experiments failed: in most cases no
TPO was detected after reaction (Table S1). So MCM-41
supported vanadium (V/MCM-41) was designed as the oxi-
dation catalyst for the synthesis of TPO. Inorganic vanadium
compounds (NH VO and V O ) were used as precursors
2.3 Oxidation Synthesis
of 2,4,6‑Trimethylbenzoyldipenylphosphine
Oxide (TPO)
TPO was synthesized through the oxidation of α-hydroxy-
(2,4,6-trimethylbenzyl)-diphenyl phosphine oxide (α-HDPO,
Scheme 1). α-HDPO was obtained by the reaction of diphe-
nylphosphine oxide (DPO) and 2,4,6-trimethylbenzalde-
hyde (TMBA). The structure of product was confirmed by
4
3
2
5
1
31
13
H NMR, P NMR and C NMR (shown in Supporting
Information). Typical procedure was as follows.
Firstly, TMBA (0.1 mol) and DPO (0.1 mol) were dis-
solved in 150 mL 1,2-dichloroethane (DCM). The mixture
was stirred at room temperature for 6 h (TLC analysis).
The solvent was evaporated in vacuo, and crude product of
α-HDPO was purified by washing with EtOAc (3×80 mL).
Secondly, TBHP (10.28 mmol) was added to a stirred
solution of α-HDPO (8.57 mmol) and catalyst (1 mol% V
as α-HDPO) in 30 mL DCM at 5 °C. After 30 min, the mix-
ture was then stirred at room temperature for another 6 h.
Fig. 1 Chemical structure of 2,4,6-trimethylbenzoyldipenylphosphine
oxide (TPO)
1
3