New Synthesis of Diethyl Trimethylsilyl Phosphite

Article abstract of DOI:10.1134/S1070428019090276

Diethyl phosphonate rapidly reacted with hexamethyldisilazane at 20°C in the presence of 52 mol % of zinc(II) chloride to give 76% of diethyl trimethylsilyl phosphite.

Full text of DOI:10.1134/S1070428019090276

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2019, Vol. 55, No. 9, pp. 1442–1443. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Organicheskoi Khimii, 2019, Vol. 55, No. 9, pp. 1469–1471.
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New Synthesis of Diethyl Trimethylsilyl Phosphite
V. P. Morgalyuka,* T. V. Strelkovaa, A. G. Buyanovskayaa, and V. K. Brela
a Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, Russia
*e-mail: morgaliuk@mail.ru
Received March 5, 2019; revised April 9, 2019; accepted April 22, 2019
Abstract—Diethyl phosphonate rapidly reacted with hexamethyldisilazane at 20°C in the presence of
52 mol % of zinc(II) chloride to give 76% of diethyl trimethylsilyl phosphite.
Keywords: diethyl phosphonate, hexamethyldisilazane, diethyl trimethylsilyl phosphite, catalysis, catalyst–
reactant, zinc(II) chloride.
DOI: 10.1134/S1070428019090276
Michaelis–Arbuzov reaction is one of the key reac-
tions in the synthesis of organophosphorus com-
pounds. It was shown that Michaelis–Arbuzov reaction
with trimethylsilyl esters of phosphorus(III) acids
provides better yields than analogous reaction with
trialkyl phosphites [1, 2]. Diethyl trimethylsilyl phos-
phite (1) is a needed reagent for these reactions, and it
is widely used in the synthesis of various organophos-
phorus compounds [2, 3]. A known procedure for the
preparation of phosphite 1 is based on the reaction of
diethyl phosphonate (2) with chloro(trimethyl)silane in
the presence of bases [4, 5]. Another method involves
the reaction of 2 with hexamethyldisilazane (3);
however, this reaction requires fairly harsh conditions,
heating for 2 h at 110°C in an inert atmosphere [6, 7].
the reaction mixture recorded after 20 h). A probable
reason may be reversibility of this reaction in which
the equilibrium established at 72–82% conversion of 2
(Scheme 1).
In order to improve the yield and shift the equilib-
rium toward formation of target phosphite 1, it was
necessary to find a catalyst capable of not only facili-
tating the reaction but also binding liberated ammonia
thus shifting the equilibrium to the right, i.e., acting as
a catalyst–reactant. Among the examined salts, the
most suitable one proved to be cheap and accessible
zinc(II) chloride. It efficiently bound ammonia to form
strong complex [Zn(NH3)2]Cl2 [11] (decomposition
temperature >245°C [12]) and therefore shifted the re-
action equilibrium toward target diethyl trimethylsilyl
phosphite (1) (Scheme 2).
In continuation of our previously initiated studies
[8–10], we were the first to demonstrate that the reac-
tion of diethyl phosphonate (2) with hexamethyldi-
silazane (3) can be catalyzed by Li, Mg, Ca, Sr, Ni, Zn,
and Cu(I) chlorides and bromides, as well as by potas-
sium fluoride (Scheme 1). In the presence of a catalytic
amount (1–2 mol %) of these salts, phosphonate 2
reacted with hexamethyldisilazane (3) even at 20°C
with evolution of heat (the reaction mixture spontane-
ously warmed up to 40–45°C). The reaction was fairly
fast, but in all cases the conversion of 2 did not
Scheme 2.
ZnCl2 (0.5 equiv)
20°C
2(EtO)2P(O)H + (Me3Si)2NH
2(EtO)2POSiMe3
–[Zn(NH3)2]Cl2
2
3
1
Diethyl phosphonate (2) reacted with hexamethyl-
disilazane (3) in the presence of ZnCl2 at 20°C; the
optimal amount of the catalyst was 52 mol % (relative
to liberated ammonia, Table 1). After 2 h, the conver-
sion of 2 correlated with the number of ammonia
molecules in [Zn(NH3)2]Cl2, equal to 2 [11]. In the
presence of 20 mol % of ZnCl2, the conversion of 2
was 42%, in the presence of 30 mol % of ZnCl2, the
conversion was 58%, and so on (Table 1), which con-
31
exceed 72–82% (according to the P NMR spectra of
Scheme 1.
Catalyst
2(EtO)2P(O)H + (Me3Si)2NH
2(EtO)2POSiMe3 + NH3
2
3
1
1442

NEW SYNTHESIS OF DIETHYL TRIMETHYLSILYL PHOSPHITE
1443
Table 1. Conversion of diethyl phosphonate (2), depending
on the reaction time and amount of ZnCl2
phosphorus and silicon contents were determined spec-
trophotometrically using a Cary 100 Scan instrument.
Conversion, %
ZnCl2,
ACKNOWLEDGMENTS
mol %
0.5 h
1 h
2 h
20 h
This study was performed under financial support
by the Ministry of Science and Higher Education of
the Russian Federation using the equipment of the
Molecular Structure Research Center at the
Nesmeyanov Institute of Organoelement Compounds
(Russian Academy of Sciences).
20
30
40
50
52
41
56
42
57
42
58
74
77
75
78
80
81
96
94
95
96
0.99.4
0.99.4
0.99.4
0.99.4
CONFLICT OF INTERESTS
No conflict of interests is declared by the authors.
REFERENCES
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likely to be related to losses during the isolation proce-
dure because of its volatility under reduced pressure,
which is typical of trimethylsilyl ethers.
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 9 2019