New access to organoacyloxytrialkylsilanes

Article abstract of DOI:10.1080/00397910701462740

In this article, we present the synthesis of acetoxytributylsilane, obtained from methoxytributylsilane and acetic anhydride, under different conditions (catalyst, temperature, reaction time). Access to other acyloxytributylsilanes from different anhydrides is also presented. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701462740

Synthetic Communicationsw, 37: 3879–3884, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701462740
New Access to Organoacyloxytrialkylsilanes
`
David Mancardi and Michele Sindt
Laboratory of Chemistry and Methodology for the Environment (LCME),
Paul Verlaine-Metz University, Metz, France
Jean-Michel Paul
Arkema, Research and Development Centre (CRDE), Saint-Avold,
France
Jean-Luc Mieloszynski
Laboratory of Chemistry and Methodology for the Environment (LCME),
Paul Verlaine-Metz University, Metz, France
Abstract: In this article, we present the synthesis of acetoxytributylsilane, obtained
from methoxytributylsilane and acetic anhydride, under different conditions
(catalyst, temperature, reaction time). Access to other acyloxytributylsilanes from
different anhydrides is also presented.
Keywords: acetoxytributylsilane, acyloxytributylsilane, catalyst, silane
INTRODUCTION
In organic chemistry, silanes have been used for years as protecting group
reagents. They can protect various functions,[1] such as alcohols, amines,
and acids. Silanes are still intermediates in organic synthesis, or specialty
products of agro and pharmaceutical chemistry. Among numerous silylated
derivatives, halosilanes and silanols are the most frequently used. Acetoxyalk-
ylsilanes constitute an alternative to those compounds and are often very
sensitive to experimental conditions. For instance, Schuyen et al.[2] have
Received in Poland October 4, 2006
`
Address correspondence to Michele Sindt, Laboratory of Chemistry and Method-
ology for the Environment (LCME), Paul Verlaine-Metz University, Metz, France.
E-mail: sindt@univ-metz.fr
3879

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D. Mancardi et al.
shown that acetoxysilanes could replace dimethyldichlorosilanes when used
as a water-repellent coating on cotton textile. By hydrolysis, acetoxysilane
forms less corrosives acids than hydrochloric acid produced by halosilanes,
which weaken seriously clothes.
Those compounds, beside their use as protecting groups, find application
as reticulating agents at room temperature in vulcanization of silicon rubber in
single-component systems.[3]
Organoacyloxytrialkylsilanes are generally prepared by reaction of
chlorosilane with acid or acid anhydride.[3] Papers describe the preparation
of acyloxysilane from trialkylsilanes by reaction with carboxylic acid and
catalyzed by mineral acid, iodine, copper complex,[4] or palladium acetate.[5]
Disiloxanes are also good precursors, by reaction with acid anhydride in
presence of zinc chloride as catalyst.[6] This reaction failed with maleic and
succinic anhydride.
In this article, we present the synthesis of acetoxytributylsilane (1a, R ¼
Me). The reaction between methoxytributylsilane and acetic anhydride has
been studied under different conditions (catalyst, temperature, reaction
time). Access to other acyloxytributylsilanes 1 from different anhydrides is
also presented (Scheme 1).
RESULTS AND DISCUSSION
In the literature, acetoxytrialkylsilanes are often prepared by reaction between
trialkylsilane and carboxylic acid or their mercury salt because of the lability
of hydrogen in the Si-H bond, subject to hydrolysis cleavage.[7] In this case,
the use of a catalyst is necessary, such as strong mineral acids (H2SO4, HI),
aluminium, iodine, or colloidal nickel; recent works show the efficiency of
copper complex[4] or palladium acetate.[5] Substitution of hydrogen in the
Si-H bond by the acetoxyl group is described in the case of trialkoxysilane[8]
(Scheme 2).
In equimolar quantities of acetic anhydride and triethoxysilane, the
reaction leads to the interchange of acetate and ethoxyl group; only an
excess causes the substitution of hydrogen.
To obtain acetoxytributylsilane (1a, R ¼ Me), we first explore the
reaction of tributylsilane with acetic anhydride in presence of different
catalysts (Table 1).
The reaction is carried out without solvent under nitrogen at 908C. This
temperature was found to be better than 80 and 858C. Three catalysts
among those tested gave relatively good yields (entries 1, 4, and 7).
Scheme 1. Synthesis of acyloxytributylsilanes.

New Access to Organoacyloxytrialkylsilanes
3881
Scheme 2. Synthesis from triethoxysilane.
Amberlyst 15 is less efficient than zinc chloride with the same reaction
time. K10 montmorillonite gives about 60% yield in only 4.5 h. During
the reaction, some by-products are formed, such as hexabutyldisiloxane
[(Bu3Si)2O] (,8%) and tributylsilanol (Bu3SiOH) (,2%), observed by
gas chromatography-mass spectroscopy (GC-MS).
We turned to the synthesis of acetoxytributylsilane (1a, R ¼ Me), using
methoxytributylsilaneinstead ofH-tributylsilane. ResultsarereportedinTable2.
With 1-methylimidazole (entry 3), Amberlyst 15 (entry 4), and K10 mon-
tmorillonite (entry 7), yields are up to 80%. Moreover, we can see that the use
of methoxytributylsilane gave better results than the use of H-tributylsilane.
Amberlyst 15 has been chosen as catalyst of the reaction of methoxytributyl-
silane with other anhydrides (Table 3).
The access to new acyloxytributylsilanes is possible from propionic,
butyric, or benzylic anhydride with relatively good yields (49–77%).
However, the conditions of the reactions did not permit us to obtain the
same result with succinic or phtalic anhydride (yields: 8–14%). This is
probably because in those two cases, compounds are solid and cause hetero-
geneity in the media.
Table 1. Influence of catalyst in the synthesis of acetoxytributylsilane 1a from tribu-
tylsilanea
Entry
Catalyst
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
ZnCl2
24
24
24
24
72
24
4.5
24
58
4.5
4
4-Dimethylaminopyridine (DMAP)
1-Methylimidazole (1-MIM)
Amberlyst 15
46.5
,1
,1
59
Triphenylphosphine
KSF Montmorillonite
K10 Montmorillonite
2-Chloro-1-methylpyridinium iodide
(CMPI)
,1
9
10
11
12
Imidazole
24
24
24
28
0
0
0
0
Acetylacetonate de zirconium
Trimethylchlorosilane
—
aReaction conditions: tributylsilane: 10 mmol, acetic anhydride: 10 mmol, catalyst:
5%wt, temp.: 908C.

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D. Mancardi et al.
Table 2. Influence of catalyst in the preparation of acetoxytributylsilane 1a from
methoxytributylsilanea
Entry
Catalyst
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
ZnCl2
2
6
72
66
85
86
5.5
72
79
68
4-Dimethylaminopyridine (DMAP)
1-Methylimidazole (1-MIM)
Amberlyst 15
24
2
Triphenylphosphine
KSF Montmorillonite
K10 Montmorillonite
2-Chloro-1-methylpyridinium iodide
(CMPI)
24
3.5
1.75
72
9
10
11
13
14
Imidazole
24
12
36
0
N,N0-Dicyclohexylurea
1,10-Carbonyldiimidazole
Trimethylchlorosilane
—
24
12
61
50
30
288
aReaction conditions: methoxytributylsilane: 5 mmol, acetic anhydride: 5 mmol,
catalyst: 5%wt, temp. 908C.
EXPERIMENTAL
1H NMR and 13C NMR spectra were recorded on a Brucker AC-250 (250-
MHz) spectrometer with deuterated chloroform (CDCl3) as solvent with
chloroform (7.26 ppm) as internal reference. Chemical shifts are reported in
parts per million (ppm): s: singlet, d: doublet, t: triplet, q: quartet, and m:
multiplet, and coupling constants (J) are in Hertz. Mass spectra were
Table 3. Preparation of acyloxytributylsilane 1 from methoxytributylsilanea
Acid
anhydride
Entry
Product no.
Yield (%)
1
2
3
1b
1c
1d
Propionic
Butyric
Benzylic
70
77
49
aReaction conditions: methoxytributylsilane: 5 mmol, acid anhydride: 5 mmol,
catalyst: 5%wt, temp. 908C, catalyst: Amberlyst 15.

New Access to Organoacyloxytrialkylsilanes
3883
recorded on a Hewlett-Packard (model 5971 A) in electronic impact (70 eV)
coupling with a gas chromatograph equipped with a capillary column (WCOT
fused silica, 25 m ꢀ 0.25 mm), whose stationary phase is CPSil5CB
(0.12 mm). Helium is used as gas carrier, detector temperature is 3008C,
and injector temperature is 2808C.
Typical Procedure
A mixture of methoxytributylsilane (5 mmol), acid anhydride (5 mmol), and
catalyst (5% wt) is stirred at 908C under nitrogen. The catalyst is filtered,
and the product is purified by distillation under low pressure.
1a: Bp: 1028C (8.7 1022 torr) 1H NMR (CDCl3): d 2.05 (3H, s), 1.33 (6H, m),
0.89 (9H, t, J ¼ 6.6 Hz), 0.76 (6H, m); 13C NMR (CDCl3): d 171.53, 26.51,
24.68, 22.68, 13.91, 13.41; GC-MS (70 eV): 43 (15), 85 (5), 145 (10), 210
1
(100). 1b: Bp: 1158C (8.7 1022 torr); H NMR (CDCl3): d 2.32 (2H, q,
J ¼ 7.5 Hz), 1.29 (12H, m), 1.09 (3H, t, J ¼ 7.6 Hz), 0.87 (9H, t,
J ¼ 6.9 Hz), 0.76 (6H, m); 13C NMR (CDCl3): d 174.84, 29.16, 26.31,
25.07, 13.6, 13.2, 9.27; GC-MS (70 eV): 57 (10), 73 (6), 159 (12), 199 (2),
1
215 (100). 1c: Bp: 1228C (6.2 1022 torr). H NMR (CDCl3): d 2.27 (2H, t,
J ¼ 7.3 Hz), 1.63 (2H, st), 1.30 (12H, m), 1.02 (3H, t, J ¼ 7.2 Hz), 0.94
(9H, m), 0.73 (6H, m); 13C NMR (CDCl3): d 174.03, 37.88, 26.26, 25.1,
18.55, 13.7, 13.25; GC-MS (70 eV): 43 (10), 71 (11), 173 (4), 199 (5), 229
1
(100). 1d: Bp: 153–1568C (5.7 1022 torr) H NMR (CDCl3): d 8.09 (2H,
m), 7.59 (1H, m), 7.46 (2H, m), 1.31 (12H, m), 0.91 (9H, m), 0.77 (6H, m);
13C NMR (CDCl3): d 162.24, 132.69, 130.04 (2C), 129.60, 128.47 (2C),
26.26, 25.40, 13.77, 13.27; GC-MS (70 eV): 105 (65), 205 (5), 263 (100).
CONCLUSION
We have presented here a new route to synthesize organoacyloxytrialkylsi-
lanes and particularly acetoxytributylsilane by reaction between H-tributylsi-
lanes or methoxytributylsilane and acetic anhydride with different catalysts.
The reaction with H-tributylsilane did not take place except with the use of
three catalysts: ZnCl2, Amberlyst 15, and montmorillonite K10, but yields
still remained average. Better results were obtained with methoxytributylsi-
lane and reached to 86% with Amberlyst 15. This method has been
extended to other anhydrides with success.
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