Improved Synthesis of CsN3
Michael Gerken a, Stefan Schneider a, Thorsten Schroer a, Ralf Haigesa, and Karl O. Christea,b,
*
a
Los Angeles, CA / USA, Loker Hydrocarbon Research Institute, University of Southern California
Edwards Air Force Base, CA / USA, Air Force Research Laboratory,
b
Received December 24th, 2001.
Dedicated to Professor Joachim Strähle on the Occasion of his 65th Birthday
Abstract. Cesium azide can conveniently be prepared from anhy-
drous CsF and (CH3)3SiN3 in SO2 solvent in high purity and yield.
In this reaction, the initially generated SO2FϪ anion is converted
in SO2 solvent to solvated azide, (SO2)nN3Ϫ, which is labile and
releases SO2 under dynamic vacuum yielding pure CsN3.
Keywords: Cesium azide; Fluorosulfite; Azidosulfite
Verbesserte Synthese von CsN3
Inhaltsübersicht. Caesiumazid kann bequem durch die Reaktion
von wasserfreiem CsF und (CH3)3SiN3 in SO2-Lösung in hoher
Reinheit und Ausbeute dargestellt werden. In dieser Reaktion wird
das zuerst gebildete SO2FϪ-Anion in SO2-Lösung zu dem solvati-
sierten Azid, (SO2)nN3 umgesetzt, das im dynamischen Vakuum
labil ist und unter SO2-Verlust reines CsN3 ergibt.
Ϫ
Sodium azide is a widely used reagent and is technically prepared
form NaNH2 and N2O [1]. The heavier alkali metal azides are gen-
erally prepared starting from NaN3. Two general methodologies for
the preparation of heavier alkali metal azides such as CsN3 have
been employed. The most common preparative route utilizes an
aqueous solution of HN3 which is neutralized by the corresponding
alkali metal hydroxide or carbonate [2Ϫ4]. Aqueous HN3 is gener-
ally prepared from NaN3 and H2SO4 [2]. In the second approach,
cesium and rubidium azide have been prepared via ion exchange
chromatography starting from aqueous NaN3 [5]. Since the hand-
ling of HN3 is potentially hazardous, a facile synthetic route to
CsN3 without the use of HN3 is highly desirable. Circumventing
the use of HN3 and laborious chromatographic techniques,
[N(CH3)4][N3] has been prepared from [N(CH3)4][F] and
(CH3)3SiN3 in CH3CN solvent [6]. In the present note, we present
present. The sluggishness of these reactions is presumably a conse-
quence of the insufficient solubility of CsF in CH3CN and
(CH3)3SiN3. The removal of (CH3)3SiF and addition of fresh
(CH3)3SiN3 did not result in a significantly faster conversion, indi-
cating either the absence of an equilibrium reaction or a coating of
the starting material by the product.
Anhydrous CsF reacts with SO2 solvent to the fluorosulfite anion,
SO2FϪ (eq. (1)) [7]. The reaction of [Cs][SO2F] suspended in SO2
with excess (CH3)3SiN3 results in complete azide-fluoride exchange
within less than one hour yielding a clear, yellow solution of
[Cs][(SO2)nN3] according to eq. (2).
Ǟ
CsF ϩ SO2 ᎏᎏ [Cs][SO2F]
(1)
SO2
Ǟ
[Cs][SO2F] ϩ (CH3)3SiN3 ϩ nSO2 ᎏᎏ
a
new facile laboratory preparation of CsN3 starting from
(CH3)3SiN3 and CsF in SO2 solvent.
[Cs][(SO2)nϩ1N3] ϩ (CH3)3SiF
(2)
Removal of the volatiles (SO2 and (CH3)3SiF) at ambient tempera-
ture results in precipitation of yellow [Cs][(SO2)2N3] which is con-
verted to [Cs][SO2N3] and [Cs][N3] upon prolonged pumping [8,9].
Pure [Cs][N3] is obtained after SO2 removal under dynamic vacuum
at 55 °C yielding a white solid. Since [Cs][SO2F] does not lose SO2
Results and Discussion
In analogy to the synthesis of [N(CH3)4][N3], the preparation of
CsN3 was attempted from anhydrous CsF and excess (CH3)3SiN3
in refluxing CH3CN solvent. The reaction in CH3CN solvent was
found to be slow and did not yield pure CsN3 even after five days.
The reaction of CsF with neat (CH3)3SiN3 was also found to be
slow; even after three days at temperatures close to the boiling
point of (CH3)3SiN3 (93 °C) significant amounts of CsF were still
Ϫ
at 55 °C, the complete conversion of FϪ to N3 can be verified
by the absence of signals associated with the SO2FϪ anion in the
Raman spectrum.
Experimental
Materials and Apparatus. All volatile materials were handled in a
Pyrex vacuum line equipped with Kontes Teflon valves. Nonvolatile
materials were handled in the dry argon atmosphere of a dry box.
The solvents, CH3CN (Baker) and SO2 (Aldrich, >99.9%) were
dried over P4O10 and CaH2 and were freshly distilled prior to use.
The CsF (KBI) was fused in a platinum crucible, transferred while
hot to the dry box, and finely powdered. Trimethylsilyl azide (Ald-
* Prof. K. O. Christe
Loker Hydrocarbon Research Institute, University of Southern
California
University Park
Los Angeles, CA 90089-1661/ USA
FAX: 001-(213) 740 6679
E-mail: karl.christe@edwards.af.mil
Z. Anorg. Allg. Chem. 2002, 628, 909Ϫ910 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 0044Ϫ2313/02/628/909Ϫ910 $ 20.00ϩ.50/0
909
Gerken, Michael
