On the influence of the nature of the iron(III) salt catalyst precursor for the preparation of sodium amide

Article abstract of DOI:10.1016/j.crci.2010.11.008

Our recent experiments, for the formation of sodium amide from liquid ammonia and sodium metal, revealed the necessity to employ Fe(NO ₃)₃?9H₂O as the catalyst precursor, and not FeCl₃. In the presence of FeCl₃, we observed several times the ignition of the mixture during the hydrolysis, and the desired product was not obtained.

Full text of DOI:10.1016/j.crci.2010.11.008

C. R. Chimie 14 (2011) 434–436
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Preliminary communication/Communication
On the influence of the nature of the iron(III) salt catalyst precursor
for the preparation of sodium amide
a
b,
a
Nicolas Galy , Henri Doucet *, Maurice Santelli
a
Laboratoire chimie Provence, UMR 6264, facult e´ des sciences de St-J e´ r oˆ me, universit e´ d’Aix-Marseille, avenue Escadrille-Normandie-Niemen,
3397 Marseille cedex 20, France
1
b
Institut sciences chimiques de Rennes, UMR 6226, universit e´ de Rennes 1 « catalyse et organom e´ talliques », campus de Beaulieu, 35042 Rennes, France
A B S T R A C T
A R T I C L E I N F O
Article history:
Our recent experiments, for the formation of sodium amide from liquid ammonia and
sodium metal, revealed the necessity to employ Fe(NO O as the catalyst precursor,
ꢁ9H
and not FeCl . In the presence of FeCl , we observed several times the ignition of the
Received 21 May 2010
3
)
3
2
Accepted after revision 24 November 2010
Available online 28 January 2011
3
3
mixture during the hydrolysis, and the desired product was not obtained.
ß 2010 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Keywords:
Iron
Catalysis
Sodium amide
1
. Introduction
But, recently, instead of using iron(III) nitrate as the
3
catalyst precursor, we employed anhydrous FeCl in the
Our strategy for the synthesis of unnatural steroids
same amount. However, when this iron catalyst was
employed, the hydrolysis appeared to be a very dangerous
step. During the course of the hydrolysis, we observed
several times the ignition of the mixture. Moreover, after
usual work-up, the products 3 [4] and 4 [5] (Scheme 1)
corresponding to a drastic reduction of 1 were obtained,
and the formation of 2 was not observed. Clearly, in the
presence of iron trichloride, sodium amide has not been
formed and we have only, in the reaction mixture, the
sodium metal dissolved in the liquid ammonia. The
catalysis mechanism is uncertain, but appears to involve
the rapid reduction of iron(III) to very finely divided
metallic iron, which is probably the actual catalytic agent.
Without catalyst, the sodium amide is formed very slowly
[6]. Some old preparations describe the passing of dry
ammonia gas over the molten sodium [7].
involves the preparation of the benzocyclobutene 2 from
phenylpropiononitrile 1 according to the Mukaiyama
procedure [1]. For this cyclization reaction, a large excess
ofsodium amide(CAS number:7782-92-5) is employed. We
generally prepare this sodium amide in situ, by the addition
at À33 8C of pieces of sodium to liquid ammonia (2.5 L for
each mol of sodium) containing ꢀ0.6 mmol (2.5 g) of
coarsely powdered Fe(NO
2]; and then phenylpropiononitrile 1 was added. After
3
)
3
ꢁ9H
2
O for each mol of sodium
[
addition of diethyl ether, the ammonia was allowed to
evaporate, and solid ammonium chloride was added. Then,
classical work-up gave rise to 2 in 60% yield (Scheme 1).
2
. Results
During 10 years, we performed many successful
experiments according to the Mukaiyama protocol and
using undistilled ammonia from a commercial cylinder [3].
The first catalyst used for the preparation of sodium
amide by addition of sodium in liquid ammonia, was
divided platinum [8]. The use of iron salts, and specially
iron(III) nitrate has been described for the first time in
1934 [9]. Since these reports, many preparative methods
recommend the use of hydrated ferric nitrate, in particular
*
Corresponding author.
E-mail address: henri.doucet@univ-rennes1.fr (H. Doucet).
in the various synthetic methods described in Organic
1
631-0748/$ – see front matter ß 2010 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2010.11.008

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N. Galy et al. / C. R. Chimie 14 (2011) 434–436
435
Na
Fe(NO3)3 9H O
2
CN
Br
/
NH
3
MeO
CN
MeO
1
2
Scheme 1.
Syntheses [2] or Org. Proc. Res. Dev [10]. However, for some
reports including patents [11], and other procedures
described in Organic Synthesis [12], it is recommended
to use anhydrous ferric chloride [13]. Even a recent
encyclopedia such as e-EROS indicated ‘‘preparative
method: combination of ammonia, small quantities of
an iron(III) salt and sodium. . .’’ [14]. In a very detailed
study concerning the Birch reaction, industrial investiga-
tors showed that the ferric chloride catalyzes efficiently
the reaction between sodium and alcohols in liquid
ammonia [15]. Iron is a well-known transition metal
playing an important role as catalyst in organic syntheses
When the anhydrous FeCl
3
salt was employed, when
the mixture was pourred on ice, the presence of some
pyrophoric compounds result in the repeated ignition of
the mixture. After hydrolysis, the crude product was
chromatographed on silica gel to give 3-ethylanisole 3
(CAS number: 10568-38-4) (16%) and 3-ethylphenol 4
1
(CAS number: 620-17-7) (9%). 3-Ethylanisole 3: H NMR
(300 MHz, CDCl
J = 7.6 Hz, 2H), 1.26 (t, J = 7.6 Hz, 3H); C NMR (75 MHz,
CDCl ), 159.8 (s), 146.0 (s), 129.4 (d), 120.4 (d), 113.8 (d),
110.9 (d), 55.2 (q), 29.0 (t), 15.6 (q). 3-Ethylphenol 4:
NMR (300 MHz, CDCl ), 7.15–6.7 (m, 4H), 5.25 (s, 1H),
2.60 (q, J = 7.6 Hz, 2H), 1.22 (t, J = 7.6 Hz, 3H); C NMR
(75 MHz, CDCl ), 155.5 (s), 146.4 (s), 129.6 (d), 120.7 (d),
3
), d 7.22–6.76 (m, 4H), 3.81 (s, 3H), 2.65 (q,
1
3
3
d
1
H
3
d
1
3
[
16].
In summary, the nature of the iron salt has a huge
3
d
influence on the reaction for the formation of sodium
amide from liquid ammonia and sodium metal.
115.0 (d), 112.7 (d), 28.8 (t); 15.5 (q).
Fe(NO
yield; whereas, the use of FeCl
and to give unexpected products.
3
)
3
ꢁ9H
2
O led to the desired sodium amide in good
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