G Model
CRAS2C-3802; No. of Pages 6
2
A. Khojastehnezhad et al. / C. R. Chimie xxx (2013) xxx–xxx
2 4 2
Scheme 1. N-formylation of amines in the presence of NiFe O @SiO –PPA.
recycling of this catalyst. In the present work, an efficient
method for the preparation of PPA-functionalized silica-
continuously stirred for 90 min. The resulting precipitate
was then purified by four-times repeated centrifugation
(4000–6000 rpm, 20 min) and decantation. Coating of a
2 4 2
coated magnetic nanoparticles [NiFe O @SiO –PPA] is
reported. The prepared composite was successfully used
as the catalyst for the N-formylation of amines.
2 4
layer of silica on the surface of the NiFe O nanoparticles
was achieved by (ultrasonically) premixing a dispersion of
the nanoparticles (8% w/w, 25 mL) obtained with ethanol
for 2 h at 60 8C. A concentrated ammonia solution was
added and the resulting mixture was stirred at 60 8C for
40 min. Then, tetraethylorthosilicate (TEOS) (1.0 mL) was
added to the reaction mixture and continuously stirred at
60 8C for 24 h. The silica-coated nanoparticles were
collected by an external magnet, followed by washing
three times with methanol and drying in vacuum for 48 h.
After that, the resulting magnetic nanoparticles were
calcined at 800 8C for 4 h. Polyphophoric acid (PPA) (2.2 g)
N-formylation of amines is a very important reaction in
organic synthesis and medicinal chemistry. A variety of
medicinally active compounds have formamides as their
intermediates [14]. N-Formyl protection gained popularity
in peptide synthesis [15], since N-formyl deprotection can
easily be achieved without affecting the peptide bond, and
it may serve as a precursor for isocyanide [16] and
formamidine [17] synthesis. Reported literature methods
for the N-formylation [17–21] use reagents, such as chloral,
2
formic acid–DCC, formic acid–EDCI, formic acid–ZnCl ,
formic acid–PEG 400, formic acid esters, CMT, DMF–
NaOMe, formic acid–thiamine hydrochloride, imidazole–
was charged in the round-bottom flask, and CHCl
(100 mL) was added. After the mixture had been stirred
at 50 8C for 1 h, NiFe @SiO (5.0 g) was added to the
solution, and the mixture was stirred for another 4 h. The
CHCl was removed with a rotary evaporator and the
3
DMF, HClO
4
–SiO
2
, and formamide–NaOMe. Most of these
2
O
4
2
methods suffer from some disadvantages, such as harsh
reaction condition, low yield, very high reaction tempera-
ture, expensive reagents, etc. Due to our interest in the
synthesis of heterocyclic compounds and in continuation
of our previous works on the applications of reusable
catalysts in organic reactions [22–24], here, we report an
efficient and green method for the N-formylation of amines
3
resulting solid was washed with cold absolute ethanol, and
+
dried in vacuo at 70 8C for 2 h. The amount of H in the
2 4 2
NiFe O @SiO –PPA, determined by acid–base titration,
was 0.50 mmol/g.
using NiFe
2
O
4
@SiO
2
–PPA as a catalyst (Scheme 1). To the
2.2. Typical experimental procedure for N-formylation
A solution of 4-methylaniline (1.0 mmol), formic acid
best of our knowledge, this is the first report on the
synthesis, characterization and catalytic performance of a
NiFe
2
O
4
@SiO
2
–PPA catalyst.
nanocrystallites were prepared accord-
2 4
(1.5 mmol), and NiFe O @SiO2–PPA (0.02 g, 1 mol%) was
NiFe
2
O
4
@SiO
2
stirred at room temperature for 10–30 min. The progress of
the reaction was monitored by TLC. Upon completion,
ethyl acetate was added to the reaction mixture (the
ing to the reported procedure by Massart et al. with minor
modifications: fine particles are precipitated in an alkaline
solution [25]. (Scheme 2).
2 4 2
product is soluble in ethyl acetate) and NiFe O @SiO –PPA
could be placed on the side wall of the reaction vessel with
the aid of an external magnet, then the catalyst was
washed and dried to be reused in the next run. The organic
2
. Experimental
2
.1. Preparation of the catalyst (NiFe
2
O
4
@SiO
2
–PPA) [25,26]
phase was washed with a saturated solution of NaHCO
SO . The
solvent was evaporated and the resulting crude product
3
(
5 mL Â 3), water, and dried over anhydrous Na
2
4
The solution of metallic salts (FeCl
3
, 160 mL, 1 M and
NiCl , 40 mL, 1 M) was poured as quickly as possible into
the boiling alkaline solution [NaOH (1000 mL, 1 M)] under
vigorous stirring. Then, the solution was cooled and
2
was collected and give a white solid, yield 93%, mp: 52–
1
54 8C, 3291, 1664 (C5O); H NMR (300 MHz, CDCl
3
)
d
2.30
(s, 3H), 7.08–7.61 (m, 4H), 8.11 (s, 1H), 8, 15 (s, 1H).
2 4 2
Scheme 2. Preparation of polyphosphoric acid supported on NiFe O @SiO .
Please cite this article in press as: Khojastehnezhad A, et al. Polyphosphoric acid supported on silica-coated NiFe
2
O
4