CHEMSUSCHEM
FULL PAPERS
measurement, the 100 mg samples were outgassed at 423 K for
6
h under vacuum. XPS measurements were performed by using
an S-probe monochromatized XPS spectrometer (Surface Science
Instruments VG) equipped with an AlKa X-ray (1486.6 eV) mono-
chromatic source. The take-off angle was 458, and the voltage and
power of the source were 10 kV and 200 W, respectively. A base
ꢀ9
pressure of 3ꢁ10 mbar was obtained in the measuring chamber,
and the pass energy was 107 eV. The analysis surface was 250ꢁ
2
1
000 mm with a flood gun (neutralizer) setting of 4 eV on the
sample with Ni grid. The accumulation time was approximately 7 h
for each spectrum. Elemental analysis was performed by using
a Jobin Yvon Ultima spectrometer. Therefore, the LDH material
(
50 mg) was degraded by heating at 1108C in aqua regia (HNO3/
HCl=1:3 v/v; 0.5 mL) and HF (3 mL) for 1 h. After cooling to RT, de-
ionized water (10 mL) and H BO (2.8 g) were added, and the mix-
Scheme 2. Oxidative decarboxylation of 2a and 3c on a larger scale (S: se-
3
3
ture was further diluted to a final volume of 100 mL. The C and N
contents were determined according to the Dumas method by
using a Vario Max CN Analyzer.
lectivity). Reaction conditions: amino acid (10 mmol), NH
4
Br (2.5 mmol),
(100 mmol)
[
Ni,Al]-LDH-WO (0.5 g), solvent (20 mL), room temperature. H O
4
2 2
ꢀ
1
diluted in solvent (total volume: 20 mL), addition rate: 6.75 mmolh
.
Typical reaction procedure
Conclusions
Catalytic reactions were performed in glass batch reactors (11 mL)
and were stirred magnetically at RT. Unless stated otherwise,
A heterogeneous catalyst for halide oxidation, based on tung-
state immobilized on a solid [Ni,Al] layered double hydroxide
[Ni0.64Al0.36(OH)
](NO
)
0.04(CO
)
0.14(WO
)
0.02 with a tungstate loading of
2
3
3
4
ꢀ1
0
.18 mmolg was used as the catalyst. In a standard reaction,
(LDH) support was applied to the oxidative decarboxylation of
amino acid (0.5 mmol), bromide salt (0.5 mmol), catalyst (0.1 g),
amino acids using H O . Electrostatic interactions between bro-
2
2
and solvent (4 mL) were added to the reactor. H O2 (5.0 mmol;
2
mide, carboxylates, and the LDH surface are key to achieve cat-
alytic activity. High and often excellent nitrile yields were com-
bined with broad functional group compatibility. Bifunctional
nitriles, such as that derived from glutamic acid, are intermedi-
ates to high-value building blocks and can even be obtained
from cheap protein-rich side products from the agro-industry.
3
5 wt% in water) was diluted in the solvent (total volume: 4 mL)
and added continuously by using a BjBraun Perfusor Space pump
ꢀ1
at a rate of 0.33 molh . After this addition step, the heterogene-
1
ous catalyst was removed by centrifugation. Either GC or H NMR
spectroscopy was applied for analysis, which depended on the ex-
pected products.
Product analysis and identification
Experimental Section
1
Reaction mixtures were analyzed by H NMR spectroscopy to deter-
Catalyst synthesis
mine the conversion and selectivity in the oxidative decarboxyla-
1
tion reaction. H NMR spectra were recorded by using a Bruker
LDH supports were prepared by co-precipitation from the corre-
sponding metal nitrate salts in alkaline medium under ambient
conditions. Ni(NO ) ·6H O (76.8 mol) and Al(NO ) ·9H O (43.2 mol)
Avance 400 MHz spectrometer equipped with a BBI 5 mm probe.
As the reaction was performed in water for many of the amino
acids except for 2a, the NMR sample was prepared by diluting the
3
2
2
3 3
2
were dissolved in deionized water (240 mL). This aqueous solution
was added dropwise by using a BjBraun Perfusor Space pump to
deionized water (200 mL) at pH 8.5 under magnetic stirring. The
pH was kept constant during the synthesis by the addition of an
aqueous solution of NaOH (2m). Afterwards, the aqueous suspen-
sion was stirred for 24 h at RT. The green solid was precipitated by
centrifugation, washed several times with deionized water, and
dried by lyophilization. The tungstate-loaded [Ni,Al]-LDH material
was obtained through anion exchange. Therefore, the air-dry
product mixture (300 mL) in D O (300 mL) in an NMR tube. Other-
2
wise the reaction was performed in CD CN or CD OD, and the reac-
tion mixture was analyzed without further modification. The broad
signal caused by the presence of water, as a result of using aque-
3
3
ous H O2 as the terminal oxidant for oxidative decarboxylation,
2
was suppressed by the application of an adapted pulse program:
p1 8 ms; pl1 ꢀ1 db; pl9 50 db; o1P on the resonance signal of
1
water, determined from the previous H NMR spectroscopy mea-
surement: ds 2; ns 32; d1 5 s; aq 2.55 s; sw 16. In the case of GC,
the samples were analyzed by using a Shimadzu 2010 or 2014 GC
equipped with a CP-Sil 8 CB and CP-Chirasil-Dex CB capillary
column, respectively, and a flame ionization detector (FID). The
standard temperature program allowed the baseline separation of
all compounds; the temperature is increased from 50 to 3008C at
[
Ni,Al]-LDH support (3 g) was brought into contact with an aque-
ous solution (300 mL) that contained Na WO ·2H O (1.5 mmol) and
stirred for 24 h at RT. The washing and drying protocol was repeat-
ed.
2
4
2
ꢀ1
1
08Cmin . To verify the absence of any racemization in the prod-
Catalyst characterization
uct of isoleucine, chromatographic analysis was performed by
using a CP-Chirasil-Dex CB capillary column. A slightly adapted
temperature program was applied, with a start at 508C for 20 min
PXRD measurements were performed by using a STOE StadiP dif-
fractometer with CuKa radiation. SEM was performed by using
a Philips XL 30 FEG microscope after the samples were coated with
Au. Nitrogen physisorption measurements were performed by
using a Micromeritics 3Flex surface analyzer at 77 K. Before the
ꢀ1
and heating to 2008C at 108Cmin . For quantitative analysis, ben-
zonitrile (0.5 mmol, 2m in methanol) was added as a standard
when H O addition was finished; the GC peak areas were correct-
2
2
ꢀ
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 0000, 00, 1 – 9
&
7
&
ÞÞ
These are not the final page numbers!