Synthesis of 3-trifluoroacetamidobenzoyltrifluoroacetone and its luminescent europium complexes

Article abstract of DOI:10.1134/S107036321205012X

Reaction of 3-aminoacetophenone with excess of methyl trifluoroacetate proceeds in two stages and leads to the formation of 3- trifluoroacetamidobenzoyltrifluoroacetone 3-CF₃C(O)NHC ₆H₄C(O)CH₂C(O)CF₃

Full text of DOI:10.1134/S107036321205012X

ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 5, pp. 874–879. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © V.V. Semenov, N.V. Zolotareva, A.V. Cherkasov, 2012, published in Zhurnal Obshchei Khimii, 2012, Vol. 82, No. 5, pp. 770–776.
Synthesis of 3-Trifluoroacetamidobenzoyltrifluoroacetone
and Its Luminescent Europium Complexes
V. V. Semenov, N. V. Zolotareva, and A. V. Cherkasov
Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
ul. Tropinina 49, Nizhny Novgorod, 603950 Russia
e-mail: vvsemenov@iomc.ras.ru
Received March 22, 2011
Abstract—Reaction of 3-aminoacetophenone with excess of methyl trifluoroacetate proceeds in two stages and
leads to the formation of 3-trifluoroacetamidobenzoyltrifluoroacetone 3-CF3C(O)NHC6H4C(O)CH2C(O)CF3
instead of the expected 3-aminobenzoyltrifluoroacetone 3-NH2C6H4C(O)CH2C(O)CF3. The cause is the readily
proceeding reaction of CF3COOCH with amine group of the source 3-aminoacetophenone and the initial
3
formation of 3-trifluoroacetamidoacetophenone. On the basis of the synthesized β-diketone the luminescent
complexes were synthesized: europium(III) tris(3-trifluoroacetamidobenzoyltrifluoroacetonate) trihydrate and
europium(III) tris(3-trifluoroacetamidobenzoyltrifluoroacetonate)(phenanthroline). The trifluoroacetylamide
group is converted into the primary amine by treatment the solutions of the europium complexes with aqueous
alkali. The molecular and crystal structures of 3-trifluoroacetamidoacetophenone were investigated.
DOI: 10.1134/S107036321205012X
Europium and terbium complexes with functional
ligands are used as fluorescent labels for time-resolved
fluoroimmunoassay [1, 2, 3]. Covalent binding of a
coordination compound by a protein molecule is
usually achieved by introducing into the ligand
molecule of the –SO2Cl or –CNS groups interacting
with the terminal NH2 group of the polypeptide chain
[4]. The coordination compound having a primary
amino group at the periphery can be linked using the
bifunctional glutaric aldehyde H(O)C(CH2)3C(O)H.
Our efforts to synthesize a ligand with a primary
amino group by the reaction of 3-aminoacetophenone
with excess methyl trifluoro-acetate and sodium
hydride led to the formation of 3-trifluoro-
acetamidobenzoyltrifluoroacetone instead of the
expected 3-aminobenzoyltrifluoroacetone (Scheme 1).
The reaction proceeds rapidly in ether with weak heat
1
release. According to elemental analysis and H NMR
spectroscopy data, the β-diketone IV obtained after
reprecipitation with hexane contains one ether
molecule. The sublimation in a vacuum removes the
associated (C2H5)2O molecule.
Scheme 1.
O
CF3COOCH3 (II), NaH
C2H5OC2H5, 25_35oC
F3C
N
H
H2N
O
O
III
I
O
H
H
O
H
O
H
O
CF3
874
CF3
+
F3C
N
H
F3C
N
O
O
H
IVb
IVa

SYNTHESIS OF 3-TRIFLUOROACETAMIDOBENZOYLTRIFLUOROACETONE
875
Intermediate compound in this process is 3-tri-
fluoroacetamidoacetophenone (III). This is confirmed
by the following observations. Compound III is
formed readily and with high yield in the reaction of 3-
aminoacetophenone with methyl trifluoroacetate in the
absence of sodium hydride. The fact that the reactions
of esters of organofluorine acids with primary amines
proceed readily and quantitatively has been observed
earlier [5] by the example of the reaction of diethyl
perfluoroadipate with 3-aminopropyltriethoxysilane.
The HPLC method allowed us to confirm the
existence of the two forms of β-diketone IV. The separa-
tion is achieved on a column Separon Si C18 with aceto-
nitrile as the eluent.
In the mass spectrum of compound IV the most
intense peaks are those of fragment ions with the
masses 69.6, 216.2, 240.4, 258.3, and 307.1. The peak
of molecular ion with m/e 327.0 has a low intensity.
The masses 69.6, 258.3 and 307.1 indicate that the
fragmentation of the molecule of β-diketone IV begins
with the cleavage of HF (m/e 20) and the CF3 radical
(m/e 69.3).
Compound IV exists in acetone-d6 and chloroform-d
solutions as a mixture of enol and ketone forms in a
15:1 ratio. The presence of enol IVa is confirmed by
the signal at 6.91 ppm (C–H). The existence of
diketone follows from the singlet signal of two protons
of CH2 group at 4.81 ppm. In addition, in the 1H NMR
spectrum there is a broad signal of the hydrogen atoms
of the amide group at 10.46 ppm and a series of signals
of protons of the phenyl group in the range of 7.6–
8.6 ppm. The effect of electronegative CF3 group is
reflected in a marked downfield shift of the proton
signals relative to the non-fluorinated analogs.
It is known that protection of a primary amino
group can be achieved by transformation it into amide
[6]. The trifluoroacetamidate protection with the
formation of CF3C(O)NHR is the most convenient,
since to recover the amine group by the treatment of
the amide with the alkaline alcohol or potassium
carbonate solutions proceeds under milder conditions
compared with the non-fluorinated analog, CH3C(O)
NHR.
CF3COOCH3
NaOH,CH3OH,H2O
RNH2
RNHC(O)CF3
RNH2
[CF3C(O)]2O
Our attempt to synthesize 3-aminobenzoyltrifluoro-
acetone V resulted (according to H NMR, IR, HPLC
and chromato-mass spectrometry) in obtaining the
target compound in only 25% yield. Processing the
solution of compound IV in diethyl ether with sodium
hydroxide caused cleavage of the β-diketone in two
parallel directions, to the parent 3-aminobenzoyl-
acetone I and 3-trifluoroacetamidoacetophenone III.
1
H
CF3
NaOH, EtOEt, H2O
H2N
+
I
III
IV
+
O
O
H
24%
51%
V, 25%
1
In the H NMR spectrum of the reaction mixture
two singlet signals belonging to the protons of methyl
groups in compounds I (2.47 ppm) and III (2.59 ppm)
were observed. In the IR spectrum there are two bands
of stretching vibrations of the NH bond of the primary
amine group at 3370 and 3466 cm–1.The coordination
compounds VI and VII were obtained from the sodium
β-diketonate, europium chloride, and phenanthroline
(Phen) in a water–alcohol solution.
F3C
O
O
Eu 3H2O
O
F3C
N
H
Phen, EtOH
(1) NaOH, EtOH, H2O
VI
VII
IV
(2) EuCl3 6H2O
The compounds obtained are fine orange (VI) and
red (VII) powders.
3
VI
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

876
SEMENOV et al.
peaks, with m/e 140, 168, 188, 216, 231, is identical to
F3C
the peaks of fragment ions of compound III. The mass
spectrum of complex VII contains a series of peaks
from β-diketone IV, compound III, phenanthroline
(m/e = 180), and fragment ions resulting from the
splitting off β-diketone (m/e = 985 ) and then the
radical CF3 (m/e = 915), two molecules of β-diketone,
HF, and CF3 (m/e = 569).
O
O
N
N
Eu
O
F3C
N
H
Figure 1 shows the electron absorption spectra of
ligand IV and complexes VI and VII. The spectra of
compounds IV and VI are similar, they consist of two
absorption bands with peaks at 242 and 324 nm. The
similarity is due to the existence of both the ligand and
the complex as chelates. In the enol form of the ligand,
the proton bound to an oxygen atom of carbonyl group
through the intramolecular hydrogen bond plays the
role of the metal cation. The presence of neutral
phenanthroline ligand in the compound VII causes a
significant change in the spectrum, but it actually
represents a superposition of the spectra of compound
IV and phenanthroline. It is known [7] that phenan-
throline spectrum contains two peaks, at 229 and
265 nm, and both occur in the spectrum of compound
VII. The position of the long-wave band (324 nm) due
to the ligand IV remains unchanged.
3
VII
Comparison of IR spectra of ligand IV with those
of the complexes VI and VII indicates that the amide
group is not involved in the coordination with the
europium cation. The absorption band of stretching
vibrations of the N–H (3300), as well as the bands
amide I and amide II (1716 and 1590 cm–1, respec-
tively) are not practically displaced at the transition
from the original ligand to the complexes VI and VII.
1
In the H NMR spectrum of compound VI the
multiple signals of the protons of phenyl group are
shifted upfield relative to the original ligand by
0.7 ppm, and the singlet signal of the hydrogen atom of
the central methine group,by at 0.3 ppm. This indicates
that the Eu3+ cation withdraws the electron density
from the ligand to a lesser extent as compared with the
proton H+ in the compound IVa.
Removing the trifluoroacetyl protection to obtain
the europium complexes VIII and IX with amino
group was carried out under the conditions similar to
those used in the reaction of the ligand IV with NaOH.
The complexes VI and VII are moderately resistant to
the alkaline reagent. The appearance of amino group in
the reaction products VIII and IX is clearly traced by
infrared spectroscopy. The spectral region 4000–
3000 cm–1 in the spectra of the parent compound VI
and the product of reaction with NaOH is shown in
Fig. 2. The disappearance is seen of the absorption
band ν(NH) at 3300 cm–1 of the amide group and the
appearance of two bands, at 3364 and 3455 cm–1,
belonging to the primary amine group.
Analysis of the mass spectra shows that the frag-
mentation of compounds VI and VII proceeds along
the path of splitting off β-diketone IV, compound III
and phenanthroline. Thus, in the mass spectrum of
compound VI the most intense peaks are those of the
β-diketone molecular ion (m/e = 327) and the products
of cleavage from the molecules of HF (m/e = 307) and
CF3 radical (m/e = 258). The second series of intense
А
Compounds VI, VII, VIII, and IX possess intense
cationic photoluminescence (PL) in dilute acetonitrile
solutions (c = 10–6–10–7 M). Emission spectra in general
are identical (Figs. 3 and 4), while the photolumine-
scence excitation spectra (PLE) can vary significantly
(Fig. 3). At λreg = 615 nm the PLE spectrum of the
amide complex VI a single band is observed at the
excitation wavelength 370 nm, in the spectrum of
obtained from amino derivative VIII it is shifted to
longer wavelengths region 400 nm (Fig. 3). The PLE
spectra of complexes VII and IX contain two bands, at
300 and 350 nm (Fig. 4). In the PL spectra of all com-
λ, nm
Fig. 1. EAS of acetonitlile solutions (1) of ligand IV
(с 1.8×10–4 M) and (2) complexes VI (с 6.8×10–6 M.) and
(3) VII (с 3.7×10–6 M).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

SYNTHESIS OF 3-TRIFLUOROACETAMIDOBENZOYLTRIFLUOROACETONE
877
I
λ, cm
Fig. 2. IR spectra of compounds (1) VII and (2) VIII in the
region of stretching vibrations of N–H bond.
λ, nm
I
Fig. 3. Photoluminescence excitation spectra (λreg 615 nm)
and photoluminescence spectra of complexes VI (1, λex 340
nm, с 6.8×10–6 M) and VIII (2, λex 440 nm, с 3×10–3 M.) in
acetonitlile solution.
λ, nm
Fig. 4. Excitation spectra (λreg 615 nm) and photolumine-
scence spectra of complexes VII (1, λex 340 nm, с 1.9×10–6 M)
and IX (2, λex 360 nm, с 1.4×10–5 M) in acetonitlile solution.
Fig. 5. Molecular structure of 3-trifluoroacetamidoaceto-
phenone (III). The thermal ellipsoids are presented in 30%
probability.
plexes the most intense transition corresponds to 5D0 →
7F2 transition in the Eu3+ cation with λmax 615 nm.
C1AC2AO1A planes is 13(1)°. The intramolecular
distance F1A···H1A is 2.29(2) Å, the F1AH1AN1A angle is
107.7(7)°. These geometric characteristics can be
interpreted as intramolecular F···H interactions (2.25 Å
[12]). Somewhat greater length of C1A–F1A bond
[1.343(1) Å] compared with C1A–F2A and C1A–F3A
bonds [1.329(1)–1.334(1) Å] confirms this assumption.
In addition, in molecule III an intramolecular O1A···H4A
interaction occurs [the O1A–H4A bond length is 2.25(3) Å,
the C4AH4AO1A bond angle is 121.7(6)°]. In the crystal,
the molecules of III are packed in stacks along the a
axis (Fig. 6). The packing also includes the intermole-
cular F···H [2.43(1)–2.49(1) Å] and O···H [2.14(1)–
2.46(1) Å] interactions [12]. The distance between the
centers of the aromatic rings in the stack is 4.823(5) Å.
Molecular structure of compound III was
determined by XRD investigation (Fig. 5). In an
independent region of the cell there are two molecules,
whose geometric characteristics are close to each
other, so we report the geometric structure of only one
of them (the main bond lengths and bond angles are
listed in the table). The O1A–C2A and O2A–O9A distances
fall in a narrow range 1.214(1)–1.223(1) Å, which
corresponds to the length of a typical C=O double
bond [8]. The N1A–C2A [1.346(1) Å] and N1A–C3A
[1.419(1) Å] distances are appreciably different in
keeping with the electron-acceptor nature of the O1A
atom and which is characteristic of amide fragments of
the R(C=O)NHAr type [9–11].
EXPERIMENTAL
IR spectra of compounds were taken from liquid
films between KBr plates or from suspensions in
mineral oil on a FTIR spectrometer FSM 1201. The 1H
The 3-trifluoroacetamidoacetophenone molecule is
virtually flat, the maximum deviation of atom O1A is
0.25(1) Å. The angle between the aromatic ring and
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

878
SEMENOV et al.
T = 100 K): empirical formula C10H8F3NO2, М 231.17;
4.8230(2), 12.4654(5), 17.4706(7) Å;
a
b
c
α 69.869(1), β 84.520(1), γ 81.000(1)°; space group P-1,
Z 4, dcalc 1.578 g cm–3, µ 0.148 mm −1, 2θmax 52º; a =
4.82301)°, steric group P-1, Z = 4, dcalc = 1.578 g cm–3 ,
μ = 0.148 mm–1, 2θmax = 52°; 8450 reflections were
measured, of which 3778 were independent (Rint
=
0.0123), R1 (with respect to F for the reflections with
I > 2σ(I) = 0.0327, wR2 (with respect to F2 over all
reflections) is 0.0878. The structure was solved by the
direct method and refined by least-squares with respect
to F2hkl anisotropically for nonhydrogen atoms and the
hydrogen atom of the amide group. All other hydrogen
atoms were located in the geometrically calculated
positions and refined using the rider model. The
calculations were carried out within the software
package SHELXTL v. 6.10 [13]. The extinction was
accounted for using the SADABS program [14].
Fig. 6. Crystal structure of 3-trifluoroacetamidoacetophenone
(III).
NMR spectra were recorded on a Bruker Avance DPX-
200 instrument (200 MHz) at 25°C, internal reference
TMS. Fluorescence and excitation fluorescence spectra
were measured on a Perkin-Elmer LS-55 spectrofluori-
meter from solutions in acetonitrile. Electron ab-
sorption spectra were recorded on a Perkin Elmer
Lambda 25 spectrophotometer.
In the syntheses sodium hydride was used as 60%
suspension in mineral oil from Acros. 3-aminoaceto-
phenone (I) (Acros) and methyl trifluoroacetate (II)
(PIM-Invest) were used without purification.
The mass chromatograms were obtained with a gas
chromatography-mass spectrometer Polaris Q/Trace
GC Ultra. We used a capillary chromatographic
column TR-5MS, 60 m long and of 0.25 mm diameter.
The flow rate of carrier gas (helium M 60 grade) was
1.2 ml min–1, column temperature was raised from
40 to 200°C at 10 deg min–1. Mass chromatograms
were recorded at ionizing electron energy 70 eV in the
range of mass numbers 40–400. To identify the
detected substances NIST 2005 library was used.
3-Trifluoroacetamidoacetophenone (III) was ob-
tained by reacting equimolar amounts of compounds I
and II in ether and purified by recrystallization from
toluene, yield 87%. IR spectrum, ν, cm–1: 3300 (NH),
1716 (amide I), 1614, 1550 (C = O), 1590 (amide II),
1489, 1458, 1282, 1221, 1188, 1150, 1120 (CF3), 788.
1H NMR spectrum [(CD3)2CO], δ, ppm (J, Hz): 2.60 s
(3H, CH3C(O)), 7.57–7.61 t (1Harom, J 8.03), 7.87–7.89
d (1Harom) 8.00–8.02 d (1Harom) 8.33 s (1Harom), 10.44 s
(1H, NH). Found, %: C 51.06, H 3.07. C10H8F3NO2.
Calculated, %: C 51.95, H 3.49.
The products of reaction of compound IV with
NaOH were analyzed on a Knauer liquid chromato-
graph equipped with UV spectrophotometric detector,
column 6×100 mm with a sorbent Separon Si C18.
5 μm, eluent 60% acetonitrile in water. Detection was
performed at 230 nm wavelength.
3-Trifluoroacetamidobenzoyltrifluoroacetone (IV).
A three-necked flask equipped with stirrer, dropping
funnel, and reflux condenser was charged with a
solution of 3.0 g (0.075 mol) of NaH in 100 ml of
unhydrous diethyl ether, and 19.2 g (0.15 mol) of
compound II was added dropwise while stirring. Then
was added a solution of 5.0 g (0.037 mol) of 3-
aminoacetophenone I in 20 ml of anhydrous ether, the
mixture was stirred for 3 h, and then to it was added by
portions 10% solution of H2SO4 to a neutral reaction.
The ether layer was separated from water and dried
over Na2SO4. The product was recrystallized from
diethyl ether–hexane. 10.1 g of IV·O(C2H5)2 etherate
The XRD data of compound III were obtained
using a Smart APEX diffractometer (λ = 0.71073 Å,
Selected bond lengths (d) and bond angles (ω) in compound III
Bond
O1A–C2A
O2A–C9A
d, Å
Angle
ω, deg
126.24(9)
127.7(1)
117.5(1)
114.73(9)
117.22(8)
123.0(1)
118.57(8)
121.68(9)
120.09(9)
121.1(1)
118.85(9)
1.214(1)
1.223(1)
1.346(1)
1.419(1)
1.343(1)
1.329(1)
1.334(1)
1.536(2)
1.498(2)
1.502(2)
C
2AN1AC3A
O1AC2AN1A
N
1A–C2A
O
1AC2AC1A
N1AC2AC1A
8AC3AN1A
C4AC3AN1A
8AC7AC9A
C6AC7AC9A
2AC9AC7A
O2AC9AC10A
7AC9AC10A
N1A–C3A
1A–C1A
F2A–C1A
3A–C1A
C1A–C2A
7A–C9A
C9A–C10A
1
was isolated. H NMR spectrum [(CD3)2CO], δ, ppm:
F
C
1.06–1.13 t (6H, CH3CH2, J 7.03), 3.34–3.45 q (4H,
CH3CH2, J 7.03). The final purification was performed
by sublimation in a vacuum, 9.4 g (78%) of diketone
IV was isolated. IR spectrum, ν, cm–1: 3300 (NH),
3087 (C=CH), 1716 (amide I), 1614, 1550 (C=O),
F
C
C
O
C
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

SYNTHESIS OF 3-TRIFLUOROACETAMIDOBENZOYLTRIFLUOROACETONE
879
1590 (amide II), 1489, 1458, 1282, 1221, 1188, 1150,
1120 (CF3), 788. H NMR spectrum [(CD3)2CO], δ,
from water, dried over Na2SO4, the solvent was
removed in a vacuum. 0.25 g (70%) of compound VIII
was isolated as a yellow powder. IR spectrum, ν, cm–1:
3364, 3455 (NH2), 3060 (C=CH), 1719, 1682 (C=O),
1614, 1580, 1529, 1492, 1316, 1292, 1259, 1191, 1137
(CF3), 798. Found, %: C 41.06, H 2.83. C30H27Eu·
F9N3O9. Calculated, %: C 40.13, H 3.03.
1
ppm (J, Hz): 4.81 s (2H, CH2 diketone), 6.91 s (1H,
CH enol), 7.64–7.68 t (1Harom, J 8.03), 8.02–8.04 d
(1Harom), 8.08–8.1 d (1Harom), 8.44 s (1Harom), 10.49 s
(NH). Found, %: C 43.20, H 2.15. C12H7F6NO3.
Calculated, %: C 44.04, H 2.16.
Europium(III)
tris(3-aminobenzoyltrifluoro-
Europium(III) tris(3-trifluoroacetamidobenzoyl-
trifluoroacetonate) trihydrate (VI). 0.98 g (3 mmol)
of compound IV was dissolved in 15 ml of 95%
ethanol, then at vigorous stirring 3 ml of 1 N NaOH
and 5 ml of 0.2 M aqueous solution of europium
chloride (1 mmol) was added. To the mixture 100 ml
of water was poured, the mixture was heated to 60°C
and then cooled. Orange precipitate of the compound
VI formed was isolated and purified by recrystal-
lization from a dichloromethane–hexane mixture.
Yield 0.5 g (43%). IR spectrum, ν, cm–1: 3300 (NH),
3087 (C=CH), 1716 (amide I), 1614 (C=O), 1590
(amide II), 1560, 1533, 1489, 1465, 1299, 1225, 1188,
1150, 1120 (CF3), 788. 1H NMR spectrum [(CD3)2CO],
δ, ppm (J, Hz): 6.57 s (1H, CH), 6.92–7.00 t (1Harom, J
8.03), 7.15–7.18 d (1Harom.), 7.26–7.30 d (1Harom), 10.2
s (1Harom). Found, %: C 37.40, H 2.15. C36H24Eu·
F18N3O12. Calculated, %: C 36.46, H 2.04.
acetonate)(phenanthroline) (IX). Compound IX was
synthesized from the complex VII similarly to VIII.
Yield 70%. IR spectrum, ν, cm–1: 3373, 3470 (NH2),
3062 (C=CH), 1724, 1634 (C=O), 1614, 1587, 1530,
1490, 1317, 1293, 1222, 1188 , 1137 (CF3), 778.
Found, %: C 50.04, H 3.33. C42H29EuF9N5O6. Cal-
culated, %: C 49.32, H 2.84.
ACKNOWLEDMENTS
This work was supported by the Russian Founda-
tion for Basic Research (project no. 08-03-00771, 10-
03-90006 Bel), Ministry of Education and Science
(State contract 16.740.11.0015) and the Presidium of
Russian Academy of Sciences (the program “Directed
synthesis of substances with predetermined properties
and creation of functional materials based on them”).
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1
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mination Software Suite, Bruker AXS, Madison:
Wisconsin, USA, 2000.
(8H, Phen), 8.78 s (1H, CH), 9.4–9.5 m (1Harom
)
10.22–10.25 m (1Harom), 10.3–10.4 m (1Harom), 12.02 s
(1Harom). Found, %: C 43.74, H 2.23. C48H26Eu·
F18N5O9. Calculated, %: C 43.97, H 1.98.
Europium(III)
tris(3-aminobenzoyltrifluoro-
acetonate) trihydrate (VIII). To a solution of 0.5 g
(0.42 mmol) of compound VI in 20 ml of ethyl alcohol
at stirring with a magnetic stirrer was added dropwise
2 ml of 1N NaOH. The mixture was stirred for 7 h at
25°C. The excess alkali was neutralized with acid. The
solvent and water were removed in a vacuum. The dry
residue was dissolved in dichloromethane and washed
twice with water. The organic layer was separated
14. Sheldrick, G.M., SADABS v. 2.01. Bruker/Siemens Area
Detector Absorption Correction Program, Bruker
AXS, Madison: Wisconsin, USA, 1998.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012