Lanthanide(III) ion as a luminescent and catalytically active reaction center of aniline condensation with butyraldehyde

Article abstract of DOI:10.1007/s11172-007-0071-7

A new type of chemiluminescence catalytic conversion in which the lanthanide(III) ion is a luminescent and highly efficient catalytically active center was found. Chemiluminescence (CL) is generated in the condensation reaction of aniline with butyraldehyde in DMF to form 3-ethyl-2-propylquinoline. The reaction is catalyzed by LnCl₃?6H₂O (Ln = Eu, Tb, and Ho). When EuCl₃?6H₂O and TbCl ₃?6H₂O salts are used as catalysts, the CL emitters are the Eu³⁺*and Tb³⁺*excited ions. In the case of HoCl₃?6H₂O, the emitter is 3-ethyl-2-propylquinoline in the triplet-excited state.

Full text of DOI:10.1007/s11172-007-0071-7

Russian Chemical Bulletin, International Edition, Vol. 56, No. 3, pp. 443—445, March, 2007
443
Lanthanide(III) ion as a luminescent and catalytically active reaction center
of aniline condensation with butyraldehyde
R. G. Bulgakov,ꢀ S. P. Kuleschov, and A. R. Makhmutov
Institute of Petrochemistry and Catalysis, Russian Academy of Sciences,
141 prosp. Oktyabrya, 450075 Ufa, Russian Federation.
Fax: +7 (347 2) 31 2750. Eꢀmail: ink@anrb.ru
A new type of chemiluminescence catalytic conversion in which the lanthanide(III) ion is a
luminescent and highly efficient catalytically active center was found. Chemiluminescence
(CL) is generated in the condensation reaction of aniline with butyraldehyde in DMF to form
3ꢀethylꢀ2ꢀpropylquinoline. The reaction is catalyzed by LnCl3•6H2O (Ln = Eu, Tb, and Ho).
When EuCl3•6H2O and TbCl3•6H2O salts are used as catalysts, the CL emitters are the Eu3+
*
and Tb3+* excited ions. In the case of HoCl3•6H2O, the emitter is 3ꢀethylꢀ2ꢀpropylquinoline
in the tripletꢀexcited state.
Key words: chemiluminescence, lanthanide catalysis, crystalline hydrates of lanthanide
trichlorides, condensation reaction, synthesis of 3ꢀethylꢀ2ꢀpropylquinoline.
Numerous types of chemiluminescence conversions
of organic compounds are presently known,1—3 although
the lanthanide(III) ion is the emitter of chemilumineꢀ
scence (CL) and catalyst only for the decomposition of
oꢀcyclic peroxides (dioxetanes). This type of CL has been
observed4 for the first time during the decomposition of
9ꢀ(2ꢀadamantalidene)ꢀNꢀmethylacridaneꢀ1,2ꢀdioxetane
(300 K) in the presence of the Eu(fod)3 complex
(tris(1,1,1,2,2,3,3ꢀheptafluoroꢀ7,7ꢀdimethylꢀ4,6ꢀoctaꢀ
dionato)europium(III)). This CL cannot be explained only
by simple energy transfer to the Eu3+ ion from the priꢀ
mary emitter, viz., excited Nꢀmethylacridone, i.e., simiꢀ
larly to CL activation upon the liquidꢀphase oxidation
of hydrocarbons with the tris(2ꢀthenoyltrifluoroaceꢀ
tonato)phenanthrolineeuropium(III)) complex.1 It has
been found4 that the enhancement of CL is mainly caused
by the catalytic effect of the Eu(fod)3 complex on diꢀ
oxetane (DO) decomposition. Later5—7 CL has been obꢀ
served for the catalytic decomposition of adamantylꢀ
ideneadamantaneꢀ1,2ꢀdioxetane and tetramethylꢀ1,2ꢀ
dioxetane under the action of lanthanide acetylacetonates
Eu(acac)3 and Tb(acac)3. The observed effects of CL enꢀ
hancement during the decomposition of dioxetanes are
characterized5—7 as luminescence catalysis. However, the
authors4 admit that the Eu(fod)3 additives only insignifiꢀ
cantly catalyze dioxetane decomposition and an increase
in the rate constants of adamatylideneadamantaneꢀ1,2ꢀ
dioxetane and tetramethylꢀ1,2ꢀdioxetane decomposition
by the Eu(acac)3, Tb(acac)3, and Tb(ClO4)3 complexes,
according to published data,5—7 is achieved only at
[Ln3+] ≤ [DO].
would manifest the properties of efficient catalysts for the
chemical reaction in which this CL is generated. Search
for and investigation of such reactions is urgent for both
studying mechanisms of the chemical generation of exꢀ
cited states of the Ln3+* ions and understanding the
mechanism of action of catalysts based on the lanthanide
complexes.
In the present work, we studied a possibility of generaꢀ
tion of emitting electronꢀexcited states of the lanthanide
ions in the known8,9 reaction of aniline (1) condensation
with butyraldehyde (2) catalyzed by the LnCl3•6H2O
complexes. We have earlier8,9 found the catalytic effect of
LnCl3•6H2O on this reaction.
Experimental
Complex LnCl3•6H2O (reagent grade) was used. Aniline (1,
reagent grade) was purified by distillation in vacuo (70 °C,
10 Torr). Butyraldehyde (2, pure grade) and DMF (pure grade)
were distilled above hydroquinone and BaO, respectively.10 Conꢀ
densation of compounds 1 and 2 was carried out in a glass
CL cell (V = 20 mL) placed in a lightꢀproof chamber of the
CL setup. Dimethylformamide (7 mL) was added to the cell
containing a weighed sample of LnCl3•6H2O (0.54 mmol), and
stirring was switched on. After LnCl3•6H2O was completely
dissolved, compound 1 (20 mmol) was loaded, and then comꢀ
pound 2 (44 mmol) was pressed out from the doser with an
argon flow. Chemiluminescence was detected through the optiꢀ
cally transparent bottom of the cell. After the reaction, the
solution was analyzed for a content of the target product, viz.,
3ꢀethylꢀ2ꢀpropylquinoline, according to earlier published proꢀ
cedures.8,9
The photoluminescence (PL) spectrum was recorded on an
Aminco—Bowman spectrofluorimeter. The setup and CL meaꢀ
surement procedure have been described earlier.11 The CL specꢀ
Based on the aforesaid, we can assert that no examples
are described where the Ln3+ ions, being CL emitters,
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 429—431, March, 2007.
1066ꢀ5285/07/5603ꢀ0443 © 2007 Springer Science+Business Media, Inc.

444
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 3, March, 2007
Bulgakov et al.
tra were detected using boundary light filters according to a
known procedure12 (for Ln = Eu, Ho) or with an MDRꢀ23
monochromator (Ln = Tb).
ICL
IFL
1
Results and Discussion
It was found that on mixing compounds 1 and 2 in
DMF in the presence of LnCl3•6H2O CL generates,
which is observed with the unaided eye in the case of Ln =
Eu and Tb, whereas the red and green emission (CL1) is
observed in a slightly darkened room. The CL1 spectra
coincide with the PL spectra of solutions of TbCl3•6H2O
and EuCl3•6H2O in DMF (Fig. 1). Thus, the CL1 emitꢀ
ters are the excited ions Tb3+* and Eu3+*. The less proꢀ
nounced CL2 (Ln = Ho) is observed in a shorterꢀwaveꢀ
4
2
length region at λ = 450—550 nm (see Fig. 1). The Ho3+
*
5
ion cannot be a CL2 emitter, because it has no PL in
solutions,13 i.e., the CL2 emitter is one of other particiꢀ
pants of the condensation reaction, which proceeds8,9 via
Scheme 1.
Scheme 1
6
3
300
400
500
600 λ/nm
Fig. 1. Phosphorescence (1—3) and chemiluminescence (4—6)
spectra for the reaction of aniline 1 (1.67 mol L–1) and butyralꢀ
dehyde 2 (3.67 mol L–1) in DMF (300 K) in the presence of Ln3+
(4.5•10–2 mol L–1): 1, quinoline (77 K)15; 2, TbCl3•6Н2О
(4.5•10–2 mol L–1) in DMF (300 K),
λ
= 313 nm;
exc
3, EuCl3•6Н2О (4.5•10–2 mol L–1) in DMF (300 K), λ
=
exc
The major reaction product is 3ꢀethylꢀ2ꢀpropylꢀ
quinoline (3), and Nꢀbutylaniline (4) is formed in minor
amounts. The reaction occurs within 1—5 min,8,9 which
agrees with the steep fall (85—90% for ∼1—3 min) shown
by the kinetic CL curve (omitted). When the reaction
occurs without the LnCl3•6H2O catalysts, the yield of
quinoline is insignificant (≤5%) according to the GLC
data, and the CL intensity is so weak that its spectrum
cannot be measured even when using boundary light filters.
365 nm; 4, CL2 spectrum (Ln = Ho); 5, CL1 spectrum (Ln = Tb);
6, CL1 spectrum (Ln = En).
and its detection in the CL system is probably that of
higher sensitivity of CL measurements due to the absence
of the exciting light. The matter is that the lowꢀintensity
PL should be detected at the maximally open gap of the
detecting monochromator, due to which the exciting light
penetrates through the monochromator gap and thus disꢀ
guises the weak PL. Note that similar situation is often
met. For instance, the PS of benzophenone is not obꢀ
served at room temperature,16 whereas in the CL sysꢀ
tems17,18 it is easily detected at 300 K. Taking account
into account the above facts, we believe that the most
probable CL2 emitter is the tripletꢀexcited state of comꢀ
The PL spectrum of product
4 appears at
300—370 nm,14 i.e., compound 4 is not either the CL2
emitter. Published data on the PL spectrum of product 3
are lacking. We also failed to detect the PL of product 3
(300, 77 K) because, most likely, of its very low intensity.
At the same time, the PL spectrum of quinoline15 is known
(77 K), which contains phosphorescence (PS) and fluoꢀ
rescence maxima (see Fig. 1). It is seen that the PS of
quinoline appears in the same spectral region as CL2 and
positions of two most intense maxima of the compared
spectra are close. One of the difficulties in observation of
the luminescence of compound 3 upon photoexcitation
3
pound 3, i.e., С14Н17N*. Investigation of the mechaꢀ
nism of CL2 excitation is the subject of our further studies.
The condensation reaction is exothermic: the temꢀ
perature of the reaction solution after mixing of the reacꢀ
tants increases from 300 to 343 K. The estimation of the
thermal effect of the catalytic condensation by the posiꢀ

New chemiluminescence catalytic conversion
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 3, March, 2007
445
Scheme 2
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tion of the shortꢀwavelength maximum in the CL2 specꢀ
trum (400 nm) gives ∆H° ≥ 3.1 eV (71.5 kcal mol–1).
The CL kinetic curves (Ln = Tb, Eu, and Ho)
are recorded as narrow maxima, whose intensity
(Imax/photon s–1 mL–1
)
decreases in the series:
Tb (2.7•1011) > Eu (8•108) > Ho (2•108). This sequence
does not coincide with the row of catalytic activity found8,9
for the lanthanide ions Tb ≈ Ho (95) > Eu (66) from the
change in the yield of product 3 (in %). Analysis of these
series shows that at the same level of catalytic activity of
the Tb and Ho ions the brightness of CL1 and CL2 difꢀ
fers substantially, which is due to different luminescence
intensities of the CL1 (Tb3+*) and CL2 (3С14Н17N*)
emitters.
Based on the obtained results, we can propose a simꢀ
plified scheme of CL1 and CL2 excitation (Scheme 2,
Eqs (1) and (2), respectively).
Regardless of the Ln nature, the tripletꢀexcited state
3С14Н17N* is formed. Then 3С14Н17N* is deactivated via
two routes depending on the luminescence properties
of Ln3+*: via route (2) with PS emission (in the case of
Ln = Ho) or via route (1) with energy transfer to the
Ln3+ ions (Ln = Tb, Eu) to form Tb3+* or Eu3+
*
(CL1 emitters). The absence of PS of product 3 in the
CL1 spectra confirms the fact of energy transfer from
3С14Н17N* to the Tb3+ and Eu3+ ions. This is especially
clear for Eu3+*, whose luminescence spectrum contains
no maxima in the PS region of product 3.
Substantial differences between the known CL sysꢀ
tems of decomposition of dioxetanes1—5 and the CL reacꢀ
tion studied in this work should be mentioned in concluꢀ
sion. The CL observed is generated in another type of the
chemiluminescence catalytic reaction, namely, condenꢀ
sation, which exemplifies a highly efficient catalytic perꢀ
formance with the complete conversion of the substrates
in the presence of catalytic amounts of the lanthanide
compounds.
This work was financially supported by the Federal
Agency on Science and Innovations (State Contract
No. 02.434.11.2026 of August 1, 2005).
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Received December 1, 2006;
in revised form March 9, 2007