Peroxyoxalate chemiluminescence

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The peroxyoxalate , as PICL (Abbr. For peroxyoxalate-initiated chemiluminescence hereinafter) is a chemical reaction of hydrogen peroxide with derivatives of oxalic acid is emitted at the light when capable of fluorescence compounds are present.

discovery

At Bell Laboratories , Edwin A. Chandross discovered at the beginning of the 1960s that a faint, bluish-white glow ( luminescence ) occurs when hydrogen peroxide and oxalyl chloride react in aqueous solvent mixtures . The gases produced during the violent reaction caused a filter paper impregnated with anthracene to fluoresce. If the reaction of the reactants was carried out in the presence of dissolved anthracene, a bright luminescence occurred which corresponded to the fluorescent light of this compound. 9,10-diphenylanthracene and N-methylacridone were also stimulated to fluoresce.

Reaction mechanisms

Hydrogen peroxide and oxalyl chloride are bifunctional starting materials and therefore in principle have the possibility of forming oligomers . The nature of the intermediate stages that occur has long been controversial. There is no doubt about the first step of the reaction: In analogy to the hydrolysis of carboxylic acid chlorides, hydrogen chloride is released and a peroxy acid (chlorocarbonyl performic acid) is formed. This should break down into carbon monoxide, oxygen and hydrogen chloride. However, since the peroxyacid still contains the structural element of a carboxylic acid chloride, the formation of diperoxyoxalic acid can be discussed as a subsequent reaction. In the presence of water, monoperoxyoxalic acid could also be formed.

Possible reaction products from oxalyl chloride and hydrogen peroxide

Finally, intramolecular nucleophilic attack by the HO group on the Cl-C = O carbon atom could also give rise to the four-membered ring molecule 1,2-dioxetanedione . Despite a long search for this suspected, unstable intermediate, it was only recently that the oxalyl chloride was labeled with 13 C isotopes to prove that 1,2-dioxanedione occurs in the reaction with hydrogen peroxide.

Certainly several reactions compete in the reaction of oxalyl chloride with hydrogen peroxide. Which of the reactive intermediate stages (“key intermediate ”, high-energy intermediate , HEI) causes chemiluminescence is controversial; 1,2-Dioxetanedione , atomic oxygen, and electronically excited carbon dioxide (in the singlet state ) were considered. It must be taken into account that the HEI must be volatile because it is also active in the gas phase. However, different molecules in solution and in the gas phase may be responsible for triggering the luminescence.

Oxalic acid diaryl ester

Chandross' discovery was the impetus for a comprehensive investigation of the luminescence phenomenon with further derivatives of oxalic acid in the laboratories of American Cyanamid under the direction of MM Rauhut. Instead of the aggressive oxalyl chloride, which reacts violently with water, diphenyl oxalate (diphenyl oxalate) was studied. This avoids the formation of hydrochloric acid, but the phenoxy group, as a relatively good leaving group, can also make the acylation of hydrogen peroxide possible. The development of the peroxyoxalate system, which has proven to be one of the most efficient chemiluminescence processes, is based on this idea. In analogy to the perhydrolysis of oxalyl chloride (see above), it was assumed that phenyl peroxyoxalate (phenyl peroxyoxalate) is formed in the first reaction step. This primary product could cyclize to 1,2-dioxetanedione in an intramolecular ring closure reaction.

Postulated mechanism of chemiluminescence of diaryl oxalates (Ar = C 6 H 5 , 4-Cl-C 6 H 4 ); Flr = fluorescent compound (fluorophore, e.g. anthracene)

The working group around WJ Baader (University of Sao Paulo) succeeded in finding a derivative of the above. To synthesize primary product: 4-chlorophenyl peroxyoxalate. The study of this labile compound had the surprising result that an addition of bases is necessary for chemiluminescence in the presence of fluorescent compounds. The peroxyacid itself, i.e. H. 4-chlorophenyl peroxyoxalate, therefore cannot be responsible for the light emission. It was therefore postulated that the peroxyacid is deprotonated by bases and the anion undergoes ring closure to form 1,2-dioxetanedione. This is supposed to cause the luminescence, but it does not yet explain how an electronically excited state arises from the molecule in its ground state . It was postulated that electronically excited CO 2 molecules in the singlet state transfer their energy to fluorescent molecules (fluorophores, fluorescers) such as anthracene. These are excited electronically and each emit a light quantum when they return to the ground state. One can classify this case as an example of sensitized chemiluminescence. Kinetic studies, however, suggest a more complex mechanism that has been postulated for other organic peroxides as well. In order to elucidate the reaction mechanism more precisely, JW Birks' group carried out investigations into the reaction kinetics with the aid of a fluorescence spectrometer connected to a stop-flow reaction cell. The key intermediate (HEI) or its excited fragment does not give its energy directly to the fluorescent component, but it actively intervenes in the process; it acts as a chemiluminescent activator (ACT). In detail you can draw the following picture:

Hypothetical mechanism of the chemiluminescence of the peroxyoxalate system with the postulated intermediate 1,2-dioxetanedione (CIEEL mechanism). ACT = chemiluminescence activator, ACT * = activator in the electronically excited state

First, an " Encounter Complex " is created from the key intermediate (e.g. dioxetanedione) and the ACT (e.g. anthracene). An electron is now transferred from the ACT to the peroxide; a pair of radical anion and radical cation results . The OO bond of the peroxide is weakened, which ultimately leads to the bond breaking. CO 2 is eliminated from the radical anion part . In the new radical pair, the electron is transferred back to the ACT radical cation part, which changes to the electronically excited state (ACT *). This emits the fluorescent light. The whole process is called chemically initiated electron exchange luminescence (CIEEL, English Chemically Initiated Electron Exchange Luminescence ).

DNPO.png
TCPO.png


Bis (2,4-dinitrophenyl) oxalate (DNPO)
Bis (2,4,6-trichlorophenyl) oxalate (TCPO)

Even before Baader's investigation, it was found that a variation of the phenyl radical through substitution with other chlorine, nitro and other groups resulted in an increase in the light yield. Particularly suitable aryl esters are bis (2,4-dinitrophenyl) oxalate (DNPO) and bis (2,4,6-trichlorophenyl) oxalate (TCPO). The aryloxy groups of these “activated esters” are even better leaving groups and should therefore favor both the nucleophilic attack of hydrogen peroxide on the carbonyl groups of the diaryl oxalate and the postulated cyclization to 1,2-dioxetanedione.

Applications

Peroxyoxalate chemiluminescent systems are used as illuminants , e.g. B. in glow sticks . They are also used in analytics. Because of the high quantum yield and high selectivity, this reaction is suitable for the HPLC detection of amino-substituted polycyclic aromatic hydrocarbons. It can also be used to detect hydrogen peroxide or hydroxyl radicals, which are particularly important as reactive molecules in the earth's atmosphere. Porphyrins can be detected in urine and faeces using the PCL test according to Brandl and Albrecht, which is useful for diagnosing some metabolic diseases (porphyrias).

Individual evidence

  1. ^ A b Edwin A. Chandross: A new chemiluminescent system . In: Tetrahedron Letters . tape 4 , no. January 12 , 1963, doi : 10.1016 / s0040-4039 (01) 90712-9 ( PDF ).
  2. ↑ Richard Bos, Neil W. Barnett, Gail A. Dyson, Kieran F. Lim, Richard A. Russell, Simon P. Watson, Studies on the mechanism of the peroxyoxalate chemiluminescence reaction: Part 1. Confirmation of 1,2-dioxetanedione as an intermediate using 13 C nuclear magnetic resonance spectroscopy, Analytica Chimica Acta 502, 2141-147 (2004). doi : 10.1016 / j.aca.2003.10.014
  3. ↑ Sarah A. Tonkin, Richard Bos, Gail A. Dyson, Kieran F. Lim, Richard A. Russell, Simon P. Watson, Christopher M. Hindson, Neil W. Barnett, Studies on the mechanism of the peroxyoxalate chemiluminescence reaction: Part 2. Further identification of intermediates using 2D EXSY 13 C nuclear magnetic resonance spectroscopy, Analytica Chimica Acta 614, 2173-181 (2008). doi : 10.1016 / j.aca.2008.03.009
  4. ^ A b Herbert Brandl, chemiluminescence, in: Dieter Wöhrle, Michael W. Tausch, Wolf-Dieter Stohrer, Photochemistry: Concepts, Methods, Experiments, p. 247, Wiley-VCH, Weinheim 1998. ISBN 3-527-29545-3 .
  5. ↑ MM Rauhut, Acc. Chem. Res. 2, 80-87 (1969).
  6. ↑ Synthesis and characterization of an intermediate in the peroxyoxalate chemiluminescence: 4-chlorophenyl O, O-hydrogen monoperoxyoxalate, Cassius V. Stevani, Ivan P. de Arruda Campos, Wilhelm J. Baader, J. Chem. Soc., Perkin Trans. 2 , 1996, 1645-1648. doi : 10.1039 / P29960001645
  7. ↑ CV Stevani, WJ Baader, Kinetic studies on the chemiluminescent decomposition of an isolated intermediate in the peroxyoxalate reaction. Journal of Physical Organic Chemistry, 10, 593-599 (1997). doi : 10.1002 / (SICI) 1099-1395 (199708) 10: 8 <593 :: AID-POC926> 3.0.CO; 2-H <593 :: AID-POC926> 3.0.CO; 2-H
  8. ^ A b Gary B. Schuster, Chemiluminescence of Organic Peroxides. Conversion of Ground-State Reactants to Excited-State Products by the Chemically Initiated Electron-Exchange Luminescence Mechanism, Acc. Chem. Research 12, 366-373 (1979).
  9. ↑ AG Hadd, A.Seeber and JW Birks: Kinetics of Two Pathways in peroxyoxalates Chemiluminescence, Journal of Organic Chemistry, 65, (2000), 2675-2683.
  10. ↑ C. Stevani, S. Silva, W. Baader, Studies on the Mechanism of the Excitation Step in Peroxyoxalate Chemiluminescence. European Journal of Organic Chemistry, 2000, 4037-4046 (2000). doi : 10.1002 / 1099-0690 (200012) 2000: 24 <4037 :: AID-EJOC4037> 3.0.CO; 2-A <4037 :: AID-EJOC4037> 3.0.CO; 2-A
  11. ↑ Kiomars Zargoosh, Mojtaba Shamsipur, Mohammad Qandalee, Mohammad Piltan, Loghman Moradi, Sensitive and selective determination of glucose in human serum and urine based on the peroxyoxalate chemiluminescence reaction of a new Fluorophore, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 81 679-683 (2011).
  12. ↑ Juana Cepas, Manuel Silva, Dolores Pérez-Bendito, Evaluation of peroxyoxalate chemiluminescence for the sensitive determination of hallucinogenic alkaloids, Analytica Chimica Acta, 314, 87-94 (1995).
  13. ^ AG Hadd and JW Birks, in Selective Detectors: Environmental, Industrial, and Biomedical Applications, ed. RE Sievers, Wiley, New York, 1995, pp. 209-239.
  14. ^ S. Albrecht, H. Brandl, E. Köstler, Z. Klin. Med. 44, 2071 (1989).
  15. ↑ H. Brandl, S. Albrecht, Praxis Naturwiss. Chem. 39, 17 (1990).

literature

  • Wilhelm J. Baader, CV Stevani ,. Erick L. Bastos, Chemiluminescence of Organic Peroxides. Patai's Chemistry of Functional Groups. Wiley, 2009. doi : 10.1002 / 9780470682531.pat0362

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