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Chemiluminescence in Organic Compounds.

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Chemiluminescence in Organic Compounds
Dedicated to Professor Fritz Micheel on the occasion of his 65th birthday
As a result of the development of very sensitive equipment, it is now possible to show that
the chemiluminescence of organic compounds in solution is quite a common phenomenon.
Notable advances have been made during recent years in the investigation of the chemiluminescence of substituted phthalic acid hydrazides and related compounds. A new and
probably generally applicable method of producing chemiluminescence has recently been
discovered in the reaction of aromatic free-radical anions with appropriate free-radical
1. Introduction
Chemiluminescence reactions are processes in which a
molecule capable of fluorescing is raised to an excited
electronic state by chemical energy [I]. If the reaction is
to be accompanied by the emission of visible light, it
must supply an energy of at least 40-70 kcal/mole. This
is the case, for example, in free-radical chain oxidations.
There should consequently be a large number of chemiluminescence reactions, and many examples are in fact
to be found in the literature (reviews: [2-71). Only a few
reactions are known, however, in which a really brilliant
light is emitted. Owing to advances in the construction
of equipment, it is now possible to measure accurately
light intensities of some 103 photons cm-3 sec-1 [8,9], so
that even weak chemiluminescence in organic reactions
can be detected (cf. also the earlie workby Audubert [lo]).
The relationships between the constitution of organic
compounds and their ability to exhibit chemiluminescence are roughly parallel to the relationships between
constitution and ability to fluoresce [l l -151. However,
[I] Definition by: E. J. Bowen, Angew. Chem. 77, 47 (1965);
Angew. Chem. internat. Edit. 4, 81 (1965).
[2] E. H . White and M . M . Bursey, J. Amer. chem. SOC.86, 941
[2a] T . I. Quickenden, J. New Zealand Inst. Chem. 28, 10 (1964).
[2b] J. Staufand H. Schmidkunz, Z. physikal. Chem. N.F. 33,
273 (1962).
[3] H. Stork, Chemiker-Ztg. 85, 467 (1961).
[4] E. N . Harvey: A History of Luminescence. The American
Philosophical Society, Philadelphia 1957.
[5] A . Bernanose, Bull. SOC.chim. France 1952, 39 D.
[6] W. Vaughan, Chem. Reviews 43,447 (1948).
[7] R . S . Anderson, Ann. New York Acad. Sci. 49, 337 (1947).
[S] V.Y. Shlyapintokh, R . F. Vassil'ev, 0 . N . Kharpukhin, L. M .
Postnikov, and L. A. Kibalko, J. Chim. physique 57, 1113 (1960).
[gal J. Staufand G. Riimler, 2. physik. Chem. N.F. 34, 67 (1962).
191 M . Hofert, Angew. Chem. 76, 826 (1964).
[lo] R. Auduberf, Angew. Chem. 51, 153 (1938); Trans. Faraday
SOC.35, 197 (1939).
[l I ] Th. Forster: Fluoreszenz organischer Verbindungen. Vandenhoek & Ruprecht, Gottingen 1951.
just as the fluorescence of organic compounds in solution
is affected by many parameters relating to the medium,
such as concentration, pH, solvent, quenching action of
foreign substances present (cf. [15]), chemiluminescence
is further complicated by the fact that the processes
yielding the radiant energy may be accompanied by
other chemical reactions (cf. Section 8).
Bioluminescence reactions are enzyme-catalyzed chemiluminescence processes in which oxygen acts as an
electron acceptor. According to McElroy and Seliger
[17], these oxidation processes are controlled by the
enzyme so efficiently that the quantum yields are about
unity [16], in contrast to organic chemiluminescence
reactions in solution, which give quantum yields of
at most 0.05.
2. Chemiluminescence in the Slow Autoxidation
of Hydrocarbons, Aldehydes, Ketones, a n d
Unsaturated Acids a n d their Esters
The very weak chemilurninescence in the autoxidation
of hydrocarbons such as ethylbenzene, cumene, diphenylethane, cyclohexane, or tetralin can be measured
with the aid of very sensitive photoelectric measuring
devices[&9,18,18a]. In the cases of cumene, cyclohexane,
and tetralin, the emitted light has a maximum in the
blue-green region of the spectrum, corresponding to a
reaction enthalpy of approximately 55 kcal/mole [9].
[12] Th. Flirsfer in Houben-Weyl: Methoden der organischen
Chemie. Thieme, Stuttgart 1955, Vol. 312, p. 481.
1131 W. C . Price, Annual Rev. physic. Chem. 11, 133 (1960).
[ 141 H . Meier: Die Photochemie der organischen Farbstoffe.
Springer, Berlin 1963, p. 65.
[I51 B. J . van Duuren, Chem. Reviews 63, 325 (1963).
[16] E. N. Harvey: Bioluminescence. Academic Press, New York
1171 W. D . McEIroy and H. H. Seliger in W . D . McElroy and
B. Glass: A Symposium on Light and Life. The Johns Hopkins
Press, Baltimore 1961, p. 219.
1181 R . F. Vassil'ev and A. A. Vichutinskii, Nature (London) 194,
1276 (1962); R . I;: Vassil'o and I . F. Rusina, Dokl. Akad. Nauk
SSSR 156, 1402 (1964).
Angew. Chem. infernat. Edit.
1 Vol. 4 (1965) 1 No. 7
End products containing oxygen (alcohols, aldehydes,
and ketones) are particularly capable of emitting visible
light [18]. Kinetic studies show that the intensity of the
light is in most cases proportional to the oxygen consumption [19]. The lifetime of the excited state in the
oxidation of ethylbenzene (10-7 to 10-6 sec) agrees well
[IS] with that of the triplet state of acetophenone [18b].
The chemiluminescence accompanying the autoxidation
of hydrocarbons is intensified by free-radical formers
such as azobisisobutyronitrile [I81 or by X-rays [9], and
weakened by free-radical scavengers such as 2,6-di-butylp-cresol [9,20]. This fact offers a possible method of
determining the efficiencies of antioxidants [21] and
oxidation initiators 1221 with the aid of chemiluminescence reactions.
The extreme13 weak light emission (quantum yields =
10-8 to 10-10) accompanying these autoxidations becomes stronger if the reaction medium contains fluorescent molecules, such as anthra Tene, oxazole, or pyrazole
derivatives (sensitized or “activated” chemiluminescence). Thus the chemiluminescence in the oxidation of cyclohexane is intensified by a factor of almost 50 by 9,lOdibromoanthracene. The spectrum of the “activated”
chemiluminescence corresponds to the fluorescence
spectrum of the activator [18].
Other examples of autoxidative chain reactions exhibiting very weak chemiluminescence are the oxidation of
acetaldehyde [23], oleic or linoleic acid [9], methyl
oleate [18], and n-butyl oleate [9].
the chemiluminescence. The luminescent species has not
yet been established. The energy levels of HCl, CO, or
COz are too high, and the energy of an excited oxygen
singlet (38 kcal/mole) is too low to cause the observed
It is interesting that t h e vapors escaping during the reaction
of oxalyl chloride with hydrogen peroxide can excite fluorescence. One possible explanation according t o Chandross is
that the excitation energy is first absorbcd by oxalyl chloride
t o give molecules in t h e triplet s t a t e ; these are then cwi-ied
out of the liquid phase with t h e reaction gases a n d pass o n
their excitation energy to a fluorescent molecule.
Acetyl chloride exhibits no luminescence under identical
conditions. Rauhut et al. found that other derivatives of
monoperoxyoxalic acid also decompose in the presence
of sensitizers with light emission [24a], e.g. t-BuOOCOCO- C1 [24b]. The simultaneous cleavage of all bonds
involved (“concerted multiple bond cleavage”) is decisive
for the occurrence of chemiluminescence. Extremely
weak chemiluminescence (quantum yields of 10-13 to
10-15) has been observed in the reaction of adipyl chloride o r benzoyl chloride with hexaniethylenediamine or
aniline [8,25].
A blue luminescence, which persists for a relatively long
time and which is visible in the dark with the naked eye,
occurs during the reaction of certain nitriles such as
benzyl cyanide, acrylonitrile, or benzonitrile with hydrogen peroxide in alkaline solution [26]. The chemilurninescence observed with benzonitrile. however, is very
3. Chemiluminescence in the Reactions of Oxalyl
Chloride or Nitriles with Hydrogen Peroxide
Chandross [24] observed a weak bluish-white chenii-
luminescence during the reaction of oxalyl chloride with
hydrogen peroxide. He postulated the intermediate
weak. Since the reactions proceed by a heterolytic mechanism [26], molecular oxygen can initially be formed
only in an excited singlet state (cf. the investigations by
Bowen et al. [27,28] on the chemiluminescence of dissolved oxygen; see also the next section).
4. Grignard Compounds and Polyphenols
2 CO
formation of monoperoxyoxalic acid monochloride ( I ) ,
which was then assumed to decompose into oxygen,
carbon monoxide, and hydrogen chloride, with simultaneous liberation of the excitation energy required for
The chemiluminescence accompanying the autoxidation
of Grignard compounds was studied in detail as early as
1925 1293, together with the relationships between
structure and chemiluminescence. It has been shown by
a preparative method that the reaction proceeds via the
[18al G . Lundeen and R . Livingston: Symposium on Chemiluminescence. Durham N.C. 1965. Preprints p. 281.
[18b] F. Wilkinson and J. Dubois, J. chern. Physics 39, 377 (1963).
[19] R . F. Vassil’ev, Nature (London) 196, 668 (1962); R. F.
Vassil’ev, A. A . Vichutinskii, and A . S. Tcherkassov, Dokl. Akad.
Nauk S S S R 149, 124 (1962).
[20] R. F. Vassil’ev, Dokl. Akad. Nauk S S S R 144, 143 (1962).
[21] V.Ya. Shlyapintokh, 0. N . Kharpukhin, and I . F. Russina,
Zh. obshch. Khim. 33 (95), 3110 (1963).
1221 A . A. Vichutinskii, Zh. Fiz. Khim. 38, 1668 (1964).
[23] L. M . Possnikow, W . F. Schuwalow, and V. Ya. Shlyapintokh,
Izv. Akad. Nauk SSSR, Ser. Fiz. 27, 735 (1963); Chem. Zbl.
1965, No. 5 , 0759.
[24] E. A. Chandross, Tetrahedron Letters 1963, 761
[24a] M . M . Rauhut et al. in: Symposium on Chemiluminescence. Durham N.C. 1965. Preprints p. 347.
[24b] P. D. Bartlett and R. E. Pincock, J . Amer. chern. SOC.82,
1769 ( I 960).
1251 Ss.G. Enteliss, V. Ya. Shlyapintokh, 0. N . Kharpukhin, and
0.V. Nessterow, Zh. Fiz. Khim. 34, 1651 (1960).
[26] E. McKeown and W . A. Waters, Nature (London) 203, 1063
A (1964).
[27] E. J . Bowen and R . A . Lloyd, Proc. chern. SOC.(London)
1963, 305 (1963).
1281 E. J. Bowen, Nature (London) 201, 180 B (1964).
[29] W . V. Evans and E. M . Diepenhorst, J . Amer. chern. SOC.
48, 715 (1926); R.T. Dufjord, D . Nightingale, and S . Calvert,
ibid. 47, 95 (1925), and earlier papers.
Angew. Chem. internaf. Edit.
Vvl. 4 (1965)
/ No.
intermediate R-0-0-MgBr
[30]. Kinetic studies on the
autoxidation of phenylmagnesium bromide confirmed
the relationship between chemiluminescence and the
free-radical chain mechanism [31].
The intense red chemiluminescence observed during the
reaction of pyrogallol with formaldehyde, hydrogen
peroxide, and alkali has an emission band at 630 m p due
to excited oxygen molecules [27]. Srauf et al. [31a]
found that the chemiluminescence spectra of the oxidation of formaldehyde with H202, and of other organic
and inorganic oxidation reactions, correspond to the
absorption bands of ( 0 2 ) ~molecules, which should
therefore be considered as the emitting species. The
chemiluminescence that accompanies the oxidation of
pyrocatechol, resorcinol, and other polyfunctional
phenols with ozone can be sensitized by fluorescent dyes
such as rhodamine B. Quantitative investigations have
recently been carried out of the dependence of this
sensitized chemiluminescence on the structure of the
polyphenol [32].
of the chemiluminescence of “lucigenin” (6) and “luminol” ( I I ) , which will be discussed in the next section.
5. Tetrakis(dimethy1amino)ethylene
The autoxidation of the powerful electron donor tetrakis(dimethylamino)ethylene, [(CH&N]2C=C[N(CH3)&
( l a ) , and its reaction with bromine, occur with emission
of green light [32a, b], the spectrum of which agrees with
the fluorescence spectrum of ( l a ) [32c]. The products
include tetramethylurea, tetramethyloxamide, and bis(dimethy1amino)methane [32b, d], which are formed, as
shown by NMR-spectroscopy [32d], from the primary
product (Ib), which can be isolated under suitable conditions. According to kinetic studies by Paris [32e], the
carbene [(CH3)2N]zC: is an important intermediate.
6. 2,4,5-Triphenylimidazole
(“Lophine”) and Related Compounds
Fig. 1. Relative intensities of the chemiluminescence of substituted
Iophines (2) [351.
10: maximum intensity of lophine (2).
I : maximum intensity of the substituted lophine
Abscissa: o constants according t o J . H:trc f33aI-
The chemiluminescence intensities of a number of lophine derivatives containing substituents in positions 3’
or 4’ of the 2-phenyl group [33] have recently been
compared. It can be seen from Fig. 1 that the substituent
effects follow the Hammett equation. All the substituted
lophines were found to have a chemiluminescence emission maximum at 530mp, irrespective of whether the
oxidation is carried out with oxygen or with hydrogen
peroxide. Recent investigations [34] indicate that the
oxidation of (2) in alkaline media leads via the anion to
the diimidazolyl derivative (3), which exists in equilibrium with the radical (4). This radical can react with
The blue-green chemiluminescence accompanying the
oxidation of lophine (2) with oxygen in alkaline solution
[3] is one of the strongest known prior to the discovery
[30] Cf. the review by H . Hock, H. Kropf, and F. Ernst, Angew.
Chem. 7 / , 541 (1959).
1311 Th. Bremer and H . Friedmann, Bull. SOC.chim. Belges 63,
415 (1954).
[3 la] J . StauB and F.Lohmalm,Z.physik.Chem.N. F. 40,123( 1964).
[32] D . S. Bersis, Z . physik. Chem. 26, 359 (1960).
[32a] R . L . Pruett et al., J. Amer. chem. SOC. 72, 3646 (1950).
[32b] N . Wiberg and J . W. Buchler, Angew. Chem. 74,490 (1962);
Angew. Chem. internat. Edit. I, 406 (1962); Chem. Ber. 96,
3223 (1963).
[32c] H . E. Winberg, J . R . Downing, and D.D . Coffman, J. Amer.
chem. SOC.,in press.
[32d] W. H. Urry and J . Sheeto: Symposium on Chemiluminescence. Durham, N.C. 1965. Preprints p. 223.
[32e] J . P. Paris, in [32d], p. 243
[33] G. E. Philbrook and M . A . Maxwell, Tetrahedron Letters
1964, 1111.
[33a] J. Hine: Physical Organic Chemistry. McCraw-Hill, New
York 1962, p. 87.
[34] T. Hayashi and K . Mueda, Bull. SOC.chem. Japan 35, 2057
(1962); 36, 1052 (1963).
[35] T. Huyashi and K . Maeda, Bull. chem. SOC.Japan 35, 2058
( 1962).
Angew. C h e m . internut. Edit. Vol. 4 (1965) 1 NO. 7
oxygen to form the peroxide (4a) [35a], which decomposes into benzoic acid, ammonia, and other products,
with simultaneous emission of light. (4a) is relatively
stable; it can be isolated, and it chemiluminesces in warm
oxygen-free alkaline solutions or when heated to 1 10 “C
Since the chemiluminescence spectra of (2) and its
derivatives are identical with the fluorescence spectra of
diaroylarylamidine salts of the type (4b), these salts are
regarded as the emitting species [35b]. A similar reaction
sequence is also postulated for the weakly chemiluminescent oxidation of 2,3,4,5-tetraphenylpyrrole[35], i.e.
the radical ( 5 ) is an important intermediate in this case.
7. 9,9’-Diacridinium Salts
(“Lucigenin” and Related Compounds)
The intense green chemiluminescence observed during
the oxidation of “lucigenin” (6) with H z O 2 in alkaline
solution was first described by Gleu and Petsch [36] (cf.
[7]). The observation [37] that the color of the chemiluminescence changes from green to blue when the Nalkyl groups in compounds of the type (6) are replaced
by phenyl groups to form (7), was confirmed for the
CH, Clo
8. 3-Aminophthalhydrazide (“Luminol”)
and Other Hydrazides
Since the first publication [48]describing the intense blue
chemiluminescence accompanying the alkaline oxidation
of 3-aminophthalhydrazide (5-amino-l,2,3,4-tetrahydrophthalazine-1,4-dione)( I I ) , these and similar chemiluminescence reactions have been studied in great detail
[2-6,46,48]. The reader is referred in particular to
Anderson’s review [7], which presents an excellent
analysis of the position regarding the luminol problem
at the beginning of the second phase of these investigations (after 1945).
a) Constitution and Luminescence in
AIbrecht [48] had referred as early as 1928 to the cheniilumescence of N,N‘-diacylhydrazines on oxidation in
alkaline media; his investigations, however, were mainly
confined to substituted phthalhydrazides, since these
give by far the most intense effects. The chemiluminescence of acyclic diacylhydrazines was confirmed by
Kautsky and Kaiser [49], who postulated that acyclic hydrazides are in principle capable of chemiluminescing,
provided they are fluorescent (see also [50]). Ojir??ainvestigated inter alia the emission of light by monoacyl-
N,N’-di-p-tolyl compound (8) [38]. Recent spectroscopic and kinetic studies [39-461 corroborate the
finding [47] that the radiating species in the “lucigenin”
chemiluminescence is N-methylacridone (10) ; this is
probably formed in a free-radical chain reaction involving the hydroperoxide ( 9 ) [43,47a]. The peroxyacid
derivative (IQa) shows strong chemiluminescence with
+ HCl
[3Sa] J . Sonnenberg and D. M . White, J . Amer. chem. Soc. 86,
5685 (1964).
[35b] E. H . Whiteand M . J. C. Harding, J . Amer. chem. SOC.86,
5686 (1964).
1361 K . Gleu and W. Petsch, Angew. Chem. 48, 57 (1935).
[37] K . Gleu and R. Schaarschmidf, Ber. dtsch. chem. Ges. 73 B,
909 ( I 940).
[38] A. Cl~rzaszczewska,A. Braran, and M . Nowaczyk, SOC.Sci.
Lodziensis, Acta chim. 3, 93 (1958); Chem. Abstr. 53, 13 148
Angew. Chern. iiifernat. Edit. Vol. 4 (1965) No. 7
[39] B. D . Rpzhikov, Dokl. Akad. Nauk SSSR, Ser. Fiz. 20,
533 (1956).
[40] J. Kroh and Z . Czernik, Rocznikl Chem. 3 / , 915 (1957);
Chem. Abstr. 52, 6928 (1958).
[41] A. V. Karyakin, Opt. i Spektroskoplya 7, 122 (1959); Chem.
Abstr. 54, 23816 (1960).
[42] A . Dorabiatska and K . Kolodziejrzak, SOC.Sci. Lodziensis,
Acta chim. 7, 5 (1961); Chem. Zbl. 1965, Nr. 2, 0886.
[43] J. R. Tctter, V. J . Medinn, and J . L . Scoseria, J . biol. Chemistry 235, 238 (1960).
1441 J . R.Tofter, Photochem. Photobiol. 3, 231 (1964).
[45] L. Greenlee, I. Fridovich, and P . Handler, Biochemistry I ,
779 (1962).
[46] E. H. White in W. D. McHroy and B. G/arr [17], p. 183.
[47] H. Kautsky and K . H . Kaiser, Naturwissenschaften 3 / , 505
[47a] F. McCapra and D . G. Richardson, Tetrahedron Letters
1964, 3167.
1483 H . 0. Albrecht, Z . physik, Chem. 136, 321 (1928).
[49] H. Kautsky and H . Kaiser, 2. Naturforsch. 5b, 353 f 1950).
[50] J . Kroh and J. L u c ~ ~ c z e w s kRoczniki
Chem. 30,647 (1956).
hydrazines on uncatalysed oxidation with hydrogen
peroxide in alkaline solution. He found that the luminescence of anthranilhydrazide (13) is 5 orders of magnitude weaker than that of luminol ; chemiluminescence
is also observed with m-aminobenzhydrazide (14), but
not with the p-isomer (15) [2,51]. As explained in Section 8b, the deciding factor is whether the carboxylic
acid on which the hydrazide is based, or its anion, is
capable of fluorescing, as is the case with (13) and (14),
(131, R = o-NH2
1141, R = m-NH,
(IS). R = p-NH2
but not with (15). Similar behavior is found with the isomeric hydroxybenzhydrazides [5l 1, although the luminescence in this case is about ten times weaker. If, however, the hydrazinocarbonyl group is attached to a
strongly fluorescent aromatic hydrocarbon residue, as
in (16),the quantum yield of the chemiluminescence is
about 113 of that of Luminol [2].
An extremely important point with regard to chemiluminescence is that the hydrazide group remains unaltered ;
thus (17), (la),and (19) do not chemiluminesce [52,53].
It is evidently essential that the molecule contains a bond
system from which elementary nitrogen can be readily
split off.
2. The effects of substituents in position 3 of the phthalhydrazide system are more pronounced than those of
substituents in position 4; this is particularly obvious on
comparing luminol ( I I ) with the isomeric 4-aminophthalhydrazide (12), the luminescence of which is an
order of magnitude weaker than that of (11).
Deviations from Rule 1 are observed in the cases of 3methylamino- and 3-dimethylaminophthalhydrazide;
the emission of the former is only about 60%, and that
of the latter only 2%, of that of lurninol, although the
alkylamino and dialkylamino groups are stronger electron donors than the amino group [58]. This anomaly is
due to steric hindrance of resonance. Thus the dimethylamino group in position 3 cannot lie in the same plane
as the aromatic system, owing to the adjacent carboxyl
group. The compound therefore behaves essentially as
the parent phthalhydrazide system, which is only very
faintly chemiluminescent. In 3-methylaminophthalhydrazide, on the other hand, the methylamino group can
lie in the same plane as the benzene nucleus, but only in
the configuration in which the N-methyl group is turned
away from the carbonyl group. However, the steric
hindrance of resonance in the phthalhydrazides is probably less important than in the corresponding phthalate
dianions (which are the radiating particles; cf. Section 8b).
The chemiluminescence of 3-methylphthalhydrazide [52]
is weaker than that of phthalhydrazide, although the
methyl group acts as an electron donor; this is probably
again due to steric hindrance.
Drew et al. 1541 have studied how substituents in the
benzene ring affect the chemiluminescence of the phthalhydrazide, and have listed the intensities of the chemiluminescence of a number of substituted phthalhydrazides [55], which have been largely confirmed by subsequent measurements [56-581. These investigations led
to the formulation of two main rules:
1 . The chemiluminescence is strengthened by electronreleasing substituents in the benzene nucleus of the
phthalhydrazide system, and weakened by electronattracting substituents, analogously to the substituted
lophines (Section 6).
Table 1. Relative emissions of 4-dialkylaminophthalhydrazides158,591
(luminol = 100).
1937, 1841.
1525 (1950).
[57] A . A. Ponomarenko, N . A . Markar’yan, and A . I. Komlev,
Dokl. Akad. Nauk SSSR 89, 1061 (1953); cited by [3].
[58] K.-D.Gundermann and M . Drawert, Chem. Ber. 95,201 8 ( I 962).
4 - D i a 1 k y 1a mi n o p h t h a 1h y d r a z i d e s
Dialkylamino groups in position 4 of the phthalhydrazide or of the phthalate dianion are not sterically hindered,
and the luminescence in this case is an order of magnitude
stronger than that of 4-aminophthalhydrazide. The
maximum chemiiuminescence intensity of 4-diethylaminophthalhydrazide (in the hemin-catalysed oxidation) is equal to that of luminol, and the total emission
exceeds that of luminol by 20-30% [ 5 8 ] ; this was the
first hydrazide found to have a greater chemiluminescent
power than luminol. Other 4-dialkylaminophthalhydrazides exhibit cherniluminescence as strong as that of
luminol 158,591 (Table I).
[Sll H. Ojima, Naturwissenschaften 48, 600 (1961).
[52] H. D. K. Drew and R. F. Garwood, J. chem. SOC. (London)
[53] E. H . Huntress and J. V. K. Gladding, J. Amer. chem. SOC.
64, 2644 (1 942).
1541 B. E. Cross and H. D . K . Drew, J. chem. SOC. (London) 1949,
1532, and earlier papers.
[55] H . D. K. Drew and F. H. Pearman, J. chern. SOC. (London)
[56] A . Spruit van der Burg, Recueil Trav. chim. Pays-Bas 69,
S t e r i c H i n d r a n c e of R e s o n a n c e
(relative emission)
(20). R
(21). R
(231, R
1591 K.-D. Gundermann, W. Horstmann, and G. Bergmartn, Liebigs Ann. Chem. 684, 127 (1965); Angew. Chem. 76,686 (1964);
Angew. Chem. internat. Edit. 3, 637 (1964).
Angew. Chem. internat. Edit. / Vol. 4 (1965)
I No. 7
The chemiluminescence of the hydrazides (20)-(23) is
much less sensitive to alkali than that of luminol. In the
system aqueous alkali/hydrogen peroxide/hemin, the
emission of luminol reaches its optimum value at an
alkali concentration of 0.03 N, and falls off as the p H is
raised further; the emission of the 4-dialkylaminophthalhydrazides, on the other hand, reaches its optimum value
at an alkali concentration of 0.1 N, and shows no appreciable decrease between this concentration and 1.O
N (cf. [60-62]).
y) Po 1y su bs t it u t e d P h t ha1h y d r a z i d es
According to Rule 1 above, strong chemiluminescence
should be observed above all with phthalhydrazides
having several electron-releasing substituents in the
benzene nucleus. Although such compounds often exhibit very strong fluorescence, however, their ability to
chemiluminesce is by no means always equally pronounced. It is obvious, therefore, that strong fluorescent
power is not necessarily synonymous with strong chemiluminescent power, and that chemical stability in oxidizing media is also an important factor. Thus 3,6-diaminophthalhydrazide exhibits extremely weak chemiluminescence 1551 because, being a p-phenylenediamine
derivative, it is very rapidly oxidized to a red quinone
dye. The chemiluminescence of 3,5-diaminophthalhydrazide (24), however, which cannot be oxidized directly
to a quinone, is also very weak [58].
(271, R' =
R 2 = R 3 = OCH,
= I1
/ 3 3 / , R = N(CzH5)z
( 3 4 ) , R = N(n-C3H7),
(3.5), R = 1 - P y r r o l i d i n y l
(29), R = H
U O ) , R = 1-NH2
i 3 / ) , R = 8-NH2
The intense green chemiluminescence of 7-dialkylaminonaphthalene-l,2-dicarbohydrazidesof the type (32),
however, is two to three times as strong as that of
luminol (Table 2) [59]These hydrazides may be regarded
as vinylogues of the 3-dialkylaminonaphthalhydrazides,
in which the dialkylamino groups, as we have seen,cannot
exert their chemiluminescence-promoting effect, owing
to steric hindrance of resonance. The effect of the alkali
concentration on the chemiluminescence of 7-substituted
naphthaIene-l,2-dicarbohydrazidesis very similar to
that observed in the case of the 4-dialkylaminophthalhydrazides. Since compounds (32) -(35) are yellow, autoabsorption of the chemiluminescence becomes noticeable at lower hydrazide concentrations than in the case
of the colorless luminol.
Table 2. Chemiluminescence, fluorescence, and relative emission of
naphthalene-I ,2-dicarbohydrazides (luminol = 100) 1591.
Fluorescence [*I
Amax 1 w . l
124), R' = H, R2 = NH2, R3 = H
(2.7). R' = R 2 = H, R3 = OCH,
1261, R' = H, R 2 = R3 = OCH,
i 3 7 j , R = N(CH3)2
1 :;;
The compound (25) fluoresces strongly in neutral solution and gives an initially intense chemiluminescence on
hemin-catalyzed oxidation in aqueous solution; however, the intensity of the chemiluminescence falls off very
rapidly. On the other hand, the quantum yields of the
chemiluminescence of (26) and (27) in the system dimethyl suIfoxide/tert-butoxide/oxygenexceed the quantum yield of luminol by 13 and 30% respectively [2].
For a discussion of the partly sterically hindered 3,4-dimethoxyphthalhydrazide a n d of 3,4-methylenedioxyphthalhydrazide, both of which exhibit only weak chemiluminescence, see [61].
[*I Chemiluminescence under optimum conditions [591
A: fluorescence of the hydrazide in 0.2 N NaOH.
B: fluorescence after chemiluminescence has ceased.
E) 4' - D i a 1 k y 1a mi n o s t i I b e n e 2 , 3 - d i c a r b o h y d r a z i d e s [63,63a]
The trans-isomers of compounds of the type (36) are
also sterically unhindered vinylogues or phenylogues of
3-dialkylaminophthalhydrazides.In this case, however,
8) N a p h t h a l e n e d i c a r b o h y d r a z i d e s
As would be expected from the larger x-electron system,
the isomeric naphthalenedicarbohydrazides (28) and
(29) exhibit stronger chemiluminescence than phthalhydrazide [52,54]. Nevertheless, the aminonaphthalenedicarbohydrazides (30) and (31) fall far short of luminol
in intensity [52,54].
~ . . . ...
1601 K. Weber, A. Reiek, and V. Vouk, Ber. dtsch. chern. Ges. 75,
1141 (1942).
161I W. Horstmann, Doctorate Dissertation, Universitat Miinster, 1964.
[621 H. H. Seliger in W. D. McElroy and B. Glass [17], p. 204.
Angew. Chem. internat. Edit. / VoI. 4 (196s)
No. 7
the transmission of the electron-donating effect of the
dialkylamino group requires even greater "de-aromatization" than in the 7-dialkylaminonaphthalene1,2-dicarbohydrazides [64] ; consequently, the chemiluminescence emissions of these stilbene derivatives are lower
than those of the naphthalene derivatives. Thus the
[63] C. WeNhausen, Diploma Thesis, Universitat Munster, 1964.
[63a] K.-D. Cundermann: Symposium on Chemiluminescence
Durham N.C. 1965. Preprints p. 305.
[64]R. Wizinger, Chirnia 15, 89 (1961).
57 1
chemiluminescence of (36), although considerably
stronger than that of the sterically hindered 3-dimethylaminophthalhydrazide, is only about 213 as strong under
optimum conditions as that of luminol. The optimum
chemiluminescence is obtained by the addition of about
40 vol- ”/D of dimethyl sulfoxide to the aqueous alkaline
oxidation solution (H2Oz/hemin). This promoting effect
of dimethyl sulfoxide (which is also shown to a lesser
extent by dimethylformamide and by N-methylpyrrolidone) on the chemiluminescence of hemin-catalysed
oxidations has so far been observed only with stilbene
derivatives of the type (36). The chemiluminescence accompanying the oxidation of luminol in aqueous alkali
with H2Oz/hemin is greatly reduced by even small
quantities of dimethyl sulfoxide (cf. the entirely different
relationships observed in the chemiluminescence of
luminol in the system dimethyl sulfoxide/tert-butoxidel
oxygen [46]).
The emitting particles in the chemiluminescence of
the 7 - dialkylaminonaphthalene- 1,2- dicarbohydrazides
(Section 8a) are again probably not the hydrazides
themselves, but the substituted naphthalene- I ,2-dicarboxylate dianions (cf. Table 2). The same applies to
the stilbene derivatives (36) [64a].
The intermediate steps involved in the chemiluniinescence reactions of hydrazides of the luminol type are
still not known with certainty. The intermediate formation of an azodiacyl compound of the type (38) [48,49]
is unlikely, since e.g. dihydrophthalazinedione (38) prepared by another route [65,66] does not chemiluminesce
under conditions in which distinct chemiluminescence is
observed with the phthalhydrazide [2,46]. The endoperoxide (39) described by Drew and Garwood [67] is apparently a luminol salt containing H202 of crystallization [2] [*I.
b) The Mechanism of the Chemiluminescence
Reaction of Luminol
AZbrecht [48] had assumed as early as 1928 that the oxidation of luminol led to 3-aminophthalic acid and nitrogen. Since, however, he could isolate only unchanged
luminol from the reaction mixture after the chemiluminescence had ceased, he thought that luminol itself was the
emitting species. This view was also shared by other
authors (for a review see [52]).
All earlier investigations on the course of the chemiluminescence reaction of luminol were impeded by the
fact that the initial products of the reaction in aqueous
alkaline media very rapidly undergo further oxidation
and secondary reactions; for a long time, therefore, no
definite breakdown product of luminol could be isolated. It was only by the use of polar organic solvents
such as dimethyl sulfoxide, with oxygen as the oxidizing
agent and tert-butoxide as the base [46], that it became
possible to isolate 3-aminophthalic acid as a product;
the yield (as the dimethyl ester) was such as to show, on
comparison with the quantum yield of the chemiluminescence, that the dianion (37) is the product and the emitting particle of the luminol reaction, and does not result
from a “dark reaction” that accompanies the chemiluminescence reaction. The consumption of alkali and
oxygen and the quantity of nitrogen produced lead to
the overall equation :
+ 2 NaOH +
0 2
+ NZ+ 2 H2O + (37) (as the di-Na salt).
Comparison of the chemiluminescence spectrum of the
luminol reaction with the fluorescence spectra of luminol
and of (37) also shows that the radiating species is not
luminol, but (37) [2].
The mesomeric dianion (40) could be an intermediate in
the chemiluminescence reaction of luminol with oxygen,
If the oxygen used is enriched in 180, more than 85 % of
the latter is found in the 3-arninophthalic acid after the
reaction [68].
N o free-radical intermediates could be detecied in the luminol
reaction by electron spin resonance measurements [68]. A
free-radical chain mechanism may nevertheless b e assumed,
a t least in other oxidizing systems, for t h e chemiluminescence
reaction of luminol also 169-7 11. Th u s chemiluminescence
has been brought ab o u t in aqueous solutions of luminol by
the action of X-rays, a n d this effect can b e blocked by t h e
introduction of cysteine, which acts a s a free-radical interceptor [72].
Further evidence in favor of a free-radical mechanism is t o
be found in the recent extensive literature on the influence of
catalysts o n t h e chemiluminescence reaction of luminol (cf.
t h e reviews [73,74]; also [74al).
[64a] K.-D. Gundermann, unpublished work.
[65] .‘2 J. Kealy, J. Amer. chem. SOC.84,966 (1962).
I661 R . A . Clement, J. org. Chemistry 2 5 , 1724 (1960).
[67] H. D. K. Drew apd R . F. Garwood, J. chern. SOC.(London)
1938, 791.
[*] Note added in proof: W. S. Metcalf and T . J . Quickenden,
Nature (London) 206, 507 (1965) recently found that lurninol
chemiluminesces in alkaline solutions of hydroxylamine - 0 sulfonic acid, p-toluenesulfonylhydrazide,and other substances
which give rise to diimine, HC=NH, under these conditions.
The Albrecht-Kautsky mechanism is thus provided with new
experimental support.
[68] E. ff.White, 0. Zafriou, H . M . Kagi, and J. H . H i / f , J .
Amer. chem. SOC.86, 940 (1964).
[69] J . R.Totter, W. Stevenson, and C . E. Philbrook, J. physic.
Chem. 68, 752 (1964).
1701 H . Behrens, J. R . Totter, and G . E. Philbrook, Nature (London) 199, 595 (1963).
[71] ff. Ojima, J . chem. SOC. Japan, pure Chem. Sect. 80, 1375
( I 959) (formation of 0-radicals from syn-diazotates).
[72] H . Bergsfermann, Strahlentherapie 98, 474 (1955).
[73] L. Erdey, W. F. Pickering, and C . L. Wilson, Talanta 9, 653
( 1962).
[74] H . Linschitz in W. D. McEiroy and B. Glass 1171, p: 173.
[74a] A. K . Babko and L. I . Duborenko, Z . analyt. Chem. 200,
428 (1964).
Angew. Chem. internat. Edit. / Vol. 4 (1965)
No. 7
9. Chemiluminescence of Aromatic
Free-Radical I o n Pairs
When anthracene, chrysene, pyrene, and other highly
condensed aromatic hydrocarbons are electrolysed in
dimethylformamide or acetonitrile with tetraethylammonium salts as electrolytes, chemiluminescence occurs
in the neighborhood of the cathode, provided that
atmospheric oxygen (which has a quenching effect in this
case) is excluded. This chemiluminescence is due to an
excited singlet state of the hydrocarbon 1751; this presumably results from the formation at the electrodes of
hydrocarbon radical ions. -Ar0 and .Ar which then
react with each other in solution by a one-electron
This new type of chemiluminescence reaction can also be
brought about by purely chemical means. Thus the compound (41) obtained by the reaction of potassium metal
with 9,lO-diphenylanthracene (43) reacts with 9,lO-dichloro - 9,10-diphenyl - 9,lO - dihydroanthracene (42),
emitting a bright chemiluminescence that has been
identified as the fluorescence of 9,lO-diphenylanthracene [76]. Basically this reaction again involves the
transfer of an electron from the free-radical anion of the
potassium compound (41) to the acceptor (42), which is
a potential 9,lO-diphenylanthracenium dication; (43) is
then formed, partly in the excited singlet state (recombination luminescence; cf. [761).
The investigations carried out so far have indicated that
this type of chemiluminescence reaction is of general
importance; thus the free-radical anion (41) may be
replaced by another donor, such as the sodium compound of naphthalene or of N-methylacridone. Other
electron acceptors that can be used are diacylperoxides
or even aluminum chloride. The only essential point
seems to be that the free-radical anion must be derived
from a molecule that fluoresces in the visible region of
the spectrum, and that the acceptor molecule has no
quenching action.
According to Chandross, one-electron transfers of this
type are probably much faster than chemical reactions
in which covalent bonds are formed or broken. The
faster the release of chemical energy in the smallest possible volume of the reaction solution, the smaller should
be the losses due to radiationless energy transformations
1751 D. M . Hercules, Science (Washington) 145, 808 (1964); R. E.
Visco and E. A. Chandross, J . Amer. chem. SOC.86, 5350 (1964);
K . S. V. Santhanam and A. J. Bard, ibid. 87, 139 (1965).
1761 E. A. Chairdross and F. I . Sonntag, J. Amer. chem. SOC.86,
3179 (1964).
Angew. Chem. inrernat. Edit.
Vol. 4 (1965) No. 7
(into heat, etc.), and the greater the proportion of the
chemical energy transformed into excited electronic
states. It is likely, therefore, that this new type of chemiluminescence reaction comes closer than most other
types to the ideal conditions of bioluminescence reactions.
10. Firefly Luciferin
The bioluminescence of the American firefly (Photinus
pyralis) is probably the most widely studied of the biological luminescence reactions (for a review, see [17]).
The structure elucidation and synthesis of the substrate
of this reaction, i.e. firefly luciferin (44) is due to White
eta]. [77]. In vivo, (44) is converted to the dehydro compound (45), with simultaneous emission of light, by the
action of the enzyme luciferase together with adenosine
triphosphate [*I, Mg2+ ions, and oxygen. It has been
possible to study these processes in vitro, since both the
luciferin and the luciferase have been isolated in the
crystalline state [17].
The light emitted on dehydrogenation of firefly luciferin
has a maximum at 562 m p (cf. also [78]), corresponding
to an energy of at least 57 kcal/mole. (44) can also be
made to luminesce (although only very weakly) in the
absence of the enzyme by the use of powerful oxidizing
agents [79].
11. Closing Remarks
Notable progress has been made during recent years in
the investigation of the chemiluminescence of organic
compounds. Nevertheless, many questions, such as that
of the quantitative relationship between chemiluminescence and structure, have not yet been answered. The
mechanisms of many chemiluminescence reactions also
require further clarification. A possible additional
advantage of knowing these mechanisms is that they may
suggest methods of obtaining higher quantum yields than
are possible at present.
I am grateful /o Dr. Bergmann f o r many helpful discussions and for his collaboration in the experimental work.
Received: March 9th. 1965
[A 450/229 IE]
German version: Angew. Chern. 77, 572 (1965)
Translated by Express Translation Service, London
[77] E. H . White et al., J. Amer. chem. SOC.83, 2402 (1961); 8.5,
337 (1963).
[*I This bioluminescence provides a method of following the
formation of ATP in biological phosphorylation reactions: B. L .
Strehler and D . D . Hendley in W. D . McElroy and B. Glass, ref.
[17], p. 601.
[78] H. H. Seliger et al., J. gen. Physiol. 48, 95 (1964).
[79} H . H. Seliger and W. D . McElroy, Science (Washington)
138, 683 (1962).
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