Dramatic synergistic effects between hydroquinone and resorcinol derivatives for the organocatalyzed reduction of dioxygen by diethylhydroxylamine

Article abstract of DOI:10.1039/c3cc47261b

Diethylhydroxylamine reduces dioxygen in the presence of catalytic amounts of hydroquinone. A great improvement is achieved by adding resorcinol derivatives as co-catalysts. Though the formation of heterodimers does not seem to be the sole cause of the synergy, such products constitute a new class of powerful organocatalysts for dioxygen scavenging. The Royal Society of Chemistry.

Full text of DOI:10.1039/c3cc47261b

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Dramatic synergistic effects between
hydroquinone and resorcinol derivatives for
the organocatalyzed reduction of dioxygen
by diethylhydroxylamine†
Cite this: Chem. Commun., 2014,
50, 866
Received 23rd September 2013,
Accepted 12th November 2013
Raphael Lebeuf, Veronique Nardello-Rataj and Jean-Marie Aubry*
´
¨
DOI: 10.1039/c3cc47261b
www.rsc.org/chemcomm
Diethylhydroxylamine reduces dioxygen in the presence of catalytic the catalysts.11 A first approach to improve the catalytic system
amounts of hydroquinone. A great improvement is achieved by was to find more active polyphenols that led to the identifi-
adding resorcinol derivatives as co-catalysts. Though the formation cation of gallic acid as a safer alternative to hydroquinone.11,12
of heterodimers does not seem to be the sole cause of the synergy, Alternatively, antioxidants are well-known to present synergistic
such products constitute a new class of powerful organocatalysts effects in radical trapping chain transfer reactions, like the
for dioxygen scavenging.
combination of 2,5-di-tert-butyl-3-methylphenol (BHT) with
2-tert-butyl-4-hydroxyanisole (BHA),13 or tocopherol with ascorbic
In addition to being key biologically active compounds,1,2 acid.14 Such synergies between dioxygen scavengers have how-
antioxidants are ubiquitous inhibitors to prevent the oxidative ever, to the best of our knowledge, not been reported yet.
degradation of many end-use products such as polymers,
We first assessed the catalytic activity of the 3 dihydroxy-
lubricants, foods, cosmetics and fragrances.3–5 Most of them benzene regioisomers (hydroquinone 1, catechol 2 and resor-
act as radical chain breakers once the dioxygen has reacted with cinol 3a) alone or pairwise (Fig. 1). The concentration of
the substrate.6 They constitute a class of primary antioxidants dissolved dioxygen ([O2]0 E 0.28 mM) in a buffered alkaline
according to Ingold classification.7 The so-called secondary solution ([NaHCO3] = 10 mM, [Na2CO3] = 16 mM, pH = 10.1)
antioxidants prevent oxidation through any other process except containing a 3 fold excess of DEHA (0.84 mM) was monitored as
direct radical trapping. Dioxygen scavengers belong to this cate- a function of time thanks to a dioxygen electrode based on
gory as they provide anaerobic media by direct reduction of luminescence extinction, in the presence of different catalysts
dioxygen. The main industrial application of such a system is (total concentration = 16 mm). Hydroquinone 1 is a much better
the deoxygenation of boiler water, in order to prevent corrosion catalyst than catechol 2, whereas resorcinol 3a does not catalyze
of metallic surfaces.8 For this purpose, the catalytic system com- the reaction at all since the same conversion of O2 is observed
posed of diethylhydroxylamine and hydroquinone (DEHA–H2Q)
is one of the most effective9 since hydroquinone rapidly reacts
with dioxygen in aqueous basic solution.10
(1)
As H2Q is potentially carcinogenic, we sought to boost its
activity to reduce its concentration or replace it by a more
efficient catalyst. Most of the substituents grafted onto hydro-
quinone lead to the depletion of the activity. However, with
methoxy and chlorine substituents, the reactions run faster,
albeit without improving the TON because of degradation of
´
´
Universite Lille Nord de France, Universite Lille 1 and ENSCL, EA 4478 Chimie
´
´
Moleculaire et Formulation, Cite Scientifique – BP 90108, 59652 Villeneuve d’Ascq
Cedex, France. E-mail: jean-marie.aubry@univ-lille1.fr; Tel: +33 (0)320436364
† Electronic supplementary information (ESI) available: Curves for dioxygen
consumption, data for compounds 5, 6, and the proposed mechanism for the
formation of 5 herein. See DOI: 10.1039/c3cc47261b
Fig. 1 Consumption of dissolved O2 by DEHA as a function of time in the
presence of hydroquinone 1, catechol 2 and resorcinol 3a alone (K) or
pair wise in stoichiometric amounts (J). Conditions: [O2]0 = 0.28 mM,
[DEHA] = 0.84 mM, [total catalyst] = 16 mM, pH = 10.1, T = 25 1C.
866 | Chem. Commun., 2014, 50, 866--868
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without catalyst. This slow disappearance of O2 is due to the activity of the various substituted co-catalysts 3b–k with that
uncatalyzed reaction of DEHA with O2.15
of resorcinol 3a itself (entry 2) shows that a third OH group
The combination of hydroquinone 1 with catechol 2 in a 1 : 1 grafted onto the resorcinol core (pyrogallol 3b and phloro-
ratio gives the expected curve between the ones obtained using glucinol 3c) is detrimental to the synergistic effect probably
the two components separately. However, its profile is closer to because it increases their susceptibility to degradation (entries 3
that of hydroquinone than to catechol, as it levels off after and 4). The presence of a methyl group in positions 2 and 4 has
10 minutes only. This behavior suggests that the two catalysts no effects whereas in position 5 (orcinol, 3f) the synergy is
interact with each other. The mixture of catechol 2 and resorci- greatly improved, both in terms of the reaction rate and
nol 3a shows a complicated synergistic effect since no reaction conversion (entries 5–7). We then studied in more detail the
occurs at the beginning but, after a lag time of E5 min, the influence of various R5 substituents bound to this crucial
reaction starts and leads to higher O2 consumption despite the position. The electron-donating groups OCH3, COOÀ and
half lower concentration of catechol and the lack of reactivity of C6H5 have also a beneficial effect but they fail to perform better
resorcinol. A much more dramatic synergistic effect is observed than CH3 (entries 8, 11 and 12). The electron-withdrawing group
for the mixture hydroquinone 1–resorcinol 3a since almost all COOEt suppresses, almost completely, the synergistic effect
dissolved oxygens disappear within 15 min (Fig. 1).
(entry 10) whereas Cl induces the same effect as H (entry 9),
To further investigate this remarkable synergy, eleven reso- confirming that no clear correlation can be established between
rcinol derivatives 3a–k were screened to determine the influence the Hammet constants of the substituents and the reaction rate.
of the position and the electronic effects of their substituents Hence, substitution at the meta position of the resorcinol pattern
on the synergy with hydroquinone 1, and to further improve the with an electron-donating substituent other than an OH group is
catalytic system. Table 1 lists, for all the investigated systems, highly beneficial for the catalytic activity.
the maximum turnover frequency (TOFmax) reached after a
The mechanism of the binary DEHA–H2Q catalytic system
few seconds of reaction and the maximum percentage of O2 (eqn (1)) has already been discussed in detail.11 The rate limit-
consumed, conv. = D[O2]N, once the catalyst is completely ing step is believed to be the regeneration of hydroquinone H2Q
degraded (see Fig. 1). To facilitate comparisons, the turnover or its conjugated base HQÀ, either through disproportionation
numbers (TON) have also been reported. Very low concentra- of the semiquinone radical HQꢀ into H2Q and benzoquinone
tions of hydroquinone and of co-catalysts were used (1 mM for Q (Scheme 1, pathway A), or its direct reduction by DEHA
each of them) to let residual dioxygen, thus allowing compar- (Scheme 1, pathway B).
ison of the catalytic systems.
According to the mechanism of pathway A and the litera-
None of the resorcinol derivatives exhibit catalytic activity ture,16 Q is reduced by DEHA to HQꢀ. Therefore, Q can also be
when used alone at 1 mM concentrations, except pyrogallol 3b used as a catalyst instead of H2Q. Indeed, the experiment
which gives 29% of conversion (see ESI†). Comparing the carried out using benzoquinone 4 as a catalyst and orcinol 3f
as a co-catalyst shows a similar synergistic effect to that carried
out using hydroquinone 1 with 3f (compare Table 1, entries 7
and 13, and Fig. 2).
Table 1 Consumption of dioxygen dissolved in water by DEHA in the
presence of polyphenolic catalysts and co-catalysts. Conditions: [O2]0
=
0.28 mM, [DEHA] = 0.84 mM, [catalyst] = 1 mM, [co-catalyst] = 1 mM, pH = 10.1,
T = 25 1C
Although this result does not prove the formation of benzo-
quinone during the catalytic cycle, the possibility of in situ
formation of a more active catalyst from benzoquinone was
considered. This hypothesis follows the work of Kurechi’s
group, who claimed that heterodimer by-products obtained
from a mixture of two phenolic antioxidants might be respon-
sible for their synergy in radical chain trapping processes.17 For
instance, they show that the heterodimer of the couple BHA–
BHT exhibits a higher antioxidant activity than the single
compounds.13 In an attempt to form an eventual heterodimer,
concentrated benzoquinone 4 (0.2 M) and orcinol 3f (0.2 M)
a
Conv. TOFmax
(%)
Entry Cat. Co-cat. R2
R4
R5
(minÀ1
)
TONa
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
1
1
1
1
1
4
5
6
1
—
H
OH
H
Me
H
H
H
H
H
H
—
H
H
H
H
Me
H
H
H
H
H
H
H
—
—
—
H
H
OH
H
18
57
24
27
59
56
89
81
58
6
14
5
50
160
67
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3f
—
—
7
76
17
18
27
16
15
4
16
21
31
15
17
165
157
249
227
162
67
238
216
252
246
241
H
Me
OMe
Cl
CO2Et 24
CO2H 85
Ph
Me
—
9
10
11
12
13
14
15
H
H
—
—
77
90
88
86
—
Scheme 1 Proposed mechanisms for the reduction of dioxygen by the
catalytic system DEHA–H2Q.
a
Relative to catalysts only.
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and may well also form in basic medium. It would change the
redox potential of each compound and could accelerate the
regeneration of HQÀ facilitating the transfer of a hydrogen
À
atom from resorcinol or DEHA to the Qꢀ radical. The validity
of this assumption is under consideration.
In conclusion, the binary catalytic systems based on hydro-
quinone + resorcinol derivatives exhibit dramatic synergistic
activities for dioxygen reduction by DEHA. The likely formation
of a heterodimer as proposed in the literature for other anti-
oxidant synergies does not seem to be the sole explanation
herein, as revealed by the study of one of them. However, the
effectiveness of these heterodimers as oxygen scavengers will
encourage us to pursue the study of this new class of organo-
catalysts to define their mode of action, as well as their
efficiency as catalysts and/or antioxidants in other processes
involving radical chain transfer reactions.
Fig. 2 Dioxygen reduction in water as a function of time for hydroquinone
1 (1 mM), hydroquinone 1 + orcinol 3f (1 + 1 mM), benzoquinone 4 + orcinol
3f (1 + 1 mM), heterodimer 5 (1 mM), and heterodimer 6 (1 mM). Conditions:
[DEHA] = 0.84 mM, [O2]0 = 0.28 mM, pH = 10.1, T = 25 1C.
Arkema is gratefully acknowledged for financial support in
the research program concerning DEHA activation.
Notes and references
1 O. Dangles, Curr. Org. Chem., 2012, 16, 692.
2 P. C. H. Hollman, A. Cassidy, B. Comte, M. Heinonen, M. Richelle,
E. Richling, M. Serafini, A. Scalbert, H. Sies and S. Vidry, J. Nutr.,
2011, 141, 989S.
3 P. K. J. P. D. Wanasundaral and F. Shahidi, Antioxidants: Science,
Technology, and Applications, in Bailey’s Industrial Oil and Fat Products,
ed. F. Shahidi, John Wiley & Sons, Inc, 6th edn, 2005, ch. 11.
4 E. T. Denisov and I. B. Afanas’ev, Oxidation and Antioxidants in
Organic Chemistry and Biology, CRC Press, Taylor & Francis Group,
2005.
5 C. Marteau, V. Nardello-Rataj, D. Favier and J.-M. Aubry, Flavour
Fragrance J., 2013, 28, 30.
6 M. Lucarini and G. F. Pedulli, Chem. Soc. Rev., 2010, 39, 2106.
7 K. U. Ingold, Adv. Chem. Ser., 1968, 75, 296.
8 NACE International, ‘‘Oxygen Scavengers in Steam Generating
Systems and in Oil Production’’. NACE PUBLICATION 3A194, NACE
International, Houston, TX, 1994.
9 J. J. Nemes, H. W. Thompson and J. E. Waller, EP Pat. 0 161 822 A2,
1985; M. Schweinsberg, P. Gentschev, A. Arnold and W. Hater,
DE Pat. 103 45 820 A1, 2005; D. G. Cuisa, C. M. Hwa and M. L.
Salutsky, EP Pat. 0 297 916 B1, 1989.
10 L. Valgimigli, R. Amorati, M. G. Fumo, G. A. Dilabio, G. F. Pedulli,
K. U. Ingold and D. A. Pratt, J. Org. Chem., 2008, 73, 1830.
11 R. Lebeuf, Y. Zhu, V. Nardello-Rataj, J.-P. Lallier and J.-M. Aubry,
Green Chem., 2012, 14, 825.
12 R. Lebeuf, V. Nardello-Rataj and J.-M. Aubry, Top. Catal., 2013,
56, 933.
Scheme 2 Condensation reaction between benzoquinone and orcinol.
were mixed together in basic aqueous media under argon. After
a few minutes, benzoquinone was completely consumed and the
heterodimer 5 was isolated with 15% yield besides polymeric
by-products (Scheme 2).
No redox process is required for this condensation that may
involve successively 1,4-addition of 3b to 4 and two tautomeri-
zations of the adduct (see ESI†). Surprisingly, this heterodimer
has not been reported so far in the literature although similar
condensation products have been obtained by reaction of
resorcinol 3a on benzoquinone18 4 or acylbenzoquinone19
under acidic or basic conditions. Musso et al. also reported
the synthesis of a heterodimer with 21% yield by reacting
resorcinol 3a with hydroxyquinone 1 in aerobic basic solution20
but the antioxidant properties of such compounds have not
been investigated.
13 T. Kurechi and T. Kato, J. Am. Oil Chem. Soc., 1980, 57, 220.
14 K. Mukai, S. Itoh and H. Morimoto, J. Biol. Chem., 1992, 267, 22277.
15 D. Shaffer and J. Heicklen, J. Phys. Chem., 1986, 90, 4408.
As shown in Fig. 2, the heterodimers 5 and 6 are clearly more
stable than their corresponding binary catalytic systems 1 + 3f
and 4a + 3f since they lead to similar O2 conversions although 16 S. Fujita and K. Sano, J. Org. Chem., 1979, 44, 2647.
the TOFs are about two times smaller (15 and 17 minÀ1 vs. 27
17 K. Kikugawa, A. Kunugi and T. Kurechi, in Food antioxidants, ed.
B. J. F. Hudson, Elsevier Applied Science, London, 1990, ch. 3. See
also: R. de Guzman, H. Tang, S. Salley and K. Y. S. Ng, J. Am. Oil
and 31 minÀ1, entries 14 and 15 vs. 7 and 13). These results
indicate that the synergy is not only due to the formation of the
heterodimers 5 or 6, even if their formation and participation
in the catalytic process cannot be ruled out. An alternative to
Chem. Soc., 2009, 86, 459.
18 N. E. Stjernstrom, Ark. Kemi, 1963, 6, 57.
19 P. Kuser, M. Inderbitzin, J. Brauchli and C. H. Eugster, Helv. Chim.
Acta, 1971, 54, 980.
the establishment of a covalent bond between resorcinol 3a and 20 H. Musso, U. von Gizycki, U. I. Zahorszky and D. Bormann, Liebigs
Ann., 1964, 676, 10.
21 T. Ito, M. Minobe and T. Sakurai, Acta Crystallogr., 1970, B26, 1145.
22 A. K. Mukherjee and K. Datta, J. Chem. Soc., Faraday Trans., 1992,
hydroquinone 1 could be the formation of a charge transfer com-
plex (CTC). Indeed, a CTC between benzoquinone 4 and resorcinol
3a has been described in a neutral aqueous environment,21,22
88, 563.
868 | Chem. Commun., 2014, 50, 866--868
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