Study of the reaction of 3,6-di-tert-butyl-o-benzoquinone with organozinc and organocadmium compounds

Article abstract of DOI:10.1134/S1070363216010072

The effect of substituents in the reactions of 3,6-di-tert-butyl-o-benzoquinone with organozinc and organocadmium compounds, leading to three types of products: 3-alkyl-6-tert-butyl-o-benzoquinones, 4-alkyl-3,6-di-tert-butyl-o-benzoquinones, and 2-alkoxy-(or 2-phenoxy)-3,6-di-tert-butylphenols. Correlation analysis gave evidence to show that the first- and second-type products are formed by nucleophilic 1,2- and 1,4-addition, while substituted phenols result from single-electron transfer.

Full text of DOI:10.1134/S1070363216010072

ISSN 1070-3632, Russian Journal of General Chemistry, 2016, Vol. 86, No. 1, pp. 37–42. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © Yu.A. Kurskii, N.O. Druzhkov, A.N. Egorochkin, G.A. Abakumov, 2016, published in Zhurnal Obshchei Khimii, 2016, Vol. 86,
No. 1, pp. 41–46.
Study of the Reaction of 3,6-Di-tert-butyl-о-benzoquinone
with Organozinc and Organocadmium Compounds
Yu. A. Kurskii, N. O. Druzhkov, A. N. Egorochkin, and G. A. Abakumov
Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
ul. Tropinina 49, Nizhny Novgorod, 603950 Russia
e-mail: kursk@iomc.ras.ru
Received June 26, 2015
Abstract—The effect of substituents in the reactions of 3,6-di-tert-butyl-о-benzoquinone with organozinc and
organocadmium compounds, leading to three types of products: 3-alkyl-6-tert-butyl-о-benzoquinones, 4-alkyl-
3,6-di-tert-butyl-о-benzoquinones, and 2-alkoxy-(or 2-phenoxy)-3,6-di-tert-butylphenols. Correlation analysis
gave evidence to show that the first- and second-type products are formed by nucleophilic 1,2- and 1,4-
addition, while substituted phenols result from single-electron transfer.
Keywords: о-quinone, organometallic compound, correlation analysis, polarization effect
DOI: 10.1134/S1070363216010072
Two mechanisms were proposed for reactions of
quinones with organometallic compounds. The first is
heterolytic, specifically, nucleophilic addition to
unsaturated conjugated ketones to form either 1,2-
adduct by the C=O bond or 1,4-adduct by the
conjugated double bond [1]. The second mechanism is
homolytic, and it involves single-electron oxidation of
the organometallic compound with quinone, followed
by ion–radical recombination to form substituted
phenols and, possibly, 1,2-adducts [2].
Apparently, in reactions of organic compounds of
group IIB metals with quinones both mechanisms are
operative. To gain a deeper insight into the mechanism
of these reactions, we performed correlation analysis
of the effect of different electronic factors on the yield
of the reaction products. The development of excess
charges on the reaction center in the transition state,
associated with the formation of an activation
complex, induces dipoles in substituents and gives rise
to the polarization effect [9]. Therefore, in the case of a
nucleophilic addition, one can expect an essential
polarization effect of substituents. As to a radical
addition, the product yield should be controlled by
electron-transfer processes [10].
According to [3], reactions of organic compounds
of Zn, Cd, and Hg with sterically hindered о-quinones
at low temperatures occur by a single-electron
oxidation scheme. In the reactions performed at a
higher temperature, nucleophilic addition products
were found along with single-electron transfer (SET)
products [4, 5]. In later research, too, no common view
of the mechanism of reactions of organometallic
compounds with quinones has been developed. Mc
Kinley et al. [6] argued in favor of the SET mechanism
to form both 1,2-adducts and hydroquinone (a reduc-
tion product) for reactions of 1,4-benzoquinone with
organolithium and organomagnesium compounds.
Aponick et al. [7] found no other products but 1,2-
adducts (quinols) in reactions of 1,4-benzoquinone
with various organocadmium compounds, whereas
Shahidzadeh and Ghandi [8] found hydroquinones
along with quinols in the same reactions.
In the present work, in addition to the known
classical inductive, resonance, and steric effects of
substituents, in the correlation analysis of the effect of
different electronic factors on the yields of reactions of
organozinc and organocadmium compounds with
quinones we took account of the polarization effect
that enhances with increasing excess charge on the
reaction center.
To find out the effect of substituents in the
organometallic compounds on the composition of their
reaction products with 3,6-di-tert-butyl-о-benzoqui-
none (1), we took the following compounds: Me2Zn(Cd),
Et2Zn(Cd), Pr2Zn(Cd), i-Pr2Zn(Cd), t-Bu2Zn, and
37

38
KURSKII et al.
Scheme 1.
t-Bu
t-Bu
t-Bu
t-Bu
(1) H+
(2) [O]
O
O
O
O
O
O
+
+
R
H
OMR
R
t-Bu
t-Bu
OMR
R
t-Bu
t-Bu
R
t-Bu
O
O
2
3
4
5
R2M
+
t-Bu
t-Bu
t-Bu
OMR
OR
OH
OR
H+
1
t-Bu
6
Ph2Zn(Cd). All reactions were performed in THF at 1 :
1 reagent ratios. In the course of all reactions of
quinone 1 with alkylated organometallic compounds,
ESR signals of о-semiquinone derivatives of Zn and
Cd were detected [5] (Scheme 1).
compounds 2 with other alkyl substituents already at
–60°С rearrange into 3-alkyl-substituted quinones 4.
In the reaction with t-Bu2Zn analysis was per-
formed immediately after hydrolysis of the reaction
mixture. The main reaction products were 3,4,6-tri-tert-
butyl-2-hydroxycyclohexa-2,5-dien-1-one
(1,4-adduct)
Abakumov et al. [4] showed on the example of the
reactions of quinone 1 with methyl derivatives of Zn
and Cd that the primary 1,2- and 1,4-adducts are
organometallic compounds 2 and 3; after mild
hydrolysis with acetic acid the latter convert into 3,6-
di-tert-butyl-2-hydroxy-2-methylcyclohexa-3,5-dien-
1-one and 3,6-di-tert-butyl-2-hydroxy-4-methylcyclo-
hexa-2,5-dien-1-one. The rearrangement of the
organometallic 1,2-adduct at a temperature higher than
–10°С gives rise a 3-tert-butyl-6-methylpyrocatechol
derivative which is oxidized to form 3-tert-butyl-6-
methyl-о-benzoquinone 4. Thus, the yields of the 2-
hydroxycyclohexadiene derivative and quinone 4 in
the reaction with Me2Zn at 0°С are 75.0 and 1.1% and
at 30°С the yields are 40.8 and 31.1%, respectively. In
the case of ethyl-, propyl-, and isopropyl-substituted
Zn and Cd compounds, from the reaction mixtures
after hydrolysis in the presence of HCl followed by
oxidation with a weakly alkaline solution of potassium
ferricyanide we isolated and characterized by elemen-
and 2-tert-butoxy-3,6-di-tert-butylphenol. Because of
the thermal instability of t-Bu2Cd, we could not react it
with quinone 1. The only product of the reactions of
quinone 1 with diphenylzinc and diphenylcadmium in
the temperature range in study isolated after corresponding
work-up was phenoxyphenol 6. The reaction products
were analyzed by liquid chromatography (see Table 1).
As seen from the data in Table 1, the ratio of the
1,4- and 1,2-adducts increases in going from methyl-
to tert-butyl-substituted organometallic compounds
and is almost independent on the nature of the metal at
low temperatures. Presumably, this phenomenon is
associated with the steric and electronic effects of alkyl
substituents. Table 2 lists the inductive σI, resonance
σR, σR+, and σR−, polarization σα [9], and steric Es [11]
constants of the studied substituents. The σR+ and σR−
constants are quantitative characteristics of the
resonance effect of substituents on the reaction centers
bearing a positive or a negative charge, respectively.
The studied reactions proceed with high rates and form
products almost immediately after the reagents have
been mixed. Therefore, to first approximation, we
assumed that the product yields (Table 1) сan be used
as a measure of the rate of formation of these products.
1
tal analysis and IR and Н NMR spectroscopy three
types of products: 3-alkyl-6-tert-butyl-о-benzoqui-
nones 4, 4-alkyl-3,6-di-tert-butyl-о-benzoquinones 5,
and 2-alkoxy-3,6-di-tert-butylphenols 6. Unlike reac-
tions with methylated organometallic compounds,
where the organometallic 1,2-adduct underwent no
transformations at low temperatures, organometallic
To assess the electronic and steric effects of sub-
stituents on the reaction rates, we employed correlation
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 1 2016

STUDY OF THE REACTION OF 3,6-DI-tert-BUTYL-о-BENZOQUINONE
39
Table 1. Product ratios of the reactions of 3,6-di-tert-butyl-о-benzoquinone with alkyl derivatives of zinc and cadmium after
hydrolysis and oxidation
Nucleophilic addition, %
Single-electron transfer, %
1,2-Nu
1,4-Nu
R
Т, °С
R2Zn
R2Cd
R2Zn
R2Cd
R2Zn
R2Cd
Me
Et
0
76.1
71.9
4.4
24.4
22.6
6.5
30
0
1 >
9.3
16.4
23.3
10.3
17.3
23.8
12.7
18.6
20.6
11.5
14.0
19.2
12.9
14.8
20.9
31.2
38.9
51.2
92.6
81.2
71.6
83.6
80.0
80.6
69.9
55.3
77.2
68.5
49.2
55.3
43.2
27.6
30
60
0
6.3
9.3
7.9
11.7
7.8
Pr
4.8
30
60
0
5.7
9.1
i-Pr
t-Buа
9.8
12.4
13.1
2.4
25.8
28.4
37.0
45.2
62.4
70.7
62.9
57.8
49.7
52.4
36.2
26.5
30
60
0
30
60
a Analysis was performed after hydrolysis of the reaction mixture.
analysis. Apparently, the 1,4-/1,2-adduct ratios are
determined by the ratio of the rate constants of their
formation. For the alkyl substituents in the organozinc
and organocadmium compounds we deduced the linear
equation (1) relating the logarithm of the 1,4-/1,2-
adduct ratio log (1,4-Nu/1,2-Nu) with the polarization
constants σα.
more than a trend, whereas with the resonance
constants σR− no correlation was obtained at all.
There are strong reasons to suggest that in our case
a multiparameter correlation analysis [12] will provide
more information. The corresponding correlation
equation takes form (3).
P = P0 + (a1±S1)·x1 + (a2±S2)·x2 + ... + (am±Sm)·xm.
(3)
log (1,4-Nu/1,2-Nu) = –1.95 – 2.02Σσα,
(1)
(0.26) (0.23)
Here P is the property being correlated [for example,
log (1,4-Nu/1,2-Nu)]; x1, x2, ... xm , variables (in our
case, σI, σR, σR+, σR−, σα, and ES); a1, a2, ... am,
coefficients; and S1, S2, ... Sm, standard deviations for
the corresponding coefficients. Equation (3) includes
SY = 0.14, r = 0.962, n = 8.
Here and hereinafter, in parentheses under the free
term and the coefficients we give the standard errors of
their determination. Since the studied organometallic
compounds contain by two substituents, the equations
all include sums of two parameters.
Table 2. Electronic and steric constants of substituents
The correlation with the steric constants of the alkyl
substituents on Zn and Cd only is fairly poor.
R
–σI
–σR
–σR+
–σR−
–σα
–ES
Me
Et
0.05
0.05
0.12
0.10
0.10
0.12
0.13
0.13
0.26
0.25
0.25
0.25
0.19
0.30
0.13
0.14
0.14
0.12
0.14
0.10
0.35
0.49
0.54
0.62
0.75
0.81
0
log (1,4-Nu/1,2-Nu) = –0.13 – 0.50ΣES,
(2)
0.08
0.31
0.48
1.43
2.31
(0.09) (0.08)
Pr
0.05
SY = 0.19, r = 0.935, n = 8.
i-Pr
t-Bu
Ph
0.03
The linear correlation between log (1,4-Nu/1,2-Nu)
and the resonance constants σR+ of the substituents
attached to a positively charged reaction center is no
0.07
–0.12
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 1 2016

40
log (1,4-Nu/1,2-Nu)
KURSKII et al.
log (1,4-Nu/1,2-Nu) = 2.14 + 7.58ΣσR+ – 1.85Σσα + 0.27ΣES, (5)
(0.76) (1.60) (0.23) (0.11)
SY = 0.06, r = 0.994, n = 8.
The σR+, σα, and ES are statistically significant. The
polarization effect plays an important role in
nucleophilic addition, which is evidenced, in parti-
cular, by a low relative standard error 100 × S2/a2 =
100% × 0.23/1.85 = 12%. With the data for organozinc
compounds at 0°С exclusively, the three-parameter
correlation becomes excellent.
log (1,4-Nu/1,2-Nu) = 2.33 + 8.11ΣσR+ – 1.98Σσα + 0.33ΣES, (6)
(0.07) (0.15)
(0.02) (0.01)
SY = 0.004, r = 1.000, n = 5.
When the resonance constant σR+ in Eq. (5) is re-
placed by σR or σR−, the correlation coefficient de-
creases from 0.99 to 0.97, and the σR or σR− parameters
become statistically insignificant.
–σα
Linear correlation between the polarization constants of
alkyl substituents and the 1,4-/1,2-adduct ratios in the
reactions of organozinc compounds with 3,6-di-tert-butyl-
о-benzoquinone.
The 1,4-/1,2-adduct ratio in the reactions of organo-
zinc compounds with quinone 1 is almost temperature-
independent. The figure shows the linear dependences
(r = 0.97) of the logarithm of this ratio on polarization
constants for all the organozinc compounds at 0, 30,
and 60°С (11 points from Table 1).
the sample volume n (in our case, this is the number of
different substituents, for example, n = 5, if there are
five substituents Me, Et, Pr, i-Pr, and t-Bu on the Zn
atom), approximation standard error SY, and the so-
called corrected correlation coefficient r. In such an
equation, compared to any other equations, the
correlation coefficient r is maximal, the error SY is
minimal, and the coefficients a1, a2, ... am are
statistically significant. The latter fact implies that the
coefficients a1, a2, ... am all are higher than their
corresponding standard deviations S1, S2, ... Sm (am/Sm >
1). It should be noted that the sample volume n = 5 is
enough to calculate a three-parameter equation (for
example, x1, x2, x3 = σI, σR, and σα), and at n > 5, a
four-parameter equation can be calculated, in which xi
can be, for example, σI, σR+, σα, and ES. In our case, the
most general four-parameter equation with the
variables σI, σR (σR+, σR−), σα, and ES should take the
following form:
The effect of alkyl substituents [Eqs. (5) and (6)]
gives evidence showing that products 2 and 3, as well
as their derivatives 4 and 5 are formed by a nucleo-
philic mechanism. The donor–acceptor interaction of
quinone 1 with organometallic compound, preceding
the nucleophilic reaction, creates additional positive
charges δ+ on the reaction centers in the 2 and 4
positions with respect to the quinone oxygen involved
in reaction, thereby activating substituent R.
t-Bu
O
δ
R
δ
δ
M
O
δ
R
t-Bu
Therefore, in the transition states leading to
products 2 and 3, the resonance effect of substituent R
is described by the σR+ constants which relate to its
conjugation with the positively charged reaction
center. An important contribution comes from the
polarization effect. The substituent constants σα have a
clear physical meaning and are based on ab initio
quantum-chemical calculations [12]. The polarization
effect relates to ion–dipole interaction of the charge on
P = P0 + a1ΣσI + a2ΣσR(σR+, σR−) + a3Σσα + a4ΣES. (4)
(S0) (S1)
(S2)
(S3)
(S4)
The three-parameter Eq. (5) including the reso-
nance σR+, polarization σα, and steric ES effects on the
yields of the reaction products works in the best way
for R2Zn (R = Me, Et, Pr, i-Pr, t-Bu) and R2Cd (R = Et,
Pr, i-Pr).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 1 2016

STUDY OF THE REACTION OF 3,6-DI-tert-BUTYL-о-BENZOQUINONE
41
the reaction center with the dipole induced by this
charge in substituents R. The energy of this ion–dipole
interaction is known [9] to be proportional to 1/d4,
where d is the ion-to-dipole distance. Therefore, the
polarization effect on 1,2-addition is stronger com-
pared to 1,4-addition.
increasing reaction temperature (Table 1) is one more
evidence in favor of concurrent occurrence of two
processes: heterolytic and homolytic.
Thus, in the reactions of 3,6-di-tert-butyl-о-
benzoquinone with organozinc and organocadmium
compounds, two different mechanisms are operative.
The 1,2-/1,4-adduct ratio depends, along with steric,
on the polarization and resonance σR+ (conjugation with
a positive reaction center) constants of substituents R
in R2Zn and R2Cd, which confirms a nucleophilic
(heterolytic) mechanism of formation of these
products. 2-Alkoxy- and 2-phenoxy-3,6-di-tert-
butylphenols form in the studied reaction by a
hemolytic mechanism via a semiquinone radical anion
intermediate. Accordingly, the resonance interaction in
the reactions involving single-electron transfer is
described by the resonance constants σR− which
characterize conjugation with a negatively charged
reaction center.
Let us now focus on single-electron transfer. This
reaction can result in the formation of three species in
the solvent cage: semiquinone radical anion, alkyl
(aryl) metal cation, and alkyl(aryl) radical [14]. The
reaction centers in this case are the radical anion
oxygens bearing the negative charge.
t-Bu
O
+
MR
−
R
O
t-Bu
The logarithms of the yields of the single-electron
transfer products 2-alkoxy- and 2-phenoxy-3,6-di-tert-
butylphenols (SET, %) in the reactions of quinone 1
with organozinc compounds at 30°С are excellently
correlated to substituent parameters by a four-param-
eter equation (7), where σI, σR−, σα, and ES are
respectively the inductive, resonance (conjugation with
a negatively charged reaction center), polarization, and
steric constants of the substituents (Me, Et, Pr, i-Pr,
t-Bu, and Ph).
ACKNOWLEDGMENTS
The work was financially supported by the Council
for Grants for Leading Scientific Schools under the
President of the Russian Federation (NSh-271.2014.3).
REFERENCES
1. The Chemistry of the Quinoid Compounds, Patai, S. and
Rappoport, Z., Eds., Chichester: Wiley, 1988, vol. 2,
p. 537.
2. Blomberg, C., Grootveld, H.H., Gerner, T.H., and
Bickelhaupt, F., J. Organomet. Chem., 1970, vol. 24,
no. 3, p. 549. DOI: 10.1016/S0022-328X(00)84483-6.
log (SET) = −9.8 + 9.8ΣσI − 27.3ΣσR− − 5.3Σσα + 0.99ΣES, (7)
(0.6) (0.6)
(2.1)
(0.2)
(0.05)
SY = 0.06, r = 0.997, n = 6.
3. Gladyshev, E.N., Bayushkin, P.Ya., Abakumov, G.A.,
and Klimov, E.S., Russ. Chem. Bull., 1978, vol. 27,
no. 1, p. 154. DOI: 10.1007/BF01153229.
4. Abakumov, G.A., Cherkasov, V.K., Abakumova, L.G.,
Druzhkov, N.O., Nevodchikov, V.I., Kurskii, Yu.A.,
and Makarenko, N.P., Metalloorg. Khim., 1991, vol. 4,
no. 4, p. 925.
5. Abakumov, G.A., Cherkasov, V.K., Abakumova, L.G.,
Nevodchikov, V.I., Druzhkov, N.O., Makarenko, N.P.,
and Kursky, Yu.A., J. Organomet. Chem., 1995,
vol. 491, nos. 1–2, p. 127. DOI: 10.1016/0022-328X
(94)05168-B.
6. Mc Kinley, J., Aponick, A., Raber, J.C., Fritz, C.,
Mantgomery, D., and Wigal, C.T., J. Org. Chem., 1997,
vol. 62, no. 14, p. 4874. DOI: 10.1021/jo970201u.
It should be noted that if the resonance constant σR−
is replaced by σR, the correlation coefficient decreases
to 0.979, and the relative standard error in the
coefficient at σR increases from 8 to 22%. No
correlation takes place, when σR− is replaced by σR+ (a
constant that characterizes conjugation of substituents
with a positively charged reaction center).
The results of correlation analysis provide con-
vincing evidence showing that the mechanism of
formation of substituted phenols 6 cardinally differ
from the mechanism of formation of products 4 and 5.
Unlike the nucleophilic pathway, when the charge on
the reaction centers is positive, the reaction centers in
the radical anion formed by electron transfer bear a
negative charge. The fact that the yield of single-
electron transfer products much decreases with
7. Aponick, A., Mc Kinley, J.D., Raber, J.C., and Wigal, C.T.,
J. Org. Chem., 1998, vol. 63, no. 8, p. 2676. DOI:
10.1021/jo972300d.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 1 2016

42
KURSKII et al.
8. Shahidzadeh, M. and Ghandi, M., J. Organomet. Chem.,
Tetrahedron, 1978, vol. 34, no. 24, p. 3553. DOI:
2001, vol. 625, no. 1, p. 108. DOI: 10.1016/S0022-
328X(00)00898-6.
10.1016/0040-4020(78)88431-2.
12. Kuznetsova, O.V., Egorochkin, A.N., Khamaletdinova, N.M.,
and Domratcheva-Lvova, L.G., J. Organomet. Chem.,
2015, vol. 779, no. 1, p. 73. DOI: 10.1016/
j.jorganchem.2014.12.004.
9. Egorochkin, A.N., Voronkov, M.G., and Kuznetsova, O.V.,
Polyarizatsionnyi effekt v organicheskoi, elemento-
organicheskoi i koordinatsionnoi khimii (Plarization
Effect in Organic, Organoelement and Coordination
Chemistry), Nizhny Novgorod: Nizhegorod. Gos. Univ.,
2008.
10. Cherkasov, A.R., Jonsson, M., Galkin, V.I., and
Cherkasov, R.A., Russ. Chem. Rev., 2001, vol. 70, no. 1,
p. 1. DOI: 10.1070/RC2001v070n01ABEH000574.
13. Hehre, W.J., Pau, C.-F., Headley, A.D., Taft, R.W., and
Topsom, R.D., J. Am. Chem. Soc., 1986, vol. 108, no. 7,
p. 1711. DOI: 10.1021/ja00267a063.
14. Metalloorganicheskie soedineniya i radikaly (Organo-
metallic Compounds and Radicals), Kabachnik, M.I.,
Ed., Moscow: Nauka, 1985, p. 93.
11. Mac Phee, J.A., Panaye, A., and Dubois, J-E.,
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