Sodium Selenosulfate from Sodium Sulfite and Selenium Powder: An Odorless Selenylating Reagent for Alkyl Halides to Produce Dialkyl Diselenide Catalysts

Article abstract of DOI:10.1055/s-0037-1612083

Na ₂ SeSO ₃, which can be generated in situ by the reaction of Na ₂ SO ₃ with Se power, was found to be an odorless reagent for the selenenylation of alkyl halides to produce dialkyl diselenides. These products have been recently shown to be good catalysts for the Baeyer-Villiger oxidation of carbonyl compounds, for the selective oxidation of alkenes, or for the oxidative deoximation of oximes. By using aqueous EtOH as the solvent and avoiding the generation of a malodourous selenol intermediate, the selenylation reaction with Na ₂ SeSO ₃ is much more environmentally friendly than conventional methods. Owing to the cheap and abundant starting materials and selenium reagents, our novel synthetic method reduces the production costs of dialkyl diselenides as organoselenium catalysts, thereby advancing practical applications of organoselenium-catalysis technologies.

Full text of DOI:10.1055/s-0037-1612083

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© Georg Thieme Verlag Stuttgart · New York
2019, 30, A–E
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Sodium Selenosulfate from Sodium Sulfite and Selenium Powder:
An Odorless Selenylating Reagent for Alkyl Halides to Produce
Dialkyl Diselenide Catalysts
RX (X = Cl or Br)
Yonghong Liub
Hai Lingb,c
Chao Chenb
Qing Xub
Lei Yu*a,b
Xuefeng Jiang*c
EtOH
100 °C, 48 h, air
0
0
0
0-
0
0
0
1-5
6
5
9-7
2
8
9
H2O
Na2SeSO3
(in situ)
0
0
0
0-
0
0
0
2-1
8
4
9-6
5
7
2
Na2SO3
+ Se
140 °C, 48 h, N2
a Guangling College, Yangzhou University, Yangzhou, Jiangsu 225000,
P. R. of China
yulei@yzu.edu.cn
Se
R
Se
R
odorless
b School of Chemistry and Chemical Engineering, Yangzhou University,
Yangzhou, Jiangsu 225002, P. R. of China
c Department of Chemistry, East China Normal University, Shanghai,
200062, P. R. of China
R = alkyl or benzyl
18–78%
20 examples
xfjiang@chem.ecnu.edu.cn
Published as part of the Cluster Organosulfur and Organoselenium Compounds in Catalysis
Received: 12.11.2018
Accepted after revision: 26.12.2018
Published online: 07.02.2019
tential alternative to transition-metal catalysis in the syn-
thesis of medicines. A variety of organoselenium-catalyzed
reactions have been reported,6–10 and this field has recently
shown rapid progress. In our researches, we have focused
on organoselenium-catalyzed green reactions to produce
useful industrial intermediates, for example, by the Baeyer–
Villiger oxidation of carbonyl compounds,8 by the selective
oxidation of alkenes,9 or by the dehydration or oxidative de-
oximation of oximes.10 We were recently surprised to find
that dialkyl diselenides can serve as unique catalysts in
many reactions,8b,9b,9d,10a despite their possible decomposi-
tion through selenoxide elimination, as previously be-
lieved.11
DOI: 10.1055/s-0037-1612083; Art ID: st-2018-w0734-l
Abstract Na2SeSO3, which can be generated in situ by the reaction of
Na2SO3 with Se power, was found to be an odorless reagent for the se-
lenenylation of alkyl halides to produce dialkyl diselenides. These prod-
ucts have been recently shown to be good catalysts for the Baeyer–Vil-
liger oxidation of carbonyl compounds, for the selective oxidation of
alkenes, or for the oxidative deoximation of oximes. By using aqueous
EtOH as the solvent and avoiding the generation of a malodourous sele-
nol intermediate, the selenylation reaction with Na2SeSO3 is much more
environmentally friendly than conventional methods. Owing to the
cheap and abundant starting materials and selenium reagents, our nov-
el synthetic method reduces the production costs of dialkyl diselenides
as organoselenium catalysts, thereby advancing practical applications
of organoselenium-catalysis technologies.
Classic methods for the synthesis of diselenides can be
classified into three types. The first type involve selenol in-
termediates and proceed through selenylation of Grignard
or organolithium reagents under oxidative conditions or
through the reaction of ketones with pre-prepared H2Se
[Scheme 1(a)]; however, this type of reaction involves sele-
nium compounds that are toxic and malodorous. In the sec-
ond type of synthesis, which eliminate laborious proce-
dures involving selenols, inorganic salts serve as alternative
sources of selenium for the formation of diselenides from
halides, diazonium compounds, or carbonyl compounds
[Scheme 1(b)]. In the third type of synthesis, special selenium-
Key words dialkyl diselenides, alkyl halides, selenenylation, organose-
lenium catalysts, green synthesis
Owing to their unique biological and chemical activi-
ties, organoselenium compounds have a wide range of ap-
plications in biochemistry, medicinal chemistry, organic
synthesis, and materials science.1,2 Researchers have recent-
ly paid a growing amount of attention to the ecofriendly
side of organoselenium chemistry,3 and among reported
works, organoselenium catalysis4 is considered to be one of
the most significant and practical applications, because of
its clean procedures, transition-metal-free conditions, and
the metabolizable catalyst element,5 thereby affording a po-
2–
containing reagents, for example Se2 salts, are used to
construct diselenides [Scheme 1(c)]; however, a series of
safety problems has emerged in the laborious process of
preparing the raw materials for this type of reaction.12
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–E

B
Y. Liu et al.
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sary to ensure full conversion of 1a (entries 3–7). In terms
of the product yield and the atom economy of the reaction,
a 50 mol% excess of Se is favorable (entry 5). By elevating
the temperature of the Na2SeSO3-formation step (T1), the
product yield was obviously enhanced to a maximum of
74% (Table 1, entry 9). Moreover, EtOH was found to be a
necessary solvent for the selenenylation of 1a, and the yield
decreased in its absence (entry 10).
Classic Methods:
a. from -SeH
selenylation
oxidant
Se
HCl
R
R
SeH
RM
(1)
(2)
RSeM
Se
R
RM = Grignard or organolithium reagent
toxic
R'
O
R
malodorous
H2Se
+
Se
Se
R
R'
R
R'
b. from Se-salts
oxidant
base
Se
Se
R
Table 1 Optimization of the Synthesis of Dibutyl Diselenide (2a)a
RX
+
Se
R
base or borohydride
– CN
KSeCN
Se
n-Bu
1) Na2SO3, H2O, T1, t1, N2
X = halide, diazonium, and carbonyl compound
Se
n-Bu
Se
2) n-BuBr (1a), EtOH, 100 °C, t2, air
c. from special Se reagent
2a
Se–
W
Se–
Se
2
Se
3
Li2Se2
1
Entry
Se/BuBrb
T1c (°C)
t1d (h)
t2e (h)
Yieldf (%)
Se
Se
R
NH2
S
Cl3C
OR
4
1
2.0
2.0
2.0
3.0
1.5
1.2
1.0
1.5
1.5
1.5
100
100
100
100
100
100
100
120
140
140
10
24
48
48
48
48
48
48
48
48
10
24
48
48
48
48
48
48
48
48
44
48
56
58
56
49
22
62
74
63
Previous Work:
S
2
masked
Sulfur Atom Transfer
R
stable
odorless
SO3Na
R
H
3
4
This Work (new Se reagent):
5
6
Se
1. Na2SO3
2. RX
air
base-free
Se
R
R
SO3Na
Se
7
Se
R
masked-Se
8
Selenium Atom Transfer
9
Scheme 1 Methods for the synthesis of diselenides
10g
a Reaction conditions: 1a (1 mmol), H2O (2 mL), EtOH (1 mL); Na2SO3 and
Se were used in equimolar amounts.
b Molar ratio of Se to 1a.
In our studies on odorless sulfur-atom transfer, we
found that SO32– attached to a sulfur atom is an appropriate
candidate for use as a protecting group, because of its
unique properties as an electron-withdrawing group, a sus-
tained bulky group, and a conjugated group.13 By using
Na2S2O3/RS2O3Na as a sulfur source, we were able to avoid
the generation of malodorous thiol intermediates through
dissociation (Scheme 1, Previous Work). Inspired by these
findings, we surmised that selenium atoms might also be
introduced by using the similar Na2SeSO3 salt. Here, we will
describe an odorless route to the formation of dialkyl di-
selenides via Na2SeSO3 generated in situ from Na2SO3 and
Se powder (Scheme 1, This Work).
We chose the selenenylation of BuBr (1a) to give dibutyl
diselenide (2a) as a model reaction to optimize the condi-
tions. Na2SO3 was initially heated for ten hours with one
equivalent of Se powder in water at 100 °C in a sealed reac-
tion tube14 charged with N2. A solution of BuBr (1a) in etha-
nol was then added, and the mixture was heated in air for
another ten hours. The desired product (BuSe)2 (2a) was
then isolated in 44% yield (Table 1, entry 1). Further screen-
ings demonstrated that extending the reaction times for
both of the Na2SeSO3-formation step (t1) and the selenyla-
tion step (t2) enhanced the product yield (entries 2 and 3).
Next, the effect of the molar ratio of Se to BuBr (1a) was in-
vestigated, and it was found that an excess of Se was neces-
c Temperature for the first step reaction step.
d Time for the first reaction step.
e Time for the second reaction step.
f Isolated yield.
g No EtOH was added in the second step reaction.
The scope of this method was then examined under the
optimized conditions.15 Selenenylation reactions of primary
alkyl chlorides or bromides afforded the corresponding di-
alkyl diselenides 2 smoothly in moderate to good yields (Ta-
ble 2, entries 1–9), and in these cases, cheap alkyl chlorides
were the preferred substrates (entries 3, 5, 7, and 9). Nota-
ble, the reaction could be performed in a ten-times scaled-
up reaction without a decrease in the yield (entry 2). In
comparison, reactions of secondary alkyl halides produced
the related diselenides 2 in decreased yields due to the in-
creased steric hindrances of the substrates (entries 10–15).
Almost no reaction occurred with bulky tertiary alkyl ha-
lides, such as t-BuCl or t-BuBr (entry 16). Benzyl halides
were also favorable substrates, giving the related dibenzyl
diselenides 2i–m in moderate yields (entries 17–21). In
these reactions, the corresponding dialkyl selenides 3 were
also generated as minor byproducts, as observed in 1H NMR
spectra.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–E

C
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Table 2 Synthesis of dialkyl diselenides 2a
1) H2O, 140 °C, 48 h
no reaction
(1)
Se
2) n-BuBr, EtOH, 100 °C, 48 h
Na2SeSO3 (in situ)
Se
R
without Na2SO3 (standard conditions)
Se
RX
R
+
RSeR
EtOH–H2O 1:2
100 °C, 48 h, air
3
1
2
1) Na2SO4, H2O, 140 °C, 48 h
(observed in NMR)
no reaction
(2)
(3)
Se
Se
2) n-BuBr, EtOH, 100 °C, 48 h
Entry RX
Product 2 [yieldb (%)] Product 3 [yieldc (%)]
with Na2SO4 (standard conditions)
1
BuBr
2a (74)
2a (77)
2a (78)
2b (70)
2b (72)
2c (66)
2c (72)
2d (55)
2d (56)
2e (42)
2e (35)
2f (40)
2f (38)
2g (45)
2g (18)
2h (trace)e
2i (66)
3a (12)
3a (13)
3a (9)
1) NaOH, H2O, 140 °C, 48 h
2) n-BuBr, EtOH, 100 °C, 48 h
with NaOH (standard conditions)
no reaction
2d
3
BuCl
4
Me(CH2)4Br
Me(CH2)4Cl
Me(CH2)7Br
Me(CH2)4Cl
i-BuBr
3b (17)
3b (16)
3c (10)
3c (7)
Scheme 2 Control experiments
5
On the basis of the experimental results as well as re-
ports in the literature,13,16 a plausible mechanism shown, in
Scheme 3, is proposed. The reaction of Na2SO3 with Se pow-
der (A) initially generates the selenium reagent Na2SeSO3
(B),16 which rearranges to the highly nucleophilic interme-
diate species D.13 Nucleophilic attack by D on alkyl halides
leads to the organoselenium intermediate F, which is an ef-
ficient alkylselenium reagent that can be oxidized by air to
produce the diselenide 2 through a homocoupling reac-
tion.13 The reaction of F with RX might also produce the sel-
enide 3, which was the observed byproduct of the reaction,
and could be detected by NMR spectroscopy.
6
7
8
3d (28)
3d (26)
3e (4)
9
i-BuCl
10
11
12
13
14
15
16
17
18
19
20
21
i-PrBr
i-PrCl
3e (7)
c-C5H9Br
c-C5H9Cl
CyBr
3f (16)
3f (19)
3g (5)
3g (12)
–
CyCl
t-BuX (X = Cl, Br)
BnCl
3i (26)
3j (26)
3k (15)
3l (20)
3m (11)
Se
S
Na+
O
Se–
S
Na2SO3
H2O
+
–
Na2SeSO3
Se
NaO
ONa
3-FC6H4CH2Cl
4-ClC6H4CH2Cl
3-ClC6H4CH2Cl
2-TolCH2Cl
2j (73)
ONa
O
O
A
B
C
D
2k (70)
2l (62)
RX (1)
2m (70)
SeR
a The reactions were performed on a 1 mmol scale; Na2SeSO3 was prepared
in situ as described in Table 1, entry 9.
b Isolated yields based on 1.
Se–
Na+
O
O
S
ONa
R
X
Se
R
air
Se
F
R
O
S
ONa
homocoupling
Alkyl-Se
Reagent
NaX
2
O
c NMR yields.
E
d The reaction was performed on a 10 mmol scale.
e Yield < 3%.
RX (1)
RSeR (by product)
Detected by NMR
The mechanism of this interesting reaction was our next
concern. To gain information on the mechanism, we per-
formed a series of control experiments (Scheme 2). First, Se
powder was heated in water at 140 °C for 48 hours in the
absence of Na2SO3, and then the mixture was heated with
an EtOH solution of BuBr at 100 °C. However, no reaction
occurred after 48 hours (Scheme 2, eq. 1). Next, the reac-
tion of BuBr with Se in the presence of Na2SO4 was tested,
but this still gave none of the desired diselenide product
(Scheme 2, eq. 2). Moreover, although Se can disproportion-
ate into Se2–and Se4+ under alkaline conditions, no reaction
occurred when Na2SO3 was replaced with NaOH (Scheme 2,
eq. 3). These results clearly demonstrate that Na2SO3 is a
crucial carrier in the selenenylation reaction.
3
Scheme 3 Possible mechanism
In conclusion, we have developed a novel method for the
synthesis of dialkyl diselenides. The method uses Na2SO3
and Se powder as starting materials to generate the sele-
nylation reagent Na2SeSO3 in situ; this is odorless and can
convert alkyl halides into the corresponding dialkyl disele-
nides in moderate to good yields. The low cost of the start-
ing materials, as well as the green features of the proce-
dures, should permit the application of this synthetic meth-
od in large-scale production. Because dialkyl diselenides
have been found to be efficient catalysts for many reactions,
this work might promote practical applications of orga-
noselenium catalysis technologies.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–E

D
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Funding Information
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This work was supported by the Nature Science Foundation of Guan-
gling College (ZKZZ18001).()
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Acknowledgment
We thank the analysis center of Yangzhou University for assistances.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1612083.
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orit
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(14) All reactions were performed in sealed tubes.
(15) Dialkyl Diselenides 2a–m; General Procedure
A glass pressure-reaction tube equipped with a magnetic stirrer
bar was charged with Na2SO3 (189.0 mg, 1.5 mmol), Se powder
(118.5 mg, 1.5 mmol) and H2O (2 mL). The tube was then filled
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–E

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Y. Liu et al.
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Synlett
with N2 and sealed. The mixture was stirred at 140 °C for 48 h,
and then cooled to r.t. A solution of the appropriate alkyl halide
(1 mmol) in EtOH (1 mL) was added, and the tube filled with air
and sealed. The mixture was heated in air at 100 °C for 48 h. The
product was then isolated by preparative TLC (silica gel, PE).
Dibutyl Diselenide (2a)17
(16) MS (EI, 70 eV): m/z (%) = 274 (10) [M+], 57 (100).Characteriza-
tion data and NMR spectra of all of the diselenide products are
given in the Supporting Information.
(17) (a) Lai, C. W.; Lau, K. S.; Chou, P. M. Chem. Phys. Lett. 2019, 714,
6. (b) Zhong, Y.; Yin, L.; He, P.; Liu, W.; Wu, Z.; Wang, H. J. Am.
Chem. Soc. 2018, 140, 1455. (c) Wang, G.; Dong, W.; Ma, P.; Yan,
C.; Zhang, W.; Liu, J. Electrochim. Acta 2018, 290, 273. (d) Luo, J.;
Sun, J.; Guo, P. C.; Yang, Z. S.; Wang, Y. X.; Zhang, Q. F. Mater.
Lett. 2018, 215, 176.
Yellow oil; yield: 100.7 mg (74%). IR (film): 2956, 2924, 2853,
1461, 1377, 1287, 1251, 1210, 1179, 720 cm–1 1H NMR (400
.
MHz, CDCl3, TMS):  = 2.95–2.87 (m, 4 H), 1.74–1.66 (m, 4 H),
1.44–1.37 (m, 4 H), 0.92 (t, J = 7.4 Hz, 6 H). 13C NMR (100 MHz,
CDCl3):  = 33.0, 29.9, 22.6, 13.6.
(18) Crich, D.; Zou, Y. J. Org. Chem. 2005, 70, 3309.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–E