Cis-1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate as an efficient reagent for the synthesis of phenacyl thiocyanates and phenacyl azides

Article abstract of DOI:10.1080/00397911.2010.551701

Styrenes efficiently undergo thiocyanation and azidation with cis-1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate at 0C to furnish the corresponding thiocyanatoketones and azidoketones. This method is a direct, one-pot synthesis under mild condition using methanol as solvent.

Full text of DOI:10.1080/00397911.2010.551701

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Cis-1,4-bis(triphenylphosphonium)-2-
butene Peroxodisulfate as an Efficient
Reagent for the Synthesis of Phenacyl
Thiocyanates and Phenacyl Azides
Rashid Badri a & Maryam Gorjizadeh b
a Department of Chemistry, Science and Research Branch , Islamic
Azad University , Ahvaz , Iran
b Department of Chemistry , Islamic Azad University, Shoushtar
Branch , Shoushtar , Iran
Accepted author version posted online: 27 Oct 2011.Published
online: 26 Mar 2012.
To cite this article: Rashid Badri & Maryam Gorjizadeh (2012) Cis-1,4-bis(triphenylphosphonium)-2-
butene Peroxodisulfate as an Efficient Reagent for the Synthesis of Phenacyl Thiocyanates and
Phenacyl Azides, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 42:14, 2058-2066, DOI: 10.1080/00397911.2010.551701
To link to this article: http://dx.doi.org/10.1080/00397911.2010.551701
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Synthetic Communications1, 42: 2058–2066, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.551701
CIS-1,4-BIS(TRIPHENYLPHOSPHONIUM)-2-BUTENE
PEROXODISULFATE AS AN EFFICIENT REAGENT FOR
THE SYNTHESIS OF PHENACYL THIOCYANATES AND
PHENACYL AZIDES
Rashid Badri1 and Maryam Gorjizadeh2
1Department of Chemistry, Science and Research Branch, Islamic Azad
University, Ahvaz, Iran
2Department of Chemistry, Islamic Azad University, Shoushtar Branch,
Shoushtar, Iran
GRAPHICAL ABSTRACT
Abstract Styrenes efficiently undergo thiocyanation and azidation with cis-1,4-
bis(triphenylphosphonium)-2-butene peroxodisulfate at 0 ꢀC to furnish the corresponding
thiocyanatoketones and azidoketones. This method is a direct, one-pot synthesis under mild
condition using methanol as solvent.
Keywords Cis-1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate; phenacyl azide;
phenacyl thiocyanate; styrene
INTRODUCTION
The phenacyl compounds are useful intermediates in organic synthesis and
have attracted a great deal of interest.[1] Azide and thiocyanate derivatives of a-keto
compounds opened an important area of heterocyclic chemistry because many of
them are subunits of natural products and pharmaceutical agents. Phenacyl thiocya-
nates and phenacyl azides have been conventionally prepared from a-haloketones
via nucleophilic displacement with thiocyanate or azide. These methods, however,
often require drastic reaction conditions leading to poor yields of products. Recently,
some methods for the synthesis of azide and thiocyanate derivatives of a-keto
Received August 30, 2010.
Address correspondence to Maryam Gorjizadeh, Department of Chemistry, Islamic Azad
University, Shoushtar Branch, 147 64516, Shoushtar, Iran. E-mail: gorji80@yahoo.com
2058

SYNTHESIS OF PHENACYL COMPOUNDS
2059
Scheme 1. Synthesis of phenacyl thiocyanates and phenacyl azides from styrene and 1,4-bis-
(triphenylphosphonium)-2-butene peroxodisulfate as an oxidant.
compounds by using cerium(IV) ammonium nitrate,[2] iodine=MeOH,[3] Me3SiN3-
CrO3,[4] and phenacyl bromides in hydroalcoholic media[5] were reported.
Peroxodisulfate ion is an excellent and versatile oxidant, used mostly for the oxi-
dation of compounds in aqueous solution.[6] In spite of the great convenience of
using K2S2O8, Na2S2O8, or (NH4)2S2O8 and relatively high oxidation potential,
many oxidation reactions by peroxodisulfate do not proceed at a convenient rate.
This can be largely attributed to the rate-limiting homolysis, which has activation
energy of approximately 30 Kcal=mol. Thus, certain limitations may be observed
with these reagents. The decomposition of the peroxodisulfate ion requires strong
mineral acids and heavy metal ions[7] as catalysts and also protic and polar solvents
are needed. Recently, the modification of K2S2O8, Na2S2O8, or (NH4)2S2O8 has
attracted a great deal of attention.[8]
Recently,
cis-1,4-bis(triphenylphosphonium)-2-butene
peroxodisulfate
(BTPBPD), an inexpensive and environmentally safe oxidation reagent, has been
used for synthesis of 2,5-disubstituted-1,3,4-oxadiazoles,[9] iodination of aromatic
compounds,[10] and synthesis of b-nitrato alcohols.[11] Herein, we report preparation
of phenacyl thiocyanates and phenacyl azides directly from alkenes with (BTPBPD)
as an efficient oxidation reagent (Scheme 1).
RESULTS AND DISCUSSION
Cis-1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate can be readily
prepared by adding an aqueous solution of potassium peroxodisulfate to a solution
of cis-1,4-bis(triphenylphosphonium)-2-butene dichloride in water. It is a very stable
white solid that can be stored for months without losing its activity.[11]
We used 4-methoxy styrene as a model compound and reacted it with cis-1,4-
bis(triphenylphosphonium)-2-butene peroxodisulfate as an oxidant in different
solvents. Thin-layer chromatographic (TLC) analysis showed that the oxidant acted
very efficiently in methanol, and 2 mmol of the BTPBPD is enough to convert the
1 mmol of substrate to its corresponding 40-methoxy-2-thiocyanatoacetophenone
in good isolated yield. At room temperature, thiocyanation with oxidant in methanol
gave 1,2-dithiocyanate and phenacyl thiocyanate in a 1:2 ratio. This reaction was
also tested under 0 ꢀC condition; the results clearly showed that the reaction
completed in 1 h and was associated with decreasing in 1,2-dithiocyanate, whereas
the main product of the reaction was phenacyl thiocyanate (Table 1). With the

2060
R. BADRI AND M. GORJIZADEH
Table 1. Consideration of different conditions for thiocyanation of 4-methoxystyrene
Yields (%)
BTPBPD
No. Solvent (mmol) Temperature atmosphere (min)
O2
Time Conversion Phenacyl
(%)a
thiocyanate 1,2-Dithiocyanate
1
2
3
4
5
6
7
8
Et2O
CH2Cl2
CHCl3
2
2
Rt
Rt
No
No
No
No
No
No
No
Yes
120
120
120
80
50
60
5
10
10
15
30
15
50
90
30
40
45
70
60
40
40
—
2
Rt
Rt
70
CH3CN
CH3OH
CH3OH
CH3OH
CH3OH
2
100
100
70
2
Rt
60
60
1.5
2
Rt
0 ꢀC
0 ꢀC
60
60
100
100
2
aAccording to GC analysis.
reasonable assumption that oxygen takes part in the reaction leading to the phenacyl
thiocyanate, the reaction of 4-methoxystyrene with BTPBPD and ammonium
thiocyanate was conducted in an atmosphere of oxygen. In this case the phenacyl
thiocyanate was formed in 90% yield and no dithiocyanate was observed. Table 2
shows the scope and limitations of these reactions using several styrene derivatives.
The formation of products can be easily detected by the characteristic 13C signal
of the ꢁSCN group at ꢂ112 ppm.[12] Both styrene derivatives with electron-
withdrawing group and electron-donating groups provided the corresponding
a-thiocyanatoketones in good yields. To know the efficiency of this procedure, we
tested the effectiveness of the other oxidant compounds by replacing BTPBPD with
K2S2O8, (NH4)2S2O8, and saturated oxidant at the identical reaction conditions. We
have found that the formation of a-thiocyanatoketones occurred rather slowly, and
yields of products were reduced to 5–10% on average compared to the results
obtained using BTPBPD. This may be due to the low solubility of these reagents
in reaction medium. However, no reaction was observed in the absence of oxidant,
even over a long reaction time (12 h). It is noteworthy that with all substrates used in
this procedure, no evidence for the formation of 1,2-dithiocyanates as by-product of
the reactions was observed.
Prompted by the success of this reaction, we decided to explore the possibility of
synthesizing phenacyl azides using a similar strategy. The reactions worked well to
give the corresponding azidoketones with equal efficiencies in the cases of thiocyana-
tion reactions (Table 3). 13C resonance of a-carbon in phenacyl azide that shift from
ꢂ115 ppm in styrene to ꢂ55 ppm is very characteristic for azide functionality.[12]
A plausible reaction pathway for the present reaction is shown in Scheme 2.
Sulfate anion radical gained an electron from thiocyanate or azide anion and oxidized
the anion to a radical, which then reacted with styrene to form the benzylic radical.
This can trap oxygen to form the peroxyradical, which eventually oxidized by cis-1,4-
bis(triphenylphosphonium)-2-butene peroxodisulfate to form the products.
In summary, we have demonstrated that thiocyanatoketones and azidoketones
can be generated directly from styrenes in the presence of BTPBPD. The notable
features of this procedure are good conversions, simplicity in operation, cleaner
reaction profiles, and ready availability of reagents at low cost, which make it a

SYNTHESIS OF PHENACYL COMPOUNDS
2061
Table 2. Conversion of different styrenes to phenacyl thiocyanates using BTPBPD
Compound
Substrate
Producta
Time (min)
Yield (%)
85
1
50
2
3
65
80
80
70
4
5
6
7
65
80
60
80
92
80
89
65
8
80
70
aProducts were identified by comparison of their physical and spectral data with those of authentic
samples.
useful and attractive strategy for the synthesis of phenacyl compounds of synthetic
importance.
EXPERIMENTAL
All products were characterized by comparison of their physical data, infrared
1
(IR), H NMR, and 13C NMR spectra with authentic samples.[13,2] The IR spectra
1
were recorded on a Bomem FT-IR spectrometer. H NMR and 13C NMR spectra
were taken on a 400-MHz Bruker spectrometer. The C, H, P, N, S, F, and Br
analyses were performed by the microanalytical service of the Research Institute

2062
R. BADRI AND M. GORJIZADEH
Table 3. Conversion of different styrenes to phenacyl thiocyanates using BTPBPD
Compound
Substrate
Producta
Time (min)
Yield (%)
95
9
50
10
11
65
80
85
70
12
13
65
80
92
80
14
60
89
15
16
80
90
73
70
aProducts were identified by comparison of their physical and spectral data with those of authentic
samples.
Scheme 2.

SYNTHESIS OF PHENACYL COMPOUNDS
2063
of the Petroleum Industry (NIOC). Cis-1,4-bis(triphenylphosphonium)-2-butene
peroxodisulfate was prepared, and other chemicals were purchased from Merck
(Darmstadt, Germany). All of the produts reported here were pure as judged by
TLC, FTIR, and NMR analysis of the reaction mixture.
Preparation of Cis-1,4-bis(triphenylphosphonium)-2-butene
Peroxodisulfate
The oxidant was prepared as described in our previous articles.[11]
General Procedure for the Preparation of Phenacyl Thiocyanate
A stock solution was prepared by dissolving 1 mmol of styrene and 1.5 mmol
NH4SCN in CH3OH saturated with oxygen. Cis-1,4-bis(triphenylphosphonium)-2-
butene peroxodisulfate (2 mmol) was also dissolved in methanol saturated with
oxygen and then was added in small portions at 0 ꢀC to a stock solution. The progress
of the reaction was monitored by TLC. On completion of reaction, the reaction
mixture was filtered. The solvent was evaporated; water (20 mL) was added and
extracted with diethyl ether (3ꢃ 15mL). The combined organic layers were concen-
trated in vacuo; the resulting product was directly charged on a small silica-gel column
and eluted with a mixture of ethyl acetate and n-hexane (1:4) to afford the pure product.
General Procedure for the Preparation of Phenacyl Azide
A stock solution was prepared by dissolving 1 mmol of styrene and 1.5 mmol
sodium azide in CH3OH saturated with oxygen. Cis-1,4-bis(triphenylphospho-
nium)-2-butene peroxodisulfate (2 mmol) was also dissolved in methanol saturated
with oxygen and then was added in small portions at 0 ꢀC to a stock solution. The
progress of the reaction was monitored by TLC. On completion of reaction, the reac-
tion mixture was filtered. The solvent was evaporated; water (20 mL) was added and
extracted with diethyl ether (3 ꢃ 15 mL). The combined organic layers were concen-
trated in vacuo; the resulting product was directly charged on a small silica-gel
column and eluted with a mixture of ethyl acetate and n-hexane (1:4) to afford
the pure product.
Representative Examples of Spectra Data of Phenacyl Thiocyanate
1
Compound 2. Yield (0.142 g, 80%); IR: 2152 (SCN), 1689 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 4.61 (s, 2H), 7.42–7.86 (m, 5H); 13C NMR
(100 MHz, CDCl3): d ¼ 40.6 (CH2), 111.2 (SCN), 128.2 (2 ꢃ CH), 130.0 (2 ꢃ CH),
130.3 (CH), 134.1 (C), 185.1 (CO). Anal. calcd. for C9H7NOS: C, 60.99; H, 3.98;
N, 7.90; S, 18.09. Found: C, 60.87; H, 3.97; N, 7.99; S, 18.22.
1
Compound 3. Yield (0.155 g, 70%); IR: 2153 (SCN), 1681 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 4.51 (s, 2H), 7.91 (d, 2H), 8.50 (d, 2H); 13C NMR
(100 MHz, CDCl3): d ¼ 38.2 (CH2), 111.3 (SCN), 123.2 (2 ꢃ CH), 134.0 (2 ꢃ CH),

2064
R. BADRI AND M. GORJIZADEH
139.3 (C), 148.1 (C), 185.1 (CO). Anal. calcd. for C9H6N2O3S: C, 48.64; H, 2.72; N,
12.60; S, 14.43. Found: C, 48.67; H, 2.78; N, 12.59; S, 14.22.
1
Compound 4. Yield (0.235 g, 92%); IR: 2151 (SCN), 1686 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 4.60 (s, 2H), 7.41 (d, 2H), 7.88 (d, 2H); 13C NMR
(100 MHz, CDCl3): d ¼ 40.7 (CH2), 111.5 (SCN), 127.9 (C), 132.3 (2 ꢃ CH), 133.1
(C), 134.2 (2 ꢃ CH), 185.1 (CO). Anal. calcd. for C9H6NOSBr: C, 42.21; H, 2.36;
N, 5.47; S, 12.52; Br, 31.20. Found: C, 42.27; H, 2.38; N, 5.49; S, 12.62; Br, 31.35.
1
Compound 6. Yield (0.170 g, 89%); IR: 2150 (SCN), 1680 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 2.90 (s, 3H), 4.62 (s, 2H), 7.34 (d, 2H) 7.58 (d, 2H);
13C NMR (100 MHz, CDCl3): d ¼ 22.7 (CH3), 41.2 (CH2), 111.5 (SCN), 131.4
(2 ꢃ CH), 132.3 (2 ꢃ CH), 133.9 (C), 141.89 (C), 185.3 (CO).
1
Compound 7. Yield (0.143 g, 65%); IR: 2150 (SCN), 1689 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 4.62 (s, 2H), 7.81 (d, 2H), 8.38 (d, 2H), 12.98 (brs,
1H); 13C NMR (100 MHz, CDCl3): d ¼ 41.0 (CH2), 111.5 (SCN), 132.1 (2 ꢃ CH),
134.0 (2 ꢃ CH), 136.0 (C), 136.9 (C), 168.3 (COOH), 185.3 (CO). Anal. calcd. for
C10H7NO3S: C, 54.29; H, 3.19; N, 6.33; S, 14.49. Found: C, 54.37; H, 3.21; N,
6.39; S, 14.42.
1
Compound 8. Yield (0.136 g, 70%); IR: 2150 (SCN), 1687(CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 4.31 (s, 2H), 7.35 (d, 2H), 7.89 (d, 2H); 13C NMR
(100 MHz, CDCl3): d ¼ 41.0 (CH2), 111.5 (SCN), 115.3 (2 ꢃ CH), 131.3 (C), 135.0
(2 ꢃ CH), 160.8 (C), 164.7 (C), 185.3 (CO). Anal. calcd. for C9H6NOSF: C, 55.37;
H, 3.09; N, 7.17; S, 16.43; F, 9.72. Found: C, 55.39; H, 4.01; N, 7.18; S, 16.48; F, 9.72.
Representative Examples of Spectra Data of Phenacyl Azide
1
Compound 9. Yield (0.181 g, 95%); IR: 2122 (N3), 1687 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 3.81 (s, 3H), 4.53 (s, 2H), 6.86 (d, 2H), 7.73 (d,
2H); 13C NMR (100 MHz, CDCl3): d ¼ 54.3 (CH3), 55.1 (CH2), 116.2 (2 ꢃ CH),
128.8 (2 ꢃ CH), 132.7 (C), 162.7 (C), 193.1 (CO).
1
Compound 10. Yield (0.136 g, 85%); IR: 2104 (N3), 1692 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 4.51 (s, 2H), 7.36–7.56 (m, 5H); 13C NMR
(100 MHz, CDCl3): d ¼ 55.1 (CH2), 126.2 (2 ꢃ CH), 129.4 (2 ꢃ CH), 131.1 (CH),
137.1 (C), 193.1 (CO).
1
Compound 11. Yield (0.144 g, 70%); IR: 2101 (N3), 1697 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 4.53 (s, 2H), 8.09 (d, 2H), 8.43 (d, 2H); 13C NMR
(100 MHz, CDCl3): d ¼ 55.1 (CH2), 125.8 (2 ꢃ CH), 128.1 (2 ꢃ CH), 141.9 (C),
149.7 (C), 193.0 (CO).
1
Compound 12. Yield (0.220 g, 92%); IR: 2101 (N3), 1699 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 4.52 (s, 2H), 7.49 (d, 2H), 7.73 (d, 2H); 13C NMR
(100 MHz, CDCl3): d ¼ 55.1 (CH2), 127.8 (C), 128.9 (2 ꢃ CH), 133.9 (2 ꢃ CH),
134.8 (C), 193.3 (CO). Anal. calcd. for C8H6N3OBr: C, 39.95; H, 2.52; N, 17.47;
Br, 33.29. Found: C, 39.99; H, 2.50; N, 17.49; Br, 33.49.

SYNTHESIS OF PHENACYL COMPOUNDS
2065
1
Compound 13. Yield (0.156 g, 80%); IR: 2102 (N3), 1692 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 4.50 (s, 2H), 7.44 (d, 2H), 7.66 (d, 2H); 13C NMR
(100 MHz, CDCl3): d ¼ 55.1 (CH2), 128.1 (2 ꢃ CH), 129.9 (2 ꢃ CH), 136.9 (C),
139.03 (C), 193.2(CO).
1
Compound 15. Yield (0.149 g, 73%); IR: 2101 (N3), 1699 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 4.53 (s, 2H), 7.69 (d, 2H), 8.13 (d, 2H); 13C NMR
(100 MHz, CDCl3): d ¼ 55.1 (CH2), 132.8 (2 ꢃ CH), 133.4 (2 ꢃ CH), 135.9 (C),
138.73 (C), 167.0 (COOH), 193.1 (CO). Anal. calcd. for C9H7N3O3: C, 52.68; H,
3.41; N, 20.49. Found: C, 52.57; H, 3.48; N, 20.53.
1
Compound 16. Yield (0.125 g, 70%); IR: 2102 (N3), 1695 (CO) (cmꢁ1); H
NMR (400 MHz, CDCl3): d ¼ 4.53 (s, 2H), 7.29 (d, 2H), 7.83 (d, 2H); 13C NMR
(100 MHz, CDCl3): d ¼ 55.30 (CH2), 117.8 (2 ꢃ CH), 131.56 (2 ꢃ CH), 133.45 (C),
160.7 (C), 165.8 (C), 193.1 (CO). Anal. calcd. for C8H6N3oF: C, 53.63; H, 3.37;
N, 23.45; F, 10.61. Found: C, 53.57; H, 3.34; N, 23.48; F, 10.7.
ACKNOWLEDGMENT
We thank Islamic Azad University, Shoushtar Branch, for financial support of
this work.
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