Efficient one-pot thiocyanation of primary, secondary and tertiary alcohols by in situ generation of Ph3P(SCN)2. A modified procedure

Article abstract of DOI:10.1039/a906113d

The preparation of Ph₃P(SCN)₂ is modified by using a combination of Ph₃P, NH₄SCN and Br₂ at room temperature for the efficient conversion of primary, secondary and tertiary alcohols to their corresponding thiocyanates in excellent yields.

Full text of DOI:10.1039/a906113d

View Article Online / Journal Homepage / Table of Contents for this issue
676 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 676^677y
Efficient One-pot Thiocyanation of Primary,
Secondary and Tertiary Alcohols by
Generation of Ph3P(SCN)2. A Modified
Procedure
N. Iranpoor,* H. Firouzabadi* and H. R. Shaterian
Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454, Iran
The preparation of Ph3P SCN is modified by using a combination of Ph3P, NH4SCN and Br2 at room tem-
2
perature for the efficient conversion of primary, secondary and tertiary alcohols to their corresponding thiocyanates
in excellent yields.
Alkyl thiocyanates are generally prepared via nucleophilic
displacement of leaving groups attached to C by thiocyanate
ion.1 The use of di¡erent phase transfer agents for enhance-
We now report a modi¢ed procedure for one-pot conver-
sion of primary, secondary and also tertiary alcohols to
their corresponding alkyl thiocyanates in high to excellent
yields at room temperature (Scheme 1). Using this method
primary alcohols are converted to their corresponding alkyl
thiocyanates without the formation of any isothiocyanates.
In the case of secondary and tertiary alcohols, thiocyanates
were also formed as the major products together with small
amounts of the corresponding isothiocyanates (4^12%). The
results of this study are given in Table 1.
5
ment of the reaction has also been reported.1 Nucleophilic
displacement of the trimethylsilyl group with KSCN^CuBr2
has also been studied in allylic silanes.6 The reported
6
methods are applied mostly for the synthesis of primary1;3
and in some cases for the synthesis of secondary2
thiocyanates. The synthesis of tert-alkyl thiocyanates, in
moderate yields, has been achieved by the use of solid
supported potassium thiocyanate.7 Conversion of alcohols
to alkyl thiocyanates has been also achieved by using
Formation of alkyl thiocyanates from primary, secondary
and also tertiary alcohols as the major product is a major
advantage for this method. The reason for formation of alkyl
isothiocyanates as the minor product and in very low yield
from the reaction of secondary and tertiary alcohols by this
procedure could be due to the slow rate of conversion
Ph3P-diethylazodicarboxylate,
Ph3P
or
phenylene
10
alkylphosphites and (SCN)2.8
Although the two latter
procedures9;10 are convenient methods for the conversion
of alcohols to alkyl thiocyanates, they su¡er from disadvan-
tages such as the need for separation of thiocyanogen in the
procedure,9;10 low reaction temperatures (ca, 30, 40 and
80 8C, respectively)9;10 and long reaction times (4 h at
30 8C and then leaving the reaction mixture overnight at
room temperature)9 and formation of isothiocyanates as
the sole product from tertiary alcohols.9;10
‡
between Ph3P(SCN)2 and Ph3P NCS=SCN both of which
may be present in the reaction mixture.10 31P NMR studies
‡
of the conversion Ph3PꢀSCN† „ Ph3P NCS ‡ SCN shows
2
that it is much easier when lead thiocyanate is used rather
than potassium thiocyanate and furthermore is also tempera-
ture dependent.10 Other advantages of the present method
are the short reaction time and high yields of the products.
This has been shown by comparing some of the results
obtained by our method with those reported in the literature
(Table 2).
Ph3P/Br2, NH4SCN
ROH
RSCN
MeCN, room temp.
immediate reaction
In conclusion, in this modi¢ed procedure we can use
ammonium thiocyanate instead of the less available lead
thiocyanate, and the need to prepare and isolate the poison-
Scheme 1
R
primary, secondary or tertiary group
Table 1 Conversion of alcohols to thiocyanates
1
IRn SCN e/cm
dC SCN
c
Alcohol
Yield(%)a
RSCN(%)d
RNCS(%)d
CCl4
CDCl3
Octan-1-ol
Octan-2-ol
Cyclohexanol
Cyclohexyl^CH2CH2OH
PhCH2OH
PhCH2CH2OH
PhCH2CH2CH2OH
4-ClC6H4CH2OH
4-CH3OC6H4CH2OH
PhCH OH C2H5
Ph2CHOH
95
90
91
96
97
95
95
94
96
89
88
85
93
10011
0
4
0
0
0
0
0
0
0
8
10
12
0
2165
2160
2165
2165
2152
2165
2160
2160
2158
2160
2160
2150
2160
110.6
111.2
111.1
110.7
110.6
110.5
111.1
111.0
111.2
111.9
112.2
112.2
110.4
9610
1009
100 (I)
1009;10
1009
100 (II)
1009
1009:10
92 (III)
90 (IV)
88 (V)
1006;9
Ph2C Me OH
Cinnamyl alcohol
aIsolated yields. bThe products were identified by comparison of their physical data with those reported for known samples. cImmediate
reaction at room temperature. dYield of conversion by GC. Spectral data for products, I^V are given in the Experimental section. eThe IR
15
wavenumber and 13C NMR chemical shift of the ^SCN group are comparable with literature values.12
* To receive any correspondence.
ous thiocyanogen for further reaction is not required. The
This is a Short Paper as de¢ned in the Instructions for Authors,
one-pot in situ generation of Ph3P(SCN)2 at room tempera-
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is
ture provides an e¤cient and very simple method for
therefore no corresponding material in J. Chem. Research (M).

View Article Online
J. CHEM. RESEARCH (S), 1999 677
1
Table 2 Comparison of the results obtained by the present
Compound II. IR (CCl4† n/cm 3080, 3060, 3040, 2940, 2880,
method with those from literature procedures9
2160, 1500, 1460, 1280, 1260, 1080, 1040, 750, 720; dHꢀCDCl3† 2.0
(2H, q), 2.7 (2H, t), 2.9 (2H, t), 7.1^7.5 (5H, m); dCꢀCDCl3† 140.3,
129.1, 128.9, 128.8, 111.1, 34.2, 32.4, 30.1.
Present methoda
yield(%)
Literatureb
yield(%)
Alcohol
1
Compound III. IR (CCl4) n/cm 3050, 3040, 2980, 2940, 2890,
2165, 1500, 1460, 1240, 1100, 1040, 750, 690; dHꢀCDCl3† 0.96 (3H,
t), 2.1 (2H, q), 4.6 (1 H, t), 7.2^7.4 (5H, m); dCꢀCDCl3†: 137.1, 127.8,
127.7, 124.7, 111.9, 54.2, 31.3, 11.1.
PhCH2OH
97
93
95
95
80
63
48
60
Cinnamyl alcohol
PhCH2CH2OH
Octan-1-ol
a Immediate reaction at room temperature. b Stirring at 308C for
1
Compound IV.ö IR (CCl4) n/cm 3080, 3040, 2950, 2160, 1500,
1460, 1200, 1120, 1040, 1010, 750, 710; dHꢀCDCl3† 5.3 (1H, s), 7.2^7.5
(10H, m); dCꢀCDCl3† 142.9, 130.8, 127.8, 127.7, 112.2, 58.1.
Compound V. IR (CCl4) n/cm 1 3080, 3060, 3020, 2960, 2920, 2150,
1500, 1450, 1240, 1040, 750, 700; dHꢀCDCl3† 2.1 (3H, s), 7.2^7.4 (10H,
m); dCꢀCDCl3† 142.9, 130.3, 130.1, 129.5, 112.2, 70.6, 32.9.
4 h and at room temperature overnight.
We are grateful to Shiraz University Research Council for
the partial support of this work.
immediate conversion of primary, secondary and tertiary
alcohols to their corresponding thiocyanates in high to
excellent yields.
Received, 28th July 1999; Accepted, 9th August 1999
Paper E/9/06113D
Experimental
References
All the products are known compounds and were characterized by
comparison of their physical data with literature values. IR spectra
were recorded on a Perkin Elmer IR-157 G and a Perkin Elmer
781 spectrometer. NMR spectra were recorded on a Bruker Avance
DPX-250. Mass spectra were recorded on a Shimadzu GCMS-QP
1000 EX instrument.
1
D. Landini, A. Maia, F. Montanari and F. Rolla, J. Org.
Chem., 1983, 48, 3771.
W. P. Reeves and J. V. Mcclusky, Tetrahedron Lett., 1983,
1585.
2
3
4
5
6
7
H. Lehmkuhl, F. Rabet and K. Hauchild, Synthesis, 1977, 184.
J S. Kondo, Y. Takeda and K. Tsuda, Synthesis, 1988, 403.
S. Kondo, Y. Takeda and K. Tsuda, Synthesis, 1989, 862.
A. S. Guram, Synlett, 1993, 259.
T. Ando, J. H. Clark and D. G. Cork, J. Org. Chem., 1987, 52,
681.
General Procedure for the Synthesis of Primary, Secondary and
Tertiary Thiocyanates from Alcohols.öA three-necked £ask
equipped with a dropping funnel, stirrer, drying CaCl2 tube and nitro-
gen gas inlet was charged with Ph3P (2.2 mmol) and dry MeCN (5 ml).
Then Br2 (2.2 mmol) was added dropwise to the solution at room tem-
perature under an N2 atmosphere. When the addition was complete, a
solution of NH4SCN (4.4 mmol) in MeCN (5 ml) was added dropwise.
To the resulting mixture the alcohol (2.1 nmmol) was then added
dropwise. GC and TLC of the reaction mixture showed immediate
completion of the reaction after addition of the alcohol. The reaction
mixture was ¢ltered and the ¢ltrate washed with MeCN. Evaporation
of the solvent followed by column chromatography on silica gel using
light petroleum (bp 40^60 8C)±ethyl acetate (9 : 1) as eluent yielded
the corresponding thiocyanates. Spectral data for compounds I^V
are given below.
8
9
H. Loibner and E. Zbiral, Helv. Chem. Acta, 1976, 59, 2100.
Y. Tamura, T. Kawasaki, M. Adachi, M. Tanio and Y. Kita,
Tetrahedron Lett., 1977, 4417.
10 J. Burski, J. Kieszkowski, J. Michaski, M. Pakulski and A.
Skowroska, Tetrahedron, 1983, 39, 4175.
11 M. Kodomari, T. Kuzuoka and S. Yoshitomi, Synthesis, 1983,
141.
12 R. G. Guy and I. Pearson, J. Chem. Soc., Perkin Trans. 2,
1973, 1359.
13 A. Vass and G. Szalontai, Synthesis, 1986, 817.
14 F. D. Toste, V. De Stefano and I. W. J. Still, Synth. Commun.,
1995, 25, 1277.
Compound I. IR (CCl4) n/cm 1 2950, 2840, 2165, 1450, 1280, 1250,
1100, 1050; dHꢀCDCl3† 2.9 (2H, t), 1.58^1.66 (7H, m), 0.8^1.2 (6H,
m); dCꢀCDCl3† 110.7, 37.7, 36.6, 33.1, 32.2, 26.7, 26.4.
15 A. Mandelaire and Y. Fort, Synth. Commun., 1998, 28, 583.