A convenient synthesis of thioacetates and thiobenzoates using silica-gel supported potassium thioacetate and thiobenzoate

Full text of DOI:10.1080/10426500590913023

Phosphorus, Sulfur, and Silicon, 180:1447–1448, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500590913023
A Convenient Synthesis of Thioacetates and
Thiobenzoates Using Silica-Gel Supported Potassium
Thioacetate and Thiobenzoate
Tadashi Aoyama
Toshio Takido
Department of Materials and Applied Chemistry, College of Science
and Technology, Nihon University, Tokyo, Japan
Mitsuo Kodomari
Department of Applied Chemistry, Shibaura Institute of Technology,
Tokyo, Japan
Recently, many reactions using supported reagents have been reported.
We have found that potassium thioacetate can be remarkably activated
by support on silica gel, and silica gel-supported potassium thioacetate
(
CH3COSK/SiO2) reacts with alkyl halides in nonpolar solvents such
as benzene to give alkyl thioacetates in good yields.
ꢀ
R COSK/SiO2
ꢀ
X − R−−−−−−−−−−→ R COS − R
1
X=Cl,Br,I
2 or 3
2
:Rꢀ=Me,3:Rꢀ=Ph
Benzyl bromide did not react with finely ground potassium thioac-
etate suspended in benzene at room temperature. In contrast, similar
reactions with CH3COSK/SiO2 proceeded easily under similar condi-
tions to afford benzyl thioacetate in 83% yield after 1 h. Silica gel was the
most effective among the inorganic supports tested. Aluminas (neutral,
acidic, and basic) were also effective but less than silica gel (33–58%).
Molecular sieves 4A was much less effective. Kieselgur, Montmorillonite
K10, and charcoals were ineffective for activating potassium thioac-
etate. The reaction of a series of organic halides with CH3COSK/SiO2
in benzene gave the corresponding thioacetates in high yields. The re-
action of benzyl chloride with CH3COSK/SiO2 required more strong
conditions than that of benzyl bromide. Substituted benzyl bromides
were converted into the corresponding thioacetates in excellent yields
Received July 9, 2004; accepted October 5, 2004.
Address correspondence to Tadashi Aoyama, Department of Materials and Applied
Chemistry, College of Science and Technology, Nihon University, Kanda Surugadai,
Chiyoda-ku, Tokyo 101-8308, Japan. E-mail: aoyama@chem.cst.nihon-u.ac.jp
1447

1
448
T. Aoyama et al.
at room temperature independent of the substituent. For instance, 4-
methyl and 4-nitrobenzyl bromide were converted into the correspond-
ing thioacetates in 98% and 97% yields. Xylylene dibromides produced
only disubstituted compound. Mono-substituted compounds were not
detected.
The reactivity of n-alkyl halides decreased as follows: I > Br > Cl.
◦
Octyl thioacetate was obtained quantitatively from octyl iodide at 80 C
after 3 h, whereas octyl chloride gave only 32% yield of octyl thioac-
etate after 24 h. In the case of 1,4-dibromopentane, 4-bromopentyl
thioacetate was formed along with a small amount of disubstituted com-
pound, but 4-bromo-1-methylbutyl thioacetate was not detected. Using
silica gel-supported potassium thiobenzoate (PhCOSK/SiO2), the reac-
tion rapidly occurred at room temperature to give the corresponding
thiobenzoates in high yields. The reactivity of PhCOSK/SiO2 was higher
than CH3COSK/SiO2. Octyl bromide reacted with CH3COSK/SiO2 to af-
◦
ford the octyl thioacetate in 89% yield at 80 C after 8 h, whereas the
reaction with PhCOSK/SiO2 gave octyl thiobenzoate (3a) in 94% yield
after 4 h. Moreover, octyl chloride gave 3a in 52% yield after 24 h.
The present procedure using silica gel-supported potassium thioac-
etate and thiobenzoate allows for an efficient transformation of organic
halides into thioesters. The notable advantages of this procedure are
operational simplicity, good yield, and mild reaction conditions. More-
over, the products are easily isolated by filtering the used supported
reagent and removing the solvent under vacuum, and are generally
spectroscopically pure.