Talanta 63 (2004) 259–264
Mechanistic investigation of hydrolysis reactions of dithioacetal
derivatives grafted on silica gels
Hee-Jung Im
a
, Craig E. Barnes
a
, Sheng Dai
b
, Ziling Xue
a,∗
a
Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA
b
Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6101, USA
Received 11 August 2003; received in revised form 21 October 2003; accepted 21 October 2003
Abstract
Silica gels believed to be grafted with dithioacetal derivatives were recently used for Hg(II) extraction, and were found to selectively
remove 94–100% of Hg
2+
ions from metal ion mixtures. The current studies with one derivative suggest that the functional group in the
Hg(II) removal is the mercapto (–SH) ligand. The dithioacetal group in (ClCOCH
2
S)
2
CHPh (2) was hydrolyzed during its reaction with
amine (–O)
3
Si(CH
2
)
3
NH
2
(3) grafted on silica gel to give the mercapto ligand (–O)
3
Si–(CH
2
)
3
NHCOCH
2
SH (4). The silica gel grafted with
the mercapto ligand 4 selectively removed Hg
2+
ions with reported high capacities.
© 2003 Elsevier B.V. All rights reserved.
Keywords: Functional silica gels; Mercury(II) separation; Hydrolysis of dithioacetals; Mercapto ligands
1. Introduction
Functional groups for target analytes such as metal ions
play an essential role in solid phase extractions (SPE) and
separations and are of intense current interest [1–3]. Much
effort has been devoted to the design and grafting of func-
tional groups onto solid supports such as silica gel. Mercapto
(–SH) ligands are among the most widely used ligands for
Hg(II) extraction and separation [1,2]. The recent grafting of
the mercapto ligand (–O)
3
Si(CH
2
)
3
SH on mesoporous sol
gels led to materials with large Hg(II) uptake capacities and
fast Hg(II) removal [1,2].
Silica gels believed to contain tethered dithioacetal
derivatives [(–O)
3
Si–(CH
2
)
3
NHCOCH
2
S]
2
CHAr (Ar
= para-C
6
H
4
-X, X = H, 1; Me, OMe, Cl, NO
2
) were re-
cently reported to selectively remove Hg
2+
ions from a
mixture of interfering metal ions [4]. Several dithioacetals
RCH(SR
′
)
2
have been reported to undergo hydrolysis pro-
moted by Lewis acids such as Hg
2+
to yield aldehydes
RCHO and mercury thiolates Hg(SR
′
)
2
, see, e.g. [5], and
Supplementary data associated with this article can be found at
doi: 10.1016/j.talanta.2003.10.026.
∗
Corresponding author. Tel.: +1-865-974-3443;
fax: +1-865-974-3454.
E-mail address: xue@novell.chem.utk.edu (Z. Xue).
these dithioacetals have been used as protecting reagents
for carbonyl groups in organic synthesis. In particular, we
recently reported that, over a large pH range (pH = 1.00-at
least 7.0), the reactions of Hg
2+
ions with dithioacetals
o-C
6
H
4
[CH(SCH
2
COOH)
2
]
2
, PhCH(SCH
2
COOH)
2
, and
CH
3
(CH
2
)
2
CH(SCH
2
COOH)
2
in water lead to their decom-
position to mercaptoacetic acid (HSCH
2
COOH) and alde-
hydes o-C
6
H
4
(CH=O)
2
, PhCH=O and CH
3
(CH
2
)
2
CH=O,
respectively.
RCH(SCH
2
COOH)
2
+ Hg
2+
+ H
2
O
→ Hg(SCH
2
COOH)
2
↓+ 2H
+
+ RCHO,
R = Ph,n-Pr (1)
Subsequent reaction of HSCH
2
COOH with Hg
2+
ions gives
Hg(SCH
2
COOH)
2
(e.g., Eq. (1)) [6]. These reactions are
fast, giving immediate precipitation of Hg(SCH
2
COOH)
2
when Hg
2+
is added to solutions of dithioacetals. Dithioac-
0039-9140/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.talanta.2003.10.026