Environmental Engineering Reference
In-Depth Information
-
→
higher polymers
(1)
These compounds are usually polymeric substances; and only in a few
cases, monomeric compounds. They slowly polymerize on standing [4].
The bond angle is approximately 90
◦
(as
p
2
bonding), for example, 94(5)
◦
(SnF
2
) [5, 6]. In structural formula 2, a molecule with
sp
2
hybridization, a va-
cant
p
orbital and bulky groups [4, 7, 8] is shown. In this case, the bond angle
is for example 117.4
◦
in (C
5
H
5
)SnCl [9].
R
3
SnX
→
R
2
SnX
2
→
RSnX
3
→
SnX
4
(2)
It is particularly to be noted that these molecules exist in a singlet state
with their nonbonding electron paired. Since the central tin atom in either
of the structural formulaes, 1 and 2, has only six electrons in the valence
shell, polymerization forming a stable octet is expected to occur [4]. When
freshly prepared, diphenyltin is monomeric, but it readily polymerizes to
reach a pentamer or greater based on its molecular weight as shown in
Eq. 1 [10].
These bivalent tin compounds, wherever possible, adopt structures in
which the metal achieves a coordination number higher than two either by
complexation, chelation or by bridging. The bivalent tin compounds having
active lone pair electrons are utilized as catalysts [11]. The potential for bi-
valent organometallic tin species in organic syntheses has also been studied.
However, as the organotin compound, tetravalent compounds (R
n
SnX
4-
n
,Ris
alkyl, aryl, etc.; X is halogen, hydroxyl, etc.) are used, since they are very
stable and easy to handle.
The organotin compounds were first used as stabilizers for polyvinyl chlo-
ride (PVC) in 1940 [12]. Although the organotin compounds have a variety of
uses, their use as stabilizers for PVC has been the most important application
of the organotin compounds.
In 1950, the research team under the leadership of Prof. G.J.M. van der
Kerk made important contributions to the study of organotin chemistry as
described above. In particular, the powerful biocidal properties of trialkyltin
and triaryltin derivatives were established [13, 14]. The introduction of bio-
cidal uses of the triorganotin compounds began in the late 1950s, when they
were used as agricultural fungicides; their uses in wood-preserving com-
pounds began in 1960 and antifouling paints in the early 1960s [15]. Other
