phite)A salt that contains the nega-
tive ion S 2 O 4 2–, usually formed by the
reduction of sulphites with excess
SO 2. Solutions are not very stable and
decompose to give thiosulphate and
hydrogensulphite ions. The structure
is –O 2 S-SO 2 –.
sulphinic acid (dithionous acid; hy-
posulphurous acid) An unstable acid,
H 2 S 2 O 4 , known in the form of its
salts (sulphinates). See also sulphuric
acid.
sulphiteA salt or ester derived
from sulphurous acid. The salts con-
tain the trioxosulphate(IV) ion SO 3 2–.
Sulphites generally have reducing
properties.
sulphonamidesOrganic com-
pounds containing the group
–SO 2 .NH 2. The sulphonamides are
amides of sulphonic acids. Many
have antibacterial action and are also
known as sulpha drugs, including
sulphadiazine, NH 2 C 6 H 4 SO 2 -
NHC 4 H 3 N 2 , sulphathiazole,
NH 2 C 6 H 4 SO 2 NHC 5 H 2 NS, and
several others. They act by pre-
venting bacteria from reproducing
and are used to treat a variety of
bacterial infections, especially of the
gut and urinary system.
sulphonateA salt or ester of a sul-
phonic acid.
sulphonationA type of chemical
reaction in which a –SO 3 H group is
substituted on a benzene ring to
form a *sulphonic acid. The reaction
is carried out by reÛuxing with con-
centrated sulphuric(VI) acid for a
long period. It can also occur with
cold disulphuric(VI) acid (H 2 S 2 O 7 ).
Sulphonation is an example of elec-
trophilic substitution in which the
electrophile is a sulphur trioxide
molecule, SO 3.
sulphonic acids Organic com-
pounds containing the –SO 2 .OH
group. Sulphonic acids are formed by
reaction of aromatic hydrocarbons
with concentrated sulphuric acid.
They are strong acids, ionizing com-
pletely in solution to form the
sulphonate ion, –SO 2 .O–.
A- Information about IUPAC nomenclature
sulphonium compoundsCom-
pounds containing the ion R 3 S+(sul-
phonium ion), where R is any organic
group. Sulphonium compounds can
be formed by reaction of organic sul-
phides with halogen compounds.
For example, diethyl sulphide,
C 2 H 5 SC 2 H 5 , reacts with chloro-
methane, CH 3 Cl, to give diethyl-
methylsulphonium chloride,
(C 2 H 5 ) 2 .CH 3 .S+Cl–.
sulphoxidesOrganic compounds
containing the group =S=O (sulphox-
ide group) linked to two other
groups, e.g. dimethyl sulphoxide,
(CH 3 ) 2 SO.
A - Information about IUPAC nomenclature
sulphurSymbol S. A yellow non-
metallic element belonging to
*group 16 (formerly VIB) of the peri-
odic table; a.n. 16; r.a.m. 32.06; r.d.
2.07 (rhombic); m.p. 112.8°C; b.p.
444.674°C. The element occurs in
many sulphide and sulphate miner-
als and native sulphur is also found
in Sicily and the USA (obtained by
the *Frasch process). It can also be
obtained from hydrogen sulphide by
the *Claus process.
Sulphur has various allotropic
forms. Below 95.6°C the stable crys-
tal form is rhombic; above this tem-
perature the element transforms into
a triclinic form. These crystalline
forms both contain cyclic S 8 mol-
ecules. At temperatures just above its
melting point, molten sulphur is a
yellow liquid containing S 8 rings (as
in the solid form). At about 160°C,509 sulphur
s