containing aÜve-membered ring
with sulphur and nitrogen hetero
atoms, C 3 SNH 3. A range of thiazole
dyes are manufactured containing
this ring system.thienyl ring 526t
SN
ThiazoleSThiophenethienyl ringSee thiophene.thin-layer chromatography A
technique for the analysis of liquid
mixtures using *chromatography.
The stationary phase is a thin layer of
an absorbing solid (e.g. alumina) pre-
pared by spreading a slurry of the
solid on a plate (usually glass) and
drying it in an oven. A spot of the
mixture to be analysed is placed near
one edge and the plate is stood up-
right in a solvent. The solvent rises
through the layer by capillary action
carrying the components up the
plate at different rates (depending on
the extent to which they are ab-
sorbed by the solid). After a given
time, the plate is dried and the loca-
tion of spots noted. It is possible to
identify constituents of the mixture
by the distance moved in a given
time. The technique needs careful
control of the thickness of the layer
and of the temperature. See also rf
value.thiocyanateA salt or ester of thio-
cyanic acid.thiocyanic acidAn unstable gas,
HSCN.thio ethersSee sulphides.thiol group See thiols.
thiols(mercaptans; thio alcohols)
Organic compounds that contain the
group –SH (called the thiol group,
mercapto group, or sulphydrylgroup). Thiols are analogues of alco-
hols in which the oxygen atom is re-
placed by a sulphur atom. They are
named according to the parent hy-
drocarbon; e.g. ethane thiol (C 2 H 5 SH).
A characteristic property is their
strong disagreeable odour. For exam-
ple the odour of garlic is produced by
ethane thiol. Unlike alcohols they are
acidic, reacting with alkalis and cer-
tain metals to form saltlike com-
pounds. The older name, mercaptan,
comes from their ability to react with
(‘seize’) mercury.thionyl chlorideSee sulphur
dichloride oxide.thionyl group The group =SO, as
in *sulphur dichloride oxide.
thiopheneA colourless liquid com-
pound, C 4 H 4 S; m.p. –38°C; b.p. 84°C.
The compound is present in commer-
cial benzene. The ring system is also
known as a thienyl ring.thiosulphateA salt containing the
ion S 2 O 3 2–formally derived from
thiosulphuric acid. Thiosulphates
readily decompose in acid solution to
give elemental sulphur and hydro-
gensulphite (HSO 3 – ) ions.thiosulphuric acidAn unstable
acid, H 2 S 2 O 3 , formed by the reaction
of sulphur trioxide with hydrogen
sulphide. See also sulphuric acid.thiourea A white crystalline solid,
(NH 2 ) 2 CS; r.d. 1.4; m.p. 182°C. It is
used as aÜxer in photography.thixotropy See newtonian fluid.Thomson, Sir Joseph John
(1856–1940) British physicist, who be-