unpleasant odour; r.d. 1.114 (liquid at
0 °C); m.p. –111.3°C; b.p. 7°C. It is the
acid anhydride of malonic acid, from
which it can be prepared by dehydra-
tion using phosphorus(V) oxide. The
molecule is linear (O:C:C:C:O).
tricarboxylic acid cycle See krebs
cycle.
trichloroethanal (chloral)A liquid
aldehyde, CCl 3 CHO; r.d. 1.51; m.p.
–57.5°C; b.p. 97.8°C. It is made by
chlorinating ethanal and used in
making DDT. See also 2,2,2-
trichloroethanediol.
2,2,2-trichloroethanediol (chloral
hydrate)A colourless crystalline
solid, CCl 3 CH(OH) 2 ; r.d. 1.91; m.p.
57 °C; b.p. 96.3°C. It is made by the
hydrolysis of trichloroethanal and is
unusual in having two –OH groups
on the same carbon atom. Gem diols
of this type are usually unstable; in
this case the compound is stabilized
by the presence of the three Cl
atoms. It is used as a sedative.
trichloroethene (trichlorethylene)
A colourless liquid, CCl 2 =CHCl, b.p.
87 °C. It is toxic and nonÛammable,
with a smell resembling that of chlo-
roform (trichloromethane). It is
widely used as a solvent in dry clean-
ing and degreasing. It is also used to
extract oils from nuts and fruit, as
an anaesthetic, and as aÜre extin-
guisher.
trichloromethane (chloroform) A
colourless volatile sweet-smelling liq-
uid *haloform, CHCl 3 ; r.d. 1.48; m.p.
–63.5°C; b.p. 61.7°C. It can be made
by chlorination of methane (followed
by separation of the mixture of prod-
ucts) or by the haloform reaction. It
is an effective anaesthetic but can
cause liver damage and it has now
been replaced by other halogenated
hydrocarbons. Chloroform is used as
a solvent and raw material for mak-
ing other compounds.
triclinicSee crystal system.tridymiteA mineral form of *sili-
con(IV) oxide, SiO 2.triethanolamineSee ethanol-
amine.triglyceride(triacylglycerol) An
ester of glycerol (propane-1,2,3-triol)
in which all three hydroxyl groups
are esteriÜed with a fatty acid.
Triglycerides are the major con-
stituent of fats and oils and provide a
concentrated food energy store in liv-
ing organisms as well as cooking fats
and oils, margarines, etc. Their physi-
cal and chemical properties depend
on the nature of their constituent
fatty acids. In simple triglycerides all
three fatty acids are identical; in
mixed triglycerides two or three dif-
ferent fatty acids are present.
trigonal bipyramidSee illustra-
tion atcomplex.
trihydrateA crystalline hydrate
that contains three moles of water
per mole of compound.trihydric alcoholSee triol.
3,4,5-trihydroxybenzoic acid See
gallic acid.triiodomethane(iodoform)A yel-
low volatile solid sweet-smelling
*haloform, CHI 3 ; r.d. 4.1; m.p. 115°C.
It is made by the haloform reaction.
triiron tetroxide (ferrosoferric
oxide)A black magnetic oxide,
Fe 3 O 4 ; r.d. 5.2. It is formed when iron
is heated in steam and also occurs
naturally as the mineral *magnetite.
The oxide dissolves in acids to give a
mixture of iron(II) and iron(III) salts.trimethylaluminium(aluminium
trimethyl)A colourless liquid,
Al(CH 3 ) 3 , which ignites in air and re-
acts with water to give aluminium
hydroxide and methane, usually with
extreme vigour; r.d. 0.752; m.p. 0°C;535 trimethylaluminium
t