inversionA chemical reaction in-
volving a change from one optically
active conÜguration to the opposite
conÜguration. The Walden inversion
is an example. See nucleophilic sub-
stitution.iodic acidAny of various oxoacids
of iodine, such as iodic(V) acid and
iodic(VII) acid. When used without an
oxidation state speciÜed, the term
usually refers to iodic(V) acid (HIO 3 ).
iodic(V) acidA colourless or very
pale yellow solid, HIO 3 ; r.d. 4.63; de-
composes at 110°C. It is soluble in
water but insoluble in pure ethanol
and other organic solvents. The com-
pound is obtained by oxidizing io-
dine with concentrated nitric acid,
hydrogen peroxide, or ozone. It is a
strong acid and a powerful oxidizing
agent.
iodic(VII) acid (periodic acid)A hy-
groscopic white solid, H 5 IO 6 , which
decomposes at 140°C and is very
soluble in water, ethanol, and
ethoxyethane. Iodic(VII) acid may be
prepared by electrolytic oxidation of
concentrated solutions of iodic(V)
acid at low temperatures. It is a weak
acid but a strong oxidizing agent.iodideSee halide.
iodineSymbol I. A dark violet
nonmetallic element belonging to
group 17 of the periodic table (see
halogens); a.n. 53; r.a.m. 126.9045;
r.d. 4.94; m.p. 113.5°C; b.p. 184.35°C.
The element is insoluble in water but
soluble in ethanol and other organic
solvents. When heated it gives a vio-
let vapour that sublimes. Iodine is
required as a trace element (see es-
sential element) by living organ-
isms; in animals it is concentrated in
the thyroid gland as a constituent of
thyroid hormones. The element is
present in sea water and was for-
merly extracted from seaweed. It is
now obtained from oil-well brines(displacement by chlorine). There is
one stable isotope, iodine–127, and
fourteen radioactive isotopes. It is
used in medicine as a mild antiseptic
(dissolved in ethanol as tincture of io-
dine), and in the manufacture of io-
dine compounds. Chemically, it is
less reactive than the other halogens
and the most electropositive (metal-
lic) halogen. In solution it can be
determined by titration using thio-
sulphate solution:
I 2 + 25 2 O 3 2–→2I–+ SuO 6 2–.
The molecule forms an intense blue
complex with starch, which is conse-
quently used as an indicator. It was
discovered in 1812 by Courtois.
A- Information from the WebElements site
iodine(V) oxide (iodine pentoxide)
A white solid, I 2 O 5 ; r.d. 4.799; decom-
poses at 300–350°C. It dissolves in
water to give iodic(V) acid and also
acts as an oxidizing agent.
iodine valueA measure of the
amount of unsaturation in a fat or
vegetable oil (i.e. the number of dou-
ble bonds). It is obtained byÜnding
the percentage of iodine by weight
absorbed by the sample in a given
time under standard conditions.
iodoethane(ethyl iodide)A colour-
less liquid *haloalkane, C 2 H 5 I; r.d.
1.9; m.p. –108°C; b.p. 72°C. It is made
by reacting ethanol with a mixture of
iodine and red phosphorus.iodoformSee triiodomethane.iodoform testSee haloform reac-
tion.
iodomethane(methyl iodide)A
colourless liquid haloalkane, CH 3 I;
r.d. 2.28; m.p. –66.45°C; b.p. 42.4°C. It
can be made by reacting methanol
with a mixture of iodine and red
phosphorus.ionAn atom or group of atoms thatinversion 288i