Dictionary of Chemistry [6th Ed.]

SOCl 2 ; m.p. –105°C; b.p. 78.8°C. It hy-
drolyses rapidly in water but is solu-
ble in benzene. It may be prepared
by the direct action of sulphur on
chlorine monoxide or, more com-
monly, by the reaction of phospho-
rus(V) chloride with sulphur dioxide.
It is used as a chlorinating agent in
synthetic organic chemistry (replac-
ing –OH groups with Cl).

sulphur dioxide (sulphur(IV) oxide)
A colourless liquid or pungent gas,
SO 2 , formed by sulphur burning in
air; r.d. 1.43 (liquid); m.p. –72.7°C;
b.p. –10°C. It can be made by heating
iron sulphide (pyrites) in air. The
compound is a reducing agent and is
used in bleaching and as a fumigant
and food preservative. Large quanti-
ties are also used in the *contact
process for manufacturing sulphuric
acid. It dissolves in water to give a
mixture of sulphuric and sulphurous
acids. See also acid rain.

sulphuretted hydrogen See hy-
drogen sulphide.

sulphuric acid (oil of vitriol)A
colourless oily liquid, H 2 SO 4 ; r.d.
1.84; m.p. 10.36°C; b.p. 338°C. The
pure acid is rarely used; it is com-
monly available as a 96–98% solution
(m.p. 3.0°C). The compound also

forms a range of hydrates: H 2 SO 4 .H 2 O

(m.p. 8.62°C); H 2 SO 4 .2H 2 O (m.p.

–38/39°C); H 2 SO 4 .6H 2 O (m.p. –54°C);

H 2 SO 4 .8H 2 O (m.p. –62°C). Its full sys-

tematic name is tetraoxosulphuric(VI)

acid.

Until the 1930s, sulphuric acid was

manufactured by the *lead-chamber

process, but this has now been re-

placed by the *contact process (cat-

alytic oxidation of sulphur dioxide).

More sulphuric acid is made in the

UK than any other chemical product;

production levels (UK) are commonly

12 000 to 13 000 tonnes per day. It is

extensively used in industry, the

main applications being fertilizers

(32%), chemicals (16%), paints and

pigments (15%), detergents (11%), and

Übres (9%).

In concentrated sulphuric acid

there is extensive hydrogen bonding

and several competing equilibria, to

give species such as H 3 O+, HSO 4 – ,

H 3 SO 4 +, and H 2 S 2 O 7. Apart from

being a powerful protonating agent

(it protonates chlorides and nitrates

producing hydrogen chloride and ni-

tric acid), the compound is a moder-

ately strong oxidizing agent. Thus, it

will dissolve copper:

Cu(s) + H 2 SO 4 (l) →CuO(s) + H 2 O(l) +

SO 2 (g)

511 sulphuric acid

HO SOH s

OH 2 SO 3

sulphurous acid

(in sulphites)

HO SOH

O

O

H 2 SO 4

sulphuric(VI) acid

H 2 S 2 O 3

thiosulphuric acid

O

HO SOH

S

H 2 S 2 O 7

disulphuric(VI) acid

HO SO (pyrosulphuric)

O

O

OH

O

O

S

H 2 S 2 O 4

sulphinic acid

(dithionous or

hyposulphurous)

HO SS

O O

OH

H 2 Sn+2O 6

HO S (S) polythionic acids

n

O O

OH

O O

S

HO SS

O O

OH

O O

H 2 S 2 O 6

dithionic acid

Sulphur acids