Dictionary of Chemistry [6th Ed.]

sulphur cycle 510

s

the sulphur atoms form chains and

the liquid becomes more viscous and

dark brown. If the molten sulphur is

cooled quickly from this temperature

(e.g. by pouring into cold water) a

reddish-brown solid known as plastic

sulphuris obtained. Above 200°C the

viscosity decreases. Sulphur vapour

contains a mixture of S 2 , S 4 , S 6 , and

S 8 molecules. Flowers of sulphur is a

yellow powder obtained by sublim-

ing the vapour. It is used as a plant

fungicide. The element is also used to

produce sulphuric acid and other sul-

phur compounds.

Sulphur is an *essential element in

living organisms, occurring in the

amino acids cysteine and methionine

and therefore in many proteins. It is

also a constituent of various cell

metabolites, e.g. coenzyme A. Sul-

phur is absorbed by plants from the

soil as the sulphate ion (SO 4 2–). See

sulphur cycle.

A

• Information from the WebElements site

sulphur cycleThe cycling of sul-

phur between the biotic (living) and

abiotic (nonliving) components of the

environment. Most of the sulphur in

the abiotic environment is found in

rocks, although a small amount is

present in the atmosphere as sulphur

dioxide (SO 2 ), produced by combus-

tion of fossil fuels. Sulphate (SO 4 2–),

derived from the weathering and oxi-

dation of rocks, is taken up by plants

and incorporated into sulphur-con-

taining proteins. In this form sulphur

is passed along food chains to ani-

mals. Decomposition of dead organic

matter and faeces by anaerobic sul-

phate-reducing bacteria returns sul-

phur to the abiotic environment in

the form of hydrogen sulphide (H 2 S).

Hydrogen sulphide can be converted

back to sulphate or to elemental sul-

phur by the action of different groups

of photosynthetic and sulphide-oxi-

dizing bacteria. Elemental sulphur

becomes incorporated into rocks.

sulphur dichlorideSee disulphur

dichloride.

sulphur dichloride dioxide (sul-

phuryl chloride)A colourless liquid,

SO 2 Cl 2 ; r.d. 1.67; m.p. –54.1°C; b.p.

69 °C. It decomposes in water but is

soluble in benzene. The compound is

formed by the action of chlorine on

sulphur dioxide in the presence of an

iron(III) chloride catalyst or sunlight.

It is used as a chlorinating agent and

a source of the relatedÛuoride,

SO 2 F 2.

sulphur dichloride oxide (thionyl

chloride)A colourless fuming liquid,

sulphide (thio ether)

sulphonium ion

thiol (mercaptan)

sulphoxide

sulphonic acid

sulphonate ion

sulphonamide

R S R

RR

S

R

+

R S H

R

R

S O

R S OH

O

O

R S O–

O

O

R S NH 2

O

O

Sulphur compounds