Dictionary of Chemistry [6th Ed.]

less crystalline compound, C 10 H 14 O;

m.p. 51°C. It occurs in various essen-

tial oils, particularly oil of thyme,

and can be made by using iron(III)

chloride to oxidize piperitone (itself

extracted from eucalyptus oil). Its

antiseptic properties are exploited in

gargles and mouthwashes.

tie lineA horizontal line in a liq-

uid–vapour phase diagram that is

perpendicular to an *isopleth. The

starting point is theÜrst point at

which the liquid can coexist with its

vapour as the pressure is reduced;

the end point is the point beyond

which only vapour is present.

time-of-Ûight mass spectrom-

eterSee mass spectroscopy.

tinSymbol Sn. A silvery malleable

metallic element belonging to

*group 14 (formerly IVB) of the peri-

odic table; a.n. 50; r.a.m. 118.69; r.d.

7.28; m.p. 231.88°C; b.p. 2260°C. It is

found as tin(IV) oxide in ores, such as

cassiterite, and is extracted by reduc-

tion with carbon. The metal (called

white tin) has a powdery nonmetallic

allotrope grey tin, into which it

changes below 18°C. The formation

of this allotrope is called tin plague;

it can be reversed by heating to

100 °C. The natural element has 21

isotopes (the largest number of any

element);Üve radioactive isotopes are

also known. The metal is used as a

thin protective coating for steel plate

and is a constituent of a number of

alloys (e.g. phosphor bronze, gun

metal, solder, Babbitt metal, and

pewter). Chemically it is reactive. It

combines directly with chlorine and

oxygen and displaces hydrogen from

dilute acids. It also dissolves in alkalis

to form *stannates. There are two se-

ries of compounds with tin in the +2

and +4 oxidation states.

A

• Information from the WebElements
  site

tin(II) chlorideA white solid,

SnCl 2 , soluble in water and ethanol.

It exists in the anhydrous form

(rhombic; r.d. 3.95; m.p. 246°C;

b.p. 652°C) and as a dihydrate,

SnCl 2 .2H 2 O (monoclinic; r.d. 2.71;

m.p. 37.7°C). The compound is made

by dissolving metallic tin in hy-

drochloric acid and is partially hy-

drolysed in solution.

Sn2++ H 2 O ˆSnOH++ H+

Excess acid must be present to pre-

vent the precipitation of basic salts.

In the presence of additional chloride

ions the pyramidal ion [SnCl 3 ]–is

formed; in the gas phase the SnCl 2

molecule is bent. It is a reducing

agent in acid solutions and oxidizes

slowly in air:

Sn2+→Sn4++ 2e

tin(IV) chlorideA colourless fum-

ing liquid, SnCl 4 , hydrolysed in cold

water, decomposed by hot water, and

soluble in ethers; r.d. 2.226; m.p.

–33°C; b.p. 114°C. Tin(IV) chloride is

a covalent compound, which may be

prepared directly from the elements.

It dissolves sulphur, phosphorus,

bromine, and iodine, and there is evi-

dence for the presence of species

such as SnCl 2 I 2. In hydrochloric acid

and in chloride solutions the coordi-

nation is extended from four to six

by the formation of the SnCl 6 2–ion.

tie line 528

t

OH

C

CH H

3 CH 3

CH 3

Thymol