Dictionary of Chemistry [6th Ed.]

quinhydrone electrode 450

q

O

O

OH

OH

• 2H

+

Quinhydrone electrode







 













 











 







Quinoline

quinhydrone electrode A *half

cell consisting of a platinum elec-

trode in an equimolar solution of

quinone (cyclohexadiene-1,4-dione)

and hydroquinone (benzene-1,4-diol).

It depends on the oxidation–reduc-

tion reaction

C 6 H 4 (OH) 2 ˆC 6 H 4 O 2 + 2H++ 2e.

quinineA white solid,

C 20 H 24 N 2 O 2 .3H 2 O, m.p. 57°C. It is a

poisonous alkaloid occurring in the

bark of the South American cinchona

tree, although it is now usually pro-

duced synthetically. It forms salts

and is toxic to the malarial parasite,

and so quinine and its salts are used

to treat malaria; in small doses it

may be prescribed for colds and in-

Ûuenza. In dilute solutions it has a

pleasant astringent taste and is added

to some types of tonic water.

quinolSee benzene-1,4-diol.

quinolineA hygroscopic unpleas-

ant-smelling colourless oily liquid,

C 9 H 7 N; b.p. 240°C. Its molecules con-

sist of a benzene ring fused to a pyri-

dine ring. It occurs in coal tar and

bone oil, and is made from phenyl-

amine and nitrobenzene. Quinoline

is a basic compound, forming salts

with mineral acids and forming qua-

ternary ammonium compounds with

haloalkanes. It is used for making

medicines and dyes. In quinoline, the

nitrogen atom is one atom away

from the position at which the rings

are fused. In an isomer, isoquinoline,

the nitrogen atom is positioned two

atoms away from the fused ring.

quinone1.See cyclohexadiene-1,4-

dione. 2.Any similar compound

containing C=O groups in an unsatu-

rated ring.