Dictionary of Chemistry [6th Ed.]

cyanine dyesA class of dyes that
contain a –CH= group linking two ni-
trogen-containing heterocyclic rings.
They are used as sensitizers in pho-
tography.

cyanoacrylate A compound
formed by the condensation of an
alkyl cyanoethanoate and methanal.
Cyanoacrylates have the general for-
mula CH 2 :C(CN)COOR. The methyl
and ethyl esters are the basis of vari-
ous ‘superglues’, which rapidly poly-
merize in air (under the action of
moisture) to form strong adhesives.

cyanocobalaminSee vitamin b
complex.

cyanogenA colourless gas, (CN) 2 ,
with a pungent odour; soluble in
water, ethanol, and ether; d. 2.335
gdm–3; m.p. –27.9°C; b.p. –20.7°C.
The compound is very toxic. It may
be prepared in the laboratory by
heating mercury(II) cyanide; industri-
ally it is made by gas-phase oxidation
of hydrogen cyanide using air over a
silver catalyst, chlorine over acti-
vated silicon(IV) oxide, or nitrogen
dioxide over a copper(II) salt.
Cyanogen is an important intermedi-
ate in the preparation of various fer-
tilizers and is also used as a stabilizer
in making nitrocellulose. It is an ex-
ample of a *pseudohalogen.

cyano group The group –CN in a
chemical compound. See nitriles.

cyanohydrinsOrganic compounds

formed by the addition of hydrogen

cyanide to aldehydes or ketones (in

the presence of a base). TheÜrst step

is attack by a CN–ion on the car-

bonyl carbon atom. TheÜnal product

is a compound in which a –CN and

–OH group are attached to the same

carbon atom. For example, ethanal

reacts as follows

CH 3 CHO + HCN →CH 3 CH(OH)(CN)

The product is 2-hydroxypropanoni-

trile. Cyanohydrins of this type can

be oxidized to α-hydroxy carboxylic

acids.

cyanuric acidA white crystalline

water-soluble trimer of cyanic acid,

(HNCO) 3. It is a cyclic compound hav-

ing a six-membered ring made of al-

ternating imide (NH) and carbonyl

(CO) groups (i.e. three –NH–C(O)–

units). It can also exist in a phenolic

form (three –N=C(OH)– units).

cyclamatesSalts of the acid,

C 6 H 11 .NH.SO 3 H, where C 6 H 11 – is a cy-

clohexyl group. Sodium and calcium

cyclamates were formerly used as

sweetening agents in soft drinks, etc,

until their use was banned when

they were suspected of causing can-

cer.

cyclicDescribing a compound that

has a ring of atoms in its molecules.

In homocycliccompounds all the

atoms in the ring are the same type,

e.g. benzene (C 6 H 6 ) and cyclohexane

(C 6 H 12 ). These two examples are also

examples of carbocycliccompounds;

157 cyclic

N N c

N

H

H

O O

O

H

N N

OH N OH

OH

Cyanuric acid