diol(dihydric alcohol)An *alcohol
containing two hydroxyl groups per
molecule.
dioxan A colourless toxic liquid,
C 4 H 8 O 2 ; r.d. 1.03; m.p. 11°C; b.p.
101.5°C. The molecule has a six-
membered ring containing four CH 2
groups and two oxygen atoms at op-
posite corners. It can be made from
ethane-1,2-diol and is used as a sol-
vent.
dioxin(2,4,7,8-tetrachlorodibenzo-
p-dioxin)A toxic solid, formed in the
manufacture of the herbicide *2,4,5-
T and present as an impurity in
Agent Orange. It can cause skin dis-
Ügurement (chloracne) and severe
fetal defects.
dioxonitric(III) acidSee nitrous
acid.
dioxygenThe normal form of mo-
lecular oxygen, O 2 , used to distin-
guish it from oxygen atoms or from
ozone (O 3 ).
dioxygenyl compoundsCom-
pounds containing the positive ion
O 2 +, as in dioxygenyl hexaÛuoro-
platinate O 2 PtF 6 – an orange solid
that sublimes in vacuum at 100°C.
Other ionic compounds of the type
O 2 +[MF 6 ]–can be prepared, where M
is P, As, or Sb.
dipeptideA compound consisting
of two amino acid units joined at the
amino (–NH 2 ) end of one and the car-
boxyl (–COOH) end of the other. This
peptide bond (see peptide) is formed
by a condensation reaction that in-
volves the removal of one molecule
of water.
diphenylamine A colourless crys-
talline aromatic compound,
(C 6 H 5 ) 2 NH; m.p. 54°C. It is made by
heating phenylamine (aniline) with
phenylamine hydrochloride. It is a
secondary amine and is both slightly
acidic (forming an N-potassium salt)
and slightly basic (forming salts with
mineral acids). Its derivatives are em-
ployed as stabilizers for synthetic
rubber and rocket fuels.
diphenylamine testA presump-
tive test for nitrates. The reagent is a
solution of diphenylamine
((C 6 H 5 )2NH) in sulphuric acid. A posi-
tive result is indicated by a blue col-
our. It was once used in testing for
gunshot residue, but is not particu-
larly reliable.diphenylmethanone(benzo-
phenone)A colourless solid,
C 6 H 5 COC 6 H 5 , m.p. 49°C. It has a char-
acteristic smell and is used in making
perfumes. It is made from benzene
and benzoyl chloride using the
*Friedel–Crafts reaction with alu-
minium chloride as catalyst.
diphosgeneA colourless liquid,
ClCO.O.CCl 3 , originally used in 1916
by Germany in World War I as a
chemical warfare agent. It is now
used as a reagent in organic synthe-
sis. See also carbonyl chloride.diphosphane(diphosphine)A yel-
low liquid, P 2 H 4 , which is sponta-
neouslyÛammable in air. It is
obtained by hydrolysis of calcium
phosphide. Many of the references to
the spontaneousÛammability of
phosphine (PH 3 ) are in fact due to
traces of P 2 H 4 as impurities.diphosphineSee diphosphane.
diphosphonatesSee bisphospho-
nates.
dipolar bondSee chemical bond.dipoleA pair of separated opposite
electric charges. The dipole moment
(symbol μ) is the product of the posi-
tive charge and the distance between
the charges. Dipole moments are
often stated in *debyes; the SI unit is
the coulomb metre. In a diatomic
molecule, such as HCl, the dipole179 dipole
d