(p-DMAB)A substituted aldehyde
used in a presumptive test for LSD
and for psilocybin. A 1% solution of p-
BMAB is used in 10% mineral acid (ei-
ther sulphuric acid or hydrochloric
acid). This reagent is called Ehrlick’s
reagent or Van Urk’s reagent. LSD is
indicated by a purple colouration;
psilocybin by a red-brown colour.
dimethylbenzenes(xylenes)
Three compounds with the formula
(CH 3 ) 2 C 6 H 4 , each having two methyl
groups substituted on the benzene
ring. 1,2-dimethylbenzene is ortho-
xylene, etc. A mixture of the isomers
(b.p. 135–145°C) is obtained from pe-
troleum and is used as a clearing
agent in preparing specimens for op-
tical microscopy.dimethylformamide(DMF)A
colourless liquid compound,
(CH 3 ) 2 NCHO; r.d. 0.944; m.p. –61°C;
b.p. 153°C. The systematic name is
N,N-dimethylmethanamide. It can be
made from methanoic acid (formic
acid) and dimethylamine, and is
widely used as a solvent.
1,3-dimethylxanthineSee theo-
phylline.
3,7-dimethylxanthineSee theo-
bromine.
dimethylglyoxime(DMG)A
colourless solid, (CH 3 CNOH) 2 , m.p.
234 °C. It sublimes at 215°C and
slowly polymerizes if left to stand. It
is used in chemical tests for nickel,
with which it forms a dark-red com-
plex.
dimethyl sulphoxide (DMSO)A
colourless solid, (CH 3 ) 2 SO; m.p. 18°C;
b.p. 189°C. It is used as a solvent and
as a reagent in organic synthesis.
dimorphismSee polymorphism.dinitrogen The normal form of
molecular nitrogen, N 2 used to distin-
guish it from nitrogen atoms.dinitrogen oxide (nitrous oxide) A
colourless gas, N 2 O, d. 1.97 g dm–3;
m.p. –90.8°C; b.p. –88.5°C. It is solu-
ble in water, ethanol, and sulphuric
acid. It may be prepared by the con-
trolled heating of ammonium nitrate
(chloride free) to 250°C and passing
the gas produced through solutions
of iron(II) sulphate to remove impuri-
ties of nitrogen monoxide. It is rela-
tively unreactive, being inert to
halogens, alkali metals, and ozone at
normal temperatures. It is decom-
posed on heating above 520°C to ni-
trogen and oxygen and will support
the combustion of many compounds.
Dinitrogen oxide is used as an anaes-
thetic gas (‘laughing gas’) and as an
aerosol propellant.dinitrogen tetroxide A colourless
to pale yellow liquid or a brown gas,
N 2 O 4 ; r.d. 1.45 (liquid); m.p. –11.2°C;
b.p. 21.2°C. It dissolves in water with
reaction to give a mixture of nitric
acid and nitrous acid. It may be read-
ily prepared in the laboratory by the
reaction of copper with concentrated
nitric acid; mixed nitrogen oxides
containing dinitrogen oxide may also
be produced by heating metal ni-
trates. The solid compound is wholly
N 2 O 4 and the liquid is about 99%
N 2 O 4 at the boiling point; N 2 O 4 is dia-
magnetic. In the gas phase it dissoci-
ates to give nitrogen dioxide
N 2 O 4 ˆ2NO 2
Because of the unpaired electron this
is paramagnetic and brown. Liquid
N 2 O 4 has been widely studied as a
nonaqueous solvent system (self-
ionizes to NO+and NO 3 – ). Dinitrogen
tetroxide, along with other nitrogen
oxides, is a product of combustion
engines and is thought to be involved
in the depletion of stratospheric
ozone.
dinucleotideA compound consist-
ing of two *nucleotides.dimethylbenzenes 178d