methylenedioxymethampheta-
mine(MDMA)See ecstasy.
methyl ethanoate (methyl ac-
etate)A colourless volatile fragrant
liquid, CH 3 COOCH 3 ; r.d. 0.92; m.p.
–98°C; b.p. 54°C. A typical *ester, it
can be made from methanol and
methanoic acid and is used mainly as
a solvent.
methyl ethyl ketoneSee bu-
tanone.
methyl group (methyl radical)The
organic group CH 3 –.
methylidyneSee carbyne.
methyl methacrylate An ester of
methacrylic acid (2-methylpropenoic
acid), CH 2 :C(CH 3 )COOCH 3 , used in
making *methacrylate resins.
methyl orangeAn organic dye
used as an acid–base *indicator. It
changes from red below pH 3.1 to
yellow above pH 4.4 (at 25°C) and is
used for titrations involving weak
bases.
methylphenols(cresols) Organic
compounds having a methyl group
and a hydroxyl group bound directly
to a benzene ring. There are three
isomeric methylphenols with the for-
mula CH 3 C 6 H 4 OH, differing in the
relative positions of the methyl and
hydroxyl groups. A mixture of the
three can be obtained by distilling
coal tar and is used as a germicide
and antiseptic.
2-methylpropenoic acid
(methacrylic acid)A white crystalline
unsaturated carboxylic acid,
CH 2 :C(CH 3 )COOH, used in making
*methacrylate resins.methyl red An organic dye similar
in structure and use to methyl or-
ange. It changes from red below pH
4.4 to yellow above pH 6.0 (at 25°C).
methyl violetA violet dye used as
a chemical indicator and as a biologi-
cal stain. It is also the colouring mat-
ter in methylated spirits. It is a
mixture of compounds of rosaniline,
made by oxidizing dimethylpheny-
lamine with copper(II) chloride.methylxanthinesDerivatives of
xanthine in which one or more hy-
drogen atoms have been substituted
by methyl groups. The common ones
are the trimethylxanthine *caffeine
and the dimethylxanthines *theo-
phylline and *theobromine.metolSee aminophenol.metre Symbol m. The SI unit of
length, being the length of the path
travelled by light in vacuum during a
time interval of 1/(2.99 792 458 × 108 )
second. This deÜnition, adopted by
the General Conference on Weights
and Measures in October, 1983, re-
placed the 1967 deÜnition based on
the krypton lamp, i.e. 1 650 763.73
wavelengths in a vacuum of the radi-
ation corresponding to the transition353 metre
m
Methylxanthines