Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

354 OKGANIC KADICLES AS IONS
is in many respects extraordinarily similar to the one considered
here.
In both cases the degree of dissociation increases with rising temperature.
Ebullioscopic determination of the molecular weight shows
that, in boiling benzene, 30 per cent of the substance is present as
triphenylmethyl.
The dissociation of hexaphenylethane can also be demonstrated
colorimetrically. Whereas, in general, coloured solutions undergo no
change in intensity of colour on dilution, since the number of coloured
molecules observed in the colorimeter remains the same (Beer's law),
the intensity must increase if the coloured molecules become more
numerous as a result of progressive dissociation following dilution
(Piccard).
Experiments—Verify Beer's law by wrapping two test tubes in
black paper, pouring the same volume (1-2 c.c.) of a dilute solution
of a dye into each, and checking the equality of colour by looking
down both tubes against a white surface. Then dilute the contents
of one tube with 5-10 c.c. of water and again compare their colour.
The decomposition of hexaphenylethane is to be attributed to the
inadequate binding force between the two ethane carbon atoms which
are each over-much occupied by three phenyl groups. If these are
progressively replaced by diphenyl groups the combining power of the
fourth valency becomes smaller and smaller, and is finally reduced to
zero in -p-tridiphenyl-methyl (Schlenk).
This hydrocarbon I —(~ \ ) C, indeed, exists only as a free
\ \—/ \ / /3
radicle, and has even been prepared as such in the solid state in the
form of magnificent red-violet crystals.
Of the further results of the investigation of the carbon radicles,
a field still actively cultivated, only the so-called metal ketyls will be
mentioned. These addition products of the alkali metals to ketones
are also intensely coloured (Schlenk), e.g.
(C6H5)2:C=O + Na > (C6H5)2:C—ONa .
They have already been discussed on p. 224.
The Triphenylmethyl Ion.—A solution of triphenylchloromethane in
a dissociating solvent conducts the electric current (Walden). Since,
on electrolysis, triphenylmethyl is liberated at the cathode, it follows
t h a t t h e s o l u t i o n c o n t a i n s t h e i o n s ( C 6 H 5 ) 3 C a n d C l . T h e i n t e n s e l y
y e l l o w s o l u t i o n o f h e x a p h e n y l e t h a n e i n l i q u i d s u l p h u r d i o x i d e a l s o c o n -
d u c t s e l e c t r i c i t y , a n d h e n c e a l s o c o n t a i n s i o n i s e d t r i p h e n y l m e t h y l ( p o s -
i