Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

MECHANISM OF THE SYNTHESIS 237
This reaction, which can also be used with substituted phenols,
can be applied generally, but, because of side-reactions which accompany
it, it is usually rather unprofitable. Its result very distinctly
recalls that of Kolbe's salicylic acid synthesis (Chap. VI. 4, p. 249), and
we might be tempted to picture its course as proceeding in the same way
as has been demonstrated experimentally for Kolbe's synthesis, namely,
by way of a double decomposition with elimination of a molecule of
NaCl; part of the chloroform molecule would thus become attached to
the oxygen of the phenol, the two remaining chlorine atoms would
then be replaced by oxygen, and finally, in the phenyl formate so produced,
a rearrangement involving the wandering of the formyl group
(to the o- or y-position) would take place. This wandering corresponds
to that which occurs in phenyl carbonate :
/\—ONa + CLCClg ^ /N—O.CClg
I J . H 'N. J H
NaOH
More probably, however, the process consists first in an addition of
chloroform to one of the double bonds of the ring and then in a change
which is readily understood from the following formulae.:
ONa
•> I I ^ •> I I /H •>
The isolation of addition compounds which can only have been
formed in such a way (in the cases of o- and p-cresoZ; Auwers, Ber.,
1902, 35, 4207) gives decisive support to this view.
As will be seen, the primary product from o-cresol cannot reconstitute
the aromatic ring because of the CH3-group. Hence only NaCl
is eliminated. The other two chlorine atoms are not hydrolytically
removed and a quinol-like substance is formed, as the formula indicates:
In the case of y-cresol the addition of chloroform takes place in the
1 : 4-positions:
HO