Chemistry Reference
In-Depth Information
OH
OH
OH
+
+
H
OH
OH
OH
H
OH
O
OH
OH
OH
+
H
+
OH
-methylolphenols are
transitory and are present in small concentrations only. Hydrogen ions convert them to benzylic
carbocations that react rapidly with free phenol. This can be illustrated as follows:
Because the reaction is taking place at pH below 7, the above shown
p
- and
o
OH
OH
OH
+
H
+
H
2
O
CH
2
OH
OH
2
OH
HO
CH
2
+
+
HO
OH
H
+
HO
H
HO
substituted methylolphenols react in the same manner.
Further metholylation of dihydroxy diphenyl methanes takes place until all the formaldehyde
is used up. Methylol groups react with each other quickly and form methylene bridges. The
The
ortho
para
position is more reactive than
ortho
[
144
-
146
] at pH below 3. The opposite is true, however, at
pH 5-6, where the
position is more reactive. Typical novolacs formed in these reactions are
not very high in molecular weight and contain no more than six to ten benzene rings. If divalent
metal salts, like zinc acetate in acetic acid, are used to catalyze the reaction, then the
ortho
ortho
positions
