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Chapter 12
Reactions of Formaldehyde with Phenols
Phenol-formaldehyde resins are the complex final products of many
reactions involving formaldehyde and phenolic compounds. Because of
their immeave industrial importance, the art of preparing these bodies and
convening them TO useful articles of commerce has advanced rapidly since
their potential value was first realized in the early part of the twentieth
century. Exaer scientific knowledge of phenol-formaldehyde reactions and
the chemical structure of the products obtained has been a subject of
slower growth. However, in recent years, more and more emphasis has
been placed on fundamental studies. As a result, although many unsolved
problems aXxd controversial items still exist, worthwhile advances have been
made.
Of particular importance in this field of chemistry are the simple reactions
which are most amenable to exact study. These reactions are in some
cases the precursors of more complex condensations. In all cases thej- illustrate
the fundamental facts of phenol-formaldehyde chemistry and thus
afford a practical approach to the more involved problems of resin structure.
Since uur purpose is to coordinate phenol-formaldehyde reactions with the
broad field of formaldehyde chemistry, special emphasis will be placed on
these less complicated reactions which are often neglected because of the
importance of the intricate condensations that result in resin production.
Historical, The general character of phenol-aldehyde reactions was
probably first recognised by Baeyer 5 in 1872. Baeyer apparently produced
his first phenol-formaldehyde type resin by reacting phenol with methylene
acetate in the presence of hydrochloric acid. This acid hydrolyzed the
methylene ester, with liberation of formaldehyde, and catalyzed the subsequent
condensation of this product with phenol. Following commercial
production of formaldehyde in 1889, Kleeberg 32 , at the suggestion of
Emil Fisher, investigated its reactions with various phenols and published
the results in 189 L Tollens also carried out studies in this field at approximately
the same period, since in 1892 Hosaeus 30 refers to unpublished
TOrk of this investigator dealing with the action of formaldehyde on
phenol, resorcinol, pyrogallol, and phloroglucinol in the presence of acid
catalysts. Commercial applications of phenol-formaldehyde resins were
developed in the first decade of the twentieth century. In the latter part
of this decade, Baekeland discovered a technique for molding these resins.
This work, together with that of Redman and other investigators, led to the
development of the present phenolic resin industry.
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