3. Phenolic inhibitors

the most reasonable one is the use of special additives, the so-called inhibitors. Inhibitors are chemicals, which stabilize reactive monomers, they could react fast with free radicals, and so the latter are withdrawn and could not activate polymerization, notably, inhibitors stop spon-

The following substances of different chemical classes can be used as inhibitors, for example:

Every compound class has its specific action on monomer stabilizations, and so its own intrinsic advantages and disadvantages. The most common among them are the representa-

It should be noted that phenol inhibitors demonstrate some technological advantages, than

Figure 1. Surface appearances of heat exchangers T-58 EP-300 utility after application of phenol inhibitors (a) and nitroxyl

taneous polymerization. Inhibitors cut off every chain reaction until they are spent.

2. The basic classes of inhibitors

304 Phenolic Compounds - Natural Sources, Importance and Applications

(2) nitro- and nitroso compounds;

(5) different phenolic compounds;

(4) stable nitroxyl radicals;

(6) salts of aliovalent metals;

tives of four and five groups.

others (Figure 1).

radicals (b).

(3) amines and hydroxyl amines and their derivatives;

(7) sulfur- and phosphor-containing compounds, as well as

(8) high-molecular-weight inhibitors on the basis of the above classes.

(1) quinones

Among the phenol inhibitors, two main series are differentiated:


The latter are multicomponent phenol mixtures produced during thermal treatment of organic raw materials—wood and coal. These mixtures are different in their compositions and properties.

Unlike the other inhibitor classes, the phenolic compounds advantageously combine their antioxidant properties together with the capacities to trap radicals [1].

Practical applications reveal the monoatomic SHP—Ar-OH and their derivatives to be the most effective.

Diatomic phenols Ar(OH)2 (e.g., hydroquinone, pyrocatechol, pyrogallol, trimethylhydroquinone, 1,6-naphthalene diol, etc.) are more effective as radical process inhibitors in anoxic environment when compared with others. Three and more atomic phenols show their best antioxidant properties.

Phenol inhibitors can be divided into small number of classes depending on their properties and structures, according to the following characteristics:


Sterically hindered phenols dramatically differ from other phenols. They are often used as industrial antioxidants, stabilizers, and anti-polymerizers, and many of them possess very high inhibiting activities.

At present, the most common in use are SHP having tert-butyl substituents, and the most wellknown among them are as follows:

Ionol (2,6-di-tert-butyl-p-cresol, butyloxytoluene, BOT, alkophen, BP, topanol-O, DBC, topanol-OC, topanol-OF, 4M26B, CAO, Agidol-1, etc.), tert-butyl pyrocatechine (TBPC), and di-tert-butylhydroquinone.
