1. Field of the Invention
This invention relates to the color stabilization of monoalkyl phenols, which frequently discolor with age. More specifically, this invention relates to improving the color stability of monoalkyl phenols and reducing color already formed by the addition of an additive.
2. Background Discussion
Monoalkyl phenols are generally produced by reacting phenol with an olefin in the presence of an acidic alkylation catalyst. The product should be only lightly colored, but color frequently develops with age. Sometimes color development is rapid. Color development substantially reduces the commercial value of monoalkyl phenols, because many uses require material that is only lightly colored. Neither the identity of the colored species nor the mechanism of their production are exactly known. However, the speed and degree of the color development are affected by a number of factors, including: the presence of metallic impurities, of residual catalyst, and of reaction byproducts; exposure of the product to oxygen, to sunlight, to HCl, and to steel containers; and the temperature at which storage occurs.
A number of additives are known that act to inhibit color formation in alkyl phenols, including: polybasic carboxylic acids (U.S. Pat. No. 2,672,485); phosphoric acid (U.S. Pat. No. 2,752,398); dicarboxylic acid substituted abietylamines and their salts (U.S. Pat. No. 2,877,273); hypophosphorous acid and its salts used either as an additive to the product (U.S. Pat. No. 2,727,928) or as an additive to the phenol starting material (U.S. Pat. No. 3,168,578); organic phosphites (U.S. Pat. No. 3,553,272); and various arsenic compounds (U.S. Pat. No. 3,629,339). Although each of these color stabilizers is effective to some extent, with at least some alkyl phenols, none is effective under all circumstances.
The lower limit of effective concentrations disclosed for the above listed color inhibitors ranges from 0.001% by weight for phosphoric acid and the arsenic compounds to 0.15% for hypophosphorous acid. The upper limit of concentrations claimed for the above listed color inhibitors ranges from 0.1% for phosphoric acid to 5% for abietylamine derivatives.
An advantage of this invention is stabilization of color and inhibition of color development of monoalkyl phenols. A further advantage of this invention is reduction of color of monoalkyl phenols in which color development has taken place. It is still further an advantage of this invention that adequate color stability, inhibition, and reduction are accomplished with an additive used at lower concentrations than prior art additives. Further advantages will become apparent from the discussion and examples.