326 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS hydroxystearic acid with one mole of ethylene oxide and no catalyst were very similar to those of the ethoxylation of castor oil with a catalyst: Catalyst Initial acid value Final acid value Rxn time (hr) No KOH 164.2 69.2 1.5 Determined by Carboxyl ethoxylation 57.8 Acid value Hydroxyl ethoxylation 29.0 C 13 NMR PEGs 13.2 Extract ETHOXYLATION OF BLENDS In an attempt to determine if there was some catalytic effect of having both a hydroxyl and carboxyl group present in the reaction mass, we attempted to ethoxylate a blend of octadecanol and stearic acid. As anticipated, no reaction occurred without a catalyst. When no catalyst was added to the blend of octadecanol and stearic acid, the reaction rate for the blend was essentially zero. When 0.1% KOH catalyst was added to the blend of octadecanol and stearic acid, the reaction rate for the blend approximated the average of the rates of each component. These results would indicate that the mere presence of both the carboxyl and hydroxyl group in the solution was not the reason for the ethoxylation of 12-hydroxystearic acid without a catalyst. We speculated that both functionalities need to be present in the same molecule and perhaps in a specific location. The question was partly addressed by the ethoxylation of lactic acid. ETHOXYLATION OF LACTIC ACID We investigated the ethoxylation of lactic acid without a catalyst. Lactic acid is beta hydroxy propionic acid. We found that the ethoxylation does in fact occur without a catalyst and has the same kinetics as the ethoxylation of hydroxystearic acid. However, lactic acid ethoxylation without a catalyst occurs almost exclusively at the carboxyl group: Catalyst Initial acid value Final acid value Rxn time (hr) No KOH 623.4 7.0 1.5 Determined by Carboxyl ethoxylation 98.8 Acid value Hydroxyl ethoxylation 0.1 C 13 NMR PEGs 1.1 Extract While the ethoxylation of lactic acid could not answer the question of the importance of the relative position of the groups to each other, because we now only have two data points, the data does clearly show that (a) the catalyst-free ethoxylation is not limited
ETHOXYLATION OF HYDROXY ACIDS 327 to 12-hydroxystearic acid and (b) the group selectivity of the ethoxylation reaction of lactic acid differs considerably from the group selectivity of ethoxylation of 12- hydroxystearic acid. ETHOXYLATION RATES Table III outlines the amount of ethylene oxide added to various hydroxy-containing compounds. It shows that stearic acid, because of the anticipated induction period, ethoxylates significantly more slowly than the alcohols evaluated. Stearyl alcohol, castor oil, and 12-hydroxystearic acid all exhibit about the same rate of ethoxylation. No- nylphenol, which has a more acidic hydroxyl group than a primary or secondary alcohol, ethoxylates most rapidly. Table III shows the amount of ethylene oxide added to various hydrophobes using 0.1% KOH catalyst. Stearyl alcohol has added 4.2 moles of ethylene oxide in two hours, while nonylphenol has added 9.5 moles in the same time. CONCLUSIONS We have found that the ethoxylation of 12-hydroxystearic acid and lactic acid are unusual in several respects: 1. Unlike typical fatty acids or alcohols, 12-hydroxystearic acid and lactic acid both ethoxylate without a catalyst. This could be explained by the presence of both a hydroxyl and a carboxyl in the reaction solution or the presence of both groups in the same molecule. The attempt to ethoxylate a blend of fatty acid and fatty alcohol without a catalyst did not succeed. Consequently, it appears that the two groups need to be present in the same molecule. We suggest that some type of complex forms between the oxide and the carboxyl and hydroxyl groups. We would also predict that the location of the hydroxyl group relative to the carboxyl group is important, but we do not have the needed data to prove that at this time. 2. There is a high degree of group selectivity to the ethoxylation of 12-hydroxystearic acid and lactic acid. The carboxyl group ethoxylates almost exclusively under base catalyst. When no catalyst is used, 33% of the added oxide goes to the hydroxyl group and 67% to the carboxyl group when one mole of oxide is added to 12-hydroxystearic Table III Moles of Ethylene Oxide Added Versus Time at Reaction Conditions 0.1 KOH 12-hydroxy Time (hrs) Nonyl phenol Stearyl alcohol Castor oil stearic acid Stearic acid 0 0 0 0 0 0 1.0 4.9 1.1 1.4 1.0 0.5 1.5 7.5 2.5 3.3 2.2 0.6 2.0 9.5 4.2 6.1 4.3 0.8 2.5 11.1 7.0 8.2 6.8 3.0
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ETHOXYLATION OF HYDROXY ACIDS 325 Our analysis of the above reaction using one mole of ethylene oxide with one mole equivalent of hydrogenated castor oil, using 0.1% KOH as catalyst, gave the following results: Ester reaction 58% Hydroxyl group 29% Polyethylene glycol 13% 12-HYDROXYSTEARIC ACID ETHOXYLATION 12-hydroxystearic acid is prepared by the saponification and purification of hydroge- nated castor oil. Bullen (12) studied the ethoxylation of 12-hydroxystearic acid using base catalyst. His conclusions were that "it appears that the condensation product of ethylene oxide with 12-hydroxystearic acid is not affected by the type of catalyst used in its preparation and the polyethenoxy-12-hydroxystearate so obtained by using KOH, under base catalysis all the oxide was added to the carboxyl group" (6). Our base catalyzed ethoxylation of 12-hydroxystearic acid resulted in the confirmation of the Bullen results: Initial Final Rxn time Final Catalyst acid value acid value (hr) OH value % Diester 0.2 KOH 164.2 0.5 1.5 247.2 25.1 0.1 KOH 164.2 0.1 1.1 244.1 24.0 The ethoxylation of one mole of hydroxystearic acid with one mole of ethylene oxide using 0.1% KOH as a catalyst resulted in 99% of the ethylene oxide reacting at the carboxyl group, with essentially no reaction at the hydroxyl group and about 1% polyethylene glycol. The major surprise, based upon the observations of Bullen, was that the induction period normally anticipated with the ethoxylation of a fatty acid was totally absent. The rate of ethoxylation was almost identical to that of a fatty alcohol, and very dissimilar to that of a fatty acid. The distribution of products and the group selectivity were as anticipated by Bullen. As a control, one mole equivalent of stearic acid was ethoxylated with one mole equiv- alent of ethylene oxide: Initial Final Rxn time Final Catalyst acid value acid value (hr) OH value % Diester 0.2 KOH 172.2 4.06 1.25 137.3 19.9 These results matched well with the results of Wrigley (7). CATALYSTS Realizing that neither fatty alcohols nor fatty acids ethoxylate without a catalyst, we tried to ethoxylate 12-hydroxystearic acid without a catalyst. To our surprise, the material ethoxylated without an induction period. The rate was comparable to the rate of ethoxylation of the base-catalyzed fatty alcohol ethoxylation. The product types that resulted after the ethoxylation of one mole equivalent of 12-
326 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS hydroxystearic acid with one mole of ethylene oxide and no catalyst were very similar to those of the ethoxylation of castor oil with a catalyst: Catalyst Initial acid value Final acid value Rxn time (hr) No KOH 164.2 69.2 1.5 Determined by Carboxyl ethoxylation 57.8 Acid value Hydroxyl ethoxylation 29.0 C 13 NMR PEGs 13.2 Extract ETHOXYLATION OF BLENDS In an attempt to determine if there was some catalytic effect of having both a hydroxyl and carboxyl group present in the reaction mass, we attempted to ethoxylate a blend of octadecanol and stearic acid. As anticipated, no reaction occurred without a catalyst. When no catalyst was added to the blend of octadecanol and stearic acid, the reaction rate for the blend was essentially zero. When 0.1% KOH catalyst was added to the blend of octadecanol and stearic acid, the reaction rate for the blend approximated the average of the rates of each component. These results would indicate that the mere presence of both the carboxyl and hydroxyl group in the solution was not the reason for the ethoxylation of 12-hydroxystearic acid without a catalyst. We speculated that both functionalities need to be present in the same molecule and perhaps in a specific location. The question was partly addressed by the ethoxylation of lactic acid. ETHOXYLATION OF LACTIC ACID We investigated the ethoxylation of lactic acid without a catalyst. Lactic acid is beta hydroxy propionic acid. We found that the ethoxylation does in fact occur without a catalyst and has the same kinetics as the ethoxylation of hydroxystearic acid. However, lactic acid ethoxylation without a catalyst occurs almost exclusively at the carboxyl group: Catalyst Initial acid value Final acid value Rxn time (hr) No KOH 623.4 7.0 1.5 Determined by Carboxyl ethoxylation 98.8 Acid value Hydroxyl ethoxylation 0.1 C 13 NMR PEGs 1.1 Extract While the ethoxylation of lactic acid could not answer the question of the importance of the relative position of the groups to each other, because we now only have two data points, the data does clearly show that (a) the catalyst-free ethoxylation is not limited

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