Dicarboxylic acid, hydrotropic

Aqueous Solution Properties of a Fatty Dicarboxylic Acid Hydrotrope... 

The hydrotropic action of a dicarboxylic acid is discussed against the general features of hydro-tropic action the liquid crystal/isotropic solution equilibrium. It is shown that the hydrotropic action of the dicarboxylic acid in question, 8-[5(6)-carboxy-4-hexyl-cyclohex-2-enyl] octanoic acid, depends on its conformation at an interface. 

During the 1970 s, a new kind of hydrotrope was introduced, WESTVACO DIACID (9), (Fig. 2). It is a dicarboxylic acid with a total of twenty-one carbon atoms. Its basic properties have been investigated by Matijevic and collaborators (10), who determined its cmc and the association constants for the diacid in water. 

This new hydrotrope posed an intriguing problem the explanation of the hydrotropic action of such a long chain dicarboxylic acid. The problem was solved in a series of articles (11-14) which contain the essential experimental information for this article. These articles each provided a part of the total framework of the problem and we considered a unified treatment essential in order to present a systematic pattern for the different aspects Involved. 

FRIBERG AND FLAlM Hydrotropic Function of a Dicarboxylic Acid 109... 

The results are straight forward and the interpretation immediately evident. The liquid crystalline phase formed in these extremely water rich systems was destabilized by the dicarboxylic acid and transformed to an isotropic solution. The conclusion that the hydrotropic action of the dicarboxylic acid is intimately related to its capacity to destabilize a liquid crystalline phase also under the water-rich conditions during actual laundering conditions appears well justified. 

The evaluation of the conformation of the diacid monosoap from these results is unambiguous. Both the polar groups of the raonosoap are located at the water surface, giving a conformation such as the one in Fig. 6. This conformation readily provides an explanation for the hydrotropic action of the dicarboxylic acid. When acting at an interface, the molecule does not posess the extended conformation of Fig. 2 its conformation is as shown in Fig, 6. Hence, the destabilizing action may be intuitively understood in the same manner as for the traditional aromatic hydrotrope, Fig. 1. 

In recent studies, Friberg and co-workers (J, 2) showed that the 21 carbon dicarboxylic acid 5(6)-carboxyl-4-hexyl-2-cyclohexene-1-yl octanoic acid (C21-DA, see Figure 1) exhibited hydrotropic or solubilizing properties in the multicomponent system(s) sodium octanoate (decanoate)/n-octanol/C2i-DA aqueous disodium salt solutions. Hydrotropic action was observed in dilute solutions even at concentrations below the critical micelle concentration (CMC) of the alkanoate. Such action was also observed in concentrates containing pure nonionic and anionic surfactants and C21-DA salt. The function of the hydrotrope was to retard formation of a more ordered structure or mesophase (liquid crystalline phase). 

In addition to the progress in the area of traditional hydrotropes [90,91] one finds two treatments [92,93] on the action of a nontraditional hydrotrope structure in cleaning and laundry systems. Instead of the short and bulky molecule (Figure 2.8), this compound [94] is a dicarboxylic acid of considerable chain length (Figure 2.9). 

Ciassification Organic dicarboxylic acid Properties Anionic Toxicoiogy TSCA listed Uses Vise, control agent in cosmetics intermediate for soaps, esters, polyamide derive. surfactant coupling agent hydrotrope esp. in caustic systems hydrotrope, solubilizer for household, industrial, metalworking, textile, and institutional compounding... 

Chem. Descrip. Alkenyl dicarboxylic acid anhydride Uses Solubilizer, hydrotrope for laundry, hard surf., and l l cleaners Features Exc. solubilizer for fomiulations with nonionic surfactants and high electrolyte content Properties Liq. 100% act. 

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