CHAPTER NINETEEN Carboxylic Acids The metal carboxylate salts formed on neutralization of carboxylic acids are named by first specifying the metal ion and then adding the name of the acid modified by replac ing -ic acid by -ate. Monocarboxylate salts of diacids are designated by naming both the cation and hydrogen as substituents of carboxylate groups CHaCOLI CI CONa HOC(CH,)4COK Lithium Sodium p-chlorobenzoate Potassium hydrogen hexanedioate Metal carboxylates are ionic, and when the molecular weight isn' t too high, the sodium and potassium salts of carboxylic acids are soluble in water. Carboxylic acids therefore may be extracted from ether solutions into aqueous sodium or potassium hydroxide. The solubility behavior of salts of carboxylic acids having 12-18 carbons is unusual and can be illustrated by considering sodium stearate Sodium stearate ( sodium octadecanoate) Sodium stearate has a polar carboxylate group at one end of a long hydrocarbon chain The carboxylate group is hydrophilic ("water-loving") and tends to confer water solu bility on the molecule. The hydrocarbon chain is lipophilic("fat-loving")and tends to associate with other hydrocarbon chains. The compromise achieved by sodium stearate when it is placed in water is to form a colloidal dispersion of spherical aggregates called micelles. Each micelle is composed of 50-100 individual molecules. Micelles form spon taneously when the carboxylate concentration exceeds a certain minimum value called the critical micelle concentration. A representation of a micelle is shown in Figure 19 Polar carboxylate groups dot the surface of the micelle. There they bind to water molecules and to sodium ions. The nonpolar hydrocarbon chains are directed toward the interior of the micelle, where individually weak but cumulatively significant induced dipole/induced-dipole forces bind them together. Micelles are approximately spherical because a sphere encloses the maximum volume of material for a given surface area and FIGURE 19.5 A space filling model of a micelle formed by association of cal fatty acid. In general, the re inside and the carboxy- late ions on the surface bu contains voids tangled carbon with a metal ion such as Na Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteThe metal carboxylate salts formed on neutralization of carboxylic acids are named by first specifying the metal ion and then adding the name of the acid modified by replac￾ing -ic acid by -ate. Monocarboxylate salts of diacids are designated by naming both the cation and hydrogen as substituents of carboxylate groups. Metal carboxylates are ionic, and when the molecular weight isn’t too high, the sodium and potassium salts of carboxylic acids are soluble in water. Carboxylic acids therefore may be extracted from ether solutions into aqueous sodium or potassium hydroxide. The solubility behavior of salts of carboxylic acids having 12–18 carbons is unusual and can be illustrated by considering sodium stearate: Sodium stearate has a polar carboxylate group at one end of a long hydrocarbon chain. The carboxylate group is hydrophilic (“water-loving”) and tends to confer water solu￾bility on the molecule. The hydrocarbon chain is lipophilic (“fat-loving”) and tends to associate with other hydrocarbon chains. The compromise achieved by sodium stearate when it is placed in water is to form a colloidal dispersion of spherical aggregates called micelles. Each micelle is composed of 50–100 individual molecules. Micelles form spon￾taneously when the carboxylate concentration exceeds a certain minimum value called the critical micelle concentration. A representation of a micelle is shown in Figure 19.5. Polar carboxylate groups dot the surface of the micelle. There they bind to water molecules and to sodium ions. The nonpolar hydrocarbon chains are directed toward the interior of the micelle, where individually weak but cumulatively significant induced￾dipole/induced-dipole forces bind them together. Micelles are approximately spherical because a sphere encloses the maximum volume of material for a given surface area and O Na O Sodium stearate (sodium octadecanoate) CH3COLi O Lithium acetate Cl CONa O Sodium p-chlorobenzoate HOC(CH2)4COK O O Potassium hydrogen hexanedioate 744 CHAPTER NINETEEN Carboxylic Acids FIGURE 19.5 A space- filling model of a micelle formed by association of car￾boxylate ions derived from a fatty acid. In general, the hydrophobic carbon chains are inside and the carboxy￾late ions on the surface, but the micelle is irregular, and contains voids, channels, and tangled carbon chains. Each carboxylate is associated with a metal ion such as Na (not shown). Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website