Carboxylic Acids

Abstract

Abstract Carboxylic acids from formic (C‐1) to the 22‐carbon fatty acids and selected examples of higher carbon number (C‐30) are reviewed. Available physical properties are tabulated for normal saturated and selected unsaturated and substituted aliphatic acids. The physical properties as well as chemical properties are discussed briefly. Fatty acids are produced primarily from natural fats and oils such as tallow, coconut oil, and palm oil. Tall oil fatty acids are produced by the distillation of crude tall oil. Synthetic routes to fatty acids from petroleum are an important source and include catalytic oxidation of straight‐chain hydrocarbons; carboxylation and oxidation of straight‐chain 1‐olefins; and oxidation of alcohols. Branched‐chain acids are produced from branched‐chain olefins via the oxo reaction. Fatty acids are produced from natural fats and oils in essentially four steps or unit operations. Hydrolysis, the first step, is generally carried out by high temperature/pressure splitting. Glycerol is obtained as a by‐product. Second, solid or saturated fatty acids are separated from liquid or unsaturated fatty acids by solvent crystallization or by the hydrophilization process. Several newer methods of separation include adsorption and supercritical fluid extraction. The third step is hydrogenation, which converts unsaturated fatty acids into saturated fatty acids generally with the aid of a nickel catalyst. Finally, distillation is used to remove color and odor bodies and, when desired, to separate fatty acids into relatively pure materials such as lauric, myristic, palmitic, and stearic acids. Aliphatic carboxylic acids produced on a reasonably significant commercial scale range from acetic acid (two carbons or C2) through stearic acid (C18). Lesser amounts of commercially available shorter chain‐length acids such as formic (C1), and longer chain‐length acids, such as erucic (unsaturated C22) and behenic (saturated C22), are also produced. For both oleo‐based and nonoleo‐based acids production and consumption figures, prices, producers, and applications are given. Applications include coatings, chemical intermediates, soaps, detergents, ore flotation, lubricants, and adhesives. The trialkylacetic acids, carboxylic acids with three alkyl groups on the alpha‐carbon, have been manufactured in the United States and Europe since the early 1960s. The principal commercial products are the C 5 acid and the C 10 acid, although smaller quantities of other carbon number acids are also produced. The C 5 acid, 2,2‐dimethylpropionic acid, also referred to as neopentanoic acid and as pivalic acid, is a solid at room temperature and undergoes reactions typical of carboxylic acids, such as formation of the acid chloride, esterification, reduction. Because of steric hindrance of the carbonyl group, reactions often proceed less readily than with straight chain acids, but once formed derivatives of neopentanoic acid are typically more resistant to hydrolysis and oxidation. Neopentanoic acid is manufactured using variants of the Koch reaction, in which a strong acid catalyst is used in the reaction of olefin, carbon monoxide and water. Neopentanoic acid finds numerous uses in the production of polymers and resins, pharmaceuticals, agricultural chemicals, cosmetics, fuels, lubricants and transmission fluids. The C 10 trialkylacetic acid, also known as neodecanoic acid and as Versatic 10, is a mixture of isomers, resulting in a material that is a liquid at room temperature. This acid undergoes the same reactions as neopentanoic acid, such as acid chloride formation and esterification. In addition, neodecanoic acid finds a large commercial use in the preparation of metal salts. The manufacturing process is the same as that used for neopentanoic acid. Neodecanoic acid is used in a number of applications, including polymers, resins and coatings, adhesion promoters, metal‐working fluids, hydraulic fluids, metal‐extraction, fuels, lubricants, and electrical/electronic applications. Significant derivatives of neoacids include the glycidyl and vinyl esters. The glycidyl esters are used as intermediates for the production of alkyds and acrylics, and as a reactive diluent for epoxy resins. The vinyl esters are used primarily in coatings, but also in construction, adhesives, cosmetics, and in a number of miscellaneous areas.