Dimer acids

Acidity is determined by glc or titration, and the dimer content of acryhc acid by glc or a saponification procedure. The total acidity is corrected for the dimer acid content to give the value for acryhc acid. 

Dimer acids are relatively high mol wt (ca 560) and yet are Hquid at 25°C. This Hquidity is a consequence of the many isomers present, most with branching or cycHc stmctures. 

The dimer acids [61788-89-4] 9- and 10-carboxystearic acids, and C-21 dicarboxylic acids are products resulting from three different reactions of C-18 unsaturated fatty acids. These reactions are, respectively, self-condensation, reaction with carbon monoxide followed by oxidation of the resulting 9- or 10-formylstearic acid (or, alternatively, by hydrocarboxylation of the unsaturated fatty acid), and Diels-Alder reaction with acryUc acid. The starting materials for these reactions have been almost exclusively tall oil fatty acids or, to a lesser degree, oleic acid, although other unsaturated fatty acid feedstocks can be used (see Carboxylic acids. Fatty acids from tall oil Tall oil). 

Table 4. Dimer Acid Feedstock—Structure Relationship

Empol series of dimer acids, Henkel Corp., Emery Group (oleic-based, thus of lower viscosity). Hystrene series of dimer acids, Humko Chemical Div. of Witco Corporation. 

Hystrene series of dimer acids, Humko Chemical Division of Witco Corporation.  

C-21 dicarboxylic acids from piCARBOXYLIC ACIDS] (Vol 8) -dimer acids from piMER ACIDS] (Vol 8) 

Table 5. Nonpolymeric Chemical Reactions of Dimer Acids

The foUowiag are three possible stmctures of the methyl esters of dimer acids. 

In 1991, ia addition to Henkel (now including Emery), commercial producers of dimer acids ia the U.S. were Arizona Chemical, Schering Berlin, Humko Chemical Division of Witco, and Union Camp Corporation. There are other producers throughout the world. 

Most of the products Hsted in Tables 1—3 are based on manufacture from tall oil fatty acids. Dimer acids based on other feedstocks (eg, oleic acid) may have different properties. A European manufacturer recently announced availabiUty of a 44-carbon dimer acid, presumably made from an emcic acid feedstock (7). 

A scan of the literature over the years 1980—1991 shows that most of the current dimer activity iavolves the reaction of dimer acids to form a huge variety of polyamide and polyester stmctures to modify their properties for a wide range of iadustries and uses. Many of these property modifications seem to make use of the flexihili ing properties or adhesion-promoting properties of the dimer stmcture. 

The clay-cataly2ed iatermolecular condensation of oleic and/or linoleic acid mixtures on a commercial scale produces approximately a 60 40 mixture of dimer acids and higher polycarboxyUc acids) and monomer acids (C g isomerized fatty acids). The polycarboxyUc acid and monomer fractions are usually separated by wiped-film evaporation. The monomer fraction, after hydrogenation, can be fed to a solvent separative process that produces commercial isostearic acid, a complex mixture of saturated fatty acids that is Hquid at 10°C. Dimer acids can be further separated, also by wiped-film evaporation, iato distilled dimer acids and trimer acids. A review of dimerization gives a comprehensive discussion of the subject (10). 

The basic research that led to these products was done at the Northern Regional Research Center of the USD A dimer acids research in the 1940s (1—3), C-21 dicarboxyhc acid work in 1957 (4), and carboxystearic acid synthetic studies (5,6) in the 1970s (see Dicarboxylic acids). 

The mixed oxidation products are fed to a stiU where the pelargonic and other low boiling acids are removed as overhead while the heavy material, esters and dimer acids, are removed as residue. The side-stream contains predominately azelaic acid along with minor amounts of other dibasic acids and palmitic and stearic acids. The side-stream is then washed with hot water that dissolves the azelaic acid, and separation can then be made from the water-insoluble acids, palmitic and stearic acids. Water is removed from the aqueous solution by evaporators or through crystallization (44,45). 

The diacids are characterized by two carboxyHc acid groups attached to a linear or branched hydrocarbon chain. AUphatic, linear dicarboxyhc acids of the general formula HOOC(CH2) COOH, and branched dicarboxyhc acids are the subject of this article. The more common aUphatic diacids (oxaUc, malonic, succinic, and adipic) as weU as the common unsaturated diacids (maleic acid, fumaric acid), the dimer acids (qv), and the aromatic diacids (phthaUc acids) are not discussed here (see Adipic acid Maleic anhydride, maleic acid, and fumaric acid Malonic acid and derivatives Oxalic acid Phthalic acid and OTHERBENZENE-POLYCARBOXYLIC ACIDS SucciNic ACID AND SUCCINIC ANHYDRIDE). The bihinctionahty of the diacids makes them versatile materials, ideally suited for a variety of condensation polymerization reactions. Several diacids are commercially important chemicals that are produced in multimillion kg quantities and find appHcation in a myriad of uses. 

Nonfood Uses. Vegetable oils are utilized in a variety of nonedible applications, but only a few percent of the U.S. soybean oil production is used for such products (see Table 13). Soybean oil is converted into alkyd resins (qv) for protective coatings, plasticizers, dimer acids, surfactants (qv), printing inks, SoyDiesel fuel (methyl esters used to replace petroleum-based diesel fuel) and other products (76). 

The two-part epoxy adhesive, readily available in hardware stores or other consumer outlets, comes in two tubes. One tube contains the epoxy resin, the other contains an amine hardener. Common diamine room temperature epoxy curing agents are materials such as the polyamides, available under the trade name Versamid. These polyamides are the reaction products of dimer acids and aUphatic diamines such as diethylenetriamine [111-40-0]  

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