Polyfunctional Carboxylic Acids

DICARBOXYUC ACIDS, HOOC(CHj) COOH CYCLIC ANHYDRIDES 

The chemistry of dicarboxylic acids depends on the value of n. See Problem 16.18 for decarboxylations of oxalic acid (n =0) and malonic acid (n = 1). When n = 2 or 3, the diacid forms cyclic anhydrides when heated. When n exceeds 3, acyclic anhydrides, often polymers, are formed. 

Problem 16.22 Compare the products formed on heating the following dicarboxylic acids (a) succinic acid, (b) glutaric acid (1,5-p entanedioic acid), (c) longer-chain HOOClCH l COOH. A 

Problem 16.23 Show steps in the following syntheses, using any needed inorganic reagents  

Reactions of hydroxycarboxylic acids, HO(CHj) COOH, also depend on value of n. In acid solutions, y-hydroxycarboxylic acid (n = 3) and 8-hydroxycarboxylic acid (n = 4) form cyclic esters (lactones) with, respectively, five-membered and six-membered rings. 

DICARBOXYLIC ACIDS, HOOC(CH2) COOH CYCLIC ANHYDRIDES 

---

Examples of polyfunctional carboxylic acids esterified by this method are shown in Table I. Yields are uniformly high, with the exception of those cases (maleic and fumaric acids) where some of the product appears to be lost during work-up as a result of water solubility. Even with carboxylic acids containing a second functional group (e.g., amide, nitrile) which can readily react with the oxonium salt, the more nucleophilic carboxylate anion is preferentially alkylated. The examples described in detail above illustrate the esterification of an acid containing a labile acetoxy group, which would not survive other procedures such as the traditional Fischer esterification. 

The polyaddition reaction is the most commonly used type of reaction for the cure of epoxy resins. The curing agents used in this type of reaction have an active hydrogen compound, and they include amines, amides, and mercaptans. With this reaction mechanism, the most important curing agents for adhesives are primary and secondary amines containing at least three active hydrogen atoms and various di- or polyfunctional carboxylic acids and their anhydrides. 

One of the first non-formaldehyde fluorescent dye carrier systems for polyolefins was based on the reaction of polyfunctional amines with polyfunctional carboxylic acids to form relatively short chain polyamides [5].These linear thermoplastic resins showed good solubility and friability making them suitable for the incorporation of dyes, which offered increased protection from thermal and UV degradation. This fluorescent resin showed a dramatic increase in color retention upwards of 288°C, even after a 10 minute hold period at this temperature. Due to its non-ide-alized polymeric nature, the polyamide chemistry suffered from preferential plating out or migration of polar oligomeric species not incorporated into the polymer chains. 

The polyester type polyols used in polyurethane laminating adhesives are produced by the direct esterification of polyfunctional carboxylic acids and glycols. Polyester polyols provide the soft segment in polyurethane products giving the adhesive flexibility. Ester groups of the polyol also contribute to adhesion. Polyester polyols provide limited wetting and adhesion of olefinic surfaces with amide slip additives (in contrast to polyether polyols). Typical examples include adipic acid, caprolactone, maleic acid and isophthalic based polyester polyols. 

Some of dicarboxylic acids can also be distilled, without decomposition, under reduced pressures. This is at least a theoretical ground for the possibility of their direct GC analysis. Few successful attempts have been described, but these analytes require on-column injection of samples and extremely high inertness of chromatographic systems. Many types of polyfunctional carboxylic acids (hydroxy-, mercapto-, amino-, etc.) cannot be analyzed in free, underivatized form, owing to either non volatility and/or absence of thermal stability. These features are the principal reasons for the conversion of carboxylic adds, before their GC analysis, into less polar derivatives without active hydrogen atoms. 

Coma, V Sebti, L Pardon, R Pichavant, F.H. Deschamps, A. Film properties from crosslinking of ceUulosic derivatives with a polyfunctional carboxylic acid. Carbohydr. Polym. 2003, 51 (3), 265-271. 

Some of the most widely used reagents for the esterification of acids are fisted in Table 2. The general method for the silylation of mono- and polyfunctional carboxylic acids by forming for trimethylsilyl (TMS) or the more stable tert-butyldimethylsilyl (TBDMS) derivatives is similar to that for the silylation of other hydroxy-containing compounds (see Hydroxy Compounds Derivatimtion for GC Analysis, p. 1165). 

Numerous derivatives of polyfunctional carboxylic acids important for analytical practice are characterized by GC RIs and mass spectra. As an example of this information, the data for 3 compounds from 136 known natural gibbereUins are presented in Table 3. Commonly accepted... 

So, maleic anhydride Diels-Alder addition products to (conjugated) linoleic acid (CLA, Figure 3B.16, a.) may be prepared both with and without catalytical amounts of iodine, clay, or silica at a reaction temperature generally from about 100°C to about 230 °C. Similarly, the Diels-Alder addition of acrylic acid yields a C21-diacid (Figure 3B.16, b.). Under somewhat more vigorous conditions, the monounsaturated oleic/elaidic acids react with maleic anhydride at 215 °C to about 250 °C to form an ene-adduct (Figure 3B.16, c.). Diels-Alder and ene reaction products ofTOFA form polyfunctional carboxylic acids that can further be sulfonated by reaction with sulfuric acid and/or can undergo esterification or amidation reactions. - ... 

Polyfunctional aziridines are used as cross-linkers. Polyaziridines are skin irritants, and some individuals may become sensitized. Mutagenicity of polyaziridines is controversial however, dilution by coating vehicles reduces their possible toxic effects (195). Polyaziridines, such as the addition product of 3 mol of aziridine to 1 mol of trimethylolpropane triacrylate, react with polyfunctional carboxylic acids to form 2-aminoester cross-links. The main uses are to cross-hnk carboxylic acid groups on latexes and waterborne polyurethanes. Reaction with the carboxylic acid is much faster than the reaction of the aziridine groups with water, pot lives are 48-72 h. Additional cross-linker can be added to restore reactivity. 

Anhydrides of polyfunctional carboxylic acids, as well as the acids themselves, have been reported to improve the thermal resistance as well as impact toughness of cyanoacrylate adhesives.Bond hot strengths are improved substantially, even though the thermal decomposition temperatures of the polymer remain unchanged. 

Triorganotin carboxylates derived from polyfunctional carboxylic acids are compiled in this subsection. Functional groups comprise any combination of nitrogen, phosphorus, oxygen and halogen. The compounds listed in Table 206 are prepared by methods from the following scheme. 

Table 206. Unsubstituted Triorganotin Derivatives of Polyfunctional Carboxylic Acids R3 Sn02CR ...

---