Carboxylic acids and anhydrides

Cyclic anhydrides of carboxylic acid are also used as cross-linkers for epoxy resins. Curing is initiated by reaction of a hydroxyl with an anhydride to yield a half ester and a carboxylic acid group. The newly formed carboxylic acid will in turn react with the epoxy to generate an ester and a new hydroxyl group. These complementary reactions result in a cross-linked network. Etherification reactions 

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Epoxy plastics Group of plastics composed of resins produced by reactions of epoxides or oxiranes with compounds such as amines, phenols, alcohols, carboxylic acids, and anhydrides, and unsaturated compounds. 

During electrochemical fluorination retention of important functional groups or atoms in molecules is essential. Acyl fluorides and chlorides, but not carboxylic acids and anhydrides (which decarboxylate), survive perfluorination to the perfluorinated acid fluorides, albeit with some cyclization in longer chain (>C4) species [73]. Electrochemical fluorination of acetyl fluoride produces perfluoro-acetyl fluoride in 36-45% yields [85]. Electrochemical fluorination of octanoyl chloride results in perfluorinated cyclic ethers as well as perfluorinated octanoyl fluonde. Cyclization decreases as initial substrate concentration increases and has been linked to hydrogen-bonded onium polycations [73]. Cyclization is a common phenomenon involving longer (>C4) and branched chains. a-Alkyl-substituted carboxylic acid chlorides, fluorides, and methyl esters produce both the perfluorinated cyclic five- and six-membered ring ethers as well as the perfluorinated acid... 

G.A. Olah, M. Nojima, I. Kerekes, Synthetic methods and reactions. I. Seleniuum tetrafluoride and its pyridine complex. Convenient fluorinating agents for fluorination of ketones, aldehydes, amides, alcohols, carboxylic acids, and anhydrides, J. Am. Chem. Soc. 96 (1974) 925-927. 

Compared to ozonation of alkenes, much less is known about the ozonation of alkynes,710 which yields 1,2-dicarbonyl compounds, carboxylic acids, and anhydrides. 1,2,3-Trioxolene (91), analogous to 74 in alkene ozonation mechanism (Scheme 9.14), and zwitterionic intermediates (92) were formulated on the basis of IR studies and trapping experiments ... 

Subsequently, it was shown that the reaction was catalyzed by base (48M(79)106). Dicyandiamide reacts with nitriles (the most valuable method), amidines, cyanamides, ammonia, cyanates, thiocyanates, carboxylic acids and anhydrides to yield 1,3,5-triazines (Table 13). This synthetic route has been reviewed thoroughly several times (59HC(13)1, p. 219,61MI22000, p. 650, 73ZC408). The base-catalyzed reaction of dicyandiamide with alkyl or aryl nitriles (Scheme 65) proceeds via the imino ether anion and the rate determining step is solvent dependent. In DMSO the formation of the imino ether is rate determining, but in 2-methoxyethanol the reaction between the anion and dicyandiamide controls the rate (66T157). 

The reactions of carboxylic acids and anhydrides with epoxy resins have been extensively studied in a variety of investigations, particularly References 27—31. The general reaction of epoxide resins and anhydrides is... 

Tin(IV) oxide is used in various heterogeneous catalyst mixtures, e.g. Sn02/V20s for oxidation of arenes to carboxylic acids and anhydrides, and Sn02/Sb20s for selective oxidation and ammoxidation of propylene to acrolein, acrylic acid, and acrylonitrile. 

This reagent also reduces nitro, nitrile, and amide derivatives to amines, and carboxylic acids and anhydrides to alcohols. The yields of these reductions arc nearly quantitative. Esters and halobenzene derivatives are not reduced. 

Miller, R. S., Curtin, D. Y., and Paul, I. C. Reactions of molecular crystals with gases. III. The relationship of anisotropy to crystal structure in reactions of carboxylic acids and anhydrides with ammonia gas. J. Amer. Chem. Soc. 96, 6340-6349 (1974). 

Triphenylphosphine dibromide reacts with carboxylic acids and anhydrides to give acid bromides. "... 

Pudovik, A.N., and Konovalova, I.V., Reaction of chlorides of carboxylic acids and anhydrides of carboxylic acids with diethyl sodiophosphonate, Zh. Obshch. Khim., 33, 98, 1963 Chem. Abstr, 59, 656a, 1963. 

IA and O-substituted hydroxylamines (131) give anthranilic acid hydrox-ylamides (132)96 (hydroxylamine itself forms the O-acyl derivative95). Carboxylic acids and anhydrides cyclize 132 to the quinazolones 13396 (Eq. 14). 

Acylations with carboxylic acids and anhydrides have been carried out with sulfuric acid as both solvent and catalyst, the reactive acylating agents from acyl halides probably being haloacyloxonium ions. Trifluoroacetic anhydride offers a rather milder reagent for reactions of carboxylic acids, with mixed anhydrides being likely intermediates. However, polyphosphoric acid remains the most widely used dehydrating agent for acylations by carboxylic acids. 

Carboxylic acid and anhydride curing agents are used to a lesser extent in aerospace applications as compared to the amines which have mechanical properties and cure conditions that can be tailored to a wider variety of specific applications. Anhydrides tend to be somewhat brittle but offer useful service as high as 250 °C with novolac-type epoxy resins. In addition, the aliphatic dicarboxylic acid anhydrides give tough and sometimes flexible properties which are useful in encapsulation applications. 

The major classes of carbonyl compounds include aldehydes, ketones, carboxamides, esters, carboxylic acids and anhydrides, and carbonyl halides (acyl halides). These groups differ in the identity of the substituent X on the carbonyl group. At this point we concentrate on these examples, but a number of other carbonyl derivatives have important roles in synthetic and/or biological reactions. These other compounds include acyl cyanides, acyl azides, A-acylimidazoles, 0-aryl esters, and thioesters. The carbonyl compounds are arranged below in the order of the increasing reactivity toward nucleophilic addition. 

Among the carboxylic acid and anhydride functional monomers that have been employed in the synthesis of these thickener polymers are acrylic acid, methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, crotonic acid, maleic anhydride, and citraconic anhydride. The copolymers containing maleic and citraconic anhydride monomers are either hydrolyzed or partially esterified to obtain the required carboxyl functionality. Among these carboxylic monomers, maleic anhydride and particularly methacrylic acid are most frequently favored. Carboxylic homopolymers, where they can be formed, might be considered the simplest examples of ASTs were it not for the fact that they are not copolymers as defined, and some are water soluble in their un-ionized states. Examples of carboxylic homopolymers are the un-ionized free-radical-polymerized atactic forms of polyacrylic acid (i) and polymethacrylic acid (2), which are both readily soluble in water. 

The photooxidation of a nonwoven PE fabric showed hydroperoxide, alcohol, aldehyde, ketone, carboxylic acid, and anhydride groups were formed as the products of the photooxidation of the PE fabric and the relative amount of carboxyl increased as the photooxidation progressed. Distribution of the photooxidation products was inhomogeneous between the two surfaces of the fabric. The UV radiation at 254 nm caused photooxidation of PE. No photooxidation was observed in the fabric exposed to the UV radiation at 350 nm under the same conditions (288). 

Heteroatoms are important because of an inordinate contribution to properties. Large increases in asphalt hardening occur with the uptake of only 1 wt% oxygen. Petersen (64,65) has done extensive work on heteroatom analysis. A typical analysis is shown in Table 3 (65). When asphalt oxidizes, the principle increase is in ketones and sulfoxides. Carboxylic acids and anhydrides tend to concentrate at the aggregate surface in asphalt concrete and may produce sensitivity to water damage. 

Anhydrides (-CO-0-CO-) may be identified by a distinctive carbonyl band region. A strong doublet is observed in this region with components in the 1840-1800 and 1780-1740 cm ranges. Anhydrides also show a strong C-O stretching band near 1150 cm for open-chain anhydrides and at higher wavenumbers for cyclic structures. Table 4.3 summarizes the major infrared bands observed for carboxylic acids and anhydrides. 

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