Carboxylic acid diacids

Catalytic hydrocarboxylations and related esterifications as well as amidations of alkenes belong to a family of carbonylation reactions which has attracted considerable industrial interest. Minor changes in the catalyst system as well as in reaction conditions can lead to simple carboxylic acids, diacids, polyketones, or unsaturated acids as products (Scheme 1). Most importantly, these methods provide routes to monocarboxylic acids, e.g., ethylene to propanoic acid (see Section 2.1.2.2), or 1-olefins (readily available from the oligomerization of ethylene discussed in Section 2.3.1.3) to higher carboxylic acids. 

Shortly after, the same group published a study where readily available carboxylic acids, diacids, and N-protected amino acids were screened as proton sources [6]. The same substrates were used in the presence of citric acid instead of HF. This catalytic system displayed somewhat lower selectivity. For example, by using similar experimental conditions in the presence of citric acid at —10 °C, the enantioseiective protonation of silyl enol ether 5c afforded the corresponding ketone 7c in excellent yield but lower enantioselectivity (up to 75% ee, Scheme 7.4, to be compared with entry 3, Table 7.1). However, upon further optimization, this process seems appealing in terms of simplicity, practicability, environmental concerns, and cost therefore, adjustable for industrial use. 

Ester interchange reactions are valuable, since, say, methyl esters of di-carboxylic acids are often more soluble and easier to purify than the diacid itself. The methanol by-product is easily removed by evaporation. Poly (ethylene terephthalate) is an example of a polymer prepared by double application of reaction 4 in Table 5.3. The first stage of the reaction is conducted at temperatures below 200°C and involves the interchange of dimethyl terephthalate with ethylene glycol... 

As with polyesters, the amidation reaction of acid chlorides may be carried out in solution because of the enhanced reactivity of acid chlorides compared with carboxylic acids. A technique known as interfacial polymerization has been employed for the formation of polyamides and other step-growth polymers, including polyesters, polyurethanes, and polycarbonates. In this method the polymerization is carried out at the interface between two immiscible solutions, one of which contains one of the dissolved reactants, while the second monomer is dissolved in the other. Figure 5.7 shows a polyamide film forming at the interface between an aqueous solution of a diamine layered on a solution of a diacid chloride in an organic solvent. In this form interfacial polymerization is part of the standard repertoire of chemical demonstrations. It is sometimes called the nylon rope trick because of the filament of nylon produced by withdrawing the collapsed film. 

The photo-Kolbe reaction is the decarboxylation of carboxylic acids at tow voltage under irradiation at semiconductor anodes (TiO ), that are partially doped with metals, e.g. platinum [343, 344]. On semiconductor powders the dominant product is a hydrocarbon by substitution of the carboxylate group for hydrogen (Eq. 41), whereas on an n-TiOj single crystal in the oxidation of acetic acid the formation of ethane besides methane could be observed [345, 346]. Dependent on the kind of semiconductor, the adsorbed metal, and the pH of the solution the extent of alkyl coupling versus reduction to the hydrocarbon can be controlled to some extent [346]. The intermediacy of alkyl radicals has been demonstrated by ESR-spectroscopy [347], that of the alkyl anion by deuterium incorporation [344]. With vicinal diacids the mono- or bisdecarboxylation can be controlled by the light flux [348]. Adipic acid yielded butane [349] with levulinic acid the products of decarboxylation, methyl ethyl-... 

The cationic pathway allows the conversion of carboxylic acids into ethers, acetals or amides. From a-aminoacids versatile chiral building blocks are accessible. The eliminative decarboxylation of vicinal diacids or P-silyl carboxylic acids, combined with cycloaddition reactions, allows the efficient construction of cyclobutenes or cyclohexadienes. The induction of cationic rearrangements or fragmentations is a potent way to specifically substituted cyclopentanoids and ring extensions by one-or four carbons. In view of these favorable qualities of Kolbe electrolysis, numerous useful applications of this old reaction can be expected in the future. 

However, in subsequent work it was found that carboxylic acid groups readily add to ketene acetals to form carboxyortho ester linkages (24). These are very labile linkages and on hydrolysis regenerate the carboxylic acid group which then exerts its catalytic function. Because carboxylic acids add so readily to ketene acetals, very labile polymers can be prepared by the addition of diacids to diketene acetals. The utilization of such polymers is currently under investigation. 

This affinity for metals results not only from the structural organization of the new diacids but from stereoelectronic effects at carboxyl oxygen as well. The in-plane lone pairs of a carboxylate 18 differ in basicity by several orders of magnitude 16). Conventional chelating agents17> derived from carboxylic acids such as EDTA, 19a are constrained by their shape to involve the less basic anti lone pairs [Eq. (4)]. The new diacids are permitted the use of the more basic syn lone pairs in contact with the metal 19b. These systems represent a new type of chelate for highly selective recognition of divalent ions. 

These results are quite compatible with the preferred conformations of the two-chain carbonyl diacids in aqueous media mentioned above (Porter et al, 1986b, 1988). The meso-compounds preferred collinear conformation, which places the hydrogens at the asymmetric carbons in a nearly eclipsed position relative to each other (Fig. 44), is more stable than that of the ( )-diastereomer by about 1.2kcalmol 1. In this conformation, the two carboxylic acid groups at the ends of the chain can be attached to the water surface side-by-side. The entire molecule can then behave as a good-amphiphile whose structure is similar to a pair of single-chain fatty acid molecules bound side-by-side, each chain mirroring the other about the molecules plane of symmetry. 

Shown in Figure 6-A are EELS spectra of the entire series of pyridine carboxylic acids and diacids adsorbed at Pt(lll) from acidic solutions at negative electrode potential. Under these conditions all of the meta and para pyridine carboxylic acids and diacids exhibit prominent 0-H vibrations (OH/CH peak ratio near unity). In contrast, at positive potentials only the para-carboxylic acids display pronounced 0-H vibrations, Figure 6-B. All of the 0-H vibrations are absent under alkaline conditions, Figure 6-C. This situation is illustrated by the reactions of adsorbed 3,4-pyridine dicarboxylic acid ... 

The hydrogenation of HMF in the presence of metal catalysts (Raney nickel, supported platinum metals, copper chromite) leads to quantitative amounts of 2,5-bis(hydroxymethyl)furan used in the manufacture of polyurethanes, or 2,5-bis(hydroxymethyl)tetrahydrofuran that can be used in the preparation of polyesters [30]. The oxidation of HMF is used to prepare 5-formylfuran-2-carboxylic acid, and furan-2,5-dicarboxylic acid (a potential substitute of terephthalic acid). Oxidation by air on platinum catalysts leads quantitatively to the diacid. [32], The oxidation of HMF to dialdehyde was achieved at 90 °C with air as oxidizing in the presence of V205/Ti02 catalysts with a selectivity up to 95% at 90% conversion [33]. 

The preparation described here of 3-cyclopentene-1-carboxylic acid from dimethyl malonate and cis-1,4-dichloro-2-butene is an optimized version of a method reported earlier3 for obtaining this often used and versatile building block.6 The procedure is simple and efficient and requires only standard laboratory equipment. 3-Cyclopentene-1-carboxylic acid has previously been prepared through reaction of diethyl malonate with cis-1,4-dichloro(or dibromo)-2-butene in the presence of ethanolic sodium ethoxide, followed by hydrolysis of the isolated diethyl 3-cyclopentene-1,1-dicarboxylate intermediate, fractional recrystallization of the resultant diacid to remove the unwanted vinylcyclopropyl isomer, and finally decarboxylation.2>7 Alternatively, this compound can be obtained from the vinylcyclopropyl isomer (prepared from diethyl malonate and trans-1,4-dichloro-2-butene)8 or from cyclopentadiene9 or cyclopentene.10 In comparison with the present procedure, however, all these methods suffer from poor selectivity, low yields, length, or need of special equipment or reagents, if not a combination of these drawbacks. 

Polyesters are one of the most important classes of polymers in use today. In their simplest form, polyesters are produced by the polycondensation reaction of a glycol (or dialcohol) with a difunctional carboxylic acid (or diacid). Hundreds of polyesters exist due to the myriad of combinations of dialcohols and diacids, although only about a dozen are of commercial significance. 

Complexes of other metals are also capable of catalyzing useful carbonylation reactions under phase transfer conditions. For example, certain palladium(o) catalysts, like Co2(C0)g, can catalyze the carbonylation of benzylic halides to carboxylic acids. When applied to vinylic dibromides, unsaturated diacids or diynes were obtained, using Pd(diphos)2[diphos l,2-bis(diphenylphosphino)ethane] as the metal catalyst, benzyltriethylammonium chloride as the phase transfer agent, and t-amyl alcohol or benzene as the organic phase(18),... 

The most simple way to introduce carboxylic acid functionalities onto hyperbranched polyesteramides is to modify the hydroxyl functions with suitable diacid derivatives. The modification can either be done in melt or in solution. 

In the aromatic benzenedicarboxylic acid derivatives, the pattern is not dissimilar, especially since we have no oxalic acid-like anomaly. Carboxylic acid groups are electron withdrawing, and all three diacids are stronger acids than benzoic acid. On the other hand, the carboxylate group is electron donating, and this weakens the second ionization. This makes the second acid a weaker acid than benzoic acid. The effects are greatest in the ortho derivative, where there are also going to be steric factors (see Section 4.3.5). 

The mixture of the reaction products can be shifted from oxidation to reduction products depending on the method chosen to work up the reaction mixture, and can include chain scission products such as alcohols, aldehydes, ketones, carboxylic acids, and diacids. 

Consider the polyesterification of a diacid and a diol to illustrate the general form of the kinetics of a typical step polymerization. Simple esterification is a well-known acid-catalyzed reaction and polyesterification follows the same course [Otton and Ratton, 1988 Vancso-Szmercsanyi and Makay-Bodi, 1969]. The reaction involves protonation of the carboxylic acid,... 

Various combinations of reactant(s) and process conditions are potentially available to synthesize polyesters [Fakirov, 2002 Goodman, 1988], Polyesters can be produced by direct esterification of a diacid with a diol (Eq. 2-120) or self-condensation of a hydroxy carboxylic acid (Eq. 2-119). Since polyesterification, like many step polymerizations, is an equilibrium reaction, water must be continuously removed to achieve high conversions and high molecular weights. Control of the reaction temperature is important to minimize side reactions such as dehydration of the diol to form diethylene glycol... 

In addition, the reaction is not chemoselective, thus carboxylic diacid chlorides and carboxylic acid chlorides bearing an ester group give unsatisfactory yields of ketone (Scheme ll) ... 

In a side-reaction 10-15% carboxylic acids are produced by oxidative cleavage of the ketone enolates. The cleavage is favoured by higher temperatures e.g. cyclo-hexanol leads to 80% cyclohexanone and 16% adipic acid at 25 °C, whilst at 80 °C 5% ketone and 42% diacid are found. These acidic by-products are easily separated, since they remain in the alkaline solution during workup. The oxidation of 6 gave the acetal 7 as main product (28%) together with 4% of the ketone 8 and 56% of unchanged 6. The acetal 7 is probably formed by nucleophilic addition of the alcohol 6 at the activated triple bond of ketone 8. 

Carboxylic acid anhydrides generally react with sulfur tetrafluoride in the same manner as carboxylic acids to give acid fluorides, then trifluoromethyl derivatives. Various cyclic anhydrides, which are particularly stable under acidic conditions, react without cleavage to give, in a stepwise fashion, difluoro lactones and a,a,a, a -tetrafluoro ethers. Conversely, the corresponding diacids are readily dehydrated by sulfur tetrafluoride to give anhydrides in the first step of the reaction. Therefore, in this section reactions of carboxylic acids and carboxylic acid anhydrides are discussed together. 

Chemical Properties. Trimethylpentanediol, with a primary and a secondary hydroxyl group, enters into reactions characteristic of other glycols. It reacts readily with various carboxylic acids and diacids to form esters, diesters, and polyesters (40). Some organometallic catalysts have proven satisfactory for these reactions, the most versatile being dibutyltin oxide. Several weak bases such as triethanolamine, potassium acetate, lithium acetate, and borax are effective as stabilizers for the glycol during synthesis (41). 

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