Carboxylates cyclic anhydrides

After acyl halides acid anhydrides are the most reactive carboxylic acid derivatives Three of them acetic anhydride phthahc anhydride and maleic anhydride are mdus trial chemicals and are encountered far more often than others Phthahc anhydride and maleic anhydride have their anhydride function incorporated into a nng and are referred to as cyclic anhydrides... 

Hydrolysis (Section 20 6) Acid anhydrides react with water to yield two carboxylic acid func tions Cyclic anhydrides yield di carboxylic acids... 

Carbon dioxide 53 55). If excess C02 and polar solvents are used the carboxylation is quantitative and free of side reactions. In nonpolar solvents association phenomena favor ketone formation 55). An alternate way to get re-carboxylic polymers is to react the living sites with a cyclic anhydride 561. 

The scope of this reaction is similar to that of 10-21. Though anhydrides are somewhat less reactive than acyl halides, they are often used to prepare carboxylic esters. Acids, Lewis acids, and bases are often used as catalysts—most often, pyridine. Catalysis by pyridine is of the nucleophilic type (see 10-9). 4-(A,A-Dimethylamino)pyridine is a better catalyst than pyridine and can be used in cases where pyridine fails. " Nonbasic catalysts are cobalt(II) chloride " and TaCls—Si02. " Formic anhydride is not a stable compound but esters of formic acid can be prepared by treating alcohols " or phenols " with acetic-formic anhydride. Cyclic anhydrides give monoesterified dicarboxylic acids, for example,... 

Friedel-Crafts acylation can be carried out with cyclic anhydrides, in which case the product contains a carboxyl group in the side chain. When succinic... 

Maleic acid is a linear four carbon molecule with carboxylate groups on both ends and a double bond between the central carbon atoms. The anhydride of maleic acid is a cyclic molecule containing five atoms. Although the reactivity of maleic anhydride is similar to other cyclic anhydrides, the products of maleylation are much more unstable toward hydrolysis, and the site of unsaturation lends itself to additional side reactions. Acylation products of amino groups with maleic anhydride are stable at neutral pH and above, but they readily hydrolyze at acid pH values around pH 3.5 (Butler et al., 1967). Maleylation of sulfhydryls and the phe-nolate of tyrosine are even more sensitive to hydrolysis. Thus, maleic anhydride is an excellent reversible blocker of amino groups to temporarily mask them from reactivity while another... 

Commercially available hyperbranched polymer, a poly(ester-amide) is currently being marketed by DSM under the product name Hybrane [13] (Figure 8.2). It is also a hydroxyl-functionalized product, but contains both amide and ester linkages. The synthesis is accomplished in two steps cyclic anhydrides are reacted with diisopropanolamine to give an amide-intermediate, possessing two hydroxyl groups and one carboxylic acid. The subsequent polymerization takes places via an oxazolinium intermediate which results in the formation of a... 

Reactions of wood with cyclic anhydrides do not yield a by-product, leaving the modified wood polymers with a covalently bonded carboxylic group an example is reaction with succinic anhydride (SA) (Figure4.1a). With reactions above 100°C there is some formation of diester observed (Figure 4.1b), resulting in cross-linking within the cell wall matrix (Matsuda, 1987). 

The key to a controlled molecular weight build-up, which leads to the control of product properties such as glass transition temperature and melt viscosity, is the use of a molar excess of diisopropanolamine as a chain stopper. Thus, as a first step in the synthesis process, the cyclic anhydride is dosed slowly to an excess of amine to accommodate the exothermic reaction and prevent unwanted side reactions such as double acylation of diisopropanolamine. HPLC analysis has shown that the reaction mixture after the exothermic reaction is quite complex. Although the main component is the expected acid-diol, unreacted amine and amine salts are still present and small oligomers already formed. In the absence of any catalyst, a further increase of reaction temperature to 140-180°C leads to a rapid polycondensation. The expected amount of water is distilled (under vacuum, if required) from the hot polymer melt in approximately 2-6 h depending on the anhydride used. At the end of the synthesis the concentration of carboxylic acid groups value reaches the desired low level. 

Another way to synthesize carboxylic acid functional hyperbranched polyesteramides is to invert the monomer ratio by using an excess of cyclic anhydride with respect to diisopropanolamine. In this case the theoretical A2B building block consisting of 2 carboxylic acid and 1 hydroxyl function can be envisioned (Fig. 14). 

The above-mentioned concept of the synthesis of carboxylic acid functional hyperbranched polyesteramides is not limited to cyclic anhydrides as building blocks. It can be carried out with diisopropanolamine and any dicarboxylic acid as well. The same ratios as written above and calculated in Scheme 1 have been applied in the synthesis of carboxylic acid functional hyperbranched polyesteramides starting from adipic acid and diisopropanolamine. The first one (ratio 2.3 1) gelates as expected, the second one (ratio adipic acid diisopropanolamine 3.2 1) affords the expected product. Again, with GPC the amount of free adipic acid detected is in good agreement with theory (Fig. 17). 

Cis-but-2-enedioic acid is readily dehydrated to form a cyclic anhydride. However, as the carboxyl groups are on opposite sides of the C=C double bond in the trans isomer, they are not in a suitable orientation to undergo such a reaction. 

While a carboxylate anion is a potent nucleophile in an intramolecular reaction it is not powerful enough to displace methoxide or an unprotonated amine, unless the nucleophile and the carbonyl group are held even more rigidly than in the phthalate system. Kirby and Lancaster (referred to by Kirby and Fersht, 1971) have found that such displacement can occur in disubstituted maleate monoesters and amides. The estimated rate constant for cyclization of N-methyl dime thy Imaleamic acid [equation (41)] is 16,000 times greater than that for the unsubstituted compound. Below pH 5-6 hydrolysis of the cyclic anhydride becomes rate-determining. 

Epoxides readily undergo anionic copolymerization with lactones and cyclic anhydrides because the propagating centers are similar—alkoxide and carboxylate [Aida et al., 1985 Cherdron and Ohse, 1966 Inoue and Aida, 1989 Luston and Vass, 1984]. Most of the polymerizations show alternating behavior, with the formation of polyester, but the mechanism for alternation is unclear. There are few reports of cationic copolymerizations of lactones and cyclic ethers other than the copolymerizations of [5-propiolactone with tetrahydrofuran and... 

Friedel-Crafts acylation can be carried out with cyclic anhydrides,272 in which case the product contains a carboxyl group in the side chain. When succinic anhydride is used, the product is ArCOCH2CH2COOH. This can be reduced (9-37) to A1CH2CH2CFLCOOH, which can then be cyclized by an internal Friedel-Crafts acylation. The total process is called the Haworth reaction 173... 

LiAlH4 usually reduces open-chain anhydrides to give 2 moles of alcohol, With cyclic anhydrides the reaction with LiAIH4 can be controlled to give either diols or lactones572 (see 9-41). NaBH4 in THF, with dropwise addition of methanol, reduces open-chain anhydrides to one mole of primary alcohol and one mole of carboxylic acid.573 OS VI, 482. 

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. 

Cyclic tetrafluoro ethers are also the main or sole products of the sulfur tctrafluoridc fluorination of phthalic and pyromellitic acids, or their anhydrides, possessing two bulky ortho substituents (e.g., CF3. N02, Br. Cl or even Me). These substituents create steric crowding which pushes two neighboring carboxylic acid groups towards each other and forces cyclization acid anhydrides and difluoro lactones are the intermediates and they may be isolated from reactions carried out under sufficiently mild conditions. Thus, reaction of 3,6-bis(trifluoromcthyl)bcn-zcnc-1,2-dicarboxylic acid (4) with sulfur tctrafluoridc at ambient temperature results in dehydration to give exclusively the corresponding cyclic anhydride 5 at 60"C a mixture of the anhydride 5, 3,6-bis(trifluoromethyl)phthaloyI difluoride (6) and 3,3-difluoro-4,7-bis(trifluoro-methyl)isobenzofuran-l(3//)-one (7) is obtained, but at 200"C the final product, 1,1,3,3-tct-rafluoro-4,7-bis(trifluoromethyl)-l,3-dihydroisobenzofuran (8), is formed as the sole product.137... 

The first step is a Friedel-Crafts acylation reaction. The use of a cyclic anhydride introduces both the acyl and carboxyl groups into the molecule. 

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