Acetic propionic anhydride, hydrolysis

The first examples of a homogeneous reduction of this type were reported in 1971. Cobalt carbonyl was found to reduce anhydrides such as acetic anhydride, succinic anhydride and propionic anhydride to mixtures of aldehydes and acids. However, scant experimental details were recorded [94]. In 1975, Lyons reported that [Ru(PPh3)3Cl2] catalyzes the reduction of succinic and phthalic anhydrides to the lactones y-bulyrolaclone and phthalide, respectively [95], The proposed reaction sequence for phthalic anhydride is shown in Scheme 15.15. Conversion of phthalic anhydride was complete in 21 h at 90 °C, but yielded an equal mixture of the lactone, phthalide (TON = 100 TOF 5) and o-phthalic acid, which is presumably formed by hydrolysis of the anhydride by water during lactoniza-tion. Neither acid or lactone were further hydrogenated to any extent using this catalyst system, under these conditions. 

For the preparation of 70-72 Koyama etal. (28) employed the 5-3 -(indolyl)-oxazole 88 obtained from ethylindole-3-carboxylate (87) and isocyanomethyl lithium. The oxazole 88 was refluxed in acetic anhydride—acetic acid or propionic anhydride-propionic acid to afford pimprinine (70) and pimprinethine (71) in 13 and 19% yield, respectively. Hydrolysis of these reaction mixtures and that produced with phenylacetic acid anhydride-phenylacetic acid gave high yields (84-92%) of the 3-acylamidoindoles 79-81, which could be smoothly cyclized with phosphorus oxychloride to the natural products 70-72 (28). 

Cellulose esters (e.g., cellulose triacetate, cellulose diacetate, cellulose propionate, and cellulose butyrate) are prepared by initially treating cellulose with glacial acetic acid (or propionic acid and butyric acid) followed by the corresponding acid anhydride with a trace of strong acid as a catalyst in chlorinated hydrocarbon. Complete esterification reactions result in the formation of a triester, which undergoes water hydrolysis to form a diester. Cellulose acetate alone or in combination with cellulose triacetate or cellulose butyrate is used as a semipermeable membrane for osmotic pumping tablets, primarily in controlled release systems. The permeability of the membrane can be further modulated by adding water-soluble excipients to the cellulose esters. 

The reaction of oarboxylate with various substrates is an example of a system which necessitates a careful search for products. Early examples of these reactions demonstrated that direct nucleophilic attack takes place. For example, using a dilatometric method, formate was found to catalyze strongly the hydrolysis of acetic anhydride whereas propionate and butyrate slow down the reaction (Kilpatrick, 1928). These results are attributable to mixed anhydride formation with the total rate being determined by the reactivity of the mixed anhydride. The reaction of acetate with 2,4-dinitrophenyl benzoate results in the formation of an unstable mixed anhydride, as was shown in an experiment in which 0 labeled acetate was used the benzoic acid product contains 75% of the O label (Bender and Neveu, 1958). The other 25 % of the O label is presumed to be lost to acetate by solvent attack at the benzoyl carbon if direct nucleophilic interaction is the sole path. 

Among them, ansamitocins P-3 (81) and P-4 (83) were the most abundant [126]. Reductive hydrolysis of each antibiotic with LiAlH at low temperature gave maytansinol (= ansamitocin P-0) (84). Acetylation of 84 with acetic anhydride in pyridine yielded an antitumor plant product maytanacine (ansamitocin P-1) (79). Maytansinol propionate, corresponding to ansamitocin P-2 (80), could be prepared by Ae acylation of 84. Isolation procedures, chemical characterization and the structures of 79 - 83 were described [127]. 

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