Anhydrides, alcoholysis alcohols

The acid chlorides are generally more reactive than the corresponding acid anhydrides. In fact, the alcoholysis of acid chlorides is probably the best laboratory method for preparing esters. Frequentiy, basic materials are added during the course of the reaction to neutralize by-product hydrochloric acid. When the basic material is aqueous caustic, the procedure is referred to as the Schotten-Baumann procedure (73). Esterification of tertiary alcohols by acid chlorides is described in Reference 74. Esters of tertiary alcohols can also be formed through an intermediate /-butyl thioate group (75) ... 

The influence of temperature on the ortho effect has been evaluated in the alkaline hydrolysis in aqueous DMSO solutions of ortho-, meta- and para-substituted phenyl benzoates (26). The alcoholysis of phthalic anhydride (27) to monoalkyl phthalates (28) occurs through an A-2 mechanism via rate-determining attack of the alcohol on a carbonyl carbon of the anhydride (Scheme 4). Evidence adduced for this proposal included highly negative A 5 values and a p value of 4-2.1. In the same study, titanium tetra-n-butoxide and tri-n-butyltin ethanoxide were shown to act as effective catalysts of the half-ester formation from (27), the mechanism involving alkoxy ligand exchange at the metal as an initial step. ... 

Deng also showed that (DHQD)2AQN could catalyze the parallel KR (PKR) of a variety of monosubstituted succinic anhydrides via asymmetric alcoholysis [215]. The nature of the solvent was found to have a significant influence on the selectivity. Hence, increasing the size of the alcohol from methanol to ethanol resulted in increased levels of enantioselectivity, albeit with reduced reaction rates. In this context, 2,2,2-trifluoroethanol appeared to be the alcohol of choice as it allowed the ASD of 2-methyl succinic anhydride (58a) with a remarkable level of selectivity. Indeed, the use of (DHQD)2AQN (15 mol%) provided a mixture of two regioiso-meric hemiesters 59a and 60a in a 1 1 ratio with 93 and 80% ee respectively. 

Mannitol hexanitrate is obtained by nitration of mannitol with mixed nitric and sulfuric acids. Similarly, nitration of sorbitol using mixed acid produces the hexanitrate when the reaction is conducted at 0—3°C and at —10 to —75°C, the main product is sorbitol pentanitrate (117). Xylitol, ribitol, and L-arabinitol are converted to the pentanitrates by fuming nitric acid and acetic anhydride (118). Phosphate esters of sugar alcohols are obtained by the action of phosphorus oxychloride (119) and by alcoholysis of organic phosphates (120). The 1,6-dibenzene sulfonate of D-mannitol is obtained by the action of benzene sulfonyl chloride in pyridine at 0°C (121). To obtain 1,6-dimethanesulfonyl-D-mannitol free from anhydrides and other by-products, after similar sulfonation with methane sulfonyl chloride and pyridine the remaining hydroxyl groups are acetylated with acetic anhydride and the insoluble acetyl derivative is separated, followed by deacetylation with hydrogen chloride in methanol (122). Alkyl sulfate esters of polyhydric alcohols result from the action of sulfur trioxide—trialkyl phosphates as in the reaction of sorbitol at 34—40°C with sulfur trioxide—triethyl phosphate to form sorbitol hexa(ethylsulfate) (123). 

The substance is a little discolored when distilled because of slight decomposition which becomes appreciable at 160°-170°C, with the evolution of acetic anhydride. Silicon tetraacetate is vigorously decomposed by water but it dissolves to a moderate extent in inert liquids such as acetone and benzene. With ethyl alcohol it forms ethyl acetate and silicon dioxide as products of alcoholysis. 

Kinetic resolution of chiral, racemic anhydrides In this process the racemic mixture of a chiral anhydride is exposed to the alcohol nucleophile in the presence of a chiral catalyst such as A (Scheme 13.2, middle). Under these conditions, one substrate enantiomer is converted to a mono-ester whereas the other remains unchanged. Application of catalyst B (usually the enantiomer or a pseudo-enantiomer of A) results in transformation/non-transformation of the enantiomeric starting anhydride ). As usual for kinetic resolution, substrate conversion/product yield(s) are intrinsically limited to a maximum of 50%. For normal anhydrides (X = CR2), both carbonyl groups can engage in ester formation, and the product formulas in Scheme 13.1 are drawn arbitrarily. This section also covers the catalytic asymmetric alcoholysis of a-hydroxy acid O-carboxy anhydrides (X = O) and of a-amino acid N-carboxy anhydrides (X = NR). In these reactions the electrophilicity of the carbonyl groups flanking X is reduced and regioselective attack of the alcohol nucleophile on the other carbonyl function results. 

The alcoholysis of anhydrides (Reaction XVI) is similar in scope to the reaction of alcohols with acyl halides. The reaction is catalyzed by general esterification catalysts, but usually they are not needed unless the anhydride is unreactive or the di-ester (such as a phthalate) is the product sought. 

Surprisingly few studies have been directed towards the development of noncinchona alkaloid-based catalysts for the alcoholative ASD of meso-anhydrides, or indeed any of the enantioselective alcoholysis processes. Uozumi has reported a series of (2S, 4R)-4-hydroxyproline-derived 2-aryl-6-hydroxyhexahydro-lfi-pyr-rolo[l,2-c] imidazolones which mediate the methanolytic ASD of ds-hexa-hydrophthalic anhydride in up to 89% ee when employed at the 10 mol% level for 20 h at —25 °C in toluene [186]. Additionally, Nagao has described the use of a bifunctional chiral sulfonamide for the thiolytic ASD of meso-cyclic anhydrides in up to 98% ee when employed at the 5 mol% level for 20 h at rt in ether [187]. 

The arsonons esters are easily synthesized by the reaction of the dihaloarsines with alcohols or alkoxides. With alcohols, CaCl2 mnst be present because the esters are very sensitive toward hydrolysis, which leads to the reformation of the anhydride (equation 129). The reaction of an alcohol with a bisaminoarsine leads to an arsonous ester (equation 130), as does the alcoholysis of the anhydride. Reaction of diols with bis(drmethylamino)alkylarsines leads to esters of macrocycUc arsinous acid. ... 

Alcoholysis of amides is possible, although it is usually difficult. It has been most common with the imidazolide type of amides (e.g., 100). For other amides, an activating agent is usually necessary before the alcohol will replace the NR2 unit. Dimethylformamide, however, reacted with primary alcohols in the presence of 2,4,6-trichloro-l,3,5-pyrazine (cyanuric acid) to give the corresponding formate ester. Treatment of an amide with triflic anhydride (CF3SO2OSO2CF3) in the... 

Nucleophilic attack by a primary alcohol on the gamma phosphate of ATP (alcoholysis of an acid anhydride). This is a very favourable reaction. 

In 2001, Deng and coworkers found that nucleophilic catalysts such as (DHQD)2AQN (11) can also affect the parallel kinetic resolution of racemic anhydrides by alcoholysis, that is, the two substrate enantiomers are converted into regioisomeric esters. A variety of monosubstituted racemic succinic anhydrides were converted in the presence of (DHQD)2AQN (11, 15-20 mol%) and allyl alcohol as a nucleophile to both regioisomeric hemiesters 49 and 50 with synthetically reliable ee values (up to 98% ee) and yields (Scheme 11.26) [41]. The obtained regioisomeric 2-or 3- aryl succinates could be converted to the P- and a-aryl-y-butylolactones, which constitute valuable synthons for various pharmaceuticals. 

While the alcoholysis of anhydrides outlined above presumably proceeds via non-covalent catalysis, a range of chiral Lewis bases have been used for the desymmetrization of alcohol substrates using covalent strategies. As representative examples of this process, Birman utilized the isothiourea BTM 149 in an asymmetric synthesis of (—)-lobeline via desymmetrization of lobelanidine 167... 

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