Formation of Acid Anhydrides

If carboxylic acids are treated with dehydrating agents, acid anhydrides are 

Acid anhydrides are named by adding anhydride after the acid from which they  

Formation of an anhydride from an acid is similar to the formation of an ether from alcohols. When dicarboxylic acids are heated up to 200 - 300 °C, cyclic anhydrides with five or six carbons are formed. 

An alternative way to produce anhydrides is by the reaction of alkali metal salts of carboxylic acids with acid chlorides. In addition to the anhydride, alkali metal salts are formed in this reaction. 

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Therefore, no change in the sodium ethoxide consumption should be expected with samples transformed to the chlorides. A decrease points to the formation of acid anhydrides. 

Formation of acid anhydride by the reaction of carboxylic acid with acetic anhydride. 

A second requirement of the Tronov postulates—formation of acid anhydrides—is met by evidence from infrared spectra of oxidized coal samples periodically withdrawn from the reactor. As a matter of experimental record, it should be observed that such anhydrides did not appear until the later stages of reaction, by which time -COOH concentrations were already quite high. However, since initial carboxyl formation probably occurs in aliphatic structures present in the parent coal (9), appearance of anhydrides after rather... 

Compounds of phosphorus (III) are readily oxidized by [bis(acyloxy)iodo]-benzenes in this way, the reaction with triphenylphosphine led to the formation of acid anhydrides at room temperature ... 

Formation of acid anhydrides from acid chlorides and alkali salts of carboxylic acids is carried out by mixing the reactants and distilling off the anhydride formed. 

N.N-Dimethylacetamide (DMA) is dried by distillation under reduced pressure from calcium hydride. The use of DMA is essential to promote metallation. The metallation is also successful with N,N-dimethylformamide as a co-solvent, but the yield of product is significantly lowered (60-70%) because of formation of acid anhydride. ... 

Reduction of carboxylic acids to aldehydes can be carried out via in situ formation of acid anhydrides by the treatment of carboxylic acids 155 with an excess of pivalic anhydride (146). The acylpalladium intermediate, prepared in this way, is hydrogenolyzed to give aldehyde 156. Separation of the Asired aldehyde 156 from other byproducts is tedious under these conditions [61,66]. 

Table 2.6. Relative reaction rate for the formation of acid anhydrides...

The work on catalysts for C4 hydrocarbons has been relatively recent. Ai and Ikawa " have correlated acid-base properties of the catalyst with activities in a Mo-P-Bi catalyst with varying bismuth content. They suggest that increasing Bi content decreases the acidity. The formation of acid (anhydride) is favored over a low-Bi-containing catalyst, i.e., high-acidity catalyst. 

Although some dibasic acids, e.g, succinic acid and phthalic acid, readily lose water on heating with the formation of cyclic anhydrides, most monobasic... 

The first attempt to synthesize and characterize Kegj -type heteropoly acid supported on various mesoporous silicas and its application to add catalysis in the formation of acetic anhydride via dehydration of acetic acid were described in this study. A variety of characterization techniques such as Na adsorption, TEM and XRD were applied... 

Formation of dtraconic anhydride by vapor-phase decarboxy-condensation of pyruvic acid... 

The formation of citraconic anhydride increases with an increase in the feed rate of oxygen up to about 70 mmol/h (air). However, with a further increase in oxygen feed rate, the formation of citraconic anhydride levels off. It is clear that the presence of oxygen is required to form citraconic anhydride from pyruvic acid. 

The selectivity to citraconic anhydride decreases and that to acetic acid increases as the temperature is raised. The results indicate that the activation energy for the formation of citraconic anhydride is much lower than that for the formation of acetic acid. The selectivity to acetic acid decreases steadily with a lowering of the temperature. However, the highest selectivity to citraconic anhydride is obtained at 200°C. Possibly vaporization of pyruvic acid may become difficult at temperatures below 200°C. The yield of citraconic anhydride reached 71 mol% and that of acetic acid was 7 mol% at the pyruvic acid conversion of 98% the loss was about 20 mol%. 

Since formation of citraconic anhydride from pyruvic acid is one of "acid to acid type" transformations, such as reactions from isobutyric acid to methacrylic acid and from lactic acid to pyruvic acid, the required catalysts must be acidic [11). If the catalysts are basic, it may be impossible to obtained acidic products, because basic catalysts activate selectively acidic molecules and, as a result, they show a very high activity for the decomposition of acidic products [11]. 

Carboxylic acids can also be activated by the formation of mixed anhydrides with various phosphoric acid derivatives. Diphenyl phosphoryl azide, for example, is an effective reagent for conversion of amines to amides.140 The proposed mechanism involves formation of the acyl azide as a reactive intermediate. 

Accelerations (or decelerations) imposed by the cycloamyloses on the rate of an intramolecular reaction may be derived from a conformational effect. The rate of an intramolecular reaction depends not only on the proximity of the reactive groups but also on their relative orientation. For example, Bruice and Bradbury (1965) have shown that the rates of formation of cyclic anhydrides from mono esters of 3-substituted glutaric acids depend on the size of the substituent at the 3-position. This observation was interpreted as a change in the ground state population of reactive and non-reactive conformers as the 3-substituents are varied (Scheme IX). Reason-... 

One study of the Et3SiH/TFA reduction of acid anhydrides reports the formation of one equivalent each of the alcohol and the trifluoroacetate ester of the acid (Eq. 139).287... 

The second relevant set of data is for the formation of the anhydride from substituted succinic acid derivatives. Equilibrium constants for the formation of the anhydride from the acid are available for the various methyl-substituted compounds (Table A.l) and the derived EM s are compared in Table 5 with those for intramolecular nucleophilic catalysis in the hydrolysis of half-esters... 

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