Carboxylic acid anhydrides from 2 molecules

Without additional reagents Carboxylic acid anhydrides from 2 carboxylic acid chloride molecules... 

Cleavage of an ester by ammonia (or an amine) to give an amide and an alcohol, (p. 1003) (carboxylic acid anhydride) An activated acid derivative formed from two acid molecules with loss of a molecule of water. A mixed anhydride is an anhydride derived from two different acid molecules, (p. 986)... 

Acid anhydrides can be derived from two molecules of carboxylic acid by strong heating to remove 1 equivalent of water. Because of the high temperatures needed, however, only acetic anhydride is commonly prepared this way. 

Anhydride. A chemical compound derived from an acid by elimination of the atoms that make up water. Example SO3, sulfur trioxide, is the anhydride of sulfuric acid, H2SO4. Anhydrides are a class of organic compounds derived from the combination of two carboxylic acids (R-COOH) by. elimination of a molecule of water. For example, acetic acid (CH3COOH) minus water gives acetic anhydride. 

Acyl residues are usually activated by transfer to coenzyme A (2). In coenzyme A (see p. 12), pantetheine is linked to 3 -phos-pho-ADP by a phosphoric acid anhydride bond. Pantetheine consists of three components connected by amide bonds—pantoic acid, alanine, and cysteamine. The latter two components are biogenic amines formed by the decarboxylation of aspartate and cysteine, respectively. The compound formed from pantoic acid and p-alanine (pantothenic acid) has vitamin-like characteristics for humans (see p. 368). Reactions between the thiol group of the cysteamine residue and carboxylic acids give rise to thioesters, such as acetyl CoA. This reaction is strongly endergonic, and it is therefore coupled to exergonic processes. Thioesters represent the activated form of carboxylic adds, because acyl residues of this type have a high chemical potential and are easily transferred to other molecules. This property is often exploited in metabolism. 

Manufacture. Ketenes can be considered the internal anhydrides of the corresponding carboxylic acids, and as such can be made by removing a molecule of water from these acids, either direcdy or indirecdy. Numerous methods to convert a carboxylic acid or derivative to the corresponding ketene have been described (1—4). 

The reaction under consideration is typified by the formation of saturated carboxylic acids from olefins, carbon monoxide, and water. Other compounds have been used in place of olefins (alkyl halides, alcohols), and besides water, a variety of compounds containing active hydrogen may be employed. Thus, alcohols, thiols, amines, and acids give rise to esters, thio-esters, amides, and acid anhydrides, respectively (15). If the olefin and the active hydrogen are part of the same molecule, three or four atoms apart, cyclizations may occur to produce lactones, lactams, imides, etc. The cyclizations are formally equivalent to carbonylations, however, and will be considered later. 

The combination of carboxyl activation by a carbodiimide and catalysis by DMAP provides a useful method for in situ activation of carboxylic acids for reaction with alcohols.10 The reaction proceeds at room temperature. Carbodiimides are widely applied in the synthesis of polypeptides from amino acids. The proposed mechanism for this esterification reaction involves activation of the acid via isourea 28 followed by reaction with another acid molecule to form anhydride... 

Figure 10.10 The synthesis of 2R-methylbutanoic acid, illustrating the use of a chiral auxiliary. The chiral auxiliary is 2S-hydroxymethyltetrahydropyrrole, which is readily prepared from the naturally occurring amino acid proline. The chiral auxiliary is reacted with propanoic acid anhydride to form the corresponding amide. Treatment of the amide with lithium diisopropyla-mide (LDA) forms the corresponding enolate (I). The reaction almost exclusively forms the Z-isomer of the enolate, in which the OLi units are well separated and possibly have the configuration shown. The approach of the ethyl iodide is sterically hindered from the top (by the OLi units or Hs) and so alkylation from the lower side of the molecule is preferred. Electrophilic addition to the appropriate enolate is a widely used method for producing the enantiomers of a-alkyl substituted carboxylic acids...

Acid anhydrides result from substituting the acyl group of one acid for the hydroxy hydrogen of another. They are called anhydrides because they can be viewed as resulting from the loss of water from two carboxylic acid molecules (removing H from one and OH from the other). Symmetrical anhydrides derived from two molecules of the... 

Next, acetic acid is lost, just as acetate is a better leaving group than hydroxide, this step is much more favourable than the usual dehydration at the end of an aldol condensation. Elimination of acetic acid may occur either from the carboxylic acid itself or from the mixed anhydride formed from one more molecule of the acetic anhydride. Whichever route is followed, the unsaturated acid is formed in a single step with the anhydride assisting both the aldol and the dehydration steps. 

Early work had shown cinchonamine to give color reactions typical of indole alkaloids (7), and this was also evident from its UV-spectrum (8). The base differs from the major cinchona alkaloids in yielding, upon oxidation with chromic acid (6), 3-vinylquinuclidine-8-carboxylic acid (III), mp 209°, [a]D — 29° (CHCI3), which was first obtained from quinamine (9). The nature of the remainder of the molecule followed from the conversion of cinchonamine into 0,iVb-diacetylallocinchon-amine (I), mp 159°, [a]D — 7° (CHCI3), by refluxing acetic anhydride and its subsequent oxidation to 3-/3-acetoxyethylindole-2-aldehyde (H) (6). 

The word anhydride means without water. Removing one molecule of water from two molecules of carboxylic acid forms an anhydride. 

Carboxylic acids cannot be readily converted to anhydrides, but dicarboxylic acids can be converted to cyclic anhydrides by heating to high temperatures. This is a dehydration reaction because a water molecule is lost from the diacid. 

Allene carboxylic acids have been cyclized to butenolides with copper(II) chloride. Allene esters were converted to butenolides by treatment with acetic acid and LiBr. Cyclic carbonates can be prepared from allene alcohols using carbon dioxide and a palladium catalyst, and the reaction was accompanied by ary-lation when iodobenzene was added. Diene carboxylic acids have been cyclized using acetic acid and a palladium catalyst to form lactones that have an allylic acetate elsewhere in the molecule. With ketenes, carboxylic acids give anhydrides and acetic anhydride is prepared industrially in this manner [CH2=C=0 + MeC02H (MeC=0)20]. 

Introduction. The object of this experiment is to illustrate two general methods for the preparation of acid anhydrides. Two carboxyl groups may under certain conditions be dehydrated to give an anhydride. The two carboxyl groups may be derived from the same molecule, as in succinic and phthalic anhydrides, or from different molecules, as in acetic anhydride. The simple anhydrides are usually prepared in the laboratory by the action of an acyl chloride on the salt of the acid ... 

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