Carboxylic acids and acid anhydrides

The reaction with carboxylic acid and acid anhydride is carried out in the presence of a small amount of concentrated sulphuric acid. The reaction is reversible, and therefore, water is removed as soon as it is formed. The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to neutralise HCl which is formed during the reaction. It shifts the equilibrium to the right hand side. The introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation. Acetylation of salicylic acid produces aspirin. 

Carboxylic acids and acid anhydrides also serve as acylating agents in Friedel-Crafts reactions. We consider these acylating agents in Chapters 20 and 21 when we study the reactions of carboxylic acids and their derivatives. 

Schechter, L. Wynstra, J. Kurkjy, R. (1956). Glycidyl Ether Reactions with Alcohols, Phenols, Carboxylic Acids, and Acid Anhydrides. Journal of Industrial and Engineering Chemistry, Vol.48, No.l, (January 1956), pp. 86-93, ISSN 1226-086X. 

Reactions with carboxylic acids and acid anhydrides (Section 4.6)... 

The reactions of metal alkoxides with carboxylic acids and acid anhydrides can be represented by Eqs (2.231) and (2.232) ... 

Carboxylic acid anhydrides compounds of the type RCOCR can also serve as sources of acyl cations and m the presence of aluminum chloride acylate benzene One acyl unit of an acid anhydride becomes attached to the benzene ring and the other becomes part of a carboxylic acid... 

Friedel-Crafts acylation of aromatic compounds (Section 12 7) Acyl chlorides and carboxylic acid anhydrides acylate aromatic rings in the presence of alumi num chloride The reaction is electrophil ic aromatic substitution in which acylium ions are generated and attack the ring... 

In naming carboxylic acid anhydrides in which both acyl groups are the same we simply specify the acid and replace acid by anhydride When the acyl groups are dif ferent they are cited m alphabetical order... 

Amines are convert ed to amides on reaction with acyl chlorides Other acylating agents such as carboxylic acid anhydrides and esters may also be used but are less reactive... 

Acylatmg agents such as acyl chlorides and carboxylic acid anhydrides can react with phenols either at the aromatic ring (C acylation) or at the hydroxyl oxygen (O acylation)... 

The alcohol groups of carbohydrates undergo chemical reactions typical of hydroxyl functions They are converted to esters by reaction with acyl chlorides and carboxylic acid anhydrides... 

Step 2 Structurally O acylisoureas resemble carboxylic acid anhydrides and are powerful acylatmg agents In the reaction s second stage the amine adds to the carbonyl group of the O acylisourea to give a tetrahedral intermediate... 

Ethers of benzenepentol have been obtained by Dakin oxidation of the appropriately substituted acetophenone. Thus, the oxidation of 2-hydroxy-3,4,6-ttimethoxyacetophenone and 2-hydroxy-3,4,5-ttimethoxyacetophenone with hydrogen peroxide ia the presence of alkali gives l,2-dihydroxy-3,4,6-ttimethoxybenzene and l,2-dihydroxy-3,4,5-ttimethoxybenzene, respectively further methylation of these ethers yields the pentamethyl ether of benzenepentol (mp 58—59 degC) (253). The one-step aromatization of myoinositol to produce esters of pentahydroxybenzene is achieved by treatment with carboxylic acid anhydrides ia DMSO and ia the presence of pyridine (254) (see Vitamins). 6-Alkyl- or... 

By virtue of their fused /3-lactam-thiazolidine ring structure, the penicillins behave as acylating agents of a reactivity comparable to carboxylic acid anhydrides (see Section 5.11.2.1). This reactivity is responsible for many of the properties of the penicillins, e.g. difficult isolation due to hydrolytic instability (B-49MI51102), antibacterial activity due to irreversible transpeptidase inhibition (Section 5.11.5.1), and antigen formation via reaction with protein molecules. 

Friedel-Crafts acylation In the presence of aluminum chloride, acyl chlorides and carboxylic acid anhydrides acylate the aromatic ring of phenols. 

Similar additions have been successfully carried out with carboxylic acids, anhydrides, acyl halides, carboxylic esters, nitriles, and other types of compounds. These reactions are not successful when the alkene contains electron-withdrawing groups such as halo or carbonyl groups. A free-radical initiator is required, usually peroxides or UV light. The mechanism is illustrated for aldehydes but is similar for the other compounds ... 

In an alternate synthesis, the formation of thermoplastic vulcanizate (TPV) is accomplished with two polymers, wherein one polymer is grafted with a carboxylic acid anhydride, which then is reacted with an aminosilane, which reacts with the acid anhydride and then cross-links with moismre. The vulcanizates exhibit good mechanical properties and lower melt-flow index than the starting polymers. 

The classes of compounds that are conveniently considered together as derivatives of carboxylic acids include the acyl chlorides, carboxylic acid anhydrides, esters, and amides. In the case of simple aliphatic and aromatic acids, synthetic transformations... 

Direct acylation of imidazole can also be achieved with carboxylic acid anhydrides. For example, if imidazole is dissolved at room temperature in acetic anhydride, crystals of iV-acetylimidazole begin to separate out after removal of excess anhydride and the resulting acetic acid under vacuum at 60 °C, nearly pure iV-acetylimidazole (m.p. 100-102 °C) is obtained in almost quantitative yield.[4]... 

One of the most systematic investigations into the use of organic chemical microscopy was made by Dunbar and his associates, who used a series of specific reagents to develop specific tests for various functional groups. Methods were developed for amines [24,25], carboxylic acids, anhydrides, and acid chlorides [26,27], aldehydes and ketones [28], hydroxy compounds [29], amino acids [30], and cations [31]. 

Carboxylic acids were introduced by the reaction of the polysilane(II) with carboxylic acid anhydrides in the presence of an amine. Table 2 shows the results. In order to examine the effect of unsaturated bonds and halides in the side chain on photolysis, double bonds or chloride groups were introduced with the carboxylic acid. Polysilanes(III) were also soluble in polar solvents and basic aqueous solution. The solubility in tetramethyl ammonium hydroxide aqueous solution(TMAH) depended strongly... 

Acyl chlorides are converted in good yield into symmetrical carboxylic acid anhydrides upon treatment with dilute aqueous sodium hydroxide at -I0°C in the presence of a tetra- -butylammonium salt [76, 77]. Yields are considerably lower when Aliquat is used. In a similar manner, chloroformates and ethyl oxalyl chloride are converted into carbonic hemi-ester anhydrides. 

Selected examples of carboxylic acid anhydrides and carbonic hemiester anhydrides... 

---