Amines salts formed between carboxylic acids

This reaction is called the Favorskii rearrangement. Again, there are many variations for example, instead of an alkoxide anion, a hydroxide anion or even an amine may be used, in which case the salt of the carboxylic acid or the amide will be formed, respectively. This reaction may also be used so as to result in a ring contraction. Write down the mechanism for the reaction between an alkoxide anion and 2-chlorocyclohexanone. 

There are, however, numerous organic precendents. The Cannizzaro reaction, in which two equivalents of a nonenolizable aldehyde such as bezaldehyde are reacted with hydroxide to form a primary alcohol and the salt of a carboxylic acid, is thought to involve hydride transfer to one aldehyde carbonyl from the carbonyl-addition product of the other aldehyde and hydroxide. The Leuckart reaction, formation of a tertiary amine from formic acid, a primary amine and either a ketone or an aldehyde, seems to procede via hydride transfer from formate to an iminium ion. And the Meervein-Ponndorf-Verley-Oppenauer reaction, the reversible transfer of hydrogen between ketones and secondary alcohols in the presence of excess aluminum isopropoxide, is almost certainly a hydride-transfer reaction. This latter process is of particular interest to us because it requires a metal, just as GI does. The aluminum acts as a Lewis acid, coordinating the carbonyl oxygen and... 

Note that the resolving agent is recovered unchanged after this procedure and can be reused repeatedly. Because of the need to obtain crystalline adducts which are readily broken down to their components again, the ionic salts formed between amines and acids, either carboxylic or sulphonic, are ideal for resolution. Thus even in the last century very many amines were resolved by formation of salts with, for example, tartaric acid (16) or camphorsulphonic acid (29), while organic acids were resolved with bases such as quinine, cinchonine and the highly toxic alkaloids brucine (36) and strychnine (37). Although reliable resolution methods have now been worked out for... 

Salts formed between amines and carboxylic acids 94... 

This approach involves formation of salts most commonly between prochiral carboxylic acid-containing photoreactants and optically pure nonabsorbing amines. While the carboxylic acids are achiral the salts are chiral and these salts, which necessarily crystallize in chiral space groups, provide the asymmetric media in which to carry out the reactions. Clearly the opposite approach, namely forming a salt using a reactive achiral amine and a chiral acid, is also valid. 

It is assumed that the best catalytic effect can be achieved if the pA a or pA), value of the interphase material is close to 7 [71]. Some weak ion-exchange groups such as tertiary amines, phosphoric acid, carboxylic acids, or pyridine show the required dissociation constant or p ta-values. Certain heavy metal ion complexes, such as chromium(lll)- or iron(Ill)-complexes, provide the required catalytic water dissociation effect. In principle, there are many more suitable metal ions available. The metal ions or complexes are immobilized by either including an insoluble salt in the casting solution of the interface layer between the ion permeable layers or by converting a soluble form by a follow-up treatment [45]. An additional requirement for the catalytic material is to be effective and stable for a long period. It must also remain in the interphase, where it is the most active, for the anticipated lifetime of the membrane. 

There is a further contrast between the amides of the two kinds of acids. The substituted amide from a primary amine still has a hydrogen attached to nitrogen, and as a result is acidic in the case of a sulfonamide, this acidity is appreciable, and much greater than for the amide of a carboxylic acid. A monosubstituted sulfonamide is less acidic than a carboxylic acid, but about the same as a phenol (Sec. 24.7) it reacts with aqueous hydroxides to form salts. 

Water-immiscible amines are highly selective in the differentiation between acids (selectivity of about 10 for HCI/H3PO4 separation [44] compared to <2 in extraction by alkanols) and between them and their salts. They are widely used in extraction of metals (their anionic complexes) and of carboxylic acids, but most of them are too strongly basic for mineral acids. The convex distribution curve shows that extraction is very efficient, but back-extraction in free acid form would require huge amounts of water, resulting in extremely dilute, useless back-extracts. Only the very weak amines—highly branched trialkyl amines [52,53] or amines with at least one aryl group—combine efficient extraction with reversibility. Only few such water-immiscible aniline derivates and sterically hindered amines are currently produced on an industrial scale. Adjustment of their properties to treat a variety of feeds would require laborious synthesis. 

Amides require considerably more vigorous conditions for hydrolysis in both acid and base than do esters. Amides undergo hydrolysis in hot aqueous acid to give a carboxylic acid and ammonia. Hydrolysis is driven to completion by the acid-base reaction between ammonia or the amine and acid to form an ammonium salt. One mole of acid is required per mole... 

Some chiral resolving agents have been developed for the derivatization of racemic carboxylic acids to form pairs of diastereomers, which can be separated by conventional methods such as recrystallization. However, in some cases, this process requires several repetitions of salt formation between a carboxylic acid and an amine followed by recrystallization and subsequent separation of the chiral auxiliaries from the acid component to obtain a pure enantiomer. On the other hand, the conversion of a racemic substrate to enantioenriched products, commonly referred to as a kinetic resolution, is also an established method with broad applications [30, 31]. 

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