Carboxylates, ammonium, conversion

In base the tetrahedral intermediate is formed m a manner analogous to that pro posed for ester saponification Steps 1 and 2 m Figure 20 8 show the formation of the tetrahedral intermediate m the basic hydrolysis of amides In step 3 the basic ammo group of the tetrahedral intermediate abstracts a proton from water and m step 4 the derived ammonium ion dissociates Conversion of the carboxylic acid to its corresponding carboxylate anion m step 5 completes the process and renders the overall reaction irreversible... 

Among other oxidizing agents that have been used to accomplish the conversion of ArCHs to ArCHO are ceric ammonium nitrate, ° ceric trifluoroa-cetate, and silver(II) oxide.Oxidation of ArCHa to carboxylic acids is considered at 19-11. 

To avoid LC conditions involving the use of IP agents—as reported above—an alternative route was reported by Di Corcia et al. [16] for the separation and detection of breakdown products generated out of commercial LAS in a degradation test. This method was based on the conversion of the carboxylic groups into methyl esters. After this modification, the addition of 0.2 M ammonium acetate to the mobile phase sufficed to give sharp peaks. In addition, a 10-fold enhancement of the sensitivity of the ESI-MS detector was obtained. 

Sandmeyer s synthesis of aromatic nitriles is far more elegant than the removal of water from the ammonium salts of carboxylic acids, which latter reaction is also applicable to benzene derivatives. In particular, the former synthesis permits of the preparation of carboxylic acids via the nitriles, and so provides a complete substitute for Kolbe s synthesis (alkyl halide and potassium cyanide), which is inapplicable to aromatic compounds. The simplest example is the conversion of aniline into benzoic add. The converse transformation is Hofmann s degradation (benzamide aniline, see p. 152). 

E-(P-Alkylvinyl)phenyliodonium salts react with tetra-n-butylammonium halides to yield the correspondingly substituted Z-haloethenes (80-100% for chloro-, bromo- and iodo-derivatives) [41], In contrast, in the corresponding reaction with Z-(2-benzenesulphonyl-ethenyl)phenyliodonium salts, nucleophilic substitution occurs with retention of configuration to yield the Z-2-benzenesulphonyl-l-haloethenes [42], The ammonium fluorides fail to yield the fluoroethenes, but produce the ethynes by simple elimination [41]. Where carboxylic acids have low solubility in organic solvents, their conversion into the acid chlorides is frequently difficult. Phase-transfer catalysis not only allows the conversion to be effected rapidly, it also results in high yields of a wide range of acid chlorides [43]. 

Solid cyclic carboxylic anhydrides react with gaseous ammonia to give amide ammonium salts with quantitative yield. This has been observed with the labile Diels-Alder adduct 259 [25] (Scheme 38). Aliphatic amine vapors are equally able to open anhydride rings to form the amide salts from where the free amide acids can be obtained in 100% yield. The reaction of 261 with ethylamine to give 262 is an example of a large-scale preparative application [11-12]. Conversely, solid pyromellitic bis-anhydride (263) and methylamine vapor react exother-mally (rise to 95 °C) and quantitatively to yield the tetraamide 264. Interest-... 

There are three common approaches to the displacement of amine substituents from purines. First, diazotization and dediazoniation have been used to replace amine substituents, primarily with hydrogen or hydroxyl, carboxyl, and halide functionalities. Second, the S Ar reactions of quaternary ammonium substituents have provided useful synthetic adjuncts to the displacement reactions of halopurines. Finally, of increasing importance has been the conversion of aminopurines (or oxopurines) to N-linked 1,2,4-triazoles (and other azoles), which function as pseudohalogens and can be displaced by nucleophiles or take part in transition metal-catalyzed reactions. 

Reactions of pyrimido[4,5-3] [l,4]thiazines were discussed in CHEC-II(1996) <1996CHEC-II(7)737> more recently, reported reactions of this system involve nucleophilic substitution in a number of guises. Hemiaminals at C-3 react with ammonium acetate to form aminals (Equation 166) <1999CHE97>. The formation of acyl hydrazides from pyrimido[4,5-3][l,4]thiazine-2-carboxylic acids, along with their subsequent conversion to acyl azides and Curtius... 

The conversion of a carboxylic acid to a salt can serve as confirmation of the acid structure. This is conveniently done by the addition of a tertiary aliphatic amine, such as triethylamine, to a solution of the carboxylic acid in chloroform (no reaction occurs in CC14). The carboxylate ion thus formed shows the two characteristic carbonyl absorption bands in addition to an ammonium band in the 2700-2200 cm-1 region. The O—H stretching band, of course, disappears. The spectrum of ammonium benzoate, Figure 3.24, demonstrates most of these features. 

By adjusting the exposure time, quantitative conversion of carboxylic acid groups (followed near 1710 cm 1) can be obtained (fig. 5). Typical bands at 1836, 1796 and 1555 cm 1 correspond to acid fluorides, acid chlorides and ammonium carboxylates groups respectively. In the case of EMA (Ethylene-Methacrylic acid) some sodium carboxylate groups were initially present. FTIR analysis showed that these functions (1559 cm 1) were also converted into acid fluorides ... 

The Strecker synthesis is used to prepare amino acids in the laboratory. As shown in the following equation, an aldehyde is reacted with sodium cyanide and ammonium chloride in water to produce a cyanoamine. Conversion of the cyano group to a carboxylic acid completes the synthesis. Show the structure of the intermediate, A, in the following synthesis, and show the steps in the mechanism for the formation of A and for the conversion of A to the cyanoamine. (Hint Remember that NH4+ and H,0 are in equilibrium with NH3 and H-0+.)... 

Pyrrole and N-substituted pyrroles are formed by a reaction analogous to the conversion of sugars to furan aldehydes. Ammonium and substituted ammonium salts of mucic acid, H02C(CH0H)4C0jH, are cyclized and de-carboxylated by pyrolysis. The yields of pyrrole and its N-phenyl and N-methyl derivatives are about 40%. Tetrahydropyrroles (pyrrolidines) are formed from various 4-substituted amines by elimination of water, ammonia, or hydrogen halide. ... 

The direct conversion of a carboxylic acid to an amide with NH3 or an amine is very difficult, even though a more reactive acyl compound is being transformed into a less reactive one. The problem is that carboxylic acids are strong organic acids and NH3 and amines are bases, so they undergo an acid-base reaction to form an ammonium sait before any nucleophilic substitution occurs. 

---