Carboxylates, ammonium, from ammonia

Samples. For the purposes of demonstrating NMR imaging of anisotropic chemical reactions (37,38), the reactions of ammonia with solid organic acids were used. It has been shown that single crystals of acids such as 4-chlorobenzoic acid react anisotropically with ammonia. Most faces of the crystal react rapidly however, the (100) face reacts slowly as this face has an array of C-Cl units on the surface that protect the carboxylic acid function from ammonia (39). Powders of organic acids react with ammonia in 1 1 ratio to form the simple ammonium salts. 

The first step of phenylpropanoid biosynthesis is conversion of phenylalanine into cinnamic acid by cleavage of ammonium group by the enzyme phenylalanine ammonia-lyase (PAL). Reduction of carboxylic acid from the cinnamic acid leads to cinnamaldehyde, which is then acylated with acetate from acetyl-CoA to form coniferyl alcohol [14]. Reductive cleavage of coniferyl alcohol by eugenol synthase yields eugenol [15]. 

Bicyclic pyrimidin-4-ones (1100, R = H, n = 0-3 R = Me, n = 1) were also prepared from the appropriate lactim ether and EMME in the presence of ammonia or ammonium acetate [73JAP(K)34897 75MIP1]. Pyrimido[l,2-a]azepine-3-carboxylates (1100, R = H, Ph n = 2) were prepared in the reaction of 7-aminotetrahydro-2//-azepines (R = H, Ph n = 2) and EMME or in the reaction of O-methylcaprolactim and diethyl aminomethylenemalonate in ethanol [73JAP(K)34897 75MIP1]. 

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-... 

Ion exchange is widely used for the selective separa-tion/removal of metal ions from an aqueous medium either for environmental clean-up, for the removal of undesirable components, or for metal recovery. Other species that have been treated include nitrate, ammonia, and silicate. This process is normally based on the use of polymeric resins (typically styrene/divinylbenzene polymer backbones) that have chemically active groups attached to them. Sulfonic or carboxylate groups are regularly used for the removal of cations, and quaternary ammonium groups are used for the removal of anions. 

This reaction represents the best general method for amide preparation. Cold, concentrated aqueous ammonia is used as in the preparation of iso-butyramide (83%),or the reaction may be carried out by passing dry ammonia into a solution of the acyl halide in anhydrous ether as in the formation of cyclopropanecarboxamide (91%). Separation of the amide from ammonium chloride is usually accomplished by extraction of the amide by organic solvents. Aqueous sodium hydroxide is employed to take up the hydrogen chloride when amine hydrochlorides are used in place of the free amines as in the preparation of N-methylisobutyramide (75%). When phosphorus trichloride is added to a mixture of an amine and a carboxylic acid, phosphazo compounds, RN=PNHR, rather than acyl halides, are believed to be intermediates. These compounds have been shown to react with carboxylic acids to give amides. ... 

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. ... 

Aromatic acids are reduced by metal-ammonia solutions very much more readily than simple hydrocarbons and ethers. In contrast to the normal requirements for the latter derivatives, it is often possible to achieve reduction with close to stoichiometric quantities of metal. The addition of aromatic carboxylic acids to liquid ammonia (or vice versa) results in the immediate precipitation of the ammonium salt. As the metal is added, however, the precipitate usually dissolves as reduction proceeds, especially if lithium is used. If reduction is carried out in carefully dried, redistilled ammonia, as little as 2.2 mol of lithium are consumed in some cAses, thereby demonstrating that the substrate is reduced much more readily than the ammonium ions, which instead react with the intermediates from reduction of the substrate. However, protonation by NH4 is not essential since reduction proceeds equally well on preformed metal car-boxylates (although low solubility is then often a problem). The addition of an alcohol is not necessary, but it may serve as a useful buffer and can often improve solubility. The presence of alcohol can nevertheless be deleterious, since it facilitates isomerization of the initially formed 1,4-dihydro isomer to the 3,4-isomer and in this way affords the possibility of further reduction. ... 

The variable loss of the methoxy substitutent is in fact a feature common to most 2-methoxybenzoic acid derivatives and appears to stem from the ammonium ions which are generated on mixing of the acid with ammonia. Pretreatment with one equivalent of base prevents hydrogenolysis completely in most cases, although the reduced solubility of the carboxylate salt can lead to incomplete reduction. Potassium salts are reasonably soluble, but reduction of the benzoate esters may afford the best solution (see Section 3.4.3.T). 

Keto acid (170) has been transformed into the diastereomeric mixture of keto acids (171) and (172), where the predominant reaction pathway involves approach of the electrophile anti to the carboxylate group (Scheme 31). It was found to be essential to neutralize the ammonium ions generated from addition of the substrate acid to the liquid ammonia before adding the potassium metal, however. ... 

As oxalic acid is the product obtained by this hydrolysis it must have the constitution as represented, i.e., it is di-carboxyl. In fact, when cyanogen is hydrolyzed ammonium oxalate is obtained which, of course, results from the combination of the oxalic acid and ammonia as first formed. 

The ammonolysis of acyl chlorides is commonly employed whenever the preparation of an amide is desired for the identification of a carboxylic acid. The acyl chloride is prepared and treated with aqueous ammonia, or, if the amide is very soluble in water, with ammonia in benzene. In the latter case the ammonium chloride is filtered off, and the amide obtained by evaporation of the benzene with powdered ammonium carbonate. The preparation of amides from carboxylic acids is based upon the formation of an equilibrium mixture when the ammonium salts of the acid are heated ... 

Conventionally the acyl derivatives of acyloins and benzoins may readily be obtained by reaction with acid anhydrides. The acyloin esters can more conveniently be prepared by allowing the corresponding a-bromo ketones and the sodium or potassium salts of the appropriate carboxylic acid to react, either in ethanol or in the acid to be esterified. The esters may not necessarily be isolated, and the oxazoles are obtained directly by adding the ammonium salt to, or passing ammonia through, the mixture, which is then boiled.84 The reaction then becomes useful for the preparation of oxazoles (53) from a-bromo ketones and carboxylic acids.84 121... 

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