Elimination of ammonia from

The balance between those molecules which are protonated and those which are not has emerged as an inportant function in determining the course of any reaction occurring within the Interlamellar region. One carefully studied reaction is that of the elimination of ammonia from amines (21), a reaction proceeding by two sinple steps... 

Alkyl and aryl nitriles 151 react with thiosemicarbazide 138 under acidic conditions to give 1,3,4-thiadiazoles (Scheme 14 and Table 8) <1995BML1995, 1996IJB273, 1997IJB394>. The acidic conditions promote the elimination of ammonia from the intermediate iminothioacylhydrazine 152. 

Chloro-triammino-platinous Chloride, [Pt(NH3)3Cl]Cl, may be obtained by the addition of ammonia to dichloro-diammino-platinum, [Pt(NH3)2Cl2], or by the elimination of ammonia from tetrammino-platinous chloride by the action of hydrochloric acid thus ... 

This series of compounds may be produced by the elimination of ammonia from the previous series by means of hydrochloric acid. It is probable that the acid, [Pt(NH3)R.3]H, is formed, but this has not been isolated, and only the potassium, ammonium, and silver salts are known. 

Robinson (J. C. S., 113, 639 125, 827) has put forward the hypothesis that the fundamental reactions involved are, in succession, a rearrangement to an unsaturated hydrazine, an isomeric change of the o-benzidine type, and finally the elimination of ammonia from the resulting diamine ... 

Lyases are an attractive group of enzymes from a commercial perspective, as demonstrated by then-use in many industrial processes.240 They catalyze the cleavage of C-C, C-N, C-O, and other bonds by means other than hydrolysis, often forming double bonds. For example, two well-studied ammonia lyases, aspartate ammonia lyase (aspartase) (E.C. 4.3.1.1) and phenylalanine ammonia lyase (PAL) (E.C. 4.3.1.5), catalyze the trans-elimination of ammonia from the amino acids, l-aspartate and L-phenylalanine, respectively. Most commonly used in the synthetic mode, the reverse reaction has been used to prepare the L-amino acids at the ton scale (Schemes 19.30 and 19.31).240 242 These reactions are conducted at very high substrate concentrations such that the equilibrium is shifted, resulting in very high conversion to the amino acid products. 

A remaining question about the elimination process on a solid surface is the geometric structure of the adsorbed molecule during reaction. If the elimination is a concerted reaction, the acidic function of the catalyst surface (which binds the amine part of the reactant) and the basic function (which abstracts the p -hydrogen atom) should act simultaneously. In that case, it seems as if the reacting amine can assume only a configuration close to the syn configuration shown in Fig. 7. However, syn eliminations are less common than trans eliminations, and we have shown that the elimination of ammonia from amines occurs primarily via trans elimination [F. Rota, V. Ranade, and R. Prins, J. Catal. 200 (2001), to be published]. This problem was realized even... 

Many amino acids can lose ammonia to give an unsaturated acid. The enzymes that catalyse these reactions are known as amino acid ammonia lyases. The one that concerns us at the end of the shikimic acid pathway is phenylalanine ammonia lyase, which catalyses the elimination of ammonia from phenylalanine to give the common metabolite cinnamic acid. 

The formation of tertiary amines is also explained by the analogous reactions shown in eqs. 7.7 and 7.8. In this case, however, elimination of ammonia from the addition product 4 to form an azomethine type compound is not possible, but tertiary amines may be formed either by direct hydrogenolysis of 4 or through the formation of an enamine 5 followed by hydrogenation. 

The 1,2-migration of amino groups in /3-aminoalkyl radicals such as 24 has also been of interest because of the involvement of these species in the enzyme-catalyzed elimination of ammonia from 1,2-amino alcohols.47-50 These studies have also been reviewed recently by Radom et al45... 

An elimination of ammonia from 256 to purine followed by reduction of this compound is also possible. 

Elimination of Ammonia from Phenylhydrazones (Fischer Indole Synthesis). 844... 

An important general method for preparing indoles involves the catalytic elimination of ammonia from phenylhydrazones of carbonyl compounds having an a-roethylene group. Catalysts include zinc chloride, cuprous chloride, boron fluoride etherate, dilute sulfuric acid, alcoholic hydrochloric acid, and glacial acetic acid. ... 

Poppe L, Retey J. Eriedel-crafts-type mechanism for the enzymatic elimination of ammonia from histidine and phenylalanine. Angew. Chem. Int. Ed. 2005 44 3668-3688. 

An elimination of ammonia from LXXXIV to purine followed by reduction of the latter may also be possible [468] such a reduction route is analogous to that of 4-amino-quinazoline in acid solution [409], in which quinazoline can be detected as an intermediate during the reduction. A similar reaction, a reduction followed by elimination of an amine and further reduction is found for the herbizide hexazinone (3-cyclohexyl-6-(dimethyla-mino)-1 -methyl-1.3.5-triazine-2,4( 1 H,3H)-dione [469]. 

Pyrolysis results for poly(N-isopropylacrylamide), CAS 25189-55-3, with the idealized formula -CH2-CH[CONH(i-C3H7)]- n are very similar to that of poly(acrylamide). The reaction of elimination of 2-propanamine that was detected in the pyrolysate is similar to the elimination of ammonia from polyacrylamide. A pyrogram of a poly(N-isopropylacrylamide) sample with M = 20,000-25,000 is shown in Figure 6.7.18. The conditions for pyrolysis and for the analysis of pyrolysate were the same as those used for the analysis of other example polymers previously discussed (see Table 4.2.2). The peak identification in the pyrogram was done using MS library searches and is given in Table 6.7.12. 

The reaction of elimination of 2-propanamine, shown below, takes place at a lower extent compared to the elimination of ammonia from polyacrylamide, and a relatively larger amount of monomer is generated from the pyrolysis of the N-substituted polymer ... 

Thermal elimination of ammonia from malonyldisulfamide yields dithia-triazocine 240 (48AG316), and alkylation of benzothiadiazine 27 with methylene iodide produces the dimeric compound 32 (71M1055). 

In the case of HDN, an additional interesting possibility also consistent with the heterolytic mechanism arises, since substrates like the pyridines -or intermediate alkyl or aryl amines- are sufficiently basic to promote the activation of hydrogen so as to form a metal hydride plus a protonated base (e.g. a pyridinium or an alkylammonium cation). Furthermore, some of the most widely accepted amine HDN mechanisms include the initial protonation of the amine nitrogen, followed by elimination of ammonia from the ammonium cation. Therefore, it is very easy to combine the idea of a heterolytic hydrogen activation promoted by, say n-pentylamine, with a subsequent degradation by a Hoffmann mechanism, to conform a reasonable HDN catalytic cycle. A simplified representation of this idea is given in Fig. E4. 

Maquestian et al. (84BSB1073) (Scheme 112) describe the reaction of pyrazol-3-ones 363a-e with ethyl 3-aminobut-2-enoate 364 as taking place in two steps, possibly because intermediate 365 is relatively stable. After initial conjugate addition, elimination of ammonia from 365 yields (E/Z) ethyl 3-(5-oxopyrazol-4-ylidene)butanoates 366a-e. 

Enzymes can be either totally specific for a given substrate, to such an extent that they will not tolerate any structural or configurational changes in the substrate, or they can be broadly specific for a given type of functional group, and they will still operate on substrates with structural variations around that functional group. An example of the former is the enzyme aspartase, Asp, which catalyzes both the addition of ammonia to fumaric acid and the elimination of ammonia from L-aspartic acid by the following reactions ... 

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