Aminal, formation

DCHA is normally obtained in low yields as a coproduct of aniline hydrogenation. The proposed mechanism of secondary amine formation in either reductive amination of cyclohexanone or arene hydrogenation iHurninates specific steps (Fig. 1) on which catalyst, solvents, and additives moderating catalyst supports all have effects. 

Alkali moderation of supported precious metal catalysts reduces secondary amine formation and generation of ammonia (18). Ammonia in the reaction medium inhibits Rh, but not Ru precious metal catalyst. More secondary amine results from use of more polar protic solvents, CH OH > C2H5OH > Lithium hydroxide is the most effective alkah promoter (19), reducing secondary amine formation and hydrogenolysis. The general order of catalyst procUvity toward secondary amine formation is Pt > Pd Ru > Rh (20). Rhodium s catalyst support contribution to secondary amine formation decreases ia the order carbon > alumina > barium carbonate > barium sulfate > calcium carbonate. 

Reactions of the carboxyl group include salt and acid chloride formation, esterification, pyrolysis, reduction, and amide, nitrile, and amine formation. Salt formation occurs when the carboxyUc acid reacts with an alkaline substance (22)... 

V-(l-Isopropyl-4-nitro-2-oxo-3-pyrrolin-3-yl)amine Formation/Cleavage ... 

Enamines derived from aldehydes can usually be obtained by the reaction of 2 equivalents of a secondary amine with the carbonyl compound, in the presence of anhydrous potassium carbonate, followed by pyrolytic distillation of the aminal with elimination of one of the amine groups (10,15, 30-36). Ketones are directly converted to enamines under the conditions of aminal formation. The azeotropic removal of water with excess aldehyde has also been described (32,37). 

Reductive alkylation with chiral substrates may afford new chiral centers. The reaction has been of interest for the preparation of optically active amino acids where the chirality of the amine function is induced in the prochiral carbonyl moiety 34,35). The degree of induced asymmetry is influenced by substrate, solvent, and temperature 26,27,28,29,48,51,65). Asymmetry also has been obtained by reduction of prochiral imines, using a chiral catalyst 44). Prediction of the major configurational isomer arising from a reductive alkylation can be made usually by the assumption that amine formation comes via an imine, not the hydroxyamino addition compound, and that the catalyst approaches the least hindered side (57). 

A common technique for minimizing secondary amine formation is to carry out the hydrogenation in the presence of ammonia (21,23,42). Ammonia is thought to complete with the primary amine in attack on the intermediate imine. Anhydrous ammonia is preferred to prevent hydrolysis reactions,... 

Solvents influence the hydrogenation of oximes in much the same way as they do hydrogenation of nitriles. Acidic solvents prevent the formation of secondary amines through salt formation with the initially formed primary amine. A variety of acids have been used for this purpose (66 ), but acids cannot always be used interchangeably (43). Primary amines can be trapped also as amides by use of an anhydride solvent (2,/5,57). Ammonia prevents secondary amine formation through competition of ammonia with the primary amine in reaction with the intermediate imine. Unless the ammonia is anhydrous hydrolysis reactions may also occur. 

Z)-compounds are formed in reactions with hydroxide, methoxide, cyanide, and sulfite ions, whereas (ii)-compounds are formed in most reactions with amines (formation of triazenes) and with diazo coupling components such as phenols and aromatic tertiary amines. 

BRITT c, GOMAA E A, GRAY j I and BOOREN A M (1998) Influence of cherry tissue on lipid oxidation and heterocyclic aromatic amine formation in groimd beef patties, JAgric Food Chem, 46, 4891-7. 

The mechanism of NPYR formation has been studied by Coleman (37) and Bharucha et al. ( ). Coleman (37) reported that the requirement for a high temperature, the inhibitory effects of water and antioxidants, and the catalytic effect of a lipid hydroperoxide are consistent with the involvement of a free radical in the formation of NPYR. Similarly, Bharucha et al. (29) suggested that, since both NPYR and NDMA increase substantially towards the end of the frying process, N-nitros-amine formation during frying of bacon occurs essentially, if not entirely, in the fat phase after the bulk of the water is removed and therefore by a radical rather than an ionic mechanism. These authors speculated that, during the frying of... 

Research on the formation of NDMA in beer has centered on three possible sources of amine precursors (74). N-Nitros-amine formation from amines such as hordenine, famine and methyltyramine which are formed endogenously in the germination of barley has been discussed elsewhere in this symposium (75). The Brewers Association of Canada (74) investigated the... 

Supported iron catalysts are notoriously difficult to reduce [6-8] and thus a substantial fraction of the iron can be expected to remain inactive for the catalysis of hydrogenation. Particular attention has therefore been paid to the preparation of Fe/MgO catalysts by several different methods and examination of their effectiveness in producing metallic iron of adequate specific surface area after reduction in hydrogen. The activity and selectivity for primary amine formation have been determined for the hydrogenation of ethanenitrile (acetonitrile) and propanenitrile. 

Complex amine formation from cyclic anhydride and aromatic amine formation of triaryl phosphine Sterling Organics Amery et al. (1994)... 

Isophorone diamine is synthesized traditionally by aminoreduction of iso-phoronenitrile. Raney cobalt was used for this process. More recently, a new two-step process was patented. The first step consists of synthesizing the imine and the second one of hydrogenating the latter. Ra-Ni was used as catalyst at 150°C and 60 bar hydrogen pressure. Under these conditions, the catalyst reduces the nitrile groups and is able to cleave the N-N bonds, too. Ammonia is required to promote primary amine formation during nitrile hydrogenation (Scheme 4.151).554... 

The intramolecular insertion reactions of nitrenoids into G-H bonds as described above provide an attractive alternative to conventional methods of amine formation. Both carbamate and sulfamate C-H insertions have been applied successfully to the total syntheses of natural products. - The first application of carbamate G-H insertion was reported by Trost in the total synthesis of methyl-L-callipeltose 118 (Equation (92)).230 Intermolecular G-H insertion of carbamate 117 using 10mol% Rh2(OAc)4, PhI(OAc)4, and DTBMP (2,6-di-/ / -butyl-4-methylpyridine) in dichloromethane (40 °C) furnished methyl-L-callipeltose 118 in 63% yield. In an another independent total synthesis of 118, Panek performed this step in refluxing benzene and improved the yield to 93%.231... 

Homoallylic amine formation resulting from a change in the mode of addition of reagents. 

The activity of decarboxylase can be an indirect measurement of the potential for biogenic amine formation. A study by Middlebrooks et al. (1988)... 

Biogenic amine formation in fish and fish products. 

Hernandez-Jover, M., Izquierdo-Pulido, M., Veciana-Nogues, M.T., Marine-Font, A. and Vidal-Carou, M.C. (1997). Effect of starter cultures on biogenic amine formation during fermented sausage production, J. Food Prot., 60, 825. 

Wendakoon, C., Murata, M. and Sakaguchi, M. (1990). Comparison of nonvolatile amine formation between the dark and white muscles of mackerel during storage, Nippon Suisan Gakkaishi, 56, 809. 

Wendakoon, C. and Sakaguchi. M. (1992A). Elfects of spices on growth of and biogenic amine formation by bacteria in fish muscle, in Huss, H., Jakobsen, M. and Liston, J., Quality Assurance in the Fish Industry, Developments in Food Science, Elsevier, Amsterdam, pp. 305-313. 

Scheme 32 Further examples of amine formation from alcohols...

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