Amines replacement reactions

Primary and secondary amines are susceptible to oxidation and replacement reactions involving the N—H bonds. Within the development of peptide synthesis numerous protective groups for N—H bonds have been found (M, Bodanszky, 1976 L.A. Carpino, 1973), and we shall discuss five of the more general methods used involving the reversible formation of... 

A liquid-phase double-replacement reaction between bromine cyanide (A) and methyl-amine takes place in a PFR at 10°C and 101 kPa. The reaction is first-order with respect to each reactant, with kA = 2.22 L mol 1 s 1. If the residence or space time is 4 s, and the inlet concentration of each reactant is 0.10 mol L-1, determine the concentration of bromine cyanide at the outlet of the reactor. 

Some reactions of 2,2 -bipyridine /V-oxides have been reported. The l,T-dioxide is nitrated readily to 4,4 -dinitro-2,2 -bipyridine 1,T-dioxide. ° ° °" 2,2 -Bipyridine 1-oxide is also nitrated in the 4 position. The nitro groups in 4,4 -dinitro-2,2 -bipyridine l,T-dioxide are reactive, being replaced by chlorine with concentrated hydrochloric acid," by bromine with acetyl bromide, by hydroxyl with dilute sulfuric acid, and by alkoxy groups with sodium alkoxides. Some of the dialkoxy derivatives are useful catalysts for the oxidation of aromatic compounds. The dinitro dioxide is deoxygenated to 4,4 -dinitro-2,2 -bipyridine with phosphorus trichloride in chloroform, and other substituted l,T-dioxides behave similarly, but with phosphorus trichloride alone, 4,4 -dichloro-2,2 -bipyridine results. The dinitro dioxide is reduced by iron powder in acetic acid to 4,4 -diamino-2,2 -bipyridine, whereas 4,4 -dichloro-2,2 -bipyridine l,T-dioxide is converted to its 4,4 -diamino analogs with amines. Related reactions have been described. ... 

Thioxo and alkylmercapto groups are easily replaced by other groups. The sulfur in the 5-position of the 1,2,4-triazine ring is the most reactive and is replaced initially. Water, alcohols, amines, hydrazine and hydroxylamine can replace the thioxo or alkylmercapto group. Scheme 10 summarizes these reactions. Since the preparation of 3-thioxo-l,2,4-triazines is very easy and proceeds in high yield, these replacement reactions at the 3-position are of much preparative value. 

Methylthio substituents in position 2 or 5 are replaced by ethoxy groups on reaction with sodium ethoxide.46,50 Similarly, aliphatic amines replace methylthio substituents by alkylamino groups.50... 

Primary and secondary amines react with acid halides to form amides. This reaction is a nucleophilic acyl substitution the replacement of a leaving group on a carbonyl carbon by a nucleophile. We will study nucleophilic acyl substitution in detail in Chapters 20 and 21. In this case, the amine replaces chloride ion. 

With a primary amine, the reaction need not stop at that stage as the product is still nucleophilic and a second addition can occur to replace the second hydrogen atom on nitrogen. 

Additional reactions which need to be highlighted are the reductive alkylation of alcohols and amines with aldehydes leading to the green synthesis of ethers and amines. These reactions are generally catalyzed by palladium [35]. This reaction can replace the classical Williamson s synthesis of ethers which requires an alcohol and an alkyl halide together with a base, and always results in the concomitant production of salt. The choice of Pd/C as catalyst is due to the low efficiency of this metal for the competitive carbonyl reduction. Analysis of the... 

Just as primary aromatic amines replace the CH3S group of the isotrithionium salts (259) to form protonated anils or hydrazones (261), the reaction with aliphatic amines such as piperidine or morpholine leads to 303. 

On the other hand, conjugated nitroalkenes are very useful electron-poor alkenes, prone to act as nucleophilic acceptor, mainly in the Michael reaction (Berestovitaskaya et al., 1994) or in the Diels-Alder cycloaddition (Denmark and Thorarensen, 1996). Moreover, the nitro group can be easily turned into a respectable array of functional groups such as its reduction to a primary amine, replacement with hydrogen (Ballini et al., 1983 Ono, 2001), conversion into a carbonyl (Nef reaction) (Ballini and Petrini, 2004), and transformation into other important functionalities such as nitrile, nitrile oxide, oximes, hydroxylamines, and thiols (Colvin et al., 1979). 

Vitamin Be has a central role in the metabolism of amino acids in transaminase reactions (and hence the interconversion and catabolism of amino acids and the synthesis of nonessential amino acids), in decarboxylation to yield biologically active amines, and in a variety of elimination and replacement reactions. It is also the cofactor for glycogen phosphorylase and a variety of other enzymes. In addition, pyridoxal phosphate, the metabolically active vitamer, has a role in the modulation of steroid hormone action and the regulation of gene expression. 

A very wide range of Mannich bases can be subjected to replacement reaction with —SH derivatives, including ketobases producing optically active y-ketosulfides [275, R = PhCO-CH(Me) , when the reaction is carried out in the presence of catalytic amounts of chiral amine of the cinchonidinc type. ... 

Deamination has also been recognized as the rate-determining step in some replacement reactions carried out on phenolic and indolic Mannich ba-ses. - In phenolic derivatives, in particular (Fig. 88), a pre-equilibrium takes place similar to that described above for p-aminoketones, and is followed by the elimination of amine via an E cB-type mechanism. ... 

Although in many cases products 256 can be directly prepared by Mannich synthesis, the replacement reaction is particularly convenient (l)in the case of primary amines, as it yields a secondary amine derivative hardly obtainable through other synthetic routes, and (2) in the case of arylamincs, as it makes it possible to avoid engaging an activated, reactive, aryl group in the direct Mannich reaction. Moreover, the method is frequently adopted in the synthesis of polymeric substances (Chap. III). 

In contrast to the preceding carbonyl group reactions, cations [(CgHg)Mn(CO)3] and [(MegCg)Re(CO)3] reacted with primary amines with loss of the arene group to give derivatives of the type [(RNH2)3M(C0)3] 14). Arene replacement reactions have also been... 

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