Schiff base amines

Abbreviations NH3/RCN molar ratio t=reaction time C=conversion of nitrile RNH2, SB and R2NH=selectivity of primary amine, Schiff-base and secondary... 

The malonaldehyde-amine reaction has been extensively studied by Tappel and co-workers (2), by Csallany et al. (3), by Privett and co-workers (4), Knook et al. (5), Buttkus and Bose (6 ), as well as many others. As shown in Figure 1, malonaldehyde may react with a primary amine to produce an initial ene-amine Schiff base ( 7 ), then by further condensation with another amine, an amino-imino-propene compound. Heat and acid are required in the usual model reaction. The model compounds (lysine with malonaldehyde, for example) fluoresce between 430 and 470 nm when excited between 350 and 360 nm (8). These are typical of the "aging" pigments, the organic solvent-soluble lipofuscin in oxidizing tissue. 

Aldehyde Amine carbohydrates Aldehyde-amine Schiff base or glycosylamine... 

Thus, the majority of the catalytic power of acetoacetate decarboxylase resides in the properties of the catalytic amino group. The remaining rate enhancement may be principally due to conformational effects. In solution, it is likely that an acetoacetate-amine Schiff base will exist in a planar conformation not suitable for decarboxylation. The enzyme can enforce the proper conformation, thus presumably providing the final catalytic factor. 

Dialkyl phosphites react with (hydroxymethyl)amines, giving a-amino phosphonic esters the same products can often be obtained by reaction of the phosphite with aminals, Schiff bases, or an aldehyde plus an amine321 (cf. page 708). Free phosphorous acid can itself be a-aminoalkylated in an acid medium, when according to the amine selected (ammonia can also be used) up to three methylenephosphonic acid groups can be attached to one nitrogen atom 322... 

Acylation is the most common method as amides are preferred over other kinds of derivatives. Their basicity is significantly less than that of amines and, hence, the pH of samples indicates that the influence is not as strong as on initial amines. Schiff bases and especially iV-trimethyl-silyl (TMS) derivatives are sensitive to postreaction hydrolysis. 

Chemical Stability Since all inhibitors contain functional groups (carboxylic acids, amines, Schiffs bases, phosphates, phosphonates, sulfur derivatives, and many more), they are pH sensitive, and therefore, their activity varies over actually fairly narrow pH ranges. For example, it has been shown that certain amines in sour systems lose activity if the pH of the environment shifts from 4 to 7 [S], while in CO2 systems the reverse has been observed [9]. 

After oxidation, the tissue slides are washed and tested for aldehydes. Schifif s reagent is almost always used. Insoluble aldehydes are colored red. The intensity of color is generally assumed to indicate the amounts of aldehyde produced and of the presumed vicinal glycols initially present. Other aldehyde reactions, such as the formation of some colored Schiflf bases 49), or the reduction of alkaline silver nitrate 48), have sometimes been used. The relative intensity of reaction at particular tissue sites will differ somewhat with various aldehyde reagents. After oxidation by periodic acid, glycogen is diflScult to color by certain organic amines (Schiff-base... 

When diethyl ketals are refluxed with primary amines, Schiff bases are obtained (equation 8) . Aromatic amines give considerably better yields than aliphatic amines. 

Sharif, S., Powell, D.R., Schagen, D., Steiner, T.M., Toney, M.D., Fogle, E., and Limbach, H.H. (2008) X-ray crystallographic structures of enamine and amine Schiff bases of pyridoxal and its 1 1 hydrogen bonded complexes with benzoic acid derivatives evidence for... 

So, how does this whole thing work It s as simple as it sounds. An alcoholic solution of nitromethane and MDP2P is dripped into a mass of amalgamated aluminum immersed in alcohol first reducing the nitromethane to methylamine, allowing the Schiff base of the amine and ketone to form which is then further reduced to the desired MDMA. 

The nucleophilicity of amine nitrogens is also differentiated by their environments. In 2,4,5,6-tetraaminopyrimidine the most basic 3-amino group can be selectively converted to a Schiff base. It is meta to both pyrimidine nitrogens and does not form a tautomeric imine as do the ortho- and /xira-amino groups. This factor is the basis of the commercial synthesis of triamterene. 

The Schiff base obtained is converted in good yield (60 to 80%) to amines by the action of Raney Ni (209). This reductive condensation provides a good synthetic method and was used to prepare thiazole analogs (62) of folic acid (Scheme 43) (210). These Schiff bases under... 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

Primary amines form Schiff bases, (CH3 )2C=NR. Ammonia induces an aldol condensation followed by 1,4-addition of ammonia to produce diacetone amine (from mesityl oxide), 4-amino-4-methyl-2-pentanone [625-04-7] (CH2)2C(NH2)CH2COCH2, and triacetone amine (from phorone),... 

Analogously, aldehydes react with ammonia [7664-41-7] or primary amines to form Schiff bases. Subsequent reduction produces a new amine. The addition of hydrogen cyanide [74-90-8] sodium bisulfite [7631-90-5] amines, alcohols, or thiols to the carbonyl group usually requires the presence of a catalyst to assist in reaching the desired equilibrium product. 

Pentafluoroaniline. Pentafluoroaniline [771 -60-8] i2is been prepared from amination of hexafluoroben2ene with sodium amide inbquid ammonia or with ammonium hydroxide in ethanol (or water) at 167—180°C for 12—18 h. It is weakly basic (p = 0.28) and dissolves only in concentrated acids. Liquid crystals have been prepared from Schiff bases derived from pentafluoroaniline (230). 

Reactions with Amines and Amides. Hydroxybenzaldehydes undergo the normal reactions with aUphatic and aromatic primary amines to form imines and Schiff bases reaction with hydroxylamine gives an oxime, reaction with hydrazines gives hydrazones, and reactions with semicarbazide give semicarbazones. The reaction of 4-hydroxybenzaldehyde with hydroxylamine hydrochloride is a convenient method for the preparation of 4-cyanophenol (52,53). 

Rhodium complexes with oxygen ligands, not nearly as numerous as those with amine and phosphine complexes, do, however, exist. A variety of compounds are known, iucluding [Rh(ox)3] [18307-26-1], [Rh(acac)3] [14284-92-5], the hexaaqua ion [Rh(OH2)3] [16920-31 -3], and Schiff base complexes. Soluble rhodium sulfate, Rh2(804 )3-a H2 0, exists iu a yellow form [15274-75-6], which probably coutaius [Rh(H20)3], and a red form [15274-78-9], which contains coordinated sulfate (125). The stmcture of the soluble nitrate [Rh(N03)3 2H20 [10139-58-9] is also complex (126). Another... 

Primary aromatic amines react with aldehydes to form Schiff bases. Schiff bases formed from the reaction of lower aUphatic aldehydes, such as formaldehyde and acetaldehyde, with primary aromatic amines are often unstable and polymerize readily. Aniline reacts with formaldehyde in aqueous acid solutions to yield mixtures of a crystalline trimer of the Schiff base, methylenedianilines, and polymers. Reaction of aniline hydrochloride and formaldehyde also yields polymeric products and under certain conditions, the predominant product is 4,4 -methylenedianiline [101 -77-9] (26), an important intermediate for 4,4 -methylenebis(phenyhsocyanate) [101-68-8], or MDI (see Amines, aromatic amines, l thylenedianiline). 

An important modification improves the yields by first reduciag the Schiff base to an amine, which is then cycli2ed to a 4-hydroxy iatermediate (167). This compound is converted to the 1,2,3,4-tettahydtoisoquinoline (34). The entire process takes place under mild conditions and ia good yield. 

Schiff bases, also known as imines, ate formed by the condensation of carbonyl compounds with ammonia or primary amines. Hydrogenation of the resulting Schiff bases forms amines, such as benzylamine and dibenzylamine. 

Dibenzjiamine, [103-49-17, CgH CH2NHCH2CgH (bp, 300°C at 101.3 kPa) is produced by reaction of benzyl amine with benzaldehyde and hydrogenation of the Schiffs base. It is used in mbber and tire compounding, as a corrosion inhibitor, and as an intermediate in the production of mbber compounds and pharmaceutical products. 

Most ring syntheses of this type are of modern origin. The cobalt or rhodium carbonyl catalyzed hydrocarboxylation of unsaturated alcohols, amines or amides provides access to tetrahydrofuranones, pyrrolidones or succinimides, although appreciable amounts of the corresponding six-membered heterocycle may also be formed (Scheme 55a) (73JOM(47)28l). Hydrocarboxylation of 4-pentyn-2-ol with nickel carbonyl yields 3-methylenetetrahy-drofuranone (Scheme 55b). Carbonylation of Schiff bases yields 2-arylphthalimidines (Scheme 55c). The hydroformylation of o-nitrostyrene, subsequent reduction of the nitro group and cyclization leads to the formation of skatole (Scheme 55d) (81CC82). 

Nitrogen chirality may also be produced by the action of an achiral peroxyacid on a Schiff base containing a chiral amine (75JOC3878). In this case the oxaziridine contains a configurationally known centre of chirality relative to this, absolute configurations of the centres of chirality at nitrogen and carbon, and thus the complete absolute configuration of the molecule, can be determined (see Section 5.08.2.2). 

It was reported only recently that A-methyl transfer from an oxaziridine to an amine occurs with formation of an N—N bond (79JA6671). N—N bond forming reactions with A-unsubstituted oxaziridines had been found immediately after discovery of this class of compound (64CB2521) and have led to simple hydrazine syntheses (79AHC(24)63). Secondary amines like diethylamine or morpholine are A-aminated by (52) in the course of some minutes at room temperature with yields exceeding 90% (77JPR195). Further examples are the amination of aniline to phenylhydrazine, and of the Schiff base (96) to the diaziridine (97). 

Oxaziridines are generally formed by the action of a peracid on a combination of a carbonyl compound and an amine, either as a Schiff base (243) or a simple mixture. Yields are between 65 and 90%. Although oxygenation of Schiff bases is formally analogous to epoxidation of alkenes, the true mechanism is still under discussion. More favored than an epoxidation-type mechanism is formation of a condensation product (244), from which an acyloxy group is displaced with formation of an O—N bond. 

This type of amination by an oxaziridine is assumed to be the key step of a novel process for hydrazine manufacture, in the course of which butanone in solution with ammonia is reacted with hydrogen peroxide and acetonitrile. The smooth formation of oxaziridines from Schiff bases and hydrogen peroxide-nitrile mixtures is as well known as NH transfer from an oxaziridine like (300), suggesting the intermediacy of (300) as the N—N forming agent (72TL633). 

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