Schiff bases from carbonyl compounds

The carbonyl compounds (100 pi of each) were shaken with 100 ml of saturated 2,4-dinitrophenylhydrazine 

4-DinUrophenylhydrazjones from carbonyls in liquid soaps, organic binders and engine exhaust [28] 

The steroid (O.l-l.Omg) was dissolved in 0.1-0.2ml of anhydrous N,N-dimethylhydrazine and about 0.05 ml of glacial acetic acid was added as catalyst, if necessary. After 1-2 h at room temperature, the excess reagent was removed in a stream of N2. The residue was dissolved in tetrahydrofuran and the solution was used directly for GC on a column of 1% SE-30 on Gas-Chrom P. 

The position of the carbonyl group and the reaction conditions determined the extent of the condensation reaction. A quantitative reaction in 1-2 h at room temperature occurred for 3-ones. A catalytic amount of acetic acid was necessary for 20-, 16- and 17-ones. The 11-keto group failed to react even after 12 h. 

Aliquots of carbonyl compounds (200—500/xg each) in aqueous solution were placed in 15 ml vials with Teflon-lined screw-caps. The volume was adjusted to 10 nJ with distilled water and 50 mg of O-benzylhy-droxylamine (BHA) or p-nitrobenzylhydroxylamine was added, followed by 10 drops of triethylamine. The sealed vials were heated at 65-70 °C for 1 h and allowed to cool. The solutions were transferred to 60 ml separatory funnels, acidified with 2 ml of 2N HCl and extracted with three 3 ml portions of diethyl ether. The ether was evaporated to near dryness using N2 at room temperature and the volume was reconstituted to 1 ml. Aliquots of 0.1—0.3 y were injected for GC with N-selective thermionic detection. 

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Electron-withdrawing substituents will favor the addition by increasing the positive character of the carbonyl carbon atom, thereby making it more susceptible to nucleophilic attack. Positive p (or p ) values obtained in Hammett plots for equilibrium and rate constants of the addition step verify the destabilization of the carbonyl compound relative to the carbinolamine by electron-withdrawing substituents. The p value for the equilibrium constants of the addition step in semicarbazone formation from substituted benzaldehydes is +1-81 while that for Schiff base formation from toluidine and substituted benzaldehydes, which follows a more closely than a, has a. p value of -I-0-66 . The p" " value for the rate constants of the addition step in semicarbazone formation from substituted benzaldehydes is + 0-94 , while that for the addition step leading to benzyhdene-aniline formation is +0 39 . The apparently uncatalyzed addition of nitrogen bases to carbonyl compounds is more susceptible to inductive effects than is the acid-catalyzed addition. In the case of semicarbazide attack on substituted benzaldehydes p = +0-94 for the water-catalyzed and +0-71 for the hydronium ion-catalyzed addition step... 

Schiff bases formed from carbonyl compounds and miscellaneous primary amines have seen occasional use for protection. In the steroid field a A -3-ketone group reacts preferentially with benzylamine in the presence of another at C20 [201] and in the case of a 3,6-diketone the one at C3 reacts preferentially with o-phenylene diamine [202, 203]. 

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. 

The process can be still more simplified. It is not always necessary to use a pre-formed Schiff s base. Often it is sufficient to bring the carbonyl compound and the amine together in an inert solvent and to add the peracid to the mixture later, - In this way oxaziranes can be obtained in good yield even if the Schiff s base is unknown or can only be obtained in poor yield. For example, formaldehyde gives with aliphatic amines usually only trimers of the Schiff s bases (4). On the other hand, the synthesis of 2-cyclohexyl-oxazirane (5) from cyclohexylamine, formaldehyde, and peracetic acid proceeded in 66%... 

When monomeric metaphosphate anion POf (102) is generated form the phos-phonate dianion 170 in the presence of the hindered base 2,2,6,6-tetramethylpiper-idine, it undergoes reaction with added carbonyl compounds147), Thus, it phosphoryl-ates acetophenone to yield the enol phosphate, whereas in the presence of acetophenone and aniline the Schiff base is formed from both compounds, probably by way of the intermediate C6H5—C(CH3) (OPO e) ( NH2C6HS). This reactivity pattern closely resembles that of monomeric methyl metaphosphate 151 (see Sect. 4.4.2). 

Schiff bases provide useful mixed donor sets. The carbonyl function of the most frequently used ligands is derived from either 1,3-dicarbonyl compounds or salicylaldehyde. Favourable combinations involve O-, N- and S-donor atoms. A range of technetium and rhenium complexes exist with bi-, tri-, tetra- and pentadentate ligands. The geometry of these complexes depends on the number and type of coordinating atoms as well as on the chain length between the donor atoms in the SchifF-base ligands. 

The synthesis of phthalimidines by dicobalt octacarbonyl-catalyzed carbonylation of Schiff bases was first described by Pritchard78 and the scope of the reaction was evaluated by Murahashi et a/.79 Later Rosenthal et al.80-83 subjected a variety of related compounds to carbonylation, and also achieved a phthalimidine synthesis directly from benzonitrile under the conditions of the oxo process.84 An example illustrating the formation of a phthalimidine is shown in Scheme 49 a comprehensive review of the scope and mechanism of reactions of this type is available.85... 

The practical applications of NaBH4 reductions on mineral surfaces for in situ generated SchifFs bases have been successfully demonstrated. The solid-state reductive amination of carbonyl compounds on various inorganic solid supports such as alumina, clay, silica etc. and especially on K 10 clay surface rapidly afford secondary and tertiary amines [126]. Clay behaves as a Lewis acid and also provides water from its interlayers thus enhancing the reducing ability of NaBH4 [22],... 

A class of ligands which is very flexible in terms of its denticity, donor atom geometry, and steric demands are Schiff bases derived from salicyladehyde or related carbonyl compounds carrying additional hydroxo groups. The use of bi- and tridentate ligands of this type allows the synthesis of mixed-chelate complexes with a number of O N, N N or N S bidentate ligands. The products are of considerable interest for nuclear medical applications as well as for homo-... 

According to the Cd 18-90 AOCS ° official method, the ANV is 100 times the optical density measured in a 1 cm cell, at 350 nm, of a solution containing 1.00 g of oil in 100 ml of the test solution. The measured absorbance is due to Schiff bases (167) formed when p-anisidine (166) undergoes condensation reaction with carbonyl compounds, according to equation 55. The carbonyl compounds are secondary oxidation products of lipids, such as a, S-unsaturated aldehydes and ketones derived from the hydroperoxides (see Scheme 1 in Section n.A.2.c), and their presence points to advanced oxidation of the oil. 

Other organic mediators act as hydride atom-abstracting agents. This is true, for example, with 2,2-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and the oxoammonium ion which is anodically accessible from 2,2,6,6-tetramethylpiperidyl oxide (TEMPO). DDQ has been electrochemically regenerated either externally or internally The in situ electrochemical oxidation, of TEMPO to the active oxoammonium ion is performed in lutidine-containing acetonitrile. Thus, primary alcohols can be oxidized to the aldehydes, while secondary ones are stable Primary amines are transformed to nitriles. If water is present, the amines are cleaved via the Schiff bases to the corresponding carbonyl compounds... 

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