Schiff base, hydrolyses

A very simple and elegant alternative to the use of ion-exchange columns or extraction to separate the mixture of D-amino add amide and the L-amino add has been elaborated. Addition of one equivalent of benzaldehyde (with respect to die D-amino add amide) to the enzymic hydrolysate results in the formation of a Schiff base with die D-amino add amide, which is insoluble in water and, therefore, can be easily separated. Add hydrolysis (H2SQ4, HX, HNO3, etc.) results in the formation of die D-amino add (without racemizadon). Alternatively the D-amino add amide can be hydrolysed by cell-preparations of Rhodococcus erythropolis. This biocatalyst lacks stereoselectivity. This option is very useful for amino adds which are highly soluble in die neutralised reaction mixture obtained after acid hydrolysis of the amide. 

Hydrolyses of Schiff Bases. The behavior of Schiflf bases and their complexes has been sufficiently studied so that the similarities of the kinetic paths of their hydrolyses can be clearly delineated. The reaction is interpreted in terms of a change in the rate determining step as the pH is changed. In neutral solutions the rate determining step is considered (7) the hydration step ... 

The kinetic parameters above are very similar to those for the hydrolysis of a simple Schiff base, benzalaniline, having an activation energy of 13.2 kcal. and an entropy of activation of about —37 e.u. (40). It appears that the rate determining step for hydrolyses of the complexes is the second step, the splitting off of the aldehyde. Under suitable conditions, the intermediates in such hydrolyses for bis complexes (of Schiff bases derived from ethylenediamine) have been isolated. Only one of the ligands is hydrolyzed, and the nitrogen which had been present in the Schiff base is still coordinated to the central metal (17). 

Mark M. Jones There is one change that I could make in the paper. About ten years ago Daryle Busch and John Bailar (1) reported an intermediate type described under hydrolyses of Schiff bases, and I want to apologize for omitting it in the literature. 

In a 500 ml. flask, fitted with a reflux condenser, place 53 g. of 1-chloro-methylnaphthalene (Section IV,23), 84 g. of hexamethylenetetramine and 250 ml. of 1 1 acetic acid [CAUTION 1-Chloromethylnaphtha-lene and, to a lesser degree, a naplithaldehyde have lachrymatory and vesicant properties adequate precautions should therefore be taken to avoid contact with these substances.] Heat the mixture under reflux for 2 hours it becomes homogeneous after about 15 minutes and then an oil commences to separate. Add 100 ml. of concentrated hydrochloric add and reflux for a further 15 minutes this will hydrolyse any SchifFs bases which may be formed from amine and aldehyde present and will also convert any amines into the ether-insoluble hydrochlorides. Cool, and extract the mixture with 150 ml. of ether. Wash the ether layer with three 50 ml. portions of water, then cautiously with 50 ml. of 10 per cent, sodium carbonate solution, followed by 50 ml. of water. Dry the ethereal solution with anhydrous magnesium sulphate, remove the ether by distillation on a steam bath, and distil the residue under reduced pressure. Collect the a-naphthaldehyde at 160-162°/18 mm. the yield is 38 g. 

The evidence for the intermediate is that the enzyme is irreversibly inhibited when sodium borohydride is added to the complex with the substrate. Borohy-dride is known to reduce Schiff bases, and the hydrolysate of the inhibited protein is found to contain isopropyl-lysine (equation 2.38). The carbon in the Schiff base is activated to the attack of... 

The effects of surfactants on the hydrolyses of Schiff bases are given in Table 10. 

Investigation of the mechanism of these reactions has suggested ways in which the yields can be improved. Acidic conditions (pH 2) will prevent Cannizzaro rearrangement of any glyoxal-type species and also serve to hydrolyse any Schiff bases which result from side reactions of aldehyde and amine. Conditions should be adjusted so that the rate of hydrolysis of linear products is equal to the rate of cyclocondensation, allowing accumulation of the imidazole products. From glyoxal, formaldehyde and ammonium chloride the yield of imidazole can be inereased to 85% by careful control of the conditions. With an appropriate alkylammonium chloride, 1-substituted imidazoles are also accessible (e.g. 1-methyl (56%), 1-isopropyl (46%), 1-cyclohexyl (49%), 1-n-butyl (55%), 1-t-butyl (25%)). The process may have some applications, but yields drop off with branched alkyl compounds [22 j. Imidazolium salts are also available under similar conditions when two molar equivalents of a primary alkylamine are used [23]. 

This Schiff base (biochemists call iminesSchIff bases) is in equilibrium with an isomeric imine, which can be hydrolysed to pyridoxal and alanine. These reactions are, of course, all controlled by enzymes, and coupled to the degradation of unwanted amino acids (the latter process... 

Other derivatives that can be prepared are the Schiff bases and semicarbazones. Condensation of the aldehyde with an equivalent of primary aromatic amine yields the Schiff base, for example aniline at lOtP for 10-30minutes. Semicarbazones are prepared by dissolving semicarbazide hydrochloride ca Ig) and sodium acetate (ca 1.5g) in water (8-lOmL) and adding the aldehyde or ketone (0.5-lg) with stirring. The semicarbazone crystalhses out and is recrystallised from ethanol or aqueous ethanol. These are hydrolysed by steam distillation in the presence of oxalic acid or better by exchange with pyruvic acid (Hershberg7 Org Chem 13 542 1948) [see entry under Ketones]. 

Anil formation can also be effected in alcoholic solution in the presence of catalytic amounts of sodium carbonate or piperidine the Schiff bases (usually deeply colored) are then precipitated and can be hydrolysed by acid in the usual way. 

Oxidation of primary aliphatic amines by sodium perpxysulfate in an alkaline medium containing catalytic amounts of silver nitrate affords Schiff bases, which are hydrolysed by boiling 2N-hydrochloric acid in 10 min to the initial amine and the aldehyde 598 the yields of aldehyde are between 15% and 95%. 

Most ketals are hydrolysed instantaneously by very dilute acid. Cyclic acetals and ketals are relatively stable, as are acetals of aldehydes containing basic groups. Hydrolysis of the last-mentioned class may lead to aldol condensation or formation of the Schiff base, so that concentrated acids are used in such cases. 

Another unequivocal method of converting primary into secondary amines involves intermediate formation of Schiff bases and their quaternization. The quaternary salts are obtained almost quantitatively by heating the base with a lower alkyl halide in a sealed tube for several hours they are readily hydrolysed to the secondary amine. Benzaldehyde is usually taken to form the Schiff base. A number of A-alkyl-/ -methylphenethylamines have been prepared in excellent yield by this route.496 Also the allylmethylamine described above was obtained from allylamine in 71% yield by way of the anil.497... 

The usual procedure in practice is to boil the a-oxo acid with aniline until loss of water is complete then the water and aniline are distilled off, the residue is taken up in mineral acids, which hydrolyse the Schiff base, and the aldehyde produced is then isolated. This can be exemplified by directions for preparation of p-propylbenzaldehyde 40... 

The coenzyme-enzyme Schiff base in aspartate aminotransferase was reduced with NaB H4, and the resulting derivative hydrolysed to give [4 - H]pyridoxyl-lysine. The latter on A-chlorination, followed by base catalysed dehydrohalogenation gave... 

All nematic liquid crystal mixtures have good lubricating properties at room temperature. However, those having an azomethine central link (Schiff bases) as EBBA, MBBA or ROTN 200 are unstable in humid atmosphere because they hydrolyse. 

The presence of the l,ll-diamino-6-oxoundecane in hydrolysates of heat-treated nylon-6 [359] thus is obviously the result of the hydrolysis of the Schiff base moiety. The absence of the corresponding oxo-structure in the hydrolysates of gelled nylon-6,6 may be indicative of an analogous decarboxylation mechanism entailing intramolecular acid amide interaction Hydrolysis of the Schiff base structure yields, as indicated, hexamethylene diamine and cyclopentanone, both of which have been found. 

The very different basicities of water and of ammonia lead to different reactivity patterns for iSNlcb base hydrolyses of cobalt(iii) compounds. The latest contribution in this area has been a study of base hydrolysis of a series of complexes [Co(NH3)6(RNHa)] + in liquid ethylenediamine. The basicity or solvating power of the solvent determines the form of the rate law for substitutions at copper(ii)-Schiff base complexes. The term corresponding to solvolysis is, of course, only significant for solvents with an affinity for copper(ii). ... 

Thiazetidine 1,1-dioxide, prepared by the cyclization of 2-amino-ethanesulphonyl chloride hydrochloride under dry basic conditions, reverted to starting material on treatment with hydrogen chloride in dry solvents, but with water it hydrolysed slowly to taurine. Benzoylsulphene, generated by treatment of benzoylmethanesulphonyl chloride with triethylamine, underwent [2 + 2]cycloaddition with anils to give 1,2-thiazetidine 1,1-dioxide derivatives. With benzylidene-alkylamines the only products in the presence of triethylamine were those of [4 + 23-cycloaddition, but, unexpectedly, in the absence of triethylamine, 1,2-thiazetidine 1,1-dioxide derivatives were also formed benzylideneaniline gave only 4-benzoyl-2,3-diphenyl-l,2-thiazetidine 1,1-dioxide, and other Schiff-bases reacted similarly. ... 

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