Showing papers on "Schiff base published in 1968"

The preparation and magnetic properties of some Schiff base–iron(III) halide complexes

Abstract: The preparation and magnetic susceptibilities over the temperature range 80–300°K of eighteen iron(III)–Schiff base chloro- or bromo-complexes are reported. The complexes fall into two groups, uninuclear and binuclear. The magnetic data for the binuclear complexes have been interpreted by use of the dipolar coupling approach and values of the exchange integral, J, found to be in the range –6·5 to –8·0 cm.–1.

Mössbauer and infrared studies of some Schiff-base iron(III) compounds

Abstract: Previous studies on iron(III) Schiff-base compounds such as (Fe salen Cl) indicate that either dimeric or monomeric compounds can be prepared depending on the solvent used for recrystallization. These compounds usually contain one or more solvent molecules in the crystal structure. We report Mossbauer and i.r. spectra and magnetic susceptibilities of a number of iron(III) Schiff-base compounds, many of which have not been prepared previously.On recrystallization of (Fe salen Cl) and (Fe salen Br) from acetone, chloroform, methanol, and pyridine, very similar Mossbauer spectra are obtained, and the i.r. spectra all show a rather intense band around 850 cm.–1, which may be atributed to an Fe–O–Fe band. The evidence suggests that these are binuclear. However, on recrystallization of (Fe salen Cl) from nitromethane and methyl cyanide, appreciably different Mossbauer spectra are obtained, and the i.r. band at 850 cm.–1 is very weak. These compounds appear to be monomeric. On recrystallization of (Fe salen Br) from nitromethane and methanol, both dimeric and monomeric compounds are obtained, whereas from methyl cyanide, a monomer is obtained.The Mossbauer and i.r. spectra indicate that magnetic susceptibility is not a reliable method for determining the molecularity of these compounds. The use of the Mossbauer parameters centre shifts (C.S.), quadrupole splitting (Q.S.), and line-widths for the elucidation of the molecularity, spin state of FeIII, and the bonding in these compounds is discussed.

Kinetics of reactions of Schiff-base complexes of iron(II). Part III. Reactions of tris-[N-(2-pyridylmethylene)aniline] complexes with peroxodisulphate and of tris-[α-(2-pyridyl)benzylideneaniline] complexes with acid, with hydroxide, and with peroxodisulphate

Abstract: The kinetics of reactions of several substituted tris-[N-(2-pyridylmethylene)aniline]iron(II) complexes with peroxodisulphate in aqueous solution; of tris-[α-(2-pyridyl)benzylideneaniline]iron(II) complexes with acid, hydroxide, and peroxodisulphate in aqueous ethanolic solution; and of bis(maleonitriledithiolato)cobaltate(II) with acid and with peroxodisulphate in aqueous solution are reported. The kinetic behaviour of the tris-[α-(2-pyridyl)-benzylideneaniline]iron(II) complexes in acid and alkaline solution is similar to that of the related tris-(1,10-phenanthroline)iron(II) complex. Reaction of peroxodisulphate with tris-[N-(2-pyridylmethylene)aniline]-iron(II) complexes takes place by parallel ligand dissociation and complex oxidation, whereas reaction of the tris-[α-(2-pyridyl)benzylideneaniline]iron(II) and bis(maleonitriledithiolato)cobaltate(II) complexes is entirely dissociative with no evidence for any direct oxidation of these complexes to the corresponding iron(III) and cobalt(III) compounds.

The magnetic properties of some manganese(II) Schiff-base complexes and the oxidation products of NN′-ethylenebis(salicylaldiminato)manganese(II)

Abstract: The magnetic properties of Mn(salen) and several other manganese(II) Schiff-base complexes have been studied over the temperature range 80–300°K. These measurements, coupled with X-ray powder data, suggest a binuclear structure for Mn(salen), in which there is antiferromagnetic exchange. The data for the other complexes are discussed in terms of possible structures for these compounds. The magnetic properties of the aerial oxidation products of Mn(salen) are reported and discussed in terms of a binuclear compound (salen)Mn–O–Mn(salen),H2O.

Convenient synthesis of myristicinaldehyde

Abstract: The conversion of isomyristicin to a Schiff base of myristicinaldehyde is described. The subsequent hydrolysis of this base to the free aldehyde establishes a convenient preparation of this materia...

Zirconium(IV) complexes with schiff bases derived from salicylaldehyde and hydroxyalkylamines

Abstract: The reactions of zirconium isopropoxide with the Schiff bases derived from salicylaldehyde and hydroxyalkylamines have been studied and derivatives of the type Zr(OPr i ) 2 (L) and Zr(L) 2 , (where L is salicylidene-2-hydroxyethylamine or salicylidene-2-hydroxy- n -propylamine) have been isolated. The interchange reactions of diisopropoxy zirconium Schiff base complexes with phenol, tert. -butanol and ethane 1: 2 diol have also been carried out. The ultraviolet and infrared spectra of some of these derivatives have been recorded and their molecular weights determined ebullio-scopically in benzene.

Substitution der 6‐Aminopenicillansäure am Kohlenstoffatom 6

Abstract: The hydroxyalkylation of the penicillin nucleus at C-6 with benzaldehyde and formaldehyde is reported. 6-aminopenicillanic acid (6-APA) (2) was used as starting material. Protection of the functional groups and activation of the C-6 position were effected by converting 6-APA successively into the Schiff base 13, the methyl ester 14 and the copper complex 15. The latter gave with benzaldehyde the C-6 monosubstituted complex 17, and with formaldehyde the disubstituted complex 18. The direct α-hydroxybenzylation of 6-APA at C-6 was also carried out with an excess of benzaldehyde at pH 7,5 leading to the SCHIFF base 19. Mild hydrolysis of 19 gave 6-amino-6-(α-hydroxybenzyl)-penicillanic acid (21). Phenylacetylation of the latter yielded the penicillin G analogue 22. Direct reaction of 6-APA with formaldehyde took place only in the presence of salicylaldehyde, giving the oxazolidine 24, from which the amino acid 25 could not be obtained. The new compounds showed only weak antibacterial activity as compared with penicillin G.

N-Substituted salicylaldimine complexes of iron(III). II. Magnetic properties

Abstract: The magnetic susceptibilities of iron(111) N-substituted salicylaldimine complexes of types Fe(sal-XR)3, Fe(sal-NR)2X, [Fe(salH-KR)2X]X, (X = Cl, Br), and [Fe(sal-NR)2]2O have been measured over the temperature range 90-300oK.? The mononuclear complexes exhibit normal high-spin (S = 5/2), Curie-Weiss behaviour. The binuclear oxygen-bridged complexes show antiferromagnetic behaviour and the results have been analysed using the spin-spin coupling mechanism. The exchange interaction is found to be independent of the nature of the N-substituent on the Schiff base. It appears that bulk susceptibility measurements alone cannot unambiguously specify the formal spin state of the ferric ion in these binuclear complexes.

Binuclear complexes of copper(II) and zinc(II) halides with bidentate and quadridentate Schiff base complexes

Abstract: Binuclear complexes of the types CuB,CuCl2, CuB,ZnCl2, ZnB,ZnCl2, and CuL2,CuCl2 have been obtained where BH2 is a quadridentate Schiff base derived from salicylaldehyde and a polyrnethylenediamine and LH is an N-alkylsalicylaldimine. The stereochemistry of the copper atoms in the binuclear complexes is inferred from comparisons of their reflectance spectra with the spectra of the simple copper complexes CuB and CuL2. The structures of the zinc complexes are discussed by reference to near ultraviolet spectra of the ligands and infrared spectra in the 1500-1560 cm-1 region. The evidence suggests that in the complexes of the type MB,M'Cl2 either but not both metal atoms may approach a tetrahedral environment. The chemistry of the complexes ZnB,ZnCl2 is complicated by the possibility of either or both zinc atoms becoming 5 coordinate by addition of solvent molecules; in some of these complexes the zinc chloride appears to be attached to a solvent molecule in a 5-coordinate Schiff base unit, rather than by bridging through phenolic oxygen atoms. The oomplexes CuL2,CuCl2 apparently have a symmetrical binuclear structure based on a trans arrangement of the Schiff base units rather than an unsymmetrical structure resembling that of the complexes CuB,CuCl2. Complexes of the types CuL2,ZnCl2 and ZnL2,ZnCl2 could not be obtained.

Polymeric Schiff bases. XIV - The synthesis of cross-linked polymeric azomethines by exchange reactions.

Abstract: Schiff base cross-links effect on synthesis of polymeric azomethines produced by bis exchange reactions, carbonyl and amine

Kinetics and Mechanisms of Schiff Base Formation from Pyridoxal in Methanol

Abstract: Formation of Schiff bases of pyridoxal with glycine and glycinamide in methanol were studied kinetically by the changes of electronic absorption spectra. When glycine or glycinamide was added to carbinolamine formed from pyridoxal and sarcosine, Schiff base was also formed. Both sarcosine catalyzed and direct (under sarcosine-free) Schiff base formation followed the first order kinetics as long as amines were excess over pyridoxal. From variations of the pseudo first order rate constants with acid-alkaline concentration, following conclusions were obtained ; in direct Schiff base formation of glycine, rate determining step was dehydration in acidic region and carbinolamine formation in neutral and alkaline methanol ; in the case of glycinamide, carbinolamine formation was always rate determining step. Formation of Schiff base of glycine from Schiff base of glycinamide and glycine, transaldimination, was rapid reaction.

Reactions of co-ordinated ligands. Part IV. The use of aminomagnesium compounds in the preparation of α-amino-acid amides from α-amino-acid ethyl esters

Abstract: The action of benzylamine and magnesium methoxide on the Schiff bases formed from glycine ethyl ester and salicylaldehyde, 2-hydroxy-1-naphthaldehyde, and pentane-2,4-dione results in benzyl amide formation and, in the case of the first two Schiff bases, amine-exchange. It is suggested that the benzyl amide formation occurs by means of chelates which involve the Schiff bases and an aminomagnesium compound. An analogous explanation is offered to account for the large variation in the yields of benzyl amides obtained when various ethyl esters are heated with benzylaminomagnesium iodide and benzylaminozinc iodide. Treatment of the Schiff bases formed from α-amino-acid ethyl esters and either pentane-2,4-dione or 1-phenylpropane-1,3-dione with the ethyl(amino)magnesium compounds prepared by addition of primary or secondary amines to diethylmagnesium affords good yields of the expected Schiff base amides. The parent α-amino-amides can be obtained (as hydrohalides) from these by hydrolysis with hydrochloric acid or by treatment with bromine water.

Schiff base equilibria. VI. n- and t-Butylimines of pyridine-2-aldehyde

Abstract: Equilibrium constants at 25o have been measured for the formation of Schiff bases of pyridine-2-aldehyde with n-butylamine (1.45 x 108) and t-butylamine (93). The Schiff base of salicylaldehyde with t-butylamine has a formation constant 9.1 x 108 and pK 13.0.