Determination of primary amines by means of fluorescent schiff base derivatives

The formation of Schiff bases from the reaction of primary amines and several aromatic aldehydes has been studied. In many cases the Schiff bases were too unstable or feebly-fluorescent to be of analytical value. 1-Pyrenealdehyde and 2-fluorenealdehyde, however, were found to be suitable fluorigenic reagents for primary aliphatic amines, forming Schiff bases that were very stable and intensely fluorescent in acidic ethanol. The derivatives of 1-pyrenealdehyde could be detected at concentrations less than 1 ng ml^-1 in pure solution. Derivatives of 1-pyrenealdehyde could be readily produced by reactions at the surface of a t.l.c. plate. Combination of this approach with a simple deproteinizing procedure permitted analysis for nanograna quantities of primary amines in blood serum.     

Chiral enrichment of 2-amino-2′-hydroxy-1,1′-binaphthyl

A new synthetic procedure for the formation of 2-amino-2′-hydroxy-1,1′-binaphthyl, and a new purification procedure through the formation of Schiff bases, purification of the Schiff bases, and breakdown of the Schiff bases through amine exchange, are described. Through the new purification procedure, greater than 99% purity of the compound can be obtained easily and reliably. A set of procedures were examined to compare the efficiency and reliability to resolve 2-amino-2′-hydroxy-1,1′-binaphthyl into enantiomers. A new procedure was discovered to enrich enantiomeric excess from less than 10% to 95–99% in one step. Even a racemic mixture from an achiral procedure can be enriched to 67% e.e. in about 4% yield. The X-ray crystal structure of the racemic mixture [rhombohedral, space group Iba2, a=15.718(2) Å, b=21.703(2) Å, c=8.5398(9) Å, V=2913.2(5) ų, R1=0.0705, Z=8, d_calcd=1.301 g/cm³, F(000)=1200 e] was solved to elucidate the intriguing behavior of this compound.     

Structural investigation on phenyl‐ and pyridin‐2‐ylamino(methylene)naphthalen‐2(3H)‐one. Substituent effects on the NMR chemical shifts

Schiff bases bearing phenyl and pyridyl groups were synthesized by condensation of appropriate amines with 2‐hydroxynaphthaldehyde. These Schiff bases were obtained as colored crystalline solids. The proton NMR spectra of these compounds showed a doublet for the NH protons indicating a keto tautomer for these Schiff bases. The pyridyl‐substituted Schiff bases containing hydroxyl moiety were found to show the most downfield shift for the NH protons in DMSO solvent, and this was rationalized due to the formation of a six‐ and five‐membered ring using hydrogen bonds for these two compounds. Correspondingly, the olefinic proton of the Schiff bases is also found to be a doublet due to coupling to the amine proton. These Schiff bases exhibited thermochromic properties. Detailed NMR spectral analysis for both the phenyl‐ and pyridyl‐substituted Schiff bases is presented. Copyright © 2010 John Wiley & Sons, Ltd.     

Polymeric Schiff Bases. III. Some Prototype Exchange Reactions of Schiff Bases

The amine moiety in Schiff bases can be exchanged quantitatively by another amine to yield new Schiff bases if the volatility of the replacing amine is lower than the derived amine, thereby allowing the latter to distilled from the reaction mass. This amine exchange was shown to be quantitative also for diamines and di-Schiff bases. Similarly, quantitative conversions were found for aldehydes and acetal exchanges with Schiff bases for both monofunctional and difunctional reactants. The bis exchange, involving two complementary Schiff bases, was quantitative also when the reactants were so selected that one of the new derived Schiff bases could be removed by distillation. The bis exchange was demonstrated with mono and di-Schiff bases.

Mechanisms are suggested for these Schiff base exchange reactions: attempts to isolate the proposed intermediates physically were unsuccessful; however spectroscopic evidence indicates the formation of intermediate compounds.

The Schiff base exchanges involving polyfunctional reactants are of interest in the synthesis of polymers.     

Kinetics and mechanism of transaldimination of amino acids and aromatic amines with pyridoxal

Kinetics and mechanism of transaldimination of amino acids and aromatic amines with pyridoxal have been studied by means of UV spectroscopy and polarimetry. It has been shown that aminal intermediates are formed in reaction of the Schiff’s bases with p-aminobenzoic acid and β-alanine. The structure of aminal and Schiff’s base is determined by the spatial arrangement of the amino acid and aromatic fragments with respect to the pyridine ring plane. The presence of OH and CH₂-OH groups in the o-positions in pyridoxal structure turns amino groups by 90° with respect to the pyridine ring. The scheme of Schiff’s bases transaldimination by amino acids and biological amines has been developed according to stereospecific, energy, and geometric factors.     

Solvent-free one-pot reactions for annulating a pyrimidine ring on thiazoles under microwave irradiation

One-pot reactions of glycine, acetic anhydride and thiazole Schiff bases (2a-f) diastereoselectively and expeditiously annulate a pyrimidine ring on the thiazole nucleus to yield 6,7-dihydro-5H-thiazolo[3,2-a]pyrimidin-5-ones (4a-f) under microwave irradiation and solvent-free conditions.     

New polycatenar Schiff bases derived from 1,3,4-thiadiazole: synthesis,mesomorphism and luminescence behaviour

Two new series of columnar liquid crystal materials based on tetra- and hexacatenar Schiff bases were synthesised by reaction of 4-aminophenyl-1,3,4-thiadiazole derivatives with terephthalaldehyde (series 2a–f) and with 2,5-thiophenedicarbaldehyde (series 3a–f). The mesomorphic properties of these compounds were studied by differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction (XRD). The mesomorphic behaviour was found to be dependent on the nature of the central ring (benzene in series 2a–f, thiophene in series 3a–f), on length and on number of alkoxy chains. Both tetra- and hexacatenar compounds in series 2a–f display an enantiotropic hexagonal columnar phase. Whereas, in the case of the series 3, only the tetracatenar Schiff bases (3a, 3c and 3e) display enantiotropic hexagonal columnar mesomorphism, hexacatenar Schiff bases (3b, 3d and 3f) do not show mesomorphic properties. Photophysical studies were realised in solution and in solid state. Also, a thermogravimetric analysis was performed. A fibre obtained from compound 3b was analysed by POM showing that the mesophase is maintained in the fibre.     

Some Corrosion Inhibitors Based on Schiff Base Surfactants for Mild Steel Equipments

Two series of Schiff base amphiphiles were prepared throughout condensation of benzaldehyde or anisaldehyde and three different fatty amines with various alkyl chain length; namely: dodecyl, hexadecyl and octadecyl amine. The chemical structures of the prepared Schiff bases were confirmed using elemental analysis, FTIR, and ¹H-NMR spectra. The data of structural analysis for these compounds were confirmed the chemical structures and the purity of the synthesized amphiphiles. The synthesized Schiff base amphiphiles were evaluated as corrosion inhibitors for low carbon steel (mild steel) in various acidic media (HCl and H₂SO₄) using weight loss technique. The corrosion inhibition measurements of these inhibitors showed high protection of the low carbon steel alloys against corrosion process in the tested acidic media at different periods as well as they have good biocidel effectagainest SRB. The discussion was correlated the efficient corrosion inhibition of these inhibitors to their chemical structures.     

An approach to fused pyrimidine derivativesvia Schiff bases of aromaticortho-nitrocarbaldehydes. An investigation of substituent effects on the reaction course

The synthesis of fused pyrimidines from the Schiff bases of aromatic ortho-nitrocarbaldehydes is reported. The Schiff bases after selective reduction of the nitro group on 10% Pd/C, followed by condensation of the amines formed with orthoesters, are transformed to the corresponding imidates. Heating of the latter in a sealed tube with an excess of ammonia (or with ammonia in ethanol) gives fused pyrimidines. The influence of various substituents in the aromatic ring of the imine moiety of the Schiff bases on the overall yield of fused pyrimidine derivatives has been investigated. Moderate electron-withdrawing groups gave the best results.Institute of Organic Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, PL-01-224 Warszawa, PolandTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 799–805, June, 2000.     

Substituted γ-lactones: On the structural elucidation of the reaction products from 4-aroyl-3-hydroxy-2(5H)-furanones and 1,2-diamines

The reaction pathway of 4-aroyl-3-hydroxy-2(5H)-furanones 1 with diamines depends on the nature of the amine as well as on the applied reaction conditions. Thus, the reaction of 1a-d with 5,6-diamino-1,3-dimethyluracil 5 led to the formation of two isomeric Schiff bases 7a-d and 8a-d . Conversely type 1 compounds reacted with 4,5-diaminopyrimidine 9 or 2,3-diaminopyridine 10 to form the mono acid-base adducts 11a and 11b respectively. When type 1 compounds were reacted with aliphatic diamines 13a-d or p-phenylenediamine and p-xylenediamine, respectively also an immediate formation of acid-base adducts 15a-f was observed. The reaction of a number of O-methylated type 1 compounds with 1,2-ethylenediamine afforded the novel seven-membered ring compounds 18a-d in good yields. The analogous reaction of O-alkylated 1a with o-phenylenediamine 2 or 2,3-diaminonaphthalene gave the expected tricyclic ring systems 19 or 20 .     

Determination of the rates of formation and hydrolysis of the Schiff bases formed by pyridoxal 5′-phosphate and copolypeptides containing l-lysine

We determined the apparent rate constants of formation (k₁) and hydrolysis (k₂) of the Schiff bases formed between pyridoxal 5′-phosphate (PLP) and l-lysine and l-alanine copolymers of different compositions, as well as those formed between PLP and l-lysine and l-glutamic acid copolymers, at various pH values, a temperature of 25 °C and an ionic strength of 0.1 M. The k₁ values obtained in neutral and acidic media were independent of the copolymer composition. The efficiency of the intramolecular acid catalysis for the formation of the Schiff bases was found to be somewhat higher than that of PLP—primary amine systems (the slope of the Brøwted plot was α=0.77). The most stable of the Schiff bases studied was that with a protonated imine nitrogen and phosphate group and a unprotonated pyridine nitrogen.     

Design of Schiff base-like postmetallocene catalytic systems for polymerization of olefins: X. Synthesis of phenoxy imino ligands with bulky substituents

Reactions of primary amines with salicylaldehydes containing bulky substituents (tert-butyl, 2-phenylpropan-2-yl, triphenylmethyl) in positions 3 and 5 gave a number of new Schiff bases as ligands for complex formation with transition metals.     

Synthesis of Various Schiff Bases Containing Isoxazole Ring and Their Applications with Thioglycollic Acid and Diverse Phosphorus Reagents

A series of Schiff bases bearing isoxazole and pyrazole rings were synthesized. Application of thioglycollic acid on two selective synthesized Schiff bases afforded the corresponding thiazolidin‐4‐one derivatives. On the other hand, following the multicomponents one‐pot Kabachnik– Fields reaction, the Schiff base generated in situ from 4‐chlorobenzaldehyde and 5‐methyl isoxazol‐3‐amine was trapped by phosphorus reagents to produce the corresponding amino phosphonates in moderate yields. However, the latter products could also be obtained in better yields (≥78%) by directly applying the dialkylphosphites to a selective synthesized Schiff base. Similarly, a series of α‐aminophosphonates could be obtained from 5‐chloro‐3‐methyl‐1H‐pyrazol‐4‐carbaldehyde, 5‐methylisoxazol‐3‐amine, and phosphorus reagents. Moreover, applying hexaalkyl triamido phosphites to the N‐(4‐chlorobenzylidene)‐5‐methylisoxazol‐3‐amine in ethanol afforded methylphosphonic diamide derivatives, whereas N‐((5‐chloro‐3‐methyl‐1H‐pyrazol‐4‐yl)methylene)‐5‐methylisoxazol‐3‐amine underwent dechlorination through reaction with hexaalkyl triamido phosphites to give the respective amine derivatives.     

Three ways of reactions of 5-(3,5-dimethyl-1<Emphasis Type="Italic">H</Emphasis>-pyrazol-1-yl)-2-phenyl-1,3-oxazole-4-carbonitrile and its analogs with nitrogen-containing bases

Substituted 5-(3,5-dimethyl-1H-pyrazol-1-yl)-1,3-oxazole-4-carbonitrile differently react with nitrogen bases having different numbers of labile hydrogen atoms. Treatment of the title compounds with secondary amines or morpholine results in nucleophilic replacement of the pyrazolyl substituent at C⁵, the ozaxole ring remaining unchanged. Their reactions with primary amines are accompanied by cleavage of the oxazole ring with formation of the corresponding enamino nitriles. Hydrazine hydrate acts in a similar way, but enehydrazino nitriles thus formed undergo fast cyclization to give new 4,5-diaminopyrazole derivatives. The latter can be converted into substituted pyrazolo[1,5-a]pyrimidines whose structure has been proved by X-ray analysis.     

Qualitative gas chromatographic analysis of bacterial amines as their Schiff bases and other derivatives

Summary Columns of SE-30 and OV-17 on Chromosorb W, Apiezon N on Chromosorb G and Tenax-GC porous polymer were compared for their ability to separate bacterial amines converted to carbethoxy, dinitrophenyl, trimethylsilyl, Schiff base and fluorinated Schiff base derivatives.Tenax-GC performed less well than the other packings with respect to the number of plates and peak resolution. Dinitrophenyl and trimethylsilyl derivatives were both unsatisfactory for analysis of bacterial amines. Schiff bases and their fluorinated derivatives were found to be the most suitable. However, the former were preferred as the use of fluorinated Schiff bases confered little advantage when a flame ionization detector was employed. A maximum of 16 amines was separated, using columns of OV17 on Chromosorb W programmed from 110 °C to 280 °C at 5.5 °C min^–1 after an initial holding time of 6 min. The application of the method to analysis of cultures ofProteus mirabilis yielded two amines tentatively identified asiso-butylamine andiso-amylamine.     

Stereoselective synthesis of trans-3-functionalized-4-pyrazolo[5,1-b]thiazole-3-carboxylate substituted β-lactams: Potential synthons for diverse biologically active agents

Abstract

An efficient protocol for the stereoselective synthesis of pyrazolo[5,1-b]thiazole-3-carboxylate tethered β-lactam conjugates 8a–j from novel pyrazolo [5,1-b]thiazole-3-carboxylate substituted Schiff’s bases 6a–f is reported here. The reaction between various ketene precursors and novel Schiff’s bases 6a–f afforded exclusive formation of trans-β-lactams 8a–j. The substrate scope of this approach was investigated extensively by varying different groups (R, Z). All the novel compounds were characterized using various spectroscopic techniques, such as FT-IR, ¹H NMR, ¹³C NMR, elemental analysis, ¹³C NMR (DEPT-135), and mass spectrometry in representative cases. Single crystal X-ray crystallographic study of trans-ethyl 7-(1-(4-methoxyphenyl)-4-oxo-3-phenoxyazetidin-2-yl)-6-methyl-2-(methylthio)pyrazolo[5,1-b]thiazole-3-carboxylate 8a has confirmed the molecular structure and the stereochemical outcome. To the best of our knowledge, the synthesis of such types of Schiff’s bases and β-lactam conjugates has not been reported so far.     

Acyl iodides in organic synthesis: XI. Unusual N-C bond cleavage in tertiary amines

Acyl iodides reacted with excess primary and secondary amines in a way similar to acyl chlorides, yielding the corresponding carboxylic acid amide and initial amine hydroiodide. Reactions of tertiary amines with acyl iodides were accompanied by cleavage of the N-C bond with formation of the corresponding N,N-di(hydrocarbyl)carboxamide and alkyl iodide. In the presence of excess tertiary amine the latter was converted into quaternary tetra(hydrocarbyl)ammonium iodide.     

Facile and efficient method for preparation of schiff bases catalyzed by P2O5/SiO2 under free solvent conditions

A simple and convenient method for the preparation of Schiff bases is developed. In this method, the Schiff base compounds were prepared from the reaction of carbonyl compounds with primary amines. In this reaction, P₂O₅/SiO₂ have catalyzed the Schiff base formation in dry media under solvent‐free conditions. Advantages of this method are use of an inexpensive and efficient catalyst, high yields of products, short reaction times, and simpli‐city of the reaction and workup. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:43–47, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20383     

Observation and Kinetic Characterization of Transient Schiff Base Intermediates by CEST NMR Spectroscopy

In aqueous solution, many biochemical reaction pathways involve reaction of an aldehyde with an amine, which progresses through generally unstable, hydrated and dehydrated, Schiff base intermediates that often are unobservable by conventional NMR. There are 4 states in the relevant equilibrium: 1) gem‐diol, 2) aldehyde, 3) hemiaminal, and 4) Schiff base. For the reaction between protein amino groups and DOPAL, a highly toxic metabolite of dopamine, the ¹H resonances of both the hemiaminal and the dehydrated Schiff base can be observed by CEST NMR, even when their populations fall below 0.1 %. CEST NMR reveals the quantitative exchange kinetics between reactants and Schiff base intermediates, explaining why the Schiff base NMR signals are rarely observed. The reactivity of DOPAL with N^α‐amino groups is greater than with lysine N^?‐amines and, in the presence of O₂, both types of Schiff base DOPAL–peptide intermediates rapidly react with free DOPAL to irreversibly form dicatechol pyrrole adducts.     

Oxidative Kopplung von Kohlendioxid mit substituierten Furfuryliden‐iminen an Nickel(0)‐Zentren: Struktur und Reaktivität der gebildeten Nickelacyclen

Furfurylidene‐imines as Components of the Oxidative Coupling with CO₂ at Nickel(0) centers: Influence of the Substituents on the Structure of the resulting Nickelacycles The oxidative coupling between benzaldehyd‐N‐furfurylidene‐imine, CO₂ und Ni(cod)₂ results in THF or 1.4‐dioxane in the formation of the organometallic macrocycle 1a , even if a large excess of Schiff base was used. 1a reacts with Ph₃P under partial elimination of CO₂ to form the tetranuclear complex 2 , which contains two nickela‐aziridine rings linked with two nickelacyclic carbamates. Surprisingly, the protolysis of 1 followed by elimination of CO₂ results in the formation of the organometallic product 3 which also contains a Ni‐C bond in a (protonated) nickelaaziridine ring. Para‐hydroxybenzaldehyd‐N‐furfurylidene‐imine ( B ), CO₂ und Ni(cod)₂ react under oxidative coupling to form the nickelacycle 4 , in which the monomeric metallacyclic units are connected by a hydrogen‐bonded network to form a polymeric supramolecular system. Two of the Schiff bases B coordinate as N‐donors at the Ni^II center, the third Schiff base acts as the substrate for CO₂. Ferrocene‐carbaldehyde‐N‐furfurylidene‐imine forms in the presence of bipy the monomeric nickelacycle 22 containing the intact ferrocenyl unit. The solid‐state structures of 2, 3, 4, and 22 were determinated by X‐ray crystallography. Comparison of CO valence frequencies allows to indicate the coordination mode in nickelacycles with other Schiff bases.