Über die Reduktionsformen einiger nichtenolisierenden aromatischer Ketone und Chinone,welche die Vinylpolymerisation zu initiieren vermögen

It is known that the reduction forms of aromatic carbonyl compounds (ACC) initiate anionic polymerization of vinyl monomers. The ability of the reduction forms to transfer an electron to the interacting molecules is defined also by the electron affinity of the partners. To obtain data about the electron affinity the half-wave potentials of polarographic reduction were measured and compared with the values of the lowest antibonding molecular orbital, according to theHückel's method. A linear correlation between the potentials of polarographic reduction and the energy of the lowest antibonding molecular orbit was found. The results prove the correctness of the previously determined electroaffinity defined by electron transfers between the reduction forms and neutral molecules. From the data of quantum chemical calculation and the polarographic reduction ofACC the changes of the free energy, enthalpy and the equilibrum constant for electron transfer reaction were calculated. The initiation ability of the reduction forms ofACC and the elctron affinity discussed.     

Diagnostic criteria for characterization of mechanisms corresponding to the second reduction polarographic wave of carbonyl compounds in acidic medium

Expressions of i-E funtions are developed, either by the reaction layer approach or from the assumption that the reactions take place at the surface of the electrode, for different possible mechanisms corresponding to the second reduction polarographic wave of carbonyl compounds in acidic medium.Diagnostic criteria for their characterization are presented and applied to the pyridine-4-aldehyde reduction. Close agreement between the experimental and theoretical results is obtained for a mechanism with a reversible transfer reaction followed by a protonation reaction of the compound formed.     

Polarographic determination of semicarbazones

Acetone, methyl isobutyl ketone, acetaldehyde, formaldehyde, cyclohexanone, butyraldehyde, crotonaldehyde, and acrolein semicarbazones all give polarographic waves suitable for quantitative analysis in an acetate buffer at pH 4.6 .The half-wave potentials are —1.3, —1.3, —1.16 —1.05, —1.2,—1.11, —1.06,–0.99 V vs. S.C.E., respectively, for the compounds listed above. The diffusion current constants of these compounds average approximately 7 in the concentration range of 10^-2 to 10^-1 mM, giving an extremely sensitive method of carbonyl compound analysis. A supporting electrolyte that is 0.1M each in acetic acid, sodium acetate, sodium chloride, and semicarbazide, and 0.0016% in Triton X-100, is satisfactory both for polarograph analysis and for the quantitative absorption of acetone, acetaldehyde, cyclohexanone, and crotonaldehyde from air samples by means of a scrubber.     

A specific gas chromatographic detector for carbonyl compounds, based on polarography

The evaluation of a specific gas Chromatographie detector for carbonyl compounds is described. This is based on the polarographic reduction of the Girard T hydrazone derivative which is formed when the carbonyl compound is absorbed in a buffered supporting electrolyte containing the carbonyl reagent. The detector was used to monitor the separation of a homologous series of alkanals.     

A polarographic study of some N-oxygenated products of N-ethyl-β-methoxy-β-(3'-trifluoromethylphenyl)-ethylamine (sk and f 40652a)

The polarographic behaviour of N-hydroxy-β-methoxy-β-(3'-trifluoromethylpbenyl)-ethylamine, N-ethyl-N-hydroxy-β-methoxy-β-(3'-trifluoromethylphenyl)ethylamine and (3-methoxy-β-(3'-trifluoromethylphenyl)acetaldoxime has been studied over the pH range 0—14. The hydroxylamines gave rise to anodic and cathodic behaviour whereas the oxime gave only a cathodic wave. The mechanism of the oxidation and reduction processes was investigated by d.c. polarography and preparative micro-coulometry. The optimum pH values for analytical purposes were 7, 8 and 4 for the two hydroxylamines and the oxime, respectively. The polarographic behaviour of a mixture of the three compounds was studied and the determination of traces of such compounds by differential pulse polarography is discussed.     

Differential-pulse polarography of amino acids in acetaldehyde-borax medium

A differential-pulse polarographic method for the determination of amino acids is reported, based on the formation of Schiff's base compounds in borax buffer solution (pH 10.10) containing acetaldehyde. The compounds are reduced at a mercury electrode with peak potentials of about ?1.5 V (vs. SCE) and well defined polarographic waves are obtained which can be used to determine amino acids in borax medium. The differential-pulse polarographic method was found to be the most sensitive and suitable for the determination of amino acids in the concentration range 1 × 10^?6–8 × 10^?4 M (lysine) and 2.8 × 10^?6–1 × 10^?3 M (arginine). The polarographic characteristics of these waves were studied by differential-pulse polarographic and cyclic voltammetric methods. The waves are ascribed to the reduction of the imido group in the Schiff's base compounds. The procedure was applied to the determination of lysine and arginine in foodstuffs and the total proteins in serum samples.     

Voltammetric determination of agriculturally-significant benzenearsonic acids

Direct current and differential pulse polarographic measurements are reported on a series of substituted benzenearsonic acid compounds that are important in agricultural applications. Compounds studied were o-aminobenzenearsonic acid, p-aminobenzene-arsonic acid, p-nitrobenzenearsonic acid, p-ureidobenzenearsonic acid, and 3-nitro-4-hydroxybenzenearsonic acid. Polarographic reduction potentials varied with pH for all compounds, shifting to more negative values as the pH was increased. Although diffusion-controlled reduction waves were observed in all cases, some compounds exhibited a dependence of E$\text{1}\text{2}$ on concentration, especially at relatively high concentrations. Differential pulse polarographic peak currents were proportional to concentration from 10^-4 M to 10^-6 M.     

A new synthesis of α,α-disubstituted carbonyl compounds from carbonyl compounds with one-carbon homologation

Lithium α-sulfinyl carbanions of 1-chloroalkyl p-tolyl sulfoxides were reacted with carbonyl compounds to afford adducts in high to quantitative yields. The adducts were treated with t-BuMgCl or LDA to give magnesium or lithium alkoxides, which were treated with i-PrMgCl or t-BuLi to afford the enolate with one-carbon elongation through β-oxido carbenoids. The enolate intermediates were found to be able to be trapped with electrophiles to give α,α-disubstituted carbonyl compounds in moderate to good yields. As a whole, this procedure offers a new and good method for synthesis of α,α-disubstituted carbonyl compounds from carbonyl compounds with one-carbon homologation in only two synthetic steps.     

TMS·OTf-Catalyzed α-bromination of carbonyl compounds by N-bromosuccinimide

Various carbonyl compounds undergo α-bromination reaction under a mild and practical condition utilizing N-bromosuccinimide (NBS), catalyzed by trimethylsilyl trifluoromethanesulfonate (TMS·OTf). This method is also effective for the side-chain bromination of heteroaromatic carbonyl compounds without the ring brominations.     

A short synthesis of α-allenic alcohols from α,β-unsaturated carbonyl compounds with dichloromethyl p-tolyl sulfoxide

The reaction of the α-sulfinyl carbanion of dichloromethyl p-tolyl sulfoxide with α,β-unsaturated carbonyl compounds gave 1-chlorocyclopropyl p-tolyl sulfoxides having a carbonyl group in good to high yields. The carbonyl groups in the products were reduced or treated with alkylmetals to give alcohols. Finally, the alcohols were treated with Grignard reagent to give α-allenic alcohols via the rearrangement of the cyclopropylmagnesium carbenoid intermediates, which were generated by the sulfoxide-magnesium exchange reaction, in good to high yields. This procedure provides a new method for a short synthesis of various α-allenic alcohols in two or three steps from relatively easily available α,β-unsaturated carbonyl compounds.     

A new method for synthesis of α,α-disubstituted carbonyl compounds from carbonyl compounds with one-carbon homologation through β-oxido carbenoid rearrangement as the key reaction

The addition reaction of carbonyl compounds with lithium α-sulfinyl carbanions of 1-chloroalkyl p-tolyl sulfoxides gave adducts, α-chloro β-hydroxy sulfoxides, in high to quantitative yields. The adducts were first treated with a base to give alkoxides, which were treated with i-PrMgCl or t-BuLi to give β-oxido carbenoids via a sulfoxide-metal exchange reaction. The β-oxido carbenoid rearrangement then took place to afford the enolates with one-carbon elongation. The enolate intermediates were found to be able to be trapped with electrophiles such as aldehydes, ethyl chloroformate, benzoyl chloride, haloalkanes to give α,α-disubstituted carbonyl compounds in moderate to good yields. This method provides a new and efficient way for synthesis of α,α-disubstituted carbonyl compounds from carbonyl compounds with one-carbon homologation in only two synthetic operations.     

On-line derivatization coupled to flow injection permanganate chemiluminescence detection of total carbonyl compounds in natural waters and drinking water

This work describes the development of a fast assay for the determination of low molecular weight carbonyl compounds based on the oxidative chemiluminescence of 2,4-dinitrophenylhydrazine with acidic permanganate, which is enhanced during conversion to the corresponding phenylhydrazone-carbonyl derivatives. By exploiting the common derivatization pathway and oxidation mechanism of phenylhydrazones under kinetically controlled conditions in a flow configuration, a common light emission is produced which corresponds to the total aqueous concentration of carbonyl compounds. The experimental conditions that afford the optimum analytical features were optimized for acetone, acetaldehyde and formaldehyde which constitute the most abundant carbonyl compounds in environmental samples. The method was successfully applied to the determination of total carbonyl content in natural waters and drinking water at the low μg L⁻¹ levels with satisfactory recoveries (94.0-99.5%) and very good reproducibility (RSD = 1.58-2.99%, n = 8, C = 2 μg L⁻¹). Validation of the results was performed with gas chromatography suggesting that the proposed method provides a fast alternative to the routine screening of low molecular weight carbonyl compounds in natural waters.     

The interaction of rhodium carbenoids with carbonyl compounds as a method for the synthesis of tetrahydrofurans

The transition metal catalyzed reaction of α-diazo carbonyl compounds has found numerous applications in organic synthesis, and its use in either heterocyclic or carbocyclic ring formation is well precedented. In contrast to other catalysts that are suitable for carbenoid reactions of diazo compounds, those constructed with the dirhodium(II) framework are most amenable to ligand modification that, in turn, can influence reaction selectivity. The reaction of rhodium carbenoids with carbonyl groups represents a very efficient method for generating carbonyl ylide dipoles. Rhodium-mediated carbenoid–carbonyl cyclization reactions have been extensively utilized as a powerful method for the construction of a variety of novel polycyclic ring systems. This article will emphasize some of the more recent synthetic applications of the tandem rhodium carbenoid cyclization/cycloaddition cascade for natural product synthesis. Discussion centers on the chemical behavior of the rhodium metal carbenoid complex that is often affected by the nature of the ligand groups attached to the metal center.     

Nitration et dosage de la phénylalanine

This paper comprises a study of the conditions for nitrating phenylalanine and an investigation of the compounds obtained, polarographic and chromatographic methods being employed. At the same time some nitrobenzoic acids that are found among the nitration products of nitrophenylalanine were examined by both these methods.A method has been proposed for the polarographic determination of phenylalanine, by means of which as little as 30γ of this substance can be detected in 10 ml solution. With concentrations between 2.4.10^-4M and 6.10^-3Mt, the error is less than 2.5%, with those of the order of 2.10^-5M it approaches 12%.     

Poly(N-bromoacrylamide): an efficient and useful catalyst for the protection of carbonyl compounds as dithiolanes, dithianes and oxathiolanes under solvent-free and microwave conditions

Poly(N-bromoacrylamide) (PNBA) was prepared and used as a heterogeneous electrophilic catalyst under solvent-free and microwave conditions for the mild and efficient protection of carbonyl compounds as their dithiolane, dithiane and oxathiolane derivatives with 1,2-ethanedithiol, 1,3-propanedithiol and 2-mercaptoethanol, respectively in good to excellent yields. This method is simple, efficient and straightforward for synthesis of 1,3-oxathiolanes, 1,3-dithiolanes and 1,3-dithianes from carbonyl compounds. The catalyst is recoverable and reusable.     

Pd(0) or Pd(II)-catalyzed ring-opening reactions of benzylidene- and alkylidenecyclopropyl ketones and aldehydes

Pd(0) catalyzed reactions of methylenecyclopropyl carbonyl compounds afforded a convenient method for the synthesis of conjugate (E,E)-1,3-diene derivatives 2 in good to excellent yields. Moreover, we also found that Pd(II)-catalyzed reactions of methylenecyclopropyl carbonyl compounds with water gave 1,5-diketones in good to high yields via a carbene-palladium intermediate. The plausible reaction mechanisms have also been provided on the basis of control and ¹⁸O-labeling experiments.     

A polarographic and spectral study of some C- and N-nitroso compounds.

A wide range of N-nitroso compounds was investigated polarographically and spectrophotometrically. In general, the =N-N0 group is reduced in a 4-electron step in acidic media, which is most suitable for differential pulse polarographic analysis at the trace level. If the groups R and/or R' attached to the nitrosamine group are saturated entities, then the resulting differential pulse polarographic peaks are broad and of little use in the resolution of mixtures. The limit of detection is of the order of 10^-6M. If R and R' are unsaturated, the polarographic peaks are much sharper, mixtures can be resolved and the limit of detection is of the order of 10^-7M, C-Nitroso and C-nitro compounds are best determined by differential pulse polarography, because the waves are comparatively large and sharp, and because the reductions occur at relatively positive potentials where co-extractible interferences from foods, etc., will interfere to a minimal degree.     

Effect of substituents on the polarographic behaviour of α-arylhydrazononitriles: Further evidence for the mechanism of polarographic reduction of α-arylhydrazononitriles

The polarographic behaviour of the α-arylhydrazonomesoxalonitrile derivatives (IIb-i) and of 2-arylhydrazono-3-keto-3-phenylpropionitriles (IIIb-f) was investigated. With the exception of the nitro-substituted derivatives IIh, i and IIIf all the investigated compounds showed polarographic waves similar to that of their respective parent compounds IIa and IIIa. The m-nitro derivatives IIh and IIIf were firstly reduced in a 4 e wave to the corresponding hydroxylamino derivatives which were subsequently reduced in the manner common to other α-arylhydrazononitriles. On the other hand, the p-nitro derivative IIi was first reduced to the hydroxylamino derivative which then lost water to yield the corresponding quinoneimine. Reduction of the latter product in a 2 e wave gave the p-amino derivative IIe, which then underwent 4 e reduction to p-phenylenediamine and aminomalonitrile. The E_1/2 values corresponding to reduction of the arylhydrazonic moiety of compounds IIa-i and IIIa-f at different pH values were correlated to Hammett's different sigma sets. Analysis of the results provided evidence for the suggested mechanism for reduction of these compounds.     

Acid—base equilibria of some benzhydryl piperazine derivatives

The ultraviolet spectral and polarographic behaviour of several benzhydryl piperazine derivatives is described. Attempts have been made to associate the pK data obtained with protonations at various nitrogen atoms in the molecules. Analysis of the plots of E_{$\text{1}\text{2}$} vs. pH have yielded direct polarographic methods for determining some of these compounds in the presence of possible metabolic products.     

A pulse polarographic investigation of parathion and some other nitro-containing pesticides

The polarographic behaviour of parathion, its major metabolites (paraoxon and p-nitrophenol), and of methylparathion, EPN and pentachloronitrobenzene has been studied over a wide pH range. Differential pulse polarography is used to differentiate between parathion, p-nitrophenol and pentachloronitrobenzene. An indirect determination of parathion in the presence of paraoxon can be based on their respective rates of hydrolysis in 0.5 M sodium hydroxide solution. The electrochemical behaviour of these compounds has also been investigated in solutions containing tetraalkylammonium salts as the supporting electrolyte.