Microwave‐assisted Chemical Reactions

Microwave (MW) radiation has been used in chemical analysis and chemical synthesis. MW heating under controlled conditions offers distinct advantages over conventional heating. The reactions are carried out in environmentally clean and safe solvents and in many cases, reactions can be carried out under solvent‐free conditions. This method of synthesis has grown rapidly and found its use in various sectors. This paper reviews some of the reactions that have been accelerated with higher yields under MW irradiation. The application of MW‐assisted synthesis in the medicinal and pharmaceutical industries will be emphasized.     

MOLECULAR REARRANGEMENT OF SULPHUR COMPOUNDS (PART I). PYROLYSIS OF SOME SUBSTITUTED RHODANINE

Abstract

Thermal rearrangement of 3-phenylrhodanine (I) and 5-benzylidene-3-phenylrhodanine (IV) in air has been thoroughly investigated. Homolytic cleavage of (C—S) and (C—N) bonds occurred, followed by a series of hydrogen abstractions, coupling, and cyclization reactions. The isolated products of compound (I) are CS₂, CO, H₂S, NH₃, aniline, dibenzylamine, tribenzylamine, thioglycolic acid, phenyl isothiocyanate, bibenzyl. stilbene, p-arninoacetophenone, thiocarbanilide, 2-thioxoindole and 2,3,4,5-tetraphenylthiophene. In case of compound (IV), the isolated products are CS₂, H₂S, H₂O, CO, phenyl isothiocyanate, benzothiophene, 2-phenylquinoline, aniline, thiocarbanilide, 2-phenylindole, cinnamic acid and polystyrene. A suitable mechanism has been suggested to account for the obtained products.     

REACTIONS OF ARYLSULPHONYL FLUORIDES

Abstract

Substituent effects have been investigated for both nucleophili -ic and reduction reactions of arylsulphonyl fluorides in aqueous media. The significance of the results will be discussed in relation to the reactions of arylsulphonyl chlorides.     

Bestimmung der Extraktionskonstanten der Tellur-Pyrasolindithiocarbaminate

Abstract

In this work the exchange reactions between the ion Te(IV) in the aqueous phase and the aryl substituted pyrasolindithiocarbaminates of zinc into chloroform have been investigated. The equilibrium (exchange) constants of these reactions have been determined experi mentally. The extraction constants and two-phase stability constants of Te(PDTC)₄ have been calculated.     

SOME COMPLEXES OF AROMATIC ORTHO-BIS(METHYLTHIO)ETHERS

Abstract

The reactions of some partially fluorinated aromatic ortho-bis(methylthio)ethers with various metal ions and metal carbonyls have been examined. All the complexes formed have been characterized.     

Preparation of 5-Cyano-4,6-dimethyl-2H-pyran-2-one and 3-Cyano-5-methoxy-4-methyl-5H-furan-2-one via a One-Pot,Domino-Knoevenagel Process

5-Cyano-4,6-dimethyl-2H-pyran-2-one (1) has been prepared via a simple one-pot domino-Knoevenagel reaction starting from ethyl acetoacetate (2) and cyanoacetone (3). Similarly, a new racemic 3-cyano-5-methoxy-4-methyl-5H-furan-2-one (7) has been prepared from 1,1-dimethoxyacetone (6) and cyanoacetic acid (4). The new alkylidene derivatives (Z/E)-ethyl-4-cyano-3-methylbut-3-enoate (5), (Z/E)-ethyl 5-amino-4-cyano-3-methyl-5-oxopent-3-enoate (9), and (2,2-dimethoxy-1-methylethylidene)malononitrile (11) have been prepared via the Knoevenagel reactions. The easy access to these new compounds in good yields shows that ammonium acetate/acetic acid–catalyzed Knoevenagel reactions and domino-Knoevenagel reactions have a broad scope of application.     

SULPHUR CONTAINING HETERODIPOLAROPHILES. VARIABLE STEREOCHEMISTRY OF THE CYCLOADDITION OF THIOBENZOPHENONES TO KETENIMINES

Abstract

The thermal cycloaddition between thiobenzophenones (1) and ketenimines (2) takes place according to two reaction modes, the stereochemical course being determined by the type of substituent at nitrogen on the cumulene. Specifically, N-arylketenimines (2a) (X = H) react with (1) as a formal 4π system giving as final products 4H-3,1-benzothiazines (3) (1,4-cyclisation), whereas N-aryl ortho-disubstituted compounds (2b) (X = Me), as well as N-alkyl derivatives (2c), behave as 2π component to give 2-iminothietans (4) (1,2-cyclisation) (Scheme I). In the formation of the six membered ring compound (3), the ketenimine (2a) can be viewed to act as a 1,4-heterodiene to give the intermediate (3a) by addition of (1) across the C[dbnd]N bond and the C[dbnd]C of the N-aryl ring. Both reactions proved to be stereoselective.     

THE MECHANISM OF INTERACTION OF SULPHUR AND p-PHENYLENEDIAMINE

Abstract

Several studies which have been undertaken on reaction of sulphur and p-pheaylenediamine give controversial proposals of mechanisms. Many authors postulate an attack of sulphur diradicals directed onto amino group.     

The Mechanism and Stereochemistry of Wittig Reactions of Phosphonium Ylide-Anions

Abstract

Schmidbaur's group have extensively investigated¹ the coordination properties of phosphonium 1,3-ylide-anions (1) in organometallic chemistry and more recently Cristau² has reported the potential usefulness of these compounds in synthetic organic chemistry. There have been a few studies³ of specific phosphonium 1,1-ylide-anions (2), however their only use in the Wittig reaction appears to be that of (2a).⁴ We have set out to study the stereochemistry and mechanism of Wittig reactions of (1) and (2) and to carry out some preliminary investigations on the arsenic analogues (3).     

Selective chemical reactions in supercritical carbon dioxide,water, and ionic liquids

Abstract

Alternative solvents such as supercritical carbon dioxide, water, and ionic liquids are receiving an increase of interest as better replacements for conventional solvents in chemical reactions. They have been called sustainable green solvents because they are highly promising reaction mediums for organic synthesis. This review presents an overview of some selected chemical reactions that have been developed in these green solvents with a particular emphasis on metal-catalyzed reactions.     

Kinetics and Mechanism of the Oxidation of Some Aldoses by Cerium(IV)

Abstract

The kinetics of oxidation of some aldoses by cerium(IV) have been studied spectrophotometrically in sulphuric acid medium. The reactions are second order; first order with respect to both cerium(IV) and aldose concentration. The reaction rate decreases with increase in sulphuric acid concentration. The mechanisms for the reactions are discussed.     

Thermal and photochemical reactivity of phosphaalkenes

Abstract

The reactivity of acyclic dicoordinated phosphorus derivatives has intensively been studied. Nevertheless, up to date, a very few examples of photochemical reactivity of these compounds have been described. We wish to report here some thermal and photochemical reactions of phosphaalkenes 1–4. ¹     

METALLAPHOSPHENES AND DIPHOSPHENES

Abstract

Transient metallaphosphenes (rbnd2;M[dbnd]P[sbnd]) have been obtained by exchange reactions between disilylphosphines and organometaldihalides (M = Ge, Sn), or by thermolysis of 2-metallaphosphetanes (M = Si, Ge). They are characterized by trapping reactions with strained heterocycles. The first stable germaphosphene 12 has been synthesized by dehydrohalogenation from the parent halogermylphosphine and isolated in form of orange crystals. It is very reactive toward compounds with active hydrogen.

Transient diphosphenes ([sbnd]P[dbnd]P[sbnd]) have been prepared by the same type of exchange reactions between disilylphosphines and dichlorophosphines and characterized by trapping reactions on dienes. The second stable diphosphene 18 has been obtained by addition of t-BuLi on trisyldichlorophosphine. Its structure has been determined by X-ray diffraction and some aspects of its reactivity are described. The reaction of bisyltrichlorogermylphosphine with DBU affords the new stable and potentially reactive diphosphene 30.     

Bioorganic Chemistry of Hypothiocyanite

Abstract

Hypothiocyanite (OSCN^?) plays an important role in the human host defense system as a nonimmunological antimicrobial agent. Although many conjugate reactions of proteins have been attributed to OSCN^?, there is little precedence for such reactions in small-molecule chemistry. We will discuss the derivative species that are in equilibrium with OSCN^?, including hypothiocyanous acid (HOSCN), thiocyanogen [(SCN) ₂ ], and trithiocyanate [(SCN) ₃ ^?], the first organic derivatives of this mixture to be fully characterized, and we will describe a new method of synthesizing hypothiocyanite.     

Acid-Catalyzed Hydrolysis of Some N,N-Dibenzylalkanesulfinamides in 50% Acetonitrile–Water

Abstract

The hydrolysis of some N,N-dibenzylalkanesulfinamides (RSONH(CH₂Ph)₂; 1, R = Me; 2, R = ⁱPr; 3, R = ^tBu; 4, R = 1-adamantyl) has been studied in 50% (v:v) acetonitrile–water solutions of hydrobromic and hydrochloric acids, mainly at 44.8 °C, using ultraviolet (UV) spectrophotometry to determine pseudo first-order rate constants. The compounds were found to hydrolyze by concurrent bimolecular neutral, acid-catalyzed, and acid-dependent nucleophilic (halide ion) catalysis pathways. The last-named is predominant in reactions in HBr solutions, but in HCl solutions, the acid-catalyzed pathway is predominant. The results indicate that both steric and electronic effects are important in these reactions. There appears to be no mechanistic switchover in the series 1→4.     

Reactions of quinones with some aryl phenols and synthesis of new quinone derivatives

In the present study, the reactions of p-chloranil (1a) and 2,3-dichloro-1,4-naphthoquinone (DCNQ) (1b) with some aryl phenols were investigated. The structures of all compounds were characterized using spectroscopic methods (FT-IR, ¹H NMR, ¹³C NMR, and MS) and microanalysis. The electrochemical behaviors of some benzoquinone and naphthoquinone derivatives have also been investigated in unbuffered aprotic solutions.     

FROM 1,3-DIPHOSPHETANE-2,4-DIYLS TO CYCLIC ANIONS AND CATIONS

The interest in diradicals has grown by the increasing number of stable diradicals which have been synthesized during the last few years. The diphosphacyclobutane-diyles have a diradicaloid molecular structure and they were the first diradicals to be prepared in the gramme scale. The combination of stability and high yield synthesis creates the opportunity both to change the substitution pattern or to prepare different valence isomers. Current experimental and computational studies reveal that electron transfer reactions of maintain the cyclic system. In the contribution, the oxidation reaction of 1 to the radical cation 2 and the cyclic diphosphaallyl cation 3 will be reported. Additionally, the remarkable mechanism of the reaction of 1 at first to the radical anion 4 but particularly to the diphosphacyclobutadiene dianion 5 under reductive conditions will be presented in detail.     

THERMAL AND PHOTOCHEMICAL REACTIONS BETWEEN α, α′-DIBROMOKETONES AND FIVE-MEMBERED HETEROCYCLES IN THE PRESENCE OF IRON NONACARBONYL

Abstract

[3 + 4] Cycloaddition reactions of 2-oxyallilic cations to furan¹ to form seven-membered oxobicyclic compounds have been known for some time. The purpose of this paper has been to try to extend the reaction to five-membered heterocycles with more aromatic character than furan. An analogy has been found between the behavior of thiophene, selenophene and tellurophene in these reactions and in oxetane-forming reactions. The higher the aromaticity of the heterocycle, the more difficult it is to achieve the formation of the seven-membered ring. Contrary to what is observed in oxetane-forming reactions, where it is not possible to isolate a stable tellurium compound, the tellurabicyclic compound was isolated and identified by spectroscopic methods in the present investigation.     

Crown Ethers and Phase Transfer Catalysis in Polymer Chemistry

Abstract

This paper is the first half of a two part review on the applications of crown ethers, cryptands, glymes and various onium ion salts to polymer chemistry. Part 1 surveys the use of these phase transfer catalysts (PTC's) in the synthesis and modification of macromolecules. Applications to ring-opening and vinyl polymerizations generally have involved solubilization and activation by PTC's of organic and inorganic salts which serve as anionic initiators. Change in the polymerization rates, polymer yields and product microstructure often resulted from association of the PTC with the active chain end.

Polymer modification and functionalization reactions have been enhanced by the use of PTC's. Macromolecular substrates have included both soluble and insoluble polymers, although the most popular have been the readily-available Merrifield resins. Generally these two-phase reactions have involved polymer solutions interacting with insoluble reagents or insoluble polymers reacting with the reagent solution. Some of the groups incorporated have been thiols, nitriles, carboxylic acids, esters, and crown ether analogs themselves. Most of this work has aimed at synthesis of polymer derivatives which can serve as chelating agents, catalysts and reagents in subsequent reactions. In almost all cases described, phase transfer catalysis offers definate advantages in selectivity and yield over conventional methods. The outline below gives the general subject areas of both Part 1 and Part 2; the latter will be published shortly.     

Neue rhodanilatähnliche Verbindungen mit Morpholin

Substitution reactions of K₃[Cr(NCS)₆] with morpholine were studied. The formula of the complex anion, [Cr(NCS)₄(morph)₂]^–, was established.23 new complex compounds of these types have been prepared from the hydrochlorides of some aliphatic or heterocyclic amines, alkaloids and cobalt(III)ammine bases resp.Their thermal behaviour and the mechanism of pyrolysis of these salts was studied by derivatographic methodes. From UV and IR spectra some structural problems are resolved and discussed.

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