Reactions between a superoxide anion and alkyl bromides in dimethyl sulfoxide

The activation parameters of the reactions between a superoxide anion (O₂^·−) and alkyl bromides are measured. An ab initio study of the transition states for various mechanisms of this reaction is performed. The mechanism of radical separation in a polar solvent becomes competitive upon an increase in the number of alkyl groups in an alkyl bromide molecule and depends on their arrangement relative to a reaction center.     

Reactions of substituted phenacyl bromides with various bases. o- and p-nitrophenacyl bromide. I

The products obtained from the reaction of o- and p-nitrophenacyl bromide with various bases is described.     

Reactions of substituted phenacyl bromides with various bases: p-methyl- and p-methoxyphenacyl bromide. II

The products obtained from the reaction of p-methyl- and p-methoxyphenacyl bromide with various bases are described.     

Regioselective alkylation of isopropylidene- and cyclohexylidenepropanedinitrile with phenacyl bromides

Alkylation of isopropylidene- and cyclohexylidenepropanedinitrile with phenacyl bromides gave 2,2-bis(2-aryl-2-oxoethyl)propanedinitriles. Direct alkylation of propanedinitrile with phenacyl bromides afforded only 2-(2-aryl-2-oxoethyl)propanedinitriles.     

Kinetics and mechanism of the pyridinolysis of phenacyl bromides in acetonitrile

Kinetic studies of the reactions of substituted phenacyl bromides (YC6H4COCH2Br) with pyridines (XC5H4N) are carried out in acetonitrile at 45.0 degrees C. A biphasic Bronsted plot is obtained with a change in slope from a large (betaX approximately equals 0.65-0.80) to a small (betaX approximately 0.36-0.40) value at pKa = 3.2-3.6, which can be attributed to a change in the rate-determining step from breakdown to formation of a tetrahedral intermediate in the reaction path as the basicity of the pyridine nucleophile increases. This mechanism is supported by the faster rates with pyridines than with anilines and the change of cross-interaction constant rhoXY from a large positive (rhoXY = +1.4) to a small positive (rhoXY approximately +0.1) value. The large magnitude of Hammett rhoX (= -5.5 to -6.9) values for the pyridines with electron-withdrawing substituents and positive deviations of the pi-acceptors, p-CH3CO and p-CN, are quite similar to those for the pyridinium ion formation equilibria. The activation parameters are also in line with the proposed mechanism.     

Polarography of polyhalogen-substituted benzyl bromides and the corresponding benzylmercuric bromides

Conclusions On the basis of a comparison of the polarographic behavior of a series of polybromine-substituted benzylmercuric bromides and the corresponding substituted benzyl bromides it was shown in the case of benzyl bromides active in the preparative reaction with metallic mercury that the reduction takes place through the initial formation of organomercury compounds at the surface of the mercury electrode.Translated from Izvestiya Akademii Nauk SSSR. Seriya Khimicheskaya, No. 3, pp. 546–548, March, 1985.     

Synthesis of imidazolyl dithiocarbamates and their reactions with phenacyl bromides

The reactions of ethyl (5-carbamoyl-3H-imidazol-4-yl)dithiocarbamate with phenacyl bromides afford the S-alkylation products as a mixture of E/Z-isomers, which undergo cyclization to 5-(2-oxo-4-arylthiazol-3-yl)-1H-imidazole-4-carboxamides under the action of a base.     

Spectrophotometric determination of dimethyl sulphoxide

A spectrophotometric method for the determination of milligram quantities of dimethyl sulphoxide in aqueous solutions has been developed. The method is based on the medium effect on the visible absorption spectra of metal salt solutions. Out of several compounds investigated, iron(III) alum was chosen as most suitable for this purpose. Beer's law is obeyed for dimethyl sulphoride concentrations up to 20 mg ml at 410 nm. Dimethyl sulphone does not interfere and dimethyl sulphide can be tolerated in amounts up to 25 % of the sulphoxide present. Possible interferences caused by metal cations can be avoided by passing the sample through a cation-exchanger before adding the reagent. The molar absorptivity is 3 l.mole(-1).cm(-1) at 410 nm, and the average relative error +/- 0.5%.     

Superoxide generation in alkaline dimethyl sulphoxide

The generation of superoxide (O₂) in alkaline dimethyl sulphoxide (DMSO) is investigated by using electron spin resonance and chemiluminescence for the detection of oxygen species. The concentration of superoxide in this system corresponds to the concentration of oxygen dissolved in DMSO. In tightly stoppered vessels, the superoxide is stable for more than 24 h; agitation of the mixture in open vessels rapidly decreases its concentration. The presence of hydroxyl, carbon-centred and superoxide radicals is demonstrated by spin trapping. Alkaline DMSO is not recommended for superoxide dismutase assays.     

Diminished reactivity of ortho-substituted phenacyl bromides toward nucleophilic displacement

A systematic increase of substitution rates by tert-butylamine on alpha-bromopropiophenones is observed with meta or para substituents with increasing electron-withdrawing ability (k x 10(3) L M(-1) min(-1) = 12.7 (p-CH(3)), 15.7 (o-F), 20.5 (H), 20.0 (p-Cl), 23.6 (m-Cl), 27.3 (p-CF(3))). Within an ortho-substituted series, the reactivities decrease (k x 10(3) L M(-1) min(-1) = 7.64 (o-OCH(3)), 5.31 (o-CH(3)), 2.85 (o-Cl), 2.40 ( o-CF(3))). Ortho-substitution results occur from rotational barrier effects and an Adelta(sigma)+ Bdelta(sigma)+ repulsion. The major bonding contribution between reaction and alpha-substituent centers (A-B) is only the sigma bond. When pi bonding is allowed between A and B (meta/para-substitution), delocalization and stabilization of the reacting center occurs.     

Carbon-13 NMR spectra of some 4-substituted phenacyl bromides

The ¹³C NMR signals for some 4- substituted phenacyl bromides were assigned. The experimental chemical shifts of the aromatic ring carbons are in close agreement with those calculated using substituent chemical shifts. Both the carbonyl and the α-methylene carbons exhibit upfield shifts compared with those of the corresponding 4-substituted acetophenones.     

Some dimethyl sulphoxide and sulphide complexes of ruthenium

Some dimethyl sulphoxide (DMSO) and dimethyl sulphide (DMS) compounds of ruthenium, viz. [Ru(DMSO)₆]X₃ (X = Cl, ClO₄), yellow and red isomers of [Ru(DMSO)₄Cl₂], M[Ru(DMSO)₂Cl₄] [M = Na, Bu₄N (Bu₄N = tetrabutylammonium)], [Ru(DMS)₃Cl₃] and [Ru(DMS)₃Cl₃]₂ have been prepared and their conductivities, thermograms and IR spectra are discussed. Ru-S(DMSO) and Ru-O(DMSO) bonding is found to be present in those complexes containing more than two DMSO ligands. In the case of [Ru(DMSO)₂Cl₄]⁻, Ru-DMSO bonding involves only sulphur coordination. Form far IR data, [Ru(DMS)₃Cl₃] and its dimer are assigned a mer-configuration.     

Molar cotton-mouton constants and anisotropy of magnetic susceptibility of benzyl chlorides and benzyl bromides

Conclusions Due to thearom^–gsC-Hal* interaction, the magnetic susceptibility ellipsoids of -haloalkylbenzenes, with the exception of ,'-p-xylylidene bromide, undergo rearrangement of the semimajor axes with a decrease in the diamagnetic component in direction 1, 4 and along the axis of symmetry of the electrons in the ring.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No No. 7, pp. 1552–1557, July, 1986.     

Quantitative determination of esters by saponification in dimethyl sulphoxide

A method is given for the quantitative determination of esters which makes use of the unusually rapid rate of their alkaline hydrolysis in aqueous dimethyl sulphoxide medium. Only 5 min heating on a steam-bath is needed for quantitative hydrolysis of most esters, and many react completely in 5 min at room temperature. When hydrolysis is complete, the excess of base is titrated with standard acid, using a visual indicator.     

Debromination of phenacyl and benzylic bromides with tertiary stibine and the mechanistic consideration

Tributylstibine is an efficient reagent for debromination of phenacyl and arylmethyl bromides. The mechanistic difference between stibine and phosphine is discussed briefly.     

Formation of homoallylic bromohydrins in indium-mediated allylation reactions of phenacyl bromides in aqueous solution

A method is described for carrying out indium-mediated allylation reactions of phenacyl bromides in aqueous solution that form homoallylic bromohydrins. By employing subsequent base treatment, the homoallylic bromohydrins were converted to allylic epoxides. Finally, the process has been used as a key step in a concise sequence for the synthesis of 3-allylbenzofuran.