A crossed molecular beam study of the O(1D) + C(3)H(8) reaction: multiple reaction pathways.

The O((1)D) + C(3)H(8) reaction has been reinvestigated using the universal crossed molecular beam method. Three reaction channels, CH(3) + C(2)H(4)OH, C(2)H(5) + CH(2)OH, and OH + C(3)H(7), have been observed. All three channels are significant in the title reaction with the C(2)H(5) formation process to be the most important, while the CH(3) formation and the OH formation channels are about equal. Product kinetic energy distributions and angular distributions have been determined for the three reaction channels observed. The oxygen-containing radicals in the CH(3) and C(2)H(5) formation pathways show forward-backward symmetric angular distribution relative to the O atom beam, while the OH product shows a clearly forward angular distribution. These results indicate that the OH formation channel seems to exhibit different dynamics from the CH(3) and C(2)H(5) channels.     

Total synthesis of scytophycin C. 2. Coupling reaction of the C(1)-C(18) segment and the C(19)-C(31) segment, a key macrolactonization, and the crucial terminal amidation reaction

[reaction: see text] Stereoselective syntheses of the C(1)-C(18) segment (segment A) and the C(19)-C(31) segment (segment B) are described in the preceding paper. This paper reports the key coupling reaction of both segments, 22-membered lactonization, and the crucial terminal amidation reaction culminating in the total synthesis of scytophycin C.     

Titanium(IV) chloride and quaternary ammonium salt promoted Baylis-Hillman reaction.

The Baylis-Hillman reaction of aldehydes with alpha,beta-unsaturated ketones can be drastically affected by the reaction temperature and Lewis bases. When the reaction was carried out at -78 degrees C using catalytic amounts of quaternary ammonium salts (R4N+X-, X = Cl, Br, I) as Lewis bases, in the presence of titanium(IV) chloride, the chlorinated aldol adduct 1 was obtained as the major product. Quaternary ammonium bromides and iodides (R4N+X-, X = Br, I) have higher catalytic activity than corresponding chlorides (R4N+Cl-). Quaternary ammonium fluorides (R4N+F-) do not have activity at all. The amounts of Lewis acid and quaternary ammonium salts used affect the reaction rate and product. A plausible reaction mechanism is proposed. If the reaction was carried out at room temperature (about 20 degrees C) in the presence of titanium(IV) chloride and quaternary ammonium salts (R4N+X-, X = Cl, Br, I), the elimination product 3, derived from 1, was formed as the major product.     

Iron(II)-chloramine-T reaction

When a large excess of the oxidant is used in the iron(II)-chloramine-T reaction at pH 2.56-5.6 the amount of oxidant consumed is well above the stoichiometric amount required to oxidize iron(II) to iron(III). This has been attributed to the formation and subsequent behaviour of free radicals during the reaction. The formation of free radicals has been experimentally demonstrated. They apparently dimerize to give products of the type R-NCl-NCl-R (R = CH(3)C(6)H(4)SO(2)), which are further oxidized by chloramine-T. The dimerized species liberate iodine very slowly from acidified potassium iodide. This explanation satisfactorily accounts for the observed extent and rate of destruction of excess of chloramine-T in presence of small amounts of Fe(II) or bromide at pH 2.65-4.70. The storage of chloramine-T in metal containers might cause extensive destruction of the oxidant by a similar free radical mechanism and should be avoided.     

Polyfuryl(aryl)alkanes and their derivatives 9. Polyfuryl(aryl)methanes in the diels-alder reaction

The reaction of polyfuryl(aryl)methanes with N-(3,5-dichlorophenyl)maleimide has been studied. It was found that tetrasubstituted methanes do not react. Difurylmethane, gem-difurylethane, gem-difurylethane, and trifurylmethane form mono- and diadducts, and difurylarylmethanes form only monoadducts. The molecular and crystal structure of the diadduct of gem-difurylethane- gem-bis {4-aza-7-methyl-10-oxa-4-(3,5-dichlorophenyl)tricyclo-[5,2,1,0 _2,6]deca-8-en-3,5-dion-1-yl}ethane has been studied.For Communication 8, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 751–758, June, 1993.     

Kinetics of bromate-cerium(III) reaction

The induction period and the fast, and slow rates of the bromate-cerium(III) reaction were examined. It was found that the duration of the induction period was inversely proportional to both the bromate and acid concentrations, and that the fast reaction rate was proportional to the square of bromate concentration.

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(III). , , .

     

The photo-dehydro-Diels-Alder (PDDA) reaction

The photo-dehydro-Diels-Alder (PDDA) reaction is a valuable extension of the classical Diels-Alder (DA) reaction. The PDDA reaction differs from the DA reaction by the replacement of one of the C-C-double bonds of the diene moiety by a C-C triple bond and by the photochemical triggering of the reaction. This entails that, in contrast to the DA reaction, the PDDA reaction proceeds according to a multistage mechanism with biradicals and cycloallenes as intermediates. The PDDA reaction provides access to a considerable variety of compound classes. For example, 1-phenylnaphthlenes, 1,1'-binaphthyls, N-heterocyclic biaryls, and naphthalenophanes could be obtained by this reaction.     

Stoichiometry of the reaction between iron(II) and chromium(VI)

The suitability of potassium dichromate as a standard oxidant has been examined by comparing direct oxidation of iron(II) solutions with alternative back-titration procedures.     

Poly(ethyleneglycol) (PEG): a rapid and recyclable reaction medium for the DABCO-catalyzed Baylis-Hillman reaction

PEG (400) has been used as a rapid and recyclable reaction medium for the Baylis-Hillman reaction with the conventional basic catalyst DABCO (20 mol %) with very good yields of products. Recyclability is achieved with no further addition of DABCO to the reaction medium for over four runs without substantial loss in yields. Incidentally, DABCO is recycled for the first time in this transformation.     

Microdetermination of arsenic(III) and osmium(VIII) through osmium-thiourea reaction

Osmium-thioureau reaction is slow under conditions described in earlier methods. In the present study it has been observed that arsenic(III) catalyzed the reaction. Based on this, qualitative and quantitative methods are described for the determination of both osmium and arsenic. Interference study of 30 ions showed they do not interfere.     

Photoexcitation of octacyano complexes of molybdenum(IV) and tungsten(IV) with ethylene diamine. Kinetics and reaction mechanism

Summary The kinetics of thermal reactions of photochemically generated aquaheptacyano Mo^IV and W^IV complexes and their protonated and deprotonated forms have been studied spectrophotometrically in buffer solutions at pH 5.0–10.0, and ionic strength, 8×10^–2 M at 25°C. A reaction scheme for the photochemical and thermal reactions of the Mo^IV and W^IV octacyano complexes with ethylene diamine is proposed. Rate constants and quantum yields for these systems are maximal at pH 8.0. At pH>8.0, the reverse reaction, generating octacyano complexes from heptacyano species, is faster; at low pH the ligand is protonated and is less reactive. Quantum yields are higher for Mo than for W owing to the shorter life time of excited state species. This is because physical deactivation is expected to be more rapid in the heavier element due to enhanced spin-orbit coupling. Furthermore Mo-induced splitting is larger in [W(CN)₈]^4– as compared to [Mo(CN)₈]^4– which results in greater bond strength for tungsten.     

Kinetics and mechanism of indigo carmine-acidic iodate reaction. An indicator reaction for catalytic determination of Ru(III) ion

A kinetic study of uncatalyzed and Ru(III) catalyzed oxidation of indigo carmine(IC) (disodium 3,3′-dioxobi-indolin-2,2′-ylidene-5,5′-disulphonate) by iodate ion in aqueous sulphuric acid solution is reported. The uncatalyzed reaction order was found to be four; one each with respect to IC and iodate ion and second order with H⁺ ion. The Ru(III) catalyzed reaction was of fifth order, second order with respect to H⁺ and first order with respect to reductant, oxidant, and catalyst. Stoichiometric ratios of both reactions were the same with a 3:2 reductant-oxidant ratio. In both uncatalyzed and catalyzed reactions isatin-5-monosulphonic acid (2,3-dioxoindoline-5-sulphonic acid) was observed as the oxidation product. Rate constants for both the reactions are reported. Reaction mechanisms consistent with the experimental data are suggested. Further, a fixed time method is described for the determination of Ru(III), based on its ability to catalyze the oxidation of IC by acidic iodate. Using [H⁺] 2.25M, [iodate] 1.00 × 10^?3M and [IC] 5.0 × 10^?5M, in presence of Ru(III), the reaction followed first order kinetics with respect to IC. The interference of various cations, neutral salts, and potassium iodide on the determination of Ru(III) was studied using synthetic mixtures. The selectivity of the method and the recommended procedure are described.     

Perfluoro-1-(butylimino)butyl isothiocyanate. Synthesis and reaction with n-propylamine

The reaction of perfluoro-5-azanon-4-ene with KSCN in an aprotic dipolar solvent provides perfluoro-1-(butylimino)butyl isothiocyanate. The latter was reacted with n-propylamine in the presence of triethylamine to obtain fluoro-substituted derivatives of thiourea, heptafluoropropionic acid, and 1,3,5-thiadiazine.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1655–1658.Original Russian Text Copyright © 2004 by Furin, Zhuzhgov.This revised version was published online in April 2005 with a corrected cover date.     

Tris(trimethylsilyl)silane promoted radical reaction and electron-transfer reaction in benzotrifluoride

Tris(trimethylsilyl)silane (TTMSS) promoted free radical reaction in benzotrifluoride (BTF) was investigated. Compared to same reaction using environmentally less desirable tri-n-butyltin hydride (TBTH) in benzene, less quantity of BTF than that of benzene can be used because of slower hydrogen atom transfer from TTMSS than that from TBTH toward primary alkyl radicals. Also, electron-transfer reactions promoted by tris(p-bromophenyl)aminium hexachloroantimonate (TBPA) and FeCl₃ were conducted in BTF. Then, TBPA was found to be effective in BTF comparably to that in methylene chloride. In addition, an interesting observation that FeCl₃ promoted reaction was accelerated by the addition of imidazolium salt was made. All the results suggest that BTF is a tolerable solvent for free radical reaction with TTMSS and electron-transfer reactions using TBPA as well as FeCl₃.     

Fvp of bis- and tris-(pyrazol-1-yl)methane. A radical reaction

Flash vacuum pyrolysis of bis- and tris-(pyrazol-1-yl) methane was carried out. Alpha, gamma and radical eliminations were considered. The products actually formed correspond to a radical reaction. In the case of bis-(pyrazol-1-yl) methane, working at higher temperatures, pyrimidine was obtained. This compound is formed by rearrangement of a PzCH₂ radical.     

Kinetic-catalytic determination of vanadium(IV) using methyl orange-bromate redox reaction.

Determination of V(IV) based on its catalytic effect on the reaction between Methyl Orange and bromate in thepresence of citric acid was studied. The calibration curve obtained by fixed-time method was linear in the range of 2.5-300 ng ml(-1). By use of slope method, a calibration curve containing two linear portions were obtained. Using fixed-time and slope methods, we obtained detection limits of 0.8 and 1.5 ng ml(-1), respectively. Fe2+, As(III), V(V) and Hg2+ interfered. The method was successful for analysis of water samples.     

Electroreductive cyclization. A comparison of the electrochemical and analogous chemical (MIRC) reaction

Several examples which illustrate the contrasting and complementary aspects of electroreductive cyclization and MIRC reactions are presented. A brief mechanistic discussion of the electrochemical reaction is given and two examples of the use of an electrochemically generated base are provided.