- Nonequilibrium solvent polarization in kinetics of SN2 reactions
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The solvent effect on the experimental activation barriers for the reactions of methyl iodide with chloride and thiocyanate ions was analyzed according to the Marcus and Shaik theories, considering SN2 mechanism in terms of a single electron shift. The linear increase in the solvent reorganization energy of the Marcus theory (after removing contributions from the specific solvation) with the solvent Pekar factor, describing the effect of the nonequilibrium solvent polarization, was observed for six aprotic solvents. The direct support of the title effect based on the Shaik theory was less evident; however, in general, the calculated activation barriers in 10 solvents change parallel with the experimental ones.
- Jaworski
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- Halomethane biosynthesis: Structure of a SAM-dependent halide methyltransferase from arabidopsis thaliana
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It's a gas ! The structure of the halomethane-producing halo/thiocyanate methyltransferase enzyme from plants has been determined. The halide ion and the methyl group of S-adenosyl-L-methionine (SAM) were modeled into the active site (see picture; chloride: green sphere; SAM: C green, O red, S yellow, N blue), which indicated their predisposition for reaction. (Figure Presented)
- Schmidberger, Jason W.,James, Agata B.,Edwards, Robert,Naismith, James H.,O'Hagan, David
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- Vapor generation of inorganic anionic species after aqueous phase alkylation with trialkyloxonium tetrafluoroborates
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Aqueous phase reaction of trialkyloxonium tetrafluoroborates, R 3O+BF4- (R=Me, Et) has been tested in the alkylation of simple inorganic anionic substrates such as halogen ions, cyanide, thiocyanate, sulphide an
- D'Ulivo, Alessandro,Pagliano, Enea,Onor, Massimo,Pitzalis, Emanuela,Zamboni, Roberto
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experimental part
p. 6399 - 6406
(2010/04/06)
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- Polymer-supported thiocyanate as new, versatile and efficient polymeric reagent for conversion of alkyl halides to corresponding alkyl thiocyanates under mild conditions
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Crosslinked poly(N-methyl-4-vinylpyridinium)thiocyanate [P 4-Me]SCN (II) is prepared easily and is used as a new polymeric reagent for synthesis of alkyl thiocyanates from alkyl halides under mild and nonaqueous conditions. The used polymeric reagent usually can be removing quantitatively and be regenerated.
- Zarchi, Mohammad Ali Karimi
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p. 1299 - 1302
(2008/02/13)
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- Using Kamlet-Taft solvent descriptors to explain the reactivity of anionic nucleophiles in ionic liquids
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In this paper, we report the effect of ionic liquids on substitution reactions using a variety of anionic nucleophiles. We have combined new studies of the reactivity of polyatomic anions, acetate, trifuoroacetate, cyanide, and thiocyanide, with our previous studies of the halides in [C4C 1Py][Tf2N], [C4C1py][TfO], and [C4C1im][Tf2N] (where [C4C 1im]+ is 1-butyl-3-methylimidazolium and [C 4C1py]+ is 1-butyl-1-methylpyrrolidinium) and compared their reactivities, k2, to the same reactions in the molecular solvents dichloromethane, dimethylsulfoxide, and methanol. The Kamlet-Taft solvent descriptors (α, β, π*) have been used to analyze the rates of the reactions, which were found to have a strong inverse dependency on the α value of the solvent. This result is attributed to the ability of the solvent to hydrogen bond to the nucleophile, so reducing its reactivity. The Eyring activation parameters (ΔH? and ΔS?), while confirming the reaction mechanism, do not offer obvious correlations with the Kamlet-Taft solvent descriptors.
- Crowhurst, Lorna,Falcone, Ruben,Lancaster, N. Llewellyn,Llopis-Mestre, Veronica,Welton, Tom
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p. 8847 - 8853
(2007/10/03)
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- Flash vacuum pyrolysis (F.V.P.) of 1,2,4-benzotriazine derivatives
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Flash vacuum pyrolysis of 3-methylsulfanyl-1,2,4-benzotriazine N-oxide, 3-methylsulfanyl-1,2,4-benzotriazine, and 3-phenyl-1,2,4-benzotriazine are described. The N-oxide derivative underwent deoxygenation between 500 and 600°C, whereas at higher temperatures both methylsulfanyl compounds, besides yielding the same products, also gave benzimidazole formed by an independent mechanism. Transformation of these derivatives between 600 and 750°C led to formation of a complex reaction mixture indicating the radical nature of the processes. The phenyl substituted derivative was studied between 575 and 650°C and afforded benzonitrile and traces of biphenylene.
- Riedl, Zsuzsanna,Hajós, Gy?rgy,Peláez, Walter J.,Gafarova, Ioulia T.,Moyano, Elizabeth L.,Yranzo, Gloria I.
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p. 851 - 856
(2007/10/03)
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- Nucleophilicity towards a Saturated Carbon Atom: Rate Constants for the Aminolysis of Methyl 4-Nitrobenzenesulfonate in Aqueous Solution. A Comparison of the n and N+ Parameters for Amine Nucleophilicity
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Second-order rate constants (kNu) have been measured in aqueous solution (I = 0.1 mol dm-3, 25 deg C) for the SN2 reactions of methyl 4-nitrobenzenesulfonate with ammonia, 41 primary amines, 20 secondary amines,29 tertiary amines and 7-anionic nucleophiles.For the aminolysis reactions, Broensted-type correlations of nucleophilicity with basicity require the classification of all amines in terms of strictly defined structural classes with βnuc in the range 0.15-0.39.Swain-Scott plots indicate that simple amines, water and other light-atom nucleophiles (hydroxide, azide and cyanide anions) are five times more reactive than heavy-atom nucleophiles (thiosulfate, thocyanate, iodide and bromide ions).For amine nucleophiles there is a close linear correlation (of slope 0.44 , and including both primary and secondary amines) between log kNu for the aminolysis of methyl 4-nitrobenzenesulfonate and log kNu for amine addition to the 1-methyl-4-vinylpyridinium cation.This correlation demonstrates a close linear relationship between the Swain-Scott n parameter and Ritchie's N+ parameter for amine nucleophiles in aqueous solution (N+ = 2.1n - 4.3).
- Bunting, John W.,Mason, Jacqueline M.,Heo, Christina K. M.
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p. 2291 - 2300
(2007/10/02)
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- Biomimetic catalysis of SN2 reactions through cation-π interactions. The role of polarizability in catalysis
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Cyclophane hosts 1 and 2 have been shown to be effective catalysts for both the alkylation of quinoline structures to produce quinolinium salts and the dealkylation of sulfonium salts to produce sulfides. Thus, reactions that develop positive charge in the transition state and reactions that destroy positive charge are accelerated. The former observation is not surprising, given the well-documented ability of these hosts to bind cations through the cation-π interaction. The catalysis of the dealkylation reactions, however, along with several other observations, suggests that some other factor is involved in the catalysis. It is proposed that the high polarizability of the transition states is well matched to the very polarizable hosts and that this contributes to the catalysis.
- McCurdy, Alison,Jimenez, Leslie,Stauffer, David A.,Dougherty, Dennis A.
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p. 10314 - 10321
(2007/10/02)
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- N-Phenylpyrazole derivatives
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The invention provides N-phenylpyrazole derivatives of the formula: wherein R1 represents alkyl optionally substituted by halogen, R2 represents alkyl, alkenyl or alkynyl optionally substituted by halogen, R3 represents a phenyl group substituted in the 2--position by halogen; in the 4-position by optionally halo substituted alkyl or alkoxy; and optionally in the 6-position by halogen; and m and n are independently 0, 1 or 2; which are active against arthropod, plant nematode, helminth and protozoal pests.
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- A SIMPLE, BIOGENETICALLY MODELED SYNTHESIS OF 4-(METHYLTHIO)BUTYL THIOCYANATE: THE REACTION OF THIOCYANATE ANION WITH S-METHYL-(1,n)-EPITHIONIUM IONS
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The reaction of S-methylthiolanium fluorosulphate with thiocyanate ion gives predominantly 4-(methylthio)butyl thiocyanate, a result which is in accord with a hypothesis for the biogenesis of this compound, and which has implications for the natural occurrence of analogous thiocyanates.
- Benn, M. H.,Singh, Vinod K.
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p. 940 - 942
(2007/10/02)
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- 1,3-Oxazines and Related Compounds. IX. Alkylation, Acylation, and Cleavage Reaction of 6-Methyl-4-oxo-2-thioxo-3,4-dihydro-2H-1,3-oxazine
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Alkylation of the title compound (2) with alkyl halides in the presence of Et3N proceeded exclusively on the sulfur atom to give the alkyl-1,3-oxazine derivatives.Acylation with acyl chlorides took place regioselectively on the nitrogen atom, giving the N-acyl derivatives. 1,3-Oxazine 2 was found to undergo cleavage of the ring into acetylketene and thiocyanic acid.Hence, treatment of 2 with alkyl halides in the presence of K2CO3 gave alkyl thiocyanates; treatment with active methylene compounds afforded γ-pyrone derivatives.N-Acyl derivatives of 2 also underwent thermal cleavage of the ring, leading to the corresponding acyl isothiocyanates.Keywords - 2-thioxo-4-oxo-1,3-oxazine; acetylketene; thiocyanic acid; acyl isothiocyanate; alkyl thiocyanate; acylation; alkylation; substituted γ-pyrone.
- Yamamoto, Yutaka,Morita, Yasuo
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p. 2957 - 2962
(2007/10/02)
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- Solvent Properties of Dichloromethane. 1. The reactivity of Dichloromethane toward Some Ionic Nucleophiles. Dichloromethane as Solvent for Finkelstein Reactions
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The reactions of dichloromethane with variuos pseudohalide ions, N-3, NC-, NCTe-, NCSe-, NCS- and OCN-, have been studied kinetically under homogeneous conditions in dichloromethane as solvent at 25.0 deg C.In the 10-3 M concentration range the half-lives of the reactions are 70 min(N-3), 80 min(NC-), 15 h(NCTe-), 60 h(NCSe-), 400 h(NCS-) and 600 h(OCN-). 1,2-Dichloroethane in 1,2-dichloroethane is slightly more reactive toward N-3 and NCS- with half-lives of 60 min and 150 h, respectively.CH2Br2 in CH2Br2 is 400 times as reactive as is CH2Cl2 in CH2Cl2 toward NCS-; half-life 60 min.The homogeneous Finkelstein reactions between methyl iodide and NCS- and Cl- in CH2Cl2 were studied kinetically at 25.0 deg C.For equal initial concentrations of NCS- (1.2x10-2 M) the reactivity order is SCN>Ph4AsSCN>Bu4NSCN as anticipated from their association constants in CH2Cl2.When corrected for ion-pairing the second order rate constants are fairly independent of the counterion.The MeI-NCS- and the MeI-Cl- reactions proceed as rapidly in dichloromethane as in the usual dipolar aprotic solvents of considerably higher dielectric constants.The relative uncorrected second order rate constants for the MeI-NCS- reaction inCH2Cl2 in 1,2-dichloroethane and 1,1,2,2-tetrachloroethane are 1:0.8:0.2 at 25.0 deg C.
- Bekkevoll, Steinar,Svorstoel, Idar,Hoeiland, Harald,Songstad, Jon
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p. 935 - 946
(2007/10/02)
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- SYNTHESIS OF ISOTHIOCYANATOPHOSPHORANES AND ISOTHIOCYANATOPHOSPHONIUM SALTS VIA OXIDATIVE ADDITION OF THIOCYANOGEN AND LIGAND SUBSTITUTION. NOVEL REAGENTS FOR CONVERTING HYDROXY GROUPS INTO THIOCYANATE AND ISOTHIOCYANATE FUNCTIONS UNDER MILD CONDITIONS
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The oxidative addition of thiocyanogen to triphenilphosphine has been investigated by (31)P NMR spectroscopy showing the formation of the isothiocyanatophosphonium salt 8.The analogous reaction between thiocyanogen and alkyl o-phenylene phosphites 7 leads to diisothiocyanatophosphoranes 9.The same products were prepared via ligand substitution from the corresponding chlorophosphonium salt 12 and alkyldichloro-o-phenylene phosphoranes 13 by the action of potassium thiocyanate in the presence of 18-crown-6-ether or more conveniently using lead thiocyanate.The phosphonium salt 8 and phosphoranes 9 were employed as convenient novel reagents for converting hydroxy groups into thiocyanate and isothiocyanate function with high stereoselectivity under very mild conditions.The efficient synthesis of acylisothiocyanates RCONCS,R2P(O)NCS and R2P(S)NCS via addition of thiocyanogen to mixed anhydrides is of special interest.
- Burski, J.,Kieszkowski, J.,Michalski, J.,Pakulski, M.,Skowronska, A.
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p. 4175 - 4182
(2007/10/02)
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- Gasphase Reactions, 33. Reactivity of Cyanogen Towards White Phosphorus and Towards Dimethyl Disulfide
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The experimental advantages of the optimization of gasphase reactions using a photoelectron spectrometer are exemplified by investigating the reaction of cyanogen with white phosphorus and with dimethyl disulfide.Whereas NCCN does not react with any of the components of the thermal equilibrium P4 P2 even at 1470 K (!), H3CSSCH3 at 950 K is quantitatively converted, the main product being CH3SCN.
- Bock, Hans,Wittmann, Joerg,Mueller, Hartmut
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p. 2338 - 2345
(2007/10/02)
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- Comparison of the Thermal, Photochemical, and Mass Spectrometric Fragmentation of Sulphur Heterocycles with cis-Dithioethene-Structure
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The mass spectrometric primary fragmentation of 3-methylthio-1,4,2-dithiazines 1, 1,4-dithiins 2, 2,3-dihydro-1,4-dithiin-2-ones 4, 1,3-dithiole-2-ones 5, 2-imino-1,3-dithioles 6 and 1,3-dithiole-2-thiones 7 is compared with their thermolytical and photochemical reaction.In the mass spectra an intense peak of the dithiete radical ion is observed, if in the compounds an energetically favourable neutral molecule is preformed: in 1 methyl rhodanide, in 3 ethene, in 4 ketene, in 5 carbon monoxide and in 6 hydrogen cyanide.The substances 1, 3-6 - with the restriction by 3 - yield photochemically the dithiete, too.The photolysis of dithiazines 1 is wave length dewpendent.Mass spectrometrically, thermally and photochemically the dithiins 2 form thiophenes.The dithiolethiones 7 decompose mass spectrometrically and thermally into carbon disulfide, sulfur and ethynes, but photochemically they form tetrathiafulvalenes.The fragmentation of the compounds 1-6 is analogous in mass spectrometry and photolysis; 2, 3, 5 and with reservation 1 show similar mass spectrometric, thermal and photochemical reactivity.Posible reasons for these analogies are discussed.The dithietes, generated by photolysis of the compounds 1, 4, 5 or 6 react with iron penta-, nickel tetra-, molybdenum hexa- and tungsten hexacarbonyl in the preparative scale to the corresponding dithiolene complexes.
- Fanghaenel, E.,Poleschner, H.
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- The chemistry of small ring compounds. Part 45. Thermolysis and photolysis of 1-(alkylthio)cyclopropyl azides
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1-(Alkylthio)cyclopropyl azides - readily accessible from the corresponding chlorides and bromides - are smoothly decomposed at 70 deg C with nitrogen evolution.The main process is a ring enlargement to 2-(alkylthio)azetines 2, accompanied by cleavage to thiocyanate and alkene.Reaction parameters for the thioazetine formation suggest a two-step mechanism involving an intermediate cyclopropylnitrene.Ring enlargement can be averted if the alkylthio group contains a double bond.Thus, the allylthiocyclopropyl azide 8 gives a nitrene that can interact not only with the three-membered ring but also with the double bond, leading to spirocyclic products (15 and 16 in Scheme 1).The photolysis (300 nm) of these azides gives exclusively the fragmentation products thiocyanate and olefin.
- Jorritsma, R.,Steinberg, H.,Boer, Th. J. de
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p. 307 - 312
(2007/10/02)
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- REACTION OF METHYL AND PHENYL PICRATES WITH NUCLEOPHILES
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The reactions of 2,4,6-trinitroanisole with various nucleophiles Me3SnM, Me3SiLi, BuLi, Me4NBBu4, PhMgI, CN-, lithium (potassium) succinimide, F-, Cl-, Br-, SCN-, NO2-, NO3-, HCO3-, PhSO2-,AcO-, S2- were investigated.It was found that the final products are the picrate and the corresponding methyl derivatives.The formation of intermediate ? complexes was detected in a series of the reactions (Me3SnLi, potassium succinimide, Bu4B-, CN-, NO2-, PhSO2-).Possible mechanisms for the reaction are examined.Reactions of 2,4,6-tricyanoanisole and phenyl picrate with certain nucleophiles were also investigated.
- Artamkina, G. A.,Egorov, M. P.,Beletskaya, I. P.,Reutov, O.A.
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