Halide Substitution Research Articles

Photochemical Arylation Reactions by 4‐Chlorothioanisole

AbstractThe photochemistry of 4‐chlorothioanisole (1) was investigated in various solvents, and it was found to involve the reduction to thioanisole as the main process. This occurs by heterolytic fragmentation of the triplet state of 1 and formation of the triplet 4‐thiomethoxyphenylium ion, as supported by DFT calculations. The cation is trapped by alkenes and, less efficiently, by benzene, resulting in new examples of the recently emerging arylation reactions by SN1 substitution of phenyl halides. The products from alkenes involve the phenonium ion as a further intermediate. The product distribution differs from the analogous reactions via 4‐methoxyphenylium for including a larger proportion of 4‐(β‐substituted alkyl)‐ rather than 4‐allylthioanisoles derivatives in alcohols, for the lower fraction of rearranged α‐substituted 4‐alkylthioanisoles and for the formation of some 4‐cyclopropylthioanisole with allyltrimethylsilane. The difference is accounted for by the more developed dipolar character of the C–C cyclopropane bonds in the intermediate phenonium, as indicated by DFT calculations.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Hybrid Perovskite Resulting from the Solid-State Reaction between the Organic Cations and Perovskite Layers of α1-(Br-(CH2)2-NH3)2PbI4

The alpha1-(Br-(CH(2))(2)-NH(3))(2)PbI(4) hybrid perovskite undergoes a solid-state transformation, that is, the reaction between the organic cations and the perovskite layers to give the new hybrid perovskite (Br-(CH(2))(2)-NH(3))(2-x)(I-(CH(2))(2)-NH(3))(x)PbBr(x)I(4-x), based on mixed halide inorganic layers. This transformation has been followed by a conventional powder X-ray diffraction system equipped with a super speed detector, and both solid-state (13)C NMR and ESI/MS measurements have been adopted in the estimation of the rate of halide substitution. The first reaction step leads to the special composition of x approximately 1 (A phase), while the complete substitution is not achieved even at elevated temperature (x(max) approximately 1.85 (B phase)). This unprecedented solid-state reaction between organic and inorganic components of a hybrid perovskite can be considered as a completely new strategy to achieve interesting hybrid perovskites.

Ionic Transformations in Extremely Nonpolar Fluorous Media: Phase Transfer Catalysis of Halide Substitution Reactions

Fluorous solutions of alkyl halides Rf8(CH2)mX (m = 2, 3; X = Cl, Br, I) are inert toward solid or aqueous NaCl, NaBr, and KI, but halide substitution occurs in the presence of fluorous phosphonium salts (10 mol %, 76-100 degrees C).

Comment on “A Novel and Simple Solvent‐Free Method for Nucleophilic Aromatic Substitution of Inactive Aryl Halides”

Inability to reproduce the results of Ref. 1 is reported.

Photoinduced Nucleophilic Substitution of Aryl Halides with Potassium Thioacetate – A One‐Pot Approach to Aryl Methyl and Diaryl Sulfides

AbstractAryl methyl sulfides and diaryl sulfides were prepared by photoinduced reactions of potassium thioacetate with aryl halides under entrainment conditions. Without isolation, the arene thiolates obtained by the aromatic substitution were quenched with methyl iodide to afford the aryl methyl sulfides in 26–59 % yields in a “one‐pot” procedure together with the diaryl sulfides in variable yields (3–31 %). By optimization of the reaction conditions it was possible to improve the formation of the Ar2S, going from moderate to good yields (64–83 %). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, Structure, and Unusual Reactivity of β-Halovinyl Cobalt Porphyrin Complexes

The preparation, structures, and reactivity of tetraphenylporphyrin (TPP) cobalt halovinyl complexes are reported. Beta-halovinyl complexes of (TPP)Co(E-CHCHX) (X = Br and I) were prepared from the insertion of acetylene into the cobalt halide bonds of the corresponding halide complexes. The reactivity of these compounds and of the previously reported (TPP)Co(E-CHCHCl), was studied in depth, and it was found that complex reactivity increased with the leaving group ability of the halide. A trans-dichlorovinyl cobalt porphyrin complex, (TPP)Co(Z-CClCHCl), was also prepared through the reaction of (TPP)CoNa and TCE. The structures of (TPP)Co(E-CHCHBr), (TPP)Co(Z-CClCHCl), and (TPP)Co(C(2)H) are reported. The C-C bond length of the vinyl group was found to vary for the beta-halovinyl complexes (TPP)Co(E-CHCHX) from 1.211 A for X = Br to 1.234 A for X = Cl and 1.320 A for (TPP)Co(Z-CClCHCl). A comparison of these structures to many chlorovinyl cobalt complexes shows that trans-2-halo substitution results in a dramatically decreased vinyl C-C bond length. The mechanism of halide substitution for the beta-halovinyl complexes was investigated with kinetic experiments that indicated a dissociative mechanism and supported the intermediacy of a cobalt acetylene complex.

Formation of Carbon—Carbon and Carbon—Heteroatom Bonds by Electron Transfer Nucleophilic Substitution of Alkyl Halides

AbstractFor Abstract see ChemInform Abstract in Full Text.

Inside the beltway: The skinny on burning industry issues being addressed by federal agencies and lawmakers

The effect of I–/Cl–and I–/Br–mixing on the thermal and photochemical degradation of organometallic perovskite MeNH3PbI3 (MAPbI3) was studied by X-ray photoelectron spectroscopy, which revealed the opportunity to essentially increase the photo and thermal stabilities of the material depending on the level and position of halide-mixing. The largest positive effect was observed for the small concentration of chloride substituent (MAPbI2.7Cl0.3), while the full halide substitution (MAPbBr3) had a negative effect on the stability of hybrid perovskite.

Ab initio Study of Ni(II) Complexes with Malonic Dialdehyde and Its Derivative

Ab initio quantum-chemical calculations of Ni(II) complexes with malonic and chloromalonic dialdehydes are performed in order to establish their structures and the effect of halide substitution on the structure of chelate cycle of diketonate type in transition metal complexes. The results of calculations with the use of core potential were found to qualitatively agree with the results obtained with direct account of the internal electrons. The basis augmented with polarization functions, as well as by its further splitting, does not give quantitatively new results as compared to standard double-zeta basis. Introduction of halogen atom brings about polarization of a cycle, in particular, M-O bond.

Laboratory Determination of the Carbon Kinetic Isotope Effects (KIEs) for Reactions of Methyl Halides with Various Nucleophiles in Solution

Large carbon kinetic isotope effects (KIEs) were measured for reactions of methyl bromide (MeBr), methyl chloride (MeCl), and methyl iodide (MeI) with various nucleophiles at 287 and 306 K in aqueous solutions. Rates of reaction of MeBr and MeI with H2O (neutral hydrolysis) or Cl− (halide substitution) were consistent with previous measurements. Hydrolysis rates increased with increasing temperature or pH (base hydrolysis). KIEs for hydrolysis were 51 ± 6%0 for MeBr and 38 ± 8%0 for MeI. Rates of halide substitution increased with increasing temperature and greater reactivity of the attacking nucleophile, with the fastest reaction being that of MeI with Br−. KIEs for halide substitution were independent of temperature but varied with the reactant methyl halide and the attacking nucleophile. KIEs were similar for MeBr substitution with Cl− and MeCl substitution with Br− (57 ± 5 and 60 ± 9%0, respectively). The KIE for halide exchange of MeI was lower overall (33 ± 8%0) and was greater for substitution with Br− (46 ± 6%0) than with Cl− (29 ± 6%0).

S‐Trifluoromethyl Esters of Thiocarboxylic Acids, RC(O)SCF3.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Malononitrile as a Carbonyl Synthon: A One‐Pot Preparation of Heteroaryl Amide via a SNAr‐Oxidation—Displacement Strategy.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis and characterisation of hydrophobic modified polyacrylamide

AbstractPolyacrylamide has been modified hydrophobically with low amounts of N‐alkyl groups by a transamidation method, using alkylamines. The amide group in the polymer backbone has been N‐substituted in water solutions, where the substituting amine is water‐soluble. The alkyl groups include N‐alkyl (up to octyl), N,N‐diethyl, N,N‐dipropyl, N‐isopropyl, N,N‐diisopropyl and N‐cyclohexyl groups. This transamidation method is more convenient compared with the traditional micellar copolymerisation methods and the direct method using alkyl halide substitution. However, a limitation of the method is due to the failure to achieve substitution of highly hydrophobic groups such as dodecyl. The mutual insolubility of dodecylamine and the potential substituted product, with N‐dodecyl substitution of polyacrylamide, makes it impractical to carry out the reaction in water. Other mixed solvents were used for the amine substitution, including water with dimethylsulfoxide and ethylene glycol, without transamidation occurring, since these solvents decreased the solubility of polyacrylamide. The NMR and IR spectra of modified polyacrylamides are reported. The mechanism of the reaction under acid‐ and base‐catalysed situations is discussed. Copyright © 2004 Society of Chemical Industry

S-Trifluoromethyl esters of thiocarboxylic acids, RC(O)SCF 3

S-Trifluoromethyl esters of different types of thiocarboxylic acids have been prepared in moderate to excellent yields from halide substitution reactions of the corresponding acid chlorides and tetramethylammonium trifluoromethylthiolate. C 6F 5C(O)SCF 3 undergoes a surprising rearrangement on attempted isolation to give 4-CF 3SC 6F 4C(O)F, which was converted into the corresponding acid.

Malononitrile as a carbonyl synthon: a one-pot preparation of heteroaryl amide via a SNAr-oxidation–displacement strategy

Malononitrile could be utilized as a synthon for the carbonyl moiety via a one-pot process that was initiated via base-mediated SNAr substitution of a heteroaryl halide. Subsequent peracetic acid oxidation of the resultant anion delivered an electrophilic acyl nitrile in situ that readily reacted with added nucleophiles to afford heteroaryl carboxylic acid derivatives. The reaction of the sodium salt of malononitrile with a series of heteroaryl chlorides followed by the subsequent addition of an amine and peracetic acid provided the corresponding heteroaryl amides.

Dihydrobenzoxazines and Tetrahydroquinoxalines by a Tandem Reduction‐Reductive Amination Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The First C2 Selective Halide Substitution Reaction of 2,3‐Epoxy Alcohols by the Use of (CH3O)3B—MX (X: I, Br, Cl) System.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Novel and Simple Solvent Free Method for Nucleophilic Aromatic Substitution of Inactive Aryl Halides

A simple, high yield, and short time method for nucleophilic displacement reaction of inactive aryl halides is reported. The reaction is performed in microwave oven under thermal condition with montmorillonite supported AgNO3.

The first C2 selective halide substitution reaction of 2,3-epoxy alcohols by the use of (CH 3O) 3B–MX (X=I, Br, Cl) system

The first C2 selective halide substitution reactions of 2,3-epoxy alcohols have been realized by the use of the (CH 3O) 3B–MX (X=I, Br, Cl) system, which proceed through novel endo-mode epoxide-opening of intramolecular boron chelates to afford the corresponding C2 halohydrin derivatives with high regio- and stereoselectivity.

Dihydrobenzoxazines and tetrahydroquinoxalines by a tandem reduction‐reductive amination reaction

AbstractA tandem reduction‐reductive amination reaction has been applied to the synthesis of 3,4‐dihydro‐2H‐1,4‐benzoxazines and 1‐acetyl‐1,2,3,4‐tetrahydroquinoxalines. The nitroketones required for the benzoxazine ring closures were prepared by (A) alkylation of the anion derived from 2‐nitrophenol with an allylic halide or (B) nucleophilic aromatic substitution of an allylic alkoxide on 2‐fluoro‐1‐nitrobenzene followed by ozonolysis. Precursors for the quinoxalines were prepared by alkylation of the anion of 2‐nitroacetanilide with an allylic halide followed by ozonolysis. Catalytic hydrogenation of the nitroketones using 5% palladium‐on‐carbon in methanol then gave the target heterocycles by a reduction‐reductive amination sequence. The N‐methyl derivatives for both ring systems were easily prepared by adding 5‐10 equivalents of aqueous formaldehyde prior to the reduction. The dihydrobenzoxazines were isolated in high yield following purification by chromatographic methods; tetrahydroquinoxalines were isolated in a similar manner and possessed differentiated functionality on the two nitrogens.