Regioselective bromination of aromatic compounds with Br2/SO2Cl2 over microporous catalysts

A new selective brominating system Br₂/SO₂Cl₂/zeolite, has been discovered. Partially cation-exchanged Ca²⁺-Y zeolite efficiently catalyzes the selective para-bromination of neat chlorobenzene (CB) by Br₂/SO₂Cl₂ affording a CB conversion of ∼89% and a para-selectivity of ∼97%. During the bromination reaction, SO₂Cl₂ oxidizes HBr, prevents its accumulation within the zeolite pores and yields a more active brominating species. The Ca²⁺-Y catalyst was found to be stable under the bromination conditions, and can easily be regenerated by calcination. The Br₂/SO₂Cl₂/Ca²⁺-Y brominating system could be applicable to other activated aromatic compounds such as o-xylene, toluene and fluorobenzene.     

Real-time mass-spectrometric study of the chemistry initiated by infrared-laser photolysis: CF2Cl2

The infrared-laser photolysis/mass-spectrometric (ILP/MS) technique was used to monitor directly in real time the free-radical and stable reactants and products present in the reactive system initiated by the multiphoton-induced dissociation of CF₂Cl₂. It was found that contrary to conclusions based on final-products analyses, the C₂F₄ observed as a final product in this system is not formed solely through the recombination of: CF₂ radicals, but rather C₂F₄ is produced in a complex series of secondary reactions.     

Perfluoralkyljod-verbindungen: Darstellungen und eigenschaften von CF3JO,CF3JOF2 und CF3JO2

Perfluoroalkyl iodine compounds: preparations and properties of CF₃IO, CF₃IOF₂, and CF₃IO₂. The trifluoromethyl iodine compounds CF₃IO, CF₃IOF₂, and CF₃IO₂ are formed from the reactions of CF₃I, CF₃IF₂ or CF₃IF₄ with ozone or silicon dioxide respectively. Their preparartions, properties, ¹⁹F-nmr spectra, and ir spectra are described.     

Chlorine isotope enrichment in CO2 TEA laser photolysis of CF2Cl2

A number of lines from a CO₂ TEA laser were used to photolyze CF₂Cl₂. Enrichment of the ³⁵Cl and ³⁷Cl isotopes in the molecular chlorine formed during the photolysis was observed using a mass spectrometer. Maximum enrichment was about 1.8. The dependence of enrichment on wavelength, reactant concentration, inert gas pressure, and the presence of SiF₄ is reported. Of particular interest is the persistence of significant enrichment at pressures up to several hundred torr (≈ 10⁵ Pa). Aside from the practical significance of this enrichment at high pressures, it suggests that there are important contributions from isotopically specific interactions after the laser pulse.     

Electron chemistry. Chemical reactions in CCl4, CFCl3 and CF2Cl2 induced by low-energy electrons

Reactions of fragments produced by low-energy (<0.5 eV) electron impact on CCl₄, CFCl₃ and C₂F₂Cl₂ are found to be very specific. This is in contrast to reactions, brought about by photons (either UV or multiple IR) or by electrons of higher energies, e.g. in a discharge. Furthermore, negative ion formation in these molecules is discussed. New values for ΔH_f(CCl₂), ΔH_f(CFCl) and ΔH_f(CF₂) are presented.     

Ionothermal synthesis of the mixed-anion material, Ba3Cl4CO3

A low-temperature ionothermal method for the facile synthesis of the halide carbonate, Ba₃Cl₄CO₃, in single-crystalline form has been developed. This has enabled the first determination of the crystal structure of this material to be carried out. Analysis of single-crystal X-ray diffraction data indicates that barium chloride carbonate crystallises in the orthorhombic space group Pnma (Z=4), with a=8.4074(11), b=9.5886(12), c=12.4833(15) Å (R_w=0.0392). It exhibits a complex structure in which a three-dimensional network is formed from cross-linking of chains of anion-centred octahedra that share faces.     

Electrochemical preparation of graphite intercalation compounds containing a cyclic amide, [CF2(CF2SO2)2N]

Graphite intercalation compounds (GICs) containing the cyclo-hexafluoropropane-1,3-bis(sulfonyl)amide anion, [CF₂(CF₂SO₂)₂N]⁻, are prepared for the first time. Stages 2 and 3 GICs are obtained by electrochemical oxidation of graphite in a nitromethane electrolyte. Gallery heights of 0.85-0.86 nm are determined by powder X-ray diffraction, and the intercalate anion orientation within the intercalate galleries is modeled using an energy minimized anion structure. GIC compositions are determined by thermogravimetric, fluorine and nitrogen analyses. The chemical preparation and bifluoride displacement reactions are compared with a GIC containing the linear bis(trifluoromethanesulfonyl)amide anion, [(CF₃SO₂)₂N]⁻.     

Matrix isolation study of the interaction of excited argon atoms with CF2Cl2, CF2ClBr,and CF2Br2. Infrared spectra of the CF2Cl+ and CF2Br+ molecular ions

The infrared absorptions associated with the two CF stretching fundamentals of CF₂Cl⁺ and CF₂Br⁺ have been identified in studies of the matrix-isolated products of the interaction of excited argon atoms with CF₂Cl₂, CF₂ClBr, and CF₂Br₂. The exceptionally high values of the CF stretching frequencies obtained in these experiments are consistent with the implications of previous experimental and theoretical studies.     

Syn-stereoselective epoxidation of allylic ethers using CF3CO3H.

Good $\text{syn}$-stereoselectivity is observed in the epoxidation of allylic silyl ethers with CF₃CO₃H, indicating a new type of hydrogen-bonded transition state.     

C(CF3)2OH → OCH(CF3)2 Isomerism in some sulfur and phosphorus compounds

The insertion of (CF₃)₂CO into the PH bond of Me_nH_3?nP yields Me_nH_2?nPC(CF₃)₂OH and Me_nH_1?nP[C(CF₃)₂OH]₂ (n=O, 1), respectively [1]. MeP[C(CF₃)₂OH]₂ rearranges giving the diphosphine [MePOCH(CF₃)₂]₂ and the phosphorane MeP[OCH(CF₃)₂]₄. Me₂PH reacts with (CF₃)₂CO forming several products, e.g. MePF[OCH(CF₃)₂]₂ and Me₂PPMe₂ [1]. The phosphines tBu(R)PH(R=Me, tBu), however, add (CF₃)₂CO giving rise to the phosphinites tBu(R)POCH(CF₃)₂, which furnish stable phosphonium salts upon treating with MeI. (CF₃)₂CO inserts into the SH bond of RSH to yield RSC(CF₃)₂OH (R=H,Me,Ph), which were reacted with MeI, too. Reacting SCl₂ with LiOCH(CF₃)₂ gives S[OCH(CF₃)₂]₂ which is oxidised by chlorine to the sulfurane ClS[OCH(CF₃)₂]₃ [2]. The sulfurane is able to transfer (CF₃)₂CHO groups to phosphorus (III) compounds, e.g. P[OCH(CF₃)₂]₃ and Me₃P yielding P[OCH(CF₃)₂]₅ and [Me₃POCH(CF₃)₂]⁺Cl^?. ClS[OCH(CF₃)₂]₃ gives a stable salt upon reaction with SbCl₅, like ClP[OCH(CF₃)₂]₄. The mechanisms for these reactions are discussed.     

CF3CO2ZnEt-mediated highly regioselective rearrangement of bromohydrins to aldehydes

A highly efficient and selective rearrangement reaction of bromohydrins to aldehydes mediated by CF₃CO₂ZnEt was described. The secondary and tertiary aldehydes were prepared under mild conditions in good to excellent yields (85-99%). The scope and limitations of this rearrangement process were also investigated.     

Perfluormethyl-element-liganden : XXXI. Ligandeneigenschaften von Me2PP(CF3)2 und Me2AsP(CF3)2

The coordinating properties of the trifluoromethyl elemental compounds Me₂PP(CF₃)₂ and Me₂AsP(CF₃)₂ have been studied by the synthesis and spectroscopic investigations (IR, NMR, MS) of their complexes cis-M(CO)₄L₂ (A), [(CO)₄ML]₂ (B) and [(CO)₅M]₂L (C) (M = Cr, Mo, W). Complexes of type A with L = Me₂PP(CF₃)₂ are obtained in good yield by reaction with M(CO)₄NBD (NBD = norbornadiene), whereas with L = Me₂AsP(CF₃)₂ the homobinuclear compounds B are formed. The attempt to prepare the cis-M(CO)₄[Me₂AsP(CF₃)₂]₂ complexes by treating M(CO)₄(Me₂AsH)₂ with P₂(CF₃)₄ is successful only for M = W. Binuclear compounds of type B or C, in general, can be prepared by stepwise reaction of the ligands with either M(CO)₄NBD or M(CO)₅THF.     

Negative ion formation in CF2Cl2, CF3Cl and CFCl3 following low energy (0—10 eV) impact with near monoenergetic electrons

Negative ion formation in CF₂Cl₂, CF₃Cl and CFCl₃ under low-energy electron impact has been investigated using a trochoidal monochromat The ions observed are F^?, Cl^?, FCl^?, Cl₂^?, CFCl₂^? from CF₂Cl₂; F^?, Cl^?, FCl^?, CF₂Cl Quoting available thermochemical data, it can be shown that most of the observed negative ions arise from dissociative attachment processes. Appearance The extremely high yield of Cl^? in CFCl₃, which is observed at ε = 0.0 eV, will be discussed with regard to the lifetime of this molecule i     

The luminescence of Cs3Bi2Cl9 and Cs3Sb2Cl9

The luminescence properties of Cs₃Bi₂Cl₉, α-Cs₃Sb₂Cl₉, and β-Cs₃Sb₂Cl₉ are reported and compared with those of Cs₃Bi₂Br₉. The first two compounds have comparable luminescence properties which can be described in terms of a band model. Deep center emission is observed for both compounds, whereas edge emission is observed only for Cs₃Bi₂Cl₉. The optical transitions of β-Cs₃Sb₂Cl₉ are localized on the Sb³⁺ ion. The orientation of the lone-pair orbitals of the ns² ions seems to play an important role in the formation of the cationic valence band. The α-β transformation must therefore have a considerable influence on the spectral properties of Cs₃Sb₂Cl₉.     

High-pressure structure of Li2CO3

The high-pressure behavior of Li₂CO₃ is studied up to 25 GPa with synchrotron angle-dispersive powder X-ray diffraction in diamond anvil cells and synthesis using a multi-anvil apparatus. A new non-quenchable hexagonal polymorph (P6₃/mcm, Z=2) occurs above 10 GPa with carbonate groups in a staggered configuration along the c-axis—a=4.4568(2) Å and c=5.1254(6) Å at 10 GPa. Two columns of face-shared distorted octahedra around the Li atoms are linked through octahedral edges. The oxygen atoms are coordinated to one carbon atom and four lithium atoms to form a distorted square pyramid. Splittings of X-ray reflections for the new polymorph observed above about 22 GPa under non-hydrostatic conditions arise from orthorhombic or monoclinic distortions of the hexagonal lattice. The results of this study are discussed in relation to the structural features found in other Me₂CO₃ carbonates (Me: Na, K, Rb, Cs) at atmospheric conditions.     

Dansylation of aromatic, aliphatic, and medicinal carboxylic acid compounds in 1 M Na2CO3 buffer

Dansyl chloride (DNS-Cl) is a sulfonyl chloride compound which is utilized as a fluorescent probe for quantitative analysis or structural studies of complex molecules. The fluorescent emission was sufficiently strong to permit detection of less than 10 μg of the carboxyl compounds studied here. The dansylation of aromatic carboxyl compounds (i.e. aspirin), aromatic primary amines, and aliphatic carboxyl compounds was accomplished in 1 M Na₂CO₃ buffer at pH 11. The fluorescent labeled analytes were then isolated by thin layer chromatography (TLC) or the aqueous mixture was pre-extracted with proline (or glycine) to eliminate back-ground emission originating from the hydrolized or sulfonic acid form of DNS-Cl. Fluorescent labeled analytes are clearly discerned under ultraviolet light. Limits of detection for dansylated carboxyl compounds was 1-5 μg, however for amines it was approximately 1 μg. Dansylation of aromatic primary amines proceeded much faster (15 min) than that of carboxyl compounds (≥1.5 h) at 25 °C. Despite the aqueous solubility of analytes, which ranged from less than 0.004-5.30 mg/ml, the dansylation of carboxyl compounds was effective. Various organic solvents for extracting derivatives from aqueous mixture were evaluated.     

Novel ammonium hexafluoroarsenate salts from reaction of (CF3)2NH,CF3N(OCF3)H,CF3N[OCF(CF3)2]H,CF3NHF and SF5NHF with the strong acid HF/ASF5.

Reactions of the fluorinated amines (CF₃)₂NH, CF₃N(OCF₃)H, CF₃N[OCF(CF₃)₂]H, CF₃NHF and SF₅NHF with the strong acid HF/AsF₅ form the corresponding ammonium salts R_f¹R_f²NH₂⁺AsF₆^? and R_fNFH₂⁺ AsF₆^? in high yield. [R_f¹=CF₃, R_f²=CF₃, CF₃O, (CF₃)₂CFO; R_f=CF₃, SF₅] The colorless crystalline solids are stable for prolonged periods at 22°C in sealed FEP containers. They have dissociation pressures at 22°C ranging from ～5 torr (R_fNFH₂⁺ AsF₆^?) to ～50 torr [CF₃N(OCF₃)H₂⁺AsF₆^?]. ¹⁹F NMR and Raman spectroscopy were used to identify the compounds.     

Microwave-assisted methylation of phenols with tetramethylammonium chloride in the presence of K2CO3 or Cs2CO3

We have evaluated the potential of using tetramethylammonium chloride (Me₄NCl) as an alternative methylating agent for phenols under microwave-assisted conditions. Its chemical behavior was tested in a reaction with 2-naphthol in the presence of various bases and solvents. The method was then applied in 1,2-dimethoxyethane or toluene under heterogeneous conditions for the O-methylation of a series of phenolic compounds. We found that many simple phenols can be methylated in the presence of K₂CO₃, whereas some other less-reactive phenols require the presence of the more reactive Cs₂CO₃.