Zn Dust Research Articles

Cu-catalyzed trifluoromethylation of aryl iodides with trifluoromethylzinc reagent prepared in situ from trifluoromethyl iodide.

The trifluoromethylation of aryl iodides catalyzed by copper(I) salt with trifluoromethylzinc reagent prepared in situ from trifluoromethyl iodide and Zn dust was accomplished. The catalytic reactions proceeded under mild reaction conditions, providing the corresponding aromatic trifluoromethylated products in moderate to high yields. The advantage of this method is that additives such as metal fluoride (MF), which are indispensable to activate silyl groups for transmetallation in the corresponding reactions catalyzed by copper salt by using the Ruppert–Prakash reagents (CF3SiR3), are not required.

ChemInform Abstract: Recent Developments in the Reformatsky—Claisen Rearrangement

AbstractReview: 31 refs.

Recent Developments in the Reformatsky-Claisen Rearrangement

The rearrangement of allyl α-bromoacetates with Zn dust is known as the Reformatsky-Claisen rearrangement. Whereas the Ireland-Claisen rearrangement has been widely used in the synthesis of a diverse range of natural products, the Zn-mediated Reformatsky-Claisen rearrangement has not been utilized so often. In this article, we will provide an overview of recent advances in the Reformatsky-Claisen rearrangement field, including the In-mediated Reformatsky-Claisen rearrangement we have recently developed.

An efficient and general procedure for the synthesis of alkynyl chalcogenides (selenides and tellurides) by alumina-supported Cu(II)-catalyzed reaction of alkynyl bromides and diphenyl dichalcogenides

Alumina (Al2O3) supported Cu(II) efficiently catalyzes the reaction of alkynyl bromides and diphenyl diselenides and ditellurides in presence of Zn dust or indium(I) bromide to provide the corresponding alkynyl selenides and tellurides. The reactions of a wide variety of substituted alkynyl bromides have been addressed. The zinc dust or InBr is required for the cleavage of diphenyl selenides/tellurides. The mechanism of the reaction is established. The yields of products are high and the catalyst is recycled.

Reductive Cleavage of 2,2,2-Trichloroethyl Esters by Titanocene Catalysis

Esters are of widespread use for protecting carboxylic acids in organic synthesis. However, methods to cleave esters often employ harsh conditions. Herein, we report a new and mild method for the reductive cleavage of 2,2,2-trichloroethylesters (TCE esters). Our radical method employs Cp(2)TiCl as an electron transfer catalyst and Zn dust as stoichiometric reducing agent. It avoids the use of strong Brønstedt-acids as well as aqueous conditions and can be carried out at room temperature.

Spectrophotometric Determination of Metronidazole via Diazotization Reaction with p-Hydroxy Benzaldehyde as a Coupling Reagent

A New, simple and sensitive spectrophotometric method for the determination of Metronidazole (MN) has been developed. The method is based on reduction of nitro group of MN to amine group by Zn dust and concentrated hydrochloric acid in hot ethanol under stirring, then the diazonium ion was prepared and coupled with para hydroxyl benzaldehyde (p-HB) to yield Insoluble water yellow dye indicated at 410nm. The linearity of the method was between 5.8×10 -5 M-52.2×10 -5 M, the molar absorptivity was 7131.121 L.mol -1 .cm -1 and Sandell index was 0.0240µg.cm -2 . The method has been successfully applied to the assay of MN in pure and pharmaceutical forms.

Titanocene(III) Chloride Mediated Radical Induced Allylation of Aldimines: Formal Synthesis of C-Linked 4′-Deoxy Aza-disaccharide

Titanocene(III) chloride (Cp(2)TiCl) mediated radical induced allylation of aldimines for the preparation of homoallyl amines is described. The radical was generated from the allyl bromide using Cp(2)TiCl as the radical source. Formal synthesis of C(4)-C(5')-linked 4'-deoxy aza-disaccharide is demonstrated and a study toward the bicyclic skeleton of alkaloids was also accomplished. The radical initiator Cp(2)TiCl was prepared in situ from commercially available titanocene dichloride (Cp(2)TiCl(2)) and Zn dust in THF under argon.

Synthesis of α-fluoro-β-amino acids via the Reformatsky reaction of chiral N-tert-butylsulfinylimines with ethyl bromofluoroacetate

Abstract Treatment of chiral N-tert-butyl sulfinylimines with ethyl bromofluoroacetate in the presence of activated Zn dust in THF afforded the α-fluoro-β-amino acid derivatives in good yields (70–86%) and moderate diastereoselectivity (66:34–92:8).

Zn in ionic liquid: an efficient reaction media for the synthesis of diorganyl chalcogenides and chalcogenoesters

A straightforward and efficient methodology is described to synthesize structurally diverse diorganyl selenides, sulfides, seleno- and thioesters by using commercially available Zn dust in ionic liquid. Excellent yields were achieved under neutral conditions at room temperature in a short time. The solvent/ionic liquid is reusable and exhibited higher performance as compared with organic solvents.

Regioselective hydrodehalogenation of 3,5-dihaloisothiazole-4-carbonitriles: synthesis of 3-haloisothiazole-4-carbonitriles

3,5-Dibromoisothiazole-4-carbonitrile 1 treated with Zn or In dust (5 equiv) and HCO 2H undergoes regioselective hydrodebromination to give 3-bromoisothiazole-4-carbonitrile 3 in 70–74% yield. Similarly, 5-bromo and iodo 3-chloroisothiazole-4-carbonitriles 8 and 9 give 3-chloroisothiazole-4-carbonitrile 4 in 77 and 85% yields, respectively. Also hydrodeamination of 5-amino-3-chloroisothiazole-4-carbonitrile 7 using isoamyl nitrite gives the latter in 95% yield. The dibromoisothiazole 1 reacts with Zn dust in either DCO 2D or HCO 2D to give 3-bromo-5-deuterioisothiazole-4-carbonitrile 10 in 71 and 58% yields, respectively. The 3-bromoisothiazole 3 reacts with cyclic dialkylamines to give the corresponding 2-(dialkylaminomethylene)-malononitriles and not the expected 3-dialkylaminoisothiazole-4-carbonitriles. Finally, the 3-bromoisothiazole 3 is readily converted into both 3-bromoisothiazole-4-carboxamide 19 and the carboxylic acid 20. All products are fully characterized.

Reductive amination of ketones: novel one-step transfer hydrogenations in batch and continuous-flow mode

Various ketones were efficiently transformed into the corresponding amines using ammonium formate in the presence of Zn dust or 10% Pd/C. The low-cost Zn dust method proved to be effective in amine formation from carbonyl groups at the benzylic side-chain position of aromatic systems, whereas 10% Pd/C was an efficient catalyst in the reductive aminations of carbonyl groups non-conjugated with any π-system. The 10% Pd/C-catalyzed reductions were performed more effectively in a continuous-flow X-Cube reactor than in the batch system.

The Corrosion Protection Behaviour of Zinc Rich Epoxy Paint in 3% NaCl Solution

Electrochemical impedance spectroscopy (EIS) in the l00 kHz-10 mHz frequency range was employed as the main electrochemical technique to study the corrosion protection behaviour of zinc rich epoxy paint in 3% NaCl solution. The EIS results obtained at the open-circuit corrosion potential have been interpreted using a model involving the impedance of particle to particle contact to account for the increasing resistance between zinc particles with immersion period, in addition to the impedance due to the zinc surface oxide layer and the electrical resistivity of the binder. Galvanic current and dc potential measurements allowed us to conclude that the cathodic protection effect of the paint takes some time to be achieved. The loss of cathodic protection is due to a double effect: the decrease of the Zn/Fe area ratio due to Zn corrosion and the loss of electric contact between Zn to Zn particles. Even when the cathodic protection effect by Zn dust become weak, the substrate steel is still protected against corrosion due to the barrier nature of the ZRP film reinforced by Zn.

"On water" sp3-sp2 cross-couplings between benzylic and alkenyl halides.

Organic-solvent-free cross-couplings between benzylic and alkenyl halides have been developed. Various alkenyl halides can be efficiently benzylated by combining the precursor halides in the presence of Zn dust and a Pd catalyst at room temperature, in water as the only medium.

Palladium-catalyzed hydrophenoxycarbonylation of internal alkynes by phenol and CO: the use of Zn for the formation of active catalyst

The palladium-catalyzed hydrophenoxycarbonylation of internal alkynes by phenol and carbon monoxide was successfully realized by Pd(OAc) 2/dppp catalyst system in the co-presence of Zn dust.

A new route to prepare the mixed oxo-ethylidyne-capped trinuclear tungsten(IV) cluster and the crystal structure of H2Na3[W3O(CCH3)-(O2CCH3)6(H2O)3][H2W12O40]·13.5H2O

The synthesis and the structural characterization of the title compound H2Na3[W3O(CCH3)-(O2CCH3)6(H2O)3][H2W12O40]·13.5H2O are described. It is known that the mixed oxo-ethylidynecapped tritungsten cluster can be obtained by Zn dust reduction of Na2WO4·2H2O in acetic anhydride. The title compound has been characterized by X-ray diffraction, UV/VIS and 1H NMR spectra. The tungsten atoms in the cluster cation and anion are in the oxidation states of W(IV) and W(VI) respectively. The crystal is rhombohedral with the space group R32, a = 17.058 (3)A, c = 49.665 (9)A, γ=120°, V=12516(9)A3, Z=6, final R = 0.037 for 2071 reflections with I ≥3σ (I). Both the cluster cation and anion have a C3 symmetry. The important interatomic distances in angstroms for the cluster cation are: W—W, 2.730(2); W—μ3−O, 2.00; W—O (carboxy1), 2.12; W—Ot 2.18 (2).

An isotope dilution method to measure nitrification rates in the northern Gulf of Mexico and other eutrophic waters

An isotope dilution method is described to determine nitrification rates in the northern Gulf of Mexico (NGOMEX) and other eutrophic waters using high performance liquid chromatography (HPLC). A N 15 H 4 + isotope tracer method was not successful for NGOMEX waters due to excessive levels of unlabeled nitrogen (N) captured on sample filters. Nitrification rates were estimated by measuring the dilution of added N 15 O 3 − by N 14 O 2 − + N 14 O 3 − (= 14NO X ) generated from in situ N 14 H 4 + during sample incubations. NO X in pre- and post-incubation samples was reduced to NH 4 + with zinc (Zn) dust following sample acidification. Samples were analyzed by HPLC for NH 4 + concentration and atom% 15N composition. Results were corrected for background natural abundance NH 4 + concentrations measured in sub-samples collected before the reduction step. Nitrification rates were calculated using the difference between initial and final corrected NO X isotopic ratios and concentrations before and after the incubations. Laboratory experiments demonstrated that Zn reduction of NO X to NH 4 + averaged 102% (±0.2–0.8%) within 30 min. Different levels of N 14 O 3 − were added to sub-samples of coastal sea water containing a pool of added N 15 O 3 − to simulate a range of nitrification rates. Analysis of the resulting solutions produced a linear relationship ( R 2=0.9895; p<0.01) between added N 14 O 3 − concentration and isotope ratio and indicated a detection sensitivity of better than 2 atom%, making the method suitable for eutrophic waters with high nitrification rates. Nitrification rates estimated using both isotope dilution and tracer methods in coastal waters produced comparable results. Nitrification rates of up to 150 nmol N L −1 h −1 were measured in the NGOMEX hypoxic zone by isotope dilution. Advantages of the method include: (1) unaltered substrate ( NH 4 + ) concentrations, (2) small sample volume, (3) minimal sample handling, and (4) direct 24 h nitrification rate assessment.

Simple Synthesis of α,ω-Diarylpolyynes Part 1: Diphenylpolyynes

A series of α,ω -diphenylpolyynes were synthesized through the Cadiot Chodkiewicz reaction starting from Cu(I)-phenylacetylide and diiodoacetylene. The complete series of diphenylpolyynes Φ -(C≡C)n-Φ with n = 2,3,4 and 5 was obtained and analyzed by electronic absorption spectroscopy, liquid chromatography (HPLC-diode array) and FT-IR spectroscopy. The diphenylpolyynes when treated with nascent hydrogen produced by the action of HCl on Zn dust are changed into a mixture of diphenylpolyenes as shown by UV spectroscopy and HPLC.

ChemInform Abstract: Ni(0)-Catalyzed Reactions of Aryl and Vinyl Halides with Alkenes and Alkynes.

Ni(P(OPh)3)4 and Ni(P(OEt)3)4 catalyze tile reaction of aryl and vinyl halides with olefins (l-leck reaction) and alkynes. © 1997 Elsevier Science Ltd. The formation of C-C bonds by the reaction of aryl halides with olefins (Heck reaction) in presence of palladium catalysts is a well studied reaction) We have been investigating the use of other metal catalysts for this reaction based on the known mechanism of the Pd catalyzed vinylation reaction. The key step in the reaction mechanism is the oxidative addition of a low valent coordinatively unsaturated metal complex to the aryl halide followed by olefin coordination, migratory insertion and reductive elimination. We have reported the use of Co(1), Rh (I) (Wilkinson's Catalyst) and Ir(1) (Vaska's complex) successfully based on this rationale, 2 We decided to investigate other new catalysts for the Heck reaction based on the reaction mechanism viz. a metal complex capable of oxidative addition reductive elimination and undergoing ligand dissociation and association. NiCI2(PPh3)2 is known to catalyze the reaction of aryl and aliphatic halides with olefins in the presence of Zn dust to give mixtures of addition and substitution products) But it is not a very useful catalyst for the Heck reaction because it gives different types of products with ethylacrylate (addition product) and styrene (substitution product). The highly active and air sensitive complex, Ni(PPh3)4, generated in situ by the action of Et3AI on Ni(acac)2, has been used for the intramolecular reaction of aryl halides with olefins to form indoles: Ni(P(OPh)3)4 and Ni(P(OEt)3)4 are stable metal complexes of Ni(0) and are well known to undergo ligand dissociation, oxidative addition and reductive elimination reactions and have been used to catalyze the reaction of allyl acetates with nucleophiles, s We report here, the first use of these stable Ni(0) metal complexes, for the activation of aryl halides for reaction with olefins (Heck reaction) and alkynes.

ChemInform Abstract: Studies in Sulfoxide Rearrangement: Regioselective Synthesis of Thieno[3,2-f]quinolin-7(6H)-one Derivatives.

Abstract 6-Mercapto-1-methylquinolin-2(1 H )-one ( 3 ) was prepared in situ by the reductive cleavage of the corresponding disulfide 2 with Zn dust and acid. The disulfide 2 was in turn prepared via xanthate after diazotisation of 6-amino-1-methylquinolin-2-(1 H )-one ( 1 ). 6-(4-Aryloxybut-2-ynylthio)-1-methylquinolin-2(1 H )-ones ( 5a-e ) were prepared from thiol 3 and 1-aryloxy-4-chlorobut-2-ynes ( 4 ). The sulfides 5a-e were then converted into the corresponding sulfoxides 6a-e by treatment with one equivalent of m -CPBA in CH 2 Cl 2 at 0–5°C for 30 min. The sulfoxides 6a-e were refluxed in CCl 4 for 1 h to give the monothio-hemiacetals 7a-e in almost quantitative yields which were then converted into the 1-aryloxyacetyl-1,2-dihydro-6-methylthieno[3,2- f ]quinolin-7(6 H )-ones ( 11a-e ) in almost quantitative yields by simply dissolving in absolute MeOH. Dehydrogenative elimination of product 11a-e when treated with acid generates 1-acetyl-6-methylthieno[3,2- f ]quinolin-7(6 H )-one ( 12 ) in 70–76% yield.

ChemInform Abstract: Synthesis of 3-Substituted and 2,3-Disubstituted 4-Chlorofurans.

A simple method for the synthesis of 3-substituted and 2,3-disubstituted 4-chlorofurans is described which involves CuCl/bipy-catalysed regioselective cyclisation of 1-acetoxy-2,2,2-trichloroethyl allyl ethers followed successively by dechloroacetoxylation with Zn dust and tandem dehydrohalogenation–aromatisation with ButOK/18-crown-6.