The electronic structure of CrO43− as studied by EPR in K2SO4 single crystals

EPR and ENDOR investigations are carried out on irradiated K₂SO₄ crystals doped with CrO₄^2? ions. They indicate the formation of CrO₄^3? centers interacting with a nearby proton. The identification of the CrO₄^3? centers is based on their g values, the orientation of the g tensor and the symmetry requirements. The results are compared with related studies on MnO₄^2? in K₂SO₄ and K₂CrO₄ hosts.     

Cationic ring-opening polymerization of 2-isopropenyl-4-methylene-1,3-dioxolane

Preparation and cationic ring-opening polymerization of 2-isopropenyl-4-methylene-1,3-dioxolane ( VI ) was performed. Unsaturated cyclic acetal VI was prepared by dehydrochlorination of 2-isopropenyl-4-chloromethyl-1,3-dioxolane, which was easily obtained from methacrolein and epichlorohydrin, with sodium methoxide at ambient temperature. The cationic polymerization of VI with BF₃OEt₂ or CF₃SO₃H at ?78°C afforded only crosslinked polymers, whereas the polymerization by CH₃SO₃H gave soluble poly(keto-ether) which consisted of units VII containing an isopropenyl group in the side chain and units VIII containing a carbon-carbon double bond in the main chain. The reaction of VI with ethanethiol in the presence of protic acid was also carried out as a model reaction of the polymerization. The reaction initiated by the addition of proton to the 4-methylene group of VI , and quantitative ring-opening isomerization followed by the addition of ethanethiol afforded acyclic ketone IX and X . On the basis of the model reaction, the polymerization mechanism is also discussed. © 1993 John Wiley & Sons, Inc.     

Approaches to the synthesis of cytochalasans. Part 8. Further transformations and optical resolution of the tetrahydroisoindolinone subunit

The bicycle aldehyde 7 was prepared from the hydroxy ester 3 for the attachment of teh macrocyclic moiety of the cytochalasans. To protect the C(6),C(7)-double bond the intermediates 8 , 9 and 13 were transformed into the epoxides 10 , 11 and 14 , respectively. Treatment of 10 and 11 with Al(i-PrO)₃ gave the allylic alcohol 12 . Protection of the olefinic double bond was also effected by hydroxylation with OsO₄. The triol 17 obtained from 3 , after acetalization of 18 , was oxidized to the aldehyde 20 . Attachment of the ylide of the phosphonium salt 1 to 20 gave 24 , an intermediate of proxiphomin ( 2 ). Removal of the C(6), C(7)-diol group was achieved via the thiocarbonate 23 .     

A New Oxidative Conversion of Carbohydrate Benzyl Ethers to Benzoyl Esters with RuCl3-NaIO

Abstract

The benzyl group is often used in organic synthesis, especially in carbohydrate chemistry, as one of the most useful of the hydroxyl protecting groups. Benzyl ethers are stable to basic conditions and the benzyl group is removed easily by hydrogenolysis or under Birch reduction conditions. Alternatively, the benzyl ether group is oxidized to benzoyl ester and removed under basic conditions. A few oxidation methods have been reported using more than a stoichiometric amount of chromium reagents such as CrO₃-H₂SO₄ (Jones reagent)¹ or CrO₃-AcOH₂. Here we report a new and mild oxidation of benzyl ether to benzoyl ester with a catalytic amount of RuO₄ derived from RuCl₃ and NaIO₄. This method has proved effective in removing benzyl ether groups chemoselectively in the presence of benzylidene acetal and benzyl glycosidic functions.     

The chemistry of chromyl fluoride III. Reactions with inorganic systems

Reactions of CrO₂F₂ with MF or MF₂ gave the corresponding M₂CrO₂F₄ and MCrO₂F₄ fluorochromates. With the Lewis Acids (SO₃, TaF₅, SbF₅) and (CF₃CO)₂O known and new chromyl compounds [CrO₂(CF₃COO)₂, CrO₂(SO₃F)₂, CrO₂FTaF₆, CrO₂FSbF₆, CrO₂FSb₂F₁₁] were produced. Chromyl fluoride and inorganic salts (CF₃COONa and NaNO₃) produced the following complexes - Na₂CrO₂F₂(CF₃COO)₂ and Na₂CrO₂F₂(NO₃)₂. Unusual solid products were obtained with CrO₂F₂ and NO, NO₂, SO₂.A new method of preparing CrO₂F₂ is also presented.     

Alstonia scholaris: Struktur des Indolalkaloides Narelin

Alstonia scholaris: The structure of the indole alkaloid nareline Besides the known akuammidine, picralinal, picrinine and pseudoakuammigine a new indole alkaloid called nareline (M=352) was isolated from Alstonia scholaris R. BR. , which belongs to the plant family of Apocynaceae. Its structure 2 was deduced by single crystal X-ray diffraction. 2 represents the absolute configuration. The spectroscopic data of 2 and its derivatives (Scheme 1) as well as their chemical behavior support this structure. In biogenetic sense nareline is related to the bases akuammiline ( 4 ) and picraline ( 5 ) (Scheme 2). In contrast to those the C-atom 5 is exocyclic and represents an aldehyde group which forms together with the oxygen atom of the N (4)-hydroxylamine group a cyclic half acetale. - By oxidation (CrO₃/CH₃COOH) of 2 the oxindol derivative 19 (oxonareline) is formed which contains a cyclic acetal as a partial structure element (Scheme 4).     

Cyclic Voltammetrically‐Prepared MnO2 Coated on an ITO Glass Substrate

For the first time, nanostructured manganese dioxide was successfully electrodeposited onto an ITO (indium tin oxide) glass substrate by cyclic voltammetry (CV) method from an aqueous solution of 0.1 M Na₂SO₄ containing 5 × 10⁻³ M MnSO₄. The obtained manganese dioxide‐modified ITO glass substrates were characterized by energy dispersive spectrometry (EDS), Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM), respectively. All results not only proved the existence of MnO₂ on an ITO glass substrate but also demonstrated that the morphology of the obtained MnO₂ was greatly affected by the electrodeposition conditions. Also, this MnO₂‐modified ITO electrode was systematically investigated by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS) in an aqueous electrolyte of 0.1 M Na₂SO₄. The results obtained from electrochemical measurement indicated that this developed MnO₂‐modified ITO electrode has a satisfied specific capacitance value of 264 F·g⁻¹ and exhibits excellent electrochemical stability and reversibility.     

Easy, inexpensive and effective oxidative iodination of deactivated arenes in sulfuric acid

Two ‘model’ deactivated arenes, benzoic acid and nitrobenzene, were effectively monoiodinated within 1 h at 25-30 °C, with strongly electrophilic I⁺ reagents, prior prepared from diiodine and various oxidants (CrO₃, KMnO₄, active MnO₂, HIO₃, NaIO₃, or NaIO₄) in 90% (v/v) concd sulfuric acid (ca. 75 mol% H₂SO₄). Next, an I₂/NaIO₃/90% (v/v) concd H₂SO₄ exemplary system was used to effectively mono- or diiodinate a number of deactivated arenes. All former papers dealing with the direct iodination of deactivated arenes are briefly reviewed.     

Synthesis of 2‐Azabicyclo[3.2.2]nonane‐Derived Monosaccharide Mimics and Their Evaluation as Glycosidase Inhibitors

The racemic 2‐azabicyclo[3.2.2]nonanes 5 and 18 were synthesized and tested as β‐glycosidase inhibitors. The intramolecular Diels–Alder reaction of the masked o‐benzoquinone generated from 2‐(allyloxy)phenol ( 6 ) gave the α‐keto acetal 7 which was reduced with SmI₂ to the hydroxy ketone 8 . Dihydroxylation, isopropylidenation (→ 12 ), and Beckmann rearrangement provided lactam 15 . N‐Benzylation of this lactam, reduction to the amine 17 , and deprotection provided the amino triol 19 which was debenzylated to the secondary amine 5 . Both 5 and 19 proved weak inhibitors of snail β‐mannosidase (IC₅₀ > 10 mM ), Caldocellum saccharolyticum β‐glucosidase (IC₅₀ > 10 mM ), sweet almond β‐glucosidase (IC₅₀ > 10 mM ), yeast α‐glucosidase ( 5 : IC₅₀ > 10 mM ; 19 : IC₅₀ = 1.2 mM ), and Jack bean α‐mannosidase (no inhibition detected).     

Knoevenagel condensation of 2-carbethoxycyclohexanone and malononitrile: Synthesis of 4-cyano-3-ethoxy-1-hydroxy-5,6,7,8-tetrahydroisoquinoline,an isomer of the abnormal product

The structure of the abnormal product 1a formed in the Knoevenagel condensation of 2-carbethoxycyclohexanone and malononitrile has been further confirmed. Oxidation of the tetrahydroisoquinoline 3b using Na₂Cr₂O-AcOH-H₂SO₄ gave the keto isoquinoline 3d and the isoquinoline-1-carboxylic acid 5a. The acid chloride of 5a was condensed with diethyl ethoxymagnesiomalonate to afford after decarbethoxylation the methyl ketone 5d which on Baeyer-Villiger oxidation gave a mixture of the acetate 1g and the title compound 1b. The unambiguous synthesis of 1b confirms the structure assigned earlier to the title compound also formed during the partial hydrolysis of the diethoxy compound 1c. Condensation of 2-acetylcyclohexane-1,3-dione with malononitrile gave the quinoline derivative 4c which on ethylation yielded the ketoquinoline 4d. The present studies have confirmed that the quinoline compound 4a is also formed in the condensation of 2-acetylcyclohexanone and cyanoacetamide.     

Cyclic Phosphorochloridites,Phosphorochloridates, and Phosphorochloridothioates Based on Calix[4]resorcinolarenes

Phosphorylation of calix[4]resorcinolarenes with PCl₃ yields cyclic phosphorochloridites. Cavitands containing cyclic phosphorochloridite fragments in the upper rim are readily oxidized with SO₂Cl₂ to the corresponding phosphorochloridates and take up four equivalents of sulfur on heating to form cyclic phosphorochloridothioates.     

Effect of the Catalyst Nature on the Structure of Products of the Reaction of 4-(Dibromomethyl)Benzaldehyde with Trialkyl Orthoformates

Reactions of 4-(dibromomethyl)benzaldehyde with trialkyl orthoformates in the presence of both Brønsted (H₂SO₄) and Lewis (ZnCl₂) acids involved acetalization of the aldehyde group. In the first case, the corresponding acetal is formed as the only product, whereas in the second case the reaction is accompanied by transformation of the dibromomethyl group to give terephthalaldehyde and its mono- and bis-acetals.     

DTA studies on preparation of MnSO4 by reacting pyrite and pyrolusite at high temperatures

The preparation of MnSO₄ by reacting pyrolusite at high temperatures with SO₂ generated from pyrite was followed by DTA, and the process conditions were optimized to fix the minimum time and temperature of reaction required to obtain the maximum yield of pure MnSO₄ from stoichiometric amounts of reactants in a natural draught of air. The presence of MnO and Fe₃O₄ in the reaction products, detected by DTA, indicates that the SO₂ is initially oxidized to SO₃ by reducing MnO₂, Mn₂O₃ and Fe₂O₃ to MnO and Fe₃O₄. SO₃ finally attacks MnO to form MnSO₄. When an intimate stoichiometric blend of pyrite and pyrolusite is heated at temperatures ranging from 873 K to 973 K for 3 hrs, about 93% of the Mn is converted to ironfree MnSO₄.     

Contribution à l'étude du système quaternaire K+—NH4+—CrO4−−—SO4−−—H2O: I. les isothermes de 25° des systèmes ternaires limites

The four ternary limiting isotherms of the system K⁺− NH₄⁺ CrO₄⁻⁻ SO₄⁻⁻ H₂O are given for 25° C. In the systems K₂SO₄ (NH₄)₂SO₄ H₂O and K₂SO₄ K₂CrO₄ H₂O only one solid phase has been encountered; both systems belong to the type I of the ROOZEBOOM classification. A miscibility gap is present in the systems (NH₄)₂CrO₄ K₂CrO₄ H₂O and (NH₄)₂CrO₄ (NH₄)₂SO₄ H₂O; they belong to ROOZEBOOM'S type V.     

Natural specimen of triple solid solution ettringite–thaumasite–chromate-ettringite

Three natural minerals of ettringite group were investigated by TG to refine their chemical composition. Two samples are ettringite Ca_5.97Mg_0.01Sr_0.02Al_1.99Cr_0.01(SO₄)₃(OH)₁₂·23.7H₂O and bentorite Ca_5.99Mg_0.01Cr_1.95Al_0.01Si_0.03(SO₄)_2.82·(CO₃)_0.20(OH)₁₂·19.4H₂O, but the third one Ca_5.99Na_0.01Al_1.38Si_0.62(SO₄)_2.49·(CrO₄)_0.36·(CO₃)_0.46(OH)₁₂·15.8H₂O has found to be a solid solution among ettringite, thaumasite, and chromate-ettringite, not registered yet as a new mineral species. Similar phase is well known in concrete formed with Cr⁶⁺ admixture, but is found for the first time as a natural compound. X-ray single-crystal investigation allowed us to refine the structure and support substitution (SO₄)^2? ? (CrO₄)^2? in natural minerals of ettringite group.     

Syntheses of Cyclopropyl Silyl Ketones

The synthesis of the cyclopropyl silyl ketones 1 – 4 is described. The trimethylsilyl ketone 1 was prepared from geraniol ((E)- 5 ) in ca. 10% overall yield by cyclopropanation leading to 6 , CrO₃ oxidation to the aldehyde 8 , reaction of the latter with trimethylsilyl anion to 14A + B , and CrO₃ oxidation to 1 . Also for the (t-butyl)dimethylsilyl ketones 2 – 4 , an efficient four-step synthesis with overall yields of 48%, 85%, and 13%, respectively, was elaborated, starting from the allylic alcohols (E)- 5 , and 23 . The method of preparation involves as the key step a Wittig rearrangement of the silylallyl ethers ((E/Z)- 20 , 24 ) to the silyl alcohols ((E/Z)- 21 , 25 ), subsequent cyclopropanation ( 19A + B , 22A + B , 26 ), and oxidation to the cyclopropyl silyl ketones 2 – 4 .     

Dual-activation protocol for tandem cross-aldol condensation: An easy and highly efficient synthesis of α,α′-bis(aryl/alkylmethylidene)ketones

Commercially available lithium hydroxide monohydrate (LiOH·H₂O) was found to be a novel ‘dual activation’ catalyst for tandem cross-aldol condensation between cyclic/acyclic ketones and aromatic/heteroaromatic/styryl/alkyl aldehydes leading to an efficient and easy synthesis of α,α′-bis(aryl/alkylmethylidene)ketones at r.t. in short times. The reaction of aryl, heteroaryl, styryl and alkyl aldehydes with acyclic and five/six-membered cyclic ketones afforded excellent yields after 2 min to 1.25 h. The reaction conditions were compatible with various electron withdrawing and electron donating substituents, e.g. Cl, F, NO₂, OMe and NMe₂. The rate of the cross-aldol condensation was influenced by the nature of the ketone and electronic and steric factors associated with the aldehyde. The reaction took place at a faster rate for acyclic ketone (e.g., acetone) than that for cyclic ketone (e.g., cyclohexanone). In case of cycloalkanones, the rate of the reaction was dependent on the size of the ring of the cycloalkanone. The cross-aldol condensation of cyclopentanone was faster than that of cyclohexanone for a common aldehyde. In case of reactions involving aliphatic aldehyde having α-hydrogen atom no self-aldol condensation of the aldehyde took place.     

Cyclic Voltammetrically Prepared MnO2‐Polyaniline Composite and Its Electrocatalysis for Oxygen Reduction Reaction (ORR)

The composite of manganese dioxide‐polyaniline (MnO₂‐PANI) was successfully prepared by cyclic voltammetry (CV) from a 0.5 M H₂SO₄ solution containing 0.2 M aniline and 0.5 M MnSO₄. Scanning electron microscopy (SEM) images revealed that cauliflower like manganese dioxides entangled with PANI were generated. The spectra obtained from UV‐vis spectrophotometry (UV‐vis) and Fourier transform infrared spectrometry (FTIR) strongly demonstrated that this novel composite was composed by MnO₂ and PANI, and also there was an interaction between MnO₂ and PANI. Then, for the first time, this resultant composite was modified on a graphite electrode and employed in the oxygen reduction reaction (ORR), subsequently, the obtained cyclic voltammograms (CVs) verified that ORR could proceed on this resultant composite of MnO₂‐PANI. Lastly, the possible catalysis mechanism of MnO₂‐PANI towards ORR was proposed based on the results we acquired. Developing a novel substrate on which ORR could proceed is the main contribution of this work.     

Surface analysis on discharged MnO2 cathode using XPS and SIMS techniques

Manganese dioxide (MnO₂) appears to be an effective cathode material for a battery system. No studies on lithium insertion in aqueous media are known to the best of our knowledge. However, in one of our previous papers we reported that lithium could be intercalated into a MnO₂ host compound using an aqueous LiOH electrolyte; however simple chemistry suggests that it should not. It is found that a battery with LiOH electrolyte functions quite differently from the cell that uses Li₂SO₄. This paper describes the surface modifications that accompany the electrochemical behavior of MnO₂ during redox (discharge) processes in the lithium hydroxide and sulfate media. XPS and SIMS techniques were used to study the resultant surface of the MnO₂ cathode and the spectra reveal that the formation of an insoluble layer of Li₂CO₃ precedes the process of reduction. SEM was used to study the microstructure of the MnO₂ cathode. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation and some properties of 2H-imidazole 1,3-dioxides,derivatives of alicyclic 1,2-dioximes

The corresponding 2H-imidazole 1,3-dioxides were obtained by the reaction of cyclohexanedione and cycloheptadione 1,2-dioximes with acetone, cyclopentanone, and methyl ethyl ketone. The reactions of these compounds with hydroxylamine hydrochloride, NaBH₄, a Grignard reagent, and acetic anhydride in the presence of H₂SO₄ were studied in the case of 2,2-dimethyl-4,5,6,7-tetrahydro-2H-benzimidazole 1,3-dioxide. Bromination of the latter and 2,2-dimethylcyclohepta-2H-imidazole 1,3-dioxide with N-bromosuccinimide gave the corresponding dibromo derivatives, the bromine atoms in which are replaced by acetoxy and hydroxy groups. 4,7-Dihydroxy-2, 2-dimethyl-4,5,6,7-tetrahydro-2H-benzimidazole 1,3-dioxide, which was obtained by oxidation with MnO₂ was converted to a quinone, viz., 2,2-dimethyl-4,7-dioxo-4,7-dihydro-2H-benzimidazole 1,3-dioxide. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 808–813, June, 1980.