Water-Soluble imide-amide copolymers. II. Preparation and characterization of poly (acrylamide-co-p-maleimidobenzoic acid)

The comonomer required, p-maleimidobenzoic acid (MBA) was first prepared in good yield by refinements of published methods. p-Carboxysuccinanilic acid (CSA), and p-succinimidobenzoic acid (SBA), were also prepared to provide models useful for IR and NMR for spectroscopic assignments of the new copolymers. Polymerization of MBA with acrylamide in glacial acetic acid at 60°C gave copolymers with estimated viscosity average molecular weights of 60,000 to 90,000. Yields and viscosity average molecular weights decreased as the MBA to acrylamide monomer feed ratio was increased. The rate of incorporation of MBA into the copolymer rose from 7 to 23% when the mole ratio in the feed was raised from 5 to 20%. Decreasing the initiator concentration increased molecular weights by less than predicted and reduced the yield of copolymer for any given feed ratio of MBA to acrylamide. In all cases about 30–40% of the MBA units in the purified copolymers were hydrolyzed. A change to dimethyl sulfoxide solvent gave good, and poor yields of copolymer at 5 and 10 mol % MBA, respectively, and no copolymer at 20 mol % MBA. Viscosity average molecular weights of the copolymer products prepared in DMSO were somewhat lower than obtained for the copolymers prepared in acetic acid. Polymerization in a DMSO-water mixture gave a negligible yield of polymeric product. Instead, only hydrolysates of MBA precipitated when the coloured polymerization solutions were added to methanol.     

Zwei neue pentacyclische dimere des cycloheptatriens

Titanium - catalyzed dimerization of cycloheptatriene affords pentacyclo[7.5.0.0^2,8.0^5,14.0^7,11]tetradeca-3,12-diene, $\text{3}$, and pentacyclo[8.4.0.0^3,7.0^4,14.0^6,11]tetradeca-8,12-diene, $\text{4}$. By heating, $\text{3}$ is converted quantitatively into $\text{4}$.     

Interactions des alcynes avec les complexes carbéniques du tungstène portant une double liaison carbone— carbone: Accès aux dérivés bicyclo[4,1,0] heptaniques par insertion-cyclopropanation

Treatment of VO(acac)₂ with the facial-tridentate organometallic ligand [η-CpCo{P(O)(OEt)₂}₃]^? affords a new binuclear compound [η-CpCo{P(O)(OEt)₂}₃VO(acac)] (I). This compound undergoes protonation with HPF₆ in the presence of 1,10-phenanthroline (phen), or 2,2′-bipyridyl (bipy), to yield binuclear cationic derivatives [η-CpCo{P(O)(OEt)₂}₃VO(phen))]⁺PF₆^? (II), and [η-CpCo{P(O)(OEth)₂}₃VO(bipy)]⁺PF₆^? (III). The X-ray crystal structure determination and full characterization of I has been performed. The catalytic oxygenation and oxygen transfer to 3,5-di-t-butylcatechol in the presence of I, II⁺, or III⁺ complexes is reported.     

Diffusion of organic vapors at low concentrations in glassy PVC, polystyrene, and PMMA

Diffusion coefficients of various C₁ to C₆ organic vapors, at concentrations 0.5 wt. percent, have been determined by gravimetric sorption rate measurements on emulsion and suspension-polymerized powder samples of PVC, polystyrene, and PMMA. Fickian diffusion kinetics were observed at the lowest concentrations, with a second-stage, relaxation-controlled sorption appearing at higher concentrations. In conjunction with published data for diffusivities of fixed gases in these polymers, the results indicate that diffusivity decreases exponentially, and that diffusion activation energy (E_D) increases linearly, with increasing diameter of “spherical” penetrant molecules (e.g., the noble gases, CH₄, SF₆, CCl₄, and neopentane). Much of the observed scatter in these correlations is attributable to uncertainty in the molecular diameters. For C₄ and larger n-alkanes and other elongated or flattened molecules, diffusivities are higher, and E_D lower, than for spherical molecules of similar molar volume. This finding suggests that anisometric molecules are oriented and move along their long axes during diffusion through the glassy polymer matrix. Correlations of diffusivities with molecular dimensions suggests that transport of anisometric molecules is governed by a diameter smaller than the mean (equivalent sphere) diameter but larger than the minimum dimension of their extended-chain conformation. Among the three polymers studied, diffusivity of each penetrant, at a given temperature, decreases in the order polystyrene> PVC ≥ PMMA.     

Synthesis of nucleosides of substituted 3-hydroxypyrazoles

N-Glucoside analogs of the antibiotic pyrazofurine were obtained by fusion of 3-hydroxy-4-ethoxycarbonylpyrazole with tetra-O-acetyl-ß-D-ribofuranose in the presence of iodine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1512–1514, November, 1981.     

Zum Dissoziationsverhalten dimerer Metallhalogenide und zur Bildung von MnAl2Cl8

Dissoziation Behaviour of Dimerie Metal Halides and the Formation of MnAl₂Cl₈ The thermal dissoziation was measured of the gaseous dimeric metal halides Al₂Cl₆, Ga₂Cl₆, In₂Cl₆, and Mn₂I₄ and the formation of the gaseous chloride complex MnAl₂Cl₈ by MnCl_2,f and Al₂Cl_6,g in a membrane manometer. The enthalpy and the entropy of these reactions were derived.     

Identification of inhibitors for UDP-galactopyranose mutase

The flavoenzyme uridine 5'-diphosphate (UDP)-galactopyranose mutase (UGM) plays a key role in the cell wall biosynthesis of many pathogens, including Mycobacterium tuberculosis. Using a synthetic fluorescent ligand, we screened 16 000 compounds in a fluorescence polarization assay. Effective inhibitors of UGM were identified.     

Determination of vanadium by solid-phase spectrophotometry after its preconcentration as an Eriochrome Cyanine R complex on a dextran-type exchanger

A method is described for the determination by solid phase spectrophotometry (SPS) of trace amounts of vanadium in natural water and crude petroleum samples. The procedure is based on fixation on a dextran-type anion exchanger of the complex V(IV)-Eriochrome Cyanine R. The absorbance of the gel, at 563 and 750 nm, packed in a 1 mm cell, is measured directly. Vanadium can be determined in the 0.6-25.0 mug l(-1) range with a relative standard deviation of 2.2%. The comparison of the SPS method and the gallic acid persulphate method shows that the linearity, analytical sensitivity and precision were better for the SPS method, and that the latter method has lower detection and quantification limits than the gallic acid persulphate method.     

Iodine(V) reagents in organic synthesis. Part 3. New routes to heterocyclic compounds via o-iodoxybenzoic acid-mediated cyclizations: generality, scope, and mechanism

The discovery and development of the o-iodoxybenzoic acid (IBX) reaction with certain unsaturated N-aryl amides (anilides) to form heterocycles are described. The application of the method to the synthesis of delta-lactams, cyclic urethanes, hydroxy amines, and amino sugars among other important building blocks and intermediates is detailed. In addition to the generality and scope of this cyclization reaction, this article describes a number of mechanistic investigations suggesting a single electron transfer from the anilide functionality to IBX and implicating a radical-based mechanism for the reaction.