Purines. Part XVI

A series of N‐substituted 8‐aminoxanthines (=8‐amino‐3,7(or 3,9)‐dihydro‐1H‐purine‐2,6‐diones) 8 – 16 and 34 – 37 were synthesized from the corresponding 8‐nitroxanthines 1 – 7, 30 – 33 , and 8‐(phenylazo)xanthines 17 and 18 by catalytic reduction. Another approach was derived from 6‐amino‐5‐(cyanoamino)uracils (=N‐(6‐amino‐1,2,3,4‐tetrahydro‐2,4‐dioxopyrimidin‐5‐yl)cyanamides) 23, 24 , and 27 by base‐catalyzed cyclization yielding 25 – 28 . All 8‐aminoxanthines 8 – 29 and 34 – 37 were acetylated to the corresponding 8‐(acetylamino)xanthines 40 – 57 , and prolonged heating led to 8‐(diacetylamino)xanthines 58 and 59 . Several 8‐aminoxanthines 8 – 13 were diazotized forming 8‐diazoxanthines 60 – 64 . Coupling reactions of isolated 62 and 64 and intermediary formed 8‐diazoxanthines with 1,3‐dimethylbarbituric acid (=1,3‐dimethylpyrimidine‐2,4,6(1H,3H,5H)‐trione; 66 ) resulted in 5‐[(xanthin‐8‐yl)diazenyl]‐1,3‐dimethylbarbituric acids=3,7(or 3,9)‐dihydro‐8‐[2‐(1,2,3,4‐tetrahydro‐1,3‐dimethyl‐2,4‐dioxopyrimidin‐5‐yl)diazenyl]‐1H‐purine‐2,6‐diones) 67 – 80 . The newly synthesized xanthine derivatives were characterized by the determination of their pK_a values, the UV‐ and NMR spectra, as well as elemental analyses.     

Fluorocyclohexanes. Part XVII. Dehydrofluorinations of the cis and the trans isomers of 2H-1-(difluoromethyl)decafluorocyclohexane

2H-1-(Difluoromethyl)octafluorocyclohex-1-ene (I) and cobalt trifluoride at 165 °C afforded 2H-1-(trifluoromethyl)octafluorocyclohex-1-ene (IV) and four decafluorocyclohexane derivatives: the cis (III), and trans (V), -2H-1-(trifluoromethyl)-; the cis (VII), and trans (VI), 2H-1-(difluoromethyl) compounds. Dehydrofluorination of VII, using aqueous potassium hydroxide, gave only one alkene, 1-(difluoromethyl)nonafluorocyclohex-1-ene (VIII). In a slower reaction VI afforded two alkenes, mainly VIII, But also an isomer, 1-(difluoromethyl)nonafluorocyclohex-2-ene (IX) (ratio 2:1).     

Preparation,characterization and thermal decomposition of phenylenediammonium sulfate salts Part. XVI

Polyaniline/α-Al₂O₃ (PANI/α-Al₂O₃) composites were synthesized by in situ polymerization through ammonium persulfate ((NH₄)₂S₂O₈, APS) oxidized aniline using HCl as dopant. XRD and FTIR were used to characterize the PANI/α-Al₂O₃ composites. The thermal stabilities and glass transition temperature (T _g) of PANI/α-Al₂O₃ composites were tested using thermogravimetric (TG) method and modulated differential scanning calorimetry (MDSC) technique. The results of TG showed that the thermal stability of PANI/α-Al₂O₃ composite increased and then decreased with the increase in α-Al₂O₃ content. The derivative thermogravimetry (DTG) curves showed one step degradation of PANI when the α-Al₂O₃ content was lower than 52.5 mass%, and exhibited two steps degradation when the α-Al₂O₃ content was higher than 63.6 mass%. The MDSC curves showed that the T _g of PANI/α-Al₂O₃ composites increased and then decreased with the augment of α-Al₂O₃ for the interaction between PANI chains and the surface of α-Al₂O₃.     

Infrared spectra of Li2SeO4.H2O,Li2SO4.H2O and Li2(S,Se)O4.H2O

On of the hydrogen bonds formed by water molecules in lithium selenate monohydrate is evidently stronger than in the corresponding sulfate, whereas the other one is weaker. The temperature dependence of the stretching and bending modes of water is similar in both compounds, their frequencies decreasing on lowering the temperature. The study of mixed sulfate—selenate compounds made it possible to clearly show that the effective symmetry of the tetrahedral ions is higher than their local crystallographic one.     

H atom yields from the reactions of CN radicals with C2H2, C2H4, C3H6, trans-2-C4H8, and iso-C4H8

The kinetics and H atom channel yield at both 298 and 195 K have been determined for reactions of CN radicals with C2H2 (1.00+/-0.21, 0.97+/-0.20), C2H4 (0.96+/-0.032, 1.04+/-0.042), C3H6 (pressure dependent), iso-C4H8 (pressure dependent), and trans-2-C4H8 (0.039+/-0.019, 0.029+/-0.047) where the first figure in each bracket is the H atom yield at 298 K and the second is that at 195 K. The kinetics of all reactions were studied by monitoring both CN decay and H atom growth by laser-induced fluorescence at 357.7 and 121.6 nm, respectively. The results are in good agreement with previous studies where available. The rate coefficients for the reaction of CN with trans-2-butene and iso-butene have been measured at 298 and 195 K for the first time, and the rate coefficients are as follows: k298K=(2.93+/-0.23)x10(-10) cm3 molecule(-1) s(-1), k195K=(3.58+/-0.43)x10(-10) cm3 molecule(-1) s(-1) and k298K=(3.17+/-0.10)x10(-10) cm3 molecule(-1) s(-1), k195K=(4.32+/-0.35)x10(-10) cm3 molecule(-1) s(-1), respectively, where the errors represent a combination of statistical uncertainty (2sigma) and an estimate of possible systematic errors. A potential energy surface for the CN+C3H6 reaction has been constructed using G3X//UB3LYP electronic structure calculations identifying a number of reaction channels leading to either H, CH3, or HCN elimination following the formation of initial addition complexes. Results from the potential energy surface calculations have been used to run master equation calculations with the ratio of primary:secondary addition, the average amount of downward energy transferred in a collision DeltaEd, and the difference in barrier heights between H atom elimination and an H atom 1, 2 migration as variable parameters. Excellent agreement is obtained with the experimental 298 K H atom yields with the following parameter values: secondary addition complex formation equal to 80%, DeltaEd=145 cm(-1), and the barrier height for H atom elimination set 5 kJ mol(-1) lower than the barrier for migration. Finally, very low temperature master equation simulations using the best fit parameters have been carried out in an increased precision environment utilizing quad-double and double-double arithmetic to predict H and CH3 yields for the CN+C3H6 reaction at temperatures and pressures relevant to Titan. The H and CH3 yields predicted by the master equation have been parametrized in a simple equation for use in modeling.     

Kristallstrukturen von Säurehydraten und Oxoniumsalzen. XVI Zur Kenntnis der Verbindung H2TeI6 · 8 H2O

Crystal Structures of Acid Hydrates and Oxonium Salts. XVI. On the Compound H₂TeI₆ · 8 H₂O Crystals of H₂TeI₆ · 8H₂O are obtained as dark-brown needles with a metallic lustre in incident light from solutions of tellurium iodides in concentrated hydroiodic acid on cooling. Under standard conditions the phase is stable only in contact with its saturated solution; decomposition by formation of HI, H₂O, and TeI₄ takes place in vacuo. H₂TeI₆ · 8 H₂O is orthorhombic, space group Pnnm, Z = 2, with a = 12.672(15) Å, b = 10.825(14) Å, c = 8.322(8) Å. Structurally, the compound is to be described as bis(diaquooxonium)-hexaiodotellurate dihydrate, (H₇O⁺₃)₂[TeI^2?₆] · 2 H₂O. Isolated TeI^2?₆ octahedra are surrounded by a water structure which consists of disordered chains of hydrogen-bonded H₂O and H₇O⁺₃ species.     

Synthesis of Aristotelia‐Type Alkaloids,Part XVI

Two independent total syntheses of the Aristotelia alkaloid (−)‐serratenone ((−)‐ 1 ) are disclosed, one starting with (−)‐α‐pinene, the other one with (S)‐α‐terpineol. These correlations led to a revision of the originally proposed absolute configuration of the natural product. In the course of systematic investigations of the behavior of the indole alkaloids (+)‐makomakine ((+)‐ 18 ) and (−)‐hobartine ((−)‐ 22 ) towards oxidizing reagents, it was found that treatment with I₂ leads to no less than five different products. Depending on the exact reaction conditions, each of them can be obtained as the major component in yields between 40 and 60%. One of these compounds was shown to be identical with the natural product (+)‐11,12‐didehydromakonin‐10‐one ((+)‐ 28 ).     

Reactivity of positively charged cobalt cluster ions with CH4, N2, H2, C2H4, and C2H2

Reactivity of positively charged cobalt cluster ions (Co _n ⁺ ,n=2?22), produce by laser vaporization, with various gas samples (CH₄, N₂, H₂, C₂H₄, and C₂H₂) were systematically investigated by using a fast-flow reactor. The reactivity of Co _n ⁺ with the various gas samples is qualitatively consistent with the adsorption rate of the gas to cobalt metal surfaces. Co _n ⁺ highly reacts with C₂H₂ as characterized by the adsorption rate to metal surfaces, and it indicates no size dependence. In contrast, the reactions of Co _n ⁺ with the other gas samples indicate a similar cluster size dependence; atn=4, 5, and 10?15, Co _n ⁺ highly reacts. The difference can be explained by the amount of the activation energy for chemisorption reaction. Compared with neutral cobalt clusters, the size dependence is almost similar except for Co ₄ ⁺ and Co ₅ ⁺ . The reactivity enhancement of Co ₄ ⁺ and Co ₅ ⁺ indicates that the cobalt cluster ions are presumed to have an active site for chemisorption atn=4 and 5, induced by the influence of positive charge.     

A population analysis of the bonding in N2O4, B2Cl4, B2F4, C2H4 and C3H4

Population matrices have been calculated from molecular orbital wave functions of N₂O₄, B₂Cl₄, and B₂F₄ in order to understand further the bonding in these molecules which are isoelectronic in valence electrons but different in structure. C₂H₄ and C₃H₄ have been included in this study as check cases.

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Zusammenfassung Ausgehend von Molekülorbitalen werden Besetzungsmatrizen für N₂O₄, B₂Cl₄ und B₂F₄ berechnet, um die Bindung in diesen Molekülen, die in den Valenzelektronen isoelektronisch sind, aber unterschiedliche Strukturen aufweisen, besser zu verstehen. C₂H₄ und C₃H₄ sind in dieser Untersuchung als Prüffälle eingeschlossen.

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Résumé Des matrices d'occupation ont été calculées à partir des orbitales moléculaires de N₂O₄, B₂Cl₄ et B₂F₄, afin de comprendre plus profondément la liaison dans ces molécules, qui sont isoélectroniques par leurs électrons de valence, mais qui n'ont pas la même structure. C₂H₄ et C₃H₄ sont considérés dans cette étude à titre de vérification.

     

ChemInform Abstract: Sulfur Compounds. Part 200. Structures and Energies of Various Isomers of Dithionous Acid,H2S2O4, and of Its Anion HS2O4-.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

GF Calculations for some tricyclic molecules: C3H6, C3H4, C2H4NH,C2H4O and C2H4S

We have functions expressed as antisymmetrized products of strongly orthogonal geminals have been evaluated for some three membered ring molecules. GF results are compared with previously computed SCF-MO results, obtained employing the same atomic basis. Transferability features of bonds and inner shells are shown.     

Untersuchungen zurFriedel-Crafts-Reaktion. XVI. Darstellung isomerer 2-Acyl- und 3-Acyl-4-methoxyphenole

Acylation of 4-methoxy phenol according toFriedel andCrafts, as well as the rearrangement of its esters according toFries lead always to 2-acyl-4-methoxy phenols or to their demethylated compounds. The unknown 3-acyl-4-methoxy phenols were prepared in two steps: First, the ester is acylated with the corresponding acyl chloride and SnCl₄ in nitromethane. In the second step the resulting ketoesters are hydrolysed. This is a general method. The yields ofmeta-acylphenols are between 40 and 90%. The isomeric 2-acyl-4-methoxy-phenols which were partly unknown or accessible only in low yields have also been prepared for comparative spectral studies (UV, IR, NMR, MS) ofortho- andmeta-acylphenols.

     

Photochemistry of 4-Thia-2-cycloalkenones. Part 2

Methyl 2-allyl-3-oxo-2,3-dihydrothiophene-2-carboxylate ( 2 ) photocyclizes selectively to methyl 2-oxo-7-thiatricyclo[3.2.1.0^3,6]octane-1-carboxylate ( 4 ). In contrast, 4-thia-2-cyclohexenone 3 , on irradiation, affords only low yields of dimers, cycloadducts (2-methylpropene) or RH reduction products (i-ProH).