A kinetic study of the reactions of the hydrogen atom with the cyclohexadiene isomers in the gas phase

Absolute values of the rate constants for the reaction of hydrogen atoms with cyclic olefins in the gas phase have been measured in a discharge-flow system under 3.5, 16, and 22 torr Ar at 23°C. The attenuation of hydrogen atom concentration in the reaction tube in the presence of a large excess of olefin was measured with an ESR spectrometer, and the products were analyzed by gas chromatography. Cyclic C₆ hydrocarbons were the only significant products obtained when the hydrogen atom concentration was 2.6 × 10^?10 mole/1., the olefin concentration was in the range of 9 to 22 × 10^?8 mole/1., and the pressure was 16 torr Ar. The values for the rate constants for reaction with cyclohexadiene-1,3, cyclohexadiene-1,4, and cyclohexene are, respectively, (9 ± 2) × 10⁸, (12 ± 1) × 10⁸, and (6 ± 1) × 10⁸ l./mole-sec, and they are not changed significantly by a sixfold change in total pressure. The fraction of the total interaction that proceeds by addition is 84% in the cyclohexadiene-1,3 system, but only 18% in the cyclohexadiene-1,4 system, and the cyclohexadienyl radical is therefore the dominant radical species in the latter system. The pattern of interaction between the hydrogen atom and the cyclohexadienyl radical was determined, and comprises 65% of disproportionation, and 13% and 23% of combination to yield cyclohexadiene-1,3 and cyclohexadiene-1,4, respectively. These results are consistent with the general patterns of reactivity emerging from studies of the reactions between free radicals and olefins in related systems.     

A simple synthesis of trans,trans-1,3-dienes from terminal alkynes using CoCl2/Ph3P/NaBH4

The cobalt hydride reagent prepared in situ in THF at −20°C using CoCl₂/NaBH₄ Ph₃P in the 1:1:4 ratio hydrodimerizes terminal alkynes into the corresponding trans, trans-1,3-dienes in good yields (65 to 86%).     

Some aspects of copolymerization of dienes under the influence of π-allyl complexes of nickel

π-Allyl complexes of nickel induce stereospecific homopolymerization of cyclohexadiene-1,3 and 2,3-dimethylbutadiene with the formation of crystalline polymers. These polymers consist of 1,4-monomer units in cis-configuration for polycyclohexadiene and in trans-configuration for poly-2,3-dimethylbutadiene. Peculiarities of copolymerization of cyclohexadiene-1,3 with butadiene and isoprene and of 2,3-dimethylbutadiene with butadiene under the influence of various π-allyl complexes of nickel are studied. By i.r.- and NMR-spectroscopy and radiochemical methods, the composition of copolymers for the above pairs of monomers are determined and the reactivity ratios are found. Influence of the monomers on the microstructure of the chain in copolymerization is established; the mechanism of this phenomenon is discussed.     

Cyclo- and cyclized diene polymers. XIII. γ-Ray-initiated polymerization of 1,3-dienes

The γ-ray-initiated polymerization of butadiene, isoprene, and 2,3-dimethylbutadiene-1,3 was carried out at temperatures of 20°C. and ?78°C. Polymers of butadiene and isoprene with mixed linear and cyclic structure were proved to result from the polymerization at ?78°C. A monocyclic structure was found for the 2,3-dimethylbutadiene-1,3 polymers initiated either at ?78°C. or in the thiourea canal complex at 20°C.     

Crystal Structure Analysis of a trans,trans-Cyclodeca-1, 6-diene Derivative

An X-ray crystal structure analysis of the higher melting diastereoisomer of 2,7-dibromo-3,8-dimethoxy-trans,trans-cyclodeca-1,6-diene (Monoclinic; a = 5.76, b = 10.43, c = 11.32 Å, β = 94.04°; space group P2₁/n; Z = 2) has confirmed the NMR. assignment of the molecular conformation and the trans configuration of the methoxy groups. The trans,trans-cyclodeca-1,6-diene ring adopts a centrosymmetric crown conformation with a C? C?C? C torsion angle of 162°.     

Regioselectivity of the hydrolysis of 2-(1-alkoxyvinyl)-substituted imidazolidines, 1,3-thiazolidines,and 1,3-oxazolidines

2-(1-Alkoxyvinyl)-1,3-thiazolidines reacted with H₂O or D₂O in the presence of 105 mol % of p-toluenesulfonic acid or trifluoroacetic acid (20°C, 1 h) to give 2-acetyl-1,3-thiazolidine in quantitative yield. 2-(1-Alkoxyvinyl)-3,5-diphenylimidazolidines underwent hydrolysis in the presence of 20 mol % of an acid (20°C, 24 h) at the vinyloxy group with high regioselectivity yielding 2-acetylimidazolidines. Hydrolysis of 2-(1-alkoxyvinyl)-3-phenyl-1,3-oxazolidines in the presence of 10 mol % of p-toluenesulfonic acid (20°C, 5 days) takes two pathways, one of which involves the endocyclic C-O bond with ring opening and the other involves the vinyloxy group to produce 2-acetyl-3-phenyl-1,3-oxazolidine. Unlike phenyl-substituted 1,3-thiazolidines and imidazolidines, hydrolysis of their 3-methyl- and 3,5-dimethyl-substituted analogs in acid medium occurs mainly via ring opening. The observed hydrolysis pathways were interpreted in terms of B3PW91/6-311G(d,p) quantum-chemical calculations.     

Properties of crystallized trans 1,4-polyisoprene

Stirrer crystallization of a trans-1,4-polyisoprene fraction(M?_n = 3 × 10⁵) was carried out from n-butyl acetate and from n-heptane solutions (2% w/v). Fibrous crystals in the ß form were obtained at temperatures of 46-48°C in the two solvents, respectively. At 36-46°C from n-butyl acetate and 25-35°C from n-heptane lamellar crystallization took place leading predominantly to the α form. Melting endotherms and densities for various samples were obtained. The maximum TENDO for α was 74°C and for ß 79°C and the maximum weight fraction crystallinity for ß was 0.78. The stability of performed α nuclei in n-butyl acetate and n-heptane using a fraction with M?_n = 2.5 × 10⁵ was monitored as a function of temperature. The dissolution temperature of fibrous ß-TPI with the maximum TENDO was measured in 13 liquids and the results analyzed in terms of the Flory-Huggins parameter. The heats of fusion for the α and ß forms, obtained by extrapolation of heat of fusion versus change in specific volume, were found to be 8.0 and 10 kJ mol^?1, respectively. The pressure coefficients of the melting temperature were calculated to be 38 and 43 K kbar^?1 and the fold-surface free energies recalculated to be 42 ± 1 and 53 ± 1 erg cm^?2 for the α and ß forms, respectively. The number of monomer units per average noncrystalline chain traverse for the most crystalline fibrous ß-TPI was estimated at 36.     

Isolation and cationic ring-opening polymerization of 2,3,5,6-tetrahydroimidazo[2,1-b][1,3]oxazole to produce a thermally stable polyurea

A bicyclic pseudourea, 2,3,5,6-tetrahydroimidazo[2,1-b][1,3]oxazole ( 1 ), was isolated for the first time, and its cationic and spontaneous polymerizations were examined. Both polymerizations gave poly(1,3-imidazolidin-2-one-1,3-diylethylene) ( 2 ) in high yields. The polymer is a crystalline solid with glass transition and melting temperature of 51°C and 286°C, respectively. Thermogravimetry showed that it is stable up to 450°C under nitrogen.     

Thermally stable polymers based on acetylene-terminated adamantanes

1,3-Diethynyl-5,7-dimethyladamantane, 1,3-diethynyl-5-phenyladamantane, 1,3,5-triethynyladamantane, and 3,3′-diethynyl-1,1′-biadamantane, were synthesized and polymerized thermally at 210°C. The thermoset resins obtained were post-cured at 300°C for 16 h to give materials that exhibited onsets of degradation (TGA) in air at 460–477°C and in helium at 460–485°C. The fully cured materials did not exhibit any detectable DSC transitions between 25 and 400°C. An attempt to thermally polymerize 1-ethynyl-3-phenyladamantane was unsuccessful. © 1992 John Wiley & Sons, Inc.     

Two-step regioselective synthesis of 1,2-difluorobenzenes from chlorotrifluoroethylene and buta-l,3-dienes

Russian Chemical Bulletin - The gas-phase copyrolysis of chlorotrifluoroethylene with buta-1,3-diene, penta-1,3-diene, or isoprene in a flow reactor at 440–480°C gave...     

Acyl- und Alkylidenphosphane. XXII [1]. Synthese und Struktur des 1, 3-Dimethyl-2,2,4,4-tetrakis-(trimethylsilylsulfano)-1,3-diphosphetans

Acyl- and Alkylidenephosphines. XXII. Synthesis and Structure of 1, 3-Dimethyl-2,2,4,4-tetrakis(trimethylsilylsulfano)-1,3-diphosphetane At ?30°C methylbis(trimethylsilyl)phosphine reacts with carbon disulfide to give a red adduct first which rearranges to [bis(trimethylsilylsulfano)methylidene]methylphosphine 1a . In contrast to the thermally stable phenyl derivative 1b [2], this compound with its insufficiently shielded P?C group dimerizes fast with increasing temperature. 1,3-Dimethyl-2,2,4,4-tetrakis(trimethylsilylsulfano)-1,3-diphosphetane 2a formed by this reaction, crystallizes in the triclinic space group P1 with following dimensions of the unit cell, determined at a temperature of measurement of ?80 ± 3°C: a = 1024.7(3); b = 1360.2(5); c = 1326.3(6)pm; α = 117.85(4); ß = 111.05(3); γ = 72.09(3)°; Z = 2. Due to ring folding at the P1? P2 axis of 149.1°, the molecule shows pseudosymmetry C_s. Characteristic averaged bond lengths and angles obtained at an R_w-value of 0.030, are: P? C(endocyclic) 188 and 191; P? CH₃ 184; C? S 183; S? Si 216 pm; C? P? CH₃ 105; P? C? S 113; S? C? S 114; C? S? Si 108; P? C? P 90 and C? P? C 86°.     

Phospha-s-triazines. IV. Degradation studies of 1-diarylphospha-3,5-bis(perfluoroaliphatic)-2,4,6-triazines and 1,3,-bis(diarylphospha)-5-perfluoroaliphatic-2,4,6-triazines

Thermal and thermal oxidative stability evaluations were performed on mono- and diphospha-s-triazines at 235 and 316°C using sealed Pyrex ampoules. The specific compounds studied were: 1-diphenylphospa-3,5-bis(perfluoro-n-heptyl)-2,4,6-triazine, 1-diphenylphospha-3,5-bis(perfluoro-alkylether)-2,4,6-triazines, their respective pentafluorophenyl analogues, 1,3-bis(diphenylphospha)-5-perfluoro-n-heptyl-2,4,6-triazine and 1,3-bis(diphenylphospha)-5-perfluoroalkylether-2,4,6-triazine. All the compounds wherein phenyl groups were present on the phosphorous exhibited good thermal stability up to 316°C; the analogous pentafluorophenyl substituted materials were degraded extensively at these temperatures. The oxidative stability of both the mono- and diphospha-s-triazines was excellent at 235°C, but at 316°C some degradation was observed. This was more pronounced in compounds containing the perfluoroalkyl moiety on carbon than in the perfluoroalkylether substituted members of the series.     

Inorganic Chemistry. Topics in Current Chemistry 124 : Edited by F.L. Boschke, Springer-Verlag, Berlin, Heidelberg, New York, Tokyo, 1984. vii + 138 pages, DM 68. ISBN 3-540-13534-0.

Ruthenium trichloride hydrate combined with tributylphosphine catalyzes the reaction between 1,3-propanediol and an aminoarene at 180°C, providing a novel route to quinoline derivatives under non-acidic conditions.     

Acyl- und Alkylidenphosphane. XIX. Molekül- und Kristallstruktur des 2,4-Bis(dimethylamino)-1,3-diphenyl-1,3-diphosphetans

Acyl and Alkylidenephosphines. XlX. Molecular and Crystal Structure of 2,4-Bis (dimethyl-amino) ?1,3-diphenyl-l, 3-diphosphetane 2,4-Bis(dimethylamino)-1,3-diphenyl-1,3-diphosphetane 2a which is isolated as a byproduct in the synthesis of (E)-(dimethylamino)methylidene-phenylphosphine 1a crystallizes in the monoclinic space group P2₁/c. The dimensions of the unit cell determined at ?65 ± 5°C are: a = 1 004(1); b = 1 018(3); c = 1 873(2) pm; β = 105.15(8)°; Z = 4. As it is shown by a low temperature X-ray structure determination (R_g = 3.5%) the phenyl groups are placed above and the dimethylamino groups below the folded 1,3-diphosphetane ring; the molecule with its differently twisted substituents, however, deviates considerably from point symmetry mm2. The dihedral angle between the P1? C1n? P2 planes (n = 1 or 2) is found to be 153°. The relatively long Pn? C1n bond distances (187 to 191 pm) indicate a strained ring system; in solution 2a decomposes to some extent and forms monomeric 1a again. Further characteristic average bond distances and angles are: Pn? C4n (phenyl) 184; C? N 146 pm; P1? C1n? P2 93°; C11? Pn? C12 84° and Pn? C1n? Nn 116°.     

Unique Thermal Structural Phase Transitions Exhibited by Unsymmetrical Organometallic Gold(III)-Dithiolene Complexes with Pentylthio and Hexylthio Groups

Unsymmetrical gold(III)-dithiolene complexes are potential candidates for molecular materials that exhibit thermal structural phase transitions. In this study, unsymmetrical ppy-gold(III) (ppy⁻=C-deprotonated-2-phenylpyridine(−)) complexes [AuC5] and [AuC6] coordinated by dithiolene ligands containing tetrathiafulvalene (TTF) skeletons with pentylthio (2-{bis(pentylthio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate(2−)) and hexylthio groups (2-{bis(hexylthio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate(2−)) were synthesized. Both complexes exhibited a large absorption band at approximately 508 nm, owing to intramolecular ligand-to-ligand charge transfer. One-dimensional columnar structures with head-to-tail molecular arrangements around the metal ions were constructed in the crystals. The flexible alkylthio groups were intercalated into crystalline spaces between dithiolene ligands in the columns. [AuC5] exhibits a simple phase transition at 198 °C between crystalline and isotropic phases irreversibly. The crystalline phase of [AuC6] observed at 25 °C melted at 148 °C. Another crystalline phase grew above 148 °C with a very slow crystallization rate from the liquid phase and was completely transformed into an isotropic phase at 200 °C.     

Copolymerization of styrene with (Z)-1,3-pentadiene in the presence of a syndiotactic-specific catalyst

Copolymerization of styrene with (Z)-1,3-pentadiene affords copolymers mostly containing 1,2 pentadiene units. Both the styrene and the pentadiene units are in syndiotactic arrangement but the comonomer sequence distribution is far from bernoullian. Interestingly, the behavior of (Z)-1,3-pentadiene does not change much when polymerization temperature raises from −20 to +20°C, notwithstanding that (Z)-1,3-pentadiene affords a 1,2-syndiotactic homopolymer at −20°C but a prevailingly 1,4 cis homopolymer at +20°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2697–2702, 1997     

Ab Initio Study of Conformational Properties of Heteroatom-Containing 1,2-Bisketene Analogues

Abstract

Minimum-energy and transition-state geometries of 4-oxobuta-1,3-diene-1-thione, buta-1,3-diene-1,4-dithione, 4-selenoxobuta-1,3-diene-1-thione, 4-selenoxobuta-1,3-diene-1-one, and buta-1,3-diene-1,4-diselenone were calculated using HF, B3LYP, and MP2 levels of theory and 6–31 + G* basis set by rotation around the related ?C?C? single bonds. In all of the above-mentioned molecules, the s-trans conformation was obtained as the most stable conformer with the 180° dihedral angle. In buta-1,3-diene-1,4-dithione, 4-selenoxobuta-1,3-diene-1-thione, and buta-1,3-diene-1,4-diselenone, the s-cis form of these compounds corresponded to the other energy-minimum geometry. Their skew geometries, with torsional angles approximately 100°, were a transition state for conformational interconversion between the two global minima forms. In 4-oxobuta-1,3-diene-1-thione and 4-selenoxobuta-1,3-diene-1-one, geometries with the C?C?C?C dihedral angles about 51 and 43° (respectively) were attributed to the second energy-minimum geometry. Transition-state structures from both molecules were found in the torsional angles at about 0 and 100°.

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GRAPHICAL ABSTRACT     

Reaction of thiourea and substituted thioureas with 1,3-dibromopropyne

4-Bromomethylidene-2-imino(phenylimino, acetylimino)-1,3-thiazolidine hydrobromides and 4-bromomethylidene-2-acetylimino-1,3-thiazolidine are synthesized by the reaction of thiourea, N-phenylthiourea, N,N′-diphenylthiourea and N-acetylthiourea with 1,3-dibromopropyne in glacial acetic acid, absolute methanol, acetonitrile at 20°C or upon heating (60°C).     

Trapping of Tricarbonyl(η1,η2‐homoallyl)iron and Tricarbonyl(η3‐allyl)iron Anion Intermediates with 2‐(Phenylsulfonyl)‐3‐phenyloxaziridine

The addition of reactive carbanions to (η⁴‐1,3‐diene)Fe(CO)₃ complexes at ?78 °C and 25 °C produced putative homoallyl and allyl anion complexes, respectively. Reaction of the reactive intermediates with 2‐(phenylsulfonyl)‐3‐phenyloxaziridine afforded nucleophilic substituted (η⁴‐1,3‐diene)Fe(CO)₃ complexes.     

Hydroalkylation of Styrenes with Benzylamines by Potassium Hydride

A method for the synthesis of 1,3-diarylpropylamines through hydroalkylation of styrenes with benzylamines by potassium hydride has been developed. The protocol is initiated by solvothermal treatment of benzylamines with KH at 100 °C to generate deprotonated anionic species, which undergo selective C-alkylation with arylalkenes at 0 °C to ambient temperature to afford 1,3-diarylpropylamines as the major product.