- Infrared Multiple-Photon Decomposition of Cyclopentene
-
The infrared multiple-photon decomposition of cyclopentene yields cyclopentadiene as the major hydrocarbon product (>95percent).The other products are 1,4-pentadiene and cis- and trans-1,3-pentadiene, along with trace amounts of fragmentation products.The 1,3-pentadienes have not been previously reported in cyclopentene pyrolysis.Typical conversions obtained by focussing the laser beam into the sample ranged from less than 1percent to as much as 20percent per 1E3 pulses with estimated beam waist fluences of approximately 150 J/cm2, indicating that cyclopentene excitation is strongly bottlenecked.No products were detected with collimated beams of 1 J/cm-2 and after 1.7E4 pulses.Reaction product yields increase with increasing wavelength in the fundamental absorption band centered at 1048 cm-1.Excitation originating in the Q branch of this transition results in very small yields.Total C5 yields increase rapidly with increasing fluence at 1029 and 1033 cm-1.A simple model of dissociation in which the focused beam geometry is a circular hyperboloid of revolution predicts fluence-yield behavior that is consistent with experimental observations.Conversion of cyclopentene decreases with increasing cyclopentene pressure between 0.01 and about 0.5 torr, and thereafter increases rapidly with increasing pressure.On the other hand, addition of N2, up to about 200 torr, causes total C5 yields to decrease monotonically over the entire pressure range.A limited number of experiments were done with 1-methylcyclopentene.At the same wavelength (1019 cm-1), pressure, fluence, and weak field absorbance, dehydrogenation of 1-methylcyclopentene gives yields that are as much as 20 times greater than yields from cyclopentene.
- Shoemaker, James O.,Carr, Robert W.
-
-
Read Online
- Multiphoton infrared initiated thermal reactions of esters: Pseudopericyclic eight-centered cis-elimination
-
Multiphoton infrared absorption from a focused, pulsed CO2 laser was used to initiate gas-phase thermal reactions of cis- and trans-3-penten-2-yl acetate. By varying the helium buffer gas pressure, it was possible to deduce the product distribution from the initial unimolecular reactions, separate from secondary reactions in a thermal cascade. Thus, trans-3-penten-2-yl acetate gives 54 ± 5% of β-elimination to give trans-1,3-pentadiene, 40 ± 3% of [3,3]-sigmatropic rearrangement to give cis-3-penten-2-yl acetate and 6 ± 4% of cis-1,3-pentadiene. Similar irradiation of cis-3-penten-2-yl acetate gives 45 ± 1% of β-elimination to give cis-1,3-pentadiene, 32 ± 2% of [3,3]-sigmatropic rearrangement to give trans-3-penten-2-yl acetate and 23 ± 2% of trans-1,3-pentadiene. The latter process is an eight-centered δ-elimination, which is argued to be a pseudopericyclic reaction. Although β-eliminations have been suggested to be pericyclic, B3LYP/ 6-31G(d,p), MP2 and MP4 calculations suggest that both β- and δ-eliminations, as well as [3,3]-sigmatropic rearrangements of esters are primarily pseudopericyclic in character, as judged by both geometrical, energetic and transition state aromaticity (NICS) criteria. Small distortions from the ideal pseudopericyclic geometries are argued to reflect small pericyclic contributions. It is further argued that when both pericyclic and pseudopericyclic orbital topologies are allowed and geometrically feasible, the calculated transition state may be the result of proportional mixing of the two states; this offers an explanation of the range of pseudopericyclic and pericyclic characters found in related reactions.
- Ji, Hua,Li, Li,Xu, Xiaolian,Ham, Sihyun,Hammad, Loubna A.,Birney, David M.
-
-
Read Online
- CATALYTIC HYDROCARBON DEHYDROGENATION
-
A catalyst for dehydrogenation of hydrocarbons includes a support including zirconium oxide and Linde type L zeolite (L-zeolite). A concentration of the zirconium oxide in the catalyst is in a range of from 0.1 weight percent (wt. %) to 20 wt. %. The catalyst includes from 5 wt. % to 15 wt. % of an alkali metal or alkaline earth metal. The catalyst includes from 0.1 wt. % to 10 wt. % of tin. The catalyst includes from 0.1 wt. % to 8 wt. % of a platinum group metal. The alkali metal or alkaline earth metal, tin, and platinum group metal are disposed on the support.
- -
-
Paragraph 0056; 0122; 0123
(2021/03/13)
-
- High yields of piperylene in the transfer dehydrogenation of pentane catalyzed by pincer-ligated iridium complexes
-
Conjugated dienes are desirable reagents for several important applications. We report that sterically uncrowded PCP-pincer iridium complexes, including precursors of (iPr4PCP)Ir and (Me2tBu2PCP)Ir, catalyze the transfer d
- Kumar, Akshai,Hackenberg, Jason D.,Zhuo, Gao,Steffens, Andrew M.,Mironov, Oleg,Saxton, Robert J.,Goldman, Alan S.
-
p. 368 - 375
(2016/12/16)
-
- Ring Opening of Biomass-Derived Cyclic Ethers to Dienes over Silica/Alumina
-
We show that cyclic ethers, such 2-methyltetrahydrofuran (2-MTHF), can undergo dehydration to produce pentadienes over SiO2/Al2O3. The catalyst exhibited reversible deactivation due to coke deposition, with the yield to pentadienes decreasing from 68% to 52% at 623 K over 58 h time on stream. A reaction network for 2-MTHF dehydration was proposed on the basis of the results of space time studies. Pentadienes can be produced directly by a concerted hydride shift and dehydration of carbenium intermediates or indirectly through dehydration of pentanal and pentenol. Reaction kinetics studies were performed at temperatures ranging from 573 to 653 K and 2-MTHF partial pressures from 0.21 to 2.51 kPa. The apparent activation energy barrier for 2-MTHF conversion to pentadienes and the reaction rate order for ring opening were determined to be 74 kJ mol-1 and 0.24, respectively, indicating strong interaction between 2-MTHF and the SiO2/Al2O3 surface. Other solid acids such as γ-Al2O3, H-ZSM-5, and Al-Sn-Beta were found to be active for 2-MTHF dehydration to pentadienes. The rate of ring opening decreased in the order 2,5-dimethyltetrahydrofuran > 2-MTHF > tetrahydropyran > tetrahydrofuran. Over SiO2/Al2O3, the dehydration of 2,5-dimethyltetrahydrofuran resulted in 75% yield to hexadiene isomers. (Figure Presented).
- Kumbhalkar, Mrunmayi D.,Buchanan, J. Scott,Huber, George W.,Dumesic, James A.
-
p. 5248 - 5256
(2017/08/17)
-
- CATALYTIC DEHYDRATION OF ALCOHOLS AND ETHERS OVER A TERNARY MIXED OXIDE
-
A ternary V—Ti—P mixed oxide is shown to catalytically dehydrate 2-methyl-tetrahydrofuran in high conversion to give piperylene, in good yield. Volatile products collected from this reaction contain piperylene in concentrations as high as 80 percent by weight. Dehydration of glycerol to acrolein in high conversion and moderate selectivity is also demonstrated. The catalyst is also shown to dehydrate other alcohols and ether substrates. The catalyst is resistant to deactivation and maintains activity between runs.
- -
-
Paragraph 0029; 0046
(2013/03/28)
-
- Propylene and isoprene production
-
A process for producing propylene and isoprene from a feed stream comprising 1-butene and isobutene is disclosed. The feed stream is reacted in a catalytic distillation reactor containing an olefin isomerization catalyst to produce an overhead stream comprising 2-butene and isobutene and a bottoms stream comprising 2-butene. The overhead stream is reacted in the presence of a metathesis catalyst to produce propylene and isoamylenes. Isoprene is produced by dehydrogenation of isoamylenes.
- -
-
Page/Page column 3-4
(2009/03/07)
-
- Moving bed process for producing propylene, recycling a fraction of used catalyst
-
The invention concerns a process for producing propylene from a steam cracking and/or catalytic cracking light olefinic cut, said process comprising a moving bed catalytic cracking step with a catalyst regeneration loop. The process recycles a portion of the used catalyst to the inlet of the moving bed reactor. The conversion is high using the process of the invention, with a good yield and good propylene selectivity.
- -
-
Page/Page column 5-6
(2008/06/13)
-
- Gas-phase kinetic and mechanistic studies of some interconverting alkylcyclopropene pairs: Involvement of dialkylvinylidene intermediates and their quantitative behaviour
-
The pyrolyses of two isomeric pairs of alkylcyclopropenes, namely 1,3-dimethyl- (15) and 1-ethyl-cyclopropene (16), and 1,3,3-trimethyl- (5) and 1-isopropyl-cyclopropene (17), have been studied in the gas phase. Complete product analyses at various conversions up to 95% were obtained for the decomposition of each compound at five temperatures over a 40°C range. The time-evolution data showed that the isomerisation reactions 15?16 and 5?17 were occurring. Kinetic modelling of each system allowed the determination of rate constants for these and all other decomposition processes. Tests confirmed that all reactions were unimolecular and homogeneous. Arrhenius parameters are reported for overall reactions and individual product pathways. Further kinetic analysis allowed us to extract the propensities (at 500 K) for 1,3-C-H insertion of the dialkylvinylidene intermediates involved in the rearrangements as follows: kprim:ksec: ktert = 1:16.5:46.4. Additional experiments with 13C-labelled cyclopropenes yielded alkyl group migration aptitudes for the dialkylvinylidenes (from the pattern of 13C in the alkyne products) as follows: Me:Et:iPr=1:3.1:1.5. Explanations for these trends are given. Another important finding is that of the dramatic rate enhancements for 1,3-diene product formation from the 1-alkylcyclopropenes; this can be explained by either hyperconjugative stabilisation of the vinylcarbene intermediates involved in this pathway, or their differing propensities to 1,2 H-shift. The observed large variations in product distribution amongst these four cyclopropenes is interpreted in terms of these specific effects on individual pathways.
- Graf Von Der Schulenburg, Wilhelm,Hopf, Henning,Walsh, Robin
-
p. 1963 - 1979
(2007/10/03)
-
- (E)- And (Z)-1-(Phenylsulfonyl)-4-(trimethylsilyl)-2-butenes: Synthetic Equivalents for the 1-(1,3-Butadienyl) Anion and the 1,1-(1,3-Butadienyl) Dianion
-
(E)- and (Z)-1-(phenylsulfonyl)-4-(trimethylsilyl)-2-butenes (7 and 8) are converted by n-BuLi to (E)- and (Z)-1-lithio-1-(phenylsulfonyl)-4-(trimethylsilyl)-2-butenes (15 and 16) with retention of initial stereochemistries. Reactions of 15 and 16 with electrophiles (protio and deuterio acids, primary, secondary, and benzyl halides, chloroformates, chlorothioformates, acid chlorides, epoxides, trialkylsilyl chlorides, and triethylgermanyl chloride) in THF or THF/HMPA give the corresponding (E)- and (Z)-1-(phenylsulfonyl)-1-substituted-4-(trimethylsilyl)-2-butenes (32) with stereochemical retention. That β,γ-unsaturated silyl sulfones 32 are formed instead of their α,β-unsaturated (conjugated) isomers are attributed to stabilizing multiple anionic and cationic hyperconjugation and to steric effects as in 29-31. Of importance in synthesis is that 32 are eliminated by TBAF at -20 to 0°C, thermally, or by column chromatography to (E)- (100 to > 93%) rather than (Z)-1-substituted-1,3-butadienes (38). Further, 32 undergo conversions by n-BuLi and various alkylating agents to (unconjugated) 1-(phenylsulfonyl)-1,1-disubstituted-4-(trimethylsilyl)-2-butenes (46) with retention of stereochemistry. Eliminations of 46 by fluoride ion, acid catalysis, or heat yield 1,1-disubstituted-1,3-butadienes (53). Silyl sulfones 7 and 8 are thus synthetic equivalents for the (E)-1-(1,3-butadienyl) anion (44) and the 1,1-(1,3-butadienyl) dianion (57). Silyl sulfones 7 and 8 also undergo efficient stereospecific intramolecular conversions by n-BuLi and α,ω-dihalides to 1,1-cycloalka-1-(phenylsulfonyl)-4-(trimethysilyl)-2-butenes (62 and 71) that are eliminated by fluoride ion, heat, or adsorption chromatography to 1,1-cycloalka-1,3-butadienes (72).
- Meagher, Timothy P.,Yet, Larry,Hsiao, Chi-Nung,Shechter, Harold
-
p. 4181 - 4192
(2007/10/03)
-
- Homolytic Bond Dissociation Enthalpies of the C-H Bonds Adjacent to Radical Centers
-
Homolytic bond dissociation enthalpies (BDEs) at 0 and 298 K of the C-H bonds adjacent to various radical centers have been obtained from ab initio CBS-4 (complete basis set) model calculations and experimental data available in the literature. The BDEs of the G-H bonds adjacent to the radical centers derived from 11 saturated hydrocarbons were found to be 33.5 ±3 kcal/mol at 298 K. The BDEs of the C-H bonds adjacent to nine allylic and benzylic radical centers were found to be 48 ±3 kcal/mol at 298 K, but the benzylic C-H BDE of the PhCH2CH2 radical was found to be only 29.7 and 30.5 kcal/mol at 0 and 298 K, respectively. The BDEs of the vinylic C-H bonds adjacent to four vinylic radical centers were found to be 35.5 ±3.5 kcal/mol at 298 K. The BDEs of the vinylic C-H bonds adjacent to three allylic radical centers were found to be 56.5 ±3 kcal/ mol at 298 K. These results suggest that the radical centers weaken the adjacent C-H bond strengths by about 50-70 kcal/mol. The calculated BDEs agree within ±2 kcal/mol with most of the available experimental results. Isomerization enthalpies of butenes and pentenes have been obtained. Substituent effects on BDEs have also been examined.
- Zhang, Xian-Man
-
p. 1872 - 1877
(2007/10/03)
-
- STANNYLDIENES, NEW TOOLS FOR ORGANIC SYNTHESIS. PREPARATION AND REACTIVITY.
-
Tributylstannyl-1,3-dienes could be considered synthetic equivalents of conjugated dienic anions.The preparation of differently substituted 2- and 3-trialkylstannyl-1,3-dienes is reported starting from propargyltrimethylsilane.The position of the stannyl moiety on the dienic skeleton can be controlled by hydrostannylation of (trimethylsilyl)propargyl alcohols or stannyl cupration of (trimetylsilyl)propargyl ketones.The so obtained stannyldienes are submitted to Diels Alder reaction and the corresponding cycloadducts functionalized through the C-Sn bond.Stannyldienes are also suitable for a regiocontrolled transfer of the dienic structure by : a) tin-lithium exchange and further reaction with aldehydes to give conjugated dienic alcohols; b)coupling with acyl chlorides in the presence of palladium catalysts to give conjugated dienic ketones; c) AlCl3 promoted reaction with acyl chlorides to give allenic ketones.
- Nativi, Cristina,Taddei, Maurizio,Mann, Andre
-
p. 1131 - 1144
(2007/10/02)
-
- Non-perfect Synchronisation of β-Scission with Product Stabilisation in Radical Ring-opening Reactions
-
Reduction of cyclobut-2-enylmethyl bromide with tri-n-butyltin hydride gave 3-methylcyclobutene together with trans- and cis-penta-1,3-diene and penta-1,4-diene.The diene products are formed by β-scission of the intermediate cyclobut-2-enylmethyl radicals to give pentadienyl radicals which accept hydrogen at the terminal and central carbon atoms.The rate constants and activation energies of β-scission in the series of radicals cyclobutylmethyl, 3-methylenecyclobutylmethyl, cyclobut-2-enylmethyl were shown to change little with the large increase in product radical stabilisation.This was accounted for in terms of the principle of non-perfect synchronisation, i.e. bond scission occours before the development of resonance delocalisation.Semi-empirical MNDO calculations for the same series of radicals were in full agreement with this interpretation.
- Walton, John C.
-
p. 173 - 178
(2007/10/02)
-
- HOMOGENEOUS CATALYTIC HYDROGENATION AND ISOMERIZATION OF LINEAR AND CYCLIC MONOENES AND DIENES IN THE PRESENCE OF THE HETEROMETALLIC CLUSTER (η5-C5H5)NiRu3(μ-H)3(CO)9
-
The complex (η5-C5H5)NiRu3(μ-H)3(CO)9 catalyses the selective hydrogenation of the therminal double bond of conjugated linear dienes in homogeneous conditions; isomerization of non-conjugated to conjugated dienes and of pent-1-ene to pent-2-ene also occurs.Selective hydrogenation and isomerization of cyclic hexenes and hexadienes takes place without opening of the ring; a reaction scheme is proposed, and the activity of the cluster itself relative to that of its decomposition products is discussed.Its behaviour is compared with the analogous complex (η5-C5H5)NiOs3(μ-H)3(CO)9.
- Castiglioni, Mario,Giordano, Roberto,Sappa, Enrico
-
p. 167 - 182
(2007/10/02)
-
- Infrared Multiphoton Isomerization Reactions of Alkenes and Dienes
-
The infrared multiphoton laser-induced unimolecular isomerization reactions of several simple alkenes, conjugated alkenes, and pentadienes have been investigated.Excitation of (E)-2-butene, pentene, and hexene results in contrathermodynamic E -> Z isomerization and fragmentation, the isomerization/fragmentation ratio decreasing with increasing chain length and increasing laser fluence.These results are in qualitative agreement with RRKM calculations for average reactant energies of 75-85 kcal/mol.In addition to products of C-C homolysis observed with all three alkenes, 1-butene and 1,3-butadiene are formed from (E)-2-butene. (E)-Crotononitrile undergoes laser-induced isomerization without fragmentation, resulting in quantitative conversion to the Z isomer.In contrast, (E)-methyl crotonate undergoes both isomerization and fragmentation, while (E)-ethyl crotonate undergoes essentially quantitative elimination of ethylene.Irradiation of (E)- or (Z)-1,3-pentadiene at low laser fluences results exclusively in E Z isomerization resulting in steady-state isomer ratios which depend upon the relative magnitude of the single photon cross sections of the two isomers.At higher fluences, both isomers are converted to cyclopentadiene and trace amounts of 1,4-pentadiene.Irradiation of 1,4-pentadiene results in efficient isomerization to (E)- and (Z)-1,3-pentadiene which reacts further to yield cyclopentadiene.The factors which govern these and related infrared multiphoton reactions are discussed.
- Lewis, Frederick D.,Teng, Peter,Weitz, Eric
-
p. 2818 - 2826
(2007/10/02)
-
- SILVER ION PERTURBATION OF OLEFIN PHOTOCHEMISTRY
-
Ag(I) catalysis and inhibition of alkene E/Z photoisomerisation, and its effect on tetramethylethylene photochemistry are reported.
- Morrison, Harry,Koviak, Carol
-
p. 2711 - 2714
(2007/10/02)
-
- Facile chloropalladation of vinylcyclopropanes. Isolation of ring-opened 1,2,5-η3-σ,π chelates as kinetic precursors to 1-3-η3-π-allyl final products
-
Reactions of vinylcyclopropane (1a), isopropenylcyclopropane (1c), and α-cyclopropyl-4-fluorostyrene (1d) (all are vinylcyclopropanes) with PdCl2(PhCN)2 in low polarity aprotic media (e.g., CDCl3) leads to rapid cyclopropane chloropalladation with formation of 1,2,5-η3-σ,π chelates. In one case (1a) the precursor to chloropalladation - a π complex that may involve Pd(II)-cyclopropane interaction also - is observed by 1H and 13C NMR. The 1,2,5-η3-σ,π complexes rearrange in solution over periods of hours to days to 1-3-η3-π-allyls. In the case of the 1,2,5-η3-σ,π complex from 1a, namely, 6, allyl formation is accompanied by rearrangement (hydrogen shift). Compound 6 rearranges to a π-allyl also in the solid state, but in this case the hydrogen shift path is not followed. Dynamic NMR experiments conducted on 6 lead to the conclusion that very fast chloropalladation/dechloropalladation occurs in solution, in such a way that the carbon alternately getting and losing chlorine dynamically inverts its configuration. This observation leads to a better understanding of earlier published results for chrysanthemate ester isomerizations catalyzed by PdCl2(PhCN)2. In the course of the present work, the molecular structures of the following two compounds were determined by X-ray diffraction: bis(μ-chloro)bis(1,2,5-η 3-2-methyl-3-chloro-1-penten-5-yl)di-palladium(II) (5) and (acetylacetonato)(1-3-η 3-2-methyl-5-chloro-1-penten-3-yl)palladium(II) (9). Crystal data for compound 5: space group P1 (no. 2); a = 5.487 (3) A?, b = 11.959 (2) A?, c = 6.902 (2) A?; α = 89.06 (2)°, β = 107.2 (3)°, γ = 106.3 (3)°; V = 414.1 (5) A?3; Z = 2. The refinement for 5 was based on 1263 reflections with I > 3σ(I) with a final R = 3.4% and Rw = 5.2%. Crystal data for compound 9: space group P21/c (no. 14); a = 4.529 (2) A?, b = 17.026 (3) A?, c = 16.580 (3) A?; β = 92.49 (3)°; V = 1277 (1) A?3; Z = 4. The refinement for 9 was based on 1740 reflections with I > 3σ(I) with final R = 3.4% and Rw = 4.4%.
- Parra-Hake, Miguel,Rettig, Michael F.,Williams, Jimmie L.,Wing, Richard M.
-
p. 1032 - 1040
(2008/10/08)
-
- Untersuchungen zur Kinetik und zum Mechanismus der Addition von Methylradikalen an Vinylacetylen
-
The addition of methyl radicals to vinylacetylen has been studied at 573 K.The methyl radicals were produced by thermolysis of azomethane.The attack occurs exclusively in the terminal positions and predominantly at the triple bond.The value of the rate constant amounts to k2.1 + k2.2 = 5.1E6 l mol-1s-1.The main steps and the formed types of radicals are deduced from the stable products.Without azomethane vinylacetylene is consumed by a slow conversion of second order.The activation parameters of this dimerisation were estimated at 553-593 K.
- Scherzer, K.,Claus, P.,Karwath, M.
-
p. 321 - 328
(2007/10/02)
-
- An Investigation of the Thermal Decomposition of the Methohydroxides and Methodeuterio-oxides of Some 5-N,N-Dimethylaminopent-1-enes
-
The base-catalysed thermal decomposition of a number of quaternary bases of the type (R1)2C=CH(R2)2C(R3)2CH2N+Me3X- (R1 = H, Me; R2 = H, 2H; R3 = H, 2H, Me; X = OH, O2H) has been investigated.It is shown that the reaction is initiated by attack of base (OH-, O2H-, ylide) on an allylic proton or .A mechanism for the reaction is suggested.
- Cocker, Wesley,Geraghty, Niall W. A.,McMurry, T. Brian H.,Shannon, Patrick V. R.
-
p. 2245 - 2254
(2007/10/02)
-
- Heats of Hydrogenation, III. Influence of Fluoro Substituents on the Thermal Rearrangement of Cyclopropane Systems
-
The influence of the fluoro substituents on the isomerisation of 1,1-difluoro-2-vinylcyclopropane (1) and of cis-1,1-difluoro-2-methyl-3-vinylcyclopropane (11) is demonstrated by kinetic methods and by heat of hydrogenation measurements to be a ground state effect (destabilisation of the cyclopropane by 12 - 14 kcal/mol).The transition states of the vinylcyclopropane rearrangement of 1 and of the 1,5-homodienyl hydrogen shift of 11 are more or less effected, depending on their cyclopropane character.
- Roth, Wolfgang R.,Kirmse, Wolfgang,Hoffmann, Wilfried,Lennartz, Hans-Werner
-
p. 2508 - 2515
(2007/10/02)
-
- THE REACTIONS OF TRIFLUOROMETHYL AND TRICHLOROMETHYL RADICALS WITH CONJUGATED AND METHYLENE-INTERRUPTED DIENES AND ENYNES
-
The photochemical addition of CF3I to buta-1,3-diene and vinylacetylene in the gas phase gave 1,4-adducts as the main products.In gas phase reactions only products derived from hydrogen abstraction were detected in the CF3I penta-1,3-diene system, but the 1,4-adducts again predominated in the liquid phase.CCl3Br similarly gave a mixture of 1,2- and 1,4-adducts, the latter predominating, on photochemical reaction with penta-1,3-diene.The 1,2-adduct was the main product from the CCl3Br/pent-1-en-4-yn reaction, but some hydrogen abstraction was observed.The preference shown by conjugated dienes to give 1,4-adducts in the trans- configuration is interpreted in terms of steric factors and the propensity of dienes to adopt the s-trans conformation.
- Soueni, Amr. El,Tedder, John M.,Walton, John C.
-
-
- Infrared Multiphoton Photochemistry of Vinylcyclopropane. Variation of Yield and Branching Ratio with Experimental Parameters
-
The infrared photochemistry of vinylcyclopropane has been comprehensively investigated.Irradiation of vinylcyclopropane at relatively low pressures with the partially focused output of a CO2 laser leads to a mixture of the C5 products cyclopentene, cyclopentadiene, 1,4-pentadiene, and cis- and trans-1,3-pentadiene.The composition of the product mixture as well as the total product yields are a sensitive function of experimental parameters.The effects of bath gas pressure, laser power, laser intensity, laser frequency, and number of pulses have been systematically examined.A simple physical picture of the multiphoton activation and resulting decomposition is developed.RRKM theory is employed to calculate energy-dependent unimolecular reaction rates.The model is quite successful in rationalizing these data, providing good evidence for the qualitative validity of a rate equation description of infrared multiphoton dissociation.
- Farneth, William E.,Thomsen, Marcus W.,Schultz, Nancy L.,Davies, Mark A.
-
p. 4001 - 4006
(2007/10/02)
-
- Chemistry of Dienyl Anions. II. Crystalline Bis(dienyl)magnesium. Selective Dienylation and Structure in Solution and in the Solid State
-
Seven different crystalline bis(dienyl)magnesium TMEDA complexes of open chain or cyclic structure were prepared by metal exchange reaction of corresponding potassium dienides.They are fluxional in solution due to the rapid 1,3-rearrangement.Terminally ?-bonded trans or (E) structure exists primarily in the open chain complexes while centrally ?-bonded cis structure in cyclic dienylmagnesium TMEDA complexes.The former gave 1,3-dienes exclusively but the latter gave 1,4-dienes upon hydrolysis.Molecular structure of bis(2,4-dimethyl-2,4-pentadienyl)magnesium determined by X-ray crystallography showed that it has terminally ?-bonded structure.Addition of dienylmagnesium compounds to acetone followed by hydrolysis gave 1,4-diene derivatives regioselectively but that to diisopropyl ketone gave 1,3-diene derivatives selectively.Unsaturated alcihols with an elongated carbon chain were synthesized by thermal cracking of cyclic ether complexes. 1,3,7-Trienes can be obtained selectively by reaction of appropriate allyl halides in the presence of CuCl catalyst and regiosective dienylation occured by using TiCl2(η5-C5H5)2 as catalyst.
- Yasuda, Hajime,Yamauchi, Michihide,Nakamura, Akira,Sei, Tsuyoshi,Kai, Yasushi,et al.
-
p. 1089 - 1100
(2007/10/02)
-
- Mechanistic Aspects of Gas-Phase Photodecarbonylation Reactions of Bicyclohexanones
-
The gas-phase photodecarbonylation and photofragmentation reactions of substituted bicyclohexan-3-ones have been studied in detail.Photolysis of these ketones yields 1,3-dienes, vinylcyclopropanes, and 1,4-dienes as detectable products.The possible mechanisms for these reactions are discussed in light of the regiochemical and stereochemical results obtained.In addition, methyl substitution at C-6 and C-2 of these ketones has been shown to have a pronounced effect on both product ratios and overall reaction efficiency.These effects are discussed in terms of stereoelectronic and electronic controls of rates of cyclopropane ring opening of intermediate acylcyclopropylcarbinyl diradicals.
- Mariano, Patrick S.,Bay, Elliott,Watson, Darrell G.,Rose, Timothy,Bracken, Christopher
-
p. 1753 - 1762
(2007/10/02)
-
- Addition of Pentenes to Slowly Reacting Mixtures of Hydrogen and Oxygen at 480 deg C
-
A detailed analysis has been made of the products formed when 1percent of pent-1-ene and of cis-pent-2-ene are added to slowly reacting mixtures of H2 + O2 in aged boric-acid-coated vessels at 480 deg C.The primary products are formed through four different types of attack on the pentenes of almost equal importance, radical addition of H, OH, and HO2, and H atom abstraction from the pentenes by all three radicals.Penta-1,3-diene is the only C5 diene observed, in marked contrast to an earlier study of pentene oxidation.From measurements of the initial relative yields of penta-1,3-diene and buta-1,3-diene, a value of k2 = 2.1 x 1E6 dm3 mol-1 s-1 at 480 deg C is obtained. This is the first value determined for a reaction of this type and is at least ten times lower than rate constants for the formation of an alkene from an alkyl radical.This decrease is consistent with the considerably lower enthalpy change in reaction (2).Product analysis suggests that H atoms add almost equally at the two positions in pent-2-ene, and in the ratio of 0.65 +/-0.2 for non-terminal/terminal addition in pent-1-ene.In contrast to the behaviour of vibrationally-excited propyl and butyl radicals formed by H atom addition to alkenes, there is no evidence for an enhanced rate of decomposition of the pentyl radicals formed from the pentenes.Conjugate oxirans are formed mainly by HO2 addition to the pentenes, and lower aldehydes mainly by OH addition.
- Baldwin, Roy R.,Bennett, Joan P.,Walker, Raymond W.
-
p. 2396 - 2412
(2007/10/02)
-