- Fabricating nickel phyllosilicate-like nanosheets to prepare a defect-rich catalyst for the one-pot conversion of lignin into hydrocarbons under mild conditions
-
The one-pot conversion of lignin biomass into high-grade hydrocarbon biofuels via catalytic hydrodeoxygenation (HDO) holds significant promise for renewable energy. A great challenge for this route involves developing efficient non-noble metal catalysts to obtain a high yield of hydrocarbons under relatively mild conditions. Herein, a high-performance catalyst has been prepared via the in situ reduction of Ni phyllosilicate-like nanosheets (Ni-PS) synthesized by a reduction-oxidation strategy at room temperature. The Ni-PS precursors are partly converted into Ni0 nanoparticles by in situ reduction and the rest remain as supports. The Si-containing supports are found to have strong interactions with the nickel species, hindering the aggregation of Ni0 particles and minimizing the Ni0 particle size. The catalyst contains abundant surface defects, weak Lewis acid sites and highly dispersed Ni0 particles. The catalyst exhibits excellent catalytic activity towards the depolymerization and HDO of the lignin model compound, 2-phenylethyl phenyl ether (PPE), and the enzymatic hydrolysis of lignin under mild conditions, with 98.3% cycloalkane yield for the HDO of PPE under 3 MPa H2 pressure at 160 °C and 40.4% hydrocarbon yield for that of lignin under 3 MPa H2 pressure at 240 °C, and its catalytic activity can compete with reported noble metal catalysts.
- Cao, Meifang,Chen, Bo,He, Chengzhi,Ouyang, Xinping,Qian, Yong,Qiu, Xueqing
-
supporting information
p. 846 - 857
(2022/02/09)
-
- Rodlike Tetracene Derivatives
-
Efficient and versatile synthetic access to rodlike tetracene derivatives was developed by means of Diels–Alder cycloaddition, halogenation, halogen–metal exchange, and transition metal mediated coupling reactions. Herein, the synthesis and structural, electrical, and charge-transport properties of three of the resulting materials, namely, 2-(tetracen-2-yl)tetracene, 1,4-bis(2-tetracenyl)benzene, and 2,5-bis(2-tetracenyl)thiophene, are presented. Good crystallization behavior on SiO2 substrates, narrowing of the bandgap by 0.2 eV, and a decrease of the ionization potential of more than 0.5 eV compared to tetracene were observed. Charge-carrier field-effect mobilities on the order of 10?1 cm2 V?1 s?1, on/off ratios of 105, and threshold voltages Vth15 V were found in thin-film organic field-effect transistors prepared by standard high-vacuum deposition techniques.
- Roth, Michael,Ahles, Marcus,Gawrisch, Christian,Schwalm, Thorsten,Schmechel, Roland,Melzer, Christian,von Seggern, Heinz,Rehahn, Matthias
-
p. 13445 - 1345
(2017/09/14)
-
- Thermochemistry and photochemistry of spiroketals derived from indan-2-one: Stepwise processes versus coarctate fragmentations
-
Coarctate reactions are defined as reactions that include atoms at which two bonds are made and two bonds are broken simultaneously. In the pursuit of the discovery of new coarctate reactions we investigate the fragmentation reactions of cyclic ketals. Three ketals with different ring sizes derived from indan-2-one were decomposed by photolysis and pyrolysis. Particularly clean is the photolysis of the indan-2-one ketal 1, which gives o-quinodimethane, carbon dioxide and ethylene. The mechanism formally corresponds to a photochemically allowed coarctate fragmentation. Pyrolysis of the five-ring ketal yields a number of products. This is in agreement with the fact that coarctate fragmentation observed upon irradiation would be thermochemically forbidden, although this exclusion principle does not hold for chelotropic reactions. In contrast, fragmentation of the seven-ring ketal 3 is thermochemically allowed and photochemically forbidden. Upon pyrolysis of 3 several products were isolated that could be explained by a coarctate fragmentation. However, the reaction is less clean and stepwise mechanisms may compete.
- Bucher, Goetz,Heitmann, Gernot,Herges, Rainer
-
p. 1668 - 1676
(2013/10/22)
-
- Oligo-Tetracenes, Production and Use Thereof
-
Described are oligotetracenes of formula I which may either be unsubstituted or carry one or more substituents R and R′ which are selected from the group comprising halogen,CN,alkyl or alkoxy radicals containing 1 to 18 carbon atoms,aryl radicals containing up to 10 carbon atoms which may also contain one or moreheteroatoms, and/orfluorinated or perfluorinated alkyl or alkoxy radicals containing 1 to 18 carbon atoms, where n is an integer from 1 to 20, preferably 1 to 6, very particularly preferably 1 or 2, and X stands for a single bond, an alklyene group containing 1 to 6 carbon atoms, a hydrocarbon chain having one or more conjugated double bonds, an aryl group, or a system composed of one or more condensed aromatic rings. In the oligotetracenes according to the invention, one or more of the condensed aromatic six-atom rings may be substituted by a five-atom ring which may also contain a heteroatom. Also described is a method for preparing the referenced oligotetracenes, and use thereof as semiconductors in organic field-effect transistors (OFET's), organic light-emitting diodes (OLED's), sensors, and organic solar cells.
- -
-
Page/Page column 2-3
(2008/12/08)
-
- Synthesis of optically active benzocyclobutene and biphenylene based unusual α-amino acid derivatives
-
Optically active benzocyclobutene and biphenylene based unusual α-amino acid derivatives have been prepared via a six step sequence using Schoellkopf chiral auxiliary in a very high diastereoselective manner.
- Kotha, Sambasivarao,Halder, Somnath
-
p. 863 - 872
(2007/10/03)
-
- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
-
Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
-
p. 402 - 415
(2007/10/03)
-
- Determination of the photochemical efficiency of o-quinodimethane ring closure in room-temperature solutions by using time-delayed, two-color photolysis technique
-
Photochemical efficiency of o-quinodimethane (3) ring closure at room temperature was determined by using a time-delayed, two-color photolysis technique. o-Quinodimethane (3) was generated by the photolysis of 1,2- bis[(phenylseleno)methyl]benzene (1) by a KrF (248 nm) laser pulse and thus- generated 3 was photolyzed by a subsequent XeCl (308 nm)/XeF (351 nm) laser pulse with varying delay time of 0 to 3 s. The time profile of 3 was monitored by the chemical analyses of benzocyclobutene (5) (a photochemical product of 3), which was formed by a one-photon process, and the spiro dimer of 3 (4) (a thermal product of 3) in the two-color photolysis experiments. The time profile of 3 followed a second-order decay kinetics. The photochemical efficiency was obtained by the analysis of the delay-time dependence of the product yields; those of the consumption of 3 and the conversion 3 → 5 by a single pulse of the excimer laser were 81% and 5.7% for the XeCl laser, and 73% and 2.3% for the XeF laser. This difference was attributed to the different excited states involved in the photolysis. In contrast to the photolysis of 3 in argon or rigid organic matrixes, it was revealed that photochemical conversion 3 → 5 was not the main path in the solutions, and intermolecular reactions predominated.
- Ouchi, Akihiko,Sakuragi, Masako,Kitahara, Haruo,Zandomeneghi, Maurizio
-
p. 2350 - 2357
(2007/10/03)
-
- Cyclization of benzyne-tethered alkyllithiums: Preparation of 3-substituted benzocyclobutenes and 5-substituted tetralins
-
A five-step, one-pot preparation of isomerically pure 3-substituted benzocyclobutenes or 5-substituted tetralins in 20-40% yield from the appropriate α-(2-fluorophenyl)-ω-iodoalkane, involving generation and subsequent 4-or 6-exo cyclization of a benzyne-tethered alkyllithium, is described.
- Bailey, William F.,Longstaff, Sarah C.
-
p. 6899 - 6901
(2007/10/03)
-
- First synthesis of optically active benzocyclobutene and biphenylene-based unusual α-amino acid derivatives
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Various optically pure benzocyclobutene and biphenylene-based α-amino acid derivatives are prepared in a very high diastereoselective manner via a six step sequence using Schollkopf chiral auxiliary.
- Kotha, Sambasivarao,Sreenivasachary, Nampally,Halder, Somnath
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p. 2565 - 2568
(2007/10/03)
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- Dehalogenation of organic halides by flash vacuum pyrolysis over magnesium: A versatile synthetic method
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Flash vacuum pyrolysis over magnesium at 600°C results in efficient dehalogenation of a variety of organic halides and provides a preparatively useful method for C-C bond formation and other reactions.
- Aitken, R. Alan,Hodgson, Philip K. G.,Oyewale, Adebayo O.,Morrison, John J.
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p. 1163 - 1164
(2007/10/03)
-
- Fragmentation Patterns in the Gas-Phase Pyrolysis of Some Bi- and Tri-cyclic Sulfolanes Related to the 8-Thiabicyclonon-3-ene 8,8-Dioxide Ring System
-
Depending upon the degree of ring strain, the thermal breakdown of cis-8-thiabicyclonon-3-ene 8,8-dioxide 5 and related ring systems in the gas phase follows widely differing pathways.Decomposition of 5 occurs only under forcing conditions, resulting in complete fragmentation of the sulfolane ring to give a benzene and toluene, while pyrolysis of the 2,5-bridged analogues 6-8 proceeds by a retro-Diels-Alder reaction at much lower temperatures to give 1,3-dienes and the decomposition products of 3-sulfolene, buta-1,3-diene and SO2.Epoxidation of the double bond in the compounds results in a marked change in their thermal fragmentation behaviour; only SO2 is lost to produce novel divinyl epoxides.The corresponding N-ethoxycarbonylaziridines, formed by photolysis of the unsaturated sulfones in ethyl azidoformate, undergo extensive decomposition on pyrolysis and do not yield any useful products.The saturated sulfone 28 gives an expected octa-1,7-diene upon flash vacuum pyrolysis (FVP), but only under relatively severe conditions.Three isomeric diene sulfones 30-32 have also been examined and show a varied pattern of reactivity under FVP conditions.
- Aitken, R. Alan,Cadogen, J. I. G.,Gosney, Ian,Newlands, Stephen
-
p. 2301 - 2308
(2007/10/02)
-
- Intramolecular Reactivity of Arylcarbenes: Derivatives of o-Tolylcarbene
-
Various CH2X groups have been attached to the ortho position of phenylcarbene.If 2'- or 3'-C-H bonds are present, as in 23 (X = Me), 71 (X = CMe3), and 58 (X = SiMe3), C-H insertion leading to five- or six-membered rings predominates in the gas phase and competes with intermolecular reactions in solution.The formation of benzocyclobutenes via insertion into 1'-C-H bonds is a very minor reaction path of 23 and 71.In contrast, 58 produces substantial amounts of the benzocyclobutene 59 by way of C-Si insertion, particularly in the gas phase.Insertion into the Si-Me bonds of 58 also occurs while the C-F bonds of 37 (X = CF3) and 50 (X = F) are inert.In the gas phase, 37 and 50 give mainly benzocyclobutenes whereas intermolecular reactions prevail in solution.The effects of sensitization and of solvent polarity suggest that benzocyclobutenes arise from singlet arylcarbenes.The amount of carbene-carbene rearrangement decreases in the order 7 (X = H) > 37 (X = CF3) > 23 (X = Me); no rearrangement was observed with 50 (X = F), 58 (X = SiMe3), and 71 (X = CMe3).
- Kirmse, Wolfgang,Konrad, Wolfgang,Schnitzler, Dirk
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p. 3821 - 3829
(2007/10/02)
-
- Synthesis and cycloreversion of benzocyclobutene- and benzocyclobutadiene-anthracene adducts
-
The [4+2]-cycloadducts of anthracene and benzocyclobutene or benzocyclobutadiene were synthesized and their cycloreversion was investigated.
- Okada,Kawai,Oda
-
p. 257 - 260
(2007/10/02)
-
- A high-yield route to 1,2-dihydrocyclobutazene-3,6-dicarboxylic acid
-
A simple five-step method for preparing the previously unknown 1.2-dihydrocyclobutabenzene-3,6-dicarboxylic acid (XTA) in high yield is presented. All intermediates were crystalline compounds which allowed the preparation to be scaled up without complication. The title compound is of interest as a crosslinkable derivative of the widely used monomer, terephthalic acid (TA).
- Walker,Markoski,Moore
-
p. 1265 - 1268
(2007/10/02)
-
- Reductive Coupling by Chromium(0) - (Bibenzyl)- and (Stilbene)tricarbonylchromium(0) Complexes by a One-Pot Reaction from Benzylic Halides
-
Reaction of Cr(CO)3(NH3)3 with benzylic mono-, di-, and trihalides leads to the formation of 1,2-diarylethanes, -ethenes, and diphenylethyne in satisfactory yields.Di(halomethyl)benzene derivatives yield product mixtures containing both reduction products and coupling products.With a higher excess in chromium(0), under otherwise unchanged reaction conditions, the corresponding (arene)tricarbonylchromium(0) complexes of the coupling products are formed in a one-pot reaction from the benzylic halides.
- Wey, Hans G.,Butenschoen, Holger
-
-
- Homogeneous gas-phase decyclization of tetralin and benzocyclobutene
-
Tetralin has been decomposed in single pulse shock tube experiments in the temperature range of 1000-1400 K. The initial unimolecular decomposition channels involve the formation of benzocyclobutene and o-allyltoluene. Benzocyclobutene decomposes to form styrene. The main products from the hydrogen atom induced decomposition of tetralin are dihydronaphthalene, styrene, indene, and naphthalene. The following rate expressions have been determined: k(tetralin → ethylene + benzocyclobutene) = 3.5 X 1015 exp(-40 003/T)s-1,k(tetralin → o-allyltoluene) = 1.2 X 1015 exp(-40 111/T)s-1,k(benzocyclobutene → styrene) = 1.2 X 1015 exp(-37 396/T)s-1, k(H + tetralin → H2 + 4-phenylbutyl radical) ≥ 0.55 X k(H + mesitylene → o-xylene + CH3). Comparisons are made with published results from laser-powdered pyrolysis and shock tube studies, and it is concluded that in both cases initial unimolecular channels are accessed. The temperatures in the laser experiments are at least as high in the shock tube studies. The rate expressions for tetralin decomposition are compatible with a biradical mechanism and follow the general patterns for related cyclic compounds.
- Tsang,Cui
-
p. 1665 - 1671
(2007/10/02)
-
- Rearrangements of the Isomeric Tolylmethylenes
-
We present evidence for a mechanism in which the isomeric tolylmethylenes interconvert via methylcycloheptatetraene intermediates.Photolysis (>470 nm) of diazo compounds 1-4, matrix isolated in argon at 10 K, generates triplet tolylmethylenes 8-11.Photoly
- Chapman, Orville L.,Johnson, Jeffery W.,Mahon, Robert J. Mc,West, Paul R.
-
p. 501 - 509
(2007/10/02)
-
- 2,3-Dihydro-2,3-dimethylenethiophene, Dihydrocyclobutathiophene and the Mutual Interconversion of Both Compounds
-
The title compounds 2,3-dihydro-2,3-dimethylenethiophene (5) and 1,2-dihydrocyclobutathiophene (6), are generated and characterized by UV-photoelectron (5) and UV/VIS-absorption (5 and 6) spectroscopy.The gas-phase equilibrium 56 is discussed.According to the photoelectron (gas phase) and UV/VIS-absorption (argon matrix) spectroscopic product analyses only 5 is present in the gas phase.The interconversion of 5 and 6, however, is possible in an argon matrix by irradiating with light of appropriate wavelengths.
- Muenzel, Norbert,Schweig, Armin
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p. 791 - 794
(2007/10/02)
-
- Thermal isomerization of benzocyclobutene
-
Thermolysis of benzocyclobutene 13CH2, 99percent gives styrene labeled in the β (48percent), ortho (30percent), α (14percent), meta (4percent), and para (4percent) positions.The major labels (β and ortho) are consistent with a mechanism involving interconversions of the isomeric tolylmethylenes and the methylcycloheptatrienes.This mechanism also involves interconversion of o-tolylmethylene with o-xylylene and p-tolylmethylene with p-xylylene.A minor mechanism produces 25percent of styrene.This mechanism involves cleavage of the aryl carbon to the methylene carbon bond in benzocyclobutene followed by hydrogen transfer to produce styrene.Thermolysis of p-xylylene produced from paracyclophane gives styrene (55percent), p-xylene (31percent), benzocyclobutene (4percent), benzene (4percent), and toluene (3percent).Thermolysis of metacyclophane gives styrene (18percent), p-xylene (25percent), m-xylene (3percent), benzocyclobutene (1percent), benzene (7percent), and toluene (22percent).
- Chapman, Orville L.,Tsou, Uh-Po Eric,Johnson, Jeffery W.
-
p. 553 - 559
(2007/10/02)
-
- THE REARRANGEMENT OF CHEMICALLY ACTIVATED HENYLMETHYLENES AT 77K
-
The cocondensation of atomic carbon with o, m and p-tolualdehyde at 77K results in deoxygenation to the o, m p-tolylmethylenes which possess sufficient energy to rearrange to benzocyclobutene and styrene.
- Rahman, M.,Shevlin, Philip B.
-
p. 2959 - 2960
(2007/10/02)
-
- The Unsymmetrical Cyclooctadienynes: 1,3-Cyclooctadien-5-yne and 1,6-Cyclooctadien-3-yne
-
Different synthetic pathways are discussed for the title compounds 15 and 45, which can be trapped in solution.Their average lifetimes are to low for an isolation in pure state.Isomerisations on the C8H8-energy hypersurface lead to styrene (47) and/or benzocyclobutene (22).
- Hanold, Norbert,Meier, Herbert
-
p. 198 - 209
(2007/10/02)
-
- THE PHENYLCARBENE REARRANGEMENT REVISITED
-
The evolution of mechanistic ideas about the phenylcarbene rearrangement has been reviewed, and three closely linked problems have been identified toward whose solution this research has been aimed: 1.Why do the ratios of the stable end products from the rearrangements of o-, m- and p-tolylmethylene differ when all three reactions have been thought to pass through a common intermediate? 2.Why does the rearrangement of 2-methylcycloheptatrienylidene lead to exclusive formation of styrene? 3.What is the mechanism of styrene formation from o-tolylmethylene? New mechanisms have been proposed in which m- and p-tolylmethylene can rearrange to styrene without necessarily being converted to o-tolylmethylene.The formation of a small amount of 2,6-dimethylstyrene from the rearrangement of 3,4,5-trimethylphenylmethylene is viewed as evidence for such a mechanism, and a set of interconverting norcaradienylidenes are believed to be the crucial intermediates.Other alternatives are considered and rejected on the basis of the rearrangement products of 3,5-dimethyl- and 3,4,5-trimethylphenylmethylene.
- Gaspar, Peter P.,Hsu, Jong-Pyng,Chari, Sarangan,Jones, Maitland Jr.
-
p. 1479 - 1508
(2007/10/02)
-
- Benzocyclobutenes. Part 9. Synthesis of Bromo-, Chloro-, and Oxo-derivatives of Benzocyclobutene and Naphthocyclobutene
-
Addition of benzyne to 1,1-dichloro- and 1,1,2-trichloro-ethene gave the corresponding di- (61percent) and tri- (18percent) chloro derivatives of benzo-cyclobutene.Similarly 2,3-didehydronaphthalene and 1,1-dichloroethene gave 1,1-dichloronaphthocyclobutene.Some reactions, including reduction, chlorination, bromination, and hydrolysis of these cyclobutenes and of related compounds are described.
- Abou-Teim, Omar,Goodland, Michael C.,McOmie, F. W.
-
p. 2659 - 2662
(2007/10/02)
-
- Intramolecular Reactions of o-Alkoxy- and o-Alkylthio-benzyl Radicals
-
We report new gas-phase reactions of o-substituted benzyl radicals produced by flash vacuum pyrolysis of 2,3-dihydro-1,3,2-benzoxazaphosph(V)oles (4)-(6), dibenzyl sulphone (8), and dibenzyl oxalates (9)-(11).Both o-ethoxy- and o-methoxy-benzyl radicals rearrange to o-tolualdehyde via intramolecular hydrogen transfer, as shown by experiments using 2-methoxybenzyl radicals. o-Methylthiobenzyl radicals do not give the corresponding thioaldehyde, but produce a mixture of benzocyclobutene and isomeric dihydrobenzothiophens by novel rearrangement reactions. o-Ethylthio- and o-propylthio-benzyl radicals give o-methylstyrene and o-propenyltoluenes respectively as major products.
- Cadogan, J. I. G.,Husband, James B.,McNab Hamish
-
p. 697 - 702
(2007/10/02)
-
- A KINETIC STUDY OF PYROLITIC PATHWAYS TO BENZOCYCLOBUTENE
-
A simple gas flow reactor simulating flash vacuum pyrolysis conditions is described which yields approximate rate values for monomolecular gas phase reactions and which has been used for a comparison and optimisation of pyrolitic elimination reactions leading to benzocyclobutene.
- Schiess, Peter,Rutschmann, Suzanne,Toan, Van Vien
-
p. 3665 - 3668
(2007/10/02)
-
- Flash Pyrolysis of Selenides. Syntheses of Bibenzyls, Olefins, and Related Compounds
-
Pyrolyses of a series of selenides and diselenides were studied. Selenides and diselenides bound with an active methylene group like benzyl gave a variety of substituted bibenzyls and related ethane derivatives in high yields. Other diselenides were easily caused to cleave to give various aromatic and aliphatic olefins in good yields together with elemental selenium. Lepidopterene, paracyclophane, and benzocyclobutene were prepared by thermal cleavage of their corresponding phenylselenomethyl-substituted compounds as an application of the pyrolysis concerned.
- Higuchi, Hiroyuki,Otsubo, Tetsuo,Ogura, Fumio,Yamaguchi, Hachiro,Sakata, Yoshiteru,Misumi, Soichi
-
p. 182 - 187
(2007/10/02)
-
- FORMATION OF SUBSTITUTED BENZOCYCLOBUTENES THROUGH FLASH VACUUM PYROLYSIS
-
Benzocyclobutenes carrying a substituent in the four membered ring are obtained in high yield from 2-methyl benzaldehydes through a reaction sequence involving a pyrolitic 1,4-elimination of HCl in the crucial step.
- Schiess, Peter,Rutschmann, Suzanne,Toan, Van Vien
-
p. 3669 - 3672
(2007/10/02)
-
- Absorption Spectra and Photochemical Rearrangements in Phenylalkene Cations in Solid Argon
-
Matrix photoionization experiments with phenylalkenes produced and trapped the parent molecular cations in solid argon at 20 K.In the substituted styrene cation cases, structure was resolved in red and ultraviolet absorption bands and assigned to Ph-C stretching and Ph-C=C bending modes.Molecular ion rearrangements were observed during sample formation and upon the photolysis of the cold sample; allylbenzene cation rearranged to β-methylstyrene cation and indan cation with 290 nm irradiation.The matrix absorption bands were substantially sharper than photodissociati on spectra, which suggests that excess internal energy may contribute substantially to the bandwidth of gaseous molecular ions produced by electron impact.
- Andrews, Lester,Harvey, James A.,Kelsall, Benuel J.,Duffey, Donald C.
-
p. 6415 - 6422
(2007/10/02)
-
- NEW SYNTHETIC METHOD OF PARACYCLOPHANE, BENZOCYCLOBUTENE, AND LEPIDOPTRENE: PYROLYSIS OF ARYLMETHYL PHENYL SELENIDES
-
The flash vacuum pyrolysis of benzyl phenyl selenides gave bibenzyls and diphenyl diselenide in excellent yields.This type of reaction was successfully applied to the synthesis of the title compounds.
- Higuchi, Hiroyuki,Sakata, Yoshiteru,Misumi, Soichi,Otsubo, Tetsuo,Ogura, Fumio,Yamaguchi, Hachiro
-
p. 627 - 630
(2007/10/02)
-
- Kinetic Evidence for the Formation of Discrete 1,4-Dehydrobenzene Intermediates. Trapping by Inter- and Intramolecular Hydrogen Atom Transfer and Observation of High-Temperature CIDNP
-
Upon being heated, alkyl-substituted cis-1,2-diethynyl olefins undergo cyclization to yield reactive 1,4-dehydrobenzenes; the products isolated may be derived from either unimolecular or bimolecular reactions of the intermediate. (Z)-4,5-Diethynyl-4-octene (4) undergoes rearrangement to yield 2,3-di-n-propyl-1,4-dehydrobenzene (17).Solution pyrolysis of 4 in inert aromatic solvent produces three unimolecular products, (Z)-dodeca-4,8-diyn-6-ene (7), benzocyclooctene (9), and o-allyl-n-propylbenzene (10), in high yield.When 1,4-cyclohexadiene is added to the pyrolysis solution as a trapping agent, high yields of the reduced product o-di-n-propylbenzene (12) are obtained.The kinetics of solution pyrolysis of 4 in the presence and absence of trapping agent establish that 2,3-di-n-propyl-1,4-dehydrobenzene is a discrete intermediate on the pathway leading to products.When the reaction was run in the heated probe of an NMR spectrometer, CIDNP was observed in 10.This observation, along with kinetic and chemical trapping evidence, indicates the presence of two additional intermediates, formed from 17 by squential intramolecular hydrogen transfer, on the pathway to products.The observation of CIDNP, coupled with the reactivity exhibited by 17 and the other two intermediates, implicates a biradical description of these molecules.Biradical 17 has been estimated to have a lifetime of about 10-9 s at 200 deg C and to lie in a well of about 5 kcal per mole with respect to the lowest energy unimolecular pathway ( hydrogen transfer).Ring opening (expected to be the lowest energy process for 1,4-dehydrobenzenes in which intramolecular hydrogen transfer is unlikely) to the isomeric diethynyl olefin 7 appears to have an activation enthalpy of about 10 kcal/mol.Upon thermal reaction in the gas phase (400 deg C) or in solution in inert solvents (Z)-2,3-diethylhexa-1,5-diyn-3-ene (5) rearranges in good yield to the isomeric diethynyl olefin (Z)-deca-3,7-diyn-5-ene (8) again presumably via 2,3-diethyl-1,4-dihydrobenzene 20 (addition of 1,4-cyclohexadiene to the reaction solution leads to a good yield of o-diethylbenzene, the expected trapping product of biradical 20).The absence of products due to intramolecular hydrogen transfer indicates that this process is at least 1 or 2 orders of magnitude slower than hydrogen transfer in 17.At 500 deg C in the gas phase products due to hydrogen transfer begin to appear.
- Lockhart, Thomas P.,Comita, Paul B.,Bergman, Robert G.
-
p. 4082 - 4090
(2007/10/02)
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- Flash Vacuum Pyrolysis of 2,3-Dialkyltetralins
-
The cleavage of alkyl groups from the 2- and 3-positions of tetralins is a facile process and the retro-Diels-Alder reaction of tetralins appears to be concerted.
- Trahanovsky, Walter S.,Swenson, Karl E.
-
p. 2984 - 2985
(2007/10/02)
-
- Energy Profile of the o-Quinodimethane Benzocyclobutene Equilibrium, II
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The kinetics of the decomposition of keton 3 yielding o-quinodimethane (2) (Ea = 25.6 kcal/mol; A = 3.1x1013s-1) and its cyclisation to benzocyclobutene (1) (Ea = 26.9 kcal/mol; A = 2.1x1012s-1) is measured by shock tube technic.From the temperature dependence of the equilibrium 1 2, which is studied by the same method, the enthalpy of formation of o-quinodimethane (2) is established to be ΔH0f(g) = 60.8 kcal/mol.
- Roth, Wolfgang R.,Scholz, Bernhard P.
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p. 3741 - 3750
(2007/10/02)
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- Laser-Powered Homogeneous Dissociation of Tetralin
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In an effort to determine the products and mechanism of the truly homogeneous thermal dissociation of the aromatic hydrocarbon tetralin, we have examined the products formed from this compound upon energization by infrared multiphoton excitation and SiF4-
- Comita, Paul B.,Berman, Michael R.,Moore, C. Bradley,Bergman, Robert G.
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p. 3266 - 3276
(2007/10/02)
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- Benzocyclobutenylidene-Cycloadditions, Reactivity, and Multiplicity
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EHT and CNDO/2 calculations on benzocyclobutenylidene (6) are described.Flash pyrolysis of the tosylhydrazone salt 7 affords benzocyclobutene and o-xylene in low yield, along with the formal syn and anti carbene dimers 13 and 14.Condensed-phase reactions were achieved by photolysis of the salt 15.Benzocyclobutenylidene (6) gave rise to the formal carbene dimers 17 and 18.Insertion of carbene 6 into the carbon-hydrogen bonds of 2,3-dimethylbutane produced the benzocyclobutenes 20 and 21 (insertion ratio tertiary:primary = 9:1).Cycloaddition of 6 to olefins gave only spirohexene derivatives 22.Multiplicity studies of 6 with cis or trans olefins indicated that 6 undergoes cycloaddition in a stereospecific manner.Competition experiments using dienes and monoolefins implicate an equilibrium between singlet and triplet 6.Further competition experiments with styrene/para-substituted styrene pairs demonstrated that 6 reacts faster with electron-poor styrenes.Possible explanations for this apparent anomaly are discussed.
- Duerr, Heinz,Nickels, Helmut,Pacala, Luba A.,Jones, Maitland
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p. 973 - 980
(2007/10/02)
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- Aromatization of 1,4-Dihydrobenzocycloalkenes, 1,4-Dihydronaphthocycloalkenes, and Related Systems
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A series of methyl-substituted 1,4-dihydrobenzenes has been prepared, and the rates of oxidation of these molecules by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) have been measured.Existing evidence points to the involvement of a positively charged intermediate which is formed as an ion pair in an initial rate-limiting hydride transfer to DDQ.Series of cycloalkyl-fused 1,4-dihydrobenzenes and 1,4-dihydronaphthalines (fused 1,2 and 2,3) have been prepared and the rates of their DDQ induced aromatization have been studied.The results are explained on the basis of inductive effects associated with the size of the fused ringand exocyclic vs. endocyclic bond order preferences.
- Thummel, Randolph P.,Cravey, Wesley E.,Cantu, David B.
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p. 1633 - 1637
(2007/10/02)
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