DOCSLIB.ORG

Ketenes 25/01/2014 Part 1

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Baran Group Meeting Hai Dao Ketenes 25/01/2014 Part 1. Introduction Ph Ph n H Pr3N C A brief history Cl C Ph + nPr NHCl Ph O 3 1828: Synthesis of urea = the starting point of modern organic chemistry. O 1901: Wedekind's proposal for the formation of ketene equivalent (confirmed by Staudinger 1911) Wedekind's proposal (1901) 1902: Wolff rearrangement, Wolff, L. Liebigs Ann. Chem. 1902, 325, 129. 2 Wolff adopt a ketene structure in 1912. R 2 hν R R2 1905: First synthesis and characterization of a ketene: in an efford to synthesize radical 2, 1 ROH R C Staudinger has synthesized diphenylketene 3, Staudinger, H. et al., Chem. Ber. 1905, 1735. N2 1 RO CH or Δ C R C R1 1907-8: synthesis and dicussion about structure of the parent ketene, Wilsmore, O O J. Am. Chem. Soc. 1907, 1938; Wilsmore and Stewart Chem. Ber. 1908, 1025; Staudinger and Wolff rearrangement (1902) O Klever Chem. Ber. 1908, 1516. Ph Ph Cl Zn Ph O hot Pt wire Zn Br Cl Cl CH CH2 Ph C C vs. C Br C Ph Ph HO O O O O O O O 1 3 (isolated) 2 Wilsmore's synthesis and proposal (1907-8) Staudinger's synthesis and proposal (1908) wanted to make Staudinger's discovery (1905) Latest books: ketene (Tidwell, 1995), ketene II (Tidwell, 2006), Science of Synthesis, Vol. 23 (2006); Latest review: new direactions in ketene chemistry: the land of opportunity (Tidwell et al., Eur. J. Org. Chem. 2012, 1081). Search for ketenes, Google gave 406,000 (vs. allenes: 950,000 ) Jan 23,2014. Structure and Physical properties Frontier orbitals Resonance structure Dipole moment Spectroscopy data Nu C C O Cβ Cα β α H C C O C O H LUMO C C O (2.27 D) IR: distinctive absorptions near 2200-2100 cm-1 (vs. alkene: 1680 cm-1, alkynes: 2200 cm-1; allenes: 1950- 1960 cm-1, carbonyl 1760-1665 cm-1). (IR is frequently used to detect the formation of reactive H ketene species) C C O C C O H HOMO 13 (1.45 D) C NMR: δCα =203-178 ppm; δCβ = 48-33 ppm. E Saturday, January 25, 14 Baran Group Meeting Hai Dao Ketenes 25/01/2014 Part 2. Synthesis of Ketenes Due to its highly reactivity, many ketenes are synthesized in situ as intermediates which then react with other reagents to generate products 2.1 Ketenes from Carboxylic Acids and Their Derivatives From Esters From Acyl halides and Activated Acids (Wedekind's Method) E1cB mechanism (crowed esters...) or similar pathway o OLi 25 C Me3Si Me3Si O LDA Me3Si NCbz O H C O Cl(H2C)3 O Et3N t o t 60% Me3Si Cl(H2C)3 Me3Si O Bu −78 C Me3Si O Bu C O 75% Cl cyclohexane N Rethke, M. W. et al. J. Org. Chem. 1977, 2038. Cbz reflux Cl(H2C)3 H Cevasco, G.; Thea, S. et al. J. Org. Chem. 1999, 5422. 2.2 Ketenes from Diazo Ketones (Wolff's Rearrangement) From α-Halo Carboxylic Derivatives (Staudinger's Method) O Me HMe Me Et O xylene H 70% H O Zn, DME Cl PhC CEt C O Cl C C O N2 3 Et O Cl reflux Cl 2 Cl 88% Ph O O O ultrasound Cl H H O H Rizzo, C. J. et al. Synth. Commun. 1995, 2781. From Acid Anhydrides Miller, R.D., et al. J. Org. Chem. 1991, 1453 Et Me O O o O quinidine 500 C C O H O O Ph2C O Ph2C Ph2C Me MeOH O Me DCM, −78 oC hν C O CO2Me 2 O 99% ee Me Me Ph2C N2 Ph C Calter, M. A. et al. Org. Lett. 2001, 1499. Ph2C 2 From Acids Ueda, K.; Toda, F. et al. Chem. Lett. 1975, 1421. i Pr2NEt, MeCN OHC CO2H + OHC C nanocluster (Ag) 4 3 O n N Cl rt CO2H Ph 4 N2 Ph I Me proposed 4 Ph 4 O dioxane 80-91% H o C O 60 C, H2O 2-98 Mukaiyama's reagent 9-O-acetylquinine O 51%, 86% ee O Sudrik, S. G. et al. Org. Lett. 2003, 2355. H other metal catalysts: Ag, Cu, Rh Saturday, January 25, 14 Baran Group Meeting Hai Dao Ketenes 25/01/2014 2.3 Ketenes from Metal Carbene Complexes From Cycloalkanones and Enones through Photolysis Cr(CO)5 OMe O O Cr(CO)3 OMe O H C CO2Me h hν MeOH OMe ν C [2+2] O tBu tBu tBu tBu THF 78% O 96% Norrish Type I O Agosta, W. C.; Wolff, S. et al. J. Am. Chem. Soc. 1976, 4182. MeO Cr(CO) C 5 [2+2] OMe Cr(CO)3 45 oC O CO2H 63% H H mechanism OH OMe OH hυ, MeOH HO HO Hegedus, L. S. et al. J. Am. Chem. Soc. 1996, 7873. 20% N2 Me MeO2C Ph (30% decarboxylation) Me O O O Pd2(dba)3 Me C Me C Ph Buscemi, S. et al. Photochem. Photobiol., A, 2003, 145. + N Ph PdLn CO, PhMe 93% N Ph O Ph O Ph From Cyclohexadienones and Other Cycloalkenones 60 oC Ph Bn Wang, J. et al. J. Am. Chem. Soc. 2011, 4330. O Ph N O Ph C PhCH=NBn O 2.4 Other Methods Me From Cyclobutanones and Cyclobutenones Ph Ph O Me Me EtO C CO Et 2 O EtO2C H O EtO2C Barton-Quinkert reaction 2 2 Quinkert, G. et al. Helv. Chim. Acta 1997, 1683. C O CO2H N2 Rh cat 75% From Dioxinones Cai, W. -L. et al. J. Chem. Soc. Perkin 1 1996, 2337. O O O C O OH O OH O O Δ EtO O EtO O O ArLi 1, Δ EtO C EtO O O O 68% O 2, FeCl3 84% O EtO O O EtO O EtO OH O EtO comercial available Boeckmann, R. K. et al. J. Am. Chem. Soc. 1989, 8286. OH squaric acid O derivative Moore, H. W. et al. Org. Synth 1990, 220. Saturday, January 25, 14 Baran Group Meeting Hai Dao Ketenes 25/01/2014 3.1 [2+2] Cycloaddition Part 3. Reaction of Ketenes Reaction Mechanism: Concerted [π2s+π2a] vs. Two-step Reaction Involving a Dipolar Intermediate R' O R' O H R H R H H R H R H R H H H H C O C O C O + C O C O R' R' R' R' R' H R H R + H R H R H R R R R R less hindered bond rotation Features and Supported Evidences Features and Supported Evidences - stereospecific to thermodynamically less stable cyclobutanones - initial orthogonal approach of the ketene to alkene from the least - Z olefins are more reactive than E olefine hindereddirection following by rotation at C2 lead to the same H O stereochemisty outcome as in concerted mechanism tBu - high level calculation by Houk showed that the forming bond + C O CN length of the carbonyl carbone is 1.78 Å; the other is 2.43 Å NC - solvent effects observed (it could be a ground state effect only) H tBu - evidence from studies of intramolecular [2+2] H O tBu C O H + C O CN H NC O H tBu Montaigne, R. et al. Angew. Chem., Int. Ed. 1968, 221. relative reactivity: stereochemisty = a net [π2s+π2s] Cl2C C O > Ph2C C O > Me2C C O > H2C C O Retigeranic acid synthesis: Corey, E. J. et al. J. Am. Chem. Soc. 1985, 4339. [2+2] Cycloaddition with Alkynes [2+2] Cycloaddition with Electrorich Olefins: Stepwise Mechanism R' O H SO R' O Cl R R' 2 4 O O O Ph Ph C O O Ph Ph Cl Cl C O Cl + R Cl R O Cl Cl Cl O Zn, AcOH O O O R' O O Reynolds, P. W. et al. J. Am. Chem. Soc. 1984, 4566. R' C R' C Cl O Cl O Bn Cl R C C O + NH R R O bisketene Cl OR 69% vinylketene dr = 94:6 RO Bn Danheiser, R. L. et al. Tetraherdon Lett. 1987, 3299; RO Bn Ammann, A. A. et al. Helv. Chim. Acta 1987, 321. Kanazawa, A. t al. J. Org. Chem. 1998, 4660. Saturday, January 25, 14 Baran Group Meeting Hai Dao Ketenes 25/01/2014 chiral organic base or NHC catalysis [2+2] Cycloaddition with Imines: Staudinger Ketene-Imine Cycloaddition Et O Ph uncatalyzed mechanism: stepwise formation of zwitterion followed by Boc contotatory ring closure to give cis-product Ph NHC, Cs2CO3 N C O + N o C6H4Cl Boc Et C H Clo 6 4 THF, rt cis:trans = 91:9 R O R O 71% 99%ee R1 R conrot. C imine N + C O N R2 N N Cs CO N 2 1 2 2 3 N R 1 R R R NPh NPh ketene NPh cis-adduct N N N planar BF4 Ph O Ph Ph OTBS Ph Ph Arrieta, A. et al. J. Org. Chem. 1998, 5869. Ph Ph OTBS TBSO Et NHC Me Bn BnO O Zhang, Y. -R. et al. Org. Lett. 2008, 277. N BnO OTBS O + N β-amino CO2Bn NTs C O Me O 80% Bn acids N O Me OTBSO BQ, In(OTf) O 3 N O N Cl Et3N BnO2C Ts o CO Ph Palomo, C. et al. Chem. Commun. 1996, 1269. PhMe, -78 C cis:trans = 99:1 2 59% 99%ee BQ Townsend, C. A. et al. Org. Lett. 2009, 3609. Me CO Bn N 2 CO2Bn general reaction mode (apart from concerted [π2s+π2a] ): BnN O N Me BnN O C solvents + CO2Bn R C R R X E N NR' substrates BnN 2 N NR'2 C O C intra- or intermolecular C O R R or catalysts R O reactions - R electrophilic X nucleophilic CO2Bn more stable 3.2 Other Cycloadditions BnN O Formal [4+2] Cycloaddition: with electro-deficient dienes con.
Recommended publications
  • 4-Dimethylamino Pyridine (Dmap) Catalyst with Fluxional Chirality

    4-Dimethylamino Pyridine (Dmap) Catalyst with Fluxional Chirality

    4-DIMETHYLAMINO PYRIDINE (DMAP) CATALYST WITH FLUXIONAL CHIRALITY: SYNTHESIS AND APPLICATIONS A Dissertation Submitted to the Graduate Faculty of the North Dakota State University of Agriculture and Applied Science By Gaoyuan Ma In Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Major Department: Chemistry and Biochemistry November 2015 Fargo, North Dakota North Dakota State University Graduate School Title 4-Dimethylamino Pyridine (DMAP) Catalyst with Fluxional Chirality: Synthesis and Applications By Gaoyuan Ma The Supervisory Committee certifies that this disquisition complies with North Dakota State University’s regulations and meets the accepted standards for the degree of DOCTOR OF PHILOSOPHY SUPERVISORY COMMITTEE: Prof. Mukund P. Sibi Chair Prof. Gregory R. Cook Prof. Pinjing Zhao Prof. Dean C. Webster Approved: 11/30/2015 Prof. Gregory R. Cook Date Department Chair ABSTRACT Organocatalysis using small organic molecules to catalyze organic transformations, has emerged as a powerful synthetic tool that is complementary to metal-catalyzed transformations and remarkably promote stereoselective synthesis. Our group has designed useful templates, ligands, and additives that use fluxional groups to control and/or enhance stereoselectivity in a variety of asymmetric transformations. A key feature of this strategy is that the size of the fluxional substituent can be varied readily. As an extension of this strategy we became interested in developing efficient and broadly applicable and adjustable 4-dimethylaminopyridine (DMAP) organocatalysts. In our design, we surmised that a fluxional group would be effective in relaying stereochemical information from the fixed chiral center to the catalytic center of DMAP. Presented herein the synthesis of novel fluxionally chiral DMAP catalysts and their application in the acylative kinetic resolution of secondary alcohols and axially chiral biaryls, dynamic kinetic resolution of chiral biaryls with low rotation barriers and allylic substitution reactions.
  • UNITED STATES PATENT of FICE 1926,642 PROCESS of OBTAINING REACTION PRODUCTS of RETENE Charles O

    UNITED STATES PATENT of FICE 1926,642 PROCESS of OBTAINING REACTION PRODUCTS of RETENE Charles O

    Patented Sept. 12, 1933 1926,642 UNITED STATES PATENT of FICE 1926,642 PROCESS OF OBTAINING REACTION PRODUCTS OF RETENE Charles O. Young and George H. Reid, South Charleston, W. Wa, assignors to Carbide & Carbon Chemicals. Corporation, a corporation of New York No Drawing. Application December 2, 1930 Serial No. 502,005 8 Claims. (C. 260-06) The invention is an improved process of mak plied in any desired manner, for example the ap ing reaction products of ketene (CH2=C-O). In paratus for quenching the hot vapors may take general, the process of our invention comprises the form of a packed tower scrubber, spray-scrub thermally decomposing a substance which will ber or any other suitable means for rapidly cool form ketene, and rapidly cooling the hot gaseous ing the hot vapors in intimate contact with the 80 products of this pyrolysis in intimate contact with abSOrbing medium. a reacting absorbing medium. The absorption or quenching means may be The principal object of the invention is to pro operated at ordinary temperatures, and in such Wide a method of making ketene and reaction a case the resultant liquid will contain the reac 0 products thereof which will result in the forma tion product of ketene and the absorbing medium, 65 tion of a maximum amount of valuable product excess absorbing medium and condensed un and which will minimize losses of the ketene changed acetone. The liquid may be circulated formed. until Sufficiently reacted with ketene and then sep In the manufacture of ketene by the pyrolysis arated from the diluent acetone, or it may be oth 15 of organic compounds, e.g., acetone, two primary erwise treated for the separation or recovery of O difficulties in Securing useful quantities of ketene its several constituents.
  • Solvent Effects on Structure and Reaction Mechanism: a Theoretical Study of [2 + 2] Polar Cycloaddition Between Ketene and Imine

    Solvent Effects on Structure and Reaction Mechanism: a Theoretical Study of [2 + 2] Polar Cycloaddition Between Ketene and Imine

    J. Phys. Chem. B 1998, 102, 7877-7881 7877 Solvent Effects on Structure and Reaction Mechanism: A Theoretical Study of [2 + 2] Polar Cycloaddition between Ketene and Imine Thanh N. Truong Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, UniVersity of Utah, Salt Lake City, Utah 84112 ReceiVed: March 25, 1998; In Final Form: July 17, 1998 The effects of aqueous solvent on structures and mechanism of the [2 + 2] cycloaddition between ketene and imine were investigated by using correlated MP2 and MP4 levels of ab initio molecular orbital theory in conjunction with the dielectric continuum Generalized Conductor-like Screening Model (GCOSMO) for solvation. We found that reactions in the gas phase and in aqueous solution have very different topology on the free energy surfaces but have similar characteristic motion along the reaction coordinate. First, it involves formation of a planar trans-conformation zwitterionic complex, then a rotation of the two moieties to form the cycloaddition product. Aqueous solvent significantly stabilizes the zwitterionic complex, consequently changing the topology of the free energy surface from a gas-phase single barrier (one-step) process to a double barrier (two-step) one with a stable intermediate. Electrostatic solvent-solute interaction was found to be the dominant factor in lowering the activation energy by 4.5 kcal/mol. The present calculated results are consistent with previous experimental data. Introduction Lim and Jorgensen have also carried out free energy perturbation (FEP) theory simulations with accurate force field that includes + [2 2] cycloaddition reactions are useful synthetic routes to solute polarization effects and found even much larger solvent - formation of four-membered rings.
  • Accurate Enthalpies of Formation of Astromolecules: Energy, Stability and Abundance

    Accurate Enthalpies of Formation of Astromolecules: Energy, Stability and Abundance

    Accurate Enthalpies of Formation of Astromolecules: Energy, Stability and Abundance Emmanuel E. Etim and Elangannan Arunan* Inorganic and Physical Chemistry Department, Indian Institute of Science Bangalore, India-560012 *email: [email protected] ABSTRACT: Accurate enthalpies of formation are reported for known and potential astromolecules using high level ab initio quantum chemical calculations. A total of 130 molecules comprising of 31 isomeric groups and 24 cyanide/isocyanide pairs with atoms ranging from 3 to 12 have been considered. The results show an interesting, surprisingly not well explored, relationship between energy, stability and abundance (ESA) existing among these molecules. Among the isomeric species, isomers with lower enthalpies of formation are more easily observed in the interstellar medium compared to their counterparts with higher enthalpies of formation. Available data in literature confirm the high abundance of the most stable isomer over other isomers in the different groups considered. Potential for interstellar hydrogen bonding accounts for the few exceptions observed. Thus, in general, it suffices to say that the interstellar abundances of related species are directly proportional to their stabilities. The immediate consequences of this relationship in addressing some of the whys and wherefores among astromolecules and in predicting some possible candidates for future astronomical observations are discussed. Our comprehensive results on 130 molecules indicate that the available experimental enthalpy
  • Reaction Mechanism

    Reaction Mechanism

    Reaction Mechanism A detailed sequence of steps for a reaction Reasonable mechanism: 1. Elementary steps sum to the overall reaction 2. Elementary steps are physically reasonable 3. Mechanism is consistent with rate law and other experimental observations (generally found from rate limiting (slow) step(s) A mechanism can be supported but never proven NO2 + CO NO + CO2 2 Observed rate = k [NO2] Deduce a possible and reasonable mechanism NO2 + NO2 NO3 + NO slow NO3 + CO NO2 + CO2 fast Overall, NO2 + CO NO + CO2 Is the rate law for this sequence consistent with observation? Yes Does this prove that this must be what is actually happening? No! NO2 + CO NO + CO2 2 Observed rate = k [NO2] Deduce a possible and reasonable mechanism NO2 + NO2 NO3 + NO slow NO3 + CO NO2 + CO2 fast Overall, NO2 + CO NO + CO2 Is the rate law for this sequence consistent with observation? Yes Does this prove that this must be what is actually happening? No! Note the NO3 intermediate product! Arrhenius Equation Temperature dependence of k kAe E/RTa A = pre-exponential factor Ea= activation energy Now let’s look at the NO2 + CO reaction pathway* (1D). Just what IS a reaction coordinate? NO2 + CO NO + CO2 High barrier TS for step 1 Reactants: Lower barrier TS for step 2 NO2 +NO2 +CO Products Products Bottleneck NO +CO2 NO +CO2 Potential Energy Step 1 Step 2 Reaction Coordinate NO2 + CO NO + CO2 NO22 NO NO 3 NO NO CO NO CO 222In this two-step reaction, there are two barriers, one for each elementary step. The well between the two transition states holds a reactive intermediate.
  • Nucleophilic Aromatic Substitution

    Nucleophilic Aromatic Substitution

    NUCLEOPHILIC AROMATIC SUBSTITUTION Ms. Prerana Sanas M.Pharm (Pharmceutical Chemistry) Asst.Professor, NCRD’s Sterling Institute of Pharmacy Nerul Navi Mumbai Nucleophilic aromatic substitution results in the substitution of a halogen X on a benzene ring by a nucleophile (:Nu– ). Aryl halides undergo a limited number of substitution reactions with strong nucleophiles. NAS occurs by two mechanisms i) Bimoleccular displacement (Addition –Elimination) ii) Benzyne Formation( Elimination –Addition) 7/5/2019 Ms.Prerana Sanas 2 Bimolecular displacement (Addition – Elimination) Aryl halides with strong electron-withdrawing groups (such as NO2) on the ortho or para positions react with nucleophiles to afford substitution products. For example, treatment of p-chloronitrobenzene with hydroxide (– OH) affords p-nitrophenol by replacement of Cl by OH. Nucleophilic aromatic substitution occurs with a variety of strong nucleophiles, including – OH, – OR, – NH2, – SR, and in some cases, neutral nucleophiles such as NH3 and RNH2 . 7/5/2019 Ms.Prerana Sanas 3 Mechanism…… The mechanism of these reactions has two steps: Step i) Addition of the nucleophile (:Nu– ) forms a resonance-stabilized carbanion with a new C – Nu bond—three resonance structures can be drawn. • Step [1] is rate-determining since the aromaticity of the benzene ring is lost. In Step ii) loss of the leaving group re-forms the aromatic ring. This step is fast because the aromaticity of the benzene ring is restored. 7/5/2019 Ms.Prerana Sanas 4 Factors affecting Bimolecular displacement Increasing the number of electron-withdrawing groups increases the reactivity of the aryl halide. Electron-withdrawing groups stabilize the intermediate carbanion, and by the Hammond postulate, lower the energy of the transition state that forms it.
  • Possible Gas-Phase Syntheses for Seven Neutral Molecules Studied Recently with the Green Bank Telescope

    Possible Gas-Phase Syntheses for Seven Neutral Molecules Studied Recently with the Green Bank Telescope

    A&A 474, 521–527 (2007) Astronomy DOI: 10.1051/0004-6361:20078246 & c ESO 2007 Astrophysics Possible gas-phase syntheses for seven neutral molecules studied recently with the Green Bank Telescope D. Quan1 and E. Herbst2 1 Chemical Physics Program, The Ohio State University, Columbus, Ohio 43210, USA e-mail: [email protected] 2 Departments of Physics, Chemistry and Astronomy, The Ohio State University, Columbus, OH 43210, USA Received 9 July 2007 / Accepted 17 August 2007 ABSTRACT Aims. With the Green Bank telescope (GBT), seven neutral molecules have been newly detected or confirmed towards either the cold interstellar core TMC-1 or the hot core source Sgr B2(N) within the last 1–2 years. Towards TMC-1, the new molecules seen are cyanoallene (CH2CCHCN) and methyl triacetylene (CH3C6H) while methyl cyanoacetylene (CH3CCCN) and methyl cyanodiacety- lene (CH3C5N) were confirmed. Towards Sgr B2(N), the three newly detected molecules are cyclopropenone (c-C3H2O), ketenimine (CH2CNH), and acetamide (CH3CONH2); these are mainly seen in absorption and are primarily located in an envelope around the hot core. In this work, we report a detailed study of the gas-phase chemistry of all seven molecules. Methods. Starting with our updated gas-phase chemical reaction network osu.01.2007, we added formation and depletion reactions to treat the chemistry of each of the seven molecules. Some of these were already in our network but with incomplete chemistry, while most were not in the network at all prior to this work. We assumed the standard physical conditions for TMC-1 and assumed that these also hold for the envelope around Sgr B2(N).
  • Nov 15, Ketene Chemistry and the Application in Synthesis by Xuan Zhou

    Nov 15, Ketene Chemistry and the Application in Synthesis by Xuan Zhou

    Ketene chemistry and the application in synthesis Dong group at UT Austin Xuan Zhou Nov 14, 2013 Ketene chemistry Content • A brief history of ketene • Type of ketenes • Ketene preparation • Ketenes in synthesis Reviews about ketenes: T. T. Tidwell, Ketenes, 2nd ed., wiley interscience, Hoboken, NJ, 2006. T. T. Tidwell, Eur. J. Org. Chem. 2006, 563-576. T. T. Tidwell, Angew. Chem. Int. Ed. 2005, 44, 5778-5785. A brief history of ketene The first reported ketene: Diphenylketene Wedekind Ketene and its Dimer: N.T.M. Wilsmore, J. Chem. Soc. 1907, 91, 1938 Asymmetric reactions of ketene: H. Pracejus, Justus liebigs Ann. Chem. 1969, 722, 1-11 Bisketenes First prepared bisketenes by Wolf in 1906 O. Diels, B. Wolf, Ber. Dtsch. Chem. Ges. 1906, 39, 689-697 First observed bisketenes in 1982 G. Maier, H. P. Reisenauer, T. Sayrac, Chem. Ber. 1982, 115, 2192 Substituent effects of ketene Melvin Newman Shchukovskaya Cycloadditions of ketenes Lee Irvin Smith Derek H.R. Barton Angew. Chem. Int. Ed. 2005, 44, 5779-5785 Type of ketenes Carbon-substituted ketenes • Alkylketenes 2 3 4 • Alkenylketenes 5 6 7 • alkynylketenes and cyanoketenes 8 9 10 Type of ketenes • Arylketenes 1 2 3 • Acylketenes 4 5 6 • Imidoylketenes 7 azetinones 8 Nitrogen-substituted ketenes 1 Nitroketene Azidoketene Isocyanatoketene 2 Oxygen-substituted ketenes 3 4 5 6 Halogen-substituted ketenes 1 2 3 4 Silyl-ketenes 5 6 7 Phosphorous, sulfur, metal-substituted and bis ketenes 1 2 5 6 7 8 9 10 11 12 Ketene preparation Ketenes from ketene dimers •Pyrolysis of ketene dimer 1 2 3 4 •Photolysis
  • The Interactions and Reactions of Atoms and Molecules on the Surfaces of Model Interstellar Dust Grains

    The Interactions and Reactions of Atoms and Molecules on the Surfaces of Model Interstellar Dust Grains

    The Interactions and Reactions of Atoms and Molecules on the Surfaces of Model Interstellar Dust Grains A thesis submitted for the degree of Doctor of Philosophy Helen Jessica Kimber Department of Chemistry University College London 2016 -I, Helen Jessica Kimber, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Signed, i Abstract The elemental composition of the known universe comprises almost exclusively light atoms (~99.9% hydrogen and helium). However, to date, close to 200 different molecules have been detected in the interstellar medium (ISM) where their distribution is far from uniform. The vast majority of these molecules are contained within vast clouds of gas and dust referred to as interstellar clouds. Within these interstellar clouds, many of the molecules present are formed via gas-phase ion-neutral reactions. However, there are several molecules for which known gas-phase kinetics cannot account for observed gas-phase abundances. As a result, reactions occurring on the surface of interstellar dust grains are invoked to account for the observed abundances of some of these molecules. This thesis presents results of experimental investigations into the interaction and reactions of atoms and molecules on the surface of model interstellar dust grains. Chapters three and four present results for the reaction of (3P)O on molecular ices. Specifically, the reaction of (3P)O and propyne or acrylonitrile. After a one hour dosing period, temperature programmed desorption (TPD), coupled with time-of-flight mass spectrometry (TOFMS), are used to identify (3P)O addition products.
  • Hydroxyacetonitrile (HOCH2CN) As a Precursor for Formylcyanide (CHOCN), Ketenimine (CH2CNH), and Cyanogen (NCCN) in Astrophysical Conditions

    Hydroxyacetonitrile (HOCH2CN) As a Precursor for Formylcyanide (CHOCN), Ketenimine (CH2CNH), and Cyanogen (NCCN) in Astrophysical Conditions

    A&A 549, A93 (2013) Astronomy DOI: 10.1051/0004-6361/201219779 & c ESO 2013 Astrophysics Hydroxyacetonitrile (HOCH2CN) as a precursor for formylcyanide (CHOCN), ketenimine (CH2CNH), and cyanogen (NCCN) in astrophysical conditions G. Danger1, F. Duvernay1, P. Theulé1, F. Borget1, J.-C. Guillemin2, and T. Chiavassa1 1 Aix-Marseille Univ, CNRS, PIIM UMR 7345, 13397 Marseille, France e-mail: [email protected] 2 Institut des Sciences Chimiques de Rennes, École Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, Avenue du Général Leclerc, CS 50837, 35708 Rennes Cedex 7, France Received 8 June 2012 / Accepted 19 November 2012 ABSTRACT Context. The reactivity in astrophysical environments can be investigated in the laboratory through experimental simulations, which provide understanding of the formation of specific molecules detected in the solid phase or in the gas phase of these environments. In this context, the most complex molecules are generally suggested to form at the surface of interstellar grains and to be released into the gas phase through thermal or non-thermal desorption, where they can be detected through rotational spectroscopy. Here, we focus our experiments on the photochemistry of hydroxyacetonitrile (HOCH2CN), whose formation has been shown to compete with aminomethanol (NH2CH2OH), a glycine precursor, through the Strecker synthesis. Aims. We present the first experimental investigation of the ultraviolet (UV) photochemistry of hydroxyacetonitrile (HOCH2CN) as a pure solid or diluted in water ice. Methods. We used Fourier transform infrared (FT-IR) spectroscopy to characterize photoproducts of hydroxyacetonitrile (HOCH2CN) and to determine the different photodegradation pathways of this compound. To improve the photoproduct identifications, irradiations of hydroxyacetonitrile 14N and 15N isotopologues were performed, coupled with theoretical calculations.
  • Chapter 14 Chemical Kinetics

    Chapter 14 Chemical Kinetics

    Chapter 14 Chemical Kinetics Learning goals and key skills: Understand the factors that affect the rate of chemical reactions Determine the rate of reaction given time and concentration Relate the rate of formation of products and the rate of disappearance of reactants given the balanced chemical equation for the reaction. Understand the form and meaning of a rate law including the ideas of reaction order and rate constant. Determine the rate law and rate constant for a reaction from a series of experiments given the measured rates for various concentrations of reactants. Use the integrated form of a rate law to determine the concentration of a reactant at a given time. Explain how the activation energy affects a rate and be able to use the Arrhenius Equation. Predict a rate law for a reaction having multistep mechanism given the individual steps in the mechanism. Explain how a catalyst works. C (diamond) → C (graphite) DG°rxn = -2.84 kJ spontaneous! C (graphite) + O2 (g) → CO2 (g) DG°rxn = -394.4 kJ spontaneous! 1 Chemical kinetics is the study of how fast chemical reactions occur. Factors that affect rates of reactions: 1) physical state of the reactants. 2) concentration of the reactants. 3) temperature of the reaction. 4) presence or absence of a catalyst. 1) Physical State of the Reactants • The more readily the reactants collide, the more rapidly they react. – Homogeneous reactions are often faster. – Heterogeneous reactions that involve solids are faster if the surface area is increased; i.e., a fine powder reacts faster than a pellet. 2) Concentration • Increasing reactant concentration generally increases reaction rate since there are more molecules/vol., more collisions occur.
  • Download The

    Download The

    The Final Program The Final Program for this Symposium was modified from that presented in the Book of Abstracts mainly due to the unforeseen incidence of the coronavirus in late January, 2020. We are grateful to the distinguished scientists who were able to take the place of those who were unable to come, and we regretted the absence of the distinguished scientists who had planned until the last hours to be with us. The SCHEDULE that is posted on this web site is the Final Schedule. That which is in the Book of Abstracts is the schedule that was expected to be the final schedule two weeks prior to the event. Strongly Donating 1,2,3-Triazole-Derived Carbenes for Metal-Mediated Redox Catalysis Simone Bertini, Matteo Planchestainer, Francesca Paradisi, Martin Albrecht Department of Chemistry & Biochemistry, University of Bern, CH-3012 Bern, Switzerland [email protected] Triazole-derived N-heterocyclic carbenes have become an attractive addition to the family of NHC ligands, in parts because their versatile and functional group-tolerant synthesis through click- chemistry,1 and in other parts because of their stronger donor properties to transition metals when compared to ubiquitous Arduengo-type carbenes.2. We have been particularly attracted recently by the high robustness of these ligands towards oxidative and reductive conditions, which provides appealing opportunities for challenging redox catalysis. We have exploited these properties for example for developing iridium complexes as highly active and molecular water oxidation catalysts.3 Here we will present our efforts to use triazole-derived carbenes to enable 1st row transition metals as catalytically competent entities.