DOCSLIB.ORG

7-Reactions of Alkenes and Alkynes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
7-Reactions of Alkenes and Alkynes Chapter Objectives Present reactions of alkenes and alkynes Reactions related to those found in biology Must know reactions Fall, 2007 1 Preparation of Alkenes Precursors Alcohols (especially in biological chemistry) Alkyl Halides (industrial chemistry) OH stro n g a cid H dehydration X strong base H dehydrohalogenation Fall, 2007 2 Biological Dehydration Rarely done on free alcohol Generally done on molecules containing carbonyl and hydroxyl groups H2O - CO - HO CO 2 2 - - - - O C CO O C CO 2 2 2 aconitase 2 Fall, 2007 3 1 Reaction with X 2 Halogenation Reaction with Cl 2 and Br 2 C l 2 C l C l B r 2 B r B r Fall, 2007 4 Stereochemistry Reaction provides the trans product Fall, 2007 5 Explanation Not a carbocation intermediate as shown Bromonium ion intermediate forms H H Br H Br + H Br Br - Fall, 2007 6 2 Biological Halogenation Marine organisms Haloperoxidase - - + H2O2 oxidizes Cl or Br to X B r C l C l B r Fall, 2007 7 Reaction with X 2 in H 2O Cl 2 in water yields HO -Cl (hypochlorous acid) Br 2 in water yields HO -Br ( hypobromous acid) Br /H O 2 2 OH Br Fall, 2007 8 Hydration of Alkenes Alkenes react with water to give alcohols Require high temperatures and pressures H2O CH 3CH 2OH Does not work well in the laboratory Fall, 2007 9 3 Biological Hydration of Alkenes O O OH O- -O -O fumarase O O fumarate maleate Relatively rare reaction Cellular constraints are not present. Fall, 2007 10 Cellular Constraints Solvent is water Narrow pH range Fixed temperature Limited elemental choice Fall, 2007 11 Laboratory Hydration of Alkenes Oxymercuration Mercuric Acetate in THF Markovnikov Product Fall, 2007 12 4 Laboratory Hydration of Alkenes Hydroboration Non -Markovnikov Product Fall, 2007 13 Mechanism of Hydroboration Borane is a Lewis acid Alkene is Lewis base Transition state involves anionic development on B The components of BH 3 add across C=C Fall, 2007 14 Reduction and Oxidation Carbon always has 4 bonds Oxidation changes are more difficult to see Reduction: Increase in H content Decrease in O content Oxidation: Decrease in H content Increase in O content Fall, 2007 15 5 Reduction of Alkenes: Hydrogenation Addition of H 2 Requires Pt or Pd catalyst (or NR) Heterogeneous Reaction Process is not in solution Fall, 2007 16 Mechanism of Catalytic Hydrogenation Heterogeneous – reaction between phases Addition of H -H is syn Fall, 2007 17 Biological Reductions Rare Reaction Uses NADPH as reducing agent N NH2 O O O O O O N N N P P O N H O O HO OH - - H -2 HO OPO2 O NH2 Nicotinamide Adenine Dinucleotide Phosphate Fall, 2007 18 6 Oxidation of Alkenes: Epoxides mcpba O CH 2Cl 2 H O OOH peroxide mcpba = Cl Reaction with a peracid Epoxide or oxirane Cyclic ether Fall, 2007 19 Epoxide Preparation From Halohydrin Br 2/H 2O OH base O Br bromohydrin Fall, 2007 20 Biological Epoxidation Present in variety of processes Does not involve peracids Peroxides formed by reaction with O 2 Very selective reaction (see Figure 7.8) Fall, 2007 21 7 Hydroxylation of Alkenes Diol formation + H3O OH O OH Laboratory and Biological Reaction Biological process useful for detoxification Fall, 2007 22 Laboratory Hydroxylation Reaction with osmium tetroxide Stereochemistry of addition is syn (product is cis ) Product is a 1,2 -dialcohol or diol (also called a glycol ) Fall, 2007 23 Reaction with Carbenes H2C: The carbene functional group Carbenes are electrically neutral with six electrons in the outer shell They add symmetrically to double bonds giving cyclopropanes Fall, 2007 24 8 Formation of Dichlorocarbene Base removes proton from chloroform Stabilized carbanion remains Unimolecular Elimination of Cl - gives electron deficient species, dichlorocarbene Fall, 2007 25 Reaction of Dichlorocarbene Addition of dichlorocarbene is stereospecific cis Fall, 2007 26 Simmons-Smith Reaction Equivalent of addition of CH 2: Reaction of diiodomethane with zinc -copper alloy produces a carbenoid species Forms cyclopropanes by cycloaddition Fall, 2007 27 9 Radical Reactions Mechanism of addition of HBr was hotly debated Non -Markovnikov product was observed Peroxides form readily in starting material HBr Br On occasion HBr Br + Br Fall, 2007 28 Radical Reactions - HBr If reaction is done with HBr /peroxides Get the non -Markovnikov product HBr/peroxides Br Fall, 2007 29 Radical Reactions: Polymer Formation Polymer – a very large molecule made of repeating units of smaller molecules (monomers) Biological Polymers Starch Cellulose Protein Nucleic Acid Fall, 2007 30 10 Polymers Alkene polymerization Initiator used generally is a radical n re p e a tin g u n it Fall, 2007 31 Mechanism Initiation Propagation Termination See page 241 in text for details High reactivity of radicals limits usefulness Not true in biological chemistry Fall, 2007 32 Biological Radical Reactions Enzyme permits a single substrate at a time at the active site Greater control over reactivity Radical reactions are common Example given on page 244 for biosynthesis of the PGAs Fall, 2007 33 11 Dienes Contain two double bonds Non -conjugated Conjugated Fall, 2007 34 Common Feature in Nature Fall, 2007 35 Conjugation Absorption of visible light produces color Conjugated hydrocarbon with many double bonds are polyenes Lycopene - red color in tomatoes Carrotene – orange color Extended conjugation in ketones (enones ) found in hormones such as progesterone Fall, 2007 36 12 Conjugated Dienes Chemistry is slightly different More stable than non -conjugated dienes Heat of hydrogenation Fall, 2007 37 Greater Stability Why? Orbital Picture of alkene bonding Fall, 2007 38 Fall, 2007 39 13 Orbital picture of conjugated diene Electrons are delocalized (spread -out) over the entire pi framework Impact upon the chemistry Fall, 2007 40 Fall, 2007 41 Reactions With HBr Br (71%) HBr H Br (29%) H Why? Fall, 2007 42 14 Mechanism Fall, 2007 43 Allylic Cation Fall, 2007 44 Some Data H H HX X X 1,4 product 1,2 product Nucleophile 1,2 Product 1,4 Product Bromide 71% 29% Chloride 30% 70% If HBr is added at 0 oC we see the above data. If the reaction is done at 40 oC, we see 30% of the 1,2 product and 70% of the 1,4 product. How do we explain these results? Fall, 2007 45 15 A B + C B forms faster than C Energy of activation is lower for B than C C is more stable than B Constructing reaction energy diagram energy B A C reaction progress Fall, 2007 46 Thermodynamic Control Transition state leading to more stable species is higher in energy, therefore, it is easier to get to the less stable product Reaction is reversable At high temperatures, sufficient E for both reactions to occur A B (fast) and A C (slower) or B A C We see more stable product dominate. Fall, 2007 47 Kinetic Control At low temperatures Reaction is not reversable Equilibrium is not reached Insufficient energy for A to C Sufficient energy for A to B Less stable product dominates. Fall, 2007 48 16 Reactions of Alkynes Alkynes are rare in biological chemistry Chemistry is similar to alkenes Generally less reactive than alkenes Reactions can be stopped at alkene stage using one equivalent of the reagent Fall, 2007 49 Reactions with HX Regiochemistry is Markovnikov Fall, 2007 50 Reactions with X 2 Initial addition gives trans intermediate Product with excess reagent is tetra -halide Fall, 2007 51 17 Reactions with H 2 Reduction using Pd or Pt does not stop Alkene is more reactive than alkyne Fall, 2007 52 Reactions with H 2 Lindler’s catalyst is poisoned Not as reactive Stops at cis -alkene Fall, 2007 53 Reduction using dissolving metals Anhydrous ammonia (NH 3) is a liquid below -33 ºC Alkali metals dissolve in liquid ammonia - Provide a solution of e in NH 3 Alkynes are reduced to trans alkenes with sodium or lithium in liquid ammonia Fall, 2007 54 18 Hydration of Alkynes Hydration (Hg +2 ) of terminal alkynes provides methyl ketones Hydration (BH 3) of terminal alkynes provides aldehydes Fall, 2007 55 Alkyne Acidity: Acetylide Anion Terminal alkynes are weak Br ønsted acids pK a is approximately 25 alkenes and alkanes are much less acidic Reaction of strong anhydrous bases with a terminal acetylene produces an acetylide ion Fall, 2007 56 Alkylation of Acetylide Anions Acetylide ions are nucleophiles Acetylide ions are bases React with a primary alkyl halides Fall, 2007 57 19 PROBLEMS ON ALKENE CHEMISTRY ©2004 OCHeM.com 1. Answer the following questions concerning the three alkenes shown below. Your answer should use words and illustrations. 1 2 3 4 5 6 CH3 O CH3 CF3 A B C a) Which alkene would be most reactive with H+ ? Why? b) Which alkene would be least reactive with H+ ? Why? c) Which alkene would be most reactive under conditions of catalytic hydrogenation? Why? d) Will all three alkenes undergo Markovnikov addition of HBr? If not, which alkene or alkenes won’t and why? 1 PROBLEMS ON ALKENE CHEMISTRY ©2004 OCHeM.com 2. Provide a mechanism for the following reaction. Then, predict the reaction energy diagram for the entire reaction in the space provided. In your diagram, you must indicate the ΔH of the reaction, label the activation energy (Ea) of the rate-determining step, and clearly identify all intermediates and products of the reaction. H Br Br y g r e n E Reaction Coordinate 2 PROBLEMS ON ALKENE CHEMISTRY ©2004 OCHeM.com 3. What starting materials & reagents are needed to produce the following compound? Br Br 4. Draw the major product of each of the following reactions.
Load more

Recommended publications
  • The Progression of Chiral Anions from Concepts to Applications in Asymmetric Catalysis Robert J
    REVIEW ARTICLE PUBLISHED ONLINE: 24 JULY 2012 | DOI: 10.1038/NCHEM.1405 The progression of chiral anions from concepts to applications in asymmetric catalysis Robert J. Phipps, Gregory L. Hamilton and F. Dean Toste* Despite the tremendous advances of the past four decades, chemists are far from being able to use chiral catalysts to con- trol the stereoselectivity of any desired reaction. New concepts for the construction and mode of operation of chiral catalysts have the potential to open up previously inaccessible reaction space. The recognition and categorization of distinct approaches seems to play a role in triggering rapid exploration of new territory. This Review both reflects on the origins as well as details a selection of the latest examples of an area that has advanced considerably within the past five years or so: the use of chiral anions in asymmetric catalysis. Defining reactions as involving chiral anions is a difficult task owing to uncertainties over the exact catalytic mechanisms. Nevertheless, we attempt to provide an overview of the breadth of reactions that could reasonably fall under this umbrella. 9 ithin the broader field of science, organic chemistry is Of significantly greater acidity (pKa around 2–4) are chiral phos- often referred to as a mature field of study. In spite of this, phoric acids, commonly derived from BINOL (1,1′-bi-2-naphthol). Wnew avenues of inquiry seem to arise with relative fre- These catalysts have risen to prominence over the past decade quency. Perhaps we take it for granted that expansions of the field because their high acidity permits activation of a broad range of are sparked when one or two chemical laboratories uncover a new substrates3,10.
    [Show full text]
  • Organic Chemistry
    Wisebridge Learning Systems Organic Chemistry Reaction Mechanisms Pocket-Book WLS www.wisebridgelearning.com © 2006 J S Wetzel LEARNING STRATEGIES CONTENTS ● The key to building intuition is to develop the habit ALKANES of asking how each particular mechanism reflects Thermal Cracking - Pyrolysis . 1 general principles. Look for the concepts behind Combustion . 1 the chemistry to make organic chemistry more co- Free Radical Halogenation. 2 herent and rewarding. ALKENES Electrophilic Addition of HX to Alkenes . 3 ● Acid Catalyzed Hydration of Alkenes . 4 Exothermic reactions tend to follow pathways Electrophilic Addition of Halogens to Alkenes . 5 where like charges can separate or where un- Halohydrin Formation . 6 like charges can come together. When reading Free Radical Addition of HX to Alkenes . 7 organic chemistry mechanisms, keep the elec- Catalytic Hydrogenation of Alkenes. 8 tronegativities of the elements and their valence Oxidation of Alkenes to Vicinal Diols. 9 electron configurations always in your mind. Try Oxidative Cleavage of Alkenes . 10 to nterpret electron movement in terms of energy Ozonolysis of Alkenes . 10 Allylic Halogenation . 11 to make the reactions easier to understand and Oxymercuration-Demercuration . 13 remember. Hydroboration of Alkenes . 14 ALKYNES ● For MCAT preparation, pay special attention to Electrophilic Addition of HX to Alkynes . 15 Hydration of Alkynes. 15 reactions where the product hinges on regio- Free Radical Addition of HX to Alkynes . 16 and stereo-selectivity and reactions involving Electrophilic Halogenation of Alkynes. 16 resonant intermediates, which are special favor- Hydroboration of Alkynes . 17 ites of the test-writers. Catalytic Hydrogenation of Alkynes. 17 Reduction of Alkynes with Alkali Metal/Ammonia . 18 Formation and Use of Acetylide Anion Nucleophiles .
    [Show full text]
  • 3-Monochloropropane-1,2-Diol Esters and Glycidyl Esters
    www.nature.com/scientificreports OPEN Monitoring of heat‑induced carcinogenic compounds (3‑monochloropropane‑1,2‑diol esters and glycidyl esters) in fries Yu Hua Wong1, Kok Ming Goh1,2, Kar Lin Nyam2, Ling Zhi Cheong3, Yong Wang4, Imededdine Arbi Nehdi5,6, Lamjed Mansour7 & Chin Ping Tan1* 3‑Monochloropropane‑1,2‑diol (3‑MCPD) esters and glycidyl esters (GE) are heat‑induced contaminants which form during oil refning process, particularly at the high temperature deodorization stage. It is worth to investigate the content of 3‑MCPD and GE in fries which also involved high temperature. The content of 3‑MCPD esters and GE were monitored in fries. The factors that been chosen were temperature and duration of frying, and diferent concentration of salt (NaCl). The results in our study showed that the efect was in the order of concentration of sodium chloride < frying duration < frying temperature. The content of 3‑MCPD esters was signifcantly increased whereas GE was signifcantly decreased, when prolong the frying duration. A high temperature results in a high 3‑MCPD ester level but a low GE level in fries. The present of salt had contributed signifcant infuence to the generation of 3‑MCPD. The soaking of potato chips in salt showed no signifcant efect on the level of GE during the frying. The oil oxidation tests showed that all the fries were below the safety limit. Hence, the frying cycle, temperature and the added salt to carbohydrate‑based food during frying should be monitored. Deep-fat frying is commonly being used to process food. During the process, heat transfer between the fried food and oil is occurs.
    [Show full text]
  • Chapter 7, Haloalkanes, Properties and Substitution Reactions of Haloalkanes Table of Contents 1
    Chapter 7, Haloalkanes, Properties and Substitution Reactions of Haloalkanes Table of Contents 1. Alkyl Halides (Haloalkane) 2. Nucleophilic Substitution Reactions (SNX, X=1 or 2) 3. Nucleophiles (Acid-Base Chemistry, pka) 4. Leaving Groups (Acid-Base Chemistry, pka) 5. Kinetics of a Nucleophilic Substitution Reaction: An SN2 Reaction 6. A Mechanism for the SN2 Reaction 7. The Stereochemistry of SN2 Reactions 8. A Mechanism for the SN1 Reaction 9. Carbocations, SN1, E1 10. Stereochemistry of SN1 Reactions 11. Factors Affecting the Rates of SN1 and SN2 Reactions 12. --Eliminations, E1 and E2 13. E2 and E1 mechanisms and product predictions In this chapter we will consider: What groups can be replaced (i.e., substituted) or eliminated The various mechanisms by which such processes occur The conditions that can promote such reactions Alkyl Halides (Haloalkane) An alkyl halide has a halogen atom bonded to an sp3-hybridized (tetrahedral) carbon atom The carbon–chlorine and carbon– bromine bonds are polarized because the halogen is more electronegative than carbon The carbon-iodine bond do not have a per- manent dipole, the bond is easily polarizable Iodine is a good leaving group due to its polarizability, i.e. its ability to stabilize a charge due to its large atomic size Generally, a carbon-halogen bond is polar with a partial positive () charge on the carbon and partial negative () charge on the halogen C X X = Cl, Br, I Different Types of Organic Halides Alkyl halides (haloalkanes) sp3-hybridized Attached to Attached to Attached
    [Show full text]
  • Activity 33. Hydrohalogenation & Hydration of Alkynes
    Chem 201, Fall 2010 Activity 33, M Nov 22 Activity 33. Hydrohalogenation & Hydration of Alkynes Alkynes undergo many of the same addition reactions that alkenes do, including additions that require carbocation intermediates. Different energy and geometry changes may be required for additions to an alkyne and an alkene so some surprising outcomes may occur with alkynes. Model 1. Addition of HX Hydrogen halides (HCl, HBr, HI) add to alkynes to make vinyl halides . A carbocation mechanism is followed when the reaction is performed in the dark in a peroxide-free solvent. This addition obeys Markovnikov’s rule. A free-radical-chain mechanism is followed when HBr addition is initiated by organic peroxides. This addition gives an anti-Markonikov product. Critical Thinking Questions 1. Draw the carbocations indicated by the two bouncy curved arrows (below). Based on the observation that the carbocation mechanism yields a Markovnikov product, circle the more stable carbocation. 2. (CI) Draw the free radicals indicated by the two competing pathways (below). Based on the observation that the free-radical mechanism yields an anti-Markovnikov product, circle the more stable free radical. 3. The cations and radicals in CTQ #1 and #2 are called vinyl cations and vinyl radicals , respectively. Based on the regioselectivities reported in Model 1, what effect do alkyl substituents at the charged/radical carbon have on the energies of these species? Is this consistent with, or opposed to, their effect on R 3C+ and R 3C• species? 4. The geometry of a vinyl cation can be anticipated using VSEPR. Count electron domains in the cation below and predict all of the HCC bond angles.
    [Show full text]
  • An Indicator of Triplet State Baird-Aromaticity
    inorganics Article The Silacyclobutene Ring: An Indicator of Triplet State Baird-Aromaticity Rabia Ayub 1,2, Kjell Jorner 1,2 ID and Henrik Ottosson 1,2,* 1 Department of Chemistry—BMC, Uppsala University, Box 576, SE-751 23 Uppsala, Sweden; [email protected] (R.A.); [email protected] (K.J.) 2 Department of Chemistry-Ångström Laboratory Uppsala University, Box 523, SE-751 20 Uppsala, Sweden * Correspondence: [email protected]; Tel.: +46-18-4717476 Received: 23 October 2017; Accepted: 11 December 2017; Published: 15 December 2017 Abstract: Baird’s rule tells that the electron counts for aromaticity and antiaromaticity in the first ππ* triplet and singlet excited states (T1 and S1) are opposite to those in the ground state (S0). Our hypothesis is that a silacyclobutene (SCB) ring fused with a [4n]annulene will remain closed in the T1 state so as to retain T1 aromaticity of the annulene while it will ring-open when fused to a [4n + 2]annulene in order to alleviate T1 antiaromaticity. This feature should allow the SCB ring to function as an indicator for triplet state aromaticity. Quantum chemical calculations of energy and (anti)aromaticity changes along the reaction paths in the T1 state support our hypothesis. The SCB ring should indicate T1 aromaticity of [4n]annulenes by being photoinert except when fused to cyclobutadiene, where it ring-opens due to ring-strain relief. Keywords: Baird’s rule; computational chemistry; excited state aromaticity; Photostability 1. Introduction Baird showed in 1972 that the rules for aromaticity and antiaromaticity of annulenes are reversed in the lowest ππ* triplet state (T1) when compared to Hückel’s rule for the electronic ground state (S0)[1–3].
    [Show full text]
  • Classifying Halogenoalkanes Reactions Of
    10 Halogenoalkanes H Naming Halogenoalkanes H H H H C H H H H Based on original alkane, with a prefix indicating halogen atom: H C C C H Fluoro for F; Chloro for Cl; Bromo for Br; Iodo for I. H C C C C H Br H H H Cl H H Substituents are listed alphabetically 1-bromopropane 2-chloro-2-methylbutane Classifying Halogenoalkanes Halogenoalkanes can be classified as primary, secondary or tertiary depending on the number of carbon atoms attached to the C-X functional group. H H H H H H H H C H H H H H C C C H H C C C H H C C C C H Br H H H Br H H Cl H H Primary halogenoalkane Secondary halogenoalkane Tertiary halogenoalkane One carbon attached to the Two carbons attached to the Three carbons attached to the carbon atom adjoining the carbon atom adjoining the carbon atom adjoining the halogen halogen halogen Reactions of Halogenoalkanes Halogenoalkanes undergo either substitution or elimination reactions Nucleophilic substitution reactions Substitution: swapping a halogen atom for another atom or groups of atoms - - Nucleophile: electron pair donator e.g. :OH , :NH3, CN :Nu represents any nucleophile – they The Mechanism: We draw (or outline) mechanisms to always have a lone pair and act as show in detail how a reaction proceeds electron pair donators Nu:- The nucleophiles The carbon has a small attack the positive H H H H positive charge because carbon atom of the electronegativity H C C X H C C + X- δ+ δ- Nu difference between the carbon and the halogen H H H H We use curly arrows in mechanisms (with A curly arrow will always two line heads) to show the movement of start from a of electrons or two electrons lone pair the centre of a bond The rate of these substitution reactions depends on the strength Bond enthalpy / of the C-X bond kJmol-1 The weaker the bond, the easier it is to break and the faster the reaction.
    [Show full text]
  • A Palladium-Catalyzed Approach to Allenic Aromatic Ethers and First Total
    Chemical Science EDGE ARTICLE View Article Online View Journal | View Issue A palladium-catalyzed approach to allenic aromatic ethers and first total synthesis of terricollene A† Cite this: Chem. Sci.,2021,12,9347 a b b b a a a All publication charges for this article Chaofan Huang, Fuchun Shi, Yifan Cui,‡ Can Li,‡ Jie Lin,‡ Qi Liu,‡ Anni Qin,‡ have been paid for by the Royal Society Huanan Wang,‡a Guolin Wu,‡a Penglin Wu,‡a Junzhe Xiao, ‡b Haibo Xu,‡b of Chemistry Yuan Yuan,‡a Yizhan Zhai,‡b Wei-Feng Zheng,‡a Yangguangyan Zheng, ‡a Biao Yu*b and Shengming Ma *ab A palladium-catalyzed C–O bond formation reaction between phenols and allenylic carbonates to give 2,3- allenic aromatic ethers with decent to excellent yields under mild reaction conditions has been described. A Received 7th April 2021 variety of synthetically useful functional groups are tolerated and the synthetic utility of this method has Accepted 4th June 2021 been demonstrated through a series of transformations of the allene moiety. By applying this reaction as DOI: 10.1039/d1sc01896e the key step, the total syntheses of naturally occurring allenic aromatic ethers, eucalyptene and rsc.li/chemical-science terricollene A (first synthesis; 4.5 g gram scale), have been accomplished. Creative Commons Attribution-NonCommercial 3.0 Unported Licence. Introduction Results and discussion Aromatic ethers are prevalent and prominent in a variety of In contrast to the well-established metal-catalyzed coupling natural products, pharmaceuticals, and agrochemicals.1 Tradi- reactions between aryl halides and phenols or aliphatic alcohols tional methods for the preparation of aromatic ethers include (Scheme 1b),9 metal-catalyzed coupling reactions of aryl halides the Williamson ether synthesis,2 direct nucleophilic substitu- tion reactions,3 Mitsunobu reaction,4 Ullman-type couplings of alkoxides with aryl halides,5 etc.
    [Show full text]
  • Kinetics and Products Distribution of Selective Catalytic Hydration of Ethylene­ and Propylene Oxides in Concentrated Aqueous Solutions
    Organic Process Research & Development 2002, 6, 660-664 Kinetics and Products Distribution of Selective Catalytic Hydration of Ethylene­ and Propylene Oxides in Concentrated Aqueous Solutions I. A. Kozlovsky, R. A. Kozlovsky,* A. V. Koustov, M. G. Makarov, J. P. Suchkov, and V. F. Shvets D.I.Mendeleev University of Chemical Technology of Russia, Chair of Basic Organic and Petrochemical Synthesis, 9 Miusskaya Square, Moscow 125047, Russia Abstract: and metalate anions.I" The kinetics and reaction mechanism The kinetics of selective hydration of ethylene- and propylene of the hydration of a-oxides using homogeneous catalysis oxides in concentrated aqueous solutions is studied during by salts have been explicitly studied.3,IO,1l The kinetic data homogeneous catalysis by sodium bicarbonate. The mathemati­ obtained have shown that at a concentration of some salts cal model of the process with determined parameters adequately of about 0.5 molJL the distribution factor b = klko is reduced describing the rate of the reaction and products distribution is lO-fold more (to 0.1-0.2). This enables the production of developed. monoglycol with high selectivity at water/oxide molar ratios close to 1. We have used hereinafter homogeneous nucleo­ philic catalysts with the above-mentioned properties for the Introduction creation of industrial heterogeneous catalysts of a selective The reaction of ethylene- and propylene oxides hydration hydration of ethylene- and propylene oxides by means of is an industrial way of obtaining of glycols, in particular an immobilization of anions of salts on heterogeneous ethylene glycol-one of the most-produced large-scale carriers. 12-17 The largest ethylene glycol producers Shell, 18-24 products of industrial organic synthesis, with the world (4) Masuda, T.
    [Show full text]
  • Than Was the Monoleucyl Ester of Cis-Cyclopentane-1,2-Diol
    SOME OBSERVATIONS ON THE MECHANISM OF THE ACYLATION PROCESS IN PROTEIN SYNTHESIS* BY BEVERLY E. GRIFFIN AND C. B. REESE UNIVERSITY CHEMICAL LABORATORY, CAMBRIDGE, ENGLAND Communicated by Lord Todd, January 2, 1964 During recent years much attention has been given to the mechanism of synthesis of proteins in biological systems.' Although the process is by no means fully understood, some of the steps involved appear to be well established.2-4 Before amino acids can be incorporated into polypeptide chains they must first be "activated." The "activation" process involves ribonucleic acids of comparatively low molecular weight, known as "transfer" or "soluble" ribonucleic acids (sRNA), adenosine-5' triphosphate (ATP) as an energy source, and a specific enzyme for each amino acid. In the first step of the "activation" process, the amino acid reacts with ATP to form a mixed anhydride with adenosine-5' phosphate (AMP) releasing inorganic pyrophosphate; this mixed anhydride then acylates a specific sRNA on its terminal nucleoside (adenosine) residue to yield a 2' (or 3')-aminoacyl ester-the "activated" amino-acid. These processes are reversible. ATP + amino acid aminoacyl-AMP + pyrophosphate (1) sRNA + aminoacyl-AMP aminoacyl-sRNA + AMP (2) Beyond this point our knowledge of the process of polypeptide synthesis is less certain. The "activated" amino acids are believed to be transferred to the ribo- somes-the site of assembly of polypeptide chains-and then the amino acids become linked together in a genetically controlled order to synthesize a specific protein.5 Although there is as yet no definite evidence regarding this final step, it is frequently assumed that it involves a simple acylation as indicated in step (3).
    [Show full text]
  • The Arene–Alkene Photocycloaddition
    The arene–alkene photocycloaddition Ursula Streit and Christian G. Bochet* Review Open Access Address: Beilstein J. Org. Chem. 2011, 7, 525–542. Department of Chemistry, University of Fribourg, Chemin du Musée 9, doi:10.3762/bjoc.7.61 CH-1700 Fribourg, Switzerland Received: 07 January 2011 Email: Accepted: 23 March 2011 Ursula Streit - [email protected]; Christian G. Bochet* - Published: 28 April 2011 [email protected] This article is part of the Thematic Series "Photocycloadditions and * Corresponding author photorearrangements". Keywords: Guest Editor: A. G. Griesbeck benzene derivatives; cycloadditions; Diels–Alder; photochemistry © 2011 Streit and Bochet; licensee Beilstein-Institut. License and terms: see end of document. Abstract In the presence of an alkene, three different modes of photocycloaddition with benzene derivatives can occur; the [2 + 2] or ortho, the [3 + 2] or meta, and the [4 + 2] or para photocycloaddition. This short review aims to demonstrate the synthetic power of these photocycloadditions. Introduction Photocycloadditions occur in a variety of modes [1]. The best In the presence of an alkene, three different modes of photo- known representatives are undoubtedly the [2 + 2] photocyclo- cycloaddition with benzene derivatives can occur, viz. the addition, forming either cyclobutanes or four-membered hetero- [2 + 2] or ortho, the [3 + 2] or meta, and the [4 + 2] or para cycles (as in the Paternò–Büchi reaction), whilst excited-state photocycloaddition (Scheme 2). The descriptors ortho, meta [4 + 4] cycloadditions can also occur to afford cyclooctadiene and para only indicate the connectivity to the aromatic ring, and compounds. On the other hand, the well-known thermal [4 + 2] do not have any implication with regard to the reaction mecha- cycloaddition (Diels–Alder reaction) is only very rarely nism.
    [Show full text]
  • Cycloalkanes, Cycloalkenes, and Cycloalkynes
    CYCLOALKANES, CYCLOALKENES, AND CYCLOALKYNES any important hydrocarbons, known as cycloalkanes, contain rings of carbon atoms linked together by single bonds. The simple cycloalkanes of formula (CH,), make up a particularly important homologous series in which the chemical properties change in a much more dramatic way with increasing n than do those of the acyclic hydrocarbons CH,(CH,),,-,H. The cyclo- alkanes with small rings (n = 3-6) are of special interest in exhibiting chemical properties intermediate between those of alkanes and alkenes. In this chapter we will show how this behavior can be explained in terms of angle strain and steric hindrance, concepts that have been introduced previously and will be used with increasing frequency as we proceed further. We also discuss the conformations of cycloalkanes, especially cyclo- hexane, in detail because of their importance to the chemistry of many kinds of naturally occurring organic compounds. Some attention also will be paid to polycyclic compounds, substances with more than one ring, and to cyclo- alkenes and cycloalkynes. 12-1 NOMENCLATURE AND PHYSICAL PROPERTIES OF CYCLOALKANES The IUPAC system for naming cycloalkanes and cycloalkenes was presented in some detail in Sections 3-2 and 3-3, and you may wish to review that ma- terial before proceeding further. Additional procedures are required for naming 446 12 Cycloalkanes, Cycloalkenes, and Cycloalkynes Table 12-1 Physical Properties of Alkanes and Cycloalkanes Density, Compounds Bp, "C Mp, "C diO,g ml-' propane cyclopropane butane cyclobutane pentane cyclopentane hexane cyclohexane heptane cycloheptane octane cyclooctane nonane cyclononane "At -40". bUnder pressure. polycyclic compounds, which have rings with common carbons, and these will be discussed later in this chapter.
    [Show full text]