Alkyne Reactions
Alkyne reactions involve chemical transformations of compounds containing carbon-carbon triple bonds. These reactions can include addition reactions, where atoms or groups are added to the triple bond, as well as substitution and elimination reactions. Alkynes can undergo various reactions to form a wide range of organic compounds, making them important building blocks in organic synthesis.
4 Key excerpts on "Alkyne Reactions"
eBook - ePub- James G. Speight(Author)
- 2019(Publication Date)
- Gulf Professional Publishing(Publisher)
...However, the unsaturated hydrocarbon derivatives do offer varying degrees of reactivity. It is not the purpose of this section to present a comprehensive review of the chemical reactions of hydrocarbon derivatives but to present an overview of the types of reactions of hydrocarbon derivatives that can be of use for the commercial production of saleable products. 7.1. Alkylation Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene. An alkyl group is a piece of a molecule with the general formula C n H 2 n +1, where n is the integer depicting the number of carbons linked together. For example, a methyl group (n = 1, CH 3) is a fragment of a methane molecule (CH 4). Alkylating agents use selective alkylation by adding the desired aliphatic carbon chain to the previously chosen starting molecule. This is one of many known chemical syntheses. Alkyl groups can also be removed in a process known as dealkylation. Carbon alkylation is a process for the formation of carbon-carbon bonds and for this types of reaction, the electrophilic nature of alkyl halides is enhanced by the presence of a Lewis acid, such as aluminum trichloride (AlCl 3). The carbon alkylation reaction can also be effected by alkene derivatives in the presence of acids. Nitrogen alkylation is an important process for the formation of carbon-nitrogen bonds. Amines are readily alkylated and the rate of alkylation follows the order tertiary amine < secondary amine < primary amine. As an example, a tertiary amine can be converted into a quaternary ammonium salt by reaction with an alkyl (hailed the Menshutkin reaction): Alcohol derivatives can also be alkylated to yield ethers derivatives: for example, using an alkyl halide (the Williamson ether synthesis) ROH + R 1 X → ROR 1 Alcohols are also good alkylating agents in the presence of suitable acid catalysts...
eBook - ePub- Graham Patrick(Author)
- 2004(Publication Date)
- Taylor & Francis(Publisher)
...Synthesis of an alkene from a vicinal dibromide. Figure 2. Synthesis of an alkyne from an alkene. Alkynes Alkynes can be synthesized from alkenes through a two-step process which involves the electrophilic addition of bromine to form a vicinal dibromide (Section H3) then dehydrohalogenation with strong base (Figure 2). The second stage involves the loss of two molecules of hydrogen bromide and so two equivalents of base are required. H2 Properties of alkenes and alkynes Key Notes Structure Alkenes are planar with bond angles of 120°. The carbon atoms of the C=C bond are sp 2 hybridized and the double bond is made up of one σ bond and one π bond. Alkynes are linear with the triple bond carbons being sp hybridized. The triple bond is made up of one σ bond and two π bonds. C=C Bond The C=C bond is stronger and shorter than a C–C single bond. However, the two bonds making up the C=C bond are not of equal strength. The π bond is weaker than the σ bond. Bond rotation round a C=C bond is not possible and isomers are possible depending on the substituents present. The more substituents which are present on an alkene, the more stable the alkene is. C≡C Bond An alkyne triple bond is stronger than a C–C single bond or a C=C double bond. The two π bonds present in the triple bond are weaker and more reactive than the σ bond. Properties Alkenes and alkynes are nonpolar compounds which dissolve in nonpolar solvents and are very poorly soluble in water. They have low boiling points since only weak van der Waals interactions are possible between the molecules. Nucleophilicity Alkenes and alkynes act as nucleophiles and react with electrophiles by a reaction known as electrophilic addition. The nucleophilic centers are the multiple bonds which are areas of high electron density. Spectroscopic analysis of alkenes Alkenes show characteristic C=C stretching absorptions in their IR spectra. Absorptions due to C-H stretching and bending may also be identifiable...
- Robert J. Farrauto, Lucas Dorazio, C. H. Bartholomew(Authors)
- 2020(Publication Date)
- Wiley-AIChE(Publisher)
...CHAPTER 9 HYDROGENATION, DEHYDROGENATION, AND ALKYLATION 9.1 INTRODUCTION Selective catalytic hydrogenation of functional groups contained in organic molecules is one of the most useful, versatile, and environment-acceptable reaction routes available for organic synthesis. This important area of catalytic chemistry has been and continues to be the foundation for the development of numerous, diverse, largeand small-scale commercial hydrogenation processes, including (i) fine chemicals, (ii) intermediates for the pharmaceutical industry, (iii) monomers for the production of various polymers, and (iv) fats and oils for edible and nonedible products. Dehydrogenation reactions find a wide application in production of hydrogen, alkenes, polymers, and oxygenates. In recent years, the demand for light alkenes has grown dramatically due to increased demand for polypropylene, acrylonitrile, oxo alcohols, and propylene oxide. As a result, dehydrogenation of lower alkanes to alkenes is a rapidly expanding business. Alkylation allows smaller molecules to be coupled to for larger molecules mostly for petroleum applications. 9.2 HYDROGENATION 9.2.1 Hydrogenation in Stirred Tank Reactors With exception of a few continuous hydrogenation processes in petroleum refining, hydrogenation processes are often conducted in stirred tank reactors. This chapter focuses on hydrogenation occurring within stirred tank reactors, which are ideally suited and extensively used for liquid-phase hydrogenation reaction. For reactions where the hydrocarbon to be hydrogenated is in the liquid phase, stirred tank reactors are ideal. For hydrogenation, stirred tank reactors can be designed in two configurations, semibatch and continuous, which are illustrated in Figure 9.1...
eBook - ePub- Michael North(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
...Such reactions are not subject to the orbital overlap requirements of a cycloaddition and so may give products of different stereochemistry. 9.6.4 Cheletropic reactions Cheletropic reactions are cycloaddition reactions in which both new σ -bonds are made to the same atom. The best known such reaction is the reaction between an alkene and a carbene to form a cyclopropane as shown in Scheme 9.33. This reaction resembles a [2π + 2π] cycloaddition, yet it occurs thermally. The explanation for this reactivity is that since the LUMO of the carbene is localized on a single atom, it can react with the HOMO of the alkene in an orientation that would not be possible for the LUMO of an alkene as illustrated in Figure 9.8. The substituents on the carbene are initially parallel to the plane of the alkene, but as the new σ -bonds form they rotate to their final locations perpendicular to the plane of the alkene. As Figure 9.8 shows, the result is a syn-addition of the carbene to the alkene, arising from a suprafacial interaction between the HOMO and LUMO. Scheme 9.33 9.8 Orbital overlap during the cheletropic reaction between an alkene and a carbene. 9.7 Further reading General Stereochemistry of Organic Compounds E.L. Eliel and S.H. Wilen. Wiley: London, 1994, chapter 12. A Guidebook to Mechanism in Organic Chemistry P. Sykes. Longman: London, 1982. Stereoelectronic effects in reactions Stereoelectronic Effects in Organic Chemistry P. Deslongchamps. Pergamon: Oxford, 1983, chapters 5 and 6. Stereoelectronic Effects Oxford Chemistry Primer Number 36, A.J. Kirby. Oxford University Press: Oxford, 1996. Addition of nucleophiles to carbonyl compounds Asymmetric Synthesis Vol. 2, E.L. Eliel (J.D. Morrison ed.). Academic Press: London, 1983, chapter 5. Core Carbonyl Chemistry Oxford Chemistry Primer Number 47, J. Jones. Oxford University Press: Oxford, 1997. The aldol reaction Stereoselective Synthesis R.S. Atkinson...
