Acetylide

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In chemistry, an acetylide is a compound that can be viewed as the result of replacing one or both hydrogen atoms of acetylene (ethyne) HC≡CH by metallic or other cations. Calcium carbide is an important industrial compound, which has long been used to produce acetylene for welding and illumination. It is also a major precursor to vinyl chloride. [1] Other acetylides are reagents in organic synthesis.

Contents

Nomenclature

The term acetylide is used loosely. It apply to an acetylene RC≡CM, where R = H or a side chain that is usually organic. [2] The nomenclature can be ambiguous with regards to the distinction between compounds of the type MC2R and M2C2. When both hydrogens of acetylene are replaced by metals, the compound can also be called carbide, e.g. calcium carbide Ca2+C≡C2−. When only one hydrogen atom is replaced, the anion may be called hydrogen acetylide or the prefix mono- may be attached to the metal, as in monosodium acetylide Na+HC≡C−. An acetylide may be a salt (ionic compound) containing the anion C≡C2−, HC≡C−, or RC≡C−, as in sodium acetylide [Na+]2C≡C2− or cobalt acetylide Co2+C≡C2−. [3] Other acetylides have the metal bound to the carbon atom(s) by covalent bonds, being therefore coordination or organometallic compounds.

Ionic acetylides

Alkali metal and alkaline earth metal acetylides of the general formula MC≡CM are salt-like Zintl phase compounds, containing C2−
2 ions. Evidence for this ionic character can be seen in the ready hydrolysis of these compounds to form acetylene and metal oxides, and by solubility in liquid ammonia with solvated C2−
2 ions. [4]

The C2−
2 ion has a closed shell ground state of 1Σ+
g, making it isoelectronic to a neutral molecule N2, which may afford it some gas-phase stability. [5]

Organometallic acetylides

Some acetylides, particularly of transition metals, show evidences of covalent character, e. g. for being neither dissolved nor decomposed by water and by radically different chemical reactions. That seems to be the case of silver acetylide and copper acetylide, for example.

In the absence of additional ligands, metal acetylides adopt polymeric structures wherein the acetylide groups are bridging ligands.

Preparation

Of the type MC2R

Acetylene and terminal alkynes are weak acids: [10]

RC≡CH + R″M ⇌ R″H + RC≡CM

Monopotassium and monosodium acetylide can be prepared by reacting acetylene with bases like sodium amide [11] or with the elemental metals, often at room temperature and atmospheric pressure. [10] Copper(I) acetylide can be prepared by passing acetylene through an aqueous solution of copper(I) chloride because of a low solubility equilibrium. [10] Similarly, silver acetylides can be obtained from silver nitrate.

In organic synthesis, acetylides are usually prepared by treating acetylene and alkynes with organometallic [12] or inorganic [11] Classically, liquid ammonia was used for deprotonations, but ethers are now more commonly used.

Lithium amide, [10] LiHMDS, [13] or organolithium reagents, such as butyllithium (BuLi), [12] are frequently used to form lithium acetylides:

HC≡CH + BuLi → LiC≡H + BuH

Of the type M2C2 and CaC2

Calcium carbide is prepared industrially by heating carbon with lime (calcium oxide) at approximately 2,000 °C. [1] A similar process can be used to produce lithium carbide.

Dilithium acetylide, Li2C2, competes with the preparation of the monolithium derivative LiC2H. [11]

Reactions

Ionic acetylides are typically decomposed by water with evolution of acetylene:

CaC≡C + 2H2O → Ca(OH)2 + HC≡CH
RC≡CNa + H2O → RC≡CH + NaOH

Acetylides of the type RC2M are widely used in alkynylations in organic chemistry. They are nucleophiles that add to a variety of electrophilic and unsaturated substrates.

A classic application is the Favorskii reaction, such as in the sequence shown below. Here ethyl propiolate is deprotonated by n-butyllithium to give the corresponding lithium acetylide. This acetylide adds to the carbonyl center of cyclopentanone. Hydrolysis liberates the alkynyl alcohol. [14]

Reaction of ethyl propiolate with n-butyllithium to form the lithium acetylide. Acetylide carbonyl addition.png
Reaction of ethyl propiolate with n-butyllithium to form the lithium acetylide.

The dimerization of acetylene to vinylacetylene proceeds by insertion of acetylene into a copper(I) acetylide complex. [15]

Coupling reactions

Acetylides are sometimes used as intermediates in coupling reactions. Examples include Sonogashira coupling, Cadiot-Chodkiewicz coupling, Glaser coupling and Eglinton coupling.

Hazards

Some acetylides are notoriously explosive. [16] Formation of acetylides poses a risk in handling of gaseous acetylene in presence of metals such as mercury, silver or copper, or alloys with their high content (brass, bronze, silver solder).

See also

Related Research Articles

<span class="mw-page-title-main">Acetylene</span> Hydrocarbon compound (HC≡CH)

Acetylene is the chemical compound with the formula C2H2 and structure H−C≡C−H. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure form and thus is usually handled as a solution. Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities such as divinyl sulfide and phosphine.

<span class="mw-page-title-main">Alkyne</span> Hydrocarbon compound containing one or more C≡C bonds

In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and no other functional groups form a homologous series with the general chemical formula CnH2n−2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature. Like other hydrocarbons, alkynes are generally hydrophobic.

<span class="mw-page-title-main">Carbide</span> Inorganic compound group

In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece.

<span class="mw-page-title-main">Calcium carbide</span> Chemical compound

Calcium carbide, also known as calcium acetylide, is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of acetylene and calcium cyanamide.

The azide-alkyne Huisgen cycloaddition is a 1,3-dipolar cycloaddition between an azide and a terminal or internal alkyne to give a 1,2,3-triazole. Rolf Huisgen was the first to understand the scope of this organic reaction. American chemist Karl Barry Sharpless has referred to copper-catalyzed version of this cycloaddition as "the cream of the crop" of click chemistry and "the premier example of a click reaction".

The Corey–House synthesis (also called the Corey–Posner–Whitesides–House reaction and other permutations) is an organic reaction that involves the reaction of a lithium diorganylcuprate () with an organic halide or pseudohalide () to form a new alkane, as well as an ill-defined organocopper species and lithium (pseudo)halide as byproducts.

<span class="mw-page-title-main">Copper(II) acetate</span> Chemical compound

Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the formula Cu(OAc)2 where AcO− is acetate (CH
3CO−
2). The hydrated derivative, Cu2(OAc)4(H2O)2, which contains one molecule of water for each copper atom, is available commercially. Anhydrous copper(II) acetate is a dark green crystalline solid, whereas Cu2(OAc)4(H2O)2 is more bluish-green. Since ancient times, copper acetates of some form have been used as fungicides and green pigments. Today, copper acetates are used as reagents for the synthesis of various inorganic and organic compounds. Copper acetate, like all copper compounds, emits a blue-green glow in a flame.

<span class="mw-page-title-main">Organozinc chemistry</span>

Organozinc chemistry is the study of the physical properties, synthesis, and reactions of organozinc compounds, which are organometallic compounds that contain carbon (C) to zinc (Zn) chemical bonds.

<span class="mw-page-title-main">Organocopper chemistry</span> Compound with carbon to copper bonds

Organocopper chemistry is the study of the physical properties, reactions, and synthesis of organocopper compounds, which are organometallic compounds containing a carbon to copper chemical bond. They are reagents in organic chemistry.

<span class="mw-page-title-main">Silver acetylide</span> Chemical compound

Silver acetylide is an inorganic chemical compound with the formula Ag2C2, a metal acetylide. The compound can be regarded as a silver salt of the weak acid, acetylene. The salt's anion consists of two carbon atoms linked by a triple bond, thus, its structure is [Ag+]2[−C≡C−]. The alternate name "silver carbide" is rarely used, although the analogous calcium compound CaC2 is called calcium carbide. Silver acetylide is a primary explosive.

Copper(I) acetylide, Kupfercarbid or cuprous acetylide, is a chemical compound with the formula Cu2C2. Although never characterized by X-ray crystallography, the material has been claimed at least since 1856. One form is claimed to be a monohydrate with formula Cu
2C
2.H
2O is a reddish-brown explosive powder.

<span class="mw-page-title-main">Walter Reppe</span> German chemist (1892-1969)

Walter Julius Reppe was a German chemist. He is notable for his contributions to the chemistry of acetylene.

The Favorskii reaction is an organic chemistry reaction between an alkyne and a carbonyl group, under basic conditions. The reaction was discovered in the early 1900s by the Russian chemist Alexei Yevgrafovich Favorskii.

Dilithium acetylide is an organometallic compound with the formula Li2C2. It is typically derived by double deprotonation of acetylene. X-ray crystallography confirms the presence of C≡C subunits attached to lithium, resulting in a polymeric structure. Li2C2 is one of an extensive range of lithium-carbon compounds, which include the lithium-rich Li4C, Li6C2, Li8C3, Li6C3, Li4C3, Li4C5, and the graphite intercalation compounds LiC6, LiC12, and LiC18. It is an intermediate compound produced during radiocarbon dating procedures.

The Glaser coupling is a type of coupling reaction. It is by far one of the oldest coupling reactions and is based on copper compounds like copper(I) chloride or copper(I) bromide and an additional oxidant like air. The base used in the original research paper is ammonia and the solvent is water or an alcohol. The reaction was first reported by Carl Andreas Glaser in 1869. He suggested the following process on his way to diphenylbutadiyne:

Organosodium chemistry is the chemistry of organometallic compounds containing a carbon to sodium chemical bond. The application of organosodium compounds in chemistry is limited in part due to competition from organolithium compounds, which are commercially available and exhibit more convenient reactivity.

In organic chemistry, alkynylation is an addition reaction in which a terminal alkyne is added to a carbonyl group to form an α-alkynyl alcohol.

<i>ortho</i>-Carborane Chemical compound

ortho-Carborane is the organoboron compound with the formula C2B10H12. The prefix ortho is derived from ortho. It is the most prominent carborane. This derivative has been considered for a wide range of applications from heat-resistant polymers to medical applications. It is a colorless solid that melts, without decomposition, at 320 °C

Monosodium acetylide is an organosodium compound with the formula NaC≡CH. It is a sodium salt of acetylene, consisting of sodium cations Na+ and hydrogen acetylide anions −C≡CH. It is a derived from acetylene by deprotonation using a sodium base, typically sodium amide.

Strontium carbide (also more precisely known as strontium acetylide or strontium dicarbide) is a salt with chemical formula SrC2. It was first synthesized by Moissan in 1894.

References

  1. 1 2 Holzrichter, Klaus; Knott, Alfons; Mertschenk, Bernd; Salzinger, Josef (2013). "Calcium Carbide". Ullmann's Encyclopedia of Industrial Chemistry. pp. 1–14. doi:10.1002/14356007.a04_533.pub2. ISBN   978-3-527-30673-2.
  2. ↑ IUPAC , Compendium of Chemical Terminology , 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) " acetylides ". doi : 10.1351/goldbook.A00067
  3. ↑ Junichi Nishijo, Kentaroh Kosugi, Hiroshi Sawa, Chie Okabe, Ken Judai, Nobuyuki Nishi (2005): "Water-induced ferromagnetism in cobalt acetylide CoC2 nanoparticles". Polyhedron, volume 24, issues 16–17, pages 2148-2152. doi : 10.1016/j.poly.2005.03.032
  4. ↑ Hamberger, Markus; Liebig, Stefan; Friedrich, Ute; Korber, Nikolaus; Ruschewitz, Uwe (21 December 2012). "Evidence of Solubility of the Acetylide Ion C2−
    2    : Syntheses and Crystal Structures of K2C2·2 NH3, Rb2C2·2 NH3, and Cs2C2·7 NH3". Angewandte Chemie International Edition. 51 (52): 13006–13010. doi:10.1002/anie.201206349. PMID   23161511.
  5. ↑ Sommerfeld, T.; Riss, U.; Meyer, H.-D.; Cederbaum, L. (August 1997). "Metastable C2−
    2     Dianion". Physical Review Letters. 79 (7): 1237–1240. Bibcode:1997PhRvL..79.1237S. doi:10.1103/PhysRevLett.79.1237.
  6. ↑ Klöss, Karl-Heinz; Hinz-Hübner, Dirk; Ruschewitz, Uwe (2002). "Über eine neue Modifikation des Na 2 C 2". Zeitschrift für Anorganische und Allgemeine Chemie. 628 (12): 2701–2704. doi:10.1002/1521-3749(200212)628:12<2701::AID-ZAAC2701>3.0.CO;2-#.
  7. ↑ S. Hemmersbach, B. Zibrowius, U. Ruschewitz (1999): "Na2C2 und K2C2: Synthese, Kristallstruktur und spektroskopische Eigenschaften". Zeitschrift für anorganische und allgemeine Chemie, volume 625, issue 9, pages 1440-1446. doi : 10.1002/(SICI)1521-3749(199909)625:9<1440::AID-ZAAC1440>3.0.CO;2-R
  8. ↑ Chui, Stephen S. Y.; Ng, Miro F. Y.; Che, Chi-Ming (2005). "Structure Determination of Homoleptic AuI, AgI, and CuI Aryl/Alkylethynyl Coordination Polymers by X-ray Powder Diffraction". Chemistry: A European Journal. 11 (6): 1739–1749. doi:10.1002/chem.200400881. PMID   15669067.
  9. ↑ Schubert, Bernd; Weiss, Erwin (1983). "(PHCCLi)4(tmhda)2, A Polymeric Organolithium Compound with Cubic Li4C4 Structural Units". Angewandte Chemie International Edition in English. 22 (6): 496–497. doi:10.1002/anie.198304961.
  10. 1 2 3 4 Viehe, Heinz Günter (1969). "Chemistry of Acetylenes". Angewandte Chemie. 84 (8) (1st ed.). New York: Marcel Dekker: 170–179 & 225–241. doi:10.1002/ange.19720840843.
  11. 1 2 3 Coffman, Donald D. (1940). "Dimethylethhynylcarbinol". Organic Syntheses. 40: 20. doi:10.15227/orgsyn.020.0040.
  12. 1 2 Midland, M. M.; McLoughlin, J. I.; Werley, Ralph T. Jr. (1990). "Preparation and Use of Lithium Acetylide: 1-Methyl-2-ethynyl-endo-3,3-dimethyl-2-norbornanol". Organic Syntheses. 68: 14. doi:10.15227/orgsyn.068.0014.
  13. ↑ Reich, Melanie (August 24, 2001). "Addition of a lithium acetylide to an aldehyde; 1-(2-pentyn-4-ol)-cyclopent-2-en-1-ol". ChemSpider Synthetic Pages (Data Set): 137. doi:10.1039/SP137.
  14. ↑ Midland, M. Mark; Tramontano, Alfonso; Cable, John R. (1980). "Synthesis of alkyl 4-hydroxy-2-alkynoates". The Journal of Organic Chemistry. 45 (1): 28–29. doi:10.1021/jo01289a006.
  15. ↑ Trotuş, Ioan-Teodor; Zimmermann, Tobias; Schüth, Ferdi (2014). "Catalytic Reactions of Acetylene: A Feedstock for the Chemical Industry Revisited". Chemical Reviews. 114 (3): 1761–1782. doi: 10.1021/cr400357r . PMID   24228942.
  16. ↑ Cataldo, Franco; Casari, Carlo S. (2007). "Synthesis, Structure and Thermal Properties of Copper and Silver Polyynides and Acetylides". Journal of Inorganic and Organometallic Polymers and Materials. 17 (4): 641–651. doi:10.1007/s10904-007-9150-3. ISSN   1574-1443. S2CID   96278932.
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