Unsaturated hydrocarbons (alkynes)

Lekture 3

Lek: Alimkulova E. J.

The alkynes are also unsaturated hydrocarbons since they all contains at lease one carbom-to-carbon triple bond. Because of the greater reactivity of the triple bond, alkynes are rarely found in nature. The general molecular formula for members of the alkyne series is CnH2n-2. The IUPAC names for alkynes end in “yne”. Ethyne (common name: acetylene) is one of the most important alkynes. It is first representative of alkynes.

H-C≡C-H or C₂H₂ CH₃-C≡CH or C₃H4

IUPAC name - ethyne IUPAC name propyne

Common name - acetylene Common name (none)

Isomerism and nomenclature:

C₄H₆ butyne (common formula)

CH₃-C≡C-CH₃ CH₃-C≡C- C-CH₃

│

2-butyne (IUPAC name) CH₃

3-methyle 2-propyne (IUPAC nsme)

Isobutyne (common formula)

Chemical properties:

Alkynes like alkenes, addition reactions, but they do so in two steps/ The first step produces an alkene, the second produces an alkane.

Reaction of the hydrogenation.

CH≡CH + H₂ → H₂C=CH₂

Ethyne ethene

H₂C=CH₂ + H₂ → H₃C-CH₃

Ethene ethane

Reaction of the bromination.

CH≡CH + Br₂ → BrHC=CHBr

Ethyne 1,2-dibromethene

BrHC=CHBr + Br₂ → Br₂CH-CHBr₂

1,2-dibromethene 1,1,2,2-tetrabrometane

Alkynes will also react with KMnO4 in the Baeyer test, decolorizing the purple permanganate solution and producing a variety of oxidation products.

Reactions with hydro halogen.

HC≡CH + HI → H₂C=CHI

Ethyne 1-iodinethene

H₂C=CHI + HI → H₃C- CHI₂

1-iodiumethene 2-iodiumethane

This reaction goes on Marcovnikov”s rule.

Reaction with water. H OH

│ │

HC≡CH + HOH → H₂C=CHOH → H₃C-C=O + O → H₃C-C=O

Ethyne vine alcohol vinegar aldehyde vinegar acide

Reaction of the polymerization.

3 HC≡CH → C₆H₃

Ethyne benzene

Formation of the metal organic compounds.

HC≡CH + 2CuCl + 2NH₃ → Cu-C=C-Cu + 2NH₄Cl

Ethyne ethynic copper

Combustion of the acetylene.

The combustion of ethyne in an oxyacetylene torch produces temperatures as high as 3.000⁰C.

2C₂H₂ (g) + 5O₂ (g) → 4CO₂ (g) + 2H₂O(g)

Preparation of the acetylene.

Acetylene can be prepared in small quantities calcium carbide with water:

CaC₂ (s) + 2H₂O(g) → C₂H₂ (g) + Ca(OH) ₂ (s)

This reaction was used in the early 1900s to produce the fuel in coal miners’ lanterns. Because ethyne burns luminous flame, carbide lanterns are popular today with campers.

Glossary:

Alkynes – Алкиндер - Алкины

The alkynes are unsaturated hydrocarbons and they all contain only one carbon-to-carbon triple bond (C≡C).

Ethyne – этин – этин

Vine ethanol (alcohol) - этанол (спирт) - этанол (алкоголь), винный спирт

vinegar aldehyde - ciрке альдегидi - уксусный альдегид

References:

Frederick A. Bettelheim, Joseph M. Landesberg. Organic Chemistry

Charles H.Yenrickson, Larry C. Byrd, Norman W. Hunter. Organic Chemistry.

Cтепаненко Б.Н. Органическая химия.

Грандберг А.Г. Основы органической химии.

Ахметов А. Органикалык химия.

Elements of organic chemistry

KATU Technical Faculty

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