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Electrophilic Addition to Alkynes: Halogenation

Electrophilic Addition to Alkynes: Halogenation

Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.

Preparation of Alkynes: Alkylation Reaction

Preparation of Alkynes: Alkylation Reaction

Introduction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.

Aldehydes and Ketones with Amines: Imine and Enamine Formation Overview

Aldehydes and Ketones with Amines: Imine and Enamine Formation Overview

Primary amines react with carbonyl compounds—aldehydes and ketones—to generate imines. Imines consist of a C=N double bond and are named Schiff bases after its discoverer—the German chemist Hugo Schiff. On the other hand, secondary amines react with carbonyl compounds to give enamines. In enamines, the presence of a C=C double bond adjacent to the nitrogen atom leads to the delocalization of the lone pair.

Preparation of 1° Amines: Azide Synthesis

Preparation of 1° Amines: Azide Synthesis

Direct alkylation of ammonia produces polyalkylated amines, along with a quaternary ammonium salt. To exclusively prepare primary amines, the azide synthesis method can be used.
Azide ions act as good nucleophiles and react with unhindered alkyl halides to form alkyl azides. Alkyl azides do not participate in further nucleophilic substitution reactions, thereby eliminating the chances of polyalkylated products. Alkyl azides are reduced by hydride-based reducing agents, like lithium aluminum...

Preparation of Alkynes: Dehydrohalogenation

Preparation of Alkynes: Dehydrohalogenation

Introduction
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.

Acidity of 1-Alkynes

Acidity of 1-Alkynes

The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.

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Related Experiment Video

Updated: Jun 15, 2026

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes

Published on: September 8, 2013

Cationic Au(I) alkyne complexes: synthesis, structure and reactivity.

Thomas N Hooper¹, Michael Green, Christopher A Russell

¹School of Chemistry, University of Bristol, Cantock's Close, Bristol, UK BS8 1TS.

Chemical Communications (Cambridge, England)

|March 18, 2010

Summary

Researchers synthesized gold-alkyne complexes using phosphine ligands and silver hexafluorantimonate. Desilylation reactions were observed with substituted alkynes, forming complex gold-carbon bonding structures.

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Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes

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Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles

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Published on: August 22, 2018

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Last Updated: Jun 15, 2026

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes

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Published on: September 8, 2013

Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes

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Published on: September 12, 2018

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles

Published on: August 22, 2018

Area of Science:

Organometallic Chemistry
Coordination Chemistry
Gold Complexes

Background:

Gold complexes with alkyne ligands are valuable in catalysis and materials science.
Understanding the coordination modes of alkynes to gold is crucial for designing new complexes.

Purpose of the Study:

To synthesize and characterize novel gold(I)-alkyne complexes.
To investigate the influence of silyl substituents on alkyne coordination and reactivity.
To explore intricate gold-carbon bonding motifs.

Main Methods:

Reaction of alkynes with [AuCl(PBu(t)(3))] and AgSbF(6) in dichloromethane.
Characterization of the resulting gold complexes, [(Bu(t)(3)P)Au(eta(2)-alkyne)][SbF(6)].
Analysis of desilylation reactions in silyl-substituted alkyne systems.

Main Results:

Facile synthesis of gold(I)-alkyne complexes of the type [(Bu(t)(3)P)Au(eta(2)-alkyne)][SbF(6)].
Observation of desilylation reactions when alkynes possess one or two trimethylsilyl (Me(3)Si) substituents.
Formation of gold species exhibiting intricate bonding interactions with the C≡C fragment.

Conclusions:

The synthetic route provides ready access to gold-alkyne complexes.
Silyl substituents can induce desilylation, leading to novel bonding arrangements.
These findings expand the scope of gold-alkyne chemistry and bonding diversity.