# Alkynes: Reactions and Synthesis

## Alkynes: Preparation

Fig.
Reaction of calcium carbide with water

The reaction of calcium carbide with water is carried out at room temperature and, for a long time, was the most important method to generate acetylene.

Today, the method has been replaced by synthesis from methane. At 1500 $°C$, methane is pyrrolyzed using short reaction times. The reaction is , however, at very high temperatures it becomes exergonic (increase of entropy, four parts are formed from two parts).

Fig.
Electric arc methodology

Acetylide anion is very nucleophilic and reacts with a multitude of in $SN2$-type reactions. Using this method, terminal and internal alkynes can be synthesized.

Double of 1,1- or 1,2-dihalogen alkanes with strong bases yields the corresponding compounds with triple bonds. Under mild conditions, elimination with sodium amide in ammonia, for example, takes place at ( -33 $°C$).

Dihalogen alkanes are easily obtained from alkenes by halogenation. As mentioned above, these compounds can be transferred into alkynes by double dehydrohalogenation.

Single-metallated ethyne is being used for the alkylation of ethinyl anions. However, at ca. 30 $°C$ disproportionation to ethyne and a poorly soluble dianion (double Grignard reagent) takes place.

Fig.
Alkynes by disproportionation of single-metalled ethyne
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