Alkynes are electron rich organic molecules with a triple carbon-carbon bond. They show similar reactivity and types of reactions as alkenes. However, they are generally less than alkenes reactive towards electrophiles despite being more electron rich. The typical reactions of alkynes are:
Catalytic Hydrogenation of Alkynes
–is a reaction between hydrogen and an alkyne. Depending on the choice of a catalyst, the reaction can yield a single or a double addition of hydrogen leading to the formation of an alkene or and alkane respectively.
Nucleophilic Reactions of Acetylenic Anions
–is a reaction between the anionic species produced by terminal alkynes and electrophiles. The reaction is very useful for synthetic chemists. It is often referred to as an acetylene synthesis or an acetylene chain extension.
Reduction of Alkynes with Alkaline Metals in Liquid Ammonia
–is a selective reduction of alkynes to give trans alkenes. Reaction is typically done by a solution of Na or Li in liquid ammonia.
Hydration of Alkynes
–is a reaction between an alkyne and water typically catalyzed by Hg2+ ions and yielding ketones. This reaction can also be accomplished in an acid-catalyzed environment. However, hydration of alkynes in acidic conditions requires harsh conditions.
Hydroboration-Oxidation of Alkynes
–is a useful method to convert alkynes into aldehydes (terminal alkynes) or ketones (non-terminal alkynes). Reaction can be very regioselective when bulky boranes are used.
Ozonolysis of Alkynes
–is a cleavage reaction that “cuts” through the triple carbon-carbon bond yielding carboxylic acids. The mechanism of the reaction is not well understood. The reaction also gives 1,2-diketones as a potential minor product.
Halogenation of Alkynes
–is a reaction between alkynes and halogens. Multiple halogenations are typical, so the reaction has a limited synthetic applicability scope.
Hydroxyhalogenation (Oxyhalogenation) of Alkynes
–is a unique reaction of alkynes that produces a α-haloketone.
Alcoxyhalogenation of Alkynes
— is a similar reaction to the oxyhalogenation, however, it makes a highly functionalized ethers with a double bond and a halogen attached to it.
Hydrohalogenation of Alkynes
–is a reaction between an alkyne and hydrogen halide. The multiple additions are typical, thus the reaction has a very limited synthetic applicability.
Free Radical Hydrohalogenation of Alkynes
–is a reaction that puts a halogen onto the less substituted carbon of the triple bond. The free radical conditions often cause the substrate to polymerize making the reaction not very useful.
Reactions of Alkynes Spiderweb