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Ozonolysis of alkynes generally gives an acid anhydride or diketone product, [17] not complete fragmentation as for alkenes. A reducing agent is not needed for these reactions. The mechanism is unknown. [18] If the reaction is performed in the presence of water, the anhydride hydrolyzes to give two carboxylic acids.
A metal acetylide is formed in situ when an alkyne is treated with a strong bases such as a hydroxide or an alkoxide: [3] HC≡CH + KOH ⇌ HC≡CK + H 2 O; RR'C=O + HC≡CK ⇌ RR'C(OK)C≡CH; The metal acetylide then reacts with an aldehyde or ketone to form a propargyl alcohol.
Hydration reaction mechanism from 1-methylcyclohexene to 1-methylcyclohexanol. Many alternative routes are available for producing alcohols, including the hydroboration–oxidation reaction, the oxymercuration–reduction reaction, the Mukaiyama hydration, the reduction of ketones and aldehydes and as a biological method fermentation.
The imine can isomerise and the alkyne group is placed at the other available nitrogen alpha position. [11] [12] [13] This reaction requires a copper catalyst. The redox A 3 coupling has the same product outcome but the reactants are again an aldehyde, an amine and an alkyne as in the regular A 3 coupling. [11] [14] [15] [16]
For aldehydes and unsymmetrical ketones, the product is chiral, hence there is interest in asymmetric variants. These reactions invariably involve metal- acetylide intermediates. This reaction was discovered by chemist John Ulric Nef in 1899 while experimenting with reactions of elemental sodium , phenylacetylene , and acetophenone .
A hydroboration reaction also takes place on alkynes. Again the mode of action is syn and secondary reaction products are aldehydes from terminal alkynes and ketones from internal alkynes. In order to prevent hydroboration across both the pi-bonds, a bulky borane like disiamyl (di-sec-iso-amyl) borane is used. [5]
The oxidation of primary alcohols to carboxylic acids normally proceeds via the corresponding aldehyde, which is transformed via an aldehyde hydrate (gem-diol, R-CH(OH) 2) by reaction with water. Thus, the oxidation of a primary alcohol at the aldehyde level without further oxidation to the carboxylic acid is possible by performing the reaction ...
In broad strokes, the mechanism of the reaction is believed to first involve a Mannich-like addition of the alkynylmetal species into the iminium ion formed by condensation of the aldehyde and the secondary amine. This first part of the process is a so-called A 3 coupling reaction (A 3 stands for aldehyde-alkyne-amine