The chemistry associated with carbon-carbon triple bonds can be called as alkyne chemistry. Alkynes undergo addition reactions due to the presence of loosely held pi-electrons. Due to the presence of a triple bond in alkynes, halogens, water etc.can be added to them by the process of the addition reaction. Addition products are formed via a set of steps. The stability of vinylic cations is responsible for the formation of addition products. Markovnikov’s rule is followed by asymmetric alkynes in order to undergo addition reaction. Few addition reactions of alkynes are explained below:

Alkynes and halogens undergo addition reaction to form halogenated alkenes which further react with halogens to give halogen substituted alkanes. The reddish orange coloured solution of bromine and carbon tetrachloride gets decolorized as a result of the addition reaction. This is used as a test for unsaturation.

Unlike the hydrogentaion reaction mentioned above, most halogenation reactions can be stopped in the intermediate stage by lowering the temperature below $$0^{\circ}C$$..

Alkynes react with dihydrogen in the presence of catalysts such as Pt/Pd/Ni in order to form alkenes. The alkenes formed, further react with dihydrogen to form alkanes. It has been observed that in most reactions triple bond is converted into double bond and double bond is then converted into a single bond due to the addition reaction with dihydrogen.

The catalyst that are involved in the case of rhodium, nickel, palladium, and platinum. Hydrogenation is a step-by-step process in which initially an alkene is formed. After which it undergoes further hydrogenation to form an alkane

Slowing down the reaction in the intermediate stage is actually quite impossible as the whole reaction is really smooth. But some alkenes are isolated with the use of poisoned catalysts. One such example of a poisoned catalyst is Lindlar catalyst.

#### Lindlar catalyst

Lindlar catalyst is combined form of palladium which is coated with quinoline and absorbed on calcium carbonate.