What is the addition of alkynes?
Alkyne chemistry is the branch of chemistry that deals with carbon-carbon triple bonds. Because alkynes have loosely held pi-electrons, they can go through Addition Reaction of Alkynes. Because alkynes have a triple bond, halogens, water, and other things can be added to them through the addition reaction. Through a series of steps, the results of addition are made. The formation of addition products is due to how stable vinylic cations are. Asymmetric alkynes follow Markovnikov’s rule in order to go through an addition reaction.
Here are some reactions of alkynes that involve adding:
Addition of alkynes with halogens (halogenation)
Alkynes and halogens combine to make halogenated alkenes, which then combine with more halogens to make halogenated alkanes. As a result of the addition reaction, the reddish-orange colour of the bromine and carbon tetrachloride solution is lost. This is a test to see if something is not saturated.
Unlike the hydrogenation reaction mentioned above, most halogenation reactions can be stopped in the middle stage by lowering the temperature below 0oC.
Addition of alkynes with hydrogens (hydrogenation)
Alkenes are made when alkynes react with dihydrogen in the presence of catalysts like Pt/Pd/Ni. When the alkenes react with dihydrogen, they make alkanes. It has been seen that when dihydrogen is added to a triple bond, the triple bond changes into a double bond, and then the double bond changes into a single bond.
In the case of rhodium, nickel, palladium, and platinum, the catalysts that are used are. Hydrogenation is a step-by-step process that starts with the making of an alkene. After that, it gets more hydrogen to turn it into an alkane.
Since the whole process is so smooth, it is almost impossible to slow down the reaction in the middle stage. But poisoned catalysts are used to separate out some alkenes. Lindlar catalyst is an example of a catalyst that has been poisoned in this way.
Lindlar catalyst
The Lindlar catalyst is a combination of palladium and quinoline that is absorbed by calcium carbonate.
Addition of alkynes with water (hydration)
Alkynes can’t combine with water. Most of the time, they don’t react with water. At a temperature of 333K, alkynes can react with water in the presence of diluted sulphuric acid and mercuric sulphate. Because of this, carbonyl compounds are made.
Addition of alkynes with hydrogen halides (hydrohalogenation)
When hydrogen halide is mixed with alkynes, which are compounds with three bonds, gem halides are made. In gem halides, two halogens are attached to the same carbon atom in a molecule.
Frequently Asked Questions – FAQs
Q.1 Why do alkynes react by adding to each other?
Because alkynes have loosely held pi-electrons, they can go through addition reactions. Because alkynes have a triple bond, halogens, water, and other things can be added to them through the addition reaction.
Q.2 What is an example of an electrophilic addition reaction?
Electrophiles are compounds that lack electrons. Between two carbon atoms in the alkyne, there is one sigma bond and two pi bonds. These pi bonds are made up of atoms with a lot of electrons. When they link up with an electrophile, they cause an electrophilic addition reaction. Halogenation and the hydration reaction are examples.
Q.3 What is the use of an addition reaction?
In an addition reaction, a group of atoms or molecules add to unsaturated compounds to make saturated compounds. It is often used to make all kinds of drugs and natural products. In industrial use, vegetable oils are an unsaturated compound to which hydrogen is added in the presence of a catalyst to make vegetable ghee, which is a saturated compound.
Q.4 What is the difference between addition and elimination reactions?
When two or more compounds come together to make a single product, this is called addition. In this case, compounds that aren’t yet saturated change into compounds that are. When a reactant is split into two products, this is called an elimination reaction. In this case, compounds that are usually saturated change into compounds that are not saturated.
Q.5 How is the hydration of alkyne done?
Alkynes don’t mix with water. Most of the time, they don’t react with water. So, when diluting sulphuric acid and mercuric sulphate catalysts are present, alkynes react with water to make enols, which then change into ketones on their own.
