Alkynes: Definition, Structure, Production, Properties - GeeksforGeeks (2023)

AHydrocarbonsis an organic molecule composed entirely of hydrogen and carbon in organic chemistry. Hydrocarbons are an example of group 14 hydrides. Hydrocarbons are colorless, hydrophobic, and have only a slight odor. Due to their different molecular architectures, it is not possible to generalize further. The combustion of fossil fuels, including the manufacture and combustion of fuels, is responsible for the majority of anthropogenic hydrocarbon emissions. Plant emissions are a natural source of hydrocarbons such as ethylene, isoprene and monoterpenes.

alkynes

In the natural sciences, alkynes are unsaturated hydrocarbons with something like a triple bond between carbon-carbon particles (–C≡C–). The general recipe for this unsaturated hydrocarbon isC_norteH_2n–2,where n–2, 3, 4, 5… .

Alkynes are commonly known as acetyls. Like many hydrocarbons, alkynes are also hydrophobic.

Hydrocarbons are the simplest organic compounds with simple carbon and hydrogen components. These are found in nature in the form of objects that we use every day. As a result, hydrocarbons are considered the parents of organic compounds. On the other hand, it is believed that all other compounds were prepared by replacing one or more hydrogen atoms with functional groups.

von alcino structure

A carbon-carbon triple bond consists of one σ bond and two weak π bonds.

Nomenclatura der Alkyne

The general recipe for this unsaturated hydrocarbon is C_norteH_2n–2, where n–2,3,4,5… … . According to the IUPAC structure, alkene names have an -ine suffix, with the prefix depending on the number of carbon particles. Some names of alkynes are as follows:

Isomerism in Alcinene

The structural isomerism of alkynes is as follows:

• chain isomerism:Chain isomerism occurs in alkynes with five or more carbon atoms due to different carbon chain configurations. For example,

• Posimetry:In this case, the isomers differ in the position of the triple bond. For example, the two isomers of butene

• Functional Isomerism:Dienes have two double bonds, while alkynes are functional isomers of dienes.

• Ringetenesomeria:For cycloalkanes, alkynes exhibit ring-chain isomerism. For example,

Process for the production of alkynes.

The following are some of the more common methods used to produce alkynes:

• By dehydrogenation of dihaloalkanes:Dehydrohalogenation of vicinal dihaloalkanes in an alcoholic solution of potassium hydroxide can be used to produce alkynes. For example,

• By dehalogenation of tetrahalides:When tetrahaloalkanes are heated in methanol with zinc dust, they dehalogenate to produce alkynes. For example,

• To dehalogenate halo shapes:When chloroform and iodoform are heated with silver powder, they dehalogenate to give ethyne.

• Synthesis of carbon and hydrogen:Likewise, hydrogen gas vapor can be used to produce ethyne by passing it through an electric arc formed between two carbon electrodes. The Berthelot synthesis is the name of this method.

Physical properties of alkynes.

The properties of alkynes essentially follow patterns similar to those of alkanes and alkenes.

• Alkynes are unsaturated carbons that share triple security at the carbon locus.
• All alkynes are odorless and dark, except ethylene, which has a slight peculiar odor.
• The first three alkynes are gases and the next eight are liquids. All alkynes greater than these eleven are solids.
• Alkynes are somewhat polar in nature.
• The boiling point and melting point of alkynes increase with increasing atomic size. The boiling point increases in subatomic mass with expansion.
• Furthermore, the limits of alkynes are slightly higher than those of their alkene cousins ​​due to the presence of an additional bond at the carbon site.

Chemical properties of alkynes.

acidic nature

As for the synthetic properties of alkynes, we start with their slightly acidic nature. Currently, alkynes are slightly electronegative in nature. The triple-bonded carbon particles in alkynes are sp-hybridized, whereas, as in alkanes, the iota single bonds are sp3-hybridized, causing the difference in electronegativity. This makes it easier for them to attract the shared pair of electrons in the C-H bond. Therefore, if we react with ethyne in a solid base like NaNH2, we get sodium acetylide and hydrogen gas (H2) released. However, such reactions do not occur with alkanes and alkenes. The bottom line is that the hydrogen particles bonded to the carbon-carbon triple bond in alkynes are somewhat acidic in nature. Note that the other exposed hydrogen particles are not acidic.

HC ≡ CH + Na → HC ≡ C– Na⁺+ 1/2 standard₂

addition reaction:

Alkynes undergo hydration reactions under appropriate circumstances. When alkynes react with halogens, hydrogen and other similar elements, they create a saturated molecule. Two hydrogen atoms, halides or halogens can be added to its structure, as they contain a triple bond.

• Dihydrogen addition:A catalyst such as nickel, platinum or palladium is used to speed up the process. When hydrogen is added to an alkyne, we get an alkene.

C₃H₄(g) + 2H₂(g) → C₃H₈(GRAMS)

• Halogen addition:When alkynes and halogens react like chlorine, the halogen bonds to the alkyne backbone, resulting in halogen-substituted alkenes. The final product will be tetrachloroethane.

• Adding water:Alkynes do not react with water molecules like other hydrocarbons (alkanes and alkenes). This is called immiscibility. A reaction occurs when alkynes are bubbled through dilute (approximately 40%) sulfuric acid in the presence of mercury sulfate catalyst. Carbonyl molecules are the end products of this process known as the hydration reaction.

• Polymerization:Alkynes can polymerize both linearly and cyclically under the right circumstances. Polymerization occurs, resulting in molecules with a molecular weight greater than the starting alkyne. For example, ethyne is polymerized into polyacetylene or polyethylene (which has a higher molecular weight). High temperatures and the presence of a catalyst are required for cyclic polymerization. Such as passing ethyne through a red-hot iron tube at a temperature of at least 877 K to produce benzene.

use of alkyne

1. Because etin has an exceptionally hot fire, it is often used in oxy-fuel welding and oxy-fuel cutting. Since ethyne is ignited with oxygen, the subsequent fire is known to have a temperature of about 3600 Kelvin.
2. The alkyne substituted in acetylene is used as a fuel, with large numbers of kilograms produced annually from the partial oxidation of gaseous gasoline. With some of these alkynes mixtures of substances are produced, for example, acetic acid, acrylic acid and ethanol.
3. Ethyne is most commonly used to make natural compounds such as ethanol, caustic ethane and caustic acrylic. It is also used to make polymers and raw materials for them.
4. Acetylene splits into two parts, carbon and hydrogen. This reaction generates a lot of heat, which can ignite the gas, regardless of the absence of air or oxygen.
5. Most often, alkynes are used as starting materials in the construction of a large number of mechanically important natural compounds, such as chloroprene, vinyl chloride, etc.

sample questions

Question 1: What is an alkyne?

Responder:

In the natural sciences, alkynes are unsaturated hydrocarbons with something like a triple bond between carbon-carbon particles (–C≡C–). The general recipe for this unsaturated hydrocarbon is C_norteH_2n–2, where n–2,3,4,5… … .

Alkynes are commonly known as acetyls. Like many hydrocarbons, alkynes are also hydrophobic.

Question 2: What are the properties of alkynes?

Responder:

The first three alkynes are colorless gases, the next eight are liquids, and the higher alkynes are solids. They are odorless, insoluble in water but soluble in organic solvents due to their nonpolar nature, have high melting and boiling temperatures, and are lighter than water.

Question 3: What is the main use of alkynes?

Responder:

Acetylene, also known as ethyne, is the most common alkyne chemical. Here are some application examples:

• Gas welding uses an oxyacetylene flame.
• Both the Hawker lamp and the headlamps use acetylene as the light source.
• Acetylene is used to artificially ripen the fruit.
• Acetylene is used in the production of acetaldehydes, acetic acid, ethyl alcohol, synthetic rubber and other valuable chemicals.
• In organic chemistry, acetylene and its derivatives are commonly used to produce cis and trans alkenes, methyl ketones and other compounds.

Question 4: How are alkynes naturally acidic?

Responder:

Alkynes have a small negative charge. This is due to sp hybridization of the three-bonded carbon atoms in alkynes, making it easier for them to attract the shared electron pair. As a result, alkyne molecules can easily lose hydrogen. This increases the acidity of the hydrogen atom bonded to the triple-bonded carbon atom.

Question 5: Why do alkynes have higher boiling points?

Responder:

The melting and boiling temperatures of alkynes increase with increasing molecular weight of the alkyne. Alkynes, on the other hand, have higher melting and boiling points than alkanes and alkenes. This is because alkynes are linear and their molecules are more spatially packed.

Question 6: How are alkynes produced?

Responder:

Chlorine or bromine is mixed with an inert halogenated solvent, such as chloromethane, to produce a vicinal dihalide from an alkene. To produce an alkyne, the produced vicinal dihalide is heated and treated with a strong base.

Question 7: How can we reduce alkyne to alkene?

Responder:

Alkynes can be converted to trans-alkenes by dissolving sodium in an ammonia solution. A Na radical donates an electron to one of the P bonds in a carbon-carbon triple bond. An anion forms in an ammonia solution that can be protonated by hydrogen.