What is an Acetylide Ion Definition Types Reactions and Applications
Acetylide is a chemical compound with the chemical formulas MC≡CH and MC≡CM in organometallic chemistry, where M is a metal. The term is loosely defined and can refer to substituted acetylides with the general structure RCCM (where R is an organic side chain). Acetylides are organic synthesis reagents. Calcium acetylide, also known as calcium carbide, is a common commercial compound.
Acetylides of the type ${{R}{C}_{2}{M}}$ are widely used in organic chemistry for alkynylations. They are nucleophiles that react with a wide range of electrophilic and unsaturated substrates. The Favorskii reaction is a classic example. In the example below, ethyl propiolate is deprotonated by n-butyllithium to yield the corresponding acetylide. This acetylide reacts with cyclopentanone's carbonyl centre. The alkynyl alcohol is liberated during the hydrolytic process.
Structure and Bonding of Acetylide
Acetylide acquires ionic properties when it is bonded with an alkali metal or an alkaline earth metal. The hydrolysis of these compounds can confirm evidence for acetylide's ionic properties.
Hydrolysis of acetylide produces acetylene and metal oxide.
Acetylide has covalent properties when bonded with transition metals.
Acetylide has properties similar to its doubly substituted analogues.
Metal acetylide has a polymeric structure in the absence of a ligand, with the acetylide group acting as a bridging ligand.
Applications of Acetylide
Because of their high sensitivity to water, acetylides are used as explosives.
To detect the presence of acetylene, gaseous copper acetylide is passed through a copper (I) chloride solution.
Petrochemistry makes use of copper acetylide.
Inside pipes in industries are made of copper acetylide.
Acetylide is also used in organic synthesis to detect the presence of terminal alkynes.
Important Questions
1. How metal Acetylide is formed?
Ans: A metal acetylide is an alkyne in which a proton (hydrogen) has been removed from the terminal end by a metal such as sodium or organolithium. The alkyne $CH{≡}CH$, for example, could be deprotonated to form the acetylide ion${{C}{H}_{3}{≡}{C}^-}$. It becomes a strong nucleophile after being deprotonated. Some acetylides, such as silver or copper acetylide, are explosives. Acetylide ions are extremely useful in organic chemistry reactions involving the addition and substitution of carbon chains. Acetylides exhibit additional reactions with ketones to form tertiary alcohols as one type of reaction.
2. What is the formula of silver acetylide?
Ans: Silver acetylide, also known as a metal acetylide, is an inorganic chemical compound with the formula ${{Ag}_{2}{C}_{2}}$. The compound can be thought of as a salt of acetylene, a weak acid. The anion of the salt is made up of two carbon atoms connected by a triple bond. Although the analogous calcium compound ${{Ca}{C}_{2}}$ is known as calcium carbide, the alternate name "silver carbide" is rarely used. Silver acetylide is a highly explosive substance.
Multiple Choice Questions
1. Allylides contain
a) ${{C}^{4-}}$ ions
b) ${{C}^{2-}}$ - ions
c) ${{C}^{3-}}$- ions
d) None of the above
Answer: (a)
2. Which of the following is called acetylide?
(a)${{C}_{12}{H}_{14}{Cl}{F}_{2}{NO}_{4}{S}}$
(b)${{C}_{3}{H}_{12}}$
(c)${{C}_{4}{H}_{5}}$
(d)${{C}_{6}{H}_{6}}$
Answer: (a)
3. Which of the following is acetylide ion?
(a)${{C}^{2-}_{2}}$
(b)${{C}^{3-}_{4}}$
(c)${{C}^{3-}_{2}}$
(d)${{C}^{4-}_{4}}$
Answer: (a)
Conclusion
Acetylide is a chemical compound class in which a metal is bonded to an alkyne. Acetylide has the general formula RC≡CM, where R is an organic side chain. Acetylide acquires ionic properties when it is bonded with an alkali metal or an alkaline earth metal. The hydrolysis of these compounds can confirm evidence for acetylide's ionic properties. Because of their high sensitivity to water, acetylides are used as explosives. To detect the presence of acetylene, gaseous copper acetylide is passed through a copper (I) chloride solution.
FAQs on Acetylide Ion Structure Formation and Properties
1. What is an acetylide?
An acetylide is a compound that contains the C22- ion or a negatively charged carbon derived from a terminal alkyne. In inorganic chemistry, acetylide usually refers to salts containing the acetylide ion, while in organic chemistry it often means the conjugate base of an alkyne (RC≡C-).
- General ion formula: C22-
- Formed by deprotonation of a terminal alkyne
- Common in metal acetylides like CaC2
2. What is the formula of the acetylide ion?
The formula of the acetylide ion is C22-. It consists of two carbon atoms connected by a triple bond and carrying an overall 2− charge.
- Structure: C≡C
- Charge: −2
- Found in ionic compounds such as CaC2 and Na2C2
3. How is an acetylide ion formed from an alkyne?
An acetylide ion is formed by removing a proton (H+) from a terminal alkyne using a strong base. Terminal alkynes (RC≡CH) have an acidic hydrogen that can be deprotonated.
- General reaction: RC≡CH + NaNH2 → RC≡C-Na+ + NH3
- Requires strong bases like NaNH2 or n-BuLi
- Internal alkynes do not form acetylide ions because they lack a terminal hydrogen
4. What happens when calcium acetylide reacts with water?
When calcium acetylide (CaC2) reacts with water, it produces acetylene (C2H2) and calcium hydroxide. The balanced chemical equation is:
- CaC2(s) + 2H2O(l) → C2H2(g) + Ca(OH)2(aq)
5. What are the types of acetylides?
The main types of acetylides are ionic (salt-like) acetylides and covalent (metal) acetylides. They differ in bonding and properties.
- Ionic acetylides: Contain the C22- ion, e.g., Na2C2, CaC2
- Covalent or metallic acetylides: Found with transition metals, e.g., Cu2C2
- Organic acetylides: Alkynyl anions such as RC≡C-
6. Why are terminal alkynes acidic?
Terminal alkynes are acidic because the hydrogen attached to the sp-hybridized carbon can be removed to form a stable acetylide ion. The sp carbon has 50% s-character, which stabilizes the negative charge.
- Greater s-character increases electronegativity
- Conjugate base: RC≡C-
- Typical pKa ≈ 25 (more acidic than alkenes and alkanes)
7. What is the difference between acetylide and acetylene?
The key difference is that acetylene (C2H2) is a neutral alkyne molecule, while an acetylide is its negatively charged conjugate base or salt.
- Acetylene: HC≡CH, neutral gas
- Acetylide ion: C22- or RC≡C-
- Acetylides form when acetylene or terminal alkynes lose hydrogen ions
8. How are metal acetylides prepared?
Metal acetylides are prepared by reacting a terminal alkyne with a strong base or by direct reaction of metals with acetylene. Common preparation methods include:
- Deprotonation: HC≡CH + 2Na → Na2C2 + H2
- Industrial method: Heating lime and coke to form CaC2
- Reaction of acetylene with metal salts like silver or copper salts
9. What are the uses of acetylides?
Acetylides are mainly used in the production of acetylene gas and in organic synthesis reactions. Their important applications include:
- Industrial preparation of C2H2 from CaC2
- Formation of carbon–carbon bonds in organic chemistry
- Use in carbide lamps and welding processes
10. Are acetylides reactive and dangerous?
Yes, many acetylides are highly reactive and can be dangerous, especially metal acetylides of heavy metals. They can react vigorously with water and may be explosive.
- React with water to release flammable acetylene gas
- Silver and copper acetylides can be shock-sensitive
- Must be handled under dry and controlled laboratory conditions
