1. What is acetylide?
Acetylides refer to a class of compounds in which a metal is attached to an alkyne. The general formula for acetylides is RC≡CM, where R is an organic side chain. Acetylide is a well-known reagent used in the synthesis of organic compounds. They are also formed as intermediates in coupling reactions.
2. Write about Structure and Bonding of Acetylides?
When Acetyl Metals Combine with Alkali Metals or acetylides, alkaline earth metals exhibit ionic character. Hydrolysis of these compounds can confirm evidence of the ionic character of the acetylides.
Hydrolysis of acetylides is done and acetylene and metal oxides are formed.
When acetylides bind to transition metals, they exhibit covalent character.
Acetylide shows similar properties to its double-substituted analogue.
In the absence of ligands, metal acetylides exhibit polymeric structures with acetylide groups as bridging ligands.
3. What are the uses of acetylides?
The uses of Acetylides are -
Acetylides are highly sensitive to water and are used as explosives.
To test acetylene, gaseous copper acetylide is passed through a copper (I) chloride solution.
Copper acetylide is used in petrochemicals.
Copper acetylide is used in industry to form tubes.
Acetylide is also used to test for the presence of terminal alkynes in organic synthesis.
4. How acetylide is prepared?
It is prepared in the following way-
With the help of Alkyne
The synthesis of acetylides from alkynes uses organometallic or inorganic superbases.
Liquid ammonia is used in the synthesis of acetylides from alkenes.
Ether-based solvents are also used to synthesize acetylides from alkenes.
Organolithium reagents such as lithium amide, LiHMDS, and ethyl lithium are commonly used in the synthesis of lithium acetylides.
Inorganic reagents such as sodium amides are commonly used to synthesize sodium or potassium acetylides at room temperature and atmospheric pressure.
Copper (I) acetylide is synthesized by passing copper chloride through acetylene.
Silver nitrate is commonly used in the synthesis of silver acetylides.
Calcium carbide is produced by heating lime, or calcium oxide, with coal to about 2,000 °C.
Lithium carbide is produced by heating lithium oxide, or lithium oxide, together with carbon to about 2,000 °C. Strong bases such as KOH react with acetylene to form potassium acetylide
5. What are the dangers caused by acetylides?
Dangers caused by acetylides are-
Some acetylides are notoriously explosive.
Acetylide formation is a risk when handling gaseous acetylene in the presence of higher-grade metals or alloys.
Toxin acts on the skin system as it can cause skin irritation and allergic skin reactions.
It also affects the eye system, as contact with the eyes can cause serious eye damage and eye irritation.
It also adversely affects the respiratory tract when inhaled.
6. Why are copper acetylides often used in click chemistry?
Copper acetylides are key intermediates in copper-catalyzed azide-alkyne cycloaddition (CuAAC), a prime example of click chemistry. They form easily under mild conditions and react rapidly with azides to form 1,2,3-triazoles, making them ideal for efficient and selective chemical transformations.
7. What is the importance of acetylides in the synthesis of internal alkynes?
Acetylides are key to synthesizing internal alkynes. By reacting an acetylide with an alkyl halide, a new carbon-carbon bond is formed, resulting in an internal alkyne after workup. This method allows for the controlled placement of triple bonds within a carbon chain.
8. What is the role of acetylides in the synthesis of allenes?
Acetylides can be used to synthesize allenes through a two-step process. First, the acetylide reacts with an alkyl halide to form an internal alkyne. This alkyne can then undergo base-catalyzed isomerization to form an allene, a compound with two adjacent double bonds.
9. What role do acetylides play in the synthesis of alkynes?
Acetylides are crucial in alkyne synthesis as they allow for the extension of the carbon chain. They can react with alkyl halides or other electrophiles to form new carbon-carbon bonds, creating longer or more complex alkyne structures.
10. How do acetylides participate in cycloaddition reactions?
Acetylides can participate in cycloaddition reactions, particularly [3+2] cycloadditions. For example, copper acetylides react with azides in the copper-catalyzed azide-alkyne cycloaddition (CuAAC) to form 1,2,3-triazoles, a reaction widely used in click chemistry.
11. What is the significance of copper acetylide in organic synthesis?
Copper acetylide is an important intermediate in many organic reactions, particularly in coupling reactions like the Sonogashira coupling. It forms easily and is more reactive than the parent alkyne, allowing for the formation of new carbon-carbon bonds.
12. What is the importance of acetylides in cross-coupling reactions?
Acetylides are key intermediates in many cross-coupling reactions, such as the Sonogashira coupling. They form reactive organometallic species that can undergo transmetallation with palladium catalysts, allowing for the formation of new carbon-carbon bonds between alkynes and aryl or vinyl halides.
13. What is the role of acetylides in the synthesis of conjugated enynes?
Acetylides are crucial in the synthesis of conjugated enynes. They can react with vinyl halides in coupling reactions, such as the Sonogashira coupling, to form a new carbon-carbon bond between the alkyne and alkene moieties, resulting in a conjugated enyne system.
14. How do acetylides interact with carbonyl compounds?
Acetylides react as nucleophiles with carbonyl compounds. They attack the electrophilic carbonyl carbon, forming a new carbon-carbon bond. This results in the formation of an alkoxide intermediate, which upon protonation yields a propargyl alcohol (an alcohol with a triple bond).
15. What is the significance of the linear geometry of acetylides?
The linear geometry of acetylides, inherited from the parent alkyne, is crucial for their reactivity and properties. It allows for effective overlap of orbitals in the triple bond, influences the distribution of the negative charge, and affects the directionality of nucleophilic attacks in reactions.
16. Why are some acetylides explosive?
Some acetylides, particularly those of heavy metals like silver and mercury, are explosive due to their instability. The weak metal-carbon bond can easily break, releasing a large amount of energy and gaseous products, leading to rapid decomposition and potential explosion.
17. How do acetylides behave in radical reactions?
While acetylides themselves are not typically involved in radical reactions, the parent alkynes can participate in radical additions. However, the high electron density of the acetylide anion can sometimes lead to electron transfer processes, potentially initiating radical reactions under certain conditions.
18. How does the hybridization of the acetylide carbon affect its reactivity?
The sp-hybridization of the acetylide carbon contributes significantly to its reactivity. The linear geometry and high s-character of the orbital holding the negative charge make acetylides strong nucleophiles. This hybridization also allows for effective overlap in the formation of new bonds.
19. What is the role of acetylides in the synthesis of acetylenic ketones?
Acetylides are key in synthesizing acetylenic ketones. They can react with acid chlorides or anhydrides to form a new carbon-carbon bond. After workup, this results in an acetylenic ketone, which contains both a carbonyl group and a triple bond.
20. How does the reactivity of acetylides compare in protic vs. aprotic solvents?
Acetylides are generally more reactive in aprotic solvents. In protic solvents, acetylides can undergo proton transfer reactions, converting back to the parent alkyne. Aprotic solvents allow the acetylide to maintain its anionic character, preserving its nucleophilicity for desired reactions.
21. How do acetylides behave in elimination reactions?
While acetylides themselves don't typically undergo elimination reactions, they can induce eliminations in other molecules. As strong bases, they can abstract protons from adjacent carbons in other compounds, leading to the formation of alkenes through E2 elimination reactions.
22. What is the role of acetylides in the synthesis of propargyl compounds?
Acetylides are crucial in synthesizing propargyl compounds. They react with electrophiles like alkyl halides to form a new carbon-carbon bond at the position adjacent to the triple bond. This results in the formation of propargyl structures, which contain a triple bond and a functional group on the adjacent carbon.
23. What types of metals commonly form acetylides?
Acetylides are typically formed with alkali metals (like sodium and potassium), alkaline earth metals (like calcium), and some transition metals (like copper and silver). The choice of metal affects the properties and reactivity of the resulting acetylide.
24. How does the preparation of sodium acetylide differ from that of copper acetylide?
Sodium acetylide is typically prepared by reacting sodium metal directly with gaseous acetylene, while copper acetylide is often formed in situ by reacting a terminal alkyne with a copper(I) salt in the presence of a base. The different preparation methods reflect the different reactivities of the metals.
25. How does the presence of electron-withdrawing groups affect acetylide formation?
Electron-withdrawing groups near the triple bond increase the acidity of the terminal hydrogen, making acetylide formation easier. These groups stabilize the negative charge of the acetylide anion through inductive or resonance effects, resulting in a more stable acetylide.
26. What is the difference between a mono-acetylide and a di-acetylide?
A mono-acetylide is formed when a terminal alkyne loses one proton, resulting in a single negative charge. A di-acetylide is formed when both hydrogens of acetylene (HC≡CH) are removed, resulting in a dianion with negative charges at both ends.
27. What is the difference between a terminal acetylide and an internal acetylide?
A terminal acetylide is formed from a terminal alkyne and has the negative charge at the end of the carbon chain. An internal acetylide, which is less common, would have the negative charge on an internal carbon of the alkyne. Internal acetylides are generally less stable and more difficult to form than terminal acetylides.
28. How does the structure of an acetylide affect its nucleophilicity?
The linear structure of acetylides, combined with the localization of the negative charge at the terminal carbon, makes them strong and directional nucleophiles. This allows them to attack electrophiles specifically at the triple bond, leading to selective reactions.
29. How do acetylides participate in addition reactions?
Acetylides can undergo addition reactions with electrophiles like aldehydes or ketones. The negatively charged carbon of the acetylide attacks the electrophilic carbon of the carbonyl group, forming a new carbon-carbon bond and resulting in the formation of an alkynol after protonation.
30. How do acetylides behave in proton transfer reactions?
Acetylides are strong bases and readily accept protons from weaker acids. This proton transfer reaction converts the acetylide back into the parent alkyne. The strength of the acetylide as a base depends on the metal involved, with alkali metal acetylides being stronger bases than transition metal acetylides.
31. How does the reactivity of acetylides compare to that of Grignard reagents?
Both acetylides and Grignard reagents are strong bases and nucleophiles. However, acetylides are generally more selective in their reactions due to their linear structure and the presence of the triple bond. Grignard reagents are more reactive and less selective in many cases.
32. How does the electronegativity of the metal affect the properties of acetylides?
The electronegativity of the metal influences the ionic character of the metal-carbon bond in acetylides. Less electropositive metals form more covalent bonds, resulting in less reactive acetylides. More electropositive metals form more ionic bonds, leading to more reactive acetylides.
33. What is an acetylide and how does it differ from an alkyne?
An acetylide is the anion formed when a terminal alkyne loses its acidic hydrogen. Unlike alkynes, which are neutral molecules, acetylides are negatively charged and more reactive. The key difference is that acetylides have a carbon-metal bond at the terminal position instead of a carbon-hydrogen bond.
34. Why are terminal alkynes considered acidic?
Terminal alkynes are considered acidic because the sp-hybridized carbon atom is highly electronegative, which polarizes the C-H bond. This makes the hydrogen atom slightly positive and more easily removed as a proton, resulting in the formation of a stable acetylide anion.
35. How does the structure of an acetylide contribute to its stability?
The stability of an acetylide comes from its linear structure and the distribution of the negative charge. The sp-hybridized carbon atom can effectively distribute the negative charge through its triple bond, making the acetylide anion relatively stable compared to other carbanions.
36. How does the bonding in a metal acetylide differ from that in an alkyne?
In a metal acetylide, there is an ionic bond between the metal cation and the acetylide anion, in addition to the carbon-carbon triple bond. This ionic character makes acetylides more reactive than alkynes, which only have covalent bonds.
37. How does the acidity of terminal alkynes compare to that of other hydrocarbons?
Terminal alkynes are significantly more acidic than other hydrocarbons like alkanes, alkenes, or non-terminal alkynes. This increased acidity is due to the sp-hybridization of the terminal carbon, which makes the C-H bond more polarized and the hydrogen more easily removed as a proton.
38. What is the significance of acetylides in organometallic chemistry?
Acetylides are important in organometallic chemistry as they form stable complexes with many transition metals. These complexes, such as copper acetylides, are crucial intermediates in various catalytic cycles, particularly in coupling reactions and cycloadditions.
39. How do acetylides interact with transition metal complexes?
Acetylides can coordinate with transition metal complexes, often replacing other ligands. This coordination can occur through the pi electrons of the triple bond or through sigma bonding with the terminal carbon. These interactions are important in catalysis and in the formation of organometallic compounds.
40. What is the importance of acetylides in the synthesis of cycloalkynes?
Acetylides play a crucial role in the synthesis of cycloalkynes, especially medium and large ring systems. By reacting a di-functionalized acetylide (where both ends can react) with an appropriate di-electrophile, it's possible to form cyclic structures containing a triple bond.
41. How does the presence of nearby functional groups affect acetylide formation and reactivity?
Nearby functional groups can significantly influence acetylide formation and reactivity. Electron-withdrawing groups increase acidity and facilitate acetylide formation, while electron-donating groups have the opposite effect. These groups can also affect the nucleophilicity and basicity of the resulting acetylide.
42. What is the role of acetylides in click chemistry beyond the azide-alkyne cycloaddition?
While acetylides are best known in click chemistry for the azide-alkyne cycloaddition, they also participate in other click reactions. For example, they can undergo thiol-yne click reactions, where a thiol adds across the triple bond, allowing for the rapid synthesis of sulfur-containing compounds.
43. How do acetylides contribute to the synthesis of conjugated polymers?
Acetylides are important in the synthesis of conjugated polymers, particularly those containing alkyne units. Through coupling reactions like the Glaser coupling or Sonogashira coupling, acetylides can form carbon-carbon bonds between alkyne units, creating extended conjugated systems used in materials science.
44. What is the significance of acetylides in the formation of metal-organic frameworks (MOFs)?
Acetylides can serve as linkers in metal-organic frameworks (MOFs). The linear geometry of the acetylide unit and its ability to coordinate with metals make it useful for creating rigid, porous structures. These acetylide-based MOFs can have applications in gas storage, catalysis, and sensing.
45. How do acetylides participate in carbometalation reactions?
Acetylides can undergo carbometalation reactions, where a carbon-metal bond adds across the triple bond. This process is important in organic synthesis as it allows for the functionalization of the alkyne unit. The resulting vinyl metal species can then be used in further transformations.
46. What is the role of acetylides in the synthesis of enediynes?
Acetylides are crucial in the synthesis of enediynes, compounds containing two triple bonds connected by a double bond. By coupling an acetylide with a vinyl halide, one can form half of the enediyne structure. Repeating this process on the other side of the double bond completes the enediyne synthesis.
47. What is the importance of acetylides in the synthesis of heterocycles?
Acetylides are valuable in heterocycle synthesis. They can participate in cycloaddition reactions to form oxygen, nitrogen, or sulfur-containing heterocycles. For example, the reaction of acetylides with nitriles can lead to the formation of pyrroles under appropriate conditions.
48. How do acetylides contribute to the formation of carbon nanostructures?
Acetylides play a role in the synthesis of carbon nanostructures like carbon nanotubes and graphene. The linear structure of acetylides and their ability to form carbon-carbon bonds make them useful precursors in controlled growth processes for these nanostructures.
49. What is the significance of acetylides in asymmetric synthesis?
Acetylides can be used in asymmetric synthesis when combined with chiral auxiliaries or chiral catalysts. Their reactions with prochiral electrophiles can lead to the formation of new stereogenic centers, allowing for the synthesis of optically active propargyl compounds.
50. How do acetylides interact with main group elements other than carbon?
Acetylides can form bonds with various main group elements. For example, they can react with boron to form alkynylboranes, with silicon to form alkynylsilanes, or with phosphorus to form alkynylphosphines. These compounds are useful in organic synthesis and materials science.
51. What is the role of acetylides in the synthesis of acetylenic natural products?
Acetylides are crucial in the synthesis of acetylenic natural products, which contain triple bonds. They allow for the controlled introduction and modification of alkyne units, which are present in many bioactive natural compounds like enediynes, polyacetylenes, and certain alkaloids.
52. How do acetylides participate in multicomponent reactions?
Acetylides can participate in multicomponent reactions, where three or more reactants combine in a single step. For example, in the A³ coupling (Aldehyde-Alkyne-Amine coupling), an acetylide formed in situ reacts with an imine (formed from an aldehyde and amine) to create complex propargylamine products.
53. What is the importance of acetylides in supramolecular chemistry?
In supramolecular chemistry, acetylides can be used to create rigid, linear linking units in larger assemblies. Their ability to coordinate with metals also makes them
