Question

Outline all steps in the synthesis of (a) 1 -butyne and \(\quad\) (b) 2-butyne from acetylene using any needed organic or inorganic reagents.

Short answer

(a) Synthesis of 1-butyne from acetylene: 1. Add HCl to acetylene to form chloroethene (C2H2 + HCl -> C2H3Cl) using a Pd(II) catalyst. 2. Perform Kumada-Corriu cross-coupling reaction with vinyl chloride and n-propylmagnesium bromide using a Pd(0) catalyst: C2H3Cl + CH3CH2CH2MgBr -> HC≡CCH2CH2CH3 + MgBrCl. (b) Synthesis of 2-butyne from acetylene: 1. Add Br2 to acetylene to form 1,2-dibromoethane (C2H2 + 2Br2 -> C2H2Br2) under UV light or heat. 2. Treat 1,2-dibromoethane with magnesium in dry ether to form ethylene(magnesium bromide) Grignard reagent (C2H2Br2 + Mg -> C2H2MgBr2). 3. React the formed Grignard reagent with acetylene to form 2-butyne (C2H2 + C2H2MgBr2 -> CH3C≡CCH3 + MgBr2).

Step-by-step solution

Formation of vinyl chloride (chloroethene) from acetylene

Add hydrogen chloride (HCl) to acetylene to form chloroethene. This reaction proceeds under palladium(II) catalyst. The reaction can be represented as: \[ C_2H_2 + HCl \rightarrow C_2H_3Cl \]

Kumada-Corriu cross-coupling reaction to form 1-butyne

Use the Kumada-Corriu cross-coupling reaction by reacting vinyl chloride with an organomagnesium reagent (Grignard reagent). For this, react vinyl chloride with n-propylmagnesium bromide, using a palladium(0) catalyst like "Pd(PPh3)4" (tetrakis(triphenylphosphine)palladium) and an appropriate solvent (e.g., ether) under inert atmosphere. This will form the desired 1-butyne. The reaction can be represented as: \[ C_2H_3Cl + CH_3CH_2CH_2MgBr \rightarrow HC \equiv CCH_2CH_2CH_3 + MgBrCl \] (b) Synthesis of 2-butyne from acetylene

Formation of 1,2-dibromoethane from acetylene

Add bromine (Br2) to acetylene to form 1,2-dibromoethane. This reaction proceeds under the UV light or in the presence of a heat source. The reaction can be represented as: \[ C_2H_2 + 2Br_2 \rightarrow C_2H_2Br_2 \]

Formation of a Grignard reagent

Treat 1,2-dibromoethane with magnesium in dry ether to form ethylene(magnesium bromide), which is a Grignard reagent. The reaction can be represented as: \[ C_2H_2Br_2 + Mg \rightarrow C_2H_2MgBr_2 \]

Formation of 2-butyne through Grignard reagent reaction with acetylene

React the formed Grignard reagent (ethylene(magnesium bromide)) with acetylene. This leads to the formation of 2-butyne. The reaction can be represented as: \[ C_2H_2 + C_2H_2MgBr_2 \rightarrow CH_3C \equiv CCH_3 + MgBr_2 \]

Key concepts

Grignard Reagent

Grignard reagents are highly useful tools in organic synthesis. These compounds are formed when an alkyl or aryl halide reacts with magnesium in an aprotic solvent, such as diethyl ether or tetrahydrofuran (THF). The resulting organomagnesium halide is highly reactive and can behave as a strong base or a nucleophile.
This property makes Grignard reagents incredibly versatile, as they can effectively add carbons to a molecular framework, facilitating the creation of larger and more complex molecules.
Key features of Grignard reagents include:

• Formation involves magnesium and an organic halide.
• Highly reactive due to polar Mg-C bond.
• Acts effectively as a carbon nucleophile.

Grignard reactions are broadly used for forming carbon-carbon bonds, a critical aspect of constructing various organic compounds.

Kumada-Corriu Coupling

The Kumada-Corriu coupling is a type of cross-coupling reaction used extensively in organic chemistry for building larger, more complex structures. This reaction allows for the effective coupling of Grignard reagents with organic halides.
The process is typically mediated by a palladium or nickel catalyst, which helps in the formation of the new carbon-carbon bond.
A pivotal feature of this reaction:

• Utilizes Pd or Ni catalysts to facilitate the coupling.
• Allows for mild reaction conditions and high selectivity.
• Enables the use of a variety of Grignard reagents and organic halides.

The Kumada-Corriu coupling is invaluable for synthesizing a wide range of organic materials and complex natural products efficiently and selectively.

Vinyl Chloride

Vinyl chloride, also referred to as chloroethene, is a valuable intermediate in organic synthesis.
It is commonly produced by adding hydrogen chloride (HCl) to acetylene in the presence of a metal catalyst such as palladium(II).
This results in the formation of a key building block for numerous chemical synthesis processes, particularly in polymer and plastics manufacturing. Important aspects of vinyl chloride include:

• Synthesized from acetylene through hydrochlorination.
• Used widely as a monomer in producing polyvinyl chloride (PVC).
• Serves as an intermediate in various organic reactions.

Its role as both a precursor and synthetic intermediate makes it vital in diverse chemical industries.

Organomagnesium

Organomagnesium compounds, primarily Grignard reagents, feature a unique carbon-metal bond, lending them significant reactivity in chemical synthesis.
This bond gives rise to their innate ability to participate in various nucleophilic addition and substitution reactions.
Key characteristics of organomagnesium reagents include:

• Magnesium imparts unique reactivity to carbon atoms.
• Often prepared in ether solvents to stabilize the reactive species.
• Critical in forming new C-C bonds in organic synthesis.

These properties allow organomagnesium compounds to be central to a range of chemical transformations, particularly in forming complex organic molecules.

Acetylene

Acetylene, an unsaturated hydrocarbon, possesses a triple bond between its carbon atoms, making it a simple yet versatile precursor in organic synthesis.
This triple bond is key to acetylene's reactivity and ability to engage in various addition reactions.
Moreover, it's a starting point for producing a wide range of different organic compounds. Highlights regarding acetylene include:

• Basic molecular structure with a triple C-C bond.
• High energy due to strain in the triple bond.
• Widely used for adding halides and hydrohalides.

Acetylene's potential to easily react and form new carbon-carbon bonds marks its importance in constructing diverse and complex organic frameworks.