Answer: A. Carbon tetrachloride (CCl4) is used as a solvent and a reactant in the preparation of alkynes through a reaction known as the chloroformic esterification or the Wurtz reaction. In this reaction, an alkyne is treated with CCl4 and sodium metal to produce a chloroformate ester, which can then be hydrolyzed to the corresponding carboxylic acid.
b. Hydrogen bromide (HBr) is used in the preparation of alkynes through a reaction known as the bromination of alkynes. In this reaction, an alkyne is treated with HBr and a Lewis acid catalyst to produce a geminal dibromide, which can then be hydrolyzed to the corresponding alkyne. This reaction is useful for the synthesis of alkyne compounds that are not readily available from other sources.
Both CCl4 and HBr are commonly used reagents in organic chemistry due to their reactivity and versatility. They can be used to synthesize a wide range of compounds, including alkynes, by reacting with various organic compounds under appropriate conditions.