Question
Question: What is the product of the following reaction? 
Solution
Alkynes are unsaturated hydrocarbons consisting of triple bonds and aldehydes belong to carbonyl compounds. When aldehydes treated with reducing agents like sodium borohydride form alcohols. Alcohols undergo nucleophilic substitution by replacing the hydroxyl group. Alkyl halides react with metal forms Grignard reagent and Grignard reagent on carboxylation forms carboxylic acids.
Complete answer:
Given molecule is Hex-3-ynal which means it consists of alkyne and aldehyde. The suffix -al represents aldehyde functional group and -yne represents alkyne functional group. The root word Hex represents six carbon atoms. The number 3 indicates the position of alkyne.
When Hex-3-ynal reacts with sodium borohydride, the aldehyde converts into alcohol and now this alcohol when treated with tribromo phosphine which is a bromide source, the hydroxyl group can be replaced by bromine forms bromo alkyne. When the bromo alkyne is treated with magnesium in presence of ether it forms Grignard reagent. When Grignard reagent is treated with carbon dioxide in presence of hydronium ion it forms carboxylic acid.
CH3−CH2−C≡C−CH2−CH2−CHONaBH4CH3−CH2−C≡C−CH2−CH2−CH2OH
When the above compound is treated with tribromo phosphine, it forms
CH3−CH2−C≡C−CH2−CH2−CH2OHPBr3CH3−CH2−C≡C−CH2−CH2−CH2Br
Further, it forms
CH3−CH2−C≡C−CH2−CH2−CH2BrMg/etherCH3−CH2−C≡C−CH2−CH2−CH2MgBr
The final product will be
CH3−CH2−C≡C−CH2−CH2−CH2MgBrCO2/H3O+CH3−CH2−C≡C−CH2−CH2−CH2COOH
Thus, the product will be Hex−3−yne1−oicacid
At the position 3, triple bond is present, 1st position carboxylic acid is present.
Note:
Sodium borohydride can be used as a reducing agent, it belongs to the hydrides family, as a source of hydrides used for the reduction of aldehydes to alcohols. Tribromo phosphine is the source of bromine, the magnesium when treated with bromine forms Grignard reagent. Grignard reagent undergoes carboxylation and forms carboxylic acids.