The two most common methods to prepare primary alcohols from aldehydes are:1. Reduction using metal hydrides, such as sodium borohydride NaBH4 or lithium aluminum hydride LiAlH4 .2. Catalytic hydrogenation using a metal catalyst, such as palladium on carbon Pd/C or platinum on carbon Pt/C , and hydrogen gas H2 .I will describe the reaction mechanism for the reduction using sodium borohydride NaBH4 :1. Sodium borohydride NaBH4 is a reducing agent that can donate hydride ions H- to the carbonyl carbon of the aldehyde. The boron atom in NaBH4 has a negative charge and is bonded to four hydrogen atoms. This makes it a good source of hydride ions.2. In the first step of the reaction mechanism, the hydride ion H- from NaBH4 attacks the electrophilic carbonyl carbon of the aldehyde. This results in the formation of a new carbon-hydrogen bond and the breaking of the carbon-oxygen double bond bond .3. Simultaneously, the electrons from the carbon-oxygen double bond move to the oxygen atom, creating a negatively charged alkoxide intermediate.4. In the final step, the alkoxide intermediate abstracts a proton H+ from a solvent molecule usually water or an alcohol , which leads to the formation of the primary alcohol product.Overall, the reduction of an aldehyde using sodium borohydride results in the formation of a primary alcohol, with the carbonyl carbon being converted to an alcohol functional group.