The reaction of Grignard reagent with formaldehyde followed by acidification gives (a) An aldehyde (b) A ketone (c) A carboxylic acid (d) A primary alcohol

Grignard reagents are a cornerstone of organic synthesis, acting as a highly reactive form of carbanion equivalent. To understand how these useful compounds are created, one must delve into their chemistry.

The formation begins with an organic halide, typically a bromide or iodide due to their reactivity, reacting with metallic magnesium. This reaction must occur within dry ether, which serves as a solvent. Ether is used because it can stabilize the Grignard reagent through coordination to the magnesium atom.

An important aspect to remember about creating Grignard reagents is the stringent requirement for anhydrous conditions. Moisture must be strictly avoided because the reagent is highly reactive toward water, leading to the immediate destruction of the carbanion through protonation. Consquently, the setup and handling call for meticulous dryness, often implemented with techniques such as flame-drying glassware and using syringes or cannulas for transfers.

Once formed, the Grignard reagent can react with various electrophiles; in the case of our exercise, formaldehyde. This reaction is pivotal as it forms an alkoxide intermediate – a critical step towards synthesizing alcohols.

When the Grignard reagent (RMgX) meets formaldehyde (HCHO), the carbon atom from the Grignard reagent acts as a nucleophile, attacking the electrophilic carbon in formaldehyde. This nucleophilic addition results in the creation of an alkoxide intermediate. It's fascinating to observe how the polar bond in formaldehyde, due to the difference in electronegativity between carbon and oxygen, is a driving force that enables the nucleophilic attack to take place.

In this intermediate state, the oxygen atom bears a negative charge which is stabilized by the magnesium ion. This stability is temporary, however, as the next step involves the conversion of this charged oxygen into a neutral alcohol group. The full potential of the alkoxide is thus not realized until it is transformed into an alcohol through an acid work-up.

The final leap in the journey from a Grignard reagent to a primary alcohol is the process of acidification. The previously formed alkoxide intermediate is eager to shed its negative charge and does so by acquiring a proton from an acid, typically water or a diluted acid, in a procedure known as 'acid work-up'.

Through this acid work-up, the negatively charged oxygen of the alkoxide gets protonated, thus neutralizing its charge and converting it into a hydroxyl group. The result of this elegant chemical ballet is a primary alcohol, characterized by having the hydroxyl group (-OH) bonded to a terminal carbon atom, which itself is connected to only one other carbon atom.

This process of synthesizing primary alcohols through Grignard reaction with formaldehyde is particularly noteworthy due to the precise increase in the carbon chain by one carbon atom - the very one contributed by the formaldehyde. It serves as a fundamental method for chain elongation in organic synthesis, allowing for the systematic creation of more complex molecules from simpler ones.