Question

How can I convert formaldehyde to acetone?

Answer 1

Nucleophilic Substitution and Elimination with alkyl halides.

Explanation:

You would need to add a methyl group to each of the hydrogens of formaldehyde. My understanding is that this would be best accomplished with an alkyl halide, such as methyl chloride.

`H-CO-H + 2H_3C-Cl -> H_3C-CO-CH_3`

Answer 2

How about this?

Explanation:

Step 1. Preparation of methylmagnesium bromide

`underbrace("CH"_3"Br")_color(red)("bromomethane") + "Mg" stackrelcolor(blue)("dry ether"color(white)(mm))(→) underbrace("CH"_3"MgBr")_color(red)("methylmagnesium bromide")`

Step 2. Grignard addition to formaldehyde

`underbrace("CH"_2"(=O)")_color(red)("formaldehyde") stackrelcolor(blue)("1. CH"_3"MgBr; 2. H"^"+"color(white)(mm))(→) underbrace("CH"_3"CH"_2"OH")_color(red)("ethanol")`

Step 3. Oxidation of ethanol

`"CH"_3"CH"_2"OH" stackrelcolor(blue)("PCC"color(white)(mm))(→) underbrace("CH"_3"CH(=O)")_color(red)("acetaldehyde")`

`"PCC"` is pyridinium chlorochromate.

It is essentially a milder version of chromic acid. It oxidizes primary alcohols to aldehydes, but it does not oxidize aldehydes to carboxylic acids.

Step 4. Grignard addition of another mole of `"CH"_3"MgBr"`

`"CH"_3"CH(=O)"stackrelcolor(blue)("1. CH"_3"MgBr; 2. H"^"+"color(white)(mm))(→) underbrace("CH"_3"CHOHCH"_3)_color(red)("propan-2-ol")`

Step 5. Oxidation of propan-2-ol

`"CH"_3"CHOHCH"_3 stackrelcolor(blue)("K"_2"Cr"_2"O"_7, "H"^"+"color(white)(mm))(→) underbrace("CH"_3"C(=O)CH"_3)_color(red)("acetone")`