Question

What is the chemical equation for the decarboxylation of butyric acid with soda lime?

Answer 1

The equation is

`"CH"_3"CH"_2"CH"_2"COOH" + "2NaOH" + "CaO" → "CH"_3"CH"_2"CH"_3 + "Na"_2"CO"_3+ "Ca(OH)"_2`

Explanation:

Decarboxylation is the removal of carbon dioxide from a molecule.

For a carboxylic acid, the reaction would be `"R-COO-H" → "R-H" + "CO"_2`

However, only the sodium or potassium salt undergoes ready decarboxylation.

Soda lime is essentially a mixture of sodium hydroxide, calcium oxide, and calcium hydroxide.

The first step is the reaction of butyric acid with soda lime to form sodium butyrate.

`"CH"_3"CH"_2"CH"_2"COOH" + "NaOH" → "CH"_3"CH"_2"CH"_2"COONa" + color(red)(cancel(color(black)("H"_2"O")))`
`"CaO" + color(red)(cancel(color(black)("H"_2"O"))) → "Ca(OH)"_2`
`stackrel(————————————————————)("CH"_3"CH"_2"CH"_2"COOH" + "NaOH" + "CaO" → "CH"_3"CH"_2"CH"_2"COONa" + "Ca(OH)"_2)`

Second is the decarboxylation of the sodium salt.

`"CH"_3"CH"_2"CH"_2"COONa" + "NaOH" → "CH"_3"CH"_2"CH"_3 + "Na"_2"CO"_3`

The overall equation is the sum of the two equations.

`"CH"_3"CH"_2"CH"_2"COOH" + "NaOH" + "CaO" → color(red)(cancel(color(black)("CH"_3"CH"_2"CH"_2"COONa"))) + "Ca(OH)"_2`
`color(red)(cancel(color(black)("CH"_3"CH"_2"CH"_2"COONa"))) + "NaOH" → "CH"_3"CH"_2"CH"_3 + "Na"_2"CO"_3`
`stackrel(————————————————————————)("CH"_3"CH"_2"CH"_2"COOH" + "2NaOH" + "CaO" → "CH"_3"CH"_2"CH"_3 + "Na"_2"CO"_3+ "Ca(OH)"_2)`