2,3,4-Pentanetrione
# 2,3,4-Pentanetrione

2,3,4-Pentanetrione (or IUPAC name pentane-2,3,4-trione, triketopentane or dimethyl triketone) is the simplest linear triketone, a ketone with three C=O groups. It is an organic molecule with formula $CH_3COCOCOCH_3.$

## Production

2,3,4-Pentanetrione can be made by oxidizing 2,4-pentanedione with selenium dioxide. Ludwig Wolff made the 2,3 oxime by reacting hydroxylamine with isonitrosoacetylacetone in cold, aqueous, concentrated solution.

Yet other ways to make triones start from a β-dione, and oxidise the carbon at the α position, between the two ketone groups. Different methods include reaction with bromine to make a dibromide, and then reacting with acetaldehyde and hydrolysing. Nitrogen oxides can also be used. Another way is by reacting 2,4-pentandedione with p-nitroso-N,N-dimethylaniline; forming an α-diazo-β-dicarbonyl derivative compound, and then reacting that with triphenylphosphine, and then hydrolyzing with sodium nitrite solution. Or the α-diazo-β-dicarbonyl derivative can be treated with tert-butylhypochlorite.

## Properties

2,3,4-Pentanetrione appears as an orangy-red oil. The more intense colour is due to the greater conjugation of double bonds, and potential resonance. The type of colour centre is called a dependent chromophore, as when there are fewer C=O groups the colour is less intense or absent. So diacetyl with two carbonyls groups is yellow, and acetone with one has no colour.

At a reduced pressure of 20 mmHg it boils at 60 °C. It is hygroscopic.

The odour is strong and not bad.

## Reactions

On absorbing water, perhaps from the atmosphere, 2,3,4-pentanetrione forms a hydrate. The hydrate melts at 52 °C. The hydrate with formula $CH_3COC(OH)_2COCH_3$ is colourless.

2,3,4-Pentanetrione is a strong reducing agent. Thermal decomposition catalyzed by copper sulfate results in carbon dioxide and diacetyl.

2,3,4-Pentanetrione reacts with hydrogen peroxide to yield acetic acid and carbon monoxide. Adding HOOH between C2 and C4 yields a cyclic intermediate which decomposes.

With light or organic peroxides, a free radical reaction can take place (as with triketones), whereby the molecule is slit into $CH_3COCO^•$ and $CH_3CO^•$ fragments. These can combine with intact molecules or each other to form other ketones.

When heating 2,3,4-pentanetrione with oxygen, the oxidation products are diacetyl, acetic acid, water and carbon dioxide.

Alkalis convert it into acetic acid and formaldehyde.

2,3,4-Pentanetrione does a condensation reaction with o-phenylenediamine to yield methyl-quinoxaline-2-methylketone, a heterocyclic dicycle. In this the carbon number 2 and 3 react with the amine groups, leaving the CO on number 5 alone.

Another condensation can happen with 2,5,6-triamino-4(3H)pyrimidinone giving 6-acetyl-2-amino-7-methyl-4(3H)pteridinone.

Grignard agents react. Phenyl magnesium bromide in excess reacting with 2,3,4-pentanetrione gives phenylacetylcarbinol and also methyldiphenylcarbinol.

## Derivatives

Derivatives include 2,3,4-pentanetrione-3-oxime, 2,3,4-pentanetrione-3-(O-methyloxime), 2,3,4-pentanetrione-2-oxime, 2,3,4-pentanetrione-2,3-dioxime, 2,3,4-pentanetrionetrioxime, 2,3,4-pentanetrione semicarbazone, 2,3,4-pentanetrione phenylhydrazone, 2,3,4-pentanetrione bis(phenylhydrazone).

The 3-oxime melts at 75 °C and the bis(semicarbazone) has a melting point of 221 °C.

