Graduate University of Groningen. Worked as a chemist in companies such as Wilmar Oleochemicals B.V (Botlek Rotterdam) and SABIC (Bergen op Zoom)

Ketone Qualitative Reaction Video

Contents hide

1 Introduction

2 Theory

3 Experiment

4 Conclusion

Introduction

Ketones are widely used in laboratory syntheses, and very often there is a need to test your reaction product for the presence of ketones. The qualitative reaction of sodium nitroprusside allows this to be done. In this topic, I will present a detailed guide on how to do this, with a video tutorial.

Theory

Sodium nitroprusside (SNP) [Fe(CN)₅NO]₂⁻ 2Na⁺, also known as pentacyanonitrosylferrate II, has been documented since 1850. Despite its name, it is not a nitro compound or a prusside, but the colloquial term has become widely accepted. Its structure has been thoroughly established through UV, IR, Mössbauer, and crystallographic investigations. Under specific conditions, SNP can function as a donor of NO or NO+ and can also release cyanide ions.

SNP interacts with carbon nucleophiles, particularly ketones and other carbonyl compounds containing an acidic hydrogen atom. The reaction with acetone has received extensive scrutiny. It is hypothesized that an intermediate forms in which the carbanion (or possibly the enolate anion) binds to the nitrogen atom within the complex. Subsequently, hydrolysis occurs, leading to the release of the oxime derivative.

Ketones exhibit a positive response in this examination. They interact with alkali, producing an anion that subsequently undergoes a reaction with sodium nitroprusside, resulting in the formation of a colored complex ion. Conversely, aldehydes do not elicit a reaction in this test.

The chemical reactions with acetone as an example:

CH₃COCH₃ + OH^–→ CH₃COCH₂^– + H₂O

[Fe(CN)₅NO]^2- + CH₃COCH₂^– → [Fe(CN)₅NO.CH₃COCH₂]^3-

Note: The emergence of a red hue indicates the presence of a ketone.

Experiment

Take acetone 0.5-1 ml;
Ketone substance (in the video phenylacetone is taken) 0.5-1 ml;
An aqueous solution of sodium nitroprusside (100 ml water per 1 g sodium nitroprusside) is prepared;
An aqueous solution of NaOH (10 ml water per 1 g NaOH) is prepared;
A NaOH aqueous solution 0.5-1 ml and aqueous solution of sodium nitroprusside K2[Fe(NO)(CN)5] 0.5-1 ml are added into the test tube with ketone.

Red color confirms the ketone presence.

Ketones Phenylpropanone Qualitative Testing

Conclusion

As you can see, this method is quite simple and doesn’t take a lot of time and reagents. Every beginner chemist can repeat this elementary experiment.

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