2,4-DNP spot test for solid-supported aldehydes; hydrazones

Daniel Hamza ([email protected]),
A contribution from the Caddick Group, Sussex

Chemicals Used
2,4-dinitrophenylhydrazine solution in solid-supported aldehyde

Procedure
This test is used to look for the disappearance of an aldehyde after a solid phase reductive amination or reduction. 2,4-Dinitrophenylhydrazine reagent: Dissolve 3 g of 2,4-Dinitrophenylhydrazine in 15 mL of conc. sulfuric acid. This solution is then added with stirring to 20 mL of water and 70 mL of 95% ethanol. This solution is mixed thoroughly and filtered. A few beads of resin are swollen in a drop of DMF and a single drop of 2,4-DNP solution is added. A positive result is orange-red.

Author's Comments
It is best to wash the beads with DMF in an Alltech tube (or a Pasteur pipette with a cotton wool plug) to remove the coloured 2,4-DNP solution. Also, perform the colour test on a negative control resin containing no carbonyl functionality as well as on the starting aldehyde resin to gauge the colour change. Despite the fact that the resin tends to also be a yellow colour, this test is actually pretty reliable providing you also perform the control experiments mentioned above.

Data
N/A

Lead Reference
1. Furniss, Hannaford, Smith and Tatchell: Vogel's Practical Organic Chemistry, 5th Edition, John Wiley & Sons, New York p1218 and 1257. 2. Anal. Biochem. 1972, (49), 436. 3. Anal. Chim. Acta., 1974, (69), 481.

Other References

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