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Colorimetric detection of urea nitrate: the missing link.
1Casali Institute of Applied Chemistry, The Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel.
Forensic Science International
|November 20, 2010
Summary
This study characterizes the colored products of the urea nitrate colorimetric test. The research clarifies the structure of the protonated Schiff base and its free base, resolving previous ambiguities in explosive detection.
Area of Science:
- Analytical Chemistry
- Forensic Chemistry
Background:
- Urea nitrate is an improvised explosive.
- A colorimetric reaction with p-DMAC (UN-1 reagent) detects urea nitrate.
- The colored product was previously thought to be a free base.
Purpose of the Study:
- To elucidate the colorimetric reaction between urea nitrate and UN-1.
- To characterize the protonated Schiff base and the analogous free base.
- To resolve discrepancies in the literature regarding the colored product.
Main Methods:
- Synthesis and characterization of the unprotonated free base of the p-DMAC reaction product.
- Synthesis and characterization of the analogous free base from p-dimethylaminobenzaldehyde.
- Spectroscopic analysis of both free and protonated forms.
Main Results:
- The dark red product is a protonated Schiff base, not the free base.
- The synthesized free base exhibits distinct spectroscopic properties.
- The protonated Schiff base decomposes to the free base over time.
- Similar differences were observed for the analogous free base.
Conclusions:
- This study provides definitive structural elucidation of the urea nitrate colorimetric reaction products.
- Both colored products function as acid-base indicators.
- The findings clarify the mechanism of urea nitrate detection using UN-1 reagent.
