Patent Watch
July 27, 2009
Here’s an improvement on luminol synthesis and its use to detect blood. C. C. Lopes and co-inventors provide a simple and safe method for producing hydrazide compounds that can be made to undergo chemiluminescence under oxidizing conditions. In particular, they describe a new process for synthesizing luminol and using it in a blood-testing kit that does not require the use of UV light. (Readers who watch television programs such as CSI will be familiar with the method used to detect traces of blood at crime scenes.)
The synthesis of luminol (4) begins with the nitration of phthalic anhydride (1) with HNO3–H2SO4 to form nitrophthalic acid 2; however, no specific details are given for this step. Hydrazide 3 is made by the reaction of 2 with H2NNH2 in the presence of NbCl5. It known that this reagent is a mild Lewis acid, and its use in this reaction is the key aspect of the patent. The inventors suggest that the reaction is likely to proceed via the acid chloride because Nb2O5 is formed in this step.
The final stage to make 4 is the reduction of the nitro group in 3, but again full details are not given. The inventors briefly mention the use of Na2S2O4 or catalytic hydrogenation over a Pd/C catalyst for this reduction.
The blood-test kits consist of two solutions that, when mixed with traces of materials containing iron, produce chemiluminescence and a strong blue color. The iron catalyzes the reaction and only traces are needed—hence the use of the technique for detecting blood.
The two components are an alkaline solution of ~5 g/L of 4 and a ~3% alkaline solution of H2O2. In each case, the preferred base is an alkali metal hydroxide. By using an alkaline solution of H2O2, the chemiluminescence reaction can be seen for longer than otherwise and without the need for UV light. The inventors report that the base stabilizes the H2O2 solution and slows its degradation. Conventional kits contain weaker bases such as Na2CO3 or Na3BO3 that do not maintain the chemiluminescence reaction as long as the solutions in the present invention. (Universidade Federal do Rio de Janeiro–UFRG [Brazil]. US Patent 7,517,983, April 14, 2009; Keith Turner)
View patent information from CAS.
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