Synthesis of Fingerprint Reagents: Aromatic Nucleophilic Substitution as a Route to 5-Substituted Ninhydrins

Abstract

An efficient synthesis of 5-substituted 2,2-dimethoxy-1,3-indanediones by nucleophilic displacement of the parent 5-bromo derivative by oxygen, sulfur and selenium-based nucleophiles has been developed. Mild acid hydrolysis of the ketals enables their smooth conversion into the corresponding ninhydrins, which are potential fingerprint reagents.Despite the continuing search for alternative reagents for the development of latent fingerprints on paper, none has been found with sufficient advantages in performance and cost to supplant ninhydrin (1). Thus, while there are some drawbacks associated with the use of 1, 1-4 it is superior in terms of its combined reactivity, solubility, ease of detection, and economy. The development of the print relies upon the reaction of the ninhydrin with α-amino acid residues adhering to the paper to give a deeply colored product 2 known as Ruhemann's purple 5 and, over the years, considerable effort has been directed to the synthesis of ninhydrin analogues 6 and related compounds. 7 In a more recent development, the visualization of weakly developed prints can be enhanced by utilizing the fluorogenic properties of Ruhemann's purple when complexed with zinc(II) or cadmium(II) salts. 2,8 In view of the observation 4,9 that the complex derived from 5-methoxyninhydrin (3) has been found to possess fluorogenic properties superior to those of the product from 1, it has been suggested 9 that the modified ninhydrin most likely to produce enhanced prints is that with substitution at the C-5 position rather than at C-4. In this context, it is noteworthy that sulfur-containing ninhydrins such as 5-methylthioninhydrin (4) have recently been claimed 10 to surpass both 1 or 3 as a fingerprint reagent. Syntheses of 4 have recently been reported. 10,11 The preparation of the related species, thianinhydrin 5, has recently been described 6 and shown to be as effective as ninhydrin. Considering the favorable properties conferred by the methoxy and methylthio groups upon the Ruhemann's purple complex derived from ninhydrin (1), we felt it important to probe whether such activity could be further enhanced by the next Group VI member, the selenium-based ninhydrin 6. The preparation of 5-methylselenoninhydrin (6) was, therefore, the primary goal of this work. An additional aim, however, was to develop alternative, readily achievable, efficient and economical strategies to the synthesis of analogs of 4 and 6, such as their aryl derivatives 7 and 8. Furthermore, we were conscious of the fact that the type of chlorofluorocarbon solvents that have been commonly employed in the protocols involving development of fingerprints over many years are in the process of being phased out worldwide. It was therefore considered essential to prepare ninhydrins which have increased solubility in hydrocarbon solvents, the likely replacements for the freons. Accordingly, a further goal was the synthesis of the aryl ether 9 together with other ethers, as well as the 5-alkoxy-, 5-alkylthio-and 5-alkylseleno derivatives of ninh...

Comparison of methods to develop fingerprints on papers impregnated with AB‐PINACA and AB‐FUBINACA

“…A representative sampling of the paper is necessary for correct sample selection in the analysis [32] ble while iodine vapor would make oil-rich fingerprints apparent [5,10,[20][21][22][23]39].…”

“…Protein and amino acid components are concentrated in eccrine‐rich fingerprints, while fatty and fatty acids are concentrated in sebaceous (oil)‐rich fingerprints. Therefore, it was an expected case that ninhydrin, DFO (9‐diazafluerone), 1,2 indanedione, 5‐MTN [5‐(methylthio)ninhydrin], and termanin fingerprint development methods would make eccrine‐rich fingerprints visible while iodine vapor would make oil‐rich fingerprints apparent [5,10,20–23,39].…”

“…Iodine vapor, thermanin, ninhydrin, DFO (9‐diazaflueron), 1,2‐indanedione, and 5‐MTN‐ [5‐(methylthio)ninhydrin] combined with zinc chloride fingerprinting methods were applied to SC‐impregnated papers [10,19–25]. The paper surfaces were immersed in termanin solutions, ninhydrin, DFO (9‐diazafluerone), 1,2‐indanedione, and 5‐MTN [5‐(methylthio)ninhydrin] combined with zinc chloride, which were placed in one‐time‐used separate glass containers, and the samples were left to dry in a fume hood.…”

“…It was dipped into the working solutions placed in separate glass containers, and each paper was kept in the solutions until it was completely wet. SC-impregnated papers were left to dry for about 1 h at room temperature on a clean flat surface.2.3.4 | Development of latent fingerprintsIodine vapor, thermanin, ninhydrin, DFO (9-diazaflueron), 1,2-indanedione, and 5-MTN-[5-(methylthio)ninhydrin] combined with zinc chloride fingerprinting methods were applied to SC-impregnated papers[10,[19][20][21][22][23][24][25]. The paper surfaces were immersed in termanin solutions, ninhydrin, DFO (9-diazafluerone), 1,2-indanedione, and 5-MTN[5-(methylthio)ninhydrin] combined with zinc chloride, which were placed in one-time-used separate glass containers, and the samples were left to dry in a fume hood.…”