Joseph Almog, 1 Ph.D.; Amiram Hirshfeld, 1 Ph.D.;
and J. T. Klug,2 ph.D.
Reagents for the Chemical Development of Latent
Fingerprints: Synthesis and Properties of Some
REFERENCE: Almog, J., Hirshfeld, A., and Klug, J. T., "Reagents for the Chemical De-
velopment of Latent Fingerprints: Synthesis and Properties of Some Ninhydrin Analogues," Jour-
nalofForensic Sciences, JFSCA, Vol. 27, No. 4, Oct. 1982, pp. 912-917.
ABSTRACT: In an attempt to design new reagents for the chemical development of latent finger-
prints, a number of ninhydrin analogues were synthesized and their reactions with latent finger-
prints on paper were studied. The ring-fused and substituted ninhydrins developed latent finger-
prints with a sensitivity similar to that of ninhydrin. The most promising of the group was
2,2-dihydroxybenz[f]indane-l,3-dione, which developed latent fingerprints as dark green images
with excellent resolution.
KEYWORDS: criminalistics, fingerprints, reagents, ninhydrin
It was recognized long ago that among the ingredients of palmar sweat amino acids are
probably the most suitable substrates for the chemical development of latent fingerprints on
porous surfaces [1-3]. It appears, however, that even ninhydrin (I), a universal reagent for
the amino acids used in the development of latent fingerprints, was not developed on any
theoretical basis but was instead discovered by coincidence. Its special reactivity with amino
acids was postulated, in 1910, only after the discoverer, S. Ruhemann, had observed that the
new compound stained the skin . Ninhydrin was adopted for the detection of latent finger-
prints on paper in 1954  and since then has become the most common reagent for the
chemical development of latent fingerprints. As ninhydrin formulations suffer from certain
disadvantages [1,6, 7], several groups of researchers have tried to modify them to improve
their properties. The modifications involved variations in concentrations, solvents, and pH
. Some of these were very beneficial, such as the nonflammable ninhydrin formulation
We thought that a different approach to latent fingerprint development could be a chemi-
cal modification of the ninhydrin molecule itself. To the best of our knowledge such an ex-
periment has never been done before in forensic chemistry. The idea seemed even more en-
couraging after we read the following paragraph, which Professor Rubin wrote in 1975 :
There is no reason, a priori, why other triketones should not react with amino acids in a man-
ner analogous to ninhydrin. In fact, colored products . .. have been observed in reactions with
Received for publication 17 Nov. 1981; revised manuscript received 28 Jan. 1982; accepted for pub-
lication 4 Feb. 1982.
1Deputy head, Research and Development Division, and head, Laboratories Section, respectively,
Israel Police Headquarters, Jerusalem, Israel.
2Senior scientist, Research and Development Foundation, Ben-Gurion University, Beersheva, Israel.
Copyright © 1982 by ASTM International
ALMOG ET AL . LATENT FINGERPRINTS 913
Thus, we prepared the two benzoninhydrins, 2,2-dihydroxybenz[e]indane-l,3-dione (II)
and 2,2-dihydroxybenz[f]indane-l,3-dione (III), and the substituted ninhydrin, 2,2-dihy-
droxy-5-ehloro-6-methoxyindane-l,3-dione (IV) (Fig. 1), and examined their reactions with
latent fingerprints on paper.
The substituted and ring-fused ninhydrins (VII, Fig. 2) were prepared by adopting the
method suggested by Becket  for the synthesis of unsubstituted ninhydrin. The starting
materials were the corresponding dimethyl esters (V), which were reacted with dimethyl
sulfoxide in the presence of sodium metboxide (Fig. 2). The intermediate compounds (VI)
were not purified and no attempts were made to optimize the yields.
Latent fingerprints were collected from different persons on a commonly used white
groundwood-free paper. Three fingerprints from each hand were developed, each one by a
different ninhydrin analogue (Compounds II to IV). A fourth fingerprint was developed by
ninhydrin for comparison (Fig. 3). The reagents were applied to the latent prints by gently
I~ o H
I 2,2-dihydroxy-l,3-indanedione (ninhydrin)
I1 2,2-dihydroxybenz[e]indane-l,3-dione (benzo[e]ninhydrin)
IV 2,2-dihydroxy-5-chloro-6-methoxyindane- 1,3-dione
FIG. l--Ninhydrin and some analogues.
[~ c ~ 1 7 6 § C % S O C H 3
FIG. 2--Becker's method  as adopted for the synthesis of substituted and ring-fused ninhydrin.
914 JOURNAL OF FORENSIC SCIENCES
FIG. 3--Impressions of six-week-old latent fingerprints from a good donor obtained with the
ninhydrin analogues: (a) Compound II: (b) Compound III." (e) Compound IV," and (d) ninhydrin.
swabbing the paper with a cotton wool swab soaked with a 1% methanolic solution of the
compound containing a trace of glacial acetic acid. The prints were then developed either at
room temperature or in a dry oven (120~ for 2 min.
2,2-Dihydroxybenz[f]indane-l,3-dione (III) was prepared according to Jones and Wife
 from dimethyl naphthalene-2,3-dicarboxylate  and dimethyl sulfoxide.
2,2-Dihydroxybenz[e]indane-l,3-dione (II) was prepared on a 10-mmole scale by the same
method  from dimethyl naphthalene-l,2-dicarboxylate  and dimethyl sulfoxide. The
product (II) had the same physical properties as 2,2-dihydroxybenz[e]indane-l,3-dione
prepared earlier by a different method .
2,2-Dihydroxy-S-chloro-6-methoxyindane-l,3-dione (IV) was prepared by the same
method  from dimethyl 3-chloro-4-methoxyphthalate (Fig. 2, Compound V, R = 3-chloro-
4-methoxy-). It was fully characterized by its mass spectrum and by nuclear magnetic
resonance, infrared, and ultraviolet spectroscopy. Full details will be reported shortly.
Fresh solutions of all three ninhydrin analogues (II to IV) developed latent prints on paper
with a sensitivity similar to that of ninhydrin. Sensitivity was judged by the fingerprint tech-
nicians and was based on visual impressions of a large number of fingerprints from the same
person. The quality of the fingerprint donors was assessed by the quality of their ninhydrin-
developed latent fingerprints, and the analogues gave excellent results with latent prints taken
from good donors while poor impressions were formed from fingerprints from poor donors.
ALMOG ET AL . LATENT FINGERPRINTS 915
Rate of Reaction
The ring-fused ninhydrin (III) reacted at the same speed as ninhydrin both at room
temperature and in the oven (colors reached maximum intensity at the same time). The
substituted ninhydrin (IV) did not react as quickly under the same conditions, and the second
benzoninhydrin (II) was the slowest to react (about twice the time for complete development).
Latent fingerprints that were developed by the substituted ninhydrin (IV) came out as
purple impressions, very similar to the Ruhemann's purple obtained with ninhydrin. The
ring-fused ninhydrins, on the other hand, gave different colors: benzo[e]ninhydrin (II) gave
pink impressions while benzo[f]ninhydrin (III) gave blue-green impressions, with very good
contrast and resolution.
For a more definite color characterization all four compounds were reacted in solution
with the amino acid alanine (1% solution in methanol, boiled for 1 min) and the visible spec-
tra of the solutions were recorded after cooling. Data are listed in Table 1.
Latent fingerprints were examined at ages from a few minutes to six weeks. The quality of
the development was found to be age-independent and old fingerprints came out as well as
fresh ones with all four reagents.
A faint background discoloration of the same color as the developed prints was observed
in all the experiments, ninhydrin included. This effect was stronger when development was
accelerated by heat.
The visible impressions developed by all four compounds were stable for at least a few
months. On a few of the prints the blue-green impressions obtained with Compound III
slowly changed to dark purple, retaining the good resolution.
The present theory of the mechanism of the reaction between ninydrin and amino acids
specifies at least five consecutive stages . It was therefore difficult to assume exactly how
a certain alteration of the ninhydrin molecule would affect the reaction of the compound
with amino acids. It seemed logical, however, to try such modifications as would lead to pro-
TABLE 1--Absorption maxima of the reaction mix-
tures of ninhydrin analogues and alanine (1% meth-
anolie solution) (Cary 15 spectrophotometer).
)kmax, Absorption in nm
916 JOURNAL OF FORENSIC SCIENCES
0- 0 0- 0
0 o 0 o
FIG. 4--Ruhemann '~ purple (VIlI). the final product of the ninhydrin reaction with amino acids 
and the assumed product of the benzoninhydrin (IID with amino acids (IX).
ducts having the longer conjugated systems (Fig. 4) that are expected to show stronger ab-
sorption of light  with maximum absorption at longer wavelengths  (bathochromic
shift) as compared with Ruhemann's purple. The two benzoninhydrins (II and III) were
therefore the first candidates for preparation and examination.
Substituents on the aromatic ring, because of their electronic effects, might also affect the
physicochemical properties of the compound. Attempts to prepare ninhydrin analogues
bearing strong electron-withdrawing substitue~ts such as nitro or dichloro were not par-
ticularly successful. Using the 3- and 4-nitrophthalates (V) (R = 3-NO 2 and 4-NO2, respec-
tively) as starting materials gave highly colored products of unidentified structure while
dimethyl 3,4-dichlorophthalate (V), (R = 3,4-di-chloro) under the strong basic conditions of
the reaction gave the desired product, 2,2-dihydroxy-S,6-dichloroindane-l,3-dione (VII) (R =
5,6-di-chloro) only in very low yield, the major product being 2,2-dihydroxy-5-chloro-6-meth-
oxyindane-l,3-dione (IV). The latter compound (IV) was then prepared by an unambiguous
route from dimethyl 3-chloro-4-methoxyphthalate (V) (R = 3-chloro-4-methoxy).
As expected, the three ninhydrin analogues were found to be quite efficient developers of
The close similarity of the developing properties of ninhydrin and the substituted
ninhydrin (IV) can be attributed to the structural proximity (the combination of chloro and
methoxy substituents on the aromatic ring in Compound IV, on the basis of their electronic
effects, is not expected to vary the chemical properties a great deal).
The dark green product of benzo[f]ninhydrin (III) with amino acids and with latent
fingerprints represents a considerable bathochromic shift compared with Ruhemann's pur-
ple. However, it is too early to ascribe the green color to Structure IX because the product
has not been isolated and characterized.
In conclusion, while the sensitivity of the new reagents for detecting latent fingerprints is
not greater than that of ninhydrin, this study has nevertheless clearly shown that they can be
designed and prepared by a stepwise modification of known reagents. In addition, we have
recently obtained positive results in a similar study on the chemical modification of another
fingerprint reagent, orthophthaladehyde [t6]. That study will be reported shortly.
From an operational point of view, 2,2-dihydroxybenz[f]indane-l,3-dione (III) shows the
greatest potential as a reagent and we are studying its possible advantages over ninhydrin,
particularly its use on colored papers and for photographing the resulting images.
Most of the work on syntheses in this project was carried out at the Department of
Organic Chemistry, The Weizmann Institute of Science, Rehovot, Israel. The authors are
indebted to Professor Yehuda Mazur, Head of the Department, for this privilege. The
authors also thank Dr. Shmuel Zitrin, Head of the Mass Spectrometry Unit, Criminal Iden-
tification Division, Israel Police Headquarters, for running the mass-spectral analyses o[ the
ALMOG ET AL i LATENT FINGERPRINTS
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Part V. Derivatives of
Joseph Almog, Ph.D.
Research and Development Division
Israel Police Headquarters