characterize. Due to the complexity of the reduction to produce
the hexamethylenetetramine and the low yield of the subsequent
derivatization, reduction by sodium amalgam to give hydrazine
was favored. The reduction of RDX by sodium amalgam to give
hydrazine is the first reported chemical transformation of this
molecule that does not result in the cleavage of the N–N bond.
It should be noted that a small amount of THF as a co-solvent
to aid solubility of the RDX is necessary as without THF no
reduction is observed.
azines produced were discounted almost immediately due to the
relatively low SERRS obtained. The remaining seven were
examined in more detail (Scheme 2). All of the azines shown in
Scheme 2 gave effective SERRS, however, the best signals
were obtained from a specifically designed pyridine azo dye
synthesized by azo coupling of diazotised m-aminopyridine
with salicylaldehyde. Work into the ultra-sensitive detection of
the hydrazine produced by controlled reduction of RDX will be
reported soon as initial experiments indicate that detection of
the azine by SERRS can be achieved at 10 femtomoles.
In conclusion, the reduction of RDX has been examined in
detail and a new route that maintains the N–N bond discovered.
This allowed the formation of hydrazine from RDX as opposed
to other compounds that are harder to derivatize for subsequent
sensitive detection. Initial detection of the trapped products
indicated that ultra-sensitive detection by SERRS was possible
and shows considerable promise. It should be noted that the new
chemistry described here would work with other techniques.
The authors wish to thank the Home Office UK for funding
to C. M. and the BBSRC for the award of a David Phillips
Fellowship to D. G.
The mechanism for the reduction of RDX by the sodium
amalgam is unclear but based on our observations and those of
others we propose the following. Initially the reduction of a
nitro group to the amine occurs followed by base promoted
collapse of the ring system to give hydrazine. A report by Duden
and Scharff26 indicated that 1,3,5-trinitroso-1,3,5-triazacyclo-
hexane could be reduced to 1,3,5-triamino-2,4,6-hexahydro-s-
triazine under similar conditions, however, this compound
could only be isolated as the Schiff base derivative. Subsequent
27
28
29
reports by Stolle, Lamberton, Bonner et al. and Neilsen et
30
al. showed that these types of s-triazines were highly unstable
hence supporting our proposed mechanism to give hydrazine.
Additionally, electrochemical reductions of secondary ni-
tramines give hydrazines via the N-nitroso derivatives support-
ing our proposed mechanism.31 Further to this our experimental
evidence from the reduction of RDX by hydrogenation
indicated the presence of RDX minus one nitro group, which
then rearranged to hexamine as the stable product. In the
reduction by the sodium amalgam we could not detect any
hexamine formation indicating that the mechanism was clearly
different to that of the other reducing agents.
Notes and references
1
J. Yinon, Modern Methods and Aplications in the Analysis of
Explosives, Wiley, 1993.
2
3
4
P. Kolla, Anal. Chem., 1995, 67, 184A.
P. Kolla, Angew. Chem., Int. Ed. Engl., 1997, 36, 801.
K. G. Furton and L. J. Myers, Talanta, 2001, 54, 487.
5 R. Speller, Radiat. Phys. Chem., 2001, 61, 293.
6 G. E. Spangler, J. P. Carrico and D. N. Campbell, J. Test. Eval., 1985,
13, 234.
The trapping of the hydrazine with a number of different
carbonyl functionalities was investigated. For the species to be
useful for subsequent detection by SERRS it was desirable to
incorporate a color into the final product. This was achieved
through reaction of 2 mol of an aldehyde or ketone with 1 mol
of hydrazine. If only 1 mol of the carbonyl reacts then a
hydrazone was formed which was less favourable for SERRS.
In total 16 aldehydes and ketones were used to trap the
hydrazine and give coloured azines. The aldehydes and ketones
were chosen on the basis of previous knowledge for the design
of effective SERRS species and included surface complexing
molecules such as pyridine and 8-hydroxyquinoline. Nine of the
7
8
9
D. D. Fetterolf and T. D. Clark, J. Forensic Sci., 1993, 38, 28.
J. Yinon, Mass Spectrom. Rev., 1982, 1, 257.
J. Petrousky, Gordon Research Conference on Explosives Detection,
Queens College, Oxford, England, 1997.
1
1
1
0 D. H. Fine, FBI Academy, Quantico, USA, 1983, p. 159.
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2 J. C. Bart, L. L. Judd and A. W. Kusterbeck, Sens. Actuators B:
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4 U. Narang, P. R. Gauger and F. S. Ligler, Anal. Chem., 1997, 69,
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6 J. S. Yang and T. M. Swager, J. Am. Chem. Soc., 1998, 120, 11864.
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1
2
2
2
2
2
2
8 R. Keir, E. Igata, M. Arundell, W. E. Smith, D. Graham, C. McHugh and
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2
1 T. Urbanski, Chemistry and Technology of Explosives III, Pergamon
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2 L. Stefaniak, T. Urbanski, M. Witanowski, A. R. Farminer and G. A.
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7
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2
2
6 P. Duden and M. Scharff, Jutsus Liebigs Ann. Chem., 1895, 218.
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Scheme 2 Reagents and conditions: (i) p-C
ii) m-C NCHO, EtOH, 20 min, 64% (iii) o-C
3% (iv) p-C N(N )C (OH)CHO, EtOH, 20 min, 75% (v) p-
NCOCH , EtOH, AcOH, D, 20 min, 50% (vi) 8-HOC10 NCHO,
EtOH, 20 min, 84% (vii) (CH NC10 CHO, EtOH, AcOH, D, 12 h,
7%.
5
H
4
NCHO, EtOH, 20 min, 75%
29 T. G. Bonner, R. A. Hancock and J. C. Roberts, J. Chem. Soc., Perkin
Trans. 2, 1972, 1902.
30 A. T. Nielsen, D. W. Moore, M. D. Olgan and R. L. Atkins, J. Org.
Chem., 1979, 44, 1678.
31 M. Hudlicky, Reductions in Organic Chemistry, Ellis Horwood Ltd,
Chichester, UK. 1984.
(
9
C
H
5 4
5 4
H NCHO, EtOH, 20 min,
H
5 4
2
H
6 3
H
5 4
3
H
5
)
3 2
H
6
4
CHEM. COMMUN., 2002, 2514–2515
2515