Preparation of cyanoacrylate derivatives and comparison of dual action cyanoacrylate formulations
Introduction
The synthesis of cyanoacrylate derivatives for the purpose of fingerprint visualisation has been studied before [1]. These derivatives, to which a fingermark normally is exposed after cyanoacrylate treatment, are designed to have certain optical properties. One can choose these properties for fluorescence, IR-activity or introduce a certain colour.
The mechanism of the polymerisation has been described extensively [1]. The anionic nucleophilic addition of a fingermark constituent can initiate the polymerisation [2], [3], under catalytic influence of water [4]. The intermediate, stabilised by the two electron withdrawing groups, ethyl ester on one side and the nitrile on the other readily propagates to reasonable polymer lengths.
One of the main reasons for targeting this type of molecules is their ability to visualise latent fingermarks and keep the possibility of obtaining a DNA profile. Whereas the use of conventional fluorescent dyes has been shown to be incompatible with DNA isolation [5].
We propose a synthetic route towards cyanoacrylates, which have potential high ultraviolet (UV) activity or fluorescent properties. These properties could shorten the time needed for visualisation of latent fingermarks, as an extra enhancement step could be avoided. The development of fingermarks on rather difficult surfaces, such as masking tape, glossy paper and expanded polystyrene, could see great advantages of these developments. The difficulties mainly lie in the background staining causing interference, when conventional staining is applied.
At present methyl- or ethylcyanoacrylates are used for visualisation of fingermarks. Most of the marks developed in this way need further enhancement with fluorescent reagents to increase the visibility. Our objective is to introduce a UV active or fluorescent group at the R1 and R2 positions, Fig. 1, and at the same time retain the polymerisation potential of the acrylate.
Previous results indicate that variations at the ester group have more potential, because additions of more steric hindrance at the R2 position probably decrease the polymerisation activity. We will, however, synthesise derivates with variations at both positions. Potential UV active groups are; 2-methylthiophene, 3-methyl furan 2-methylfuran, and para-substituted benzyl and dansyl derivatives. A thiophene can easily be introduced at the R2 position.
The Steglich esterification, Fig. 2, is known as a mild method, which is used for synthesis of a series of different esters. The Steglich esterification makes use of carbodiimides with a catalytic amount of 4-(dimethylamino)pyridine (DMAP) [6].
EDC is the most popular carbodiimide for the Steglich esterification, as it is water-soluble and can easily be separated from the reaction mixture. Due to two electron-withdrawing groups, the reaction proceeds via a ketene intermediate, as suggested by Melman et al., as shown in Fig. 3 [7].
The esters were converted into cyanoacrylates via a Knoevenagel condensation, Fig. 4.
The reaction was carried out with triphenylphosphine (TPP) and three types of aldehydes: formaldehyde, furan-2-carbaldehyde and furfural. The reaction was carried out in a radiation microwave, which shortens the reaction time and delivers good results.
Triphenylphosphine acts as a mild Lewis base to induce the reaction, as proposed by Yadav and co-workers, Fig. 5 [8].
Previous results showed that the formed cyanoacrylates form oligomers or even polymers. These oligomers or polymers can be cracked, Fig. 6, and purification of the final cyanoacrylate takes place by distillation [9].
In recent years, several commercially available formulations of cyanoacrylate have been manufactured and marketed as ‘one-step’ fuming reagents. In particular CN-Yellow (TM), Lumicyano (TM) and Polycyano UV (TM) caught our attention, as the results presented by the manufacturers looked very promising. From the fact sheets provided by the manufacturers we assume that formulation of these mixtures consists of a powder form of cyanoacrylate (either in polymeric or oligomeric form) and a fluorescent dye.
In literature, as far as we could find, a paper by Weaver and Clay in 1993 is the first to report on a one-step fluorescent cyanoacrylate technique for the visualisation of fingerprints [10]. In this report cyanoacrylate is used in combination with a compound from the class of styryl colouring agents. In 1998 Hirano and co-workers report on the use of several dyes in combination with cyanoacrylate [11]. The latest reports on generating fluorescence in cyanoacrylate treated fingerprints with p-DMAB [12] and Polycyano UV [13].
In the studies described in this paper we aimed to compare laboratory prepared polycyanoacrylate derivatives with the commercially available reagents, with respect to the polymer chain length. It is in no way our aim to discover the formulation of the commercial products.
Fluorescence in a polycyanoacrylate can be induced by mixing in a colouring/fluorescent agent with a oligo- or polycyanoacrylate, or by reacting a colouring/fluorescent moiety with the acrylate monomer to produce a functionalized solid oligo or polycyanoacrylate. A brief literature search on polymerisation of ethylcyanoacrylate learned that not only the initiation of the polymerisation by secondary and tertiary amines and phosphines has been described, but also the degradation of such species [2], [14].
In respect to the comparison of the discussed formulations, we added the following question to the study: Can a fluorophore initiated oligo- or poly-cyanoacrylate be used as an agent for the visualisation of latent fingerprints? For this study we chose to use previously described fluorophores p-DMAB [12], p-DMAC [15], [16] and dansylchloride (DNSC) [17], [18].
Section snippets
Materials
Polycyano UV was purchased from Foster and Freeman (Evesham, UK), cyanoacrylate from BVDA (Haarlem, NL), DMAB, DMAC and DNSC (all > 99%) were obtained from Sigma Aldrich (Zwijndrecht, NL). CN-Yellow was purchased from Arrowhead Forensics (Lenexa, KS, USA). Lumicyano was obtained from Global Forensics (Coventry, UK). Methanol and acetone (both HPLC grade) were purchased from Fisher Scientific (UK).
Cyanoacetic acid ≥ 99%, 4-dimethylaminopyridine ≥ 99%, methylthiophene 98%, p-formaldehyde 95%,
Synthesis of derivatives
A) The alcohol (0.1 mmol) and DMAP (0.1 mmol) are added to a pre-stirred solution of cyanoacetic acid (1.2 mmol) and EDC (1.2 mmol) in acetonitrile. The reaction is refluxed for 4 h and is quenched with NH4Cl. The water layer is extracted with CH2Cl2. The organic layer is dried with sodium sulfate and the solvent removed under reduced pressure.
B) The aldehyde (1.0 mmol), ester (1.2 mmol) and the TPP (0.2 mmol) are added together in a microwave tube. The reaction takes place at 90 °C in a radiation
Synthesis of derivatives
Esterification of cyanoacetic acid with EDC proved to be a mild esterification method and provided thiophene-, furan- and dansyl derivates in good yields. The reaction with furan still contained 30% of starting material at the described reaction conditions, but can be driven to full conversion by longer reaction time. Aromatic esters are formed, but decompose on the column and for this reason we focused on the first four entries to perform the Knoevenagel condensation (shown in Table 1).
The
Synthesis of derivatives
We have synthesised a small collection of esters with an adjusted version of the Steglich esterification. With this method we theoretically are able to synthesise a larger collection of esters. We further studied the four esters 2a, 2b, 2c and 2d (Fig. 3) by performing the Knoevenagel condensation and depolymerisation of the formed polymers.
The microwave assisted Knoevenagel condensation works perfectly with TPP in MeCN and thiophene-2 carbaldehyde as aldehyde. We have prepared 3a and 3b (Fig. 4
Conclusion
The synthesis of several cyanoacrylate derivatives with fluorescent properties proved to be rather difficult, as described earlier [1]. The use of intermediates in the synthesis towards the derivatives of the monomer 3 (Fig. 4) did not result in the visualisation of latent fingerprints. The use of the monomer derivatives that were successfully prepared did not prove to visualise fingerprints as desired, although they did not decompose, as previously reported [10].
In the light of the further
Acknowledgements
The authors would like to thank Dr. E. de Ruijter for the advice on the synthesis. We would also like to thank T. Aalbers, van't Hoff Institute of Molecular Science for the SEC experiments and Dr. Mattijs Koeberg for useful comments on the manuscript. Finally we would like to thank the reviewers for the detailed comments and suggestions, they are much appreciated.
References (21)
The isolation of a zwitterionic initiating species for ethyl cyanoacrylate (ECA) polymerisation and the identification of the reaction products between 1, 2 and 3 amines with ECA
Polymer
(2001)- et al.
The detection of drugs of abuse in fingerprints using Raman spectroscopy II: cyanoacrylate-fumed fingerprints
Spectrochim. Acta A Mol. Biomol. Spectrosc.
(2004) - et al.
Effect of common fingerprint detection techniques on subsequent STR profiling
Forensic Sci. Int. Genet. Suppl. Ser.
(2011) - et al.
A new method to enhance visualization of latent fingermarks by sublimating dyes, and its practical use with a combination of cyanoacrylate fuming
Forensic Sci. Int.
(1998) - et al.
Synthesis and degradation behaviour of poly(ethyl cyanoacrylate)
Polym. Degrad. Stab.
(2008) Reagents for Infrared Chemical Imaging of Fingerprints on Difficult Surfaces
(2008)Lee and Gaensslen's Advances in Fingerprint Technology
(2012)- et al.
Selective esterifications of alcohols and phenols through carbodiimide couplings
Org. Biomol. Chem.
(2004) - et al.
Facile acylation of sterically hindered alcohols through ketene intermediates
Org. Lett.
(2001) - et al.
Phosphane-catalyzed Knoevenagel condensation: a facile synthesis of α-cyanoacrylates and α-cyanoacrylonitriles
Eur. J. Org. Chem.
(2004)
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