Journal of Wood Chemistry and TechnologyPublication details, including instructions for authors and subscription information:Biological activity of new potential wood preservatives-ammonium-and triazolium-based ionic liquids-was determined employing screening agar-plate, agar-block, and perlite-block methods. Experiments were carried out on Scots pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.) wood. This study examined the effect of the ionic liquid structure on anti-fungal efficacy, depth of penetration, and fixation in wood. It was stated that the fungicidal value of new ammonium compounds depended, above all, upon the cation structure; for Coniophora puteana, it ranged from 2.7 kg m −3 to 4.6 kg m −3 . These compounds effectively protected Scots pine wood against the action of mold fungi. Ammonium ionic liquids with a nitrite anion were characterized by strong fungitoxic properties, stronger than ammonium nitrates. The application in the amount of 15 g m −2 caused an insignificant growth of mold fungi on the surface of Scots pine wood. For the mixture of 7.5% tebuconazole and 7.5% propiconazole dissolved in ionic liquids, the synergistic effect against mold fungi at the application of 15 g m −2 was found. Dissolving tebuconazole in didecyldimethylammonium nitrate repeatedly lowered the fungicidal value against brown-rot fungi, as well as increased penetration of the ionic liquids in wood. This was associated with reduced viscosity of this ionic liquid caused by the addition of 1,2,4-triazole derivatives. Quaternary derivatives of 1,2,4-triazoles showed very high activity against blue stain and wood-decaying fungi. Additionally, most of the test compounds were well-fixed in Scots pine wood. The spectral study in infrared confirmed that nitrite, nitrate anions, and didecyldimethylammonium cation were retained in the treated wood.

This study is focused on the utilization of naturally occurring terpene alcohol in the synthesis of ionic liquids (ILs) and their application potential in wood protection. A new series of ILs containing a natural, renewable source of (−)-menthol in the cation and a saccharinate derivative as the anion were obtained with a high yield under mild process conditions. The potential applications of synthesized compounds that belong to surface-active compounds were assessed for wood preservation, and they showed positive results. Laboratory tests of their activity against fungi and saccharinate-based chiral ionic liquid (CIL) bonding with Scots pine (Pinus sylvestris L.) wood are described. The biological results for salts with alkyl substituents ranging from pentyl to octyl chains are very promising, and their activity is similar to, and even higher than, that of the commonly used material benzalkonium chloride. The fungicidal values of saccharinate-based CILs against Coniophora puteana ranged from 2.75 to 4.4 kg m–3 and were lower than those of commercial benzalkonium chloride. Moreover, those salts penetrate to some extent into pine wood, which strongly increases their potential for use in wood industries. The attenuated total reflectance infrared spectroscopy technique was used to characterize the fixing mechanism of the chiral “sweet” salts in the wood structure, and the CIL penetration depth into Scots pine wood was tested. These results were completed with the surface properties of the investigated saccharinates, the surface tension measurements, and contact angles of ILs on wood. The corrosiveness study of imidazolium saccharinate salt showed low aggressiveness against carbon steel, moreover, lower than that of IL with nitrate anion, didecyldimethylammonium nitrate, and commercially used benzalkonium chloride. The incorporation of a saccharinate anion into the IL structure may eliminate this unfavorable property of commercial protective agents based on ILs.

Research has been conducted on the biotic activity of eight chiral ionic liquids (CILs) with a natural component in the form of (−)-menthol with the configuration (1R,2S,5R) against Basidiomycetes and Fungi imperfecti. Optically active imidazolium salts were tested as follows: several asymmetric 3-alkyl-1-[(1R,2S,5R)-(−)-menthoxymethyl]imidazolium chlorides with various alkyl substituents (from methyl to dodecyl) and one symmetric 1,3-bis[(1R,2S,5R)-(−)-menthoxymethyl]imidazolium chloride containing two (1R,2S,5R)-(−)-menthol substituents. Mycological tests were carried out with brown-rot and white-rot fungi, as well as with filamentous fungi, i.e. mold fungi and blue stain fungi. The new, optically active compounds demonstrated diverse effectiveness of fungicidal activity, which was dependent on the chemical structure of the functional groups. The natural (−)-menthol component, introduced as a substituent in ionic liquids, turned out to be an optically active compound with activity against wood-destroying fungi. (1R,2S,5R)-(−)-menthol was especially active against the fungi tested. The fungicidal value of imidazolium chloride with two (−)-menthol substituents against Coniophora puteana ranged from 1.8 to 2.9 kg m−3. The adsorption processes on Scots pine wood and resistance to water leaching were examined. The sorption properties of symmetric salts with two optical active (−)-menthol substituents fitted very well with the Freundlich adsorption model. Attenuated total reflection-infrared (ATR-IR) spectra confirmed that methylene groups of the aliphatic substituent, the ring of the heterocyclic imidazole, as well as the ether bridge of the natural (−)-menthol component were fixed in the structure of the impregnated pine wood (Pinus sylvestris L.). The positive results encourage further investigation of the potential application of novel functional CILs (Figure 1) for wood protection.

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