Wood Protection Properties of Quaternary Ammonium Arylspiroborate Esters Derived from Naphthalene 2,3-Diol, 2,2′-Biphenol and 3-Hydroxy-2-naphthoic Acid
Jenny M. Carr A , Peter J. Duggan B G , David G. Humphrey A E , James A. Platts C and Edward M. Tyndall D FA CSIRO Materials Science and Engineering, Private Bag 33, Clayton South MDC, Vic. 3169, Australia.
B CSIRO Molecular and Health Technologies, Private Bag 10, Clayton South, Vic. 3169, Australia.
C School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK.
D Centre for Green Chemistry, Monash University, Melbourne, Vic. 3800, Australia.
E Present address: Arch Wood Protection (Aust) Pty Ltd, Unit 3, Aerolink Business Park, 85–91 Keilor Park Drive, Tullamarine, Vic. 3043, Australia.
F Present address: Biota Holdings Ltd, 10/585 Blackburn Road, Notting Hill, Vic. 3168, Australia.
G Corresponding author. Email: peter.duggan@csiro.au
Australian Journal of Chemistry 63(10) 1423-1429 https://doi.org/10.1071/CH10132
Submitted: 19 March 2010 Accepted: 13 May 2010 Published: 1 October 2010
Abstract
In continuation of a program aimed at developing a boron-based, high performing and environmentally benign wood preservative suitable for outdoor use, three lipophilic tetra-n-butylammonium spiroborates, tetra-n-butylammonium bis[naphthalene-2,3-diolato(2-)-O,O′]borate 4, tetra-n-butylammonium bis[2,2′-biphenolato(2-)-O,O′]borate 5 and tetra-n-butylammonium bis[3-hydroxy-2-naphthoato(2-)-O,O′]borate 6 were prepared and tested. The higher molecular weight and lipophilicity of these borates compared with related borates previously examined correlates, in the case of 5 and 6, with significantly enhanced leach resistance while termiticidal activity has been maintained. The racemic spiroborate derived from 2,2′-biphenol 5, in particular, appears to be close to an optimum balance between ease of synthesis, solubility, hydrolytic stability and termiticidal activity.
Acknowledgements
This work was funded by the Australian Research Council, Monash University and the former CSIRO Forestry and Forest Products. E.M.T. is a recipient of an Australian Postgraduate Award. Kate Cavanagh is thanked for technical assistance.
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* In contrast to results obtained with 1–3, control experiments run with naphthalene-2,3-diol, 2,2′-biphenol and TBA 3-hydroxy-2-naphthenoate in the cellulose paper termite bioassay,[8] suggest that these compounds actually have higher termiticidal and/or termitistat activity than boric acid, but less than the most active borate esters. Hence the termiticidal activity of 4–6 cannot be entirely attributed to the boron content of these compounds.
† As described in ref. [8] several semi-empirical methods were tested for their ability to reproduce the X-ray structure of spiroborate 1. AM1 was found to give the correct spiroborate structure, with BO bond lengths within 0.05 Å of experimental values. This procedure was repeated for spiroborate 5 and similar agreement was found. See Accessory Publication.
‡ Spiroborate 6 is insoluble in many solvents and was applied to timber in DMF.
