Quaternary Ammonium Arylspiroborate Esters as Organo-Soluble, Environmentally Benign Wood Protectants

Jenny M. Carr; Peter J. Duggan; David G. Humphrey; James A. Platts; Edward M. Tyndall

doi:10.1071/CH05226

RESEARCH ARTICLE

Quaternary Ammonium Arylspiroborate Esters as Organo-Soluble, Environmentally Benign Wood Protectants

Jenny M. Carr ^A , Peter J. Duggan ^B ^C ^H , David G. Humphrey ^A ^F ^H , James A. Platts ^D and Edward M. Tyndall ^E ^G

+ Author Affiliations

- Author Affiliations

^A ENSIS—Wood Processing and Products, CSIRO, Clayton South VIC 3169, Australia.

^B School of Chemistry, Monash University, Melbourne VIC 3800, Australia.

^C CSIRO Molecular and Health Technologies, Clayton South VIC 3169, Australia.

^D School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK.

^E Centre for Green Chemistry, Monash University, Melbourne VIC 3800, Australia.

^F Present address: Koppers Arch Wood Protection, Tullamarine VIC 3043, Australia.

^G Present address: Biota Holdings Ltd, Notting Hill VIC 3168, Australia.

^H Corresponding authors. Email: peter.duggan@csiro.au; david_humphrey@koppersarch.com.au

Australian Journal of Chemistry 58(12) 901-911 https://doi.org/10.1071/CH05226
Submitted: 26 August 2005 Accepted: 9 November 2005 Published: 20 December 2005

Abstract

As part of a larger project aimed at the development of leach resistant boron-based wood preservatives, the anti-fungal and termiticidal activities, and the resistance to leaching from timber, of three related tetra-n-butylammonium spiroborates, tetra-n-butylammonium bis(ortho-hydroxymethylphenolato)borate 2, tetra-n-butylammonium bis[catecholato(2–)-O,O′]borate 3, and tetra-n-butylammonium bis[salicylato(2−)-O,O']borate 4, have been examined. All three borates are found to be active against test organisms, with the following orders of activity being observed: 2 > 3 > 4 > boric acid against wood decay fungi, and 2 > 3 ≈ 4 > boric acid against termites. The most active compound in both assays 2 also has the highest calculated lipophilicity. In a test for permanence in wood, the following order of leach resistance is observed: 4 >> 3 ≈ 2 > boric acid. This order appears to correlate more closely with the stability constants of the borate esters, as determined using ¹¹B NMR spectroscopy, rather than calculated lipophilicities.

Acknowledgments

This work was funded by the ARC, Monash University, and CSIRO Forestry and Forest Products. E.M.T. is a recipient of an Australian Postgraduate Award. Noni Johnson is thanked for helpful suggestions during the drafting of this manuscript.

References

^* In bioassays of this type, concentrations are commonly expressed as μmol per unit area rather than μmol per unit volume.

^† Percentage mass loss = [(M_i – M_f)/M_i] × 100, where M_i is the initial mass of the wood block before exposure to fungus and M_f is the mass of the wood block after exposure to fungus (fungal matter was removed before weighing).

^‡ A variety of optimization methods were tested using the X-ray crystal structure of 2 as a reference,^[¹³^] with AM1 giving the best results—see Accessory Materials for more information.

^§ This solution contained some water from the 40% aqueous tetra-n-butylammonium hydroxide solution used to make up the sample.

^II A study of aqueous sodium borate showed that at boron concentrations of 0.05 M and lower, polyborate signals were not detectable.^[³⁴^] This limit is probably different for the largely non-aqueous [D₆]DMSO/DMSO system used in this study, but is a reasonable approximation.

Quaternary Ammonium Arylspiroborate Esters as Organo-Soluble, Environmentally Benign Wood Protectants

Abstract

Acknowledgments

Subscriber Login