The use of tropical hardwood, which needs no or very little artificial preservation, in agricultural, hydrological and building applications throughout the world is expected to be prohibited because the availability of hardwoods from non-durable resources, namely, from demolishing wild forest, will be severely curtailed. The problem, therefore, for the future is to develop environmentally compatible preservatives for softwoods from northern regions like Canada, Scandinavia and Siberia so that they can compete with hardwoods in commercial applications. In the United States alone, the wood preserving industry used over one hundred and seventy million pounds of preservative chemicals to pressure treat four hundred and eighty-four million cubic feet of wood in 1990. The future of the three most widely used preservatives, namely, chromated copper arsenate (CCA), pentachloro phenol (PCP) and creosote (which is a mixture of phenolic compounds) is very bleak because of their toxicity and propensity to leaching from incorporated wood. These compounds, therefore, are receiving regulatory pressure from the government environmental protection agencies and face elimination as soon as viable alternatives are found.
In addition to phenolic compounds, sulfur compounds are extensively used in agricultural field as herbicides and insecticides. Therefore, it is an objective of this invention to prepare wood preservative compounds containing both phenol and sulfur moieties in the compounds. These compounds should be in oligomeric or polymeric form so that they would have a reduced tendency to leach out from incorporated woods. Examples of the use of monomeric phenol/sulfur compounds as antioxidants in the plastics and food applications can be found in the literature. Derwent Patent Abstract 86-292906/45 (1986) describes the use of mercaptophenols (obtained by reducing polythiobisphenols) as antioxidants for rubbers and plastics; Derwent Patent Abstract 90-62763/09 (1990) describes an antibacterial composition for paints and wooden articles comprising bithionol or fenticlor and trihalogenated phenol; Derwent Patent Abstract 90-87253/12 (1990) describes a delayed release antibacterial composition comprising an inclusion compound of hinokitiol with a bisphenol; and Derwent Patent Abstract 91-248660/34 (1990) describes a bactericidal and fungicidal composition prepared from a mixture of chlorhexidine trihalogenated phenols and phenylphenols. In addition, K. Asakura et al., Journal of the American Oil Chemists' Society, Vol. 66, No. 10, October, 1989, pp. 1450-1453 report the antioxidant effect and antimicrobial activity of phenolic sulfides wherein the sulfur is attached to the alkyl side chain. These phenolic sulfides were prepared by Michael addition and radical addition reactions of ethanethiol and ethanedithiol with o-, m- and p-vinylphenol. U.S. Pat. No. 3,812,192 to R. Gabler et al. reports that certain bisphenol compounds linked together with a thio bridge are highly active fungicides having a broad spectrum of activity.
A recent disclosure that oligomeric phenol sulfide compositions exhibit antimicrobial activity is found in K. Kawada et al., J. Antibact. Antifung. Agents, Vol. 13, No. 5, pp. 205-209 where it was reported that the tested monosulfide dimers and monosulfide oligomers were found to be less active against certain bacteria and fungi than the startingf alkylphenols.