CA1042789A - Process for preserving cellulosic materials by treating them with an organotin compound and a mono quaternary compound - Google Patents

Abstract

ABSTRACT
Wood or products derived therefrom substantially uninfested with wood destroying fungi are preserved by treatment with an aqueous system of 0.01 - 0.4% of a triorganotin compound and a monoquarternary ammonium compound in amount sufficient to disperse the former, the treatment producing a loading of 0.15 - 1.5 kg of organotin per cubic metre of wood or product therefrom.

Description

104~78C~ ' The present invention relates to preservative agents for wood, and products derived therefrom such as plywood, chipboard and hardboard, The use of trialkyltin compounds, in particular tributyltin oxide as a wood preservative has been increasing in recent years. The use of such compounds, had, however, only been possible if an organic solvent has been employed for them. This has effectively restricted their use to the field of preserving joinery timber and certain remedial treatments (i.e. treatment of wood or products derived therefrom after infestation and partial destruction by wood destroying fungi) where organic solvents are habitually employed in order to prevent swelling of the wood during the treatment.
We have now found that an aqueous organotin-containing system which is similar to systems previously employed in masonry cleaning or as a biocide in a cooling water system has a surprisingly good activity as a wood pre-servative i.e. for pretreating wood before it is infected with wood destroying fungi. Indeed we have found that in the formulation applied to the wood the total amoun~ of organotin compound required to bring about a given degree of preservation i.e. a given organotin loading on the wood, is substantially less than that required when the organotin compound is applied in the form of a traditional white spirit based preparation.
The present invention provides a process for preservation of wood or a solid product derived therefrom, each substantially uninfested with wood destroying fungi, which comprises treating the wood or the product derived therefrom with an aqueous system containing 0.01 - 0.40% by weight of an organotin compound having three organic groups bound to a tin atom through Sn-C bonds and a mono quaternary ammonium compound of the formula:

R~
,, l +_ R' N R"' Z

R~

- 2 -104;~7~
wherein each of R', R", R"' and R"" may be the same or different and is a branched or unhranched saturated or unsaturated alkyl group of 1 to 20 carbon atoms, an alkaryl group of 7 to 19 carbon atoms, an aralkyl group of 7 to 27 carbon atoms, an aryl group of 6 to 20 carbon atoms, or their corresponding alkylene oxide condensates, or two or three of them taken to-q~ r~
E gether with the quartornar~ nitrogen atom may form a saturated or unsaturated heterocyclic ring of 5 to 7 ring atoms, and Z is a water solubilizing anion, in a sufficient amount to disperse the organotin compound under such con-ditions of treatment as to provide a loading of 0.15 - 1.5 kg of organotin compound per cubic meter of wood or product derived therefrom.
The present invention also provides wood or a solid product derived therefrom protected against infestation by wood destroying fungi, said wood being impregnated with (i) between about 0.15 and 1.5 kilograms of an ` organotin compound having three organic groups bound to a tin atom through Sn-C bonds per cubic meter of said wood or said product, and (ii) a mono-quaternary ammonium compound of the formula:
.~ _ _ R~ +
: R' - N - R"' Z
.,' I
R~

wherein each of R', R", R"' and R"" maybe the same or different and is a branched or unbranched saturated or unsaturated alkyl group of 1 to 20 carbon atoms, an alkaryl group of 7 to 19 carbon atoms, an aralkyl group of 7 to 27 carbon atoms, an aryl group of 6 to 20 carbon atoms, or their corresponding alkylene oxide condensates, or two or three of them taken together with the f61R1~r~70.r y quarternar)~ nitrogen atom may form a saturated or unsaturated heterocyclic ring of 5 to 7 ring atoms, and Z is a water solubilizing anion, the weight ratio of said organotin compound to said quaternary compound being between 1 :2 and 1 : 6, respectively.

~ :
- 2a -104Z78'3 ~ ,enerally in a process in accor~;mce with the present invention wood or a solid product derived therefrom each substantially uninfested with wood destroying fungi, is treate~ with an aqueous system containing 0.01 -0.4% e.g. 0.01 - n.25~ preferably 0.1-0.25 or - 2b -.. . .

104'~78~ 1 0.01 - 0.1~/~ by ~cigh~ o~ rn or~anotin compound hnvin~ thrce or~anic ~roups bound to a tin atom throu~h Sn-C bonds and a quatcrnary a~olliUm cor~lpound (usually having surfactant activity e.g. co~tainin~ an~ ~lkyl group of at least ~ carbon atOrQs) -,n sufficient amount to dispersc the organotin compoundS usually 0.02 - 5% by ~Jeight (bas~d on the weight of the aqueous system) in such conditions o~ treatment as to provide a loading of 0.15 - 1.5 0.15-1.0 kg c.g.
~g preferably/0.l5 - 0.5 kg of organotin compound per cubic nletre of ~ood or product derived therefrom. The organic groups in the organo~in compound are preferably al~yl groups of 1 - 10 carbon atomsJ especially n-butyl groups.

,, .
As used herein the term "loading" on the cellulosic material is !
used in its conventional sense, na~ely the uptake of preservati~e .. ; .
~here the organotin compound~ per unit vo~u~,e of material dete m ined ` ~rom the ~ss/~ol~e ~ preserYat~Ye Liquid of known ; concentration absorbed by a known volu~e of cellulosic material.
.. . .
Examples of suitable organotin compounds are those of the formulz P. R R

R ----Sn ~ X or R - -Sn ---Y--Sn--R
R R R
~here each R may be the same or different and is an alkyl group of from i to 10~ preferably 2 to 6 carbon atoms (especially n-butyl or hexyl), a cycloalkyl e.g.-cyclohexyl group, a hydroxy alkyl group, preferably of 2 to 6 carbon atoms, such as a hydroxyethyl group, an alkoxy group, preferably ofl to6carbon atoms SU~I as a methoxy group, or a phcnyl ~roup, X is an electronegative atom or group such as one having a l~mett ~alue of greater than -~ 0.2 when present as an ortho substituent in benzoic acid~ and Y is oxy~en or sulphur.

Atoms rnd groups represcnted by X include halo~en atoms sucl~ as fluorine, chlorine, ~rom~ne and iodlne, pscudo halo~en groups SUC}
as cyanidc~ cyanatc and thiocyanate ~roups, inorganic anions such : .

104Z78'~
as nitrate, sulphate, phosphate, thiophosphate and borate ions, carboxylate groups such as formate, acetate, propionate, acrylate, methacrylate and longer chain carboxylate groups, SUC]l as those of alkanoic acids of 3 - 10 carbon atoms e.g. hexanoate. Preferably X is an inorganic atom or group i.e. a halogen or pseudo halogen or inorganic anion, of those described above. Specific organotin compounds which are of use include:

-~ Bis (tri n- butyltin)oxide bis (tri n- butyltin) sulphide tri n - butyltin acetate tri n - butyltin acrylate tri n - butyltin methacrylate tri n - butyltin phosphate tri n - butyltin chloride ~he corresponding trihexyltin, tricyclohexyltin and triphenyltin compounds are also of particular useO Particularly preferred is tri-n-butyltin ' oxide. Quaternary ammonium compounds which may be employed fall generally into one of the following classes:
` 1) those of the general formula ~;s R~ +
R' N R"' Z
R~
where each of R', R", R"' and R"" which are the same or different, is a ~; branched or unbranched, saturated or unsaturated alkyl group of 1 - 20 carbon atoms, alkaryl group of 7 - 19 carbon atoms e.g. tolyl, aralkyl ; 20 group of 7 to 27 carbon atoms e.g. benzyl or alkyl benzyl or aryl group of 6 - 20 carbon atoms e.g. an aromatic hydrocarbyl group such as a phenyl group, or their corresponding alkylene oxide condensates, or two or three of them together may form a saturated or unsaturated heterocyclic ring with 5, 6 or 7 ring atoms and with the quaternary nitrogen atom as the only ring herero atom as in pyridine or with at least one additional hetero atom in the ring e.g. an oxygenatom to form a morpholine or oxazole ring, and Z
is a water solubilizing anion e.g. a halide ion such as chloride or bromide, or sulphate ion.

: .

i - 4 -104'~7~1 Pref~rably P~' is a benzyl, nuclear alkylated benzyl ~roup with at least1 alkyl group ~ith e.g. 1 - 20 usually 8 - 15 preferably sbout 12 carbon atoms in the alkyl group, or an alkyl group of 8 to 20, especially 12 - 16, carSon atoms, R" and R" ' are alkyl groups 1 - 6 carbon atoms especially methyl groups and R" " is a phenyl oxyalkylene or phenyl poly (oxyalkylene) group ~ith 1 - 6 usually 1 - 2 oxyalkylene radicals or an alkyl group of 1 - 20, preferably 8 to 18 carbon atoms especially about 12 carbon atoms. Alkylene radicals in the groups represented by R" " are usually of 2 - 4 carbon atoms, and sre usually ethylene or propylene radicals.
; ` Particulsr quaternary ammonium compounds which are of use include j benzalkonium chlorides of the formula -- c~

C6 H5 2 1 ¦
~; ¦ where R is a m~ ture of alkyl groups having from 8 to 18 carbon `~ atoms but is predominantly C12, benzethonium chloride I r CH3 _ CH3 ~
(CN3~3 C CN2 C - O-~ O(CNz~2 0 (CN2~2 5 -CH2C6N5¦ Cl ~ and methyl benzethonium chloride:
!
hexadecyl - pyridinium chloride (_CN2)l5 CN3 1 Cl and hexadecyl pyridinium bromide _ hexadecyl trimethyl ammonium bromide : ' ~' .
,:' . I .

. . ''' '' .
. ' '' : . - - . - ~ , ., . :

.
104~7~9 ...
j , .
C~3 -I
:, . _ .
Cl6 ~33 ~ C~13 Cl N tacylolamiuo formyl methyl) pyridinium chlori~e pheno~yethyldimetihyldodecylammonium b-;omide O C2114~ C12~i~5

- 3 Dî n octyl dimethyl ammonium bromide r 1~l3 C~17 - N _ C~7 ¦ B~

and n dodecylbenzyl trimethyl am~onium chloride ¦¦ n C12 25 C~3 ¦~ -~ CH2 ~, ~
~ ' Co~osition~0 for use in the invention are conveniently stored and : .:
- transported in the form of a concentrate. Such concentrates no~mally contain from 1 to 2070 by wcight~ preferably 5 to 151o by weight of the organotin compound and .ro:n 20 to 90% by weight preferably 35 to 50Z, of the quaternary compound, the baiance j being substantially water. Normally it is desirable that the quaternary and tile organotin compound are present in a weight ratio of from 2:1 to 6:1, preferably about 4:1, ~or use the concentrate is diluted with sufLicient water to produce an nqucous system oi the necessary concentration (i.e. O.Cl - 0~25/o organotin cor,lpollnd). This dilution is nonnally at a ratc of 1 pcrt of conceltrate to 10 to 100 parts, preferably 50 lo 500 parts of water, depending or, ~he pcrcentage oÇ tin in thc or~gi~al : . .
,,~ ..

concentr~te c.~. A eoncentrate contal~ing lOZ organotin compound can be dilutcd ~lO-1000 times preferably about 100 times.
Preservative a~ents accordlng to the process of the present invention may either be applied to wood and similar produets alone or in conjunction Wit]l other preservative materials, for exam21e conventional to~icants. The preferred quaternary ammonium salts I themselv~s have biological e.g. insecticidal activity. Addition~l materials ~hich ean be employed ~re tho 9~ conventionally ~mployed in aqueous compositions. Such additional materials include for example water soluble salts of chlorinated phenols~ such as sodiu,~ pentachlorophenate, They may also lnclude insecticidal materials. ~urthermore if desired, the preservative agents may be employed in ronjunction with mixtures of other preservative com positions, such as inorgan~e ehromates or dichromates. The preservative compounds will be applied to the wood or similar produets in varying amounts within the stated ran~e depending ` upon the nature of the substrate and i:s intended use. We have found that a treatment providing a loading of 0.15 - 0.5 kg (per eubie metre of ~ood o, produet therefrom) of organotin eompound provides useful proteetion against the eommon wood destroying , , Basidomycete fungi. A loading of about 0.25 kg/mJ-is ~enerally satisfaetory for preserv~tion in normal building use.
~'" ' . ', Application to wood or products derived therefrom may be accomplished in a number of ways. It ~ay be applied by soaking the timber to be preserved in a solution contnining the preservative until sueh time ; as suffieient absorption has been reaehed. However, it is preferably applied by vacuum and/or pressure impregnation teehniques designcd to ensure tliat ~he preservative is absorbed fully into the substrate. Thus the cellulosi~ materi~l may be eontacted with the ~queou~ system, the pressure raised to above ntmosplleric with the ma~eri~l still contacting the system ~nd th~ pressur~ r~t~r~ed eO atmospher~e~ the pr~ss~r~ d ~

'; . ' ' ~ ' ., . :

104~78~ ~
which the prcssure is maintained being sufficient to result in the desired loading. Preferably the matcrial is subjccted to a pressure lower than atmospheric beforc contact with the aqueous system. For example, th~ substrate may be placed in a chamber, the pressure in the chamber reduced, preservative composition, usually at room temperature, added to cover the substrate, the pressure increased to greater than atmospheric, m~intained there and then reduced to atmospheric, followed option~lly with a short perlod o' reduced pressure. Alternatively the initial pressure reduction can be omitted. These techniques with snd ~ithout initial pressure reduction are known as Full cell and Empty cell techniques and are described in "The Preservation of Timber" by W. P. K. Findley, Publ. Black 1962 pp 36-41 and "Wood Preservation" by ~. M. Hunt and G. A. Garratt, 3rd Ed. American Forestry Series, ~Graw-Hill, 1967.
.`j ' ' ~.
The concentration of organotin compound in the aqueous system, the size of the pressures, the time of maintenance of the super- a~d sub-stmospheric pressures snd the nature of the cellulosic material affect the loading on the material. Thus increasing the concentration, or the super-atmospheric pressure, th~ R~ ~
maintenance at super-atmospheric or sub-atmospheric pressure or decreasing the sub-atmospheric pres~ure produces an increase in the loading on the material. Changing the material for one having a higher ease of abso~ption results in an increase in the loading as does treatment of a cellulosic material of smaller cross sectional area. Generally vacuum pressure times of five minutes to t~O
hours, usually ten to thirty minutes, are used with vacu~ of les.
than lOOmm Hg. Super-atmospheric pressures of 2 - 20 ~g/cm2 e.g. 8 - 15 kg~c~- for times of 5 hours to 20 minutes, e.g.
2 hours to 30 minutes are convenient, the longer times applying to use of l~er pressures. These conditions are generally suitable for use with a~ueous s~stems conta~ning 0.05 - 0.25% of organotin compound.

'.

I _9_ , !
i .
~, . .
1 ~04'~78~
The aqueous systems used in the process of the invention are very use~ul in preselving wood (or solid product derlved thererrom) from the action of wood destreying Basidomy~ete fungi such as cerebella, Polystictus ~ersicolor, Ienzites trabea and especially Poria monticola, the last OL ~hich ~ resistant to conventional copper chrome arsenate preservatives.

! .
The in~ention is illustrated in the following Examples 3 - 6 Examples 1 and 2 describing the production of suitable concentrates.
.',~ ' , ' ' ;

`~ Example 1.
An aqueous for~ulation containing 10% bis (tri-n-butyltin) oxide and 40% alkyl benzyl di~ethyl ammoni~m chloride was prepared by mixing 1 part bis (tri-n-butyltin) oxide with ~ parts Benzalkonium hloride B.P. (a commercial aqueous formulation contain mg 50%
weigl~t allyl benzyl dimethyl ammonium chlorlde~ in which the ~ alkyl groups con;ain 8 - 1~ carbon atoms) and adding 1 part of ! water~ all concentrations and parts being by weight.

Example 2 .~ :
An aqueous formulation containing 10% bis (trl-n-butyltin) oxide nnd 40% (n-higher allcyl benzyl) trlmethyl ~mmonium chloride was prepared by mixing 1 part bis (tri-n-butyltin) exide with ~ parts Gloquat ~(a commercial aquoous o~ulation containing 50%
(n-higller all;yl benzyl) trimethyl ammonium chloride)~ and adding tr~d~ rlC

. .
',.: , , : : ' . '. , . ~ .. , . ~ .

104;~7~9 1 part of water, all concentrations ~md parts bcin~ by weight, The n-hi~her alkyl group present as a substituent in the benzyl group is believed to be an n-dodecyl group~

Example 3.
The wood preserving activity of bis ~tri-n-butyltin) oxide ~TBT0) in the formulations derived from those described in Examples 1 and 2 was compared using 8 mycological test with the activity of the same compound formulated in a light petroleum solvent. In this test, blocks of Scots Pine, Pinus sylve~tris, sapwood, 15mm. long and 10 x 7 mm. in cross - section, were treated by vacuu~ impregnation with dilutions of the three formulations to give varying retentions of bis (tri-n-butyltin) oxide. After drying, balf the blocks treated with the aqueous formulations uere leached by vacuum impregnation with deionised water followed by soaking in deionised water for 5 days, the water being changed daily. The leached blocks were then dr~ed and all the blocks exposed to fungal attaclc by the Brown rotting Basidiomycete Coniophora cerebella by placing the blocks on active soil and feeder block cultures for six weeks. The weight losses due to fungal attack are shown in the following table:
bis (tri-n-but~ltin~ oxide in li~ht petroleum solvent concentration of TBT0 Loadin of TBT0 % w_i~ht loss -i _ ~ in wood k~,/m3 due to de~
unleached 0.25 1.15 0 0.16 ~ 0.74 1.1 0.10 0.45 6.5 0.063 0.27 18.6 0.040 0.18 15.

,~
I

; ' ' '', 1~4~7891 1 ~
bis (tri-n hutyltin) o~ide ~nd b n%yl ~lkyl ~!imetllyl ammonium chlori(lc ~,~u~u !~l~ul~lioll ~rom l:x~mple 1.
oadln~ of TBT0 C/o wci~ht loss ' in solu~ion /o of w/~r in wood 1:~. ~ due to decay i, unleached I
0.063 0.44 0.040 0,28 0 0,025 0.1~ 6.0 l~
0.016 0.11 2,5 l, 0.010 0~07 12.5 lenched 0,063 0.43 o 0.040 0,2~ 4,0 0.025 0.18 3.7 0.016 0.11 2~i,3 0,010 0,07 19.6 bis (tri-n-butyltin) oxide and alkylbenzyl trimethyl ammonium chloride aqueous formulation, from E,~ample 2.
concentrntion of TBT0 Loadi~ of T~TO 70 wei~ht loss - in solution ~/~ w/win wood k~./m3due to decay ~l unleached O.OS3 0.46 0 0.040 0.~7 0 0.025 0,17 10.0 0.016 0.11 17.
0.010 0.07 18.4 ~, !
bis (tri-n-butyltin) oxide and alkylbenzyl trimethyl ammonium 9 ~5L~y __5~ tion- from Ex~ele 2.
concentration to rrBTo ~S35!!~L!~ 70 we ht loss , in solution % w/win wood kg./m3 due to decay - , leached 0,063 0.43 o - 0.040 0.27 0 j 0.025 0.17 0.5 0.016 0.11 15.0 'I 0.010 0.07 29.1 untreated - 0 0 47.6 These results indicate the following range for bis (tri-n-butyltin) oxide loadings spanning the retentions at which weight loss first ; becomes insignificant~
In petroleum solvent unleached 0.74 - 1.15 kg./m3 Aqueous quaternary ammonium formulation unleached 0.1~ - 0.2~ kg./m3 (Example 1) leached 0.20 - 0.43 kg./m3 1 " " " " unleached 0.17 - 0.27 kg,/m3 (Example 2) leached 0.17 - 0.27 kg./m3 .

., . .- . :
: :' 1()4;~71B9 ~ ' These results ~ndic~te that the activity oE bis (tri-n-butyltin) o~idc applied in ~queous qu~ternary am~onium formulations e.g.
those in Examples 1 and 2, is about fi~e times greater than when applied in the conventional way in a light petroleum solvent.

Example 4.
Timber wns treated with the formulations described in Examples 1 and 2 using a conventional Bethell Full-cell process. After sealing the timber in a cylinder an initial vacuum was applied. The cylinder was theh flooded with preservative whilst maintaining the acuum and, when flooding was complete, the vacuum was released and a pressure applied. Finally the pressure was released~ the preservative pumped away and a final vacuum applied before returning the cylinder to atmospheric pressure and removing the timber.
me preservative was diluted with water to give a concentration depending upon the final retention that was required. In addition the impregnation pressure, and the times for ~hich this pressure and the initial vacuum were applied, were varied to suit the species 3 and cross-section of the timber being treated. For instance, an initial vacuum time of 20 minutes W25 adequate for normal carcassing or framing timber used in building. If 8 pressure of about 10 kg./cm2 was applied for 90 minutes~ or a pressure of about 12~5 kg./cnt for 60 minutes, a nett absorption in excess of 200 kg.
of diluted formulstion per m was achieved in Scots Pine sapwood.
Longer times were required for the treatment of resistant species such as Douglas Fir, Hemlock and Spruce; for instance pressures of ~; 10 kg./cm for 120 minutes or 12~5 kg,/cm2 for 90 minutes. If the formulations in Examples 1 and 2 were diluted to 1~25% of the original concentratiGn with water~ i.e. 0.12570 bis ttri-n-butyltin) o~cide, this nett absorption of 200 kg. of diluted formulations per m3 gnve a nett retention of preservative of at least 2~5 kg. of concentrated formulatioll per m ~ (equivalent to 0.25 kg of 1~)4Z'789 ~.
(tri n-butyltin) oxide pcr cubic metre of wood) throughout thc sapwood; ~n 2dequatc retentlon for preservation in normal building use Example 5.
Timber was treated with the formulations described in Examples 1 and 2 using a conventional Lowry ~mpty-cell process. The process was the same as the Bethell Full-cell process described in Example 4 except that the initial vacuum was omitted and the nett absorption was reduced by about 40%. The oressures and times described in Example 4 thus gave nett absorptions in the Lowry process in excess of 120 kg. of diluted formulation per m and, if the formul-ations described in EXamples 1 and 2 were diluted to 2.1% of the original formulation with water~ i.e. 0.21~ bis (tri-n-butyltin) oxide, this nett absorption gave a nett retention of preservative o~ at least 2.5 kg. of concentrated formulation per m , equivalent to 0.25 kg. bis (tri-n-butyltin~ oxide per cubic metre of wood through-out the sapwood in the case of Scots Pine~ Pinus sylvestris. This was the same retention as that achieved by the Bethell Eull-cell process in Example 4 but the 407O reduction in nett absorption resulted in timber that was substantially drier after treatment.
.~, .
Example 6.
- The aqueous formulation of Example 2 diluted ulth water was tested as a wood preservative for its activity against various Bas~domycete fungi according to the method of British Standard 838 (19~1). The wood blocks used in the test were kept under vacuum of less than lO mm Hg for 10 minutes~ the diluted fonnulation was added and the blocks allowed to soak it up for 2 hours. The blocks were weighed to datermiL~e the ~pta~e of formulat~on The toxic limits of the various fungi are given in 1;erms of the weight of formulation (containing 10% TBTO) per m3 of wood. The res~lts are given below :; I

.. . .. . .. . . . ..... .. . . . - . , . ~
. . . ~

104Z789 l !
and are compared with th~ corresponding results for a conventional :i copper chrome arscnatc for~ulation prepared from 27.6% CuSo4 5H20, 35.47~ K2CT2O7 and 37.0% ~'a2HAsO4 7H20 ~ith ~2So4 ~dded to adjust the pH to 2.5; the toxlc li~lts for the latt~r formulation are given in the manner of BS 4072 type 2 expressed as dry solids.
, ~, Toxic Limits Poria Lenzites Polystictus ; monticola trabea versicolor 1. OrganotiD formulatio of Exa~ple 2 ur,~e~ched -~20.74 0. 75- 1. 20 0.97-1.59 l~achad ~c~.74 1.15-1.85 2.52-3.90 . j 2. Copper Chrome arseDate formulation ~.
unleached 2.93-4.ô3 3.09-4.86 1.61-2.64 i lenched :~7.55 2.95-4.88 3.78-5.47 .; . , These results show that the diluted aqueous formulation of Example 2 is better as a preservative than the than the conventional inorganic ,1 formulation especially when Poria Monticola is the main wood destroying ., . I
fungus present.

. j ;, J i l, ,1, "

,, , - ~

Claims (21)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for preservation of wood or a solid product derived therefrom, each substantially uninfested with wood destroying fungi, which comprises treating the wood or the product derived therefrom with an aqueous system containing 0.01 - 0.40% by weight of an organotin compound having three organic groups bound to a tin atom through Sn-C bonds and a mono quaternary ammonium compound of the formula:

wherein each of R', R", R"' and R"" may be the same or different and is a branched or unbranched saturated or unsaturated alkyl group of 1 to 20 carbon atoms, an alkaryl group of 7 to 19 carbon atoms, an aralkyl group of 7 to 27 carbon atoms, an aryl group of 6 to 20 carbon atoms, or their corresponding alkylene oxide condensates, or two or three of them taken together with the quarternary nitrogen atom may form a saturated or un-saturated heterocyclic ring of 5 to 7 ring atoms, and Z is a water solubil-izing anion, in a sufficient amount to disperse the organotin compound under such conditions of treatment as to provide a loading of 0.15 - 1.5 kg of organotin compound per cubic meter of wood or product derived therefrom.

2. A process according to claim 1 wherein the aqueous system contains 0.02 - 5% by weight of a quaternary ammonium compound.

3. A process according to claim 1 wherein the organotin compound is a tri alkyltin compound having 1 to 10 carbon atoms in each alkyl group.

4. A process according to claim 3 wherein each alkyl group is an n-butyl group.

5. A process according to claim 1 wherein the organotin compound is a compound of formula R3SnX or R3SnYSnR3 wherein R is an organo group, having a carbon atom for bonding to tin, X is an inorganic atom or group and Y is a sulphur or oxygen atom.

6, A process according to claim 5 wherein Y is an oxygen atom.

7. A process according to claim 2 or 6 wherein the organotin compound is tri n-butyl tin oxide.

8. A process according to Claim 1 wherein the mono quaternary ammonium compound is of formula wherein R' is a benzyl group, which is unsubstituted or substituted by at least one alkyl group of 1 - 20 carbon atoms, or an alkyl group of 8 - 20 carbon atoms, each of R" and R"', which are the same or different, is an alkyl group of 1 - 6 carbon atoms, and R"" is an alkyl group of 1 - 20 carbon atoms and Z- is an anion such that the quaternary ammonium compound is water soluble.

9. A process according to Claim 8 wherein in the mono quaternary ammoniumcompound, R" and R"' are methyl groups and either R' is a benzyl group and R"" is an alkyl group of 8 - 18 carbon atoms or R' is an alkylbenzyl group with one nuclear alkyl group having 8 - 18 carbon atoms and R"" is a methyl group.

10. A process according to Claim 9 wherein the alkyl group in the alkylbenzyl group representing R' or the alkyl group representing R"" has 12 carbon atoms.

11. A process according to any one of Claims 1, or 8 wherein the weight ratio of organotin compound to quaternary ammonium compound is 1 : 2 to 1 : 6.

12. A process according to Claim 1 wherein the wood or product derived there-from is treated with the aqueous system by subjecting the wood or product derived therefrom to a pressure less than atmospheric, then contacting the wood or product derived therefrom with the aqueous system, raising the pressure to above atmospheric pressure and finally returning the pressure to atmospheric, the pressures and times for which the pressure is maintained being sufficient to result in the desired loading on the wood product derived therefrom.

13. A process according to Claim 1 wherein the wood or product derived there-from is treated with the aqueous system by contacting the wood or product with the aqueous system raising the pressure to above atmospheric pressure and finally returning the pressure to atmospheric the pressure and time for which the pressure is maintained being sufficient to result in the desired loading on the wood or product derived therefrom.

14. A process according to Claim 12 or 13 wherein the wood or product derived therefrom is treated with an aqueous system containing 0.1 - 0.25% by weight of tri-n-butyl tin oxide and 0.02 - 5% by weight of a monoquaternary ammonium compound of formula wherein R" and R"' are methyl groups and either R is a benzyl group and R"" is an alkyl group of 8 - 18 carbon atoms or R is an alkylbenzyl group with one nuclear alkyl group having 8 - 18 carbon atoms and R"" is a methyl group.

15. A process according to Claim 12 or 13 wherein the weight ratio of organo tin compound to quaternary ammonium compound is 1 : 2 to 1 : 6 and wherein the wood or product derived therefrom is treated with an aqueous system containing 0.1 - 0.25 weight of tri-n-butyl tin oxide and 0.02 - 5% by weight of a monoquaternary ammonium compound of formula wherein R" and R"' are methyl groups and either R' is a benzyl group and R is an alkyl group of 8 - 18 carbon atoms or R' is an alkylbenzyl group with one nuclear alkyl group having 8 - 18 carbon atoms and R"" is a methyl group.

16. A process according to any one of Claims 12 and 13 wherein the weight ratio of organotin compound to quaternary ammonium compound is 1 : 2 to 1 : 6 and wherein the wood or product derived therefrom is treated with an aqueous system containing 0.1 - 0.25% weight of a tri-n-butyl tin oxide and 0.02 - 5% by weight of a monoquaternary ammonium compound of formula wherein R" and R"' are methyl groups and either R' is a benzyl group and R"" is an alkyl group of 8 - 18 carbon atoms or R' is an alkylbenzyl group with one nuclear alkyl group having 8 - 18 carbon atoms and R"" is a methyl group and the wood or product derived therefrom is impregnated with the aqueous system through all the surfaces of said wood or said product.

17. Wood of a solid product derived therefrom protected against infestation by wood destroying fungi, said wood being impregnated with (i) between about 0.15 and 1.5 kilograms of an organotin compound having three organic groups bound to a tin atom through Sn-C bonds per cubic meter or said wood or said product, and (ii) a monoquaternary ammonium compound of the formula:

wherein each of R', R", R"' and R"" maybe the same or different and is a branched or unbranched saturated or unsaturated alkyl group of 1 to 20 carbon atoms, an alkaryl group of 7 to 19 carbon atoms, an aralkyl group of 7 to 27 carbon atoms, an aryl group of 6 to 20 carbon atoms, or their corresponding alkylene oxide condensates, or two or three of them taken together with the quaternary nitrogen atom may form a saturated or unsat-urated heterocyclic ring of 5 to 7 ring atoms, and Z is a water solubilizing anion, the weight ratio of said organotin compound to said quaternary com-pound being between 1 : 2 and 1 : 6, respectively.

18. The wood of claim 17 wherein the quaternary ammonium compound is of the formula wherein R' is a benzyl group, which is unsubstituted or substituted by at least one alkyl group of 1 - 20 carbon atoms, or an alkyl group of 8 - 20 carbon atoms, each of R" and R"', which are the same or different, is an alkyl group of 1 - 6 carbon atoms, and R"" is an alkyl group of 1 - 20 carbon atoms and Z- is an anion such that the quaternary ammonium compound is water soluble.

19. The wood of Claim 18 wherein in the quaternary ammonium compound R" and R"' are methyl groups and either R' is a benzyl group and R"" is an alkyl group of 8 - 18 carbon atoms or R' is an alkylbenzyl group with one nuclear alkyl group having 8 - 18 carbon atoms and R"" is a methyl group.

20. The wood of Claims 17, 18 or 19 wherein the organotin compound is tri (n-butyl) tin oxide.

21. A process according to claim 2 or 6 wherein the organotin compound is (n-butyl) tin oxide and the weight ratio of said (n-butyl) tin oxide to quater-nary ammonium compound is 1:2 to 2:6.