WO2001081635A1

WO2001081635A1 - Phosphine compounds and their use as tanning agents, corrosion inhibitors and biocides

Info

Publication number: WO2001081635A1
Application number: PCT/GB2001/001820
Authority: WO
Inventors: Christopher Raymond Jones; Graham Philip Otter; Gareth Rhys Collins
Original assignee: Rhodia Consumer Specialties Limited
Priority date: 2000-04-27
Filing date: 2001-04-25
Publication date: 2001-11-01
Also published as: GB0010161D0; AU5050601A; AR031574A1

Abstract

The use in tanning of a THP oligomer of the formula : {HOCH2R1MP[RPR1M]n-CH2OH}x+ x/y [X]y- where R is a divalent hydrocarbon radical having from 2 to 20 carbon atoms and optionally substituted with one or more substituents selected from the set consisting of halogen, hydroxy, carboxy, amino, alkylamino or -PR1mCH2OH groups or interrupted by one or more ether or carbonyl linkages, each R1 is independently a monovalent hydrocarbon radical having from 1 to 25 carbon atoms and optionally substituted with one or more substituents selected from the aforesaid set, each m is 1 or 2, n is from 0 to 10, x is the number of groups in the molecule having m = 2 and X is a compatible anion of valency y such that the compound is water soluble. Compounds wherein at least one R1 is a C¿8-25? alkyl are preferred, and are also useful in water treatment, e.g. as corrosion inhibitors and biocides.

Description

PHOSPHINE COMPOUNDS AND THEIR USE AS TANNING AGENTS, CORROSION INHIBITORS AND BIOCIDES

The present invention relates to novel phosphine compounds which are useful as tanning agents, in the manufacture of leather or as corrosion inhibitors and biocides in water treatment.

Tanning is a process for the preservation of skins, by which is meant the collagen-containing integuments of vertebrates including mammals (e.g. cows, pigs, deer, goats, sheep, seals, antelope, mink, stoats and camels) , fish, (e.g. sharks), reptiles (e.g. snakes, lizards and crocodiles) , and birds (e.g. ostrich). Skins comprise a layer of collagen, and tanning entails reacting the collagen with a cross linking, or tanning, agent to cross link reactive sites within the collagen molecule. The product of the cross linking is leather, which is substantially less susceptible than skin to bacterial degradation.

A consequence of the cross linking is an increase in the minimum temperature at which the wet leather tends to shrink. This shrink temperature is often used as an indication of the degree of tanning.

The collagen layer of the skin is separated from fats, connective tissue and other subcutaneous protein, and optionally from the outer keratinous layer, by a combination of chemical and physical steps. The former may include liming, bating, pickling and/or degreasing.

The skin is then subjected to treatment in one or more stages with various tanning agents selected to give the desired end properties.

The main types of tannage are:- vegetable tannage, based on tannin as the active cross linking agent; mineral tannage using various polyvalent metal salts, especially salts of chromium, aluminium, iron, or zicronium; and synthetic tanning agents, referred to as "syntans". Syntans include replacement syntans which are active tanning agents capable of tanning leather when used as the sole tannage e.g. by reacting with collagen at two or more sites to form cross links, and auxiliary syntans which are added to other tannages to modify the character of the leather but which are not in themselves active tanning agents. Auxiliary syntans are absorbed by the leather or may react with collagen at one site only. Syntans include various polymers and copolymers, such as those obtained by condensing formaldehyde with, for example, phenols and/or aryl sulphonates, and acrylate, methacrylate, acrylamide and/or acrylonitrile homopolymers and copolymers. Formaldehyde itself and dialdehydes such as glutaraldehyde are also used in tanning, usually in combination with other tannages .

For centuries the production of leather was based on the vegetable tannages which produce the characteristic brown colour traditionally associated with leather. One of the first mineral tannages was alum, but currently the most widely used tanning agent is chrome, usually in the form of basic chromium sulphate, which produces a blue grey leather with high shrink temperatures. However mineral tannages in general, and chrome tannages in particular are under pressure on environmental grounds. Syntans are less environmentally harmful than mineral tanning agents. However, many syntans are derived from formaldehyde, which may be released during tanning. Formaldehyde and difunctional aldehydes present a health hazard and are unpleasant to handle.

Tetrakis (hydroxymethyl) phosphonium salts, which will be referred to generically herein as THP salts have long been used as fire-retardants for textiles and have been applied to the keratinous (fur) side of skins for this purpose. The salts may be applied directly to the fabric or in the form of precondensates which are water soluble or sparingly water soluble copolymers of THP with organic nitrogen compounds such as urea or an amine. THP salts have also been known as possible ingredients of tanning liquors for more than thirty six years. US 2 992 879 referred to THP chloride (THPC) as an unsatisfactory tanning agent on its own, and recommended a combination of THPC and a phenol such as resorcinol speculating that the two react together to form an effective tanning agent when the pH is raised. In fact THP salts do copolymerise with phenols such as resorcinol (see, for example, Textile Research Journal, December 1982, p743) . US 3 104 151 describes the use of such THPC/phenol copolymers as light pretannages for leather in which the main tannage is vegetable or mineral. GB 2 287 953 describes the use of THP salts as cross linkers in conjunction with melamine/formaldehyde or urea/ formaldehyde prepolymers, in order to form a copolymeric tanning agent in situ in the tanning liquor. EP 0 559 867 describes the use of phosphonium salts such as THP sulphate (THPS) on raw or cured skin prior to tanning e.g. in acid degreasing. EP 0 681 030 describes the use of THPS as a cross linker for casein finishes applied to leather after tanning. GB 2 314 342 describes the use of hydroxyalkyl phosphines and phosphonium salts as tanning agents in conjunction with aromatic anionic syntans and EP 0 808 908 describes the use of THP salts with condensable nitrogen compounds.

THP salts are stable under acidic conditions in the absence of air or oxidising agents. At pH above 3 and in the absence of oxidising agents they are gradually converted to the parent base, tris (hydroxymethyl) phosphine herein referred to as THP. Conversion is rapid and substantially complete between pH of about 4 and 6. Above pH 7, or in the presence of oxidising agents THP salts or THP are converted to tris (hydroxymethyl) phosphine oxide (THPO), conversion being rapid and substantially complete at pH above about 10, e.g. 12. It has been stated, e.g. in US 2 993 744, that THPO is the effective tanning agent in THP based tannages.

Contrary to statements in the art, THPO is not effective as a tanning agent for leather, and THP salts are also ineffective as tannages. Moreover THP used in conjunction with co-condensable monomers or polymers provides complex systems which are difficult to control to obtain consistent results. However THP on its own is an effective main tanning agent. THP is usually most effective when formed in situ by first impregnating the leather with a THP salt, in the substantial absence of monomers or prepolymers which react or copolymerise with THP and raising the pH above 4 and preferably above 5.

The steps required to produce leather including the pickling and degreasing which usually precede tanning, remove most of the natural oils and fats from leather. These are normally at least partially replaced after tanning by fat liquoring, which entails contacting the leather with an aqueous emulsion of oils and fats which soften and lubricate the finished leather. It has been found that leather which has been tanned with THP has a tight character and does not readily absorb fat liquor.

Many of the more effective syntans, which are derived from formaldehyde, including urea/formaldehyde, melamine/formaldehyde, and phenol/formaldehyde polymers may release detectable and sometimes objectionable amounts of formaldehyde in use.

One object of the present invention is to provide tannages which exhibit the advantages of THP but which are fuller, or more readily fat liquored. A further object is to provide effective syntans which have a reduced tendency to release formaldehyde. Corrosion inhibitors are used to treat a variety of aqueous systems such as boiler water, industrial process water, cooling water and water in central heating and air conditioning systems, to prevent corrosion of metal surfaces by soft water systems. Typically corrosion inhibitors are effective at low concentrations in the range 1 ppm to 500 ppm.

A further object of the invention is therefore to provide improved and more economic corrosion inhibitors.

We have now discovered a new class of hydroxymethyl phosphine compounds for use as tanning agents, of the formula

where R is a divalent hydrocarbon radical having from 2 to 20 carbon atoms and optionally substituted with one or more substituents selected from the set consisting of, halogen, hydroxy, carboxy, amino, alkylamino or -PR^CH_aOH groups or interrupted by one or more ether or carbonyl linkages, each R¹ is independently a monovalent hydrocarbon radical having from 1 to 25 carbon atoms and optionally substituted with one or more substituents selected from the aforesaid set, each m is 1 or 2, n is from 0 to 10 (e.g. from 1 to 10), x is the number of groups in the molecule having m = 2 and y is a compatible anion of valency y such that the compound is water soluble. We have discovered that the aforesaid compounds are very effective tanning agents.

The invention therefore, provides the use in tanning of a compound of the aforesaid formula, which will be referred to herein as a "THP oligomer" . According to a second embodiment, the invention provides a method of tanning, which comprises contacting skins with a THP oligomer. THP oligomers having at least one R¹ group a C_8-25 alkyl group are novel compounds with particularly good tanning properties and constitute a particular embodiment of the invention.

R is preferably an alkylene group especially one having from 2 to 10 carbon atoms such as ethylene, 1,3-propylene 1,4-butylene, 1,5-pentylene or 1,6-hexylene, i.e. — CH₂ — CH₂-, -CH₂ — CH₂ — CH₂-,

- CH₂ — CH₂ — CH₂ — CH₂-,

- CH₂ — CH₂ — CH₂ - CH₂ — CH₂- or - CH₂ - CH₂ - CH₂ - CH₂ - CH₂ - CH₂- respectively.

R may optionally be unsaturated, alicyclic, branched chain or aromatic. Also included as R groups are substituted alkylene or arylene groups, usually halogen, hydroxy, -PR_mCH₂OH, or carboxy substituted and ether or polyether groups.

R¹ is typically -CH₂OH, but at least some of the R¹ groups may be alkyl or alkenyl groups having up to 25 carbon atoms, or less preferably substituted alkyl groups as aforesaid.

The value of m may be selected independently for each -PR¹ group from 1 and 2, where m = 1 the group will be an electrically neutral substituted phosphine and where m = 2 the group is a cationic phosphonium group. The overall valency of the optionally cationic portion of molecule [X] , i the above formula therefore depends on the number of PR_m groups in the molecule in which m = 2. This in turn may depend upon the pH. Typically at neutral or alkaline pH, X = 0 and the molecule is a neutral base. At lower pH, X may vary from 1 to a maximum of (n + 1) and the molecule is a salt. We have found that active tanning usually requires the presence of at least two -CH₂OH groups each linked to neutral -PR¹- group or forming part of a -P(CH₂OH)₂ group. The salts according to the above formula in which all or most of the -PR¹ _™- groups have m = 2 are generally useful as precursors for the active bases. They are typically added to pickled skins at low pH e.g: 2 to 5 and then converted to the active base by raising the pH, e.g: to more than 4, especially 5 to 8.

The counter ion X^y" may be any ion, which is compatible with the hydroxyphosphonium cation. Examples include sulphate, chloride, phosphate, borate, carbonate, silicate, acetate, lactate, tartrate, succinate, or any other compatible anion.

The novel compounds of the invention may conveniently be prepared by reacting THP with a reactive dihalide of the R group, e.g: the dichloro- or, preferably, the dibromo- R. For example 1,2-dibromo ethane, 1,3- dibromopropane or 1,10-dibromodecane. The reaction may require the presence of some organic solvent, such as ethanol and is conveniently carried out under reflux, and preferably in the absence of oxygen. For example, the reaction may be carried out under a stream of nitrogen. The mole ratio of THP to dihalide may be from 1:10 to 10:1 preferably 5:1 to 1:5 especially 2:1 to 1:2, e.g. 1.2:1 to 1:1.2.

The oligomers prepared by the above method may be further substituted by reaction with mono halides of the R¹ groups, where required. The further substitution may be conducted under similar conditions and optionally in parallel with the oligomerisation reaction. It is especially preferred that the oligomers be substituted with one or more C₈.₂₀ alkyl groups, e.g: 1 to 4 especially two such groups. We prefer that the oligomer tannage be applied in conjunction with a polyhydric alcohol or water soluble carbohydrate, e.g: glycerol, sorbitol, trimethylolpropane, pentaerythritol, mannitol, glucose, sucrose, fructose, aldose, or other mono, di or oligosaccharide.

According to a preferred version of the first embodiment this invention provides a method of tanning in which skins which have been subjected to degreasing and/or partial tanning in a pretanning operation are contacted with an aqueous solution of a THP oligomer salt at a pH below 4, and the pH is raised above 4, preferably above 4.5, more preferably above 5, most preferably above 5.5 e.g. 4 to 7 to form THP oligomers and for a sufficient time to raise the shrink temperature above 75°C, typically above 80°C and preferably above 85°C.

According to a further embodiment, skins are contacted in one or more stages and in any order with at least one active tanning agent and at least one auxiliary syntan where at least one auxiliary syntan is a THP oligomer formed in_ situ in the leather by contacting the skins or partially tanned or tanned leather with an aqueous solution of the corresponding THP oligomer salt and the pH is adjusted above 4, e.g. 4 to 7.

According to a further embodiment our invention provides a method of tanning leather in which skins are contacted either simultaneously or consecutively, in one or more stages and in any order, with:-

(A) A THP oligomer as aforesaid having two CH₂OH groups in the substantial absence of a monomer or prepolymer capable of copolymerising therewith; and (B) a syntan, which is substantially unreactive with THP under normal conditions.

Preferably the syntan comprises a THP oligomer as aforesaid having one -CH₂OH group. In a preferred embodiment skins are tanned in a process involving an optional pretannage comprising a THP oligomer, and/or a syntan, a main tannage in which the shrink temperature is raised above 80°C and preferably above 85°C, and optionally a retannage wherein a THP oligomer having two -CH₂OH groups is used in at least the main tannage.

For the purpose of this specification "syntan" is used to refer to replacement syntans which are synthetic organic compounds capable of reacting with collagen at two or more sites to form cross links and also to auxiliary syntans which do not in themselves contribute substantially to the cross linking but which are physically absorbed by the leather or react at no more than one site so as to modify the physical properties of the leather. For example the term includes any water soluble polymer prepared by copolymerising formaldehyde, which is capable of increasing the shrink resistance of collagen and which comprises at least two units of the formula

where each M is an aryl group such as a phenyl, naphthyl, or aniline group substituted with one or more hydroxyl and/or sulphate, sulphone or sulphonimide groups or a urea or melamine residue. As used herein the term "syntan" also includes resin syntans which are homopolymers and copolymers of unsaturated carboxylic acids or their salts, esters, amides or nitriles, e.g. acrylic acid, methacrylic acid, acrylamide, acrylonitrile, maleic acid, fumaric acid, itaconic acid, aconitic acid, crotonic acid, isocrotonic acid, citraconic acid, mesaconic acid, angelic acid, tiglic acid and cinnamic acid. The copolymers may also comprise other vinylic comonomers such as styrene. Also included are acetone condensates with, for example sulphones and sulphonamides . Resin syntan may modify such properties as dye levelling, filling, grain appearance, break, grain strength, buffing nap, softness and tensile or tear strength.

THP oligomers tend to react with nitrogen containing syntans and with other nitrogenous compounds and also to some extent with aromatic syntans. Such reactions may compete with cross linking reactions of both the THP oligomer and the syntan resulting in chaotic behaviour when the two are used together. Such systems are so highly sensitive to the conditions of use that it may be difficult or impossible to control them so as to obtain the consistent results required for a viable commercial process. For these reasons we prefer not to use THP oligomers in a mixture with such compounds.

When tanning with THP oligomers in situ from the corresponding oligomeric phosphonium salt by raising the pH, it is preferred to use a catalyst for the formation of THP. For example a mixture of magnesium salt such as magnesium sulphate with a water soluble carboxylate salt such as sodium formate, sodium acetate, potassium propionate or other water soluble alkali metal or ammonium salt of a carboxylic acid, preferably the pH is raised above 3.5, more preferably above 4, e.g. above 4.5. High pH is preferably avoided because it may convert the phosphine group to phosphine oxide, which is substantially ineffective as a tanning agent. We prefer that THP oligomer solutions for use according to our invention should have a pH less than 10, more preferably less than 9, especially less than 8, typically less than 7.5, most preferably 4.5 to 7. We prefer that the THP oligomer contains less than 15%, more preferably less than 10%, e.g. less than 9% of THPO oligomer based on the weight thereof. Generally the less THPO oligomer present the better.

The THP oligomers are preferably used in a total concentration of from 0.01 to 20% by weight based on the total weight of the tanning liquor, more preferably 0.5 to 10%, e.g. 1 to 5%, most preferably 1.5 to 4%. The total proportion of the phosphonium salt used is preferably from 0.3 to 20% by weight based on the weight of wet skin, more preferably 1 to 15%, especially 1.5 to 10%, most preferably 2 to 5%.

We particularly prefer processes in which skins are treated with an auxiliary syntan prior to tanning with THP oligomer.

When the THP oligomer is used in combination with a syntan, the latter is preferably a polyacrylate, polymethacrylate, or copolymer of acrylic and/or methacrylic acid with acrylonitrile and/or acrylamide. Typically the polymer has a molecular weight in the range 1,000 to 200,000, more usually 3,000 to 100,000.

The syntan is preferably present at a concentration of from 0.5 to 35% by weight of the tanning liquor. E.g. 1 to 20% more preferably 2 to 10% especially 3 to 6%. The total proportion of syntan used is preferably from 1 to 20% by weight based on the wet weight of skins, e.g. 2 to 10% especially 3 to 5%.

The proportion by weight of THP oligomer to syntan may typically be from 1:10 to 10:1, preferably 1 :5 to 2:1, especially 1:2 to 1: 1. The total proportion of tannages used is preferably from 2 to 20% active weight based on the wet weight of skins, e.g. 3 to 10%, especially 4 to 8%. The total tannage used preferably comprises more than 80% by weight, more preferably more than 90% by weight, e.g. more than 95% of total THP oligomers, phosphonium salts and syntan. Where white leather is required, we prefer that the total tannages consist essentially of THP oligomer and syntan. In particular we prefer the leather is not tanned with vegetable or mineral tannage, with aldehydes or with phenols.

The THP oligomer is preferably applied in the substantial absence of monomers or prepolymers capable of copolymerising with THP such as phenol, urea, melamine or their precondensates with formaldehyde. For the purpose of this specification "the substantial absence of monomers or prepolymers" means less than the minimum that would be capable of reacting or copolymerising with 50% of the THP oligomer, more preferably less than the minimum that would be required to react or copolymerise with 20%, e.g. less than 5% by weight based on the weight of THP oligomer, most preferably less than 2%, especially less than 1%.

The THP oligomer may be applied as a first tanning step with a syntan as a retan. Preferably the THP oligomer is applied to acidified skins following aqueous degreasing. E.g. the initial pH is typically below 5, e.g. below 4. We prefer that the pH be raised above 5 and preferably maintained above 6 for the main duration of the tanning process .

The skins are preferably agitated in the tanning liquor for a sufficient time to raise the shrink temperature above 75°C, more preferably above 80°C, most preferably above 85°C. The tanned skins are typically washed with warni water and fat liquored using a suitable oil or blend of oils. Fat liquoring is normally carried out after dyeing.

According to a further embodiment of the invention oligomers according to the invention are added to potentially corrosive water systems to inhibit corrosion.

The products are useful in cooling water treatment, treatment of industrial process water, boiler water treatment, desalination plant and for treating water used or produced in oil wells including injection water, produced water, and water used for hydrostatic testing of pipelines.

They are also of value as metal chelating agents, e.g: in metal extractions. They may be used in aqueous based functional fluids such as hydraulic fluids, lubricants, cutting fluids and oilfield drilling muds.

Effective concentrations may typically range from 0.1 to 200 ppm, preferably 0.5 to 100 ppm depending on the nature of the aqueous system. For most soft waters, 1 to 50 ppm, e.g: 1.5 to 20 ppm, most preferably 2 to 10 ppm, may give useful corrosion protection.

Products according to the invention may be used in combination with one another, and/or in conjunction with the other treatment agents including: surfactants, such as anionic surfactants (e.g. C₁₀.₂o alkyl benzene sulphonates, C_ι0-20 olefin sulphonates, C_]0-₂₀ alkyl sulphates, C,₀.₂₀ alkyl 1 to 25 mole ether sulphates, Cι₀.₂₀ parafinsulphonates, C_10-20 soaps, C_10-20 alkyl phenol sulphates, sulphosuccinates, sulphosuccinamates, lignin sulphonates, fatty ester sulphonates, Cι_0-20 alkyl phenyl ether sulphates, C₁₀-₂₀ alkyl ethanolamide sulphates, Cι₀.₂₀ alpha sulphofatty acid salts, Cι₀-₂₀ acyl sarcosinates, isethionates, C_ι0.₂o acyl taurides, C₁₀.₂₀ alkyl hydrogen phosphates), non-ionic surfactants (e.g. ethoxylated and/or propoxylated C₁₀-₂o alcohols, ethoxylated and/or propoxylated Cι₀.₂₀ carboxylic acids, alkanolamides, amine oxides, and/or Cι₀.₂₀ acyl sorbitan and/or glyceryl ethoxylates) , amphoteric surfactants (e.g. betaines, sulphobetaines, and/or quaternised imidazolines) , and/or cationic surfactants (e.g. benzalkonium salts, C_ιo-20 alkyl trimethyl ammonium salts, and/or C₁₀-₂₀ alkyl trimethyl or tris (hydroxymethyl) phosphonium salts); sequestrants, chelating agents, corrosion inhibitors and/or other threshold agents (e.g. sodium tripolyphosphate, sodium ethylenedi amine tetracetate, sodium nitrilo triacetate, tetra potassium pyrophosphate, acetodiphosphonic acid and its salts, ammonium trismethylene phosphonic acid and its salts, ethylenediamine tetrakis (methylene phosphonic) acid and its salts, diethylenetriamine pentakis (methylene phosphonic) acid and its salts) ; tolyltriazole and mixtures of nitrate, benzoate, HHP and/or PTCB biocides (e.g. tetrakis (hydroxymethyl) phosphonium salts, formaldehyde, glutar aldehyde) ; oxidising biocides and/or bleaches (e.g. chlorine, chlorine dioxide, hydrogen peroxide, sodium perborate); foam controlling agents such as silicone antifoams, acetylenic diols; oxygen scavengers such as hydrazines and/or hydroxylamines; pH controlling and/or buffering agents such as amines, borates, citrates and/or acetates; chromium salts; zinc salts; and/or other water treatment agents such as polymeric dispersants and coagulants including polymaleic, poly acrylic and polyvinylsulphonic acids and their salts, starches and/or carboxy methyl cellulose and/or molybdates.

The invention provides formulations comprising an effective amount of a product of the invention as aforesaid and any of the aforesaid known water treatment agents. Such formulations may, for example, contain from 5 to 95% by weight of a product of the invention and from 5 to 90% by weight of one or more of any of the aforesaid water treatment agents. The oligomers additionally have biocidal activity. They are particularly effective against aerobic bacteria in cooling tower, central heating and air conditioning systems and against sulphide reducing bacteria in oil wells.

They are especially effective when used in conjunction with biopenetrants such as ammonium containing polymers and hydrotopes such as lower (e.g: Cι.₆) alkyl benzene sulphonates or urea or water soluble polyhydric alcohols or glycol ethers e.g: glycerol, ethylene glycol, diethylene glycol, ethylene glycol monomethyl ether and diethylene glycol monomethyl ether.

The invention will be illustrated by the following examples.

Example 1 Synthesis of P.P'-didodecyl-P.P.P'.P'-tetrakis (hydroxymethyl)-l,2- disphosphino ethane

To a 250ml 3-necked flask fitted with a reflux condenser, temperature probe and N₂ gas line was added tris (hydroxymethyl) phosphine (THP, 6g) and ethanol (25ml) . The solution was warmed to 50°C with stirring until all the THP had dissolved. To this was added a mixture of dibromethane (3.7g) and 1-bromododecane (7.1g).

The reaction temperature was increased to 70°C and maintained at reflux for 140 minutes. After which a ³¹P NMR showed a 71% conversion to product with 9% THP remaining. A further portion of 1-bromododecane (1.2g) was added and refluxing was continued for a further 2 hours. Thereafter, a ³¹P NMR showed 82% conversion to product. The reaction mixture was cooled to room temperature, transferred to a 50ml round bottomed flask and taken to dryness on a rotary evaporator. The resultant product was a viscous, lightly coloured liquid (lOg) .

Composition

Phosphonium bromides 82% Phosphine oxides 18%

Example 2

Bovine hides were tanned by contacting the pickled skins with an aqueous solution containing 7% of the sulphate salt of example 1 as a precursor and raising the pH to 6.5 over two hours by additions of sodium carbonate to form the corresponding phosphine oligomer. The tanned hides were rinsed, fat liquored and dried.

The product was examined for fullness, softness, shrink temperature, and residual formaldehyde. The results were compared with THP.

The product of example 1 gave a much fuller corium than THP with better uptake of fat liquor.

Example 3

Example 1 was repeated using 1,6-dibromohexane instead of 1,2- dibromoethane. The product was used in the method of example 2 with similar results.

Example 4

lOOg of pickled ovine pelt was added to a 100% water float containing 5% (NaCl) salt and rotated for 20 minutes. The pH of the water float was kept at 3.2 and 2% by weight of the tanning product, GPO 163, (a THP/dibromomethane reaction product) was added. The pelt was then rotated for a further 120 minutes. The water float was then basified, so as to raise the pH to about 6.5, by three additions of sodium bicarbonate (as 1 : 10 dilution in water) . Each addition was made at 30-minute intervals and comprised a dosage of 0.5%.

The shrink temperature of the treated pelt was then measured at pH 6.5. The shrink temperature was found to be 82°C.

Example 5

The procedure of Example 3 (above) was repeated. The tanning product used was GPO 218 (a THP/dibromohexane reaction product). At the basification step, an extra 0.25% dosage of sodium bicarbonate was needed to increase the pH to 6.5.

The shrink temperature of the treated pelt was then measured at pH 6.5. The shrink temperature was found to be 79°C.

Claims

1. A hydroxy methyl phosphine compound of the formula

(HOCH₂R'_m P[RPR' „ CH₂OH)^x+ - [X] - y wherein:

R is a divalent hydrocarbon radical having from 2 to 20 carbon atoms and either optionally substituted with one or more substituents selected from the group consisting of halogen, hydroxy, carboxy, amino, alkylamino and -PR'_m CH₂OH groups or interrupted by one or more ether or carbonyl linkages;

each R' is independently a monovalent hydrocarbon radical having from 1 to 25 carbon atoms and optionally substituted with one or more substituents selected from the same group as the optional substituents for R;

each m is 1 or 2; n is from 0 to 10; x is the number of groups in the molecule having m = 2; X is a compatible anion of valency y such that the compound is water- soluble.

2. A compound as claimed in Claim 1, in which n is from 1 to 10.

3. A compound as claimed in Claim 1 or 2, in which R' has from 8 to 25 carbon atoms.

4. A compound as claimed in Claim 1, 2 or 3, in which R is an alkylene group having from 2 to 10 carbon atoms.

5. A compound as claimed in Claim 4, in which R is ethylene, 1 ,3- propylene, 1,4-butylene, 1,5-pentylene, or 1,6-hexylene.

6. A compound as claimed in Claim 1, 2 or 3, in which R is an alicyclic, branched chain or aromatic group.

7. A compound as claimed in Claim 1 or Claim 4, in which R is a substituted alkylene or an arylene group.

8. A compound as claimed in Claim 7, in which the alkylene or arylene group is substituted with a halogen, hydroxy, -PR_mCH₂OH-, or a carboxy group.

9. A compound as claimed in Claim 1, in which R is an ether or polyether group.

10. A compound as claimed in Claim 1, 2 or 3, in which R' is -CH₂OH.

11. A compound as claimed in Claim 1, in which R' is an alkyl or alkenyl group having from 1 to 25 carbon atoms.

12. A compound as claimed in Claim 1 , 2 or 3, in which R' is a substituted alkyl group.

13. A compound as claimed in Claim 1, in which the value of m for each -RPR'_m- group is selected independently from 1 and 2.

14. A compound as claimed in Claim 1, in which the -PR'_m- group is electronically neutral where m is 1.

15. A compound as claimed in Claim 1, in which the -PRV group is a cationic phosphonium group where m is 2.

16. A compound as claimed in Claim 1, in which x is 0 at neutral or alkaline pH, whereby the cationic portion of the molecule (X) is a neutral base.

17. A compound as claimed in Claim 1, in which x is in the range 1 to a maximum of (n + 1) at acidic pH, whereby the cationic portion of the molecule (X) is a salt.

18. A compound as claimed in any one of the preceding claims, in which X^y- is an anion which is compatible with the hydroxy methyl phosphine cation.

19. A compound as claimed in Claim 18, in which X^y- is a sulphate, chloride phosphate, borate, carbonate, silicate, acetate, lactate, tartrate or succinate.

20. A compound as claimed in Claim 1, 2 or 3, in which R" is an alkyl group with from 8 to 20 carbon atoms .

21. A method of tanning skins by means of a compound claimed in any one of the preceding claims, in which said compound is added to pickled skins at a pH of from 2 to 5.

22. A method as claimed in Claim 21, in which, after addition to said pickled skins, said compound is converted to an active base by raising the pH to between 5 and 8.

23. A method as claimed in Claim 21 or 22, in which said compound is prepared in situ by reacting tris (hydroxymethyl) phosphine (THP) with a reactive dihalide of the R group.

24. A method as claimed in Claim 23, in which said dihalide is a dichloride or a di-bromide.

25. A method as claimed in Claim 24, in which the dihalide is 1,2- dibromoethane, 1,3-dibromopropane or 1,10-dibromodecane.

26. A method as claimed in any one of Claims 23 to 25, in which the mole ratio of THP to dihalide is from 1:10 to 10:1.

27. A method as claimed in Claim 26, in which the mole ratio of THP to dihalide is from 5:1 to 1:5.

28. A tanning agent as claimed in Claim 26 or 27, in which the mole ratio of THP to dihalide is from 2:1 to 1:2.

29. A method as claimed in Claim 26, 27 or 28, in which the mole ratio of THP to dihalide is from 1.2:1 to 1:1.2.

30. A method as claimed in any one of Claims 21 to 29, in which said compound is applied to the skins in conjunction with a polyhydric alcohol or water-soluble carbohydrate selected from the group consisting of glycerol, sorbitol, trimethylol propane, pentaerythritol, mannitol, glucose, sucrose, fructose, aldoses and other mono-,di-or oligosaccharides.

31. A method according to any one of Claims 21 to 30, in which the skins are contacted, either simultaneously or consecutively, in one or more stages and in any order, with

(i) a compound according to any one of Claims 1 to 20, in the substantial absence of a monomer or prepolymer capable of copolymerising therewith and

(ii) a syntan, which is substantially unreactive with THP.

32. A method as claimed in Claim 31, in which the syntan comprises a THP oligomer having one -CH₂OH group.

33. A method as claimed in Claim 31 or 32, in which the skins are tanned by means of an optional pretannage comprising a THP oligomer, and/or a syntan, a main tannage whereby the shrink temperature is raised to above at least 80°C and an optional retannage, a THP oligomer having two -CH₂OH groups being used for at least the main tannage.

34. A method as claimed in Claim 33, in which THP oligomers are formed in situ from the corresponding phosphonium salt, by raising the pH and in the presence of a catalyst.

35. A method as claimed in Claim 34, in which the catalyst comprises a mixture of magnesium sulphate with a water-soluble carboxylate salt selected from the group consisting of sodium formate, sodium acetate, potassium propionate and other water-soluble alkali metal and ammonium salts of a carboxylic acid.

36. A method as claimed in Claim 34 or 35, in which the pH is raised to be in the range 4.5 to 7.

37. A method as claimed in any one of Claims 33 to 36, in which the THP oligomers are used in a total concentration of 0.01% to 20% by weight, based on the total weight of the tanning liquor.

38. A method as claimed in any one of Claims 33 to 37, in which the THP oligomers are used in a total concentration of 1.5 to 4% by weight, based on the total weight of the tanning liquor.

39. A method as claimed in any one of Claims 34 to 38, in which the total proportion of the phosphonium salt used is 0.3 to 20% by weight, based on the weight of wet skin.

40. A method as claimed in any one of Claims 34 to 39, in which the total proportion of the phosphonium salt used is 2 to 5% by weight based on the weight of wet skin.

41. A method as claimed in any one Claims 31 to 40, in which the skins are treated with an auxiliary syntan prior to tanning with the THP oligomer.

42. A method as claimed in any one of Claims 31 to 40, in which the THP oligomer is used in combination with a syntan, said syntan being a polyacrylate, a polymethacrylate or a copolymer of acrylic and/or methacrylic acid with acetonitrile and/or acrylamide.

43. A method as claimed in Claim 42, in which the polymer has a molecular weight in the range 1,000 to 200,000.

44. A method as claimed in Claim 42 or 43, in which the polymer has a molecular weight in the range 3,000 to 100,000.

45. A method as claimed in Claim 41, in which the syntan is present at a concentration of from 0.5 to 35% by weight of the tanning liquor.

46. A method as claimed in Claim 45, in which the syntan is present at a concentration of from 3 to 6% by weight of the tanning liquor.

47. A method as claimed in Claim 42, in which the proportion of syntan used is from 1 to 20% by weight, based on the wet weight of skins .

48. A method as claimed in Claim 47, in which the proportion of syntan used is from 3 to 5% by weight, based on the wet weight of skins.

49. A method as claimed in Claim 31, in which the proportion by weight of THP oligomer to syntan is from 1:10 to 10:1.

50. A method as claimed in Claim 49, in which the proportion by weight of THP oligomer to syntan is from 1:2 to 1:1.

51. A method as claimed in Claim 31, in which the total proportion of tannages used is from 2 to 20% by weight, based on the wet weight of the skins.

52. A method as claimed in Claim 51, in which the total proportion of tannages used is from 4 to 8% by weight, based on the wet weight of the skins .

53. A method as claimed in Claim 31, in which the total tannage used comprises more than 95% of total THP oligomers, phosphonium salts and syntan.

54. The use of a compound according to any one of Claims 1 to 20 as a tanning agent.

55. The use of a compound as claimed in any one of Claims 1 to 20 as a water treatment additive to inhibit corrosion.

56. Use as claimed in Claim 55, in which the effective concentration of the compound is from 0.1 to 200 ppm.

57. Use as claimed in any one of Claims 53 to 56, in which said compound is used in combination with one or more additives selected from the group consisting of surfactants, non-ionic surfactants, amphoteric surfactants, cationic surfactants, sequestrants, chelating agents, corrosion inhibitors, biocides, bleaches, foam-controlling agents and pH buffering agents .

58. Use as claimed in Claim 57 as a formulation containing from 5 to 95% of said compound by weight and from 5 to 90% by weight of any one or more of said additives.

59. The use of a compound as claimed in any one of Claims 1 to 20 as a biocide.

60. Use as claimed in Claim 59, in which said compound is used in conjunction with a biopenetrant selected from the group consisting of:

(a) ammonium-containing polymers; (b) hydrotropes having from 1 to 6 carbon atoms;

(c) alkyl benzene sulphonates ;

(d) urea; and

(e) water-soluble polyhydric alcohols or glycol ethers, selected from the group consisting of glycerol, ethylene glycol, diethylene glycol, ethylene glycol monomethyl ether and diethylene glycol monomethyl ether.