WO1997046544A1

WO1997046544A1 - Acid catalysed process for preparing 2-mercaptobenzothiazole and derivatives thereof

Info

Publication number: WO1997046544A1
Application number: PCT/EP1997/002776
Authority: WO
Inventors: Alec Cobb; Rudi Peemans; Pierre Coenegrachts; Neil S. Isaacs; Mark J. Hilton; Mark Coulson
Original assignee: Akzo Nobel N.V.
Priority date: 1996-06-03
Filing date: 1997-05-26
Publication date: 1997-12-11

Abstract

A process for preparing 2-mercaptobenzothiazole or a benzo-ring-substituted 2-mercaptobenzothiazole is provided wherein (i) a substrate selected from aniline, a ring-substituted aniline, an appropriate precursor, an appropriate derivative thereof, or mixtures thereof, (ii) carbon disulphide and (iii) sulphur, are reacted under conventional conditions in the presence of a catalyst, the catalyst being an acid, acidic substance or acid-forming substance selected from the group comprising a carboxylic acid, an inorganic or organic acid, an anhydride or mixed anhydride of these acids, a Lewis-acid or a Lewis-acid in the presence of a co-catalyst, a solid acidic inorganic material, a hydroxy-aryl derivative and one or more halogens, or any mixture thereof.

Description

ACID CATALYSED PROCESS FOR PREPARING 2- ERCAPTOBENZOTHIAZOLE AND DERIVATIVES THEREOF

This invention relates to a process for making 2-mercaptobenzothiazole and derivatives thereof. In particular, the invention relates to the use of selected substances as catalyst to promote the reaction of aniline or a ring- substituted aniline, carbon disulphide and sulphur to form respectively 2-mercaptobenzothiazole and a benzo-ring-substituted 2-mercaptobenzo- thiazole.

The substance 2-mercaptobenzothiazole i.e. 2(3H)-benzothiazolethione, hereinafter "MBT", is a well-known vulcanization accelerator for rubber. Its manufacture has been the subject of considerable investigation over many years and many attempts have been made to improve the process for preparing it from aniline, carbon disulphide and sulphur. In particular, attempts have been made to find a catalyst which speeds up the reaction, improves yields and reduces side reactions leading to unwanted by¬ products, such as tars and pitches.

It was not until 1967 that a catalyst was discovered which fairly promotes the above-specified reaction. US 3,530,143 discloses the use of a diarylamido-dithiophosphoric acid and US 3,531 ,492 discloses the use of red phosphorus or mercury as a catalyst in said reaction. In GB 1 ,228,887, in addition to these catalysts, also phosphorus sulphide is disclosed as a suitable catalyst. Whilst such substances at the time may have been acceptable, present environmental considerations tend to disadvantage such catalysts, in particular the latter ones, since residues which are difficult to dispose of remain after the reaction has taken place. In these processes, the reactants aniline, carbon disulphide and sulphur are brought into reaction under conventional conditions comprising subjecting a mixture of the reactants to heat under pressure, optionally in the presence of a catalyst, the reaction being carried out in an autoclave or other suitable pressure vessel. These conditions, including, for example, temperature, pressure, ratio of reactants and reaction time, applied to cause the reaction to take place are well-known in the art and are termed herein "conventional conditions".

It has now been found that other, selected substances, i.e. certain acids, acidic substances and acid-forming substances, can be used as catalyst in the reaction of aniline, carbon disulphide and sulphur to more beneficially produce 2-mercaptobenzothiazole.

In a first embodiment the present invention provides a process for pre¬ paring 2-mercaptobenzothiazole wherein (i) aniline ~ [(i) being referred to hereinafter as the "substrate"] - , (ii) carbon disulphide and (iii) sulphur, are reacted under conventional conditions in the presence of a catalyst, characterised in that the catalyst is an acid, acidic substance or acid- forming substance, selected from the group comprising a carboxylic acid, an inorganic or organic acid, an anhydryde or mixed anhydride of these acids, a Lewis-acid, a solid acidic inorganic material, a hydroxy-aryl derivative and a halogen, or any mixture thereof.

Carboxylic acids which can be used as catalysts in the process of the invention include C_rC₃ alkanoic acids, e.g. acetic acid, and halogenated C_rC₃ alkanoic acids, e.g. mono-, di- and trihalogenated acetic acid, e.g. trichloroacetic acid, the corresponding anhydrides, and mixed anhydrides and any mixture thereof. The catalyst can also be an inorganic acid free of sulphur or a sulphur- containing inorganic or organic acid such as, for example, sulphuric acid, a sulphonic acid, a sulphinic acid, a sulphenic acid or a thiosulphonic acid, and is preferably an aryl- or alkane sulphonic acid. The aryl group can, for example, be a phenyl, biphenyl, naphthyl group, or a heterocyclic aromatic group such as, e.g. a benzothiazole group. The aryl group can be unsubstituted or substituted by one or more substituents provided the substituents do not have an undesirable effect on the process of the invention. Typical substituents include, for example, a linear or branched alkyl group or alkoxy group having from 1 to 6 carbon atoms, a halogen atom, a carboxy group, a hydroxyl group and a hydroxysulphonyl group.

The alkyl group of the alkane sulphonic acid according to the invention can be a linear or branched alkyl group containing 1 to 12 carbon atoms, which optionally can be substituted by one or more aryl groups defined above, one or more carboxy groups, one or more halogen atoms, and/or one or more hydroxysulphonyl groups. Suitable aryl sulphonic acids include, for example, benzene sulphonic acid, p-toluene sulphonic acid and 2-benzothiazole sulphonic acid. The p-toluene sulphonic acid used may be the monohydrate form, the anhydrous form, or the p-toluene sulphonic anhydride. Suitable alkane sulphonic acids include, for example, methane sulphonic acid, ethane sulphonic acid and benzyl sulphonic acid. The alkane moiety in the alkane sulphonic acid has preferably from 1 to 6 carbon atoms in branched or, preferably, linear configuration.

The acidic catalyst, independent of the type, may be used in the form of a suitable acidic ion-exchange resin. The use of such an ion-exchange resin facilitates the purification of the 2-mercaptobenzothiazole and/or derivatives thereof. The acid catalyst can be used as such, in a hydrated form, as the anhydride or as a mixture thereof. In particular, the aryl sulphonic acid catalyst was found to perform well in the hydrated form, for example, p-toluene sulphonic acid monohydrate. The inorganic acid suitable according to the invention is preferably a non-oxidising inorganic acid, such as, for example, phosphoric acid, preferably at about 85 to 89%, (% refers to percent weight/total weight, hereafter " % w/w "); an anhydrous hydrogen halide such as hydrogen fluoride, hydrogen chloride, hydrogen bromide and hydrogen iodide; an aqueous solution of a hydrogen halide, preferably a concentrated aqueous solution such as, for example, hydrofluoric acid at about 38 to 53% w/w, preferably about 47 to 53% w/w, hydrochloric acid at about 20 to 40% w/w, preferably about 36 to 38% w/w, hydrobromic acid at about 34 to 66% w/w, preferably about 40 to 50% w/w, typically about 47.5% w/w and hydriodic acid at about 45 to 57% w/w; typically about 56.9% w/w. In certain instances it is advantageous to carry out the reaction in the presence of only small amounts of water because the presence of large amounts of water may lead to the formation of significant amounts of undesirable side products.

Acidic substances which are suitable as catalyst according to the invention include acidic halides from the class of compounds generally termed Lewis- acids. This class of compounds includes halides - typically fluorides, chlorides, bromides, iodides, and mixtures thereof - of the following elements: Al, Be, Cd, Zn, B, Ga, Ti, Zr, Sn, Sb, Bi, Fe, Cu and U. Preferred Lewis-acids include halides of boron such as boron trifluoride and complexes thereof with oxa-alkanes, halides of aluminium such as aluminium chloride, halides of zinc such as zinc chloride, halides of titanium such as titanium tetrachloride, halides of iron such as ferric chloride, halides of antimony such as antimony trichloride and mixed halides of the said elements. The Lewis-acid may optionally be used in conjuction with a co-catalyst which may be either a proton donor or a substance capable of forming a cation with the metal halide. Proton donating substances include hydroxyl-containing compounds such as water and alcohols, protonic acids such as mineral acids and organic acids, for example hydrohalic acids and alkanoic acids. Cation-forming substances include alkyl halides, for example methyl chloride and methyl bromide, and aryl halides.

Acidic substances suitable as catalyst according to the invention furthermore include solid acidic inorganic materials. These substances comprise a wide variety of minerals and mineral clays, acidic oxides and sulphides. The substances can be natural ones as well as synthetic ones. Preferably they have been modified to be partly or fully in protonic form, and thus can present various degrees of acidity.

Typical minerals include a wide variety of zeolites, inter alia mordenites, and typical mineral clays include inter alia montmorillonite. In these types of solid acidic substances preferably Brόnsted acid sites have been introduced or enhanced by conventional methods, including, for example, acid treatment, thermal decomposition of an ammonium ion-exchanged form (whereby the ammonium moiety is decomposed providing a protonated form of the substance), hydrogen ion-exchange, hydrolysis of a multivaient cation during dehydration, or thermolysis of a hydrated multivalent cation form of the solid acidic substance. Both the number and strength of the acid sites may optionally be varied by acid treatment and/or hydrothermal treatment to bring about changes in the silicium to aluminium ratio, or by treatment with chelating agents.

The acidic oxides and sulphides include, particularly, partly and fully hydrated alumina, silica, alumina-silica compounds and aluminasilica mixtures, and chalcogenides. The oxides and sulphides are conventionally converted between a Lewis acid and a Brόnsted acid by calcination, hydrothermal treatment and/or the addition of water or an aqueous acid to the calcinated material, optionally followed by a subsequent thermal treatment.

The solid acidic substances are particularly suitable as catalyst according to the invention when prepared, according to conventional methods, optionally bonded with inorganic oxides or minerals, in the form of pellets, beads, or agglomerated particles. Such pellets, beads and particulate forms are particularly preferred for ease of handling, e.g. for use in fixed bed reactors, and for ease of their separation from the reaction mixture by physical methods, and for ease of their recycling.

Suitable hydroxy-aryl derivatives according to the invention include phenols such as for example phenol, substituted phenols, e.g. halogen mono- or poly-substituted phenol, benzene diols and benzene triols.

Acid-forming substances suitable as catalyst according to the invention comprise the class of halogens. The term halogens herein refers to fluorine, chlorine, bromine, iodine and any mixed halogens thereof such as, for example iodochloride (ICI) and bromochloride (BrCI).

All the foregoing acids, acidic substances and acid-forming substances are known and can be prepared and/or modified by methods which are well known in the art.

In a further embodiment of the invention, the process is optionally carried out in the presence of an additional amount of hydrogen sulphide, ranging from about 0.1 to about 20 moles per mole of substrate. The temperature used in the process of the invention can be varied within wide limits, but in practice, for preferred results, the reaction is conducted generally between about 100°C and about 300°C, preferably between about 170°C and 300°C.

The reaction can, depending upon the choice of the substrate and the other reactants be conducted at pressures within the range of from ambiant pressure up to about 120.10⁵ Pa. In one embodiment, the reaction is preferably carried out in a pressure vessel, e.g. an autoclave, at a pressure from about 20.10⁵ to 120.10⁵ Pa. The pressure vessel can be vented to allow excess carbon disulphide and/or hydrogen sulphide to escape, or to introduce further amounts of these.

The catalyst is used in a catalytically effective amount, which preferably ranges from about 0.1 to about 100, more preferably from 0.2 to 30 mole percent per mole of the substrate. For the solid acidic substance catalysts the amount preferably ranges from about 0.1 to about 50, and more preferably from 0.3 to 20 percent by weight of the total amount of reactants.

The proportions of substrate, carbon disulphide and sulphur used in the reaction, expressed by reference to 1.00 mole of substrate, are as follows : a) Carbon disulphide : 0.30 to 3.00 moles, preferably 0.50 to 1.60 moles, more preferably 0.5 to 1.2 moles; b) Sulphur : 0.60 to 1.50 moles, preferably 0.8 to 1.20 moles, more preferably 0.95 to 1.05 moles.

The process of the invention provides an improved conversion of the substrate into MBT in, among others, a significantly shortened reaction time as compared to conventional conditions. The process can be conducted as a continuous, a batch or a semi-batch operation. The terms TCA and AnBTH as used hereinafter stand for: TCA thiocarbanilide (or N.N'-diphenylthiourea);

AnBTH anilinobenzothiazole (or N-phenyl-2-benzothiazole amine). These aniline derivatives anilinobenzothiazole (AnBTH) and thiocarbanilide (TCA) are well known intermediates in the overall reaction for the preparation of 2-mercaptobenzothiazole (MBT), and it has been found that their conversion to MBT is also catalysed by the selected substances in accordance with the present invention. Accordingly, these intermediates provide appropriate derivatives of aniline which can be used as substrate in the process of the invention to substitute party or completely aniline. The intermediates AnBTH and TCA can be separately obtained by known methods e.g. by reaction of aniline and carbon disulphide, or of aniline, carbon disulphide and sulphur.

Accordingly, in a further embodiment the present invention relates to the use of TCA in a process for making MBT in which process TCA alone or in combination with aniline, used as substrate, is reacted under conventional conditions in the presence of the catalyst defined above, with a reagent selected from the group comprising sulphur; sulphur and carbon disulphide; hydrogen sulphide; hydrogen sulphide and sulphur; hydrogen sulphide and carbon disulphide; and hydrogen sulphide, sulphur and carbon disulphide.

Still another embodiment of the present invention relates to the use of AnBTH in a process for making MBT in which process AnBTH alone or in combination with aniline, used as substrate, is reacted under conventional conditions in the presence of the catalyst defined above, with a reagent selected from the group comprising hydrogen sulphide; hydrogen sulphide and sulphur; hydrogen sulphide and carbon disulphide; and hydrogen sulphide, sulphur and carbon disulphide. It is furthermore possible to replace the substrate aniline in the process according to the invention by an appropriate precursor. Typical precursors are nitrobenzene and nitrosobenzene. Typically, up to 45% by weight of the aniline, preferably up to 30% by weight of the aniline can be replaced as substrate in the process by one or more aniline precursors, e.g. by nitrosobenzene, nitrobenzene or a mixture thereof. Under certain reaction conditions levels beyond about 45% of nitrosobenzene and/or nitrobenzene tend to increase the formation of less desirable by-products. Accordingly, a further embodiment of the present invention relates to the use of an appropriate aniline precursor, particularly nitrosobenzene, nitrobenzene and a mixture thereof, preferably in combination with aniline, as substrate in the process of the invention for the preparation of MBT.

Furthermore, it has been found that also ring-substituted anilines, their appropriate precursors, typically the corresponding ring-substituted nitrobenzenes, nitrosobenzenes and mixtures thereof, and their appropriate derivatives, typically the corresponding ring-substituted thiocarbanilide and anilinobenzothiazole derivatives, can be used, mutatis mutandis, as substrate in lieu of aniline or the appropriate precursors and derivatives of aniline, in the process of the invention described hereinbefore, to produce the corresponding benzo-ring-substituted 2-mercaptobenzothiazole.

The substituent on the ring can be any group which does not interfere in an undesirable manner with the process of the invention. Typically, the substituent can be one or more groups independently selected from a linear or branched 0,-0₅ ^a'kyl group, a linear or branched C_rC₆ alkoxy group, a phenyl group, a phenoxy group, a phenyl or phenoxy group which can be substituted by a C_rC₆ alkyl group, a C C₆ alkoxy group, or a halogen atom. As an example, the use of 4-ethoxyaniline or 4-ethoxynitrobenzene in the process according to the invention yields 6-ethoxy-2-mercaptobenzothiazole.

Accordingly, in a further embodiment the invention provides a process for making a benzo-ring-substituted 2-mercaptobenzothiazole, which comprises bringing into reaction, under conventional conditions, (i) as substrate a ring-substituted aniline, an appropriate precursor, an appropriate derivative, or mixtures thereof, (ii) carbon disulphide and (iii) sulphur, in the presence of a catalyst, characterised in that the catalyst is an acid, acidic substance or acid-forming substance selected from the group comprising a carboxylic acid, an inorganic or organic acid, an anhydride or mixed anhydride of these acids, a Lewis-acid, a solid acidic inorganic material, a hydroxy-aryl derivative and a halogen, or any mixture thereof, as defined hereinbefore.

The process according to the invention can depart from aniline or a ring- substituted aniline or appropriate precursor or derivative thereof. All these products - some of which may be formed as intermediates in the process according to the invention - can be prepared separately by known methods, for example from nitrobenzene, aniline or functionally comparable raw materials.

Typical examples of substituted anilines and appropriate precursors and derivatives of aniline and ring-substituted aniline include: nitrobenzene; 4-ethoxy nitrobenzene; nitrosobenzene; 4-ethoxyaniline, 4-isopropyl aniline, 2-aminothiophenol, phenyl isothiocyanate, bis(anilino)methane, formanilide, formamidine, diphenylformamidine, triphenylguanidine, N,N'- diphenylthiourea (TCA); N-phenyl-2-benzothiazoleamine (AnBTH), and benzothiazole. For the process according to the invention wherein aniline is partly or completely substituted as substrate by one or more raw materials, i.e. precursors or derivatives, described above, the reaction conditions, such as for example, temperature, pressure, possible additional amount of hydrogen sulphide, the ratio's of substrate to the other reagents and the ratio catalyst/substrate are similar to the ones described above for aniline. If needed the appropriate reaction conditions for a specific substrate and/or a specific substrate-reagents mixture can be determined by the skilled person according to known techniques, e.g. via routine experiments.

The invention is illustrated by the following examples, which are not intended to limit the invention in any respect.

The examples illustrate the effect of some catalysts according to the subject invention on the reaction between aniline, carbon disulphide and sulphur.

Example 1.

Equimolar amounts of aniline and sulphur, together with a 25% molar excess of carbon disulphide and the indicated type and quantity (expressed as weight percent of catalyst based on the total weight of the reaction mixture) of catalyst (see Table 1 below) are charged to a reactor. The reactor is sealed prior to heating rapidly to 230°C. Following reaction at 230°C for 3.5 hours the vessel and its contents are cooled quickly to ambient temperature. The residual pressure is then released. The reaction material is extracted with 1 ,4-dioxane and the extract is analysed using high performance liquid chromatography (HPLC). A control experiment using the same reactant charges but in the absence of any acid catalyst was performed under similar reaction conditions. The examples are summarised in Table 1 below, showing the MBT obtained, expressed in percent yield based on the amount of aniline charged, after 3.5 hours reaction time.

TABLE 1.

CATALYST USED CATALYST MBT % YIELD CHARGED %w/w ON ANILINE

None - 69.7

Hydrochloric acid (37%) 0.3 86.0

Hydrobromic acid 50% 4.7 91.7

Iodine 5.9 90.3

Phosphoric acid (85%) 5.0 78.2

Aluminium chloride 1.2 90.9

Alumina silicate 13.2 85.2

Aluminium hydrosilicate 10.0 84.6 ( ontmorillonite)

Silica Alumino Phosphate 16.3 84.0

Phosphoric acid treated clay 13.6 83.7

The results given in Table 1 clearly demonstrate the catalytic effect of each of the catalysts according to the invention on the conversion of aniline to MBT.

Example 2.

Aniline, carbon disulphide and sulphur are charged in equimolar quantities to a reactor. An appropriate quantity of acid catalyst is then added (see Table 2), and the reactor sealed prior to heating rapidly to 230°C. Following reaction for the specified time the vessel and its contents are cooled quickly to ambient temperature. The residual pressure is then released and the reaction material is extracted with 1 ,4-dioxane and the extract is analysed using high performance liquid chromatography (HPLC). A control experiment using the same material charges but in the absence of any acid catalyst was performed under similar reaction conditions. The results obtained are shown in Table 2.

TABLE 2.

⁽¹⁾ p-TSA.H₂O : para-toluene sulphonic acid monohydrate

⁽²⁾ MSA : methane sulphonic acid

⁽³⁾ mole % on aniline calculated on H₂SO₄ at 100%

The results given in Table 2 show an acceleration of the rate of conversion of aniline to MBT for each of the acids used.

Example 3. This example illustrates the catalytic effect of p-toluene sulphonic acid monohydrate on the reaction of thiocarbanilide (TCA) with sulphur to form 2-mercaptobenzothiazole (MBT). The same procedure as used in Example 2 above was adopted using a 2:1 molar ratio of sulphur:TCA and 5.2 mol.% of p-toluene sulphonic acid monohydrate (p-TSA.H₂O) as catalyst. A comparative test, in the absence of catalyst, was run under similar reaction conditions. The results obtained are shown in Table 3. TABLE 3.

CATALYST Mol.% on TCA MBT Mol.% on TCA after

1.0 hour 2.0 hours

None 0.0 6.0 26.9 p-TSA.H₂0 5.2 31.0 57.4

The results given in Table 3 show an acceleration in the rate of formation of MBT from TCA and sulphur in the presence of p-TSA.

Example 4.

This example illustrates the preparation of 2-mercaptobenzothiazole from 2-anilinobenzothiazole (AnBTH), using the same general procedure of Example 2, by reacting 2-anilinobenzothiazole (AnBTH), in the presence of an excess of hydrogen sulphide, with and without (as a comparative test) p-toluene sulphonic acid (p-TSA. H₂O) as catalyst. The results obtained are shown in Table 4.

TABLE 4.

CATALYST Mol.% on AnBTH MBT Mol.% on AnBTH After 1.0 Hour

None 0.0 8.4 p-TSA. H₂O 26.2 24.0

The results given in Table 4 show an acceleration in the rate of formation of MBT from AnBTH and H₂S in the presence of p-TSA.

Claims

CLAIMS :

1. A process for preparing 2-mercaptobenzothiazole or a benzo-ring- substituted 2-mercaptobenzothiazole wherein (i) a substrate selected from aniline, a ring-substituted aniline, an appropriate precursor, an appropriate derivative thereof, or mixtures thereof, (ii) carbon disulphide and (iii) sulphur, are reacted under conventional conditions in the presence of a catalyst, characterised in that the catalyst is an acid, acidic substance or acid-forming substance selected from the group comprising a carboxylic acid, an inorganic or organic acid, an anhydride or mixed anhydride of these acids, a Lewis-acid or a Lewis-acid in the presence of a co-catalyst, a solid acidic inorganic material, a hydroxy-aryl derivative and one or more halogens, or any mixture thereof.

2. The process according to Claim 1 wherein the catalyst is an aryl- or alkane sulphonic acid, such as benzene sulphonic acid, p-toluene sulphonic acid, or p-toluene sulphonic acid monohydrate, or an anhydride or mixed anhydride of these acids, such as p-toluene sulphonic acid anhydride, or a mixture thereof.

3. The process according to Claim 1 wherein the catalyst is a C C₃ alkanoic acid, such as acetic acid, a halogenated C_rC₃ alkanoic acid, such as trichloroacetic acid, an anhydride or mixed anhydride of these acids, or a mixture thereof.

4. The process according to Claim 1 wherein the catalyst is a non- oxidising acid, such as phosphoric acid, an anhydrous hydrogen halide, or an aqueous solution of a hydrogen halide.

5. The process according to Claim 1 wherein the catalyst is a boron trihalide, e.g. boron trifluoride, an aluminium halide, e.g. aluminium chloride, a zinc halide, e.g. zinc chloride or a titanium tetrahalide, e.g. titanium tetrachloride.

6. The process according to Claim 1 wherein the catalyst is selected from the group comprising an acidic mineral, an acidic clay, and an acidic oxide or sulphide, partially or fully present in protonic form, such as alumina, silica, a mixture thereof, or an alumina silicate.

7. The process according to Claim 1 wherein the catalyst is a phenol, a substituted phenol, a benzene diol or a benzene triol.

8. The process of any of Claims 1 to 7 which is carried out in the presence of an additional amount of hydrogen sulphide.

9. The process according to any of Claims 1 to 8 wherein the starting substrate (i) is a mixture of aniline and up to 45% by weight of nitrobenzene, nitrosobenzene or a mixture thereof.

10. The process of any of Claims 1 to 9 wherein thiocarbanilide or 2-anilinobenzothiazole or a mixture thereof, or a mixture thereof with aniline is used as substrate.

11. A process for making 2-mercaptobenzothiazole which comprises reacting under conventional conditions 2-anilinobenzothiazole with hydrogen sulphide or with hydrogen sulphide and carbon disulphide or with hydrogen sulphide and sulphur or with hydrogen sulphide, carbon disulphide and sulphur, in the presence of a catalyst as defined in any of Claims 1 to 10.

12. A process for making 2-mercaptobenzothiazole which comprises reacting thiocarbanilide with sulphur or with sulphur and carbon disulphide or with hydrogen sulphide or with hydrogen sulphide and sulphur or with hydrogen sulphide and carbon disulphide or with hydrogen sulphide, sulphur and carbon disulphide, under conventional conditions in the presence of a catalyst as defined in any of Claims 1 to 10.