GB2149795A

GB2149795A - Thio substituted triaryl sulphonium salts

Info

Publication number: GB2149795A
Application number: GB08429013A
Authority: GB
Inventors: Michael Ellwood
Original assignee: Sericol Ltd
Current assignee: Sericol Ltd
Priority date: 1983-11-17
Filing date: 1984-11-16
Publication date: 1985-06-19
Also published as: EP0142384A2; GB8429013D0; EP0142384A3; JPS60166690A; EP0142384B1; GB2149795B; ATE29250T1; GB8330692D0; DE3465736D1

Abstract

Salts useful as photoinitiators are produced by introducing a halogen into a mixture of a diarylsulphide and a Lewis acid catalyst (preferably AlCl3) and from 0.2 to 2 parts by weight of inert solvent (preferably dichloromethane) per part of diarylsulphide followed by an aqueous phase anion exchange reaction with HX, NaX or KX where X is BF4, PF5, SbF5OH, AsF6, or SbF6. The products have the formula III:- <IMAGE> in which Ar<1> is a monovalent, and Ar<2> is a divalent, aromatic radical selected from phenyl, naphthyl, anthryl, thienyl, furanyl and pyrryl which may be substituted by alkyl, substituted alkyl, alkoxy, cyano, nitro, acetamido, acyl or halogen.

Description

1 GB 2 149 795 A 1

SPECIFICATION

A method for the preparation of photo-initiators Technical field

Triaryl su 1 p h on W m corn pou nds a re va 1 ua bl e as ph otoi n itiators pa rticu 1 a rly for epoxy resi n systems.

Various methods have been described for their preparation but all have suffered from low yields and complex purification procedures.

Backgroundart

Thus in US patent 4197174 bis-[4-(d i ph enyisu 1 ph on io) phenyl] sulphide bishexafl uoroph osph ate (formula 1 below) is prepared in very low yield (ca 5%) by chlorinating a solution of diphenyisulphide in dichloromethane in the presence of AIC13. The product is obtained by aqueous extraction followed by a complex procedure of sequential precipitation.

00 00 PF6 S + S -< S+ PF6 20 0 0 25 0 0 GB Patent 2069486 reveals a method of preparation whereby chlorine is introduced into a mixture of 30 diphenyisulphide and AiCI3 in the absence of any solvent. The product thus prepared has the formula ll:

0 35 Q S -< S + PF 6 40 0 6 Yields of the.final complex sulphonium salts obtained are of the order of 80%.

A disadvantage of this method is the fact that the diaryisuiphide is the only liquid reactant in the initial condensation reaction effectively also acting as a solvent. As the chlorine gas is bubbled through the reaction mix the viscosity progressively increases to such a point that the chlorine can no longer enter the reaction mix and a signification amount of the Lewis acid remains undissolved. This rapid viscosity increase 50 effectively reduces the yield obtainable from this reacting step. A further disadvantage is the need for thorough purification of the resulting crude product to remove all traces of the strongly odoriferous diaryisulphide. If this reaction is carried out on a large scale the viscosity of the reaction mix is such that a very high torque stirrer is required for efficient agitation.

2 GB 2 149 795 A 2 Summary of the invention

Thus it is an object of this invention to provide a method of preparation of a compound of this type which does not suffer, or at least mitigates, the aforementioned problems. Thus the present invention provides a method forthe preparation of a triayisulphonium salt of the formula Ill 5 Arl 2 1+ Arl-S-Ar -S X 10 Arl wherein X may be 13F4, PF6, AsF6, SbF6 or SbF501-1; Arl is a monovalent and Ar 2 a divalent aromatic radical each of which may be selected from phenyl, naphthyl, anthryl, thieny], furanyl and pyrry], these radicals optionally being substituted with one or more alkyl, substituted alkyl, alkoxy, cyano, nitro, acetamido or acyl groups or halgen atoms; which is characterised in that it comprises forming a triaryisulphonium halide in an initialreaction between a diaryisulphide Arl-S-Ar', a Lewis acid catalyst and a halogenin the presence of 20 from 0.2 to 2 parts by weight of an inert solvent per part of diaryisulphide and at a temperature between O'C and 2WC followed by an aqueous phase anion exchange between the triaryisulphonium halide and a compound of the formula NaX,KX or HX, where X is as defined above, and then separation and purification of the resultant sulphonium salt.

Preferably the initial reaction mixture containing the triaryisulphonium halide is poured directly into substantially an equal weight of a mixture of ice and water. This has the effect of hydrolysing the Lewis acid complex present.

Said initial reaction is preferably accomplished at a temperature of between 1 Wto WC. This condensation reaction can be performed at ambient temperature or above but the yield obtained at such temperatures is lower than that obtained if the reaction is carried out in an ice bath within the range 0 to 2WC or as mentioned 30 above preferably 10 to WC.

Typical inert solvents which may be used in the present invention include for example dichloromethane, carbon disulphide, nitrobenzene, or nitromethane. The preferred solvent is dichloromethane which is nonflammable, has relatively low toxicity and is easily removable due to its low boiling point. The amount of solvent utilised should be sufficient to provide solubility of the diarysulphide, 0.2 to 2 parts by weight of solvent per part of diarylsulphide is desirable and preferably 0.25 to 1 parts per part. The solvent is inert only to the extent that it does not react significantly with the diaryisulphide or the Lewis acid, the latter, of course, being extremely reactive and thus limiting the selection of "inert" solvents.

The Lewis acid catalyst may be selected from those well known for their efficiency in Friedel Craft reactions, such as aluminium chloride or bromide, boron trifluoride or trichloride, ferric chloride, stannic 40 chloride, phosphorus pentafluoride, arsenic pentafluoride or antimony pentafluoride. The catalyst is added with agitation. The amount of catalyst employed may be 0.1 to 5 moles per mole of diaryisulphide and preferably 0.25 to 1 moles per mole.

It is preferred that elemental halogen is added in the initial reaction, preferably at such a rate that the reaction temperature does not exceed WC whilst maintaining agitation. It is preferable to add from 0.2 to 2 45 moles of elemental halogen per mole of diaryisulphide.

After addition of the halogen the reaction mix may be stirrred at 10-1 50C for a further 0.5 to 2 hours.

Although the sulphonium chloride, bromide or iodide thus prepared in said initial reaction may be isolated by conventional techniques, it is nevertheless preferable to continue the preparation of the end product with the intermediate product retained in an aqueous phase.

To the aqueous reaction mix maintained at a temperature of from 2Wto 1 OWC is added, with agitation, the sodium or potassium salt or fluoroboric acid, hexafluorophosphoric acid, hexafluoroarsenic acid or hexafluoroantimonic acid. The free acids themselves may be employed in this invention but this is not preferred due to their extremely corrosive natures. These salts are added in essentially equimolar proportions with respect to the sulphonium chloride, bromide or iodide, any excess merely increasing the 55 costs of the process.

The polyhalogenometal or metalloid sulphonium salt is then recovered by decantation or filtration. The essentially pure product is washed with water and preferably an organic solvent in which the product is insoluble, such as diethylether, isopropyl alcohol or petroleum spirit. The purified product is then dried under vacuum at 40-1 OWC.

In order to illustrate the various aspects of the present invention the following non-limiting examples are detailed. All parts are by weight unless otherwise specified.

3 GB 2 149 795 A 3 Example 1

500 parts diphenyisulphide were admixed with 260 parts dichloromethane in a glass reaction vessel in an ice bath. 200 parts ground aluminium chloride were added with stirring, chlorine gas was then rapidly bubbled through the reaction mix for 3 hours during which time the temperature was maintained at 13-15'C.

After this the weight of the reaction flask and contents had increased by 50 parts. The contents of the flask were then poured onto 1,000 parts of ice.

The resultant creamy paste was heated to WC and 270 parts of potassium hexafluorophosphate were added portion wise with agitation, the whole was then heated on a steam bath to remove the dichloromethane. The solid product was isolated by decantation, washed twice with water and twice with 10 diethyl ether, then dried under vacuum at 40'C. The product was identified as 4thiophenoxytriphenyisulphonium hexafluorophosphate by virtue of its]R, UV and C13NiVIR spectra. There asobtained 683 parts of this product which represents 98% of theoretical yield based on the diphenyisulphide. The above procedure was repeated in the absence of any solvent. The product thus obtained was a white sticky solid, 435 parts representing 63% of theoretical yield based on diphenyisulphide. Confirmation 15 of the product as 4-thiophenoxytriphenyisulphonium hexafluorophosphate was achieved by IR and UV spectroscopy. This example illustrates the much higher yields obtainable using a small amount of an inert solvent.

Example 2

35 pa rts of grou nd al u miniu m chloride were added to a sol ution of 100 pa rts diphenyisul phide in 66 pa rts 20 dichloromethane. The reaction was maintained at WC whilst 43 parts of bromine were added portionwise.

After stirring for a further 4 hours the mixture was poured onto 500 parts of ice, the whole was then heated to WC and 60 parts of potassium hexafl uo rop hosp hate were added. The resultant cream coloured semi-solid was washed twice with warm water and isopropyl alcohol and dried under vacuum at 4WC. 133 parts of a white solid were obtained being 97% of theoretical yield based on diphenyisulphide; the productwas identified as 4-thiophenoxytriphenyisulphonium h exafl u orophosph ate from its IR, UV and Cl' NMR spectra.

Example 3

An exam pie i 1 lustrating the use of the above prepared sul phonium salt as a cationic photoinitiator for epoxy resins is given below.

A 3% solution of 4-thiophenoxytriphenyisulphonium hexafluorophosphate in 3,4-epoxy - cyclohexy lmethyl - 3,4-cyclohexanecarboxylate (sold under the designation CY 179 by Ciba Geigy) was draw coated onto a steel panel. This was passed through a water cooled, Colordry UV dryer (400 Win) at 135ft/min resulting in a tack free coating.

Example 4 pa rts diphenyisu 1 phide were admixed with 20 parts of carbon disu 1 phide in a glass reaction vessel cooled in an ice bath. 40 parts of g round aluminium chloride were added with stirring, chloride gas was then bubbled through the reaction mix for 7 hours at such a rate that the temperature was maintained at 13-18'C.

After this ti me the weig ht of the reaction vessel and its content had increased by 15 parts and no u ndissolved 40 aluminium chloride was present. The contents of the reaction vessel were then poured onto 500 parts of ice with stirring, a further 1000 parts of water were then added and the mixture was heated to WC. 60 parts potassium hexafluorophosphate were added portionwise with stirring and a white precipitate was formed. The aqueous layer was decanted off and the resultant semi solid washed twice with 1000 parts of warm water and filtered. The product was washed once with cold isopropanol and twice with ether and dried under 45 vacuum at WC. 118 parts of a cream coloured solid were obtained 87% theoretical yield based on diphenyisulphide, the product was identified as 4-thiophenoxy- triphenyisulphonium hexafluorophosphate from its IR and LIV spectra.

MethodA parts ground aluminium chloride were added to a solution of 100 parts diphenyisulphide in 400 parts dichloromethane. The reaction mix was maintained at 13-160C for 5 hours during which time chlorine was spraged into the system. After this addition the weight of the reaction flask and contents had increased by 30 parts. The reaction mixture was poured onto 500 parts of ice with stirring and a further 1000 parts of water were added. The whole was heated to 4WC and 60 parts potassium hexafluorophosphate were added portionwise with stirring. The resultant semi solid was washed twice with warm water, once with cold isopropanol and twice with ether, filtered, and dried at 600C under vacuum. 109 parts of a white solid were obtained, this was identified as 4-thiophenoxytriphenyisulphonium hexafluorophosphate by virtue of its]R and UV spectra.

Method A illustrates the use of a large excess of solvent and demonstrates that none of the product which 60 would be expected from USP 4197174 (Formula 1) was found.

4 GB 2 149 795 A 4

Claims

1. A method for the preparation of a triaryisulphonium salt of the formula UL- Arl 2 1+ Arl-S-Ar -S X- 1 A r 1 wherein X may be BF4, PF6, AsF6, SbF6 or SbFr,01-1; Arl is a monovalent and Ar2 a divalent aromatic radical 15 each of which may be selected from phenyl, naphthyl, anthryl, thienyl, furanyl and pyrry], these radicals optionally being substituted with one or more alky], substituted alky], alkoxy, cyano, nitro, acetamido or acyl groups or halgen atoms; which method is characterised in that it comprises forming a triaryisulphonium halide in an initiaireaction between a diaryisulphide Arl -S-Ar', a Lewis acid catalyst and a halogenin the presence of from 0.2 to 2 parts by weight of an inert solvent per part of diaryisulphide and at a temperature 20 between WC and 25T followed by an aqueous phase anion exchange between the triaryisulphonium halide and a compound of the formula NaX, KX or HX, where X is as defined above, and then separation and purification of the resultant sulphonium salt.

2. A method as claimed in claim 1 wherein the initial reaction mixture containing the triaryisulphonium halide is poured directly onto substantially an equal weight of a mixture of ice and water.

3. A method as claimed in claim 1 wherein the initial reaction is carried out at a temperatureIetween 10T and 15T.

4. A method as claimed in any of claims 1 to 3 wherein the inert solvent is dichloromethane, carbon disulphide, nitrobenzene or nitromethane.

5. A method as claimed in any of claims 1 to 4wherein the amount of solvent is 0.25to 1 parts byweight 30 per part of diaryisulphide.

6. A method as claimed in any of claims 1 to 5 wherein the inert solvent is dichloromethane.

7. A method as claimed in any of claims 1 to 6 wherein the Lewis acid is anhydrous aluminium chloride.

8. A method as claimed in any of claims 1 to 7 wherein the diaryisulphide is diphenyisulphide.

9. A method as claimed in any of claims 1 to 8 wherein the halogen is chorine, bromine or iodine.

10. A triaryisulphonium salt for incorporation in LIV initiated cationically curable formulations when produced by a method as claimed in any of claims 1 to 9.

11. A triaryisulphonium salt photoinitiator for use in epoxy resin containing LIV curable formulations when prepared by a method as claimed in any of Claims 1 to 9.

12. A method of preparing a triaryisulphonium photoinitiator substantially as herein before described 40 with reference to the foregoing Examples.

Printed in the UK for HMSO, D8818935, 4185, 7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.