WO2007102766A1

WO2007102766A1 - Process for production of a bis-phthalonitrile monomer

Info

Publication number: WO2007102766A1
Application number: PCT/SE2007/000210
Authority: WO
Inventors: Jukka Tulisalo
Original assignee: Perstorp Specialty Chemicals AB
Current assignee: Perstorp Specialty Chemicals AB
Priority date: 2006-03-06
Filing date: 2007-03-05
Publication date: 2007-09-13
Anticipated expiration: 2008-09-06
Also published as: SE530059C2; SE0600484L; KR20080098435A; CN101395201A

Abstract

Dislosed is a process for production of a bis-phthalonitrile monomer having an oligophenyl ether spacer chain, said bis-phthalonitrile of Formula (I) wherein n is 2. The process comprises (i) subjecting a 3-alkoxyphenol to reaction with a m-dihalobenzene in the presence of a base and a catalyst composition comprising a copper salt and a ligand whereby a 1,3-bis (3-alkoxyphenoxy) benzene is yielded, (ii) subjecting yielded 1 ,3-bis (3-alkoxyphenoxy) benzene to reaction with a dealkylating agent yielding 1 ,3-bis(3- hydroxyphenoxy)benzene, and (iii) subjecting yielded 1,3-bis (3-hydroxyphenoxy) benzene to reaction with a 4-nitrophthalonitrile in presence of a base yielding 1,3-bis [3-(3,4-dicyano- phenoxy)phenoxy]benzene.

Description

PROCESS FOR PRODUCTION OF A B/S-PHTHALONITRILE MONOMER

The present invention relates to a process for production of a b/s-phthalonitrile monomer having an oligophenyl ether spacer chain. Said monomer being of Formula (I)

More specifically, the present invention relates to a novel process for production of said monomer wherein n is 2. In a further aspect, the present invention refers to the use of an intermediate product, obtained in the process according to the present invention, in processes yielding a b/s-phthalonitrile monomer of Formula (I) wherein n is 4 or 6.

Phthalonitrile (PN) resins were originally developed by the U.S. Naval Research Laboratory in the beginning of 1980's as a high-temperature alternative to polyimide resins. PN resins are thermosets derived from b/s-phthalonitrile monomers. These monomers polymerise in the presence of a curing agent in an additional-type reaction forming a triazine network. The fully cured resins exhibit good thermal and oxidative stability and have long-term mechanical properties at elevated temperatures. Furthermore, the benzene rings forming the backbone structure of the monomers are very stable. The combination of these properties implies production of composite materials being very fire resistant.

Various phthalonitrile monomers and polymers are described in a large number of patents and patent applications generally teaching methods for producing and polymerising phthalonitrile monomers. Disclosed monomers typically have two phthalonitrile groups, one at each end of a connecting spacer chain. The monomers can be cured, whereby crosslinking occurs between cyano groups.

U.S. patent no. 4,587,325 disclose in examples 1 and 5 synthesis of two b/s-phthalonitrile monomers, namely 4,4'-b/s(3,4-dicyanophenoxy)biphenyl of formula (II) and 1 ,3-b/s(3,4- dicyano-phenoxy)benzene of formula (III):

(H)

(ill)

The monomers are produced by reacting 4-nitrophthalonitrile with an aromatic dio! and both monomers can be used as a precursor in production of PN resins. However, these monomers are disadvantaged by the relatively high processing temperature and, due to the high melting points of the monomers, a narrow processing window. The melting point of 4,4'-b/s(3,4- dicyanophenoxy)bipheny] is approx. 235⁰C and the melting point of 1 ,3-b/s(3,4-dicyano- phenoxy)benzene is approx. 184⁰C.

The published international patent application WO 03/091312 teaches that b/s-phthalonitrile monomers with oligomeric or polymeric aromatic ether spacer chains due to predicted lower melting points are expected to be more useful in PN resins. Compounds with a wide window between the melting point and the cure temperature are desirable to control the rate of curing and the viscosity during curing. The thermosets also have improved physical properties, such as toughness and processability, relative to systems with a short spacer chain between the terminal phthalonitrile moieties. Generally toughness and brittleness are improved with lower crosslinking densities. This can be achieved by using PN monomers with longer spacer chains. In the same patent application the inventors disclose examples for preparation of hydroxyterminated aromatic ether oligomers formed by reacting a m-dihydroxyaromatic compound, such as a resorcinol, with a m-dihaloaromatic compound, such as 1 ,3-dibromo- benzene. The reaction is performed by Ullmann synthesis in the presence of a copper salt and cesium carbonate. The chain lengths of the aromatic ether oligomers are controlled by the molar ratio between m-dihydroxyaromatic and m-dihaloaromatic compounds. The hydroxyl terminated aromatic ether oligomers are further allowed to react with 4-nitrophthalonitrile to form b/s-phthalonitrile monomers of Formula (I), wherein the ether spacer chain comprises an average of 3, 5, 7 or 9 aromatic groups corresponding to n in said Formula theoretically being 2, 4, 6 or 8.

The processes for preparation of b/s-phthalonitrile monomers disclosed in WO 03/091312 exhibit at least following disadvantages. The reaction conditions as used in the embodiment examples yield products comprising a complex mixture of b/s-phthalonitrile monomers with a wide distribution of spacer chain lengths. Yielded products are, furthermore, isolated from an acidic water solution, whereby all water insoluble by-products, such as hydroxy and haloterminated oligomers remain in the products. This may lead to serious difficulties in controlling the reactions of the products during the curing step. Hence, such mixtures are unfavourable as precursors for PN resins wherein good thermal and oxidative stability combined with improved physical properties are required.

It has been found that there is a need for a process for production of a high-purity b/s-phthalo- nitrile monomer having an oligomeric aromatic ether spacer chain. The present invention quite unexpectedly provides a novel process for production of a b/s-phthalonitrile monomer of Formula (I) wherein n is 2 and which process yields a product with a high purity, such as more than 98%. The process of the present invention comprises the steps of: i) subjecting a 3-alkoxyphenol to reaction with a m-dihal'obenzene in the presence of a base and a catalyst composition comprising a copper salt and a ligand whereby a 1 ,3-/}/s(3-alkoxyphenoxy)benzene is yielded, ii) subjecting in Step (i) yielded 1 ,3-_<b/s(3-alkoxyphenoxy)benzene to reaction with a dealkylating agent whereby 1 ,3-ib/s(3-hydroxyphenoxy)benzene is yielded, and iii) subjecting in Step (ii) yielded 1 ,3-b/s(3-hydroxyphenoxy)benzene to reaction with a 4-nitrophthalonitrile in presence of a base whereby 1 ,3-b/s[3-(3,4-dicyano- phenoxy)phenoxy]benzene represented by Formula (I) is yielded.

A 3-alkoxyphenol is in Step (i), of the process according to the present invention, reacted with a m-dihalobenzene to form 1 ,3-jb/s(3-alkoxyphenoxy)benzene as illustrated in reaction Scheme (IV) below: (IV)

wherein R is a lower alkyl group, such as a methyl, an ethyl, a propyl or a butyl group or an alkylaryl group, such as a benzyl group, and wherein X is halogen, such as bromine or iodine. Accordingly, said alkoxy is preferably methoxy, ethoxy, propoxy, butoxy or arylalkoxy, such as benzyloxy and said halo is likewise preferably iodo or bromo. Said 3-alkoxyphenol is in preferred embodiments of the present invention 3-methoxyphenol and said m-dihalobenzene is likewise preferably 1 ,3-dibromobenzene. A suitable molar ratio is for instance 2-3 moles of 3-alkoxyphenol on 1 mole of m-dihalobenzene. The reaction is in embodiments of the present invention carried out in presence of at least one polar aprotic solvent, such as dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide and/or N-methyl-2-pyrrolidinone. The most preferred solvent is N-methyl-2-pyrrolidinone. The reaction is performed as an Ullmann ether synthesis using a base and a catalyst. Suitable bases are alkali and alkaline earth metal bicarbonates, carbonates, hydroxides and alcoholates. The carbonates are generally the preferred bases and the most preferred carbonate is potassium carbonate. Suitable amount of base is 0.5-2 moles on 1 mole of 3-alkoxyphenol present in the reaction medium. The catalysts are Ullmann ether catalysts, for instance metal salts such as copper salts. The most preferred copper salts are copper(I)iodide and/or copper(l)bromide. Further suitable copper compounds include, but are not limited to, copper(l)chloride, copper(II)bromide, copper(II)sulphate and copper(ll)acetate. A suitable amount of catalyst is normally found within the range of 0.1-10, such as 0.5-2, mole-% calculated on moles of said m-dihalobenzene. The reaction activity can be further improved by addition of a proper ligand to make for instance the copper salts more soluble in the reaction medium. Some efficient ligands have been developed for copper catalysed Ullmann ether synthesis, such as aliphatic diamines, 1 ,10-phenanthroline and its derivatives, bidentate and monodentate phosphines, amino acid derivatives and 2,2,6,6-tetramethylheptane-3,5-dione. Especially N,N-dimethyl- glycine has proven to be an effective ligand under the reaction conditions in Step (i) of the present invention. A suitable amount of ligand is for instance 0.3-20, such as 1-6, mole-% calculated on moles of said m-dihalobenzene.

A typical procedure for said Step (i) can be disclosed as follows:

3-Alkoxyphenol, such as 3-methoxyphenol is charged to the reaction vessel. The solvent, for instance N~methyl-2-pyrrolidinone, is added in an amount being at least sufficient to dissolve the reactants and the product. A base, such as potassium carbonate, is added in the range of for instance 0.5-2 moles on 1 mole of 3-alkoxyphenol and finally a sufficient amount of a suitable solvent, such as toluene is added to the mixture to enable azeotropic removal of water formed during the reaction. A stream of an inert gas, such as nitrogen or argon, is most preferably passed through the reaction vessel. The temperature is raised to 130-170⁰C distilling off toluene-water azeotrope. The reaction mixture is kept at 130-170⁰C for 1- 4 hours distilling off remaining water and toluene. 0.3-0.5 moles of a m-dihalobenzene, such as 1 ,3- dibromobenzene, on 1 mole of 3-alkoxyphenol is now added followed by addition of 0.5-2 mole-% of a catalyst, such as copper(l)iodide, and 1-6 mole-% of a ligand, such as N₁N- dimethylglycine, calculated on moles of m-dihalobenzene. The reaction mixture is stirred at 100-160⁰C for 5-24 hours or until the reaction is completed. A suitable solvent, such as toluene, is after cooling to 20-40⁰C added followed by filtration of inorganic salts from the mixture. The filtrate is washed first with an aqueous base, such as 10% NaOH, then with water and finally with an aqueous 1 % NaCI solution. Solvents/water are subsequently removed by distillation under vacuum, such as less then 30 mbar, at 60-100⁰C yielding 1 ,3-£>/s(3- alkoxyphenoxy)benzene which is used in Step (ii) with or suitably without further purification.

In said Step (i) yielded 1 ,3-ύ/s(3-alkoxyphenoxy)benzene is in Step (ii), of the process according to the present invention, dealkylated to yield 1 ,3-i)/s(3-hydroxyphenoxy)benzene as illustrated in reaction Scheme (V) below:

(V)

Dealkylation

wherein R is as previously disclosed. According to the literature there is a wide variety of reagents useful for cleaving of alkylaryl ethers, such as anhydrous sulphonic acids, NaS in N- methyl-2-pyrrolidone, NaCN in dimethyl sulphoxide, AIBr₃, AICI₃, BBr₃, BCI₃ and 48% HBr and H₂ and Pd/C for benzyl ethers. A suitable way to dealkylate 1 ,3-ib/s(3-alkoxyρhenoxy)benzene as disclosed in Scheme (V), but not limited thereto, is the use of a mixture of 48% hydrobromic acid and acetic acid as cleaving agent. The acetic acid is preferably added as an anhydride to decrease the water content of the mixture and thus to increase the reaction rate. Suitable amounts of 48% hydrobromic acid and acetic anhydride are 1-6 parts, such as 2-3 parts, by weight on 1 part by weight of 1 ,3-b/s(3-alkoxyphenoxy)benzene present.

A typical procedure for said Step (ii) can be disclosed as follows:

1 ,3-ύ/s(3-alkoxyphenoxy)benzene, such as 1 ,3~b/s(3-methoxyphenoxy)benzene, as obtained in Step (i) of the process of the present invention, is mixed with 2-3 parts by weight of 48% hydrobromic acid on 1 part by weight of said ether oligomer and the mixture is heated to 80- 100⁰C. Subsequently 2-3 parts by weight of acetic anhydride on 1 part by weight of said ether oligomer is, within for instance 10-60 minutes, added to the reaction mixture at 80-110⁰C. The reaction mixture is now stirred at 100-115⁰C for 4-20 hours or until the reaction is completed. Water and a suitable solvent, such as methyl isobutyl ketone, are after cooling to 20-40⁰C added. Phases are separated after stirring at 20-40⁰C and the organic layer is washed with water. Finally the organic phase is evaporated under vacuum, such as less than 30 mbar, at 60-100⁰C yielding 1 ,3-/?/s(3-hydroxyphenoxy)benzene which is used in Step (iii) with or suitably without further purification.

In said Step (ii) yielded 1 ,3-b/s(3-hydroxyphenoxy)benzene is in Step (iii), of the process according to the present invention, reacted with a 4-nitrophthalonitrile yielding 1 ,3-6/s[3-(3,4- dicyano-phenoxy)phenoxy]benzene as illustrated in reaction Scheme (Vl) below: (VI)

A b/s-phthalonitile monomer with a phenyl ether spacer chain is typically prepared by dissolving a hydroxyterminated aromatic ether and 4-nitrophthalonitrile in a solvent and by heating in the presence of a base. The reaction is carried out in a polar aprotic solvent, such as dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide or N-methyl-2- pyrrolidinone. The preferred solvent is N,N-dimethylformamide. Suitable bases are alkali and alkaline earth metal bicarbonates, carbonates, hydroxides and alcoholates. Carbonates are the preferred bases and most preferred carbonate is potassium carbonate. Suitable amounts of 4-nitrophthalonitrile and said base are 2-3 moles on 1 mole of 1 ,3-jb/s(3- hydroxyphenoxy)benzene present in the reaction medium.

A typical procedure for said Step (iii) can be disclosed as follows:

1 ,3-jb/s(3-hydroxyphenoxy)benzene is mixed with a solvent, such as N,N-dimethylformamide in an amount being at least sufficient to dissolve the reactants and the product. 4-nitro- phthalonitriie and a base, such as potassium carbonate, are subsequently added in a molar ratio of 2-3 moles on 1 mole of 1 ,3-b/s(3-hydroxyphenoxy)benzene. A stream of an inert gas, such as nitrogen or argon, is passed through the reaction vessel. The temperature is raised to 25-80⁰C and maintained for 3-12 hours or until the reaction is completed. The hot reaction mixture is filtered to remove inorganic salts. A suitable precipitating agent, such as methanol is added to the filtrate in an amount being at least sufficient to precipitate the desired product from the mixture. The mixture is now stirred at a temperature of between for instance -10 and 3O⁰C until the product crystallises. The solid product is collected and washed with a suitable solvent, such as methanol. The crude product can be further purified by re-crystallisation in . a suitable solvent, such as a mixture of N,N-dimethylformamide and methanol, whereby 1 ,3-b/s- [3-(3,4-dicyanophenoxy)phenoxy]benzene with a purity of for instance >98% is yielded.

It is, with the novel process of the present invention, possible to produce a high-purity bis- phthalonitrile monomer, such as 1 ,3-ύ/s[3-(3,4-dicyanophenoxy)phenoxy]benzene having a melting point of approx. 12O⁰C. The process of the present invention thus gives at least the following advantages: (1) a PN resin system based on for instance 1 ,3-b/s[3-(3,4-dicyano- phenoxy)phenoxy]-benzene exhibits, due to the relatively, low melting point, a lower processing temperature and wider processing window compared to resin systems based on PN monomers such as 4,4'-£>/s(3,4-dicyanophenoxy)biphenyI and 1 ,3-b/s(3,4-dicyanophenoxy)- benzene as disclosed in Formulas (II) and (III), and (2) difficulties in controlling the reaction during the curing step can, due to the high purity of the product, substantially reduced or even eliminated.

The intermediate 1 ,3-ύ/s(3-hydroxyphenoxy)benzene, yielded in said Step (ii), is furthermore, useful in production of a hydroxyterminated aromatic ether oligomer having even longer oligophenyl ether spacer chains by Ullmann ether reaction with a 3-alkoxyhaloaromatic compound and dealkylated as illustrated in reaction Scheme (VII) below: (VII)

wherein R and X are as previously defined and suitable. A suitable 3-alkoxyhaloaromatic compound is for instance 3-methoxybromobenzene. Other preferred reactants, bases, dealkylation agents and reaction conditions are as previously disclosed. Yielded hydroxyterminated aromatic ether oligomer can be allowed to react further with 4-nitro- phthalonitrile to yield a b/s-phthalonitrile momomer of Formula (I) wherein n is 4. Yielded hydroxyterminated aromatic ether oligomer can also be subjected to a second reaction with a said 3-alkoxyhaloaromatic compound and a second dealkylation yielding a hydroxyterminated aromatic ether oligomer, which after reaction with 4-nitrophthalonitrile, yields a b/s- phthalonitrile momomer of Formula (I) wherein n is said 6.

A yielded hydroxyterminated aromatic ether oligomer may of course repeatedly be subjected to reactions with said a 3-alkoxyhaloaromatic compound and dealkylated prior to each reaction with said a 3-alkoxyhaloaromatic compound, yielding, after a final reaction with 4-nitrophthalonitrile, a b/s-phthalonitrile momomer of Formula (1) wherein n is said 8, 10, 12 etc.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilise the present invention to its fullest extent. The following preferred embodiments are, therefore, to be construed as merely illustrative and not limitative of the remainder of this disclosure in any way whatsoever. In the following, Examples 1-3 refer to preparation of a b/s-phthalonitrile monomer according to embodiments of Steps (i) to (iii) of the process of the present invention.

Example 1

64.8 g of 3-methoxyphenol, 60 ml of N-methyl-2-pyrrolidinone, 72.2 g of potassium carbonate and 100 ml of toluene were charged in a 500 ml three-necked reaction flask equipped with a thermometer, a mechanical stirrer, a distillation chain and a nitrogen inlet. A stream of nitrogen was passed through the vessel. The mixture was heated to 15O⁰C and a toluene-water azeotrope was distilled off from the mixture. Stirring was continued at 15O⁰C for 2 hours while distilling off remaining toluene and water formed during the reaction. 51.4 g of 1 ,3-dibromo- benzene, 0.40 g of copper(l)iodide and 0.66 g of N,N-dimethylglycine were subsequent a cooling to 14O⁰C added to the reaction mixture. Stirring was now continued at 14O⁰C for 11 hours, until the reaction as indicated by HPLC analysis was completed. The reaction mixture was cooied to 20-25⁰C and 200 mi of toluene was added followed by filtration of the mixture to remove inorganic salts. The filter cake was washed with 2 x 40 ml of toluene and the washings were combined with the filtrate. 200 ml of an aqueous 10% NaOH solution was added to the filtrate, the mixture was stirred for 15 minutes and the layers were separated. The organic layer was washed with 200 ml of water and finally with 200 ml of an aqueous 1 % NaCI solution. The toluene was finally removed from the organic layer by evaporation at 80-85⁰C and a vacuum of 20 mbar yielding 66.9 g of 1 ,3-b/s(3-methoxyphenoxy)benzene as a redish oil.

Example 2

65.8 g of 1 ,3-£>/s(3-methoxyphenoxy)benzene obtained in Example 1 and 170 g of a 48% hydrobromic acid was charged to a 1000 ml three-necked reaction flask equipped with a thermometer, a mechanical stirrer and a condenser. The mixture was heated to 90⁰C and 162 g of acetic anhydride was within 20 minutes added from a drop funnel at 90-105⁰C. Stirring was allowed to continue at 105-111⁰C for 10 hours, until the reaction as indicated by HPLC analysis was completed. The reaction mixture was now cooled to 20-25⁰C and 200 ml of water and 150 ml of methyl isobutyl ketone were added. The mixture was stirred for 15 minutes and the layers were separated. The methyl isobutyl ketone layer was washed with 200 ml of water and evaporated to dryness at 80-85⁰C and a vacuum of 20 mbar yielding 63.3 g of 1 ,3-bis(3- hydroxyphenoxy)benzene as a redish viscous oil.

Example 3

62.2 g of 1 ,3-£>/s(3-hydroxyphenoxy)benzene obtained in Example 2, 160 ml of N, N- dimethylformamide, 70 g of 4-nitrophthalonitrile and 70 g of potassium carbonate were added to a 500 ml three-necked reaction flask equipped with a thermometer, a mechanical stirrer, a condenser and a nitrogen inlet. A stream of nitrogen was passed through the vessel. The mixture was heated to 58-6O⁰C and stirring was continued at said temperature for 5 hours, until the reaction as indicated by HPLC analysis was completed. The reaction mixture was subsequently filtered at said temperature to remove inorganic salts and the filter cake was washed with 2 x 30 ml of N,N-dimethylformamide. The washings were combined with the filtrate and 800 ml of methanol was added. The mixture was now stirred at 20-25⁰C until the product crystallised. The solid product was after cooling to 0-5⁰C collected by suction filtration and washed with methanol. The crude product was re-crystallised from a mixture of 180 ml of methanol and 80 ml of N,N-dimethylformamide and dried at 6O⁰C yielding 47.9 g of 1 ,3-<b/s[3- (3,4-dicyanophenoxy)phenoxy]benzene as a slightly brownish powder. Obtained product exhibited a melting point of 118-122⁰C and a purity of 98.6% (HPLC).

Claims

1. A process for production of a b/s-phthalonitrile monomer. having an oligophenyl ether spacer chain, said b/s-phthalonitrile being of Formula (I)

Formula (I)

wherein n is 2 characterised in, that said process comprises the Steps of i) subjecting a 3-alkoxyphenol to reaction with a m-dihalobenzene in the presence of a base and a catalyst composition comprising a copper salt and a ligand whereby a 1,3-b/s(3-alkoxyphenoxy)benzene is yielded, ii) subjecting in Step (i) yielded 1 ,3-b/s(3-alkoxyphenoxy)benzene to reaction with a dealkylating agent whereby 1,3-b/s(3-hydroxyphenoxy)benzene is yielded, and iii) subjecting in Step (ii) yielded 1,3-<b/s(3-hydroxyphenoxy)benzene to reaction with a 4-nitrophthalonitrile in presence of a base whereby 1,3-£>/s[3-(3,4- dicyanophenoxy)phenoxy]benzene represented by formula (I) is yielded.

2. A process according to Claim 1 characterised in, that said alkoxy is methoxy, ethoxy, propoxy or butoxy.

3. A process according to Claim 1 ch a ra cte ri s e d i n, that said alkoxy is aryl- alkoxy.

4. A process according to Claim 3 c h a ra ct e ri s e d i n, that said arylalkoxy is benzyioxy.

5. A process according to any of the Claims 1-4 characterised in, that said halo is bromo or iodo.

6. A process according to any of the Claims 1-5 ch a racteri sed in, a molar ratio said 3-alkoxyphenol to said m-dihalobenzene of 2-3:1 in said Step (i).

7. A process according to any of the Claims 1-6 c h a ra ct e ri s e d i n, that 0.5-2 moles of said base is present on 1 mole of 3-alkoxyphenol in said Step (i).

8. A process according to any of the Claims 1-7 c h a ra cte ri s e d i n, that said copper salt is present in an amount of 0.1-10, such as 0.5-2, mole-% calculated on moles of said m-dihalobenzene in said Step (i).

9. A process according to any of the Claims 1-8 c h a ra cte ri s e d i n, that said ligand is present in an amount of 0.3-20, such as 1-6, mole-% calculated on moles of said m-dihalobenzene in said Step (i).

10. A process according to any of the Claims 1-9 cha racte ri s ed i n, that said 3- alkoxyphenol is 3-methoxyphenol.

11. A process according to any of the Claims 1-10 ch aracterised i n, that said m- dihalobenzene is 1,3-dibromobenzene.

12. A process according to any of the Claims 1-11 c h a racte ri sed i n, that said copper salt is copper(l) iodide.

13. A process according to any of the Claims 1-12 c h a ra cte ri s e d i n, that said ligand is N,N-dimethylglycine.

14. A process according to any of the Claims 1-13 ch aracterised in, that said 1 ,3- jb/s(3-alkoxyphenoxy)benzene is 1 ,3-ύ/s(3-methoxyphenoxy)benzene.

15. A process according to any of the Claims 1-14 c h a ra cte ri s e d i n, that said Step (i) is performed in presence of a polar aprotic solvent and at a temperature of 100- 17O⁰C.

16. A process according to Claim 15 c h a ra cte ri s e d i n, that said polar aprotic solvent is N-methyl-2-pyrrolidinone.

17. A process according to any of the Claims 1-16 c h a ra cte ri s ed i n, that said dealkylation agent is a mixture of hydrobromic acid and acetic anhydride.

18. A process according to Claim 17 characterised in, that 1-6, such 2-3, parts by weight of 48% hydrobromic acid and 1-6, such as 2-3, parts by weight of acetic anhydride on 1 part by weight of said 1,3-£>/s(3-methoxyphenoxy)benzene are used.

19. A process according to any of the Claims 1-18 c h a ra cte ri s ed i n, that said Step (ii) is performed at a temperature of 100-115⁰C.

20. A process according to any of the Claims 1-19 characterised in, a molar ratio said 4-nitrophthalonitrile to said 1,3-jb/s(3-hydroxyphenoxy)benzene of 2-3:1 in said Step (iii).

21. A process according to any of the Claims 1-20 characte rised in, a molar ratio said base to said 1,3-jb/s(3-hydroxyphenoxy)benzene of 2-3:1 in said Step (iii)

22. A process according to any of the Claims 1-21 ch ara cte ri sed i n, that said base is an alkali or alkaline earth metal carbonate

23. A process according to Claim 22 characterised in, that said alkali or alkaline earth metal carbonate is potassium carbonate.

24. A process according to any of the Claims 1-23 ch a ra cte ri sed i n, that said Step (iii) is performed in presence of a polar aprotic solvent and at a temperature of 25- 8O⁰C.

25. A process according to Claim 24 c h a ra cte ri s e d i n, that said polar aprotic solvent is N,N-dimethylformamide.

26. A process according to any of the Claims 1-25 c h a r a c t e r i s e d i n, that yielded 1 ,3-b/s[3-(3,4-dicyanophenoxy)phenoxy]benzene is re-crystallised and has a purity of at least 98% after re-crystallization.

27. Use of said 1 ,3~jb/s[3-(3,4-dicyanophenoxy)phenoxy]benzene yielded in the process according any of the Claims 1-26, in production of phthalonitrile resins.

28. Use of 1 ,3-£>/s(3-hydroxyphenoxy)benzene, yielded in Step (ii) of the process according to any of the Claims 1-18, in a process wherein said 1 ,3-<b/s(3-hydroxyphenoxy)benzene is subjected to reaction with a 3-alkoxyhaloaromatic compound yielding a hydroxyterminated aromatic ether oligomer.

29. Use according to Claim 28, in a process wherein said 3-alkoxyhaloaromatic compound is 3-methoxybromobenzene.

30. Use according to Claim 28 or 29, in a process wherein yielded hydroxyterminated aromatic ether oligomer is subjected to reaction with 4-nitrophthalonitrile yielding a bis- phthalonitrile momomer of said Formula (i) wherein n is 4.

31. Use according to Claim 28, in a process wherein yielded hydroxyterminated aromatic ether oligomer is subjected to reaction with a 3-alkoxyhaloaromatic compound yielding a hydroxyterminated aromatic ether oligomer.

32. Use according to Claim 31 , in a process wherein said 3-alkoxyhaloaromatic compound is 3-methoxybromobenzene.

33. Use according to Claim 31 or 32, in a process wherein yielded hydroxyterminated aromatic ether oligomer is subjected to reaction with 4-nitrophthalonitrile yielding a bis- phthalonitrile momomer of said Formula (I) wherein n is 6.