PROCESS FOR THE PREPARATION OF 4,4'-BIS(2-BENZOXAZOLYL)STILBENES

Abstract: A description is given of a simple and low cost process for the preparation and use of 4,4'-bis(2-benzoxazolyl)stilbene compounds of formula (1) (a) in a two-step process by reacting the compound of formula (2), with the aminophenol compound of formula (3) to give the compound of formula (5) and subsequently reacting the compound of formula (5) with a strong base to give the compound ofrmula (1); or (b) in a three-step process by reacting the compound of formula (2) with the amino compound of formula (3) to give the intermediate compound of formula (4), with subsequent ring-closure reaction of this compound to give the compound of formula (5) and subsequent reaction of the compound of formula (5) with a strong base to give the compound of formula (1); wherein in formulae (1), (3), (4) and (5) R1 is hydrogen; C1-C8alkyl; -CO2R2; -NHCOR2 or -OR2; and R2 is C1-C4alkyl. The stilbene compounds prepared according to this invention are used in polymeric materials, in particular in polyethylene terephthalate (PET).

Description: Process for the preparation of 4.4'-bis(2-benzoxazolv0stilbenes The present invention relates to the preparation of 4,4'-bis(2-benzoxazolyl)stilbenes and to the use of these compounds as optical brighteners in polymeric materials. The novel process for the preparation of 4,4'-bis(2-benzoxazolyl)stiIbenes of formula can (a) be carried out in a two-step process. In the two-step process (a), the compound of formula is reacted with the aminophenol compound of formula to give the compound of formula The compound of formula (5) is then reacted with a strong base to give the compound of formula (1). In the three-step process (b), the compound of formula (2) is reacted with the amino compound of formula (3) to give the intermediate compound of formula The compound of formula (4) is then reacted by ring-closure to give the compound of formula (5). That compound (5) is then reacted with a strong base to give the compound of formula (1). In formulae (1), (3), (4) and (5) Rι is hydrogen; C C 8 alkyl; -CO 2 R 2 ; -NHCOR 2 or -OR 2 ; and R 2 is C r C 4 alkyl. CrOjAlkyl and C C 8 alkyl are straight-chain or branched alkyl radicals, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, amyl, isoamyl, tert-amyl, hexyl, heptyl, octyl or isooctyl. The novel process of preparation preferably relates to compounds of formula (1), wherein R T is hydrogen; or CrC 5 alkyl. The reaction of the 4-(chloromethyl)benzoyl chloride (compound of formula (2)) with the un- substituted or substituted 2-aminophenol (compound of formula (3)) to the 2-[4-(chlorome- thyl)phenyl]benzoxazole (compound of formula (5), 1 st step of process (a)) can be carried out in different solvents and by addition of different condensing agents. Suitable solvents are organic solvents which are inert under the given reaction conditions. Suitable solvents are, for example, aromatic and aliphatic hydrocarbons, such as nitrobenzene, chlorobenzene, o-dichlorobenzene, 1 ,2,3-trimethylbenzene, toluene, xylene, xylene isomer mixtures, tetrahydronaphthalene, α-chloronaphthalene, acetylene tetrachloride, ethylene dichloride or polyphosphoric acid, and the like. Particularly preferred is the use of trimethylbenzene, toluene, xylene, xylene isomer mixtures, polyphosphoric acid or N-methyl-2-pyrrolidone. Suitable condensing agents are preferably boric acid, polyphosphoric acid, sulfuric acid or toluenesulfonic acid. The reaction can be carried out in a wide temperature range from 80 to 200, preferably from 100 to 150°C. The reaction is preferably carried out at the boiling temperature of the respective solvent used. The reaction is preferably continued until the HCI-evolution is finished. The reaction mixture is then allowed to cool to room temperature, after which the condensing agent is added and the mixture is refluxed until the elimination of water is complete. The compound of formula (5) is worked up in customary manner by distilling the solvent and suspending the residue for a prolonged period of time, usually over 6 to 24 hours, in a suitable suspension agent, for example sodium hydrogencarbonate solution. The residue is then collected by filtration, washed with water and dried under vacuum at elevated temperature. The reaction of the 4-(chloromethyl)benzoyl chloride with the unsubstituted or substituted 2- aminophenol (compound of formula (3)) to the N-(2-hydroxyphenyl)-4-(chloromethyl)benz- amide (compound of formula (4); 1 st step of process (b)) is preferably carried out in N,N-di- methylacetamide. The product is precipitated by addition of water. The ring-closure reaction to give the compound of formula (5) (2 nd step of process (b)) is then carried out by elimination of water in one of the above-mentioned inert organic solvents and condensing agents, preferably in p-xylene and p-toluenesulfonic acid. The preparation of the stilbene end products of formula (1) is preferably carried out in an anhydrous, aprotic, polar solvent, preferably in NMP, DMA, DMF or DMSO. Dimethylform- amide (DMF) is very particularly preferred. The dimerisation is carried out under alkaline conditions by addition of sodium hydroxide, potassium hydroxide or alcoholates, which are usually added in two- to four-fold excess, based on the chloromethyl compound. In order for the reaction to proceed smoothly, the alkali hydroxide is usually added in powder form. The reaction is usually carried out at room temperature until the entire amount of the organically bound chlorine is reacted. To bind the reaction water in the neutralisation step, it may be advantageous to add the corresponding compounds, such as Na 2 O, MgO, CaO or NaH. The reaction usually takes from 6 to 12 hours. After the reaction is complete, the reaction mixture is acidified with an acid, for example with an anhydrous organic acid, such as glacial acetic acid or, preferably, with a HCI/H 2 O mixture. For working up, the reaction mixture is heated to boiling to dissolve the by-products and is then subjected to hot suction filtration. The product is then washed with solvents and water until no chloride ions can be found anymore in the washing water. After drying, the analytically pure stilbene compound is obtained. By the process of this invention it is possible to prepare 4,4'-bis(2-benzoxazolyl)stilbene compounds at low cost and in good yields. The compounds of formula (1 ) are very suitable for use as optical brighteners for organic polymeric materials. Accordingly, this invention also relates to a process for optically brightening organic polymers, which comprises admixing at least one compound of formula (1 ) to these materials. Suitable polymers are in particular polyesters derived from dicarboxylic acids and dialcohols and/or from hydroxycarboxylic acids or from the corresponding lactones, for example polyethylene terephthalate (PET), polybutylene terephthalate, poly-1 ,4-dimethylolcyclohexane terephthalate, polyhydroxybenzoate, and block-polyether-esters derived from polyethers containing hydroxyl terminal groups; as well as polyesters modified with polycarbonates or MBS. Very particularly preferred is the use of the compounds of formula (1) in polyethylene terephthalate. The amount of the optical brightener of formula (1) added depends on the respective substrate used and on its envisaged end use. Sufficient amounts are usually from 0.01 to 5 % by weight, preferably from 0.01 to 3 % by weight, based on the polymer to be brightened. According to this invention, suitable polymers are in particular those comprising 0.01 to 5 % by weight, preferably 0.01 to 3 % by weight, of at least one compound of formula (1). In certain cases it may be advantageous to use two or more of the compounds of formula (1 ). It is furthermore also possible to use one or more than one other additive, for example antioxidants, UV absorbers and light stabilisers, metal deactivators, peroxide-scavenging compounds, fillers and reinforcing agents and other additives, such as plasticisers, lubricants, emulsifiers, pigments, flame retardants, antistatic agents and blowing agents. The compounds of formula (1 ) and possible further additives are added to the polymers in the spinning mass, i.e. before or while the polymers are being moulded, for example by blending in powder form or by addition to the melt or solution of the polymer. The polymers stabilised in this manner can be used in a very wide range of forms, for example as fibres, foils, filaments, profiles, hollow articles or sheets. The following non-limitative Examples illustrate the invention in more detail. Working Examples Example 1 : Chemical equation (101) 47.2 g (0.25 mol) of 4-(chloromethyl)benzoyl chloride are added dropwise over 1 hour to a solution which is cooled to 0 to 5°C and consists of 41.3 g (0.25 mol) of 2-amino-4-t-butyl- phenol and 200 ml of N,N-dimethylacetamide. A yellow solution is obtained which is warmed to 20 to 25°C and stirred for 2.5 h. 150 ml of water are then added dropwise at 20 to 25°C, resulting in a brownish-yellow precipitate. After stirring for 1 h and filtration, the precipitate is washed with 2 1 of water and dried under vacuum at 80°C. Yield: 77.8 g (= 97.9 %) Solids content: 99.29 % 1 H-NMR spectrum (300 MHz: CDCk) δ = 1.3 (s); 4.6 (s); 7.0 (d); 7.2 (m); 7.5 (d); 7.9 (d); 8.2 (s); 8.4 (s); at a ratio of 9:2:1 :2:2:2:1 :1 Example 2: Chemical equation: xylene (101) (102) In a 350 ml sulfonation flask, 63.4 g (0.2 mol) of the compound of formula (101 ) are suspended in 220 ml of xylene, and 3.0 g (0.016 mol) of toluene-4-sulfonic acid monohydrate are then added. A beige suspension is obtained which is refluxed until all resulting water is distilled off azeotropically. After the reaction is complete, the reaction mixture is allowed to cool to 25°C and the precipitated solid is subjected to filtration and then washed first with xylene and ethanol and then with water. The product is dried at 80°C under vacuum. Yield: 26.5 g (44.2 %) 1 H-NMR spectrum (300 MHz: rP R lDMSO) δ = 1.4 (s); 4.9 (s); 7.5 (d); 7.7 (m); 7.8 (s); 8.2 (d); at a ratio of 9:2:2:2:1 :2 Example 3: Chemical equation A 350 ml sulfonation flask is charged with 80 ml of DMF, and 8.9 g (0.03 mol) of the compound of formula (102) are then added under nitrogen. At 15 to 20°C, 4.2 g (0.075 mol) of potassium hydroxide are added. The reaction mixture turns somewhat dark and is stirred for 1 h at 15 to 20°C and then heated for 1 h to 35 to 40°C. The reaction mixture is adjusted to pH 3 with 20 ml of HCI/water (1 :1 mixture). A yellow precipitate is obtained which is subjected to filtration, washed with methanol and water and then dried under vacuum at 80°C. Yield: 6.4 g (81.0 %) 1 H-NMR spectrum (300 MHz: CDCU) δ = 1.4(s); 7.3(s); 7.5(d); 7.6(d); 7.7(d); 7.8(d); 8.2(d) at a ratio of 18:2:2:2:2:2:4 Example 4: Chemical equation: dimethylacβtamide (104) In a 100 ml sulfonation flask, 9.45 g (0.05 mol) of 4-(chloromethyl)benzoyl chloride are added dropwise over 1 hour to a solution which is cooled to 0°C and consists of 6.15 g (0.05 mol) of 2-amino-p-cresol and 50 ml of dimethylacetamide. A dark solution is obtained which is warmed to 20 to 25°C and then stirred for 1.5 h at 25°C. The solution is then diluted with 25 ml water and left standing overnight. After filtration, the product is washed with water and dried under vacuum at 60°C. Yield: 12.1 g (= 87.87 %) 1 H-NMR spectrum (300 MHz: rPnlDMSOi δ = 2.3(s); 4.8(s); 6.8(m); 7.5(s); 7.6(d); 8.0(d); 9.4(s); 9.5(e) at a ratio of 3:2:2:1 :2:2:1:1 The structure corresponds to the NMR spectrum. Example 5: Chemical equation: (105) A 750 ml sulfonation flask is charged with 250 ml of xylene and 92.25 g (0.75 mol) of 2- amino-p-cresol. 144.58 g (0.765 mol) of 4-(chloromethyl)-benzoyl chloride are then added dropwise over 1 h. This mixture is heated to 90°C, slight evolution of HCI taking place. Upon heating the mixture to 110°C, the evolution of HCI becomes stronger and then stops after about 2 h. 1 g (5.3 mmol) of toluene-4-sulfonic acid monohydrate is added to the reaction mixture and this mixture is boiled under reflux (138-142°C). The water is distilled off azeotropically at this temperature. The mixture is allowed to cool and then another 1 g of toluene-4-sulfonic acid monohydrate is added and refluxing is continued. Another 10 ml of water are distilled off. The mixture is allowed to cool to 25°C and the precipitate is subjected to filtration and the filter product is dissolved again in ethanol. This product is clarified by hot filtration and cooled overnight. The product is then subjected to filtration, washed with ethanol and dried under vacuum at 60°C. Yield: 38.0 g (19.67 %) 1 H-NMR spectrum (300 MHz: CDCk) δ = 4.7(e); 7.1 (d); 7.5(d); 7.7(m); 8.2(d) at a ratio of 2:1 :1 :3:2 The structure corresponds to the NMR analysis. Example 6: Chemical equation A 350 ml sul onation flask s c arge wt . g 0.04 mol) o the compound of formula (105) and 80 ml of DMF under a nitrogen atmosphere. 11.2 g (0.1 mol) of potassium tertiary butylate are added in increments over 1.5 h at 15 to 20°C. A dark brown suspension is obtained which is stirred for 2 h at 25°C. 20 ml of HCI/water (1 :1 mixture) are added dropwise to this suspension, resulting in a yellowish brown precipitate. After filtration, the product is washed with acetone and finally with water and then dried under vacuum at 70°C. Yield: 3.8 g (42.74 %) The structure corresponds to the NMR analysis. Example 7: Chemical equation: A 350 ml sulfonation flask is charged with 80 ml of DMF. 4.45 g (0.015 mol) of the compound of formula (102) and 3.86 g (0.015 mol) of the compound of formula (105) are added thereto under nitrogen and are dissolved at 40°C. The solution is cooled to 15 to 20°C and charged with 8.4 g (0.075 mol) of potassium tertiary butylate. The solution turns dark and is stirred for 1 h at 15 to 20°C. The pH is adjusted to 3 with 15 ml of water/HCI (1:1 mixture). A yellow precipitate is obtained which is subjected to filtration and washed with methanol and finally with water. The product is then dried under vacuum at 80°C. Yield: 6.5 g. 1 H-NMR spectrum (300 MHz: CDCI^) δ = 1.4(s); 2.5(s); 7.2(d); 7.3(s); 7.5(m); 7.8(d); 7.9(s); 8.2(d ) at a ratio of 9:3:2:2:2:4:2:4

Claims: What is claimed is 1. A process for the preparation of a compound of formula (a) in a two-step process by reacting the compound of formula with the aminophenol compound of formula to give the compound of formula and subsequently reacting the compound of formula (5) with a strong base to give the compound of formula (1); or (b) in a three-step process by reacting the compound of formula (2) with the amino compound of formula (3) to give the intermediate compound of formula with subsequent ring-closure reaction of this compound to give the compound of formula (5) and subsequent reaction of the compound of formula (5) with a strong base to give the compound of formula (1); wherein in formulae (1), (3), (4) and (5) R T is hydrogen; C C 8 alkyl; -CO 2 R 2 ; -NHCOR 2 or -OR 2 ; and R 2 is d-O t alkyl. 2. A process according to claim 1 , which relates to a compound of formula (1 ), wherein Rs is hydrogen; or Cι-C 5 alkyl. 3. A process according to either claim 1 or claim 2, wherein the 1 st step of process (a) and the 2 nd step of process (b) are carried out in an inert organic solvent. 4. A process according to claim 3, wherein the reactions are carried out in trimethylbenzene, toluene, xylene, xylene isomer mixtures, polyphosphoric acid or N-methyl-2-pyrrolidone. 5. A process according to any one of claims 1 to 4, wherein the first step of process (a) is carried out in the presence of a condensing agent. 6. A process according to claim 5, wherein the reaction is carried out in the presence of boric acid, polyphosphoric acid, sulfuric acid or toluenesulfonic acid. 7. A process according to any one of claims 1 to 6, wherein the 1 st step of process (a) is carried out at a temperature in the range from 80 to 200°C. 8. A process according to claim 7, which comprises carrying out the reaction at the boiling temperature of the solvent used. 9. A process according to any one of claims 1 to 6, which comprises carrying out the 1 st step of the process (b) in the presence of N.N-dimethylacetamide. 10. A process according to any one of claims 1 to 9, which comprises carrying out the 2 nd step of the process (a) and the 3 rd step of the process (b) in an anhydrous polar, aprotic solvent. 11. A process according to claim 10, which comprises carrying out the reactions in NMP, DMA, DMF or DMSO. 12. A process for optically brightening organic polymers, which comprises admixing at least one compound of formula (1) to these materials. 13. Use of a 4,4'-bis(2-benzoxazolyl)stilbene compound prepared according to any one of claims 1 to 11 as optical brightener for organic polymers. 14. Use according to claim 13, which comprises using the 4,4'-bis(2-benzoxazolyl)stilbene compound in polyethylene terephthalate (PET). 15. Use according to either claim 13 or claim 14, which comprises using the 4,4'-bis(2-benz- oxazolyl)stilbene compound in an amount from 0.01 to 5 % by weight, based on the polymer material used. 16. Use according to any one of claims 13 to 15, which comprises adding the 4,4'-bis(2- benzoxazolyl)stilbene compound before or during the moulding of the polymer.

Inventors: OHREN STEFAN, REINEHR DIETER, OHREN, STEFAN, REINEHR, DIETER
Applicants: CIBA SC HOLDING AG, OHREN STEFAN, REINEHR DIETER, CIBA SPECIALTY CHEMICALS HOLDING INC., OHREN, STEFAN, REINEHR, DIETER
Application year: 2000
Main classification: C07D263
IPC codes: C07D263, C08K5