Title of Invention	A PROCESS FOR PREPARING STILBENES
Abstract	The present invention relates to a process for preparing stilbenes by reacting terephthataldehyde with phosphonic esters in a diluent in the presence of a base, wherein the diluent used is a two-phase system, one phase of which is water and the other phase of which is a water-immiscible organic solvent, and the reaction is carried out in the presence of a phase transfer catalyst.

Full Text

The present invention relates to a process for preparing stableness, which are used as optical brighteners. EP-A-32 254 and EP-A-64 303 disclose the preparation of bis- (cyanostyryl)benzenes using the abovementioned products as reactants. Esters, eg. methyl glycol acetate, are used as diluents, and sodium methanol ate is used as base. However, it has emerged that the use of sodium methanolate as base is disadvantageous because by-products are often formed in its presence and have an unfavorable effect on the use propertie of the bis(cyanostyryl)benzenes when used as optical brighteners It is an object of the present invention to provide a novel pro-afe cess for preparing bis(cyanostyryl)benzenes which no longer has the said disadvantages. We have found that this object is achieved by preparing stilbene of the formula I by reacting terephthalaldehyde with phosphonic esters of the for mole II where R is C1-C6-alkyl, in a diluent in the presence of a base, when the diluent used is a two-phase system, one phase of which is water and the other phase of which is a water-immiscible organic solvent, and the reaction is carried out in the presence of a phase transfer catalyst. All the alkyl radicals R occurring in the abovementioned formula II can be either straight-chain or branched. Examples of R radicals are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, hexyl or 2-methylpentyl. 5 Particularly suitable water-immiscible organic solvents are ali¬phatic or aromatic hydrocarbons such as pentane, hexane, heptane, octane, isooctane, petroleum ether, toluene, xylene, ethylben-zene, terrain, decaling, dimethylnaphthalene, white spirit, chlo-robenzene or dichlorobenzene. 10 The use of aromatic hydrocarbons, expecially xylene, is pre¬ferred. Examples of suitable bases are alkali metal or alkaline earth 15 metal hydroxides or carbonates such as lithium, sodium, potas¬sium, magnesium or calcium hydroxide or carbonate. Particular mention should be made of alkali metal hydroxides, es¬pecially in the form of their aqueous solutions, with particular 20 emphasis on 25 to 50 % by weight sodium hydroxide solution. Suitable phase transfer catalysts are all conventional products of this type as described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A 19, pages 293 25 to 298, 1991. Particular mention may be made, for example, of quaternary ammo¬nium salts such as tetraalkyl ammonium salts, in particular the corresponding chlorides or bromides, eggs. Methyltri butyl ammonium 30 chloride, tetrabutylammonium bromide, methyl trioctyl ammonium chloride, methyltricaprylammonium chloride, benzyltrimethyl-ammonium chloride or benzyltriethylammonium chloride. The use of tetraalkylammonium chlorides or bromides is preferred, 35 and particular mention may be made of tetrabutylammonium bromide or methyltrioctylammonium chloride. As a rule, 1 to 5 mole equivalents, preferably 1.2 to 4 mole equivalents, of base are used per mole of terephthalaldehyde. 40 Based on the weight of terephthalaldehyde and phosphonic ester II, normally from 100 to 200 % by weight, preferably 140 to 160 % by weight, of diluent are used. 45 A two-phase system is used as diluent according to the invention. This two-phase system generally contains water and organic sol¬vent in the ratio from 1:1 to 1:5, preferably 1:1.5 to 1:3, by volume. 5 As a rule, based on the weight of diluent, from 0.3 to 1.0 % by weight, preferably 0.5 to 0.8 % by weight, of phase transfer cat¬alyst is used. 10 The process according to the invention is generally carried out at from 0 to 50'c, preferably 10 to 35'c. The cyano group in the stilbenes of the formula I can be in ei¬ther the ortho, meta or para position with respect to the CH=CH 15 group. It is moreover possible for symmetric or asymmetric stil¬benes of the formula I, or else mixtures of such products, to oc¬cur. Mixtures of asymmetric stilbenes are obtained, for example, by 20 reacting the terephthalaldehyde initially with an ortho-, meta-or para-cyano-substituted phosphonic ester of the formula II and then with another isomer of the phosphonic ester II. To prepare symmetric stilbenes of the formula I, the novel pro-25 cess is expediently carried out by metering terephthalaldehyde into the mixture of water, organic solvent, phase transfer catalyst, base and phosphonic ester at the abovementioned temperature with stirring. The reaction is generally complete after subsequently stirring for from 2 to 20 hours, and the 30 symmetric stilbene can, where appropriate after acidification, be filtered off with suction, washed and dried. To prepare mixtures of asymmetric stilbenes of the formula I, the novel process is expediently carried out by mixing the water, or- 35 gain solvent, phase transfer catalyst, terephthalaldehyde and, based on the amount of terephthalaldehyde, a portion of a partic¬ular phosphonic ester of the formula II and then metering in a portion of the base over a period of from 2 to 8 hours at the abovementioned temperature with stirring. After subsequently 40 stirring for from 1 to 6 hours, the remaining portion of phos¬phonic ester (in the form of another isomer) is added and then the remaining portion of the base is metered in over a period of from 2 to 8 hours with stirring. After subsequently stirring for from 1 to 8 hours, the reaction mixture can be worked up as de- 45 scribed above. The novel process, which can be carried out either continuously or batch wise, provides the required products in high yield and purity. The use of alkali metal alcoholates is moreover avoided. The organic solvent which is used can easily be removed and re-5 used. As stated above, stilbenes of the formula I are valuable optical brighteners, especially for polyesters. 10 The following examples are intended to explain the invention in detail. Example 1 15 1200 ml of xylene, 620 ml of water, 10 g of phase transfer cata¬lyst based on methyltrioctylammonium chloride, 793.15 g (3.00 mol) of diethyl o-cyanobenzylphosphonate (95.7 % pure) and 290 g (3.63 mol) of 50 % by weight sodium hydroxide solution were mixed at 30°c. Subsequently, at this temperature, 249.1 g 20 (1.67 mol) of terephthalaldehyde (89 % pure) were metered in with stirring over the course of 3.5 h, and the mixture was stirred first at 30°C for 2 h and then at 20°C for 2 h. The precipitate was filtered off with suction, and the solid was washed first with 1000 ml of xylene and then with 1500 ml of water. The resi- 25 due was dried under reduced pressure at 60°c. 420 g (84 %) of the compound of the formula 30 35 were obtained. Example 2 1000 ml of xylene, 350 ml of water, 10 g of phase transfer cata-40 lyst based on methyltrioctylammonium chloride, 431.7 g (1.58 mol) of diethyl o-cyanobenzylphosphonate (92 % pure) and 208.2 g (1.50 mol) of terephthalaldehyde (96.4 % pure) were mixed at 35*C. Subsequently, at this temperature, first 148.8 g (0.93 mol) of 25 % by weight sodium hydroxide solution were metered in over the 45 course of 4 h, and then 99.2 g (0.62 mol) of 25 % by weight sodium hydroxide solution were metered in over the course of 4 h, and the mixture was subsequently stirred for 2 h. 405.7 g (1.50 mol) of diethyl m-cyanooenzyxpnosphonate (93.1 % pure) were added. Then, at 35°C, 640 g (4 mol) of 25 % by weight sodium hydroxide solution were added to the mixture over the course of 1 h, and it was then stirred at this temperature for 8 h. It was 5 cooled to room temperature and stirred at this temperature for 1 h, and the precipitate was filtered off with suction. The solid was washed first with 1500 ml of methanol and then with 1650 ml of water. The residue was dried under reduced pressure at 60*C. 10 334 g (67 %) of a mixture containing 82.3 % of the compound of the formula 15 and 9.3 % of the compound of the formula 20 25 were obtained. Example 3 30 1000 ml of xylene, 350 ml of water, 10 g of phase transfer cata¬lyst based on methyltrioctylammonium chloride, 431.7 g (1.58 mol) of diethyl o-cyanobenzylphosphonate (92 % pure) and 208.2 g (1.50 mol) of terephthalaldehyde (96.4 % pure) were mixed at 35°C. Subsequently, at this temperature, first 148.8 g (0.93 mol) of 35 25 % by weight sodium hydroxide solution were metered in over the course of 4 h, and then 99.2 g (0.62 mol) of 25 % by weight sodium hydroxide solution were metered in over the course of 4 h, and the mixture was subsequently stirred for 2 h. 407.2 g (1.50 mol) of diethyl p-cyanobenzylphosphonate (92.7 % pure) were 40 added. Then, at 35°C, 640 g (4 mol) of 25 % by weight sodium hydroxide solution were added to the mixture over the course of 1 h, and it was then stirred at this temperature for 8 h. It was cooled to room temperature and stirred at this temperature for 1 h, and the precipitate was filtered off with suction. The solid 45 was washed first with 1500 ml of methanol and then with 1650 ml of water. The residue was dried under reduced pressure at 60'c. 354 g (71 %) of a mixture containing 87 % of the compound of the formula 5 and 8.3 % of the compound of the formula 10 15 were obtained. Example 4 20 1000 ml of xylene, 350 ml of water, 10 g of phase transfer cata¬lyst based on methyltrioctylammonium chloride, 429.4 g (1.58 mol) of diethyl m-cyanobenzylphosphonate (93.1 % pure) and 208.2 g (1.50 mol) of terephthalaldehyde (96.4 % pure) were mixed at 35°C. 25 Subsequently, at this temperature, first 148.8 g (0.93 mol) of 25 % by weight sodium hydroxide solution were metered in over the course of 4 h, and then 99.2 g (0.62 mol) of 25 % by weight sodium hydroxide solution were metered in over the course of 4 h, and the mixture was subsequently stirred for 2 h. 420.3 g 30 (1.50 mol) of diethyl p-cyanobenzylphosphonate (90.3 % pure) were added. Then, at 35'C, 640 g (4 mol) of 25 % by weight sodium hydroxide solution were metered into the mixture over the course of 1 h, and it was then stirred at this temperature for 8 h. It was cooled to room temperature and stirred at this temperature 35 for 1 h, and the precipitate was filtered off with suction. The solid was washed first with 1500 ml of methanol and then with 1650 ml of water. The residue was dried under reduced pressure at 60*C. 40 342 g (69 %) of a mixture containing 80 % of the compound of the formula 45 5 were obtained. 10 Example 5 660 g (2.37 mol) of diethyl o-cyanobenzylphosphonate were added to 1 liter of chlorobenzene, and then 500 ml of water and 12 g of 15 phase transfer catalyst based on methyltrioctylammonium chloride were added to the mixture. Then 580 g of 25 % by weight sodium hydroxide solution were slowly added drop wise, during which the temperature rose to about 35°C. After this, 167 g (1.185 mol) of terephthalaldehyde were introduced over the course of 2 h, during 20 which the internal temperature was kept at from 35 to 40°c. After the addition was complete, the mixture was stirred at this tem¬perature for 4 h and subsequently 110 g of concentrated sulfuric acid were added dropwise. 25 The precipitate was .filtered off with suction and washed with 600 ml of chlorobenzene. Chlorobenzene was subsequently blown out with steam and the filter cake was washed several times with wa¬ter. 30 314 g (80 %) of pale yellow crystalline product of the formula • (melting point 221 to 225°C) were obtained. we claim: 1. A process for preparing stilbenes of the formula I 5 10 by reacting terephthalaldehyde with phosphonic esters of the formula II 15 where R is C1-C6-alkyl, in a diluent in the presence of a 20 base, wherein the diluent used is a two-phase system, one phase of which is water and the other phase of which is a water-immiscible organic solvent, and the reaction is carried out in the presence of a phase transfer catalyst. 25 2. A process as claimed in claim 1, wherein the reaction is car¬ried out at from 0 to 50°c. 3. A process as claimed in claim 1, wherein an alkali metal or alkaline earth metal hydroxide or carbonate is used as base. 30 4. A process as claimed in claim 1, wherein the diluent used is a two-phase system in which water and water-immiscible or¬ gain solvent are present in the ratio from 1:1 to 1:5 by weight. 35 5. A process as claimed in claim 1, wherein a two-phase system composed of water and an aromatic hydrocarbon is used as din¬ luent. 40 6. A process as claimed in claim 1, wherein a tetraalkylammonium chloride or bromide is used as phase transfer catalyst. Dated this 24 day of April 1995 (M V G MENON) OF DEPENNING & DEPENNING AGENT FOR THE APPLICANTS

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