Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/30—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group
  • C07C67/333—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group by isomerisation; by change of size of the carbon skeleton
  • C07C67/343—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group by isomerisation; by change of size of the carbon skeleton by increase in the number of carbon atoms

Definitions

• This invention pertains to a novel process for the preparation of esters of 4,4'—stilbenedicarboxylic acid. More specifically, this invention pertains to a 3—step process for the synthesis of dialkyl esters of 4,4'—stilbenedicarboxylic acid from p—toluic acid and alkyl p—formylbenzoates utilizing intermediate phosphite and phosphonate compounds.
• Dialkyl 4,4'—stilbenedicarboxylates and 4,4'—stil ⁇ benedicarboxylic acid are used in the manufacture of optical brighteners or whiteners.
• U.S. Patent 4,921,964 discloses the preparation of bis(2—benzoxazolyl)stilbene compounds by the reaction of dialkyl stilbenedicarboxylate esters with various 2-aminophenol compounds in the presence of certain solvents and catalysts.
• Optical brighteners are used extensively in synthetic plastics and fibers to improve the appearance, e.g., the apparent whiteness, thereof.
• the disadvantages involved in this method for producing 4,4'—stilbene ⁇ dicarboxylic acid include (i) high temperatures in the range of 250 to 290°C are required, (ii) the product mixture containing the starting material, p-toluic acid, and the 2 products, 4,4'—bibenzyldicarboxylic and 4,4'—stilbenedicarboxylic acids, are very difficult to separate, (iii) the low yields, e.g., 40% at best, obtained, and (iv) the necessity to prevent the hydrogen sulfide produced from escaping by costly scrubbing procedures.
• a known method for synthesizing dimethyl 4,4'—stilbenedicarboxylate comprises the steps of (1) contacting methyl p—formyl— benzoate with hydrogen sulfide at 0°C in the presence of hydrochloric acid to produce a cyclic trisulfide compound and (2) heating the cyclic trisulfide compound at 220 to 260°C in the presence of copper and diphenyl ether.
• the process of the present invention provides a novel method for producing a dialkyl ester of 4,4'—stilbenedicarboxylic acid having the formula
• step (1) preparing p-(chloromethyl)benzoic acid by chlorinating p-toluic acid with sulfuryl chloride in the presence of a free radical initiator and chlorobenzene or dichlorobenzene; (2) contacting the p—(chloromethyl)benzoic acid of step (1) with a trialkyi phosphite having the formula (R 2 0) 3 P to obtain a phosphonate compound having the formula:
• step (2) contacting the phosphonate ester compound of step (2) with an alkyl p-formylbenzoate in the presence of an alkali metal alkoxide and an inert solvent to obtain the dialkyl 4,4'—stilbenedicarboxylate; wherein R 1 is alkyl of 1 to 6 carbon atoms and R 2 is alkyl of 2 to 6 carbon atoms.
• the 3—step process may be operated in general purpose equipment in which steps (2) and (3) may be carried out in the same reactor.
• the first step of the process is carried out in chlorination equipment wherein p-toluic acid is contacted with sulfuryl chloride in the presence of a free radical initiator and chlorobenzene and/or dichlorobenzene to convert the p-toluic acid to p—(chloromethyl)benzoic acid (or a—chlorotoluic acid).
• This chlorination procedure is carried out at a temperature of 70 to 100°C at ambient or autogenous pressure using at least 1, and preferable 1.1 to 2 moles of sulfuryl chloride per mole of p—toluic acid.
• the free radical initiator may be selected from various peroxides such as aroyl peroxides, e.g., benzoyl peroxide, and azo compounds such as 2,2'—azobisisobutyr- nitrile and 1,1— zobis(cyclohexanecarbonitrile) .
• the amount of free radical initiator employed typically is in the range of 0.01 to 0.10 moles initiator per mole of p—toluic acid.
• chlorobenzene, dichlorobenzene or a mixture thereof as the process solvent produces an unexpected benefit in that the desired product, p—(chloromethyl)benzoic acid, is essentially insoluble in chlorobenzene and dichloro ⁇ benzene.
• step (1) of the process defined above constitutes a separate embodiment of the present invention.
• the weight ratio of chlorobenzene and/or dichlorobenzene solvent employed to the p—toluic acid starting material normally is 1:1 to 5:1, preferably 2:1 to 4:1.
• the p-(chlorc— methyl)benzoic acid obtained from step (1) is isolated by filtration, normally washed to remove residual sulfuryl chloride and initiator and used in step (2) without further purification.
• Step (2) is carried out by simply heating a mixture of the p—(chloromethyl)benzoic acid from step (1) and a trialkyi phosphite at a temperature of 140 to 180°C.
• Step (2) conveniently is performed using an excess of the trialkyi phosphite as the reaction solvent or medium.
• the mole ratio of trialkyi phosphite to the p—(chloromethyl)benzoic acid may be in the range of 2:1 to 10:1, preferably in the range of 3:1 to 5:1.
• the excess (unreacted) trialkyi phosphite normally is removed from the product by distillation.
• step (2) the toluic acid carboxyl group is esterified with an alkyl group derived from the phosphite ester (R 2 0) 3 P.
• This esterification inherent in step (2) results in the formation of a stilbenedicarboxylic acid diester rather than a monoester.
• the third step of the process of the present invention comprises contacting the phosphonate ester compound of step (2) with an alkyl p-formylbenzoate having the structure
• alkali metal alkoxides which may be used in step (3) include the sodium, potassium, lithium and cesium alkoxides containing 1 to 4 carbon atoms.
• the amount of alkali metal alkoxide used typically is at least one mole alkali metal alkoxide per mole of alkyl p-formylbenzoate, preferably 1.2 to 2.0 moles alkali metal hydroxide per mole of alkyl p-formylbenzoate.
• Step (3) typically is carried out at a temperature of 25 to 35°C in the presence of an inert, polar, aprotic solvent.
• Inert solvents which may be used include dimethylformamide, dimethylacetamide, dimethylsulfoxide, glycol diethers, glycol diesters, glycol ether esters and haloaromatic compounds.
• step (1) the chlorination of toluene using sulfuryl chloride and benzoyl peroxide is disclosed by Kharasch et al., J. Amer. Che . Soc. , 61,
• the mixture is cooled to 15°C with an ice— ater bath and the product, p—(chloromethyl)benzoic acid, is collected by filtration, washed with cold (15°C) toluene (4 x 25 mL) and dried in a 60°C vacuum oven.
• the yield of product is 26.0 g (76% of theory) having a purity of 95% as determined by gas chromatography.
• reaction mixture then is cooled, toluene (100 mL) is added and the toluene solution of the product is washed with water (6 x 100 mL) to a pH of 4 to 5.
• the toluene is distilled off under reduced pressure (150 torr) and a temperature of less than 100°C (base temperature) over a period about 1 hour.
• the product consisting primarily of diethyl p—(ethoxycarbonyl)benzylphosphonate, is obtained in a yield of 37 g (88% of theory) and used in step (3) without further purification.
• the product is collected by filtration, washed with water (5 x 100 mL) to a pH of 6—7, washed with methanol and then dried.
• the yield of product is 29.5 g, 80% of theory.
• FDMS analysis shows that a major portion of the product is the methyl ethyl diester and a minor portion is the dimethyl diester of 4,4'—stilbenedicarboxylic acid.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)

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• 1995
  • 1995-03-06 US US08/398,841 patent/US5470998A/en not_active Expired - Fee Related
  • 1995-10-18 TW TW084110962A patent/TW307756B/zh active
• 1996
  • 1996-02-23 PL PL96322137A patent/PL322137A1/xx unknown
  • 1996-02-23 WO PCT/US1996/002463 patent/WO1996027577A1/en not_active Ceased
  • 1996-02-23 CN CN96193574A patent/CN1077879C/zh not_active Expired - Fee Related
  • 1996-02-23 EP EP96906610A patent/EP0813515B1/en not_active Expired - Lifetime
  • 1996-02-23 DE DE69609056T patent/DE69609056T2/de not_active Expired - Fee Related
  • 1996-02-23 CA CA002214637A patent/CA2214637A1/en not_active Abandoned
  • 1996-02-23 JP JP8526895A patent/JPH11501314A/ja active Pending
  • 1996-03-06 ZA ZA961843A patent/ZA961843B/xx unknown

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