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 4,4'—stilbenedicarboxylate esters. More specifically, this invention pertains to a 4—step process for the synthesis of dialkyl 4,4'—stilbene— dicarboxylates from 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. For example, 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 preparation of a mixture of 4,4'—bibenzyldicar— boxylie and 4,4'—stilbenedicarboxylic acids by heating a stoichiometric excess of p—toluic acid with sulfur is disclosed in U.S. Patent 2,677,703.
• 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.
• Dimethyl 4,4'—stilbenedicarboxylate is obtained in an overall yield, based on the methyl p—formyl- benzoate starting material, of 37.5%. Both of these methods, like the process of U.S. Patent 2,677,703, produce hydrogen sulfide. These processes require the use of special, dedicated equipment and are not well suited for use in general purpose equipment. Additional methods for preparing stilbene compounds are described by K. B. Becker, Synthesis of Stilbenes, Synthesis, May 1983, 341-368 and U.S. Patent 5,113,010. We have developed a process which does not require the use of sulfur and may be operated at moderate process conditions in general purpose, chemical manufacturing equipment. The process of the present invention provides a novel method for producing a dialkyl 4,4'—stilbenedicarboxylate having the formula
• step (1) (2) contacting the alkyl p-(hydroxymethy1)benzoate of step (1) with a trialkyl phosphite having the formula (R 2 0) 3 P to obtain a phosphite ester compound having the formula:
• step (3) contacting the phosphite ester of step (2) with a catalytic amount of iodine to rearrange the phosphite ester to a phosphonate ester having the formula:
• step (3) (4) contacting the phosphonate ester compound of step (3) with an alkyl p—formylbenzoate, e.g., having formula (II) , 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.
• an alkyl p—formylbenzoate e.g., having formula (II)
• the alkyl p—formylbenzoate, e.g. , methyl p—formyl ⁇ benzoate, used in steps (1) and (4) is produced in large amounts as a byproduct in the manufacture of dimethyl terephthalate which is used in the production of poly(ethylene terephthalate) polymer.
• the 4—step process may be operated in general purpose equipment in which steps (2) , (3) and (4) may be carried out in the same reactor.
• the first step of the process is carried out in pressure equipment wherein an alkyl p-formylbenzoate such as methyl p-formylbenzoate is selectively and catalytically hydrogenated at a temperature of 40 to 110°C and a pressure of 20 to 70 bars absolute in the presence of a nickel hydrogenation catalyst and an inert, organic solvent.
• the catalyst preferably is Raney nickel or a supported nickel catalyst such as nickel on a silica/alumina catalyst support material wherein nickel constitutes 1—70 weight percent of the catalyst.
• the hydrogenation usually is performed in the presence of an inert, organic solvent such as, for example, aliphatic and aromatic hydrocarbons, e.g., hexane, heptane, benzene, toluene and the xylenes; chlorinated, aromatic hydrocarbons, e.g. , chlorobenzene and dichlorobenzene; and alkyl carboxylate esters, e.g., C j —C 4 alkyl esters of carboxylic acids containing 2 to 4 carbon atoms.
• the preferred hydrogenation conditions comprise a temperature in the range of 60 to 75°C and a pressure of 40 to 60 bars absolute. Normally, after separation of the catalyst, for example, by filtration, and removal of most or essentially all of the solvent by distillation, the product of step (1) is used in step (2) without further purification.
• Step (2) is carried out by simply heating a mixture of the alkyl p-(hydroxymethyl)benzoate from step (1) and a trialkyl phosphite at a temperature of 120 to 160°C.
• Step (2) conveniently is performed using an excess of the trialkyl phosphite as the reaction solvent or medium.
• the mole ratio of trialkyl phosphite to the alkyl p—(hydroxymethyl)benzoate may be in the range of 10:1 to 1:1, preferably in the range of 5:1 to 2:1.
• the excess (unreacted) trialkyl phosphite may be removed from the product by distillation.
• Step (3) is carried out by heating a mixture of the phosphite ester of formula (IV) with a catalytic amount of molecular iodine at a temperature in the range of 120 to 180°C.
• the amount of iodine used usually will be an amount which gives an iodine:phosphite ester weight ratio in the range of 1:50 to 1:300 with a weight ratio in the range of 1:100 to 1:200 being preferred.
• an inert solvent may be preferred to dissipate the heat of reaction.
• Inert solvents which may be used include dimethylformamide, dimethylacetamide, glycol diethers, glycol diesters, glycol ether esters and haloaromatic compounds.
• Step (3) preferably is conducted at a temperature of 140 to 150°C.
• the fourth step of the process of the present invention comprises contacting the phosphonate ester compound of step (3) with an alkyl p—formylbenzoate in the presence of an alkali metal alkoxide and an inert solvent to obtain the dialkyl 4,4'—stilbenedicarbox ⁇ ylate.
• alkali metal alkoxides which may be used in step (4) 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 (4) typically is carried out at a temperature of 25 to 35°C in the presence of an inert, organic solvent such as the polar, aprotic solvents described above.
• step (3) the iodine—catalyzed isomerization of trimethyl phosphite to the corresponding dimethyl methylphosphonate is described by V. K. Yadav in Synthetic Communications, 20(2), 239-246 (1990) .
• step (4) the reaction of diethyl p—carboxybenzylphosphonate with p-(2—benzox— azolyl)benzaldehyde in the presence of DMSO and sodium methoxide to produce 4—(2'—benzoxazolyl)—4'—stilbene— carboxylie acid is described in Example 22 of U.S. Patent 3,586,673. Seus et al..
• step (3) The product (0.1 mole) of step (2) is added slowly over a period of 8 minutes to a hot solution of iodine (0.2 g) in diroethylformamide (DMF, 50 mL) and the mixture is maintained at 140°C for 3 hours.
• dimethyl 4,4'—stilbenedicarboxylate is obtained in a 65% yield based on the amount of methyl 4-(hydroxy- methy1)benzoate employed.

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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 US08/398,840 patent/US5473098A/en not_active Expired - Fee Related
  • 1995-10-18 TW TW084110954A patent/TW307755B/zh active
  • 1995-12-20 MY MYPI95003992A patent/MY131728A/en unknown
• 1996
  • 1996-02-23 PL PL96322138A patent/PL322138A1/xx unknown
  • 1996-02-23 DE DE69605405T patent/DE69605405D1/de not_active Expired - Lifetime
  • 1996-02-23 WO PCT/US1996/002465 patent/WO1996027578A1/en not_active Ceased
  • 1996-02-23 CA CA002214655A patent/CA2214655A1/en not_active Abandoned
  • 1996-02-23 CN CN96193573A patent/CN1183092A/zh active Pending
  • 1996-02-23 EP EP96908508A patent/EP0813516B1/en not_active Expired - Lifetime
  • 1996-02-23 JP JP8526897A patent/JPH11503411A/ja active Pending
  • 1996-03-06 ZA ZA961844A patent/ZA961844B/xx unknown

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