Process for producing chromenes by catalysis with copper salts intended for the preparation of thermosetting resins

Abstract

A process for producing chromenes intended for the preparation of thermosetting resins, includes converting an aromatic propargyl ether of general formula (I) into a chromene by homogeneous catalysis with copper salts in anisole at a temperature between 100 and 170° C. Moreover, a process for preparing a material made of thermoset resin, includes successively a) carrying out the above process; b) polymerizing the reaction product obtained in a) so as to obtain the material made of thermoset resin; c) recovering the material made of thermoset resin obtained in b).

Claims

1. A process for producing chromenes intended for the preparation of thermosetting resins, comprising the step of converting an aromatic propargyl ether of general formula (I) below: ##STR00012## wherein: R.sub.1 and R.sub.5 represent, independently of one another, a hydrogen atom, or a C.sub.2-C.sub.6 alkene, C.sub.2-C.sub.6 alkyne, O—(C.sub.1-C.sub.6)alkyl, O—(C.sub.2-C.sub.6)alkene or O—(C.sub.2-C.sub.6)alkyne group, on condition that at least one of R.sub.1 and R.sub.5 represents a hydrogen atom; R.sub.2 and R.sub.4 represent, independently of one another, a hydrogen atom, a C.sub.2-C.sub.6 alkene group, a C.sub.2-C.sub.6 alkyne group, an O—(C.sub.1-C.sub.6)alkyl group, an O—(C.sub.2-C.sub.6)alkene group or an O—(C.sub.2-C.sub.6)alkyne group; and R.sub.3 represents a hydrogen atom, an O-(C.sub.1-C.sub.6)alkyl group or a C.sub.2-C.sub.6 alkene group, the alkene group being optionally substituted with a group of general formula (II) below: ##STR00013## wherein: R.sub.6 and R.sub.9 represent, independently of one another, a hydrogen atom, or a C.sub.2-C.sub.6 alkene, C.sub.2-C.sub.6 alkyne, O—(C.sub.1-C.sub.6)alkyl, O—(C.sub.2-C.sub.6)alkene or O—(C.sub.2-C.sub.6)alkyne group, on condition that at least one of R.sub.6 and R.sub.9 represents a hydrogen atom; and R.sub.7 and R.sub.8 represent, independently of one another, a hydrogen atom, a C.sub.2-C.sub.6 alkene group, a C.sub.2-C.sub.6 alkyne group, an O—(C.sub.1-C.sub.6)alkyl group, an O—(C.sub.2-C.sub.6)alkene group or an O—(C.sub.2-C.sub.6)alkyne group; on condition that at least one of R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 does not represent a hydrogen atom or an O—(C.sub.1-C.sub.6)alkyl group; and the cis/trans isomers thereof and the optical isomers thereof, and racemic mixtures thereof into a chromene by homogeneous catalysis with copper salts in anisole at a temperature of between 100 and 170° C.

2. The process as claimed in claim 1, wherein the aromatic propargyl ether of general formula (I) is chosen from the group consisting of propargylated resorcinol, propargylated eugenol, propargylated coupled eugenol, propargylated coupled isoeugenol, propargylated isoeugenol and mixtures thereof and the cis/trans isomers thereof and the optical isomers thereof and racemic mixtures thereof.

3. The process as claimed in claim 2, wherein the molar percentage of residual propargyl functions of the chromene is less than 11% when the aromatic propargyl ether of general formula (I) is propargylated resorcinol, the molar percentage of residual propargyl functions of the chromene is less than 39% when the aromatic propargyl ether of general formula (I) is propargylated coupled eugenol and the molar percentage of residual propargyl functions of the chromene is less than 35% when the aromatic propargyl ether of general formula (I) is propargylated coupled isoeugenol.

4. The process as claimed in claim 2, wherein the aromatic propargyl ether of general formula (I) is propargylated resorcinol and wherein the chromene obtained has the formula C and/or D below ##STR00014##

5. The process as claimed in claim 4, wherein the chromene obtained is a mixture of the formulae C and D.

6. The process as claimed in claim 2, wherein the aromatic propargyl ether of general formula (I) is propargylated resorcinol.

7. The process as claimed in claim 1, which lasts between 1 and 1000 hours.

8. The process as claimed in claim 7, which lasts between 2 and 50 hours.

9. The process as claimed in claim 1, wherein the catalyst is chosen from CuCl and CuCl.sub.2.

10. The process as claimed in claim 9, wherein the catalyst is CuCl.

11. The process as claimed in claim 1, wherein the catalyst content in the reaction medium is between 10 and 10 000 ppm.

12. The process as claimed in claim 11, wherein the catalyst content in the reaction medium is between 500 and 1500 ppm.

13. A process for preparing a material made of thermoset resin, comprising the following successive steps: a) carrying out the process as claimed in claim 1; b) polymerizing the reaction product obtained in step a) so as to obtain the material made of thermoset resin; c) recovering the material made of thermoset resin obtained in step b).

14. The process as claimed in claim 13, wherein the enthalpy of polymerization of step b) is less than 500 J/g.

15. The process as claimed in claim 13, wherein the coke content of the thermoset resin obtained in step c) is greater than 50%.

16. The process as claimed in claim 1, wherein the temperature is of between 120 and 160° C.

Description

EXAMPLE 1

Conversion of Propargylated Resorcinol and Preparation of the Resin according to the Invention

(1) Synthesis of Proparaylated Resorcinol

(2) 10 g (0.091 mol) of resorcinol (Alfa Aesar) are dissolved in 50 ml of dimethylsulfoxide (DMSO), 50 g (0.363 mol) of potassium carbonate (K.sub.2CO.sub.3) are ground and then added with magnetic stirring and the medium heated to 70° C. (ext). 14.45 ml (2.2 eq.) of propargyl chloride (ABCR) are added dropwise. The reaction is monitored by TLC with a 7:3 petroleum ether:diethyl ether (volume) eluent. After filtration and dilution in 100 ml of ethyl acetate, the medium is extracted with 3×100 ml of brine. The organic phase is dried over MgSO.sub.4, filtered and concentrated under reduced pressure. The compound is purified by vacuum distillation (T° C.=120° C., 4.5 Pa). The yield is 77.4%.

(3) Conversion of Proparaylated Resorcinol

(4) 10 grams (0.054 mol) of propargylated resorcinol previously obtained, 1000 ppm of CuCl and 100 ml of anisole are introduced into a Schlenk tube surmounted by a condenser. Bubbling of argon is carried out for 10 minutes and the medium is stored under argon. The Schlenk tube is placed in an oil bath preheated to 155° C. and the reaction is continued at reflux for 4 hours. After 4 hours, the medium is filtered through a 0.20 μm PTFE filter in order to remove the precipitates possibly formed. The anisole is evaporated off under reduced pressure by means of a bulb oven and a vane pump. The proportion of residual propargyl ether function is estimated to be 5% by .sup.1H NMR. The yield is 99%. The proportion of residual propargyl ether functions of less than 11% is in accordance with the set specifications.

(5) Polymerization of the Chromene Derived from the Propargylated Resorcinol

(6) The polymerization of the propargyl-chromene mixtures is carried out by gradual increase in the temperature. In the case of a propargyl resorcinol-chromene mixture with a proportion of residual propargyl ether functions of less than 11% as obtained previously, the heat treatment applied is the following: 2 h at 80° C., 2 h at 100° C., 2 h at 110° C., 2 h at 120° C., 2 h at 130° C. and 2 h at 150° C.

(7) Annealing at 220° C. can be carried out in order to increase the thermomechanical properties.

(8) The coke content obtained before and after annealing is 65.9% and the enthalpy of reaction is 420 J/g.

EXAMPLE 2

Conversion of Propargylated Resorcinol and Preparation of the Resin according to the Invention

(9) Conversion of Propargylated Resorcinol

(10) 50 grams (0.269 mol) of propargylated resorcinol obtained according to the process indicated in example 1, 1000 ppm of CuCl and 150 ml of anisole are introduced into a 500 ml two-necked flask equipped with a magnetic stirrer and surmounted by a condenser. Bubbling of argon is carried out for 10 minutes and the medium is stored under argon. The medium is placed in an oil bath preheated to 155° C. and the reaction is continued at reflux for 7 hours until the total conversion of the propargyl ether functions into chromene functions. After 7 hours, the medium is filtered through a cellulose filter in order to remove the precipitates possibly formed. The anisole is evaporated off by distillation under reduced pressure. The proportion of residual propargyl ether functions is estimated to be less than 1% by .sup.1H NMR. The yield is 97%. The proportion of residual propargyl functions of less than 11% is in accordance with the set specifications.

(11) Polymerization of the Chromene derived from the Proparaylated Resorcinol

(12) The process carried out is identical to that described in example 1. The coke content obtained before and after annealing is 65.3% and the enthalpy of reaction is 300 J/g.

EXAMPLE 3

Conversion of Propargylated Eugenol and Preparation of the Resin according to the Invention

(13) Synthesis of Proparaylated Eugenol

(14) Eugenol (Sigma Aldrich) (200 g), K.sub.2CO.sub.3 (211 g) and dimethylformamide (DMF) (2000 ml) are introduced into a 6 L round-bottomed flask and are heated to 75° C. with mechanical stirring. Propargyl chloride (ABCR) at 70% in toluene (158.5 ml) is added dropwise by means of a dropping funnel and the reaction medium is heated and stirred at 75° C. overnight. The reaction is monitored by TLC with a 7:3 petroleum ether/diethyl ether (volume) eluent. After reaction, the reaction medium is filtered and then diluted and rinsed with ethyl acetate. The organic phase is rinsed with water until decoloring of the aqueous phase is obtained (4 times). The organic phase is dried over MgSO.sub.4 and concentrated under vacuum. The yield of the crude product is 93%. The compound is purified by vacuum distillation (p=4.5 Pa and T° C.=60° C.). The yield of the distilled compound is 90%.

(15) Conversion of Propargylated Eugenol

(16) 1 g (0.005 mol) of propargylated eugenol obtained previously, 1000 ppm of CuCl and 3 ml of anisole are introduced into a Schlenk tube. Bubbling with argon is carried out for 10 minutes, and the reaction medium is stored under argon with a coolant. The medium is introduced into an oil bath preheated to 155° C. The reaction is left at reflux and monitored by regular sampling and .sup.1H NMR analysis. After 23 h, the anisole is evaporated off in a rotary evaporator. The proportion of residual propargyl ether functions is estimated to be less than 1% by .sup.1H NMR. The yield is 90%.

(17) Polymerization of the Chromene Derived from the Propargylated Eugenol

(18) The process carried out is identical to that described in example 1 for propargylated resorcinol.

EXAMPLE 4

Conversion of Propargylated Coupled Eugenol and Preparation of the Resin according to the Invention

(19) Synthesis of the Coupled Eugenol

(20) 26.675 g (0.1625 mol) of eugenol (Sigma Aldrich) are introduced into a 50 ml three-necked round-bottomed flask with a magnetic stirrer. 0.1337 g (0.1 mol %) of 1.sup.st-generation Grubbs catalyst (Sigma Aldrich) is introduced using a pill bottle with argon countercurrent. The medium is directly placed under a strong vacuum (3 kPa) and left to stir for 12 h. A .sup.1H NMR spectrum of the crude product is performed in order to determine the eugenol conversion. The conversion is 67 mol % of coupled eugenol compounds, the remaining 37 mol % being a mixture of unreacted eugenol and its isomer, isoeugenol. The stochiometric proportion is evaluated, by .sup.1H NMR, at 34.3%/65.7% for the cis- and trans-coupled eugenol compounds respectively. The medium is dissolved in a minimum amount of ether at reflux, then left to stand at ambient temperature. The solid is filtered under reduced pressure on a frit with a porosity of 4, then washed with 4×20 ml of cyclohexane. The solid is dried under a strong vacuum using a vane pump for 10 h. In order to remove the 1.sup.st-generation Grubbs catalyst, the solid is dissolved in dichloromethane (DCM) and then filtered through celite. A black deposit is observed on the celite. The organic phase is dried under reduced pressure. The yield obtained is 25%.

(21) Synthesis of the Propargylated Coupled Eugenol

(22) 3 g (0.010 mol) of coupled eugenol obtained previously is dissolved in 30 ml (10 eqm) of DMF. 5.52 g (4 eq.) of finely ground potassium carbonate (K.sub.2CO.sub.3) are added with magnetic stirring. 2.78 ml (2.5 eq.) of propargylated bromide (Alfa Aesar) (80 m % in toluene) are added by means of a dropping funnel. The magnetic stirring is maintained for 12 h. The completion of the reaction is monitored by TLC with a 50:50 petroleum ether:ethyl acetate (volume) eluent. After filtration of the K.sub.2CO.sub.3 and washing with DMF, an excess of distilled water (200 ml) is added in order to cause the product to precipitate. The solid is recovered. 200 ml of ethyl acetate are added to the medium for the extraction. The aqueous phase is discarded. The solid previously recovered is redissolved in the organic phase. The organic phase is washed three times with distilled water (3×100 ml) and once with brine (1×100 ml). The organic phase is dried over MgSO.sub.4, filtered and concentrated under reduced pressure. The yield is 90%.

(23) Conversion of the Propargylated Coupled Eugenol

(24) 0.5 g (0.001 mol) of propargylated coupled eugenol previously obtained, 1000 ppm of CuCl and 10 ml of anisole are introduced into a Schlenk tube. Bubbling with argon is carried out for 10 minutes, and the medium is stored under argon with a coolant. The Schlenk tube is introduced into an oil bath preheated to 155° C. The reaction is monitored by regular sampling and .sup.1H NMR analysis. After 24 h of reaction, the anisole is evaporated off in a bulb oven by means of a vane pump. The proportion of residual propargyl ether functions is estimated to be 9% by .sup.1H NMR. The yield is 97%. The proportion of residual propargyl ether functions of less than 39% is in accordance with the set specifications.

(25) Polymerization of the Chromene Derived from the Propargylated Coupled Eugenol

(26) The process carried out is identical to that described in example 1 for the propargylated resorcinol, with the exception of the fact that the heat treatment applied is the following: 1 h at 80° C., 1 h at 100° C., 1 h at 120° C., 1 h at 140° C., 1 h at 160° C., 1 h at 180° C., 1 h at 200° C.

EXAMPLE 5

Conversion of Propargylated Coupled Isoeugenol and Preparation of the Resin according to the Invention

(27) Synthesis of the Coupled Isoeugenol

(28) 0.0181 g (0.017%) of Grubbs II catalyst (UMICORE M2a) is introduced into a 50 ml round-bottomed flask with a magnetic stirrer, then 20 g (0.122 mol) of isoeugenol (Sigma Aldrich) are added. The medium is placed under an argon stream and heated to 90° C. The medium becomes solid after 3 minutes of reaction. After cooling, a .sup.1H NMR spectrum of the crude product is performed in order to determine the conversion of the isoeugenol into stilbene. The degree of conversion is 90%. Only the trans-compound is observed. The product is recovered by suspension in 4 vol. of DCM, and the medium is refluxed for 1 hour until complete solubilization and then left to stand at ambient temperature overnight. The suspension is filtered on a frit and washed with 1 vol. of cyclohexane. The isolated yield is 67%.

(29) Synthesis of the Propargylated Coupled Isoeugenol

(30) 10 g (0.037 mol) of eugenol stilbene previously obtained are dissolved in 100 ml (10 eqm) of DMF. 25 g (4.5 eq.) of finely ground potassium carbonate (K.sub.2CO.sub.3) are added with magnetic stirring. 10.23 ml (2.5 eq.) of propargyl bromide (Alfa Aesar) (80 m % in toluene) are added using a syringe. The magnetic stirring is maintained for 12 h. The completion of the reaction is monitored by TLC with a 50:50 petroleum ether:ethyl acetate (volume) eluent. The conversion is total after reaction overnight. The K.sub.2CO.sub.3 is filtered off and then washed with ethyl acetate. The compound is extracted with 2×100 ml of ethyl acetate. The organic phases are washed with 4×100 ml of brine. The organic phases are dried over MgSO.sub.4, filtered and concentrated under reduced pressure. The yield of the product is 30%.

(31) Conversion of the Propargylated Coupled Isoeugenol

(32) 1 g (0.003 mol) of propargylated coupled isoeugenol obtained previously, 1000 ppm of CuCl and 20 ml of anisole are introduced into a Schlenk tube. Bubbling with argon is carried out for 10 minutes, and the medium is stored under argon with a coolant. The Schlenk tube is introduced into an oil bath preheated to 155° C. The reaction is monitored by regular sampling and .sup.1H NMR analysis. After 48 h of reaction, the anisole is evaporated off in a bulb oven by means of a vane pump. The viscosity of the resin did not make it possible to completely evaporate off the reaction solvent. The proportion of residual propargyl ether functions is estimated to be 12% by .sup.1H NMR. The proportion of residual propargyl ether functions of less than 39% is in accordance with the set specifications.

(33) Polymerization of the Chromene Derived from the Propargylated Coupled Isoeugenol

(34) The process carried out is identical to that described in example 1.

EXAMPLE 5

Conversion of Propargylated Isoeugenol and Preparation of Resin according to the Invention

(35) Synthesis of the Propargylated Isoeugenol

(36) 20 g (0.130 mol) of isoeugenol (Sigma Aldrich) are solubilized in 100 ml (5 eqm) of DMF. 33.67 g (2 eq.) of finely ground potassium carbonate (K.sub.2CO.sub.3) are added with magnetic stirring. 20.35 ml (1.5 eq.) of propargyl bromide (Alfa Aesar) (80 m % in toluene) are added by means of a dropping funnel. The magnetic stirring is maintained for 12 h. The completion of the reaction is monitored by TLC with a 70:30 petroleum ether:ethyl acetate (volume) eluent. After filtration of the K.sub.2CO.sub.3 and washing with ethyl acetate, 100 ml of ethyl acetate are added to the medium for the extraction. The organic phase is washed 3 times with distilled water (3×100 ml) and once with brine (1×100 ml). The organic phase is dried over MgSO.sub.4, filtered and concentrated under reduced pressure. The yield is 91%.

(37) The compound is purified by vacuum distillation using a bulb oven (p=15 Pa and T° C. heating=140° C.). The compound is recovered in the form of white crystals. The overall yield after purification is 73%.

(38) Conversion of the Proparaylated Isoeugenol

(39) 1 g (0.005 mol) of propargylated isoeugenol obtained previously, 1000 ppm of CuCl and 5 ml of anisole are introduced into a Schlenk tube surmounted by a condenser. Bubbling with argon is carried out for 10 minutes and the medium is stored under argon. The Schlenk tube is introduced into an oil bath preheated to 155° C. and the reaction is left at reflux. The progression of the reaction is monitored by regular sampling and .sup.1H NMR analysis. After 30 hours of reaction, the anisole is evaporated off by distillation at 80° C. by means of a bulb oven. The yield is 98%. The proportion of residual propargyl ether functions is estimated to be 10% by .sup.1H NMR.

(40) Polymerization of the Chromene Derived from the Proparaylated Isoeugenol

(41) The process carried out is identical to that described in example 1.