Thermolysis-mediated process for manufacturing chromenes intended for the preparation of thermosetting resins

Abstract

A process for manufacturing chromenes which are intended for the preparation of thermosetting resins, includes transforming an aromatic propargyl ether of general formula (I) into a chromene by flash vacuum thermolysis, at a temperature of between 300 and 600° C., at a pressure of between 4 and 10,000 Pa. It also concerns a process for preparing a material made of thermoset resin, including successively: a) implementation of the above process; b) polymerization of the reaction product obtained in a) so as to obtain the material made of thermoset resin; c) recovery of the material made of thermoset resin obtained in b).

Claims

1. A process for manufacturing chromenes which are intended for the preparation of thermosetting resins, comprising the step of transforming an aromatic propargyl ether of general formula (I) below ##STR00012## in which: R.sub.1 and R.sub.5 represent, independently of each other, a hydrogen atom, 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 from among R.sub.1 and R.sub.5 represents a hydrogen atom; R.sub.2 and R.sub.4 represent, independently of each other, a hydrogen atom, 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; and R.sub.3 represents a hydrogen atom, a O—(C.sub.1-C.sub.6)alkyl 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## in which: R.sub.6 and R.sub.9 represent, independently of each other, a hydrogen atom, 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 from among R.sub.6 and R.sub.9 represents a hydrogen atom; and R.sub.7 and R.sub.8 represent, independently of each other, a hydrogen atom, 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 from among R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 does not represent a hydrogen atom or a O—(C.sub.1-C.sub.6)alkyl group; and the cis/trans isomers thereof and the optical isomers thereof and the racemic mixtures thereof into a chromene by flash vacuum thermolysis, at a temperature of between 300 and 600° C., at a pressure of between 4 and 10,000 Pa, 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 the racemic mixtures thereof.

2. The process according to claim 1, wherein the molar percentage of residual propargyl functions in 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 in 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 in the chromene is less than 35% when the aromatic propargyl ether of general formula (I) is propargylated coupled isoeugenol.

3. The process according to claim 1, wherein the aromatic propargyl ether of general formula (I) is dissolved beforehand in a solvent before the flash thermolysis step.

4. The process according to claim 1, wherein the aromatic propargyl ether of general formula (I) is first evaporated/sublimed, before the flash thermolysis step.

5. The process according to claim 1, which is a continuous process.

6. The process according to claim 1, 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##

7. A process for preparing a material made of thermoset resin, comprising the following successive steps: a) implementation of the process according to claim 1; b) polymerization of the reaction product obtained in step a) so as to obtain the material made of thermoset resin; c) recovery of the material made of thermoset resin obtained in step b).

8. The process according to claim 7, wherein the enthalpy of polymerization of step b) is less than 500 J/g.

9. The process according to claim 7, wherein the coke content of the thermoset resin obtained in step c) is greater than 50% by mass.

10. The process according to claim 1, wherein the temperature is of between 400 and 450° C.

11. The process according to claim 1, wherein the pressure is of between 5 and 7000 Pa.

12. The process according to claim 1, wherein the aromatic propargyl ether of general formula (I) is propargylated resorcinol.

13. The process according to claim 3, wherein the solvent is toluene.

14. The process according to claim 6, wherein the chromene obtained is a mixture of the formulae C and D.

Description

EXAMPLE 1

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

(1) Synthesis of Propargylated Resorcinol

(2) 10 g (0.091 mol) of resorcinol (Alfa Aesar) are dissolved in 50 mL of dimethyl sulfoxide (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 is 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 (volume) petroleum ether/diethyl ether 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 Propargylated Resorcinol

(4) 0.5 g (0.0027 mol) of propargylated resorcinol obtained previously is dissolved in 20 mL of toluene and placed in the dropping funnel at the top of the column. The reagent is introduced into the column at an average rate of 0.5 mL/minute into a column preheated to between 410° C. and 430° C. under a vacuum of 6000 Pa. After elution of all of the reagent and cooling of the column, the vacuum is broken and the product is recovered. The toluene is evaporated off under reduced pressure on a rotary evaporator and the product is then dried using a vane pump. The crude yield obtained is 85%. The proportion of residual propargyl functions is estimated by .sup.1H NMR as less than 1%. The crude product is composed of 13 mol % of C and 79.2 mol of D. The molar proportion of compound of 2-indanone type is 7.8%. The molar proportion of residual propargyl functions of less than 11% complies with the set specifications.

(5) Polymerization of the Chromene Obtained from Proparaylated Resorcinol

(6) The polymerization of the propargyl-chromene mixtures is performed by gradual raising of 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 as follows: 2 hours at 80° C., 2 hours at 100° C., 2 hours at 110° C., 2 hours at 120° C., 2 hours at 130° C. and 2 hours at 150° C.

(7) Annealing at 220° C. may be performed to increase the thermomechanical properties.

(8) The coke content before or after annealing is 64.3% and the enthalpy of reaction is 280 J/g.

Example 2

Conversion of Propargylated Resorcinol

(9) Conversion of Propargylated Resorcinol

(10) 10 g (0.0537 mol) of propargylated resorcinol obtained as in Example 1 are dissolved in 350 mL of toluene and placed in the dropping funnel at the top of the column. The reagent is introduced at an average rate of 1.5 mL/minute into a column preheated to between 420° C. and 430° C. under a vacuum of 6000 Pa. After elution of all of the reagent and cooling of the column, the vacuum is broken and the product is recovered. The toluene is evaporated off under reduced pressure on a rotary evaporator and the product is then dried using a vane pump. The crude yield is 83.4%. The proportion of residual propargyl functions is estimated by .sup.1H NMR at 2.2%. The crude product is composed of 4.4 mol % of C and 71.3 mol % of D. The molar proportion of compound of 2-indanone type is 23.1%. The molar proportion of residual propargyl functions of less than 11% complies with the set specifications.

Example 3

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

(11) Synthesis of Propargylated Eugenol

(12) Eugenol (Sigma-Aldrich) (200 g), K.sub.2CO.sub.3 (211 g) and dimethylformamide (DMF) (2000 mL) are placed in a 6 L round-bottomed flask and heated to 75° C. with mechanical stirring. Propargyl chloride (ABCR) at 70% in toluene (158.5 mL) is added dropwise via a dropping funnel, and the reaction medium is heated and stirred at 75° C. overnight. The reaction is monitored by TLC, eluting with 7/3 (volume) petroleum ether/diethyl ether. After the reaction, the reaction medium is filtered and then diluted and rinsed with ethyl acetate. The organic phase is rinsed with water until the aqueous phase has decolourized (four times). The organic phase is dried over MgSO.sub.4 and concentrated under vacuum. The yield of 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%.

(13) Conversion of Propargylated Eugenol

(14) 0.5 g (0.0054 mol) of propargylated eugenol obtained previously is dissolved in 20 mL of toluene and placed in the dropping funnel at the top of the column. The reagent is introduced into the column at an average rate of 0.5 mL/minute into a column preheated to between 410° C. and 420° C. under a vacuum of 6000 Pa. After elution of all of the reagent and cooling of the column, the vacuum is broken and the product is recovered. The toluene is evaporated off under reduced pressure on a rotary evaporator and the product is then dried using a vane pump. The crude yield is 65%. The proportion of residual propargyl functions is estimated by .sup.1H NMR at 0%. The molar proportion of chromene compound is estimated by .sup.1H NMR at 54%. The parent phenolic compound of the propargyl ether compound, eugenol, is formed to a proportion of 46 mol %.

(15) Polymerization of the Chromene Obtained from Proparaylated Eugenol

(16) The process performed is identical to that described in Example 1 for propargylated resorcinol.

Example 4

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

(17) Synthesis of Propargylated Isoeugenol

(18) 20 g (0.130 mol) of isoeugenol (Sigma-Aldrich) are dissolved in 100 mL (5 eq.) 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 mol % in toluene) are added via the dropping funnel. Magnetic stirring is continued for 12 hours. Completion of the reaction is monitored by TLC, eluting with 70/30 (volume) petroleum ether/ethyl acetate. After filtering off 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 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 91%.

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

(20) Conversion of the Proparaylated Isoeugenol

(21) 0.5 g (0.0054 mol) of propargylated isoeugenol obtained previously is dissolved in 20 mL of toluene and placed in the dropping funnel at the top of the column. The reagent is introduced into the column at an average rate of 0.5 mL/minute into a column preheated to between 410° C. and 420° C. under a vacuum of 6000 Pa. After elution of all of the reagent and cooling of the column, the vacuum is broken and the product is recovered. The toluene is evaporated off under reduced pressure on a rotary evaporator and the product is then dried using a vane pump. The crude yield is 65%. The molar proportion of residual propargyl functions is estimated by .sup.1H NMR at 0%. The molar proportion of chromene compound is estimated by .sup.1H NMR at 43%. The parent phenolic compound of the propargyl ether compound, isoeugenol, is formed to a proportion of 57 mol % of the mixture during the reaction.

(22) Polymerization of the Chromene Obtained from Proparaylated Isoeugenol

(23) The process performed is identical to that described in Example 1.

Example 5

Conversion of Propargylated Resorcinol in the Absence of Solvent and with Sublimation/Evaporation of the Reagent and Preparation of the Resin According to the Invention

(24) Conversion of Propargylated Resorcinol

(25) 4 g (0.021 mol) of propargylated resorcinol obtained as in Example 1 are dispersed in 50 g of glass beads 4 mm in diameter and placed in a horizontal tube at the top of the column. The column is preheated to between 410 and 420° C. The thermolysis device is placed under a vacuum of 5.5 Pa. The horizontal tube containing the reagent is gradually heated to a temperature of 130° C., allowing the gradual evaporation/sublimation of the reagent and its passage into the column. The product is recovered at the outlet in a trap cooled with liquid nitrogen. After elution of all of the reagent and cooling of the column, the vacuum is broken and the product is recovered. The crude yield is 90%. The proportion of residual propargyl functions is estimated by .sup.1H NMR at 0%. The crude product is composed of 14 mol % of C and 79 mol % of D. The molar proportion of compound of 2-indanone type is 7%. The molar proportion of residual propargyl functions of less than 11% complies with the set specifications.

(26) Polymerization of the Chromene Obtained from Propargylated Resorcinol

(27) The process performed is identical to that described in Example 1.

Example 6

Conversion of Propargylated Resorcinol in the Absence of Solvent and Preparation of the Resin According to the Invention

(28) 8 g (0.043 mol) of propargylated resorcinol obtained as in Example 1 are introduced neat into the dropping funnel at the top of the column. The dropping funnel is heated to 40° C. to change the state of the reagent from solid to liquid. The reagent is introduced into the column at an average rate of 0.5 mL/minute into a column preheated to between 410° C. and 420° C. under a vacuum of 6000 Pa. After elution of all of the reagent and cooling of the column, the vacuum is broken and the product is recovered. The crude yield is 7%. The proportion of residual propargyl functions is estimated by .sup.1H NMR at 0%. The crude product is composed of 3.3 mol % of C and 79.7 mol % of D. The molar proportion of compound of 2-indanone type is 17%.

(29) Polymerization of the Chromene Obtained from Proparaylated Resorcinol The process performed is identical to that described in Example 1.

COMPARATIVE EXAMPLE 1

Attempted Conversion of Propargylated Resorcinol

(30) 1 g (0.0054 mol) of propargylated resorcinol obtained as in Example 1 is dissolved in 40 mL of toluene and placed in the dropping funnel at the top of the column. The reagent is introduced into the column at an average rate of 0.5 mL/minute into a column preheated to between 250° C. and 270° C. under a vacuum of 1000 Pa. After elution of all of the reagent and cooling of the column, the vacuum is broken and the product is recovered. The toluene is evaporated off under reduced pressure on a rotary evaporator and the product is then dried using a vane pump. The crude yield is 92%. The proportion of residual propargyl functions is estimated by .sup.1H NMR at 100%. The proportion of residual propargyl functions of greater than 11% is not in compliance with the set specifications.

(31) The temperature is thus an important parameter for obtaining the conversion of propargylated resorcinol into chromene according to the set specifications.