Synthesis of methylene malonates substantially free of impurities
The present invention provides improved methods for the chemical synthesis of methylene malonates using the Knovenagel synthesis reaction. The method of the invention provides for improved methylene malonates by significantly reducing or eliminating the formation of alternative and/or deleterious side products, significantly reducing or eliminating unwanted consumption of methylene malonates, and significantly reducing or eliminating the degradation of methylene malonates. These advantages result in methylene malonates, which upon recovery, are of higher quality, greater purity, improved yield and possess overall improved performance characteristics (e.g., improved cure speed, retention of cure speed, improved shelf-life and/or stability).
1. A method of making a methylene malonate monomer comprising: (a) reacting a malonic acid ester with a source of formaldehyde in the presence of an acidic or basic catalyst and in the absence of a solvent, to form a reaction complex; (b) optionally, inactivating the catalyst; and (c) recovering methylene malonate monomer from the reaction complex.
2. The method according to claim 1 , wherein inactivating the catalyst comprises forming an insoluble precipitate of the catalyst and removing the precipitate from the reaction mixture.
3. The method according to claim 2 , wherein the precipitate is formed by reducing the solubility of the catalyst in the reaction mixture.
4. The method according to claim 1 further comprising:
(d) minimizing the recovery of volatile latent acid forming impurities from the reaction complex.
5. The method according to claim 4 , wherein the step of minimizing the recovery of volatile latent acid forming impurities comprises:
(a) adding to the reaction mixture water and an acid having a pKa range of −8 to 5;
(b) adding to the reaction mixture a sterically hindered organic acid; or
(c) adding to the reaction mixture a non-volatile organic acid, or any combination of (a), (b) or (c).
6. The method according to claim 1 comprising the basic catalyst, wherein the basic catalyst is selected from the group consisting of potassium acetate, sodium acetate, zinc acetate, aluminum acetate, calcium acetate, magnesium acetate, magnesium oxide, copper acetate, lithium acetate, aluminum oxide and zinc oxide, and combinations thereof.
7. The method according to claim 1 comprising the acidic catalyst, wherein the acidic catalyst is selected from the group consisting of paratoluene sulfonic acid, dodecylbenzene sulfonic acid, boron trifluoride, zinc perchlorate, sulfated zirconium oxide, sulfated titanium oxide, lithium chloride, boron trifluoride etherate, ferric sulfate, zirconium oxychloride, cupric chloride, titanium tetrachloride and zinc chloride.
8. The method according to claim 1 , wherein the recovering step comprises at least one process selected from the group consisting of condensation, simple distillation, fractional distillation, flash distillation, steam distillation, vacuum distillation, short path distillation, thin-film distillation, reactive distillation, pervaporation, extractive evaporation, flash evaporation, and rotary evaporation.
9. The method according to claim 1 , wherein the recovering step is performed at reduced pressure.
10. The method according to claim 1 , wherein the malonic acid ester has the formula:
R—O—C(O)—CH2—C(O)—O—R′
wherein R and R′ are independently C 1 -C 15 alkyl, C 2 -C 15 alkenyl, halo-(C 1 -C 15 alkyl), C 3 -C 6 cycloalkyl, halo-(C 3 -C 6 cycloalkyl), heterocyclyl, heterocyclyl-(C 1 -C 15 alkyl), aryl-(C 1 -C 15 alkyl), heteroaryl or heteroaryl-(C 1 -C 15 alkyl), or alkoxy-(C 1 -C 15 alkyl), each of which may be optionally substituted by C 1 -C 15 alkyl, halo-(C 1 -C 15 alkyl), C 3 -C 6 cycloalkyl, halo-(C 3 -C 6 cycloalkyl), heterocyclyl, heterocyclyl-(C 1 -C 15 alkyl), aryl, aryl-(C 1 -C 15 alkyl), heteroaryl, C 1 -C 15 alkoxy, C 1 -C 15 alkylthio, hydroxyl, nitro, azido, cyano, acyloxy, carboxy, or ester; or
wherein R and R′ are taken together with the atoms to which they are bound to form a 5-7 membered heterocyclic ring which may be optionally substituted by C 1 -C 15 alkyl, halo-C 1 -C 15 alkyl), C 3 -C 6 cycloalkyl, halo-(C 3 -C 6 cycloalkyl), heterocyclyl, heterocyclyl-(C 1 -C 15 alkyl), aryl, aryl-(C 1 -C 15 alkyl), heteroaryl, C 1 -C 15 alkoxy, C 1 -C 15 alkylthio, hydroxyl, nitro, azido, cyano, acyloxy, carboxy, or ester.