Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-06-26
2003-04-22
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C528S299000, C528S299000
Reexamination Certificate
active
06552232
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to aldol condensation reactions, and more specifically, to ionic liquid media for carrying out these reactions.
2. Description of the Related Art
Aldol condensation reactions, or aldolization reactions, are known in the art. See U.S. Pat. No. 6,090,986 to Godwin et al., incorporated by reference herein. Currently aldol reactions are carried out in aqueous solutions, which leads to the production of large quantities of wastewater. This wastewater is detrimental to the environment and cannot be treated or recycled for other uses in a cost-effective manner.
Aldol condensation reactions are also typically accompanied by side reactions that significantly reduce the yield of desired products. The result is that the unwanted products of these side reactions must be separated from the desired products and discarded as waste.
Two types of aldol condensation reactions frequently encountered are the self-aldol condensation (Aldol I) and cross-aldol condensation (Aldol II) reactions. In an Aldol I reaction, two molecules of the same aldehyde starting material react to form a reaction product. Alternatively, in an Aldol II reaction, two different aldehyde starting materials react to form a reaction product. In practice, the condensation of two molecules of the same aldehyde (Aldol I) to form an aldol is usually followed immediately by dehydration to form an unsaturated aldehyde with twice the original number of carbon atoms. In a Aldol II reaction, however, the condensation of two molecules of different aldehydes forms an aldol and, upon dehydration, further forms an unsaturated aldehyde having the sum of the carbon atoms of the two different aldehydes. Both Aldol I and Aldol II reactions are well known in the art, as are the conditions required to effect their condensation.
An important example of Aldol I is the condensation of n-butyraldehyde to form, following a hydrogenation step, 2-ethyl-hexanol, known in the art as a Guerbet alcohol.
U.S. Pat. No. 6,090,986 to Godwin et al. discloses an important example of Aldol II in the formation of 2,4-dimethyl-2-heptenal from condensing 2-methyl-pentanal and propanal. Following the aldol condensation step, the 2,4-dimethyl-2-heptenal product is preferably hydrogenated to produce the saturated aldehyde 2,4-dimethyl-heptanal, which can be further hydrogenated to form the alcohol 2,4-dimethyl heptanol or, alternatively, can be oxidized to form 2,4-dimethyl heptanoic acid. The final alcohol and acid products are in demand commercially.
The Aldol II reaction is often run by reacting formaldehyde and a second aldehyde starting material in a basic catalyst through several steps, including several aldol addition steps and a final crossed Cannizzaro reaction step, to form a neopolyol product. By definition, neopolyols are alcohols having two or more primary alcohol functional groups (CH
2
OH) plus a tetra-substituted carbon atom. The most commercially desired neopolyol products are pentaerythritol, trimethylol ethane, trimethylol propane, and neopentyl glycol, which are derived from reacting formaldehyde with the second aldehyde starting materials acetaldehyde, propionaldehyde, n-butyraldehyde and isobutyraldehyde, respectively. The formation of neopolyols is disclosed in more detail in
Encyclopedia of Chemical Technology
, Kirk-Othmer, Fourth Edition, Vol. 1, pp. 913-925 (John Wiley & Sons 1991), incorporated by reference herein. The structural formulae for the preferred
neopolyols are as follows:
Unfortunately, each type of aldol condensation reaction results in the formation of unwanted side products. Hence, there is a need in the art for a method to increase the yield of desired aldol condensation products, while decreasing the amount of side reactions, in an efficient and cost-effective manner. There is also a need for a method to reduce the amount of wastewater produced from present aldehyde condensation reactions.
Ionic liquids are known in the art for use as solvents in various chemical reactions. See U.S. Pat. Nos. 5,824,832 and 5,731,101 both to Sherif et al., and PCT International Patent Publication Nos. WO 00/15594 and WO 00/32572, all incorporated herein by reference. An ionic liquid is a liquid that is composed entirely of ions. They are typically molten at low temperatures and are suitable for use as a catalyst and as a solvent in alkylation and polymerization reactions, as well as in dimerization, oligomerization, acetylation, metatheses, hydrogenation, hydroformylation, and copolymerization reactions.
A class of ionic liquids which is of special interest is the class of salt compositions which are salts with melting points below 100° C. Such compositions are mixtures of components which are liquid at temperatures below the individual melting points of the components.
The application of ionic liquids to aldol condensation reactions has heretofore not been disclosed in the art. One reason is because not all ionic liquids will produce advantageous results when used as the reaction medium or catalyst for such reactions.
SUMMARY OF THE INVENTION
The present invention relates to a process for forming aldol condensation products which comprises reacting at least one aldehyde starting material in the presence of a neutral ionic liquid medium, which is stable towards air and water, and a basic catalyst. In a preferred embodiment, the ionic liquid is comprised of an imidazolium- or pyridinium-based cation and a BF
4
−
or PF
6
−
anion. The preferred aldehyde starting materials are typically formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde and isobutyraldehyde, and mixtures of formaldehyde and one of the foregoing, although other aldehydes are also suitable. The use of an ionic liquid can provide for more convenient separation of the aldol product and/or recycling of the neutral ionic liquid medium.
In another embodiment, the instant invention comprises reacting at least one aldehyde starting material in the presence of a basic ionic liquid medium to form aldol condensation products. The preferred embodiment, in this case, is an ionic liquid that is rendered intrinsically basic by the presence of a hydroxyl group as an anionic species.
In a further embodiment, the present invention relates to a process for producing cross-aldol condensation products by reacting formaldehyde and a second aldehyde starting material in the presence of a neutral ionic liquid medium and basic catalyst. The condensation products are optionally, but preferably, further reacted to form neopolyol products. The preferred second aldehyde starting materials in this situation are acetaldehyde, propionaldehyde, n-butyraldehyde and isobutyraldehyde, while the resulting neopolyol products derived therefrom are pentaerythritol, trimethylol ethane, trimethylol propane, and neopentyl glycol, respectively.
In a similar vein, the just-described formation of neopolyol products may be accomplished by reacting formaldehyde with a second aldehyde starting material in a basic ionic liquid medium to produce the same condensation products and the eventual neopolyol products.
DETAILED DESCRIPTION OF THE INVENTION
The phrase “aldol condensation ” or “aldolization ” is used herein to refer to the process whereby at least 2 aldehyde starting materials are reacted and, upon immediate dehydration, form aldol condensation products. Aldol I and Aldol II are the terms used to label two types of aldol condensation.
The term “base ” or “basic ” when used with “catalyst ” or “ionic liquid ” refers to Brønsted bases having the ability to react with (neutralize) acids to form salts. The pH range of bases is from 7.1 to 14.
The word “neutral ” refers to compounds having a pH of 7 under the Brønsted acid-base theory.
The term “neutral ionic liquid ” refers to ionic liquids with a molar fraction of (x=0.5) and exhibits neither Brøonsted nor Lewis acidity. This definition is derived from the fact that Lewis acidity can be expressed by the molar fraction (x). Conventionally, when (x=0.5)
Dispenziere Nicholas Charles
Mehnert Christian Peter
Schlosberg Richard Henry
ExxonMobil Research and Engineering Company
Richter Johann
Wang Joseph C.
Witherspan Sikarl A.
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