A process for separating ketones from alcohols

Abstract: The invention relates to a process for separating ketones from alcohols by chemical interaction. More specifically, a difference in chemical reactivity between ketones and alcohols with a third compound is used as a basis for the separation. The third compound in this case is an organo-metallic compound of the general formula M(X) n . Herein is M a polyvalent metal atom, n equals the valence of the metal and X is an organic or inorganic group or atom, with the proviso that at least one organic group is present in the organo-metallic compounds according to the invention. If the ketone-alcohol mixture is subjected to the organo-metallic compounds according to the invention under suitable conditions, an exchange reaction between the alcohols and the groups X takes place, and the ketones can be isolated from the reaction mixture in a conventional way.

Description: The invention relates to a process for separating ketones from alcohols by chemical interaction. More particularly the invention relates to a process for a separation using an organo-metallic compound which preferentially reacts with alcohols rather than with ketones. From US-A-3,839,473 it is known to remove alkane-diols from alkanols by contacting the mixture with polyvalent metal compounds such as: M(OR₁) x (R₂) y and M(OR₁) x (OR₂) y where M is aluminium, titanium, or boron, R₁ and R₂ are alkyl groups, x+y is 3 or 4. The separation process is based on the preferential reaction of alkane-diols with the organo-metallic compounds. JP 84 123 501, on the other hand, describes a process for drying organic solvents. The solvent to be dried is distilled in the presence of a hydrolyzable organo-metallic compound whereby the water is removed due to reaction with the metal compound. The process is exemplified by drying lower aliphatic alcohols, acetylacetone and ethylacetate. US-A-2 305 236 (assigned to The Resinous Products & Chemical Co) discloses a process for removing methyl-n-hexyl ketone from crude octanol-2 by esterifying the alcohol with boric acid in the presence of toluene by refluxing for several hours whilst collecting the water of reaction in a trap and returning volatile distillate until the temperature of the batch rose and toluene could be distilled off. After cooling the ketone was distilled off under reduced pressure. The borate ester residue was then hydrolysed by boiling with water and the purified octanol-2, which was in the upper layer was separated and distilled to obtain virtually pure octanol-2. In many processes ketones are obtained in admixture with alcohols. Usual procedures for separating alcohols from ketones such as distillation are not always applicable or completely satisfactory because e.g. azeotrope formation occurs or the boiling point of the ketone and the alcohol concerned are too close to obtain satisfactory separation. Therefore there has been a need for a convenient process for separating ketones from alcohols in those cases where conventional procedures are impossible or undesirable or where a more complete separation is desired than can be obtained by conventional procedures. It has now been found that certain organometallic compounds can be used for such a process due to a considerable preference in chemical reactivity of such compounds to alcohols compared to ketones. Said organo-metallic compounds are of the type M(X) n , where M is a polyvalent metal chosen from the group of aluminium, titanium and boron, n is its valence and X are the same or different organic groups chosen from alkyl groups and alkoxy groups. Mixtures of various organo-metallic compounds having dissimilar metals and/or dissimilar groups X may also be used. Organo-metallic compounds according to the invention react with a mixture of one or more ketones and one or more alcohols (under suitable conditions), leading to an exchange between an aliphatic alkyl- and/or alkoxy group X and the alcohol present, whereby one or more groups X per molecule M(X) n are liberated under formation of compound HX, while the alcohol originally present in the ketone-alcohol mixture becomes bound to the organo-metallic compound. Thereafter, the ketones can be separated from the newly formed organo-metallic compound. In theory, if an organo-metallic compound of the type M(X) n is used , n molecules of the alcohol originally present could be bound to the metal. However, in practice it is preferred to use an excess of the amount of organo-metallic compound theoretically needed. The exact amount to be used will depend on, inter alia, the organo-metallic compound used, the type and amount of ketone(s) and alcohol(s) present in the mixture and the desired degree of separation. The most preferred metal M in M(X) n is titanium. All the groups X are the same or different alkyl- and alkoxy groups. The alkyl groups will be denoted by "R" and the alkoxy groups will be denoted by "OR". Preferably M(X) n is a metal alkoxide M(OR) n in which R denotes the same or different aliphatic alkyl groups having up to 10 carbon atoms. More preferred is a metal alkoxide M(OR) n in which the group OR denotes the same or different alkoxy groups having 1 to 5 carbon atoms. According to the present invention it is most preferred to use metal alkoxides wherein OR is a methoxy-, ethoxy or propoxy group, especially if the metal in the compound M(OR) n is titanium, wherein n equals 4. In the case the liberated X is an alkyl group (R), alkanes (HR) are formed due to the exchange reaction and likewise , if the liberated X is an alkoxy group (OR), alcohols (ROH) are formed. In the latter case the reaction is a transalcoholysis. If M(X) n comprises both alkyl and alkoxy groups, the above disclosed reactions may occur simultaneously or subsequently. Preferably the metal alkoxide is chosen such that the alcohol liberated by the transalcoholysis reaction (in the case a metal alkoxide is used in the process) has a boiling point below the boiling point(s) of the ketone(s) and alcohol(s) present in the mixture to be separated. Thus, the transalcoholysis can be forced to substantial completion by removing the liberated alcohol from the reaction mixture by e.g. distillation whereby the ketone(s) and the newly obtained metal alkoxide remain in the reaction mixture, whereafter the ketone(s) may be separated in any conventional way, e.g. by distillation. The process according to the invention is very suitable for removing alcohols from a ketone/alcohol mixture wherein the ketone is carvone, especially if one or more of the alcohols is a terpene alcohol. The following examples serve to illustrate the process according to the invention which is in no way limited thereto. Example 1 A mixture of carvone (27g), α-terpineol (2g, 13mmol) and titanium n-propoxide (3.7g, 13mmol) was distilled through a 15x1.5cm Vigreux column. After distilling off the isopropanol, the fraction collected at 100°C, 14mbar (1.4kPa) was carvone (25.9g) substantially free of α-terpineol, representing a 96% recovery of the carvone. Example 2 A mixture of carvone (27g), α-terpineol (2g, 13mmol) and titanium methoxide (75%)(2.2g, 9.6mmol) was distilled through a 15x1.5cm Vigreux column. After distilling off the methanol, the fraction collected at 96°C, 11mbar (1.1kPa) was carvone (25.7g) substantially free of α-terpineol, representing a 95% recovery of the carvone. Example 3 A sample of distilled crude carvone (containing carvone 95.5% w/w and α-terpineol 2% w/w) was treated with titanium ethoxide (50% in heptane), using 0.75 mol titanium ethoxide per mol of α-terpineol present. This solution was passed through a Leybold KDL-1 short-path molecular still (oil jacket temperature 115°C, pressure 40mmHg (5.3 kPa)). The carvone is obtained in solution in heptane, whereas the liberated ethanol is collected in a cold trap. The heptane was removed from the carvone by using a rotary evaporator, after which 92.6g carvone with less than 0.08% α-terpineol present was obtained, representing a 97% recovery. Example 4 A sample of distilled crude carvone (501g) containing carvone 95.5% w/w and α-terpineol 2% w/w) was treated with titanium ethoxide (50% in heptane), using 0.85 mol of titanium ethoxide per mol of α-terpineol present. This solution was distilled through a 1mx2.5cm Knitmesh fractionating column under reduced pressure. Fractions collected at 90°C, 5.5mbar (550 Pa) were 99.9+% pure and represented a 77% recovery of the carvone. Example 5 A mixture of 2-pentanone (40g), 2-butanol (3.7g, 50mmol) and titanium ethoxide (11.4g, 50mmol) was distilled through an 18cm Vigreux column at atmospheric pressure. The distillate collected from 96 to 101°C (37g), was free from 2-butanol and contained 0.5g of ethanol.

Claims: A process for separating ketones from alcohol(s), by reacting the alcohol(s) with at least one organo-metallic compound of the type M(X) n , wherein M is a polyvalent metal atom chosen from aluminium, titanium and boron, n is its valence and X are the same or different organic groups chosen from alkyl groups and alkoxy groups, liberating and separating the formed compound(s) HX substantially from the reaction mixture and separating the ketones from the organo-metallic compound formed by reaction between M(X) n and the alcohol(s) in the mixture. A process according to claim 1, in which M(X) n , is a metal alkoxide M(OR) n and OR denotes the same or different alkoxy groups having up to 10 carbon atoms. A process according to claim 2, in which in the metal alkoxide M(OR) n the group OR denotes the same or different alkoxy groups having 1 to 5 carbon atoms. A process according to any of the claims 1-3, in which M(OR) n is titanium methoxide, titanium ethoxide, titanium n-propoxide, titanium isopropoxide or a combination thereof. A process according to any of the claims 1-4, in which HX is separated by distillation. A process according to any of the preceding claims, in which the ketone is carvone. A process according to any of the preceding claims, in which the alcohol originally present in the mixture is a terpene alcohol.

Inventors: BRADLEY CHRISTOPHER K, BRADLEY, CHRISTOPHER K.
Applicants: QUEST INT NEDERLAND, QUEST INTERNATIONAL NEDERLAND BV
Application year: 1992
Main classification: C07C45
IPC codes: C07C49, C07C45