JPS6243983B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses acetaldehyde (hereinafter abbreviated as AA)
n-, which is one of the dehydrated products of aldol condensation of
This paper relates to the purification of hexenyl aldehyde (hereinafter abbreviated as HE). HE is called green leaf aldehyde and has recently attracted attention as a green note fragrance due to its blue flavor. However, at the same time, 2-vinylcrotonaldehyde (hereinafter abbreviated as 2-VCA), which is a by-product, is not easily separated by distillation, perhaps because its boiling point is close to that of HE, and its pungent odor causes it to be mixed in.
Significantly reduces the value of HE as a fragrance. It is known that the condensation and dehydration reactions of AA and BA in the presence of an alkali produce mainly four types of aldols and four types of unsaturated aldehydes, respectively. It has been found that the higher the molar ratio, the more 2-VCA is produced. These reaction equations are shown below: Although the production ratio of these compounds varies depending on the molar ratio of AA and BA, the ratio of linear aldehydes is usually lower than that of branched aldehydes. However, 2-
VCA is also a branched aldehyde, but its production rate is lower than that of other aldehydes. These unsaturated aldehyde mixtures are usually separated by distillation to separate crotonaldehyde and then repeated rectification to produce 2-ethyl crotonaldehyde and 2-ethyl crotonaldehyde.
- After separation from ethylhexenyl aldehyde, the crude
HE (to give an example of the composition, HE: 78.1%; 2-
VCA: 21.4%; 2-ECA: 0.3%; Others: 0.2
%) is obtained. This crude HE cannot be purified any further by distillation alone. Hitherto, methods for isolating and purifying branched aldehydes have been reported in Japanese Patent Publication No. 48-12721, 1972-12722, etc., but a method for selectively isolating linear aldehydes has not yet been reported. Therefore, as a result of intensive research into obtaining high-purity HE, the present inventors found that 2-
VCA is HE (boiling point: 146-147℃) by selective hydrogenation
The present invention was achieved based on the knowledge that it can be converted into 2-ethylcrotonaldehyde (boiling point: 132-134°C), which has a boiling point different from that of 2-ethylcrotonaldehyde, and can be easily separated by distillation. That is, the present invention originates from dehydrating an aldol condensation reaction product of AA and BA, by contacting HE and 2-VCA (hereinafter referred to as raw material mixture) with hydrogen gas in the presence of a platinum group catalyst, and VCA
The gist of this paper is a method for purifying HE by selectively hydrogenating HE and then distilling the resulting mixture. This is derived from dehydrating the aldol condensation reaction product of AA and BA.
The dehydrated aldol condensate with
It also includes HE-rich fractions that remain after some treatment has been performed, such as crotonaldehyde, 2-ethylcrotonaldehyde, 2-ethylhexenylaldehyde, etc., by fractional distillation. Crotonaldehyde, 2-ethylcrotonaldehyde, and 2-ethylhexenylaldehyde are useful as intermediate raw materials such as plasticizers for resins, and are partially destroyed during hydrogenation in the present invention. before implementation)
It is preferable to remove it by means such as fractional distillation. The conditions for selective hydrogenation of the raw material mixture are to avoid alcohol production due to hydrogenation of carbonyl groups, and to selectively hydrogenate only the terminal olefin of 2-VCA, leaving its internal olefin and the internal olefin of HE. Although such severe selectivity is required, nonmetallic catalysts such as nickel and copper-chromium have low selectivity. However, platinum group catalysts satisfy the above conditions for selective hydrogenation and can achieve the first objective. Such platinum group catalysts include palladium catalysts, platinum catalysts,
At least one of a ruthenium catalyst and a rhodium catalyst can be used. Specific examples include palladium black, colloidal palladium, palladium oxide, and catalysts with catalysts include palladium-carbon, palladium-barium sulfate, palladium-calcium carbonate, palladium-alumina,
Palladium-silica gel, palladium-diatomaceous earth, palladium-barium carbonate, Lindlar catalyst, etc., platinum black, platinum oxide, colloidal platinum, platinum-carbon, platinum-silica gel, platinum-alumina, ruthenium oxide, ruthenium-carbon, oxide Rhodium, rhodium-carbon, rhodium-alumina, etc. can be mentioned. Among these, palladium catalysts have by far the best selectivity;
Furthermore, the catalyst life is very long, so it is most preferable. Catalyst cost is hardly a problem since the life is very long. The amount of catalyst used in the present invention is suitably in the range of 0.01 to 30% by weight, more preferably 0.1 to 1.0% by weight, based on the raw material mixture used. The hydrogenation reaction in the present invention is advantageously carried out at a temperature of 0 to 150°C, more preferably 50 to 100°C.
When the reaction temperature exceeds 150°C, the internal olefins of 2-VCA and HE are simultaneously hydrogenated, reducing the selective hydrogenation of only 2-VCA. Further, the hydrogen partial pressure in the present invention is preferably 50 Kg/cm ² or less, more preferably in the range of 0.5 to 10 Kg/cm ² . 2 if the hydrogen partial pressure is higher than this range.
- Internal olefins such as VCA and HE are hydrogenated simultaneously, reducing selective hydrogenation of only 2-VCA. Moreover, the hydrogen gas may be not only pure hydrogen gas but also a mixed gas of an inert gas and hydrogen. Next, the hydrogenation rate of 2-VCA and HE can be considered as shown in the following equation. The rate constants for hydrogenation over platinum group catalysts are determined as follows: The reaction rate is approximately K ₁ >K ₄ >K ₂ >>K ₃ , K ₅ , and by monitoring the reaction contents by gas chromatography, it is possible to stop hydrogenation when the target substance disappears. Using this difference in reactivity, 2-
VCA is converted to 2-ethylcrotonaldehyde, which has a boiling point different from that of HE, and the reaction is stopped. Examples are shown below. In these, all compositions represent area % of the gas chromatogram. The conditions for gas chromatography are column:
PEG6000 (25%), column length: 2m, temperature: 140
°C, carrier gas: N ₂ (0.8Kg/cm ² ), detector:
It is F.I.D. Example 1 A condensation reaction was carried out in a conventional manner at a molar ratio of AA to BA of 4, followed by a dehydration reaction. The dehydration reaction is
An acetic acid aqueous solution is added to the condensation reaction liquid to make it acidic, and the mixture is charged into a distillation column and distilled using this distillation column.
The reaction was carried out while removing unreacted aldehyde. The unsaturated aldehyde produced in the dehydration reaction was distilled off by azeotropic distillation with water. By separating the aqueous layer from the distillate, an unsaturated aldehyde mixture (composition: crotonaldehyde 45.3%; 2-ethylcrotonaldehyde 37.1%; HE 8.2%; 2-VCA 2.9%; 2-ethylhexenylaldehyde 4.0%; other 2.5%)
was gotten. From this unsaturated aldehyde mixture, crotonaldehyde is separated using a distillation column, and then vacuum distillation is repeated to separate 2-ethylcrotonaldehyde and 2-ethylhexenylaldehyde, resulting in crude HE (composition: HE78.1%; -VCA21.4%; 2-
Ethyl crotonaldehyde 0.3%; other 0.2%)
was gotten. 300 g of this crude HE and 3 g of a palladium-carbon catalyst (hereinafter palladium-carbon catalyst is referred to as Pd/c catalyst) with 2% palladium supported on activated carbon (50% water-containing product) (manufactured by Engelhard Japan) were placed in one autoclave. while stirring at a reaction temperature of 80 to 100°C and a hydrogenation pressure of 6 ± 2 kg/
The reaction was carried out by intermittently injecting hydrogen at ^cm2 . Samples were taken during the reaction and the reaction was followed by gas chromatography, and the operation was stopped when 2-VCA had completely disappeared. Next, hydrogen remaining in the reactor was purged to a gauge pressure of 1 Kg/cm ² , the reactor was cooled with water to below room temperature, the reaction solution was taken out, and the catalyst was filtered off to obtain 298 g of a crude reaction solution. The composition of this reaction crude liquid is HE: 75.4%, 2-VCA: 0.0%, 2-
Ethyl crotonaldehyde: 21.9%, n-hexylaldehyde: 2.5%, and others: 0.2%.
The reaction rates of 2-VCA and HE were 100% and 3.5%, respectively. Next, the entire amount of the reaction crude liquid is fractionated using a packed column with three theoretical plates to obtain a highly pure product as shown below.
209.5 g of HE was obtained. Composition: HE99.6%; traces of 2-VCA; 2-ethylcrotonaldehyde 0.1%; other 0.3%. Example 2 Using the same reaction apparatus as in Example 1, 2% platinum carbon powder (hereinafter referred to as
(abbreviated as Pt/c) (manufactured by Engelhard Japan)
was charged in an amount of 0.1% by weight based on the amount of crude HE charged, and the reaction was carried out at a reaction temperature of 70 to 80° C. under the same hydrogenation pressure and other conditions as in Example 1. Comparative Example 1 Using the same reaction apparatus as in Example 1, 5% by weight of a copper-chromium catalyst (N-203; manufactured by JGC Chemical) was charged as a catalyst for the hydrogenation reaction based on the amount of crude HE charged, and the reaction temperature was The reaction was carried out at 100 to 150°C under the same hydrogenation pressure and other conditions as in Example 1. Comparative Example 2 Using the same reaction apparatus as in Example 1, the hydrogenation reaction conditions were a catalyst using stabilized nickel (N-103; manufactured by JGC Chemical), a reaction temperature of 100 to 105°C, a hydrogenation pressure, and other conditions. The reaction was carried out in the same manner as in Example 1. Comparative Example 3 Using the same reaction apparatus as in Example 1, the hydrogenation reaction conditions were as follows: Raney nickel (manufactured by Kawaken Fine Chemical Co., Ltd.) was used as a catalyst at a reaction temperature of 70 to 80°C, and other conditions were the same as in Example 1. The reaction was carried out in the same manner. Next, Table 1 shows Examples 1 and 2 and Comparative Examples 1, 2, and 3.
The composition of the crude HE used in this example and the reaction solution composition and reaction rate obtained in these examples are shown.

[Table] As is clear from Table 1, the reaction rate after treatment is 2 when using a platinum group catalyst (particularly a Pd/c catalyst).
-VCA→2-Even if the reaction rate of ECA is 100%, HE→HA
The reaction rate is very low. On the other hand, among the comparative examples, even the copper-chromium catalyst with relatively good selectivity
The reaction rate of VCA is 97.7%, and the reaction rate of HE is already 64.5%. This suggests that platinum group catalysts, especially Pd/
It is clear that the selectivity of the c catalyst is very good.

Claims (1)

[Scope of Claims] 1. A mixture containing n-hexenylaldehyde and 2-vinylcrotonaldehyde (hereinafter abbreviated as 2-VCA) derived from dehydrating an aldol condensation reaction product of acetaldehyde and n-butyraldehyde. (hereinafter referred to as the raw material mixture) with hydrogen gas in the presence of a platinum group catalyst,
1. A method for purifying n-hexenyl aldehyde, which comprises selectively hydrogenating n-hexenyl aldehyde and then distilling the resulting mixture. 2. The raw material mixture is a fraction rich in n-hexenylaldehyde obtained by fractionating a mixture obtained by dehydrating an aldol condensation reaction product of acetaldehyde and n-butyraldehyde. The method described in Section 1. 3. The first or second catalyst, wherein the platinum group catalyst is at least one of a palladium catalyst, a platinum catalyst, a ruthenium catalyst, and a rhodium catalyst.
The method described in section. 4. The method according to item 3, wherein the platinum group catalyst is a palladium catalyst. 5. The method according to any one of items 1 to 4, wherein the amount of the catalyst is 0.01 to 30% by weight based on the raw material mixture. 6. The method according to any one of items 1 to 5, wherein the temperature of the hydrogenation reaction is 0 to 150°C. 7. The method according to any one of items 1 to 6, wherein the hydrogen partial pressure in the hydrogenation reaction is 50 Kg/cm ² or less.