JPS6243982B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to acetaldehyde (hereinafter referred to as AA)
n-, which is one of the dehydrated products of the aldol condensation product of
This paper relates to the purification of hexenyl aldehyde (hereinafter referred to as HE).

HE is called green leaf aldehyde, and as its name suggests, it has the aroma of fresh green leaves, and is used to impart a green note to artificial flower essential oils and various floral-type blended fragrances. Furthermore, along with its acetal derivatives, it is also effective as a flavoring agent for food products, and is also used as an attractant for insects, which has attracted attention in recent years.

By the way, when AA and BA undergo a condensation and dehydration reaction in the presence of an alkali, the type of alkali and AA vs.
It is known that unsaturated aldehydes are produced in various proportions depending on the molar ratio of BA, etc. The main products are crotonaldehyde (bp.104℃),
2-Ethylcrotonaldehyde (bp.134℃), HE
(bp. 147°C), 2-ethylhexenylaldehyde (bp. 175°C), and 2-vinylcrotonaldehyde (hereinafter referred to as 2-VCA). From these mixtures, crotonaldehyde and 2-ethylcrotonaldehyde can be separated as low-boiling fractions, and 2-ethylhexenylaldehyde can be separated as high-boiling fractions. However, when trying to separate HE as a medium boiling point fraction, 2-VCA, which seems to have almost no difference in boiling point, is mixed in, so it is difficult to separate HE by distillation.
It is not possible to purify HE. To show specific numbers here, for example, the molar ratio of AA to BA is 4.0
A condensation dehydration reaction is carried out using a caustic soda catalyst, and after removing the low-boiling point fraction by distillation, the crude medium-boiling point fraction is
Get HE. This composition is, for example, HE84.9% 2-
VCA14.1% 2-ethylcrotonaldehyde 1.0
%, and even if this is rectified again, the purity of HE cannot be increased. Since 2-VCA has a pungent odor, when it is mixed into HE, its value as a fragrance material is significantly impaired.

Although methods for isolating and purifying branched aldehydes have been reported in Japanese Patent Publications No. 48-12721 and No. 48-12722, a method for selectively separating linear aldehydes has not yet been reported.

As a result of extensive research in pursuit of the separation of HE and 2-VCA, the present inventors focused on the highly reactive terminal double bond of 2-VCA, and discovered that it was possible to separate HE from molecular oxygen or molecular oxygen-containing The present invention was achieved by discovering that by oxidizing and polymerizing HE in a liquid state with a gas, it can be used as a residue during distillation, and that HE can be distilled and separated with high purity.

That is, the present invention is derived from dehydrating an aldol condensation reaction product of AA and BA, and bringing a mixture containing HE and 2-VCA (hereinafter referred to as a raw material mixture) into contact with molecular oxygen or a molecular oxygen-containing gas. The present invention summarizes a method for purifying HE by oxidizing and polymerizing the 2-VCA 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 those that have undergone some subsequent treatment, such as those that remain after removing crotonaldehyde, 2-ethylcrotonaldehyde, 2-ethylhexenylaldehyde, etc. by fractional distillation. Crotonaldehyde, 2-ethylcrotonaldehyde, and 2-ethylhexenylaldehyde are useful as intermediate raw materials for plasticizing resins, etc., and are partially destroyed by contact with oxygen gas in the present invention. It is preferable to remove it by means such as fractional distillation (before the implementation).

As the molecular oxygen or molecular oxygen-containing gas, pure oxygen or a diluted oxygen-containing gas, such as a mixed gas of oxygen and an inert gas such as nitrogen, can be used. Among them, air is the most preferable because it is inexpensive. It is preferable to carry out the reaction in the presence of such a gas at normal pressure or under elevated pressure.

Observing the contact between the raw material mixture and oxygen gas in the present invention, for example, the crude HE exemplified above
Looking at the changes over time after blowing air into the
Although 2-VCA decreases with time and peroxide concentration initially increases, a curve with a maximum value of about 0.2 mmol/g is drawn. From this, it is considered that a so-called autocatalytic reaction is proceeding in which peracid is generated from aldehyde and free radicals generated by its decomposition promote polymerization of terminal olefin. The acid value increases at an almost constant rate. This is because HE changes into carboxylic acid together with 2-VCA, but this loss of HE is unavoidable. However, the product trans-2-hexenoic acid also has value as a perfume and can actually be separated and recovered.

The autooxidation method may be a batch type stirring tank or a countercurrent type tower reactor.
The higher the reaction temperature, the greater the rate of reduction of 2-VCA, but since there is a tendency for undesirable by-products to increase, a temperature of 10°C to 100°C is appropriate. The reaction time varies depending on the 2-VCA content in the raw material mixture, the amount of air blowing, the gas-liquid contact efficiency, etc., but the content can be monitored by gas chromatography and the 2-VCA
The time may be set such that the amount of time becomes a predetermined amount (for example, 0.1% or less). The longer the reaction time, the more 2-VCA
can be removed well, but the loss of HE increases, so
It is usually best to complete the reaction in 10-40 hours.

For the purpose of shortening the reaction time, it is effective to add salts of transition metals such as iron, copper, cobalt, nickel, and manganese, and as the negative ion species, chloride or bromide is preferred. The amount of these salts added is preferably 10 to 1000 ppm of the raw material mixture, and even if it is larger or smaller than this, the speed tends to decrease. Solvents are generally effective in controlling the reaction to prevent explosive reactions, and in increasing the solubility of the metal salts of the catalyst to speed up the reaction. A solvent that does not easily undergo autoxidation, such as an aliphatic hydrocarbon, is preferable. However, it may be used without a solvent.

Distilling the reaction solution treated in this way as it is poses a risk of explosion due to the remaining peroxide, and furthermore, the decomposition of by-products may cause an unpleasant odor to the product.
It may be mixed into HE. Therefore, it is preferable to add water or blow steam into the reaction solution (if there is sufficient water from the beginning of the reaction solution, as it is) and distill it under atmospheric pressure or reduced pressure. At this time, the amount of water present in the reaction solution, water added to the reaction solution, and steam blown into the reaction solution is suitably about 0.1 to 1 times, preferably about 0.5 to 5 times, the amount of the reaction solution. This distillation may be carried out while recycling the distilled water. The amount of recycled water is calculated as the amount of water newly added to the reaction solution.
When the distilled water is recycled, the amount of water added to the reaction solution at the beginning of the distillation can be carried out even if the weight ratio to the reaction solution is 0.05. The residue after this distillation is separated into two layers, the lower organic layer being an orange and fairly viscous liquid. However, this viscous liquid can be easily washed away with acetone, methanol, etc. High purity HE can be obtained by separating the distilled organic layer and aqueous layer and subjecting the organic layer to normal vacuum distillation.

The present invention will be described in more detail below with reference to Examples. In the following examples, all compositions refer to area % of the gas chromatogram. The conditions for gas chromatography were: Column: PEG6000 (25%);
Column length: 2 m, temperature: 140°C, carrier gas: N ₂ (0.8 Kg/cm ² ), detector: FID.

Example 1 25 kg of crude HE (composition; HE:
90.7% 2-VCA, 9.1% 2-VCA, 0.2% 2-ethylcrotonaldehyde) were charged, and the mixture was reacted for 38 hours by blowing air at a rate of 8.6/min at a temperature ranging from 25°C to 30°C while stirring at 300 rpm. The composition of the reaction solution is
HE: 96.9%, 2-VCA: 0.12%, acid value is
135KOHmg/g, peroxide concentration 0.16 mmol/
It was hot at g. Add 15 kg of water to this reaction solution and raise the temperature to 100 mmHg.
Distillation was carried out at a pressure of , during which time the still was replenished little by little with an amount of water equivalent to the water distilled out. In the end, the total amount of water used was 48 kg and the organic layer distilled was 15.0 kg.
kg, and the water layer was 30.4 kg. The composition of this organic layer is
HE: 98.7%, 2-VCA: 0.09%. Next, 15.0 kg of this distilled organic layer was rectified in a 20 rectification tower (glass ring packed tower, number of theoretical plates: 10) under a pressure of 50 mmHg and a distillation temperature of 70°C, and 12.7 kg of purified HE was obtained. Ta. Its composition is HE: 98.8%, 2-
VCA: 0.08%. The recovery rate of HE was 55.3%.

Example 2 Crude HE17.0Kg (composition; HE: 92.9%, 2-VCA
Add 1.7 g of ferric chloride (Fecl _{3.6H 2} O) to 7.1%), stir at 300 rpm, and stir at 40°C with air at 8.6%
The mixture was blown in at min. and reacted for 16 hours. The composition of the reaction solution at this time was HE: 97.5%, 2-VCA: 0.3%,
The acid value was 77KOHmg/g. This reaction solution was distilled with water added in the same manner as in Example 1, and an organic layer containing 98.6% HE purity and 0.15% 2-VCA content was obtained.
Got Kg.

Claims (1)

[Claims] 1 Derived from dehydrating an aldol condensate of acetaldehyde and n-butyraldehyde, n
- A mixture containing hexenylaldehyde and 2-vinylcrotonaldehyde (hereinafter referred to as a raw material mixture) is brought into contact with molecular oxygen or a molecular oxygen-containing gas to oxidize and polymerize the 2-vinylcrotonaldehyde, and then the resulting mixture A method for purifying n-hexenylaldehyde, which comprises distilling n-hexenylaldehyde. 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 method according to item 1 or 2, characterized in that the raw material mixture and molecular oxygen or molecular oxygen-containing gas are brought into contact at 10 to 100°C. 4. The method according to any one of items 1 to 3, characterized in that air is used as the molecular oxygen or molecular oxygen-containing gas. 5. The method according to any one of items 1 to 4, characterized in that a salt of a transition metal is added to the raw material mixture and brought into contact with molecular oxygen or a molecular oxygen-containing gas. 6. The method according to any one of items 1 to 5, wherein the distillation is carried out by adding water or blowing steam into the mixture obtained by the reaction. 7. When performing the above distillation, add water or blow steam into the mixture obtained by the above reaction (if there is sufficient water in the mixture from the beginning, leave it as is)
The first method is characterized in that the amount of water present in the reaction solution, water added to the reaction solution, and steam blown into the reaction solution is 0.1 to 10 times the amount of the reaction solution.
The method according to any one of Items 1 to 5.