JP2711884B2 - Method for producing acetal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an industrial production method of an acetal which is improved for quantitatively promoting a reaction.

[Prior art and problems] Benzilidene sorbitols, which are a kind of acetal, have been used as substances having a unique performance, and have been used to date as transparency improving agents such as polypropylene resins, fluidity improving agents such as paints, inks and adhesives. A wide variety of applications have been developed, such as thixotropic agents, adhesives, solidifying agents for cosmetics, pharmaceuticals and the like.

This compound is produced, for example, by condensing a predetermined benzaldehyde with a polyhydric alcohol such as sorbitol and xylitol in the presence or absence of an acid catalyst. A method using an organic solvent and a polar organic solvent such as a lower alcohol as a reaction medium has been proposed (for example, Japanese Patent Publication No.
-43748), which is already used industrially.

The action of the lower alcohol in the acetalization reaction is extremely complicated, but as a result, it is involved in the etherification reaction with aldehydes, the aldehydes, the mixed acetalization reaction with polyhydric alcohols, and the removal of generated water, It is thought to contribute to the improvement of the selectivity of the reaction.

However, this method requires a large amount of lower alcohol, takes a long time to complete the reaction, and the reaction rate reaches a plateau and does not reach a quantitative reaction rate. There is room for improvement.

[Problems to be Solved by the Invention] The present inventors have eagerly sought to improve such disadvantages and establish an industrially excellent production method for efficiently producing the desired acetal in a short time. As a result of the examination, (1) when the amount of the lower alcohol in the system is too small, the reaction rate decreases and the selectivity of the reaction also decreases. (2) When the amount of the lower alcohol in the system is too large The fact that the ratio of lower alcohols that work effectively decreased, it took a long time to complete the reaction, the reaction rate reached a plateau, and the reaction could not be performed quantitatively, was observed.

In subsequent studies, such problems were solved by controlling the method of charging the lower alcohol, and it was found that a predetermined object was achieved, and the present invention was completed based on such findings. .

That is, an object of the present invention is to provide an industrially excellent method for producing acetal which is improved to quantitatively promote the acetalization reaction.

[Means for Solving the Problems] The method for producing an acetal according to the present invention is represented by the general formula (I) by dehydrating and condensing an aldehyde and a polyhydric alcohol in the presence of a hydrophobic organic solvent and a lower alcohol. During the production of the acetal,
It is characterized in that an additional lower alcohol is charged separately or continuously, and a mixture of the lower alcohol and water is continuously extracted.

[In the formula, A and B are the same or different and each represents an aromatic ring, a naphthalene ring or a tetrahydronaphthalene ring which may have a substituent of (X) _n or (X ') _m . X,
X 'is the same or different and represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a halogen atom, a carboxyl group or a phenyl group. m and n
Represents an integer of 1 to 5, and p represents 0 or 1. An example of a specific production formulation of the acetal represented by the general formula (I) is shown below. That is, (A) at least one of the benzaldehyde compounds represented by the general formulas (II) and (III), [Wherein, X and n are the same as those in formula I. ] [Wherein X ′ and n are the same as in general formula I]. (B) a polyhydric alcohol represented by the general formula (IV), Wherein p is the same as in general formula I. ] (C) a lower alcohol, and if necessary, (D) an acid catalyst, and (E) a hydrophobic organic solvent, are charged into a reactor, and a condensation reaction is performed.
While the lower alcohol (C) is being divided or continuously charged, a mixture of the lower alcohol and water is continuously drawn out of the system to complete the reaction.

Acetals produced by the method according to the present invention and represented by the general formula (I) include symmetric compounds in which the types and numbers of the substituents of the two aromatic nuclei are the same, or asymmetric compounds in which these are different from each other. Included, as well as each alone, as well as any mixtures thereof.

One starting material in the process of the present invention, the general formula (I
Benzaldehydes (A) represented by I) or (III)
A benzaldehyde, an alkyl group having 1 to 4 carbon atoms, a halogen atom, an alkoxy group having 1 to 4 carbon atoms, a benzaldehyde-substituted product obtained by substituting 1 to 5, especially 1 to 3 carboxyl groups, and any of them Are exemplified.

In the above substituent, particularly preferred substituents include
p-methyl, p-ethyl, p-isopropyl, p-butyl, p-phenyl, p-alkyl (C1-C12) phenyl, p-halogenated phenyl, p-alkoxyphenyl, 2,4-dimethyl, 3,4 Examples include nuclear substituents such as -dimethyl, 2,4,5-trimethyl, p-chloro, m-methyl, o-methyl, p-methoxy, p-fluoro and the like.

Also, naphthalaldehyde, 1,2,3,4-tetrahydro-6-
Also included are naphthalaldehydes and their substitutions with the same groups as above.

The other starting material, polyhydric alcohol (B), is sorbitol or xylitol, or may be a mixture of these in any proportion.

Specific examples of the lower alcohol (C) according to the present invention include saturated aliphatic alcohols having 1 to 4 carbon atoms such as methanol, ethanol, n-propanol, isopropanol and butanol.

As the acid catalyst (D), any of ordinary Bronsted acids and Lewis acids can be used, and specifically, sulfuric acid, phosphoric acid, hydrochloric acid, paratoluenesulfonic acid, having 2 to 18 carbon atoms
Benzene sulfonic acid, naphthyl sulfonic acid, G acid, R acid, zinc chloride and the like having an alkyl group of

The hydrophobic organic solvent (E) acts as a dispersion medium, and its type is preferably a boiling point in the range of about 40 to 200 ° C.
In particular, from the ease of distilling water and a lower alcohol out of the reaction system as an azeotrope, for example, a lower alkyl group having 1 to 4 carbon atoms such as benzene, toluene, xylene and the like may be used.
Benzenes which may have three substituents, cyclohexanes which may be substituted with a lower alkyl group having 1 to 4 carbon atoms such as cyclohexane, methylcyclohexane and ethylcyclohexane, hexane, heptane, octane, nonane, Linear or branched saturated hydrocarbons having 6 to 16 carbon atoms, preferably 6 to 12 carbon atoms, such as decane, undecane and dodecane are used.

The charge molar ratio of the benzaldehydes (A) and the polyhydric alcohol (B) can be appropriately selected in the range of (A) :( B) = 1: 1 to 1: 4, but the compound of the general formula (I) From the viewpoint of improving the selectivity, the ratio is preferably about 1: 1.5 to 3, more preferably about 1: 1.8 to 2.2. Hereinafter, both are collectively referred to as “reaction substrate”.

The reaction substrate may be initially charged in the reaction vessel in its entirety, or may be mixed with a lower alcohol (C) and charged as a homogeneous solution or suspension.

At this time, the amount of the lower alcohol (C) used is appropriately selected in the range of about 0.1 to 5 parts by weight based on 1 part by weight of the reaction substrate.

The acid catalyst (D) may be charged in its entirety to the reaction vessel from the beginning or may be added to the homogeneous solution or suspension to be charged. The amount of the acid catalyst (D) used is not particularly limited, but is generally not limited. It is used in an amount of about 0.05 to 10 parts by weight, preferably about 0.2 to 3 parts by weight, based on 100 parts by weight of the reaction substrate.

As the concentration of the reaction substrate, any concentration can be selected within a range of about 5 to 90% by weight. Specifically, the concentration of the reaction substrate is selected according to the form of the reaction vessel to be used, and the system is brought into a low viscosity slurry state. It can be set to either paste state or powder state. There is no particular problem even if the concentration of the reaction substrate is out of the above range, but if it is less than about 5% by weight, the reaction tends to be slow, and if it exceeds about 90% by weight, the selectivity tends to decrease.

When the concentration of the reaction substrate is about 20% by weight or less, since the system is in a slurry state, it is possible to carry out the reaction with a normal stirring blade, and the entire amount of the reaction substrate may be charged in one step. By dividing or continuously charging in the form of a solution or a suspension, a constant operating state can be obtained without a sudden increase in the load on the stirring blade, and the contents are fixed to the wall of the reaction vessel. Can be greatly suppressed.

At this time, it is also effective to heat the mixture to a temperature of about 50 to 80 ° C. to reduce the viscosity of the homogeneous solution or suspension before charging.

The method of charging the hydrophobic organic solvent is not particularly limited, and the entire amount may be charged from the beginning, or may be charged separately or continuously as the reaction proceeds.

The reaction temperature may vary depending on the type of the reaction substrate, hydrophobic organic solvent, etc., but is generally about 40 to 200 ° C, preferably about 40 to 130 ° C.

The method of the present invention is characterized in that an additional lower alcohol is divided or added continuously into the reaction system in the reaction stage, and a mixture of the lower alcohol and water is continuously withdrawn.

This method is effective for improving the reaction rate and for quantitative reaction regardless of the concentration of the reaction substrate.
It is extremely effective for a reaction in a slurry state in which the reaction substrate is 20% by weight or less.

The amount of the lower alcohol at the start of the reaction is about 20 to 150% by weight, more preferably 30 to 100% by weight based on the reaction substrate.
It can be arbitrarily selected within a range of about weight%.

The amount of the lower alcohol to be added in portions is about 3 to 40% by weight, more preferably 8 to 20% by weight, based on the reaction substrate.
It is appropriately selected within the range of the degree.

The number of times the lower alcohol is added until the completion of the reaction is not particularly limited, but is usually about 2 to 15 times.

The method for charging a lower alcohol according to the present invention is also effective when the reaction substrate is divided and charged at a reaction substrate concentration of 20% by weight or more. That is, at an optional stage of the reaction, particularly preferably at a stage of extracting about 60 to 95% by weight of the charged lower alcohol amount, 3 to 40% by weight per one time of the charged reaction substrate in the same manner as described above. A predetermined effect can be obtained by repeating the operation of adding a lower alcohol and continuously extracting a mixture of the lower alcohol and water. Even when the lower alcohol is continuously added, the lower alcohol may be charged while controlling so that the alcohol amount in the system becomes the same ratio of alcohol concentration / reaction substrate as in the case of the above-mentioned divided charging. For example, even when the reaction rate is about 80 to 90% when the division or continuous charging of the reaction substrate is completed, the reaction rate is reduced by charging / withdrawing a predetermined amount of lower alcohol about 1 to 3 times. Almost
Can be 100%.

The reaction is preferably carried out in an atmosphere of an inert gas such as nitrogen gas in order to prevent coloring of the target substance and to improve safety during the reaction.

The reaction time is usually about 2 to 10 hours, especially about 3 to 6 hours.

The reaction mixture obtained in the form of a slurry or a wet powder is filtered, if necessary, and is exemplified by an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide according to a conventional method. The acid catalyst is neutralized with a wetting agent, and then the unreacted reaction substrates, reaction intermediates and the like are washed away with water from room temperature to about 90 ° C., dried, and, if necessary, ground to obtain a product.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 Sorbitol powder 38 g (0.21 mol), benzaldehyde 44 g (0.42 mol), cyclohexane 700 ml, 50% sulfuric acid 5 g
70 ml of methanol and a cooler with a decanter, a thermometer,
It was charged into a 2 l 4-necked reaction vessel having a stirrer and a nitrogen gas inlet, and heated with stirring. Reflux begins as the temperature of the system increases. During the reaction, the temperature rose as methanol / produced water was withdrawn, and 15 ml of methanol was repeatedly added each time the reaction temperature reached 75 ° C. A sample is withdrawn at predetermined time intervals, and the composition of the acetal at that time (by weight, based on gas chromatography)
I asked. The results obtained are shown in Table 1 together with the amount of methanol added up to that point and the number of additions. 4.5
After the reaction for 7 hours, 74.8 g of dibenzylidene sorbitol was obtained (yield: 99.7% by weight).

Example 2 The reaction was carried out in the same manner as in Example 1 except that 49.8 g (0.42 mol) of p-methylbenzaldehyde was used instead of benzaldehyde. The conditions were as follows: total amount of methanol added: 220 ml, number of methanol additions: 10, and reaction time: 3.5 hours. Below, 79.9 g of p-methyl-substituted dibenzylidene sorbitol were obtained (yield 99.2% by weight).

Example 3 A reaction was carried out in the same manner as in Example 1, except that 56.5 g (0.42 mol) of p-ethylbenzaldehyde was used instead of benzaldehyde. The conditions were as follows: total amount of methanol added: 220 ml, methanol added 10 times, reaction time: 3 hours. Under the conditions, 86.2 g (yield 99.8% by weight) of p-ethyl-substituted dibenzylidene sorbitol was obtained.

Comparative Example 1 At the start of the reaction, 250 ml of methanol was charged all at once, and the target acetal was prepared in the same manner as in Example 1 except that the reaction was carried out without adding methanol during the reaction. After the reaction for 6 hours, 45 g of acetal having the composition shown in Table 1 was obtained (yield: 60% by weight).

Comparative Example 2 The target acetal was prepared according to Example 1 except that 500 ml of methanol was charged at the start of the reaction, and the reaction was carried out without adding methanol during the reaction.
After the reaction for 8 hours, 49 g (yield: 65% by weight) of acetal having the composition shown in Table 1 was obtained.

Comparative Example 3 At the start of the reaction, 800 ml of methanol was charged, and the target acetal was prepared in the same manner as in Example 1 except that the reaction was carried out without adding methanol during the reaction.
After the reaction for 10 hours, 64 g (yield: 85% by weight) of acetal having the composition shown in Table 1 was obtained.

Comparative Example 4 The objective acetal was prepared according to Example 1 except that 900 ml of methanol was charged at the start of the reaction, and the reaction was carried out without adding methanol during the reaction.
After the reaction for 12 hours, 68 g (91% by weight) of acetal having the composition shown in Table 1 was obtained.

[Effects of the Invention] By applying the method of the present invention, the desired acetal can be efficiently produced in a short time.

Claims (1)

(57) [Claims] An aldehyde and a polyhydric alcohol are dehydrated and condensed in the presence of a hydrophobic organic solvent and a lower alcohol to obtain a compound of the formula (I) [Wherein, A and B are the same or different and each represents an aromatic ring, a naphthalene ring or a tetrahydronaphthalene ring which may have a substituent of (X) n or (X ') m. X,
X 'is the same or different and represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a halogen atom, a carboxyl group or a phenyl group. m and n each represent an integer of 1 to 5, and p represents 0 or 1. In producing the acetal represented by the formula, during the reaction, an additional lower alcohol is divided or continuously charged, and a mixture of the lower alcohol and water is continuously extracted to produce an acetal. Method.