JPS6258341B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying methylal, which is characterized by adding water to crude methylal and distilling it.

Methylal is produced by the condensation reaction of methanol and formaldehyde as described below.

2CH ₃ OH+HCHO→(CH ₃ O) ₂ CH ₂ +H ₂ O Methyral is known as a special type of source of formaldehyde, ie, a formylating agent, and is used in the preparation of a variety of useful compounds.

Generally, the reaction for synthesizing methylal from methanol and formaldehyde is carried out under reflux using an acid catalyst such as sulfuric acid. As formaldehyde, an aqueous formalin solution or paraformaldehyde is used, but since this reaction is an equilibrium reaction that produces water as a by-product, the yield of methylal will be higher if paraformaldehyde with as low a water content as possible is used. Although the stoichiometric molar ratio of methanol to formaldehyde is 2, it is necessary to use an excess of methanol to increase the yield based on formaldehyde.

Methyral is known to azeotrope with methanol and water, respectively, and LHHorsley.
“Azeotropic Date”American chemical society
(1952) P7.29, the azeotrope of methylal and water has a boiling point of 42.3℃ and water content of 1.4% by weight, and the azeotrope of methylal and methanol has a boiling point of 42.3℃ and a methanol content of 7.85.
It is written as % by weight. In fact, when the reaction product of methanol and paraformaldehyde is directly distilled, it contains a small amount of water and 4 to 10% methanol.
90-96% by weight of crude methylal is distilled out. Even if this crude methylal is redistilled, the purity of methylal does not become very high, probably because of the azeotropic relationship mentioned above.

The present inventors have conducted intensive research to purify crude methylal with a purity of 90 to 96% by weight, which mainly contains methanol as an impurity.As a result, it has been found that by adding water to crude methylal and distilling it, it is possible to easily obtain a purity of 98% or more. It was discovered that methylal could be obtained, and the present invention was achieved. As a result of further studies on the amount of water to be added, it was found that water in an amount of 2 to 50 times the weight of methanol in crude methylal was effective, and the present invention was completed.

The purpose of the present invention is to provide a purification method for easily obtaining methylal with a purity of 98% or more from crude methylal through simple operations. This is a purification method characterized by adding 2 to 50 times the weight of water to methanol in crude methylal and distilling it.

In the present invention, the amount of water added to the crude methylal is suitably 2 to 50 times the weight of methanol contained in the crude methylal, particularly 3 to 30 times the weight of the methanol contained in the crude methylal. If the amount of water is less than this, the effect will be small, and if it is more than this, not only will the effect not increase significantly, but it will also be economically unfavorable in terms of equipment and heat consumption. The behavior among the three components of methylal, methanol, and water is not clear, and the mechanism of action when water is added is not fully clear, but the inventors understand that the addition of water causes the volatilization of methanol. This is thought to be due to the fact that sex is significantly suppressed.

Adding water after the reaction, which is said to have a negative effect on the progress of the reaction, for purification is an unexpected effect, and it is a great industrial advance to obtain highly pure methylal with a simple operation. It is assumed that the

The water used in the present invention does not need to be particularly purified water such as distilled water or ion-exchanged water, and ordinary tap water can be used sufficiently.

The crude methylal that is the object of the present invention is applicable to all methylal produced by a conventional method using methanol and formalin or paraformaldehyde as raw materials. It is also possible to directly add water to the reaction mixture of methanol and paraformaldehyde and distill it to obtain methylal with relatively high purity. After distilling the mixture, it is better to add a predetermined amount of water and distill the mixture to obtain a higher purity and a preferable result without lowering the yield.

It goes without saying that the present invention can be carried out under normal pressure, reduced pressure, pressurization, batchwise or continuous operation, and there is no need to pay any consideration to equipment or materials.

The present invention will be explained in more detail below with reference to Examples.

Example The apparatus used was a four-necked flask equipped with a Dimroth reflux condenser, a thermometer, and a stirrer.

This flask contains paraformaldehyde (purity 92).
%) 100g, pure methanol 320g and concentrated sulfuric acid 7.3
I put g.

The reaction was carried out while stirring the contents and gently refluxing them in a water bath.

Paraformaldehyde gradually dissolved, and approximately 10 minutes after the start of reflux, it was almost completely dissolved to become a homogeneous solution.

After continuing to heat for 5 hours, the mixture was cooled and distilled in water using a Witsmer distillation tube instead of a reflux condenser, and fractions up to a boiling point of 54°C were collected.

The crude yield was 230.6 g, and the contents of methylal, methanol, and water were determined by moisture analysis using gas chromatography and Karl-Fisscher method.
%), and water content was 0.3 g (0.1%).

This crude methylal was transferred to flask 1, and 238.5 g of water, which is equivalent to 15 times the amount of methanol by weight, was added and rectified using a Witsdomer distillation tube.
The fraction at 42.0°C was collected.

Yield is 181.9g, methylal 178.6g
(98.2%), methanol 2.0g (1.1%), water 1.3g
(0.7%).

Yield is 71.7 based on paraformaldehyde
It was %.

Similarly, the figure shows the methanol content in purified methylal when distilled by adding 2 to 50 times the weight of water to the methanol in crude methylal.

In the figure, crude methylal obtained in Example (93.0% methylal, 6.9% methanol, 0.1% water)
Rectification was carried out by changing the amount of water added.

The amount of water added was expressed by weight relative to the amount of methanol in the crude product.

Comparative Example The crude methylal obtained by reaction and distillation under exactly the same conditions as in the Example was rectified using a Widmer fractionating tube without adding water, and a fraction with a boiling point of 41.5 to 42.0°C was collected.

Yield is 175.5g, methylal 165.3g
(94.2%), methanol 9.5g (5.4%), water 0.7g
(0.4%).

Yield is 69.2 based on paraformaldehyde
It was %.

[Brief explanation of the drawing]

The figure shows the relationship between added water and methanol content in the fraction.

Claims (1)

[Scope of Claims] 1. Crude methylal obtained by reacting methanol with formaldehyde or paraformaldehyde is mixed with 2 to 50% of the methanol in the crude methylal.
A method for purifying methylal, which involves distilling it by adding twice its weight of water. 2. The method according to claim 1, wherein water is added to the crude methylal obtained by once distilling the reaction mixture.