DE1618098C2 - Process for the preparation of alkenols and alkenones - Google Patents

Description

A number of reactions of formaldehyde are known which take place at high temperature in the liquid phase '5 be performed. For example, consider the synthesis of 3-methy! Buten- (3) -ol- (l) from isobutylene and formaldehyde or the synthesis of 2-methylhepten- (1) -one- (6) from isobutylene, formaldehyde and acetone called.

Such reactions of formaldehyde have so far not found entry into technology, since the Yields of the desired reaction products are low, and in particular because deposits of insoluble condensation products were observed in the reaction vessel and after short operating times costly cleaning operations were necessary.

It has now surprisingly been found that the formation of insoluble condensation products in the preparation of alkenols and of alkenones by reacting the formaldehyde with olefins and with olefins and ketones, in each case in the temperature range between 150 and 400 ^° C. in the liquid phase under increased pressure, is practical can be completely prevented if the formation of a gas phase is largely avoided when carrying out the reactions in the reaction space.

According to the new process, due to the suppression of side reactions, the apparent run through the gas phase, much higher yield ίο achieved on the desired products. Even after long periods of operation are cleaning operations of the reaction vessel is not required.

The new process not only affects reactions that are carried out with monomeric formaldehyde, but also those with a compound which releases formaldehyde under reaction conditions. Hydrates, Acetals, oligomers and polymers of formaldehyde can be used. In many cases, an aqueous formaldehyde solution is used used. Trioxane, paraformaldehyde and hydrate forms of polyformaldehyde may also be mentioned and polyformaldehydes whose permanent hydroxyl groups are etherified or esterified.

In the new method, the reaction is carried out at temperatures between 150 and 400 ° C, preferably 180-380 ⁰ C, in particular between 200 and 350 ⁰ C, above.

When carrying out the claimed process, the reaction vessel should be practically completely, preferably be filled to more than 90%, in particular more than 97%, with the liquid reaction mixture. One achieves This is done by having an extraction valve, expediently in the form of a, at the top of the reaction vessel Overpressure valve, attaches and the reaction vessel feeds the starting materials in such an amount until out Liquid escapes from the sampling vessel. So you work at a pressure that is at least equal to the vapor pressure the mixture of the reactants or the reaction mixture corresponds to In general, mar works between 5 and 1000 atmospheres, in particular between 50 and 500 atmospheres.

With regard to the proportions in which the reactants are used, with regard to the any necessary catalysts, inhibitors, solvents or diluents, the reaction time, the temperature and the work-up of the reaction mixtures do not differ from the new one from the usual procedures. It is possible to work with the addition of customary catalysts, which is particularly advantageous is z. B. an addition of weak bases.

The new process can be carried out batchwise. However, it is advantageous to work continuously, starting materials are continuously fed to the reaction vessel and with avoidance the formation of a gas phase, the reaction mixture is advantageously discharged at the top of the vessel will.

The following examples illustrate how the new process works. The specified parts are Parts by weight. They relate to parts of space like grams to liters.

example 1

A pressure vessel of 1 volume volume is charged hourly at 275 ° C and 300 atm with a mixture of 258 parts of aqueous 37 weight percent formaldehyde solution, 1500 parts of isobutylene and 3 parts of aqueous ammonia solution (25%), taking care that there are none in the pressure vessel Gas phase forms The reaction solution obtained is worked up by distillation. From the reaction effluent per hour, in addition to 1330 parts of unconverted isobutylene and 164 parts of water, 248 parts of 2-methylbutylene- (1) -ol- (4) with a boiling point of ₉₅ ° 78 ° C. are obtained Yield is 91% based on formaldehyde.
Polymer formation is not observed
If the reaction is carried out in such a way that the reaction vessel is only 50% filled with the liquid phase, considerable deposits of insoluble polymers are observed on the vessel walls after a few hours.

Example 2

A pressure ^{vessel with a volume of 2.5 parts by volume is charged hourly at 280 °} C. and 200 atm. With a mixture of 685 parts of acetone, 590 parts of isobutylene and 183 parts of aqueous formaldehyde solution (37 percent by weight), taking care that there are none in the pressure vessel Forms gas phase. The reaction solution obtained is worked up by distillation. The reaction product obtained per hour gives 220 parts of distillate with a bp. (2) -on- (6) has a total of 75%

Example 3

A pressure vessel of 1 ^{volume volume is charged every hour at 300 0} C and 300 atm with a mixture of 360 parts of acetone, 45 parts of aqueous formaldehyde solution (37 percent by weight) and 330 parts of 2-methylbutene- (2), taking care to ensure that no gas phase forms in the pressure vessel. The reaction solution obtained is worked up by distillation. 70 parts of 23-dimethyihepten- (1) -one- (6) with bp.

115 ° C, 100 mm Hg.

Example 4

A pressure vessel of 1 ^{volume volume is charged hourly at 300 0} C and 300 atm with a mixture of 130 parts of aqueous formaldehyde solution (37 percent by weight) and 360 parts of propylene, taking care that no gas phase is formed in the pressure vessel, pas resulting reaction product is purified by distillation. 70 parts of butene- (1) -ol- (4) with a boiling point of 122 ° C. are obtained per hour.

Example 5

A pressure vessel of 1 volume volume is ^{charged at 300 °} C. and 300 atm. Hourly with a mixture of 44 parts of trioxane, 180 parts of tetrahydrofuran and 1500 parts of isobutylene, taking care that no gas phase is formed. The resulting reaction solution is worked up by distillation. 105 is obtained from the reaction mixture obtained per hour

ίο parts 3-methylbutene- (3) -ol- (l).

Claims (1)

Claim: Process for the preparation of alkenols and of alkenones by reacting the formaldehyde with olefins and with olefins and ketones, in each case in the temperature range between 150 and 400 ^° C. in the liquid phase under increased pressure, characterized in that the formation is carried out in the reaction chamber when the reactions are carried out largely avoids a gas phase.