DE1165569B - Process for the production of ª ‡ -chloroisobutyraldehyde - Google Patents

Description

Process for the preparation of α-chloroisobutyraldehyde It is known that z-chloroisobutyraldehyde can be obtained by the action of chlorine on trimeric isobutyraldehyde can produce. This produces e; -chloroisobutyraldehyde in addition to equal molars Amounts of hydrogen chloride. The process therefore has the disadvantage that 500 / o des Loses chlorine in the form of hydrogen chloride.

While the chlorination of acetone with elemental chlorine in yields over 900 / o leads to ou-chloroacetone are the best in the chlorination of isobutyraldehyde Yields obtainable with elemental chlorine in the literature are only a maximum of 400 / o (cf. H 0 u b e n - W e y 1, "Methods of Organic Chemistry", Vol. 7 [1954], part 1, p. 363).

It is also known that acetone using copper chloride in aqueous Solution can be converted into z-chloroacetone (J. Amer. Chem. Soe., 77 [1955], P. 52). However, since in this implementation at least three hours of boiling the acetone required, the transfer of this reaction to isobutyraldehyde seemed little promising in view of the fact that isobutyraldehyde by short-term Cooking in acidic solution condenses to high molecular weight products and that above In addition, any α-chloroisobutyraldehyde in aqueous solutions at higher levels Temperature is saponified very quickly to hydroxyisobutyraldehyde (cf.

Monthly books for chemistry, 21 [1900], p. 213).

The invention relates to a process for the preparation of oc-chloroisobutyraldehyde from isobutyraldehyde, which is characterized in that isobutyraldehyde at 50 up to 2000 C with aqueous copper (II) chloride solution is reacted by the reaction partially reduced copper chloride solution, optionally to remove organic Impurities heated and after adding aqueous hydrochloric acid with oxygen or oxygen-containing gases is oxidized again, the conversion of the copper (II) chloride solution with isobutyraldehyde and the reoxidation of this solution, if desired, in one Reaction step can be carried out and the chlorination product, which except ou-chloroisobutyraldehyde contains small amounts of diacetyl by extractive distillation with water or aqueous hydrochloric acid or by crystallization of the -chloroisobutyraldehyde hemihydrate is cleaned.

It was surprising that in contrast to the known implementation of acetone with copper chloride is the chlorination of isobutyraldehyde among the same Conditions is about a factor of 100 faster. It is just that fact Thanks to, that the residence times of the aldehyde in the copper chloride solution are so short can be kept that practically no saponification of the resulting oc-chloroisobutyraldehyde to oc-hydroxyisobutyraldehyde takes place.

The reaction goes particularly smoothly and with high sales, if one chooses Cl: Cu ion ratios that are greater than 2.

In the reaction of isobutyraldehyde with copper (II) chloride in aqueous Solution at normal pressure or slightly overpressure at the boiling point of the aqueous Copper (II) chloride solution creates copper (I) chloride, which reacts with oxygen or oxygen-containing gases in the presence of aqueous hydrochloric acid can be converted into copper (II) chloride.

A preferred form of the method is that by a A packed column aqueous copper (II) chloride solution trickles in countercurrent Gaseous isobutyraldehyde is introduced below and likewise at the top of the column evaporated> 900/0 pure chloroisobutyraldehyde. The copper (II) chloride solution is then by heating or by introducing water vapor of organic Products largely stripped and added by adding the calculated amount of aqueous Hydrochloric acid is treated with oxygen or air to form copper (I) chloride, which is formed in the reaction in copper (II) chloride. Then the copper chloride solution returned to the head of the column. You can also use oxygen and isobutyraldehyde Introduce into the column at the same time.

You can also use it below the discharge point for Isoburyraldehyde introduce the oxygen or gases containing oxygen and thus the heat of reaction in the oxidation of Cu 'to Cu'1 to drive off organic Recycle products.

Organic substances can form in the copper chloride solution after prolonged use Build up fractions, thereby reducing the effectiveness of the solution. These organic components can be removed by simple thermal treatment at temperatures between 150 and 250C and the corresponding pressures, optionally in the presence Quantitatively convert oxygen or oxygen-containing gases into CO2 and MCI, whereby the solution regains its original activity.

Isobutyraldehyde is used as a by-product in the reaction Copper (III) chloride has small amounts of diacetyl. One can choose the proportion of diacetyl keep it low by choosing low conversions. So it is possible with sales below 500 / o to keep the diacetyl content below 1%. But if you want high sales achieve over 900 / o, then the diacetyl content can be 4010 and more.

Diacetyl is because of its boiling point, which is very close to that of a-chloroisobutyraldehyde is difficult to separate from this by distillation. By extractive distillation with water or aqueous hydrochloric acid, preferably in a vacuum, the .X-chloroisobutyraldehyde can be obtained in high purity as a colorless product can be obtained at the top of the separating column, while the diacetyl is obtained by distillation of the column flow is to be obtained. x-Chloroisobutyraldehyde forms with water Azeotrope boiling at 75 "C. By incipient distillation, it can be converted into appropriate Devices easily circle the existing water and so an anhydrous win oc-chloroisobutyraldehyde.

The es-chloroisobutyraldehyde can also be isolated by that the crude high-percentage chlorine aldehyde in vacuo in the presence of water distilled to obtain an ion-free product, and crystallized, possibly using low temperatures, in the form of his previously unknown Brings hemihydrates of the formula 2 C4H7OCl H2O with a melting point of 88 "C to precipitate. The hydrate can be broken down into its components by distillation.

Higher-boiling products arising in the course of the distillation work-up, mainly from 1 part isobutyraldehyde and 2 parts chloroisobutyraldehyde split into the monomeric constituents by simple distillation at normal pressure.

-Chloroisobutyraldehyde is a valuable intermediate, for example as a starting material for methacrolein, oxyisobutyraldehyde, es-chloroisobutyric acid chloride or z-chloroisobutyric acid.

In the following examples, the data refer to percentages and parts by weight, unless otherwise noted.

Example Through a pipe 3 m long and 5 cm in diameter, which is connected to Raschig rings are filled every hour 101 of a copper chloride solution with 12 O / o copper and 70 / o excess hydrochloric acid sent from top to bottom. At the foot In the column, this solution is heated up by a heater to such an extent that it is at the top the column is distilled off 112 kg of steam per hour. At the same time, the lower Third of the column introduced 240 g of gaseous isobutyraldehyde. The educated w-chloroisobutyraldehyde distills together with little unreacted isobutyraldehyde and the water vapor generated in the bottom of the column at the top of the column and becomes condensed. 288 g of chloroisobutyraldehyde and 20 g of isobutyraldehyde are obtained per hour corresponding to 90 01, conversion and 90 0 /, yield. The copper chloride solution is after Leaving the column with the equivalent amount of aqueous chloraldehyde formed Hydrochloric acid added and in a 2 m high, 10 cm wide, filled with Raschig rings Column gassed with oxygen. The oxidized solution leaves the head of the second Column through an overflow and flows under its own weight into the reaction column return.

The purification of the crude product can be carried out as follows: a) 100 g of an aqueous copper chloride prepared using air and hydrochloric acid Crude 900/0 own cx-chloroisobutyraldehyde, which contains 1001o diacetyl, are used in Presence of water at 100 mm Hg and 25 to 35 "C. Distilled from the distillate is obtained by deep-freezing to -50 "C and suctioning off the precipitated crystals 20 g of dimeric chloroisobutyraldehyde hydrate. The crystals had after drying The composition 2 C4HvCIO H2O over KOH in a vacuum and melted at 80 to 83 "C. After 1 day the crystals were in the purest liquid tx-chloroisobutyraldehyde and Water that floated as easy-to-separate drops on the x-chlorobutyraldehyde, passed over. b) A 980/0 of a chloroisobutyraldehyde, which is still 20 / o n- and isobutyraldehyde contains, was at 100 mm with a reflux ratio 2: 1 in the presence of water distilled. The main fraction passed over at 29 ° C. The distillate separated out if the dimeric chlorobutyraldehyde hydrate is left to stand for 2 days at 10 "C, 20 ovo. By cooling the filtrate to -200 ° C., a further 500% of the solid hydrate could be obtained to win. c) At the top of a column 2 m high, filled with Raschig rings 1.5 liters of water at 70 "C are pumped every hour. In the middle of the column 120 g hourly of a mixture of 95 parts of x-chloroisobutyraldehyde and 5 parts Diacetyl introduced. The bladder is heated to a temperature of 97 "C from the outside. At 75 ° C., 90 g of colorless x-chloroisobutyraldehyde go with less at the top of the column than 100 ppm diacetyl above.

Claims (2)

Claims: 1. Process for the preparation of x-chloroisobutyraldehyde from isobutyraldehyde, which indicates that isobutyraldehyde at 50 to 2000 C with aqueous copper (II) chloride solution is reacted through the reaction of partially reduced copper chloride solution, if necessary for removal heated by organic impurities and after adding aqueous hydrochloric acid is re-oxidized with oxygen or oxygen-containing gases, the reaction the copper (II) chloride solution with isobutyraldehyde and the reoxidation of this solution if desired, can be carried out in one reaction step, and the chlorination product, which contains small amounts of diacetyl in addition to -chloroisobutyraldehyde, by extractive Distillation with Water or aqueous hydrochloric acid or by crystallization of the x-chloroisobutyraldehyde hemihydrate is purified. 2. The method according to claim 1, characterized in that the copper (II) chloride solution a has a molar ratio of Cl ions to Cu ions of more than 2. Considered publications: German Patent Specifications No. 739 171, 955 237.