CH652709A5 - METHOD FOR PRODUCING ESTERS OF MESOXAL ACID. - Google Patents

Description

The invention relates to a process for the preparation of esters of mesoxalic acid by oxidation of the corresponding malonic esters with nitrous gases.

It is known to produce esters of mesoxalic acid (oxomalonic acid) by oxidation of the corresponding malonic esters with nitrous gases (Organic Synth. Coll. Vol. 1, p. 267). The disadvantage of this known method is that it generally requires at least 48 hours of reaction time at room temperature, which is too long for industrial production. In addition, working up the reaction mixtures is dangerous since large amounts of the intermediate products mono- and dinitromalone esters are present in the mixture at any time and can spontaneously release larger amounts of gas during distillation.

The object of the invention is to avoid these disadvantages of the known methods.

According to the invention, this is achieved by a method according to claim 1.

A preferred embodiment of the invention consists in that the malonic ester mixture treated with nitrous gases, which is expedient by introducing nitrous gases at temperatures from 0 to 25 ° C. and in an excess of advantageously 0.2 to 3.0 mol per mol of malonic ester is obtained and that it is then, advantageously left to stand for at least 2, at most 24 hours, a three-stage heat treatment. This heat treatment advantageously takes place in such a way that the mixture is allowed to drip through an apparatus consisting of three temperature zones located one behind the other.

The individual zones are e.g. heated from the outside and connected to each other.

The mixture resulting from the treatment with nitrous gases contains mesoxalic acid esters as hydrate and mononitromalonic esters. This is converted to mesoxalic acid esters in the first heat treatment stage, at temperatures of advantageously 150 to 170 ° C.

The dinitromalonic ester present in the mixture is converted into mesoxalic acid esters in the second heat treatment zone, expediently at temperatures of 220 to 245 ° C.

The third heat treatment zone from 60 to 100 ° C is connected downstream to avoid the re-formation of a complex between mesoxalic acid ester and nitrous gases. Dry inert gases, advantageously air, are passed through in countercurrent.

The excess nitrous gases can be recovered and reused.

Heat treatment of the reaction mixture

The process of the invention is advantageously carried out, for example, in a reactor as shown in FIG. 1. The reaction mixture obtained in a reaction vessel (not shown) comes into a glass vessel with a needle valve 1 and from there it arrives in a first heating zone, consisting of a tube coil 2, which is located in a heating bath 3. The heating bath is set to the temperature necessary for converting the mononitromalone ester and stirred by a stirrer 6. The mixture then passes through the compound 12 into a second heating zone 4 which is in the temperature bath 5 at a temperature for decomposing the corresponding dinitromalonate. The thermal bath, consisting of silicone oil or other heat carriers, is stirred by the magnetic stirrer 7. From there, the mixture reaches the third heat treatment zone, consisting of a tube 8 with a heat jacket 9 and the collecting device 10. At 13, dried air is introduced in countercurrent and sucked off via a cooler 11.

example 1

Diethyl mesocalate

7.5 g of diethyl malonate were placed in a well-dried 50 ml glass flask and the whole was placed in a cold bath at about -8 ° C. (alcohol from a Kryomat). 5 ml of liquid NO2 were pipetted into another 20 ml glass flask, which already contained a spatula tip P2O5, and the glass flask was connected to the feed tube of the reaction vessel. When the temperature in the latter reached slightly above 0 ° C, one gradually distilled over NO2 by slightly warming the smaller glass vessel with lukewarm water. The NO2 dissolved in the malonic acid ester (without being blown through) with the development of heat, but without nitrous vapors escaping from the reaction device. The distillation rate of the NO2 was controlled so that the temperature of the reaction mixture was kept just above 0 ° C. Inflation time of the NO2: 20 to 30 minutes. Only small clumped P2O5 remained in the small glass flask. The flask with the reaction mixture (the content of which was yellow-brown) was transferred to a thermostated heat bath at 25 ° C. The reaction mixture reached this temperature after about 10 minutes and remained constant at this value for 1.5 to 2 hours. Then a temperature increase of 1 to 2 ° C above the temperature of the surrounding bath was found. This exothermic phase lasted 3 to 4 hours and was accompanied by a moderate escape of nitrous gases.

When the temperatures of both the reaction mixture and the bath had the same value (and also the elimination of the nitrous gases had ceased), the reaction was complete and the greenish-colored reaction mixture could be subjected to further thermal treatment. For this purpose, a temperature of 170 ° C. was set in the tube coil 2, which had a volume of approximately 50 ml, and a temperature of 245 ° C. was maintained in the tube coil 4 with the same volume. The dropping of the reaction mixture into the first coil took 45 minutes. The condensate obtained in the last stage at 100 ° C was light yellow and mainly existed

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

3rd

652 709

from the hydrate of the mesoxalic acid diethyl ester, which tended to crystallize to a white mass.

A GC determination of the condensate showed the presence of 1% mononetromalonate in addition to the mesoxalic acid diethyl ester, however, dinitromalonate was not detectable.

Distillation - dewatering in the Vigreux column: The melted condensate in the flask, which was intended for the distillation, was, together with the material recovered by washing the apparatus, under a vacuum of 15 mbar at a temperature which slowly increased from 60 to 90 ° C. in Was increased over an hour. From the point at which water began to separate from the cold parts, this was removed by tempering the pipe sockets with the aid of a warm air stream. After the water separation had ended (after about 1 hour), the temperature in the flask was raised to 98 to 100 ° C., the ethyl mesoxalate starting to distill at 92 ° C. The mesoxal ester was distilled between 92 and 110 ° C by continuously increasing the bath temperature to finally about 200 ° C.

The distillation residue consisted of a small brown coating on the flask walls. The distillate was yellow, very hygroscopic and weighed 7.5 g (absence of crystals). The distillate contained (GC determination) 98.6% ethyl mesoxalate and 1.2% mononitromaloester.

Yield: 7.40 g of mesoxalic acid diethyl ester 100% = 42.5 mmol, that is 90.6% based on the starting amount of malonate.

Example 2

Dimethyl mesoxalate

7.5 g of NO2 were added as gas to 6.2 g (46.9 mmol) of dimethyl malonate cooled to 0 ° C. within 23 minutes. The reaction mixture was then stirred in a 25 ° C bath for 22 hours. An exothermic reaction (temperature increase in the reaction mixture by 1 ° C.), which lasted about 6 hours, was found.

The reaction mixture was then subjected to a thermal treatment in the apparatus described in Example 1, namely by being in a period of 46 minutes at temperatures of 170 resp. 245 ° C through the respective coil and then carried out the third heat treatment stage with transfer of dry air.

The condensate was obtained by vacuum distillation from the reaction mixture which had previously been kept under vacuum at 80 to 100 ° C. for 45 minutes for dewatering. 5.38 g of dimethyl mesoxalate (bp 110 ° C./70 mbar) were isolated.

Purity (GC): 99.6 °. There were no spades for mono or dinitromalonic acid esters. Also, no NO or NO2 bands were found at 160 cm-1 in the IR spectrum.

Yield: 78.2%.

Example 3

Diisobutyl mesoxalate

4.5 g of NO2 was added as gas to 5 g (23.1 mmol) of diisobutyl malonate at 0 ° C. over a period of 20 minutes, as described in Example 2. The reaction mixture was then stirred at 25 ° C. for 24 hours (temperature increase for about 4 hours).

The thermal treatment (flowing through coils at 150 ° C or 245 ° C) took 30 minutes. Dry air was then passed over at 100 ° C. The condensate was obtained by vacuum distillation without a column, after dewatering the reaction mixture in vacuo at about 100.degree.

4.5 g of diisobutyl mesoxalate (bp 130 to s 132 ° C./15 mbar) were obtained.

Purity (GC): 98.6%. There were no spades for mono or dinitromalonic acid esters. Also, no band was found at 1600 cm-1 in the IR spectrum.

Yield: 83.4%.

10th

Example 4 Di-n-hexyl Mesoxalate

4.5 g of NO2 were added as gas to 6.55 g (24 mmol) of malonic acid dihexyl ester at 0 ° C. in the course of 15 minutes. The reaction mixture was then stirred at 25 ° C for 8 hours. The thermal treatment (flowing through coils at 120 ° C or 210 ° C) took 40 minutes. Dry air was then passed over at about 95 ° C. The distillation of the condensate, 20 without a column and under high vacuum, gave 4.15 g of di-n-hexyl mesoxalate (bp 112 to 120 ° C./0.05 mbar). Purity (GC): 92.5% di-n-hexyl mesoxalate. A very small band around 1600 cm- 'was observed in the IR spectrum. Before the thermal treatment, this 2s band was very large and split. By heating the distillate to 210 ° C for a few minutes, this band at 1600 cm-1 disappeared.

Yield: 55.8%.

Example 5 30 mesoxalic acid dicyclohexyl ester

4.5 g of NO2 were added as gas to 6.25 g (23.3 mmol) of malonic acid dicyclohexyl ester at 0 ° C. within 30 minutes. The reaction mixture was then stirred at 25 ° C for 7 hours. The thermal treatment (flowing through coils at 120 ° C or 225 ° C) took 28 minutes. Dry air was then passed over at 90 ° C. Resin deposits were found in the second coil. The condensate was distilled without a column under high vacuum. A fraction 40 (120 to 140 ° C / 0.03 to 0.04 mbar) of 3.1 g was isolated. From this, 1 g of solid separated out, which after recrystallization from water, according to analysis (IR; NMR), proved to be adipic acid (originating from the oxidation of the cyclohexyl residue). The rest of the distillate contained (GC determination) 91.1% mesoxalic acid dicyclohexyl ester, which was free of nitro compounds (no IR band at 1600 cm-1). Yield: 29.1%.

Note: In cases where the coils have temperatures of 120 ° C or. 205 ° C, noticeable amounts of nitromalonic acid ester remained in the reaction mixture.

Example 6 Mesoxalic acid dibenzyl ester

4.5 g of NO2 were added as gas to ss 6.9 g (24.3 mmol) of malonic acid dibenzyl ester at 0 ° C. within 25 minutes. The reaction mixture was then stirred at 25 ° C for 23.5 hours. The subsequent thermal treatment (flowing through coils at 120 ° C or 210 ° C) took 30 minutes. Subsequently, dry air was passed over at 100 ° C. By distillation without a column, a fraction (bp 155 to 160 ° C./0.07 mbar) of 4.23 g of mesoxalic acid dibenzyl ester with a purity (GC) of 91.8% was isolated in addition to 1 g of feed and 1.2 g of residue. According to the IR spectrum, no nitro compounds were present. The main component of the forerun was o-nitrotoluene.

Yield of mesoxalic acid dibenzyl ester in the main fraction: 53.6%.

6S2 7®§>

4th

Example 7

Phenyl ethyl mesoxalate

4.5 g of NO2 were added as a gas to 4.16 g (20 mmol) of malonic acid phenyl ethyl ester at 0 ° C. within 24 minutes. The reaction mixture was then stirred at 25 ° C for 8 hours. The subsequent thermal treatment (flowing through coils at 120 ° C or 210 ° C) took 20 minutes. Dry air was then passed over at 100 ° C. The distillation (high vacuum without column), after heating for 40 minutes to approx. 90 ° C. at a pressure of 15 mbar, gave a fraction (bp 90 to 95 ° C./0.03 mbar) of in addition to a residue of 1.9 g 2.0 g. Purity (GC): 92.5% phenyl mesoxalate. Traces of nitro compounds (recognizable by the IR band at 1600 cm-1) were present.

Yield: 41.7%.

An analog thermal treatment at 170 ° C respectively. 235 ° C gave a much larger amount of nitromalonic acid esters.

Example 8

Mesoxalic acid dibutyl ester

7.5 g of NO2 were added from gas to 8.3 g (38.4 mmol) of malonic acid dibutyl ester at 0 ° C. within 35 minutes. The reaction mixture was then stirred at 25 ° C for 8 hours. The thermal treatment (flowing through the coils at 145 ° C or 245 ° C) took 1 hour. The distillation, after heating for 40 minutes at 80 to 100 ° C. at a pressure of 13 mbar, gave 7.47 g of dibutyl mesoxalate (bp 133 to 135 ° C./13 mbar).

Purity (GC): 98.7%. Less than 0.5% nitro compounds were present, but these are easily removed by rectification in the Vigreux column.

Yield: 83.4%.

Example 9 5 Dipropyl Mesoxalate

7.5 g of NO2 were added as gas to 7.2 g (38.3 mmol) of malonic acid dipropyl ester at 0 ° C. within 35 minutes. The reaction mixture was then stirred at 25 ° C for 8 hours. The thermal treatment (flowing through the coils at 160 ° C or 245 ° C) lasted 47 minutes. The distillation (Vigreux column) after heating for 30 minutes to 60 to 80 ° C. at a pressure of 15 mbar gave 6.98 g of dipropyl mesoxalate (bp 110 to 112 ° C./15 mbar).

Purity (GC): 99.3%; Nitro compounds were not available.

Yield: 89.4%.

Example 10 20 Diisopropyl Mesoxalate

7.5 g of NO2 were added as gas to 7.2 g (38.3 mmol) of diisopropyl malonate at 0 ° C. within 30 minutes. The reaction mixture was then stirred at 20 ° C for 7.5 hours. The thermal treatment (flowing through the coils at 150 ° C or 245 ° C) took 1 hour. The distillation (Vigreux column) after heating for 20 minutes to 60 to 80 ° C. at a pressure of 15 mbar produced 5.57 g of diisopropyl mesoxalate (bp 100 to 102 ° C./15 mbar) and a residue of 1.71 G.

Purity (GC): 93.4%; Nitro compounds were not available.

Yield: 71.4%.

B

1 sheet of drawings

Claims (4)

652709 1. Process for the preparation of esters of mesoxalic acid by oxidation of the corresponding malonic esters with nitrous gases, characterized in that nitrous gases are added to the corresponding malonic ester in a first stage at temperatures from below 0 to a maximum of 25 ° C., this mixture after standing over a Time of at least 2 hours is first subjected to a heat treatment at temperatures from 120 to 180 ° C, then to a heat treatment at temperatures from 205 to 245 ° C and finally to a heat treatment from 60 to 100 ° C, the last heat treatment being carried out by passing dry, inert gases in countercurrent happens, and then distillation of the mesoxalic acid ester formed under reduced pressure. 2. The method according to claim 1, characterized in that one carries out the heat treatment in three separate, consecutive stages, the mixture being passed through the individual stages by slow dropping. 2nd PATENT CLAIMS 3. The method according to claims 1 and 2, characterized in that nitrous gases are used in an excess of 0.2 to 3.0 moles per mole of malonic ester. 4. The method according to claims 1 to 3, characterized in that NO2 is used as the nitrous gas.