DD144759B1 - METHOD FOR PRODUCING BENZIL - Google Patents

Description

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Title of the invention

Process for the preparation of benzil

Field of application of the invention

The invention relates to a process for the preparation of benzil, which is an important intermediate for the preparation of medicaments, for example, of 5,5-diphenylhydantoin and of 1 ^^, S-tetrachloro-1S-diphenyl-acetylenediurein.

Characteristic of the known technical solutions

3a is known to produce benzil by oxidation of benzoin · Many variants have been described for this reaction.

Benzoin, for example, can be oxidized to benzil with concentrated nitric acid (Gattermann, Praxis der organischen Chemiker, 1954, p. 194).

Hach of US Patent Hr. 2 377 749 (see also Organic Synthesis, Coll. Vol. I, page 87), equivalent amounts of copper (II) -aulfate are required for the oxidation of benzoin and according to 7 / Eigby (J. Chem. Soc. 1951, page 793), expensive bismuth (III) carbonate is used for the oxidation of benzoin.

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These processes have the following disadvantages · Nitric acid has an extremely strong corrosive effect, so that for this reason the equipment and plant components must be made of special materials · In the oxidation with nitric acid produced as a by-product nitrous gases that are absorbed due to environmental protection requirements with special absorption systems from the exhaust air The "processes based on copper (II) sulfate and bismuth (III) carbonate are ruled out due to economic considerations, since these two oxidants are very expensive and are required in equivalent amounts,

It is also known that the oxidation of benzoin is also effected in the presence of catalytic amounts of cupric sulfate (US Patent Ir · 2,658,920, M. Vfeiss and M. Appel, J. Amer. Chem. Soc · 70, page 3666) (1948)) or bismuth (III) carbonate (B. Holden, V / Rigby, J, Chem. Soc. 1951, 1924).

In these two methods, the spent catalyst must be constantly regenerated. In the case of the V / ismut- (III) carbonate, the regeneration is achieved with air and in the case of copper (II) sulfate with ammonium nitrate.

This latter method is not easily manageable. Ammonium nitrate is reduced in this process to ammonium nitrite, which decomposes in the acetic acid solution into nitrogen and water. This reaction is sometimes delayed, but then spontaneously, so that the overall process is not easy - and even on a small scale - to control. Since ammonium nitrate is also used for the production of safety explosives and in the presence of organic substances according to the Explosives Act of the GDR as an explosive

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because of its danger, this process can not be transferred to large-scale production.

The derivation of benzil by the oxidation of benzoin in dry dioxane with 1.2 equivalents of sodium antimony (V) acetate according to F, Uerdel (Chem. Ber. 97 (1), 124 131, (1964)) only honors akademiachea intereaae, there too expensive iat.

According to the USSR Patent No. 224,507 (YA Oatrowakaja, AI Adamovitach, AS Sarenko and UP Mikhailowa) benzil is oxidized with ammonium nitrate at 100 - 110 ⁰ C in the presence of a Katalyaatora. This process eliminates ammonium nitrate due to the absence of ammonium nitrate, and takes advantage of the disadvantages disclosed above.

The oxidation of 3enzoin with N-bromo-auccinimide in the presence of pyridine, as noted by R. Heilmann and P. Baret (CR Acad. Sci., Paria, C. 1968, 267 (8), 579-81), is also economically unacceptable .

After P · Manoa (. US 3,595,922 Patentachrift Ur) is benzoin at 35 - oxidized in methanoliacher Löaung and in the presence of 0.14 equivalents of copper benzoate ala catalyst while introducing air to benzil 40 ⁰ C. The disadvantages of these methods are the ablation of copper ions and the low roughness-time emission due to the insufficient solubility of benzoin in methanol.

There are still a number of other synthetic routes to benzil, but all these methods are not acceptable either economically or for environmental reasons (see

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ζ. B. Тэе-Lok Но, Chem. Ind. (London) 1972, (20), 807; S. Miaeo et al., Xakugaku Zasshi 1974, 94 (9), 1180 1182; Macaione, et al., Synthesis 1974, 10, 716; J.D. Albright, U.S. Patent Ur. 3,901,896; P. Girard, T. Letters 1975, 50, 4513-14; J. San Pilippo et al., J. Org. Chem. 1977, 42 (12), 2182-83).

3s is also known to produce benzil characterized in that, in a mixture of an aliphatic carboxylic acid, water and a mineral acid by passing oxygen or air to temperatures of 60 benzoin - 11O ⁰ C, preferably from 100 ⁰ C, heated (DD Patent Ur 126 483).

As the aliphatic carboxylic acids, formic acid and acetic acid and, as the mineral acid, hydrochloric acid, sulfuric acid or phosphoric acid are suitable. This process gives Benzil in excellent quality with a melting point between 90 and 95 ⁰ C and in 85 to 90% yield.

This procedure seems favorable at first glance. However, it is problematical to finely distribute the required quantities of air or acid in the reaction solution. In principle, this can be done either by introducing air through a drainage tube or nozzle-equipped stirrers, in which unаііе an uncatalyzed oxidation reaction times of 35- 40 hours are required, or in circulation process by pump and radiator, in which the air or oxygen intensively mixed, but even under optimal conditions, 16 to 20 hours of reaction time are still required in the industrial scale. Added to this are the corrosion problems caused by the hot acid reaction solution over this long time.

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Object of the invention

The invention makes it possible, while maintaining the high Ausbeuterrvon 90 % and excellent quality (Pp, 92-95 ° C) benzil by introducing air via suspension tubes or nozzle-equipped stirrers in a significantly shorter reaction time, about 10 to 15 Hours is very secure and, with greatly reduced corrosion problems, technologically simple and economical to produce extremely low.

Explanation of the essence of the invention:

The invention is based on the object, while maintaining the high yield of 90 ^c ß> and the excellent quality of benzil in a significantly shorter reaction time and thus with greatly reduced corrosion problems very safe and economically extremely low ·

According to the present invention, this is achieved by reacting benzoin in an anhydrous or hydrous aliphatic carboxylic acid, optionally in the presence of a mineral acid, and in the presence of a small amount of a heavy metal, heavy metal oxide or heavy metal salt as a catalyst while introducing oxygen or air to temperatures between 40 and 110 ^° C., preferably to 75-90 ^° C., heated

The amount of catalyst used can vary within wide limits. In general, amounts of from 0.1 to 10%, advantageously from 1 to 5%, are sufficient. However, it is also possible to use larger or smaller amounts of catalyst, although in most cases this does not bring any further advantages.

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As the aliphatic carboxylic acid, acetic acid or formic acid is preferably used. As mineral acids, sulfuric acid, hydrochloric acid or phosphoric acid are preferably suitable. The metal catalysts used are preferably iron salts, iron oxide or iron in the form of iron powder or iron shavings. The catalysts used in analogous reactions are small amounts of nickel, cobalt, copper or manganese in corresponding form.

The Y / assergehalt of the mixture can be Ьіз to 50 ^c / o , with increasing water content, a correspondingly larger amount of aliphatic carboxylic acid is needed. The amount of mineral acid may be 0.1 to 3.0 HU per mole of benzoin, depending on the water content of the mixture.

Exemplary embodiments Example 1

178 g of benzoin (0.88 mol) are added to a mixture of 450 ml of glacial acetic acid, 150 ml of 90% acetic acid (10 % Y / a), 85 ml of concentrated hydrochloric acid and 10 g of iron (II) sulfate. The reaction mixture is heated with stirring to 75 - 80 ⁰ C. When the temperature has reached 80 ^° C., the introduction of the air is started with vigorous stirring. Following the thin-layer chromatographic detection of the complete conversion of benzoin (a sample is dissolved in CHCl 2, eluent: benzene / Acston 9: 1), the introduction of the air is stopped.

While stirring, allowed to run in 300 ml of water slowly "After the reaction mixture with stirring at 15 - 20 ⁰ C cooled. The benzil crystallizes out and is filtered off with suction, washed with water and dried.

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Yield: 155 g of light yellow crystalline benzil, 88% of theory, Pp 92 to 95.3 ^0C.

Example 2:

178 g of benzoin (0.88 mol) are added to a mixture of 700 ml of 85% acetic acid (15% water), 50 ml of concentrated sulfuric acid and 10 g of iron (II) sulfate. This reaction mixture is further treated as described under Example 1.

By further diluting the mother liquor with an appropriate amount ater ^w you can still get about 10g · benzil from Pp. 80 - 9O ⁰ C. This is benzil by-products, for. B. benzoic acid, contaminated. Recrystallization of this contaminated benzene from methanol and in the presence of some activated carbon gives pure benzil. This applies to all examples.

Yield: 159 g = 90 o benzil theory, Pp 91.7 95.8 ⁰ C..

Example 3:

178 g of benzoin (0.88 mol) are entered sulfate emic from 600 ml of 85% formic acid in a ^G, 75 ml of concentrated hydrochloric acid and 10 g of iron (II). The procedure is as described in Example 1. Yield: 150 g = 85% of theory benzil, Pp 91 to 94.8 ^0C.

Example 4:

178 g of benzoin (0.88 mol) are added to a mixture of 450 ml of glacial acetic acid, 150 ml of 90% acetic acid and 0.2 g of iron (II) sulfate. This reaction mixture is after the

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specified in Example 1 fashion treated · Yield: 132.5 g of benzil, 75% of theory Pp 92.7 to 96.1 C ^0.

Example 5:

178 g of benzoin (0.88 mol) are added to a mixture of 450 ml of glacial acetic acid, 150 ml of 90% acetic acid (10% water content), 100 ml of concentrated hydrochloric acid and 2 g of iron powder or iron filings. The reaction mixture is treated as described in Example 1, yield: 154 g of benzil, 87 4Ό theory pp. 92.3 - 95.4 ⁰ C.

Example 6:

173 g of benzoin (0.88 g of 2JoI) are added to a mixture of 450 ml of glacial acetic acid, 150 ml of 90% acetic acid (10 l / v), 130 ml of water, 35 ml of 75% phosphoric acid and 10 g of 3-iron (II) sulphate , It continues to work according to Example 1.

Yield: 156 g Bsnzil, 88.5 lb. Theoria Pp. 91-9 $ ° C.

Example 7:

Examples 1 to 4 and Example 6 can also be carried out in analogous manner with iron (II) chloride, iron (III) chloride, iron (III) sulfate or other soluble egg salts.

Example 8:

382 g of benzoin are dissolved in a mixture of 1,200 ml of glacial acetic acid, 16 ml of water, 172 ml of hydrochloric acid and 0.5 g of iron

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(or an equivalent amount of an iron salt or iron oxide) registered. The reaction mixture is never treated as described in Example 1. Yield: 157.6 g of benzil, 89% of theory Pp 94.8 to 95.1 C ^0.

Claims (1)

21 4 2 2 1 Invention claim 1. A process for the preparation of benzil by oxidation of benzoin in an aliphatic carboxylic acid, in the presence of a mineral acid, by introducing air or oxygen at 60 to HO ⁰ C, characterized in that the oxidation in the presence of catalytic amounts of a metal from the group iron , Nickel, cobalt, copper or manganese is carried out. Process according to item 1, characterized in that the metal catalysts are added in elemental form, as metal oxide or as metal salt » Process according to items 1 and 2, characterized in that the acid radical of the metal salt can be derived from both an organic acid and an inorganic acid. Process according to points 1 to 3, characterized in that 0.1 to 10, preferably 1 to 3% catalyst based on the benzoin used; become·