NL9200374A - Method for the preparation of acyl cyanides. - Google Patents

Abstract

The invention relates to a method for the preparation of acyl cyanides with the formula R-C(O)-CN, in which R represents a possibly substituted alkyl group with 1-8 carbon atoms, a possibly substituted cycloalkyl group with 3-12 carbon atoms, a possibly substituted aryl group or a possibly substituted heterocyclic residue containing 5 or 6 ring units, which in addition can be annealed with a benzene ring by conversion of carboxylic acid anhydrides with the formula R-C(O)-C(O)-R, in which R has the meanings indicated above, with alkali metal cyanides in the absence of a catalyst, with the conversion being carried out in the liquid phase at a temperature of 50- 250 degree C and the acyl cyanides obtained being removed from the reaction medium directly after the formation thereof by distillation.

Description

Method for the preparation of acylvvanides.

The invention relates to a process for the preparation of acyl cyanides of the formula 1, in which R is an optionally substituted alkyl group with 1-8 carbon atoms, an optionally substituted cycloalkyl group with 3 * 12 carbon atoms, an optionally substituted aryl group or an optionally substituted, Represents 5 or 6 ring units containing heterocyclic moiety, which may additionally be fused with a benzene ring by reacting carboxylic anhydrides of the formula II, wherein R has the above meanings with alkali metal cyanides in the absence of a catalyst.

Such a method is known for the conversion of equivalent amounts of benzoic anhydride and potassium cyanide, whereby benzoyl cyanide is obtained in a small yield (about 10 l of the theoretical yield) (Liebigs Annalen der Chemie 287 (1895). 306). The benzoyl cyanide must be extracted with ether from the tough, very hard-hardened, dark brown mass obtained as the main product. This process is completely unsuitable for a technical application, since not only does the extraction with ether present technically insoluble difficulties, but there is no further use for the very heavily resinous dark brown masses.

It is further known that acyl cyanides can be obtained by reacting acyl halides with metal cyanides (Angew. Chem. 68 (1956), 425-35). However, this process has a number of drawbacks. It is thus laborious and technically difficult to carry out, since it concerns a two-phase reaction in which a solid is reacted with a liquid or with a dissolved compound. In addition, the conversion does not yield a homogeneous conversion product, but a difficult-to-separate mixture of compounds which, in addition to the desired acyl cyanide, also contains a relatively large amount of a corresponding dimer. Therefore, the acyl cyanide yields are relatively small. Another disadvantage of this method is that the water used for further processing, used for washing, must be thoroughly purified before the water can be discharged, because the water still contains considerable amounts of highly toxic metal cyanides, which are converted into an excess used.

It has been found that acyl cyanides can be obtained in excellent yields without the aforementioned drawbacks when the conversion according to the invention according to the invention is carried out in the liquid phase at a temperature of 50-250 ° C and the acyl cyanides obtained with Formula 1 is removed from the reaction medium immediately after formation by distillation.

It is particularly surprising that acyl cyanides of the formula I can be obtained in high yield and excellent purity by the process of the invention, since the prior art was expected to produce the same difficulties as in the reaction according to the process of acyl halides with alkali metal or heavy metal cyanides in a two-phase system or that the desired acyl cyanide is formed only in trace amounts. In particular, it could not be foreseen that no undesired dimeric acyl cyanides or resinous products are obtained at all.

The method according to the invention has a number of advantages. Thus, the method according to the invention is not limited to the preparation of a small number of certain compounds, but can be used very extensively. Furthermore, the process according to the invention yields acyl cyanides with an almost quantitative yield and excellent purity, free from disturbing or environmentally hazardous by-products.

Another decisive advantage of the method according to the invention is that the processing does not present any problems.

The alkali metal salts of the carboxylic acids obtained during the reaction are separated, for example, by filtration, and the filtrate can be distilled or used directly for further conversions. Furthermore, the alkali metal salts of the carboxylic acids obtained from the acid anhydrides of the formula II during the course of the reaction can be converted back into the anhydrides.

If benzoic anhydride and sodium cyanide are used as starting components, the course of the conversion can be shown by the reaction equation of Figure 1.

The acid anhydrides used as starting components are generally defined by formula 2 and can be prepared according to known methods. In this formula, R preferably represents a straight or branched chain alkyl group of 1 to 4 carbon atoms optionally containing one or more alkoxy groups of 1 to 4 carbon atoms, carbaroxy groups of 1 to 4 carbon atoms in the alkoxy radical, nitro groups, nitrile groups and / or halogen atoms , such as, for example, fluorine, chlorine, bromine or iodine atoms is substituted, furthermore optionally by one or more alkyl, alkoxy or carbaloxy groups with at most 4 carbon atoms, nitro groups, nitrile groups and / or halogen atoms, such as for example fluorine, chlorine - and bromine atoms, substituted cycloalkyl group with 5 or 6 carbon atoms in the ring or optionally by one or more alkyl, alkoxy or carbalkoxy groups with at most 4 carbon atoms, nitro groups and / or halogen atoms, such as, for example, fluorine, chlorine - and bromine atoms, substituted aryl group, in particular a phenyl or a naphthyl group. Finally, R preferably means an optionally substituted heterocyclic radical containing one or more alkyl, alkoxy or carbaloxy groups with at most 4 carbon atoms, nitro groups, nitrile groups and / or halogen atoms, such as, for example, fluorine, chlorine and bromine atoms. which may contain 1-3 heteroatoms, such as oxygen, sulfur and / or nitrogen atoms, in the ring and which may additionally be fused with a benzene ring.

Examples of acid anhydrides of the formula II are in particular acetic anhydride, propionic anhydride, pivalic anhydride and preferably the aromatic carboxylic anhydrides, especially substituted or unsubstituted benzoic anhydride.

Preferred alkali metal cyanides are sodium and potassium cyanide.

A diluent can optionally be used in the method according to the invention. All inert organic solvents which do not react with the carboxylic anhydrides and the metal cyanides are suitable diluents. Such solvents are, for example, o-xylene, chlorobenzene, o-dichlorobenzene, the trichlorobenzenes, nitrobenzene, tetramethylene sulfone. Preferably, the carboxylic anhydride of the formula II is used in excess as a diluent. In principle, however, it is also possible to carry out the conversion according to the invention without a diluent.

The reaction temperature is preferably 100-230 ° C.

The reaction according to the invention is generally carried out under normal pressure. If low-boiling aliphatic carboxylic anhydrides are used, however, a slightly elevated pressure is effective, for example a pressure of 1-10 bar, preferably 1-5 bar. For distilling off the acyl cyanides obtained, it may be effective to reduce the pressure, for example to a pressure of 100 to 0.006 kPa, the most effective pressure being selected depending on the acyl cyanide to be obtained and the temperature used.

According to the process of the invention, the acid anhydride is generally reacted in a stoichiometric amount with the appropriate alkali metal cyanide. However, the acid anhydride, as already noted, can also be used in excess, expediently even as a solvent.

The acyl cyanides according to the invention of the formula I are valuable starting materials, for example for the preparation of 1,2,4-triazin-5-one compounds, which have excellent herbicidal properties (see German Offenlegungsschrift 2,224,161).

For example, 3-methyl-4-amino-6-phenyl-1,2,4-triazine-5-one of the formula III can be prepared by reacting benzoyl cyanide of the formula IV in the first stage in the presence of concentrated hydrochloric acid with ethanol and reacting the obtained phenylglyoxylic acid ethyl ester in a second stage with acetylhydrazine, thereby obtaining 1-phenylglyoxylic acid ethyl ester-2-acetylhydrazone, which is reacted in the third stage with hydrazine hydrate in the presence of pyridine in the presence of pyridine. This multistage process can be illustrated according to the scheme of FIG.

The method according to the invention is further elucidated by means of the following examples.

Example I

1130 g (5 mol) of benzoic anhydride was mixed with 250 g (5 mol) of 98% sodium cyanide by weight.

The reaction vessel was a 3 liter grinding rim beaker equipped with a spiral stirrer running along the edge, a thermometer, a column head and a distillation bridge. The mixture of the benzoic anhydride and the sodium cyanide was easy to stir at 50 ° C. The mixture was brought to 150 ° C under the pressure of a water jet pump (about 15 mm mercury) within 30 minutes. After 15 minutes, the temperature was brought to 160-170 ° C. The benzoyl cyanide obtained distilled at a temperature of 105 DEG-125 DEG C. After about 2-2.5 hours, the temperature was raised to 190-200 ° C. The remaining benzoyl cyanide distilled over thereby.

Yield: 650 g of benzoyl cyanide with a melting point of 31 ° C (99% of the theoretical yield).

Example II

In a three-necked flask, 904 g (4 moles) of benzoic anhydride and 98 g (2 moles) of sodium cyanide were mixed and the mixture was heated under reduced pressure to 200 ° C, the reaction product distilling off continuously under reduced pressure (14 mm of mercury pressure) . The residue was stirred well up to 40 ° C and contained sodium benzoate, which was directly suitable for the preparation of benzoic anhydride.

Yield: 130 g of benzoyl cyanide (99% of the theoretical yield based on the sodium cyanide used).

Example III

93 g (0.5 mol) of pivalic anhydride was mixed with 24.5 g (0.5 mol) of sodium cyanide and the mixture was slowly heated under reduced pressure (15 mm of mercury pressure). The resulting reaction product was immediately distilled off and then fractionated.

Yield: 39.4 pivaloyl cyanide with a boiling point under a 2 kPa pressure of 48-54 ° C (71% of theory).

Example IV

In a 750 ml three-necked flask, 295 g (1 mol) of 3-chlorobenzoic anhydride and 65 g of potassium cyanide were mixed and the mixture was slowly heated to 230 ° C within 120 minutes. By reducing the pressure, the reaction product of the sodium salt was separated from 3-chlorobenzoic acid. Fractional distillation gave 160 g of 3-chlorobenzoyl cyanide (97% of theory); boiling point under a pressure of 1.87 kPa 11-120 ° C; mp 146-148 ° C (from benzene).

Example V

In a 400 ml flask, 105.3 g (1/3 mol) of 4-nitrobenzoic anhydride and 16.3 g (1/3) of sodium cyanide were mixed and the mixture was slowly heated to 230 ° C under reduced pressure, 55.4 g of 4-nitrobenzoyl cyanide distilling off (94% of theory); boiling point under a pressure of 0.013 kPA 116-118 ° C.

Example VI

In a 500 ml flask equipped with a stirrer and a distillator, 264 g (1 mole) of 2,5-dichlorobenzoic anhydride and 49 g (1 mole) of sodium cyanide under reduced pressure at 200 ° C for 2 hours C brought. As the temperature rose, the 2,5-dichlorobenzoyl cyanide distilled into the appropriate vessel. By fractional distillation, 194 g of 2.5 "dichlorobenzoyl cyanide, boiling point under a pressure of 1.87 kPa, of 140 DEG-142 DEG C. (97% of theoretical yield); mp 63-65 ° C (from benzene).

Example VII

Following the procedure of Example 6, 163 g (0.5 mole) of 1-naphthalene carboxylic anhydride and 25 g (0.5 mole) of sodium cyanide were heated to 200 ° C within 3 hours, with the 1-naphthalene carboxylic acid cyanide distilling off. 84 g of 1-naphthalene carboxylic acid cyanide was obtained by distillation to separate entrained traces of the starting products (93% of the theoretical yield); boiling point under a pressure of 0.011 kPa 117-119 ° C; mp 100-102 ° C (from benzene).

Example VIII

According to the procedure of Example III, in a three-necked flask, 295 g (1 m ° 1) of 4-chlorobenzoic anhydride and 49 g (1 mole) of sodium cyanide were heated to 210 ° C within 2 hours. During the weakly exothermic reaction, the resulting reaction product was distilled off under a pressure of 1.73 kPa.

Yield: 158 g of 4-chlorobenzoyl cyanide (96% of theory); boiling point under a pressure of 1.73 kPa 11-4-166 ° C.

Example IX

According to the procedure of Example 6, 286 g (1 mole) of p-methylbenzoic anhydride and 65 g (1 mole) of potassium cyanide were heated to 190 ° C within 2 hours. The distillate obtained in the receiver was very pure p-methoxybenzoyl cyanide.

Yield: 151 g of p-methoxybenzoyl cyanide (94% of theory).

Claims (1)

Process for the preparation of acyl cyanides of the formula 1, wherein R represents an optionally substituted alkyl group of 1-8 carbon atoms, an optionally substituted cycloalkyl group of 3-12 carbon atoms, an optionally substituted aryl group or an optionally substituted 5 or 6 ring units containing heterocyclic moiety which may additionally be fused with a benzene ring by reacting carboxylic anhydrides of the formula II, wherein R has the meanings indicated above with alkali metal cyanides in the absence of a catalyst, characterized in that the conversion is carried out in the liquid phase at a temperature of 50-250 ° C and the acyl cyanides obtained are removed from the reaction medium by distillation immediately after their formation.