CS224683B1 - Method for preparing cyanogen bromide solution - Google Patents

Description

Bromocyanate is a widely used agent important especially in these organic son. It is used, for example, in the von Braun reaction (see, for example, HAHageman in Org.Seactions 2, 198 (1953)), in the Gattermann syn these aldehydes (see, for example, P.Karrer: Helv.chim.Acta 2, 28 (1919) ), in the preparation of acid nitriles from olefins (see, for example, US Pat. 2,653,963) and, for example, in the introduction of a nitrile group into an aromatic hydrocarbon molecule under Friedel-Crafts reaction conditions (see, e.g., PoKarrer et al., Helv.chim.Acta 3, 261) (1920)) The most preferred preparation of cyanogen bromide to date is that described in Org. Synthesis, Cpll. Vol. 2, 150 (1943) · From the reaction of bromine and an aqueous solution of sodium cyanide, which is used in excess, distillation yields wet cyanogen bromide, which must be distilled from calcium chloride to remove moisture; yield is 73 to 85% · The process is laborious and requires special caution due to the high toxicity of cyanogen bromide. It is known that cyanogen bromide is not stable and may explode explosively. Therefore, it is not recommended to store it, but to prepare the required amount immediately before use (see ibid.).

Since solutions of cyanogen bromide in an organic solvent can be used for most of the above reactions, the present inventors have sought to find a suitable method for preparing said solutions and have found such a method.

According to the invention, a solution of cyanogen bromide in a water-miscible organic solvent can be produced by reacting bromine with equivalents at 0 ° C in a two-phase system consisting of water and methylene chloride. alkali metal cyanide, especially potassium or sodium cyanide, is then separated, and the organic phases containing the cyanogen bromide formed are separated and dried with calcium chloride »

Suitable solvents include, in addition to methylene chloride, other water-immiscible solvents such as chlorinated hydrocarbons such as chloroform or carbon tetrachloride, aliphatic ethers such as diethyl ether, aliphatic, alicyclic or aromatic hydrocarbons such as hexane, cyclohexane or benzene, or or mixtures thereof.

Potassium cyanide or sodium cyanide may be used as the alkali metal cyanide.

The reaction can be carried out preferably at 0 ° C, using the exact molar equivalent of the reactants.

Anhydrous calcium chloride may be used as an indifferent drying agent.

The process of the invention eliminates the laboriousness of preparing cyanogen bromide, the need for distillation of cyanogen bromide and the handling of solid cyanogen bromide or its melt, and the risk of exposure to the toxic effect of its vapors. In view of the ease of implementation, the invention makes it possible to prepare sufficient dry cyanogen bromide in a suitable organic solvent solution immediately immediately before its use in a practically theoretical yield. In fact, he found that using an excess of alkali cyanide (R), which is recommended in the prior art cyanogen bromide preparations, results in the formation of a non-reactive cyanogen trimer, thereby reducing cyanogen bromide yield. Maintaining the equivalence between bromine and the alkali metal cyanide of the present invention removes this drawback. Achieving equivalence is readily apparent since it is accompanied by the disappearance of the characteristic color of the reaction mixture with free bromine. The bromlyane solution prepared according to the invention is stable when stored in the cold and can therefore be stored for several days without the risk of explosive decomposition. It is suitable for the above synthetic uses.

Further details of the process for preparing the cyanogen bromide flux according to the invention and its use in von Braun demethylation are given in the examples.

Example 1

Preparation of cyanogen bromide solution

A solution of 16 g of bromine (0.1 mol) in 32 ml of methylene chloride was overlaid with 64 ml of distilled water. While stirring and cooling to 0 ° C, the mixture slowly

-3224 683 dropwise a solution of 4.9 g (0.1 mol) of sodium cyanide in 20 µl of distilled water * Upon reaching the equivalence of bromine and sodium cyanide, the original reddish-brown color turns yellow after a while and the mixture remains permanently colorless. methylene chloride phases containing cyanogen bromide are dried with calcium chloride *

Example 2

Preparation of D-6-cyano-8-cyanomethylergolim-I by Braun reaction

To a suspension of 10 g of D-6-methyl-8-cyanomethylergoline in 1400 ml of chloroform, a solution of cyanogen bromide in methylene chloride prepared above was added in one portion with vigorous stirring. After stirring for 40 h, the precipitated product is sucked and digested with 600 ml of a 2% aqueous tartaric acid solution for 2 h. The remaining undissolved product is filtered off, washed with water and dried.

After the reaction, the remaining organic phase was shaken with 1% aqueous tartaric acid and evaporated to dryness in vacuo. The two portions of D-6-cyano-8-cyanomethylergoline-I obtained after the weighing weighed 9.34 g (89.7%); mp 269-272 ° C; the product recrystallized from 95% aqueous tertiaryl showed a melting point of 276-278 ° C, [α] D 20 + 46 ° (c 0.4, pyridine).

Claims (1)

A process for the preparation of cyanogen bromide by reacting bromine with an alkali metal cyanide equivalent in methylene chloride, characterized in that in a two-phase system comprising water and methylene chloride, bromine is reacted at 0 ° C with an equivalents of ethical metal, in particular potassium or sodium cyanide. the cyanogen bromide formed is separated and dried with calcium chloride.