Diazonium chlorides, reaction with ethyl

Nucleophilic processes that generate chloroindoles are largely confined to the displacements of oxy functions and Sandmeyer reactions of diazo-nium salts [81 H( 15)547]. A low yield of 2-chloroindole was obtained by a reaction sequence that involved treatment of oxindole with phosphoryl chloride, and then treatment of the Vilsmeier salt with sodium bicarbonate [66JOC2627 86H(24)2879]. It is, however, much better to prepare this compound from 2-lithioindole (92JOC2495). With phosphoryl chloride and dimethylformamide ethyl l-hydroxyindole-2-carboxylate failed to give the expected 3-formyl derivative. Instead there was a 50% yield of the 3-chloro derivative (84CPB3678). Diazonium salts have been used as precursors in... 

Diazotised 5-aminotetrazole is unstable under the conditions recommended for its use as a biochemical reagent. While the pH of the diazotised material (the cation of which contains 87% nitrogen) at 0°C was being reduced to 5 by addition of potassium hydroxide, a violent explosion occurred [1], This may have been caused by a local excess of alkali causing the formation of the internal salt, 5-diazoniotetrazolide, which will explode in concentrated solution at 0°C [2], The diazonium chloride is also very unstable in concentrated solution at 0°C. Small-scale diazotisation (2 g of amine) and susequent coupling at pH 3 with ethyl cyanoacetate to prepare ethyl 2-cyano-(l//-tetrazol-5-ylhydrazono)acetate proceeded uneventfully, but on double the scale a violent explosion occurred [3], The importance of adequate dilution of the reaction media to prevent explosions during diazotisation is stressed [4]. 

Bases, Neutral Salts.— As a base it forms salts, in which form the diazo compound is obtained by diazotization, and which though also unstable has been isolated in small quantities and the composition and properties determined. Of the three salts, the sulphate, chloride and nitrate, the first is the most stable and the last is the least stable. They are colorless crystalline neutral compounds soluble in water, difficultly soluble in alcohol and insoluble in ether. After being prepared by the ordinary diazo reaction, with sodium nitrite in cold acid water solution, they may be precipitated in crystalline form by the addition of alcohol and ether. If the diazotization is effected in alcohol solution by means of amyl nitrite or ethyl nitrite the crystals of the diazonium salt separate at once. These salts of diazo benzene all show true salt characteristics, e.g., they lower the freezing point of solutions. The diazo radical, (CeHs—N2—) is thus basic toward strong acids, and the hydroxide, the non-isolated hypothetical diazo benzene, CeHs—N2—OH, is the free base. It may be considered as the simplest aromatic diazo compound and the mother substance of all other members of the class. 

Similarly, reaction of ethyl diazoacetate with diazonium chlorides yields carboxyalkyl hydrazidoyl chlorides X ( ). 

One hundred grams of crushed ice is added to a solution of 53 g. (0.50 mole) of o-toluidine in 97 g. of concentrated hydrochloric acid. The resulting mixture is diazotized by the addition of a solution of 36 g. (0.52 mole) of sodium nitrite in 60 g. of water. The temperature of the reaction mixture is maintained below 2° during this operation. A solution of 120 g. (0.75 mole) of potassium ethyl xanthate in 150 ml. of water is heated to 40° and stirred while the solution of the diazonium salt is added dropwise. The temperature is not allowed to rise above 45°. The cooled mixture is extracted with ether, and the ethereal solution is washed with 10% aqueous sodium carbonate, then with water. After the solution has been dried over calcium chloride. 

Occasionally it is unnecessary to isolate the hydrazone since this is itself accessible by a coupling reaction. Numerous formazans can be obtained by treating compounds containing active methylene groups directly with 2 molar proportions of a diazonium salt. For example, pyruvic acid is converted into 3-oxalo-l,5-diphenylformazan (fi4formazylglyoxalic acid ) in 94% yield by benzenediazonium chloride in potassium hydroxide solution.351 Acyl groups (CH3CO or COOH) are often eliminated in such reactions 343,344,352 thus acetoacetic ester yields ethyl l,5-diphenylformazan-3-carboxylate almost... 

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