Wislicenus process

Mackenzie and Wood obtained low yields by this method, which is the basis of both the Muller and Wislicenus processes, and recommended instead the hydrolysis of acetophenonecyanohydrin (X) into atrolaetie acid (XI), conversion of the latter by distillation under reduced pressure into atropic acid (XII), which was then treated in ethereal solution with hydrochloric acid and the halogen in the resulting, 8-chlorohydratropie acid replaced by hydroxyl, by boiling the acid with aqueous sodium carbonate solution, giving tropic acid (XIII), thus ... 

The Wislicenus process (see p. 24), for example, may be conducted as follows. Several iron boats containing sodium metal are placed in a horizontal combustion tube and heated in nitrogen to 250-300°C the gas is then changed to dry ammonia until the molten metal is converted to sodamide. The temperature is then lowered to 170-190°C and the gas changed to nitrous oxide, N2O, until no more ammonia is detected in the waste gases. The crude product (sodium azide + sodium hydroxide) is leached with water and after filtering concentrated to incipient crystallization. Some azide is retained in the caustic liquid, from which it may be precipitated with alcohol. 

The ammonia is boiled off and excess Ca precipitated with CO2 [62]. Small amounts of Ca(N3)2 have also been made with the Wislicenus process [85,120] the intermediate calcium amide forms at 20-60°C, and the azide at 90-100°C. 

Barium azide may be obtained by any of the methods described for calcium azide. When precipitating the aqueous solution, acetone should be preferred as it yields a coarser product [132] which is less likely to contain impurities. The salt has also been synthesized with hydrazine and nitrite 3.5 g barium hydroxide and 200 ml aqueous hydrazine (5% w/w) were cooled with ice and 15 g ethyl nitrite added dropwise with stirring. The next day, excess hydroxide was removed with CO2 the filtrate yielded 8 g barium azide (30% of the theoretical yield) [49]. Small samples of barium azide have also been made according to the Wislicenus process the intermediate amide formed at 260-290°C and the azide at 140-175°C [85], which is, however, already within the range of thermal decomposition. 

Using the dry Wislicenus process, N-doped zinc azide was made by reacting zinc amide with nitrous oxide at 180°C for 96 hr [85]. The product can be considered pure Zn(N3)2, but an equimolar amount of zinc hydroxide is admixed which was not separated. 

M. Hyronimus (Bntish Patent, 1,819, 1908) has patented the use of lead azide, Pb(N3)2, and describes a safe method of manufacturing it, founded on the process used by Wislicenus (Ber., 1892, 25, 20S4). 

Curtius discovered HN3 [1] by reacting benzoylhydrazine with nitrous acid (b + g-type reaction). The resulting benzoyl azide was saponified, and sodium azide was isolated from the alkaline mixture. In 1903 Wislicenus [14] synthesized sodium azide solely from inorganic compounds, namely, sodium metal, ammonia, and dinitrogen oxide (a + e). The reaction proceeds in two steps, first converting ammonia with sodium to sodamide, and then reacting this with dinitrogen oxide to yield sodium azide. Fifty percent of the sodamide is decomposed to hydroxide and ammonia, and the overall balance of the process is... 

The process is carried out in alkaline media with alkyl nitrite and yields 80% sodium or potassium azide. It was for decades competitive with Wislicenus method for commercial azide production. Unnoticed at the time, this azide retains small amounts of hydrazine as an impurity, which was later found to be indispensable for azidation reactions in organic chemistry ( active sodium azide). 

With the advent of commercial sodium azide, most of the above methods have gradually disappeared from the laboratory. Only the Wislicenus and, occasionally, the Thiele processes are still in use. 

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