Nitriles, formation reaction with hydrazoic acid

Nitriles. Nitriles usually do not react with hydrazoic acid unless concentrated sulfuric add is present, in which case they yield tetrazoles. The first step of the reaction may condst in the formation of carbodii-mideSjwhichare known to reactwith hydrazoic add to form tetrazoles. ... 

The Schmidt reaction of aldehydes has some features as follows. (1) Aldehydes react with hydrazoic acid faster than carboxylic acids. (2) The formation of for-mamides is often observed as side reaction. The factors that affect the distribution of nitriles and formamides in products have been figured out nowadays because the mechanism has been finally established [34]. (3) Since the reaction requires acidic conditions to achieve high yields, the using of aldehydes is usually limited to aromatic aldehydes due to stability reasons. For aliphatic aldehydes, only acetaldehyde could work to give acetonitrile in the presence of aqueous sulfuric acid. (4) Hydrazoic acid, handled either as a solution or generated in situ, is publicly acknowledged to be toxic and explosive especially on large scale. 

Sharpless ° found that the formation of IH-tetrazole was achieved with excellent yield by zinc salt-catalyzed cycloaddition of activated and inactivated nitriles with sodium azide in water (generally under heterogeneous conditions) at reflux (Scheme 5.31). The reaction occurs at pH 8, which minimizes the release of hydrazoic acid even at 100°C. Several zinc salts were effective. ZnBr2 was chosen as the best compromise between cost, selectivity, and... 

Schmidt reaction some experiments starting with benzaldehydes and hydrazoic and sulphuric acid, used as a catalyst, were carried out. If the reaction is carried out in 71.2% sulphuric acid, the protonated form of the aldehyde is practically absent and the only product is benzonitrile. If the acidity of the medium is increased, the proportion of ben-zonitrile gradually decreases, and in 87.4% sulphuric acid only formanilide is obtained. The effective rate constants for the formation of nitrile and formanilide at 20 °C are 64.0 and 67.0 Lmol-1 min-1, respectively. A very interesting aspect is that the change in the ratio of the reaction products takes place in the same range of sulphuric acid concentrations where acid-base equilibrium of benzaldehyde is observed. Based on these results the formation of nitrile and formanilide can be described as shown in Scheme 5. 

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