Amines conversion into diazonium salts

Benzenedlazonlum chloride is prepared by the reaction of anUme with nitrous acid at 273-278K. Nitrous acid is produced In the reaction mixture by the reaction of sodium nitrite with hydrochloric acid. The conversion of prlmaiy aromatic amines into diazonium salts is known as diazotisation. Due to its Instability, the diazonium salt Is not generally stored and is used immediately after its preparation. 

Ionization after an initial reaction that converts one functional group into a leaving group, as in protonation of an alcohol to give an oxonium ion or conversion of a primary amine to a diazonium salt, both of which ionize to the corresponding carbocation ... 

Until recently no satisfactory procedure for the direct conversion of a primary aliphatic amine into an alkyl halide was available. This contrasts sharply with the ready conversion of primary aromatic amines into aryl halides via the diazonium salt (Section 6.7, p.922). However a useful method has not been discovered which is not only applicable to the synthesis of simple alkyl and aralkyl chlorides, bromides, iodides and fluorides, but could clearly be of value when it is required to replace an amino group in a naturally occurring amine by a halogen.92... 

Diazonium salts of imidazoles have been discussed in CHEC-II(1996) <1996CHEC-II(3)168>. Recent examples of Sandmeyer reactions include conversion of amine 888 into iodide 889 <1999JOC7158> and conversion of 890 to 891 (Scheme 216) <2003JHC159>. 

Brase and coworkers were the first to introduce triazene linkers for use in SPOC in a seminal report in 2000 [18]. They found immobilized diazonium ions have high stability, which enabled their application as linkers and scavengers. Their synthesis involves the reduction of 3-amino-6-chlorobenzoic acid, which was subsequently coupled onto a Merrifield resin via standard etherification. Subsequent conversion of the amino group into a diazonium salt generated the supported diazonium tet-rafluoroborate, which was found to sequester amines (Scheme 8.12). 

If formed, the triazene can often be converted into the amino azo compound by even gentle warming with dilute acid this conversion is smoother if the triazene is warmed with the amine used for coupling and a small amount of its hydrochloride.368 The acid-catalysed rearrangement of triazenes involves intermediate reformation of the diazonium salt and the amine.369,370 So, if rearrangement of a triazene is carried out in the presence of a different, more readily coupling amine, the diazonium component reacts preferentially with the latter e.g., A,ALdimethyl-/ -(phenylazo)aniline is obtained from diazoaminobenzene and N,N-di-methylaniline.368... 

The amine (0.1 mole) is diazotized in hydrochloric or sulfuric acid solution by sodium nitrite (7 g), the volume of solution being kept as small as possible. The diazonium salt solution is neutralized with calcium carbonate and filtered, and trisodium hexanitritocobaltate (15 g) is stirred into the filtrate, whereupon the trisdiazonium salt usually separates as a solid. For conversion into the nitro compound this salt (10 g), finely powdered, is added in portions, at room temparature, with good stirring, to a solution of sodium nitrite (lOg) and copper sulfate (10 g) in water (60 ml) in which copper(i) oxide (4 g) is suspended. When evolution of nitrogen ceases the nitro compound is isolated either by extraction with a solvent, e.g., chloroform, or by basification of the solution and steam-distillation.172... 

A primary amine can be converted into a diazonium salt by treatment with nitrous acid (HNO2). Because nitrous acid is unstable, it is formed in situ, using an aqueous solution of sodium nitrite and HCl or HBr indeed, N2 is such a good leaving group that the diazonium salt is synthesized at 0 °C and used immediately without isolation. (The mechanism for conversion of a primary amino group [NH2] to a diazonium group [ N N] is shown in Section 16.12.)... 

Reactions.— An observation that dinitrogen tetroxide oxidizes amines to the corresponding alkyl nitrates in low yield has been developed into a useful synthetic method. Conversion of an amine into its trimethylsilyl derivative alters the course of the oxidation permitting isolation of the desired nitrate in high yield (Scheme 118) in a later communication, the use of THF as solvent is reported to obviate the need for prior trimethylsilylation. This reaction seems to be general for primary and secondary amines and, although the mechanism of the reaction is unknown, retention of configuration at carbon is observed the intermediacy of the solvated diazonium salt (192) is invoked when THF is solvent. 

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