Diazonium salts, aliphatic

In some of these papers (e.g., Weiss et al., 1984) it is mentioned that various attempts to synthesize stable aliphatic diazonium salts failed, although the identified reaction products indicated the involvement of aliphatic diazonium ions as intermediates (see also Olah et al., 1966). 

Aromatic diazonium salts can, of course, be isolated (see Chapter 13), but only a few aliphatic diazonium salts have been prepared (see also Ref. 383). For reviews see Laali, K. Olah, G.A. Rev. Chem. Intermed., 1985, 6, 237 Bott, K. in Patai Rappoport The Chemistry of Functional Groups, Supplement C, pt. 1 Wiley NY, 1983, p. 671 Bott, K. Angew. Chem. Int. Ed. Engl., 1979, 18, 259. The simplest aliphatic diazonium ion CH3N2 has been prepared at — 120°C in superacid solution, where it lived long enough for an nmr spectrum to be taken Berner, D. McGarrity, J.F. J. Am. Chem. Soc., 1979, 101, 3135. 

Olefins from Aliphatic Diazonium Salts Hydro-diazonio-elimination... 

Cleavage of amine oxides (Cope) 7-9 Cleavage of aliphatic diazonium salts... 

Triazenes have been prepared by the treatment of resin-bound aromatic diazonium salts with secondary amines (Figure 3.27). Regeneration of the amine can be effected by mild acidolysis (Entry 1, Table 3.23). Triazenes have been shown to be stable towards bases such as TBAF, potassium hydroxide, or potassium tert-butoxide [454], and under the conditions of the Heck reaction [455]. Primary amines cannot be linked to supports as triazenes because treatment of triazenes such as R-HN-N=N-Ar-Pol with acid leads to the release of aliphatic diazonium salts into solution [373]. Triazenes derived from primary amines can, however, be used for the preparation of amides and ureas (see Section 3.3.4),... 

Whereas cleavage of trisubstituted triazenes gives rise to secondary amines in excellent yields, cleavage of disubstituted triazene 77 gives rise to aliphatic diazonium salts. The aliphatic diazonium ion formed undergoes substitution with nu-... 

No matter how produced, RNj are usually too unstable to be isolable, reacting presumably by the S l or 8 2 mechanism. Actually, the exact mechanisms are in doubt because the rate laws, stereochemistry, and products have proved difficult to interpret. If there are free carbocations they should give the same ratio of substimtion to ehmination to rearrangements, and so on, as carbocations generated in other 8 1 reactions, but they often do not. Hot carbocations (unsolvated and/or chemically activated) that can hold their configuration have been postulated, as have ion pairs, in which OH (or OAc, and so on, depending on how the diazonium ion is generated) is the counterion.One class of aliphatic diazonium salts of which several... 

Primary aliphatic amines also react with nitrous acid to yield diazonium salts but since aliphatic diazonium salts are quite unstable and break down to yield a complicated mixture of organic products (see Problem 23.11, below), this reaction is of little synthetic value. The fact that nitrogen is evolved quantitatively is of some... 

By the decomposition of diazonium salts. If we examine the structure of an aromatic or aliphatic diazonium salt, we see that the loss of a nitrogen molecule from the cation should give rise to a carbonium ion ... 

Theoretical Investigations on Aliphatic Diazonium Salts, and on Alkane, Alkene, and Alkyne Diazo Compounds... 

Decomposition of aliphatic diazonium salts often yields a more complicated mixture of products (see Table 8) than the one formed in solvolysis. Streitwieser explains this difference that in the first case the reaction proceeds not only through carbocations but also directly from diazonium ions the latter react un-... 

Primary aliphatic amines react with nitrous acid through a reaction called diawtization to yield highly unstable aliphatic diazonium salts. Even at low temperatures, aliphatic diazonium salts decompose spontaneously by losing nitrogen to form carbocations. The carbocations go on to produce mixtures of alkenes, alcohols, and alkyl halides by removal of a proton, reaction with H2O, and reaction with X ... 

The most important reaction of amines with nitrous acid, by far, is the reaction of primary arylamines. We shall see why in Section 20.7. Primary arylamines react with nitrous add to give arenediazonium salts. Even though arenediazonium salts are unstable, they are still far more stable than aliphatic diazonium salts they do not decompose at an appreciable rate in solution when the temperature of the reaction mixture is kept below 5°C ... 

If we had done this reaction with an aliphatic compound, for example, cyclohexylamine, we would still make the diazonium salt, but aliphatic diazonium salts are much less stable than aromatic ones, and this would decompose with loss of molecular nitrogen at -50 °C. Aromatic diazonium compounds are more stable, because the aryl cation that would be produced by nitrogen loss is at an sp carbon atom, which, as we noted in Chapter 11, is very unfavorable. However, molecular nitrogen is a fabulous leaving group the N=N triple bond has lots of enthalpy, and the process also benefits from the entropy of the loss of a mole of gas. So the diazonium salt decomposes slowly to give an aromatic cation, which is then captured by any available nucleophile (Figure 13.2). 

Aromatic amines, ArNHj, are converted by nitrous acid to diazonium salts [ArNj+JX-. Unlike aliphatic diazonium salts, these are fairly stable at 0 °C. 

Amino alcohols rearrange in the presence of nitrous acid to give ketones. The intermediate is an aliphatic diazonium salt, and the reactions are concerted and stereo-electronically controlled, with the migration of the group trans-anti to the departing nitrogen. 

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