Diazonium ions reaction

This reaction is important because it provides a method to place an amino substituent onto the benzene ring, a substitution that cannot be accomplished directly by electrophilic attack. And, as illustrated in the following example, this opens all of the substitution reactions that can be accomplished through diazonium ion reactions. 

An explanation of these results would seem to follow from the interpretation already given for the solvent dependence of the stereochemistry of diazonium ion reactions. The highly polar and in some cases acidic reaction conditions, coupled with the relatively long life expectancy of a primary diazonium ion, are conducive to ion pair dissociation or destruction at the stage of the diazonium ion. Moreover, the carboxylate ion pairs that do survive to form carbonium ions might be expected to yield ester exclusively on account of the very high reactivity of the n-propyl cation. If this is the case, the bulk of the alcohol should be derived from free carbonium ions formed from already dissociated diazonium ions. 

Comparisons between diazonium ion reactions and solvolyses involving tertiary alkyl structures are of special interest because both reactions are likely to yield unsolvated carbonium ions. Cannell and Taft (1956) have measTu-ed the ratio of thiocyanate to isothiocyanate obtained when the carbonium ions formed in the solvolysis of t-butyl chloride and the deamination of t-butylamine and isobutylamine in ethanol are trapped with large amormts of added sodium thiocyanate. For the t-butyl... 

The serious problem of disentangling diazonium ion reactions from carbocation reactions makes diazonium ion rearrangements difficult to study. It seems likely that products of primary aliphatic amine nitrosation are derived from the diazonium ion rather than a primary aliphatic carbocation formed by spontaneous loss of nitrogen, since primary carbocations are unknown in solution. Products from secondary aliphatic amine nitrosation are formed from either the diazonium ion or the carbocation. 

Recent research has shed light on this problem and clearly favours the diazonium ion reaction theory. Observation of the diazonium ion in superacid shows that it can have a long lifetime while superacid conditions do not compare with normal conditions a close relationship between reaction pathways has been demonstrated, and the observation of the diazonium ion in conditions where primary aliphatic carbocations have not been observed does not favour the theory of an extremely rapid reaction. 

This leaves the question of why diazonium ion reactions give such a wide variety of rearranged products. The answer may well be because the C—N bond of a primary aliphatic diazonium ion does not break spontaneously to yield the primary carbocation. It can form a carbocation only by nucleophilic displacement by an intramolecular bond shift displacing the nitrogen molecule and leaving a rearranged secondary or tertiary carbocation. In a non-nucleophilic solvent, this becomes the only available pathway, so extensive rearrangement is observed. 

Participation by the cyano group in diazonium ion reactions has been reported. ... 

The product of this series of steps is an alkyl diazonium ion, and the amine is said to have been diazotized Alkyl diazonium ions are not very stable decomposing rapidly under the conditions of their formation Molecular nitrogen is a leaving group par excel lence and the reaction products arise by solvolysis of the diazonium ion Usually a car bocation intermediate is involved... 

Figure 22 5 shows what happens when a typical primary alkylamine reacts with nitrous acid Because nitrogen free products result from the formation and decomposition of diazonium ions these reactions are often referred to as deamination reactions Alkyl... 

An important reaction of aryl diazonium ions is their conversion to phenols by hydrolysis... 

Diazonium salt chemistry provides the principal synthetic method for the prepara tion of aryl fluorides through a process known as the Schiemann reaction In this pro cedure the aryl diazonium ion is isolated as its fluoroborate salt which then yields the desired aryl fluoride on being heated... 

A reaction of aryl diazonium salts that does not involve loss of nitrogen takes place when they react with phenols and arylamines Aryl diazonium ions are relatively weak elec trophiles but have sufficient reactivity to attack strongly activated aromatic rings The reaction is known as azo coupling two aryl groups are joined together by an azo (—N=N—) function... 

Synthetically Useful Transformations Involving Aryl Diazonium Ions (Continued) Reaction and comments General equation and specific example... 

Reaction of aryl diazonium salts with iodide ion (Section 22 17) Adding po tassium iodide to a solution of an aryl diazonium ion leads to the formation of an aryl iodide... 

Reaction with arenediazonium salts Adding a phe nol to a solution of a diazonium salt formed from a primary aromatic amine leads to formation of an azo compound The reaction is carried out at a pH such that a significant portion of the phenol is pres ent as its phenoxide ion The diazonium ion acts as an electrophile toward the strongly activated ring of the phenoxide ion... 

Schiemann reaction (Section 22 17) Preparation of an aryl fluonde by heating the diazonium fluoroborate formed by addition of tetrafluorobonc acid (HBF4) to a diazonium ion Schiffs base (Section 17 10) Another name for an imine a compound of the type R2C=NR ... 

The acid—base equiUbtia are fundamental to the kinetics of azo coupling and of practical significance for azo technology. Thus it is important that coupling reactions be carried out in a medium such that the acid—base equiUbtia of the diazo and coupling components favor as much as possible the diazonium ions and the phenolate ions or the free amine, respectively. 

Diazo coupling is expected to occur only with highly reactive systems, and experiment bears this out. Diazonium ions couple with the anions of N-unsubstituted imidazoles at the 2-position (e.g. 125 yields 126) and with indazoles (127) in the 3-position. In general, other azoles react only when they contain an amino, hydroxyl, or potential hydroxyl group, e.g. the 4-hydroxypyrazole (128), the triazolinone (129) and the thiazolidinedione (130) (all these reactions occur on the corresponding anions). 

Pyridine-2- and -4-diazonium ions are far less stable than benzenediazonium ions. Azolediazonium salts generally show intermediate stability provided diazotization is carried out in concentrated acid, many of the usual diazonium reactions succeed. Indeed, azolediazonium salts are often very reactive in coupling reactions. 

Purines, N-alkyl-N-phenyl-synthesis, 5, 576 Purines, alkylthio-hydrolysis, 5, 560 Mannich reaction, 5, 536 Michael addition reactions, 5, 536 Purines, S-alkylthio-hydrolysis, 5, 560 Purines, amino-alkylation, 5, 530, 551 IR spectra, 5, 518 reactions, 5, 551-553 with diazonium ions, 5, 538 reduction, 5, 541 UV spectra, 5, 517 Purines, N-amino-synthesis, 5, 595 Purines, aminohydroxy-hydrogenation, 5, 555 reactions, 5, 555 Purines, aminooxo-reactions, 5, 557 thiation, 5, 557 Purines, bromo-synthesis, 5, 557 Purines, chloro-synthesis, 5, 573 Purines, cyano-reactions, 5, 550 Purines, dialkoxy-rearrangement, 5, 558 Purines, diazoreactions, 5, 96 Purines, dioxo-alkylation, 5, 532 Purines, N-glycosyl-, 5, 536 Purines, halo-N-alkylation, 5, 529 hydrogenolysis, 5, 562 reactions, 5, 561-562, 564 with alkoxides, 5, 563 synthesis, 5, 556 Purines, hydrazino-reactions, 5, 553 Purines, hydroxyamino-reactions, 5, 556 Purines, 8-lithiotrimethylsilyl-nucleosides alkylation, 5, 537 Purines, N-methyl-magnetic circular dichroism, 5, 523 Purines, methylthio-bromination, 5, 559 Purines, nitro-reactions, 5, 550, 551 Purines, oxo-alkylation, 5, 532 amination, 5, 557 dipole moments, 5, 522 H NMR, 5, 512 pJfa, 5, 524 reactions, 5, 556-557 with diazonium ions, 5, 538 reduction, 5, 541 thiation, 5, 557 Purines, oxohydro-IR spectra, 5, 518 Purines, selenoxo-synthesis, 5, 597 Purines, thio-acylation, 5, 559 alkylation, 5, 559 Purines, thioxo-acetylation, 5, 559... 

Nucleophilic substitution reactions that occur imder conditions of amine diazotization often have significantly different stereochemisby, as compared with that in halide or sulfonate solvolysis. Diazotization generates an alkyl diazonium ion, which rapidly decomposes to a carbocation, molecular nitrogen, and water ... 

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