Diazonium cations alkyl

Nitrosation (Section 22 15) Nitrosation of amines occurs when sodium nitrite is added to a solution containing an amine and an acid Primary amines y e d alkyl diazonium salts Alkyl diazonium salts are very unstable and yield carbo cation derived products Aryl diazonium salts are exceedingly useful synthetic in termediates Their reactions are de scribed in Table 22 7... 

If the provoked or spontaneous acid-base reactions overcome the radical reactions of the primary radical, the secondary radical is easier to reduce, or to oxidize, than the substrate in most cases. Exceptions to this rule are scarce, but exist. They involve substrates that are particularly easy to reduce thanks to the presence of a strongly electron-withdrawing substituent (for reductions, electron-donating for oxidation), which is expelled upon electron transfer, thus producing a radical that lacks the same activation. Alkyl iodides and aryl diazonium cations are typical examples of such systems. 

Azo compounds have the general formula R -N=N-R, where R and R are alkyl or aryl groups. Aromatic azo compounds are generally strongly colored and many are easily prepared via a so-called diazo coupling reaction, in which a diazonium cation is coupled with a relatively active (i.e., highly nucleophilic) arene such as a phenol or aniline. The dye called aniline yellow, for example, is prepared as follows ... 

Primary arylamines like primary alkylammes form diazonium ion salts on nitro sation Aryl diazonium 10ns are considerably more stable than their alkyl counterparts Whereas alkyl diazonium 10ns decompose under the conditions of their formation aryl diazonium salts are stable enough to be stored m aqueous solution at 0-5°C for a rea sonable time Loss of nitrogen from an aryl diazonium ion generates an unstable aryl cation and is much slower than loss of nitrogen from an alkyl diazonium ion... 

A completely different method of synthesis of azo compounds from diazonium salts involving radical intermediates was found by Citterio et al. (1980, 1982 c), Cit-terio and Minisci (1982), and Fontana et al. (1988). It is a new general synthesis of arylazoalkanes based on the addition of an alkyl radical to an arenediazonium ion followed by reduction of the intermediate azo radical cation adduct by a metal salt (Scheme 12-80). The preferred source for the alkyl radical R in this reaction is an alkyl iodide, which gives rise to alkyl radicals cleanly in the presence of an arenediazonium salt and a Ti3+ or Fe2+ salt as in Scheme 12-81. The overall stoichiometric equation is therefore as given in Scheme 12-82. The yields vary between 36% and 79% (with respect to alkyl iodide). 

The cation 18 did not show any DNA cleavage, due probably to its inherent stability (18 would be more stable than a benzyl cation [66], relatively stable ions that do not alkylate the heterocyclic bases in DNA). The 9-diazofluorene 19 would not undergo reduction like the corresponding diazonium salts (17) because of the presence of a negative charge on the fluorenyl carbon. 

The guest cations hitherto examined cover broadly uni- to trivalent and inorganic to organic ions that include alkali, alkaline earth, heavy and transition metal ions, as well as (ar)alkyl ammonium and diazonium ions. As to the complex stoichiometry between cation and ligand, both 1 1 stoichiometric and 1 2 sandwich complexes are analyzed. The solvent systems employed also vary widely from protic and aprotic homogeneous phase to binary-phase solvent extraction. 

These X -phosphorins 720 a-c also fail to react with carbonyl compounds. However, they are attacked by electrophiles (H or alkyl cations) at the C—2 position. In this manner new 1,1-diphenyl-2,3-benzo-X-phosphorins which are sustituted at positions C—2 (and C-4) can be prepared. Diazonium ions attack at C—4 to form azocompounds if an excess is used, C—2 is also substituted Hydrolysis with hot water affords 747. The reaction with ortho-formic acid ester forms a cyanine dye having a bridge at the C—4 positions 142 The experimen-... 

The most frequently used method of this type is the reaction of hydrazones (247) with diazonium compounds to afford formazans (248). These can be cyclized with carbonyl compounds in the presence of acid to yield verdazylium cations (252) which are reduced under basic conditions to give the verdazyls (253) which can be further reduced to the tetrahydro-l,2,4,5-tetrazines (254). The formazans (248) can be alkylated and the alkylfor-mazans (249) cyclized by heating or treatment with a base to form the tetrahydrotetrazines (250). It is not necessary to isolate the alkylated compounds (249) the complete reaction (248-250) can be carried out at room temperature in the presence of barium oxide or hydroxide in DMF. Oxidation of (250) provides a synthesis of verdazyls (251) (see Section 2.21.3.4.2). 

Triazene Dyes. If diazonium salts of N-heterocyclic amines are coupled to A-alkyl anilines, e.g., diazotized 2-aminoinomethoxybenzothiazole to A-methyl-4-nitroaniline, a triazene is obtained. A cationic triazene dye (16, diazadimethine-hemicyanine dye) is formed by subsequent A-alkylation, and dyes polyacrylonitrile a very lightfast yellow shade [39],... 

Aryl cations are less stable than 1°, 2°, or 3° carbocations, so aryl diazonium salts are more stable than alkyl diazonium salts. 

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