Arylamine salts

As directed in the experiment, decolorizing charcoal is added to the aqueous solution of the arylamine salt. The charcoal absorbs impurities and subsequent filtration of the mixture, which removes the charcoal, yields an aqueous solution of the purified arylamine salt. 

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 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... 

Reductive deamination of primary arylamines The ammo substituent of an arylamine can be replaced by hydrogen by treatment of its de rived diazonium salt with ethanol or with hypophosphorous acid... 

Diazotization of an arylamine followed by treatment with fluoroboric acid gives an aryl diazonium fluoroborate salt Heating this salt converts it to an aryl fluoride... 

Diazotization of a primary arylamine followed by treatment of the diazo mum salt with copper(l) bromide or copper(l) chloride yields the corre spending aryl bromide or aryl chloride... 

In a variation of this method, isolation of the ben2hydrol derivative is not required. The methane base undergoes oxidative condensation in the presence of acid with the same or a different arylamine direcdy to the dye. New fuchsine [3248-91 -7] Cl Basic Violet 2 (16), is prepared by condensation of two moles of o-toluidine with formaldehyde in nitrobenzene in the presence of iron salts to give the corresponding substituted diphenylmethane base. This base is also not isolated, but undergoes an oxidative condensation with another mole of o-toluidine to produce the dye. 

The reaction of substituted chloronitrobenzenes with arylamines to form substituted diphenyl amines is typified by 4-rutrodiphenylamine-2-sulfoiiic acid where 4-chloronitrobenzene-3-sulfonic acid (PN salt) is condensed with aniline ia an aqueous medium at 120°C and 200 kPa (2 atm) ia the presence of alkaline buffer at low pH to avoid the competing hydrolysis of the PN salt. 

Arenediazonium salts undergo a coupling reaction with activated aromatic rings such as phenols and arylamines to yield brightly colored azo compounds, Ar—N=N—Ar. ... 

Arylamines are converted by diazotization with nitrous acid into arenediazonium salts, ArN2+ X-. The diazonio group can then be replaced by many other substituents in the Sandmeyer reaction to give a wide variety of substituted aromatic compounds. Aryl chlorides, bromides, iodides, and nitriles can be prepared from arenediazonium salts, as can arenes and phenols. In addition to their reactivity toward substitution reactions, diazonium salts undergo coupling with phenols and arylamines to give brightly colored azo dyes. 

Another possibility for ring closure to annulated 1,3-diazocines employs the thermal decomposition of the diazonium salt derived from arylamine 3.7... 

Research into the mechanism of diazotization was based on Bamberger s supposition (1894 b) that the reaction corresponds to the formation of A-nitroso-A-alkyl-arylamines. The TV-nitrosation of secondary amines finishes at the nitrosoamine stage (because protolysis is not possible), but primary nitrosoamines are quickly transformed into diazo compounds in a moderately to strongly acidic medium. The process probably takes place by a prototropic rearrangement to the diazohydroxide, which is then attacked by a hydroxonium ion to yield the diazonium salt (Scheme 3-1 see also Sec. 3.4). 

The Pd°-catalyzed arylations using arenediazonium tetrafluoroborates are limited to those diazonium salts that can be manipulated at room temperature. The reaction can, if necessary, be performed at temperatures up to 50 °C by using a mixture of an arylamine and tert-butyl nitrite in chloroacetic acid or in a mixture of chloroacetic and acetic acid (Kikukawa et al., 1981a). Styrene reacted with fourteen arylamines in the presence of 5 mol-% Pd(dba)2 to give the corresponding substituted stilbenes in yields of 46-97%. It is important for good yields to carry out these reactions in an acidic system. Without acid the yield was low (11%), and diazo tars were also formed. 

With regard to the mechanism of these Pd°-catalyzed reactions, little is known in addition to what is shown in Scheme 10-62. In our opinion, the much higher yields with diazonium tetrafluoroborates compared with the chlorides and bromides, and the low yields and diazo tar formation in the one-pot method using arylamines and tert-butyl nitrites (Kikukawa et al., 1981 a) indicate a heterolytic mechanism for reactions under optimal conditions. The arylpalladium compound is probably a tetra-fluoroborate salt of the cation Ar-Pd+, which dissociates into Ar+ +Pd° before or after addition to the alkene. An aryldiazenido complex of Pd(PPh3)3 (10.25) was obtained together with its dediazoniation product, the corresponding arylpalladium complex 10.26, in the reaction of Scheme 10-64 by Yamashita et al. (1980). Aryldiazenido complexes with compounds of transition metals other than Pd are discussed in the context of metal complexes with diazo compounds (Zollinger, 1995, Sec. 10.1). 

Rearrangement of arylamines or aryl alkyl ammonium salts... 

As discussed in Section 7.4.2.5, the reduction of tetrazolium salts to formazans often results in further reduction products. As seen in Scheme 24, reduction of formazans with ammonium sulfide leads to the hydrazidine 161. The reduction can proceed further eliminating an arylamine, yielding an amidrazone, e.g., 162.364 By contrast, alcoholic hydrogen sulfide attacks... 

The classic syntheses of the antibacterial sulfonamides involve reaction of the appropriate arylamine with an acid addition salt of p-amino-benzenesulfonyl chloride, or p-nitrobenzenesulfonyl chloride followed by reduction. Chemical interest largely resides in preparation of the corresponding arylamines. For the synthesis of sulfacytine (134), N-ethyl uracil (131) was converted to its thioamide (132) by reaction with phosphorous pentasulfide. The newly introduced sulfur is then displaced with ammonia in methanol to give 133. Standard reactions complete... 

N-AryInitrones (XIII) formed by oxidation of N-hydroxy-N-methyl arylamines, show high reactivity toward carbon-carbon and carbon-nitrogen double bonds in non-aqueous media (21,203) (Figure 10). Under physiological conditions, however, it appears that N-arylnitrones exist as protonated salts that readily hydrolyze to formaldehyde and a primary N-hydroxy arylamine and efforts to detect N-arylnitrone addition products in cellular lipid, protein or nucleic acids have not been successful (204). Nitroxide radicals derived from N-hydroxy-MAB have also been suggested as reactive intermediates (150), but their direct covalent reaction with nucleic acids has been excluded (21). 

Heavy metals are widely used as catalysts in the manufacture of anthraquinonoid dyes. Mercury is used when sulphonating anthraquinones and copper when reacting arylamines with bromoanthraquinones. Much effort has been devoted to minimising the trace metal content of such colorants and in effluents from dyemaking plants. Metal salts are used as reactants in dye synthesis, particularly in the ranges of premetallised acid, direct or reactive dyes, which usually contain copper, chromium, nickel or cobalt. These structures are described in detail in Chapter 5, where the implications in terms of environmental problems are also discussed. Certain basic dyes and stabilised azoic diazo components (Fast Salts) are marketed in the form of tetrachlorozincate complex salts. The environmental impact of the heavy metal salts used in dye application processes is dealt with in Volume 2. 

A vast array of arylamines can be converted into the corresponding diazonium salts from these diazo components and the host of available coupling components an almost limitless range of azo dyes is accessible. 

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