Nitrosylsulfuric acid synthesis

Utilization of acetic acid (90CCC718, 95BML2783) and mixtures of acetic and sulfuric acids (81JHC309), as well as triphenylmethylborofluor-ide (86JPR35), leads to 3-cyano-3,4-dihydropyridin-2-ones, which can be oxidized into the corresponding cyanopyridones by nitrosylsulfuric acid. Authors (81JHC309) have studied the synthesis of 3-cyanopyridones 264 systematically, and have shown that the latter can be obtained by different routes from 2-amino-4H-pyrans 59, as well as from related dihydro- 265 and tetrahydropyridone 266 (Scheme 104). 

The synthesis of diazonium salts of less basic amines does not proceed satisfactorily under the above conditions because of the reduced nucleophilic nature of the amino group and the reaction is usually carried out in concentrated sulfuric acid. The addition of sodium nitrite to concentrated sulfuric acid produces the stable nitrosylsulfuric acid, (NOHSO ). Diazotization of the most weakly basic amines is carried out using nitrosylsulfuric acid in a mixture of one part of propionic acid in five parts of acetic acid at 0-5 °C. The propionic acid prevents the mixture from freezing. 

The tetrazotization of m-phenylenediamine has been described also, under special conditions (nitrosylsulfuric acid in glacial acetic acid) a similar conversion of the ortho isomer has been accomplished. This procedure has been adaf>ted to the tetrazotization of certain naphthalene diamines. The simultaneous diazotization of two amino groups in the biphenyl series is illustrated by the synthesis of 4,4 -biphenylene-fejs-diazonium chloride and its 3,3 "dimethyl analog. ... 

Scheme 1 Synthesis of poly(2,7-dibenzosilole) [23]. Reagents and conditions (a) Cu, DMF, 125 °C, 88% (b) Sn, HCl, EtOH, 110 °C (bath temp), 72% (c) nitrosylsulfuric acid, concentrated H2SO4, 0°C, then aq. KI, - 10 to 50 °C, 30% (d) f-BuLi (4 equiv), THF, -90 to -78°C, then dichlorodihexylsilane or dichlorodioctylsilane, 25 °C, 52% (e) t-BuLi, diethyl ether, - 78 °C, then 2-isopropoxy-4,4/,5,5/-tetramethyl-l,3,2-dioxaboralane, 25 °C,...

Triphenylmethane derivatives can be converted into triphenylmethanol derivatives by various oxidizing agents. Triphenylmethane itself with nitric acid or with chromic acid in glacial acetic acid gives triphenylmethanol, and with lead tetraacetate gives triphenylmethyl acetate. The principal importance of this reaction lies in the technical synthesis of triphenylmethane dyes from their leuco bases, for which purpose very varied oxidants such as arsenic acid, nitrobenzene, nitrous acid, and nitrosylsulfuric acid are used. 

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