Diazonium compounds, conversion

The conversion of an aromatic diazonium compound into the corresponding arsonic acid by treatment with sodium arsenite in the presence of a catalyst, such as copper or a copper salt, is called the Bart reaction. A modification of the reaction employs the more stable diazonium fluoborate in place of the diazonium chlorid.i. This is illustrated by the preparation of />-nitrophenylarsonic acid ... 

Another possible means of conversion of functionalized arenes into the corresponding hydrocarbons is the reduction of diazonium compounds [49]. By appli-... 

The conversion may consist simply in oxidation or be the result of a more complex reaction. For example, nitrosotoluene can be converted into diazonium nitrate under the influence of nitrous acid. Bamberger [132] found in 1918 that nitrosobenzene could be converted into benzenediazonium nitrate under the influence of nitrous acid. According to Bamberger [133] and Nesmeyanov [134], mercury-aromatic compounds also give nitrates of corresponding diazonium compounds under the influence of N203, presumably also through nitroso compounds. 

Diazotization. The conversion of a primary aromatic amine to a diazonium compound is... 

It would perhaps be more correct to state that Robinson and Teuber arrived at the correct structure for calycanine on the basis of their calycanthine structure, which was derived from a presumed biogenesis from two molecules of A-methyltryptamine. It had the correct number of functional groups (two each of =NMe and =NH) and explained the readiness with which it could be coupled with diazonium compounds. Furthermore, its conversion to calycanine involved only a minor readjustment of bonds in addition to the usual dehydrogenation and loss of A-methyl. 

Amino-6-chloropyridazine 2-oxide can be diazotized to give anhydro 3-diazo-6-hydroxyp3rridazine diazonium hydroxide 2-oxide (141) the structure is supported by infrared spectrum and conversion into 3-hydroxypyridazine 1-oxide on refluxing in methanol. - When coupled with 2-naphthol in alkaline medium, the diazonium compound gives a purple dye. ... 

A generally applicable procedure for conversion of aromatic amines into phenols or naphthols consists of boiling aromatic diazonium compounds (for their preparation see page 581). This method will be illustrated here by some examples. 

Conversion of diazonium compounds to aryl chlorides, bromides, or cyanides is usually accomplished using cuprous salts, and is known as the Sandmeyer reaction. Since a CN group is easily converted to a CO2H group (eq. 10.13), this provides another route to aromatic carboxylic acids. The reaction with KI gives aryl iodides, usually not easily accessible by direct electrophilic iodination. Similarly, direct aromatic fluorination is difficult, but aromatic fluorides can be prepared from diazonium compounds and tetrafluoroboric acid, HBF4. 

Diazoninm and Azo Compounds. - Aryl diazonium compounds undergo reductive metabolism to aryl radicals, which react with DNA. Studies on the p-hydroxybenzenediazonium ion have shown that such compounds can also undergo conversion to radicals through reactions catalysed by the hydroxyl ion. 

Conversion of tryptophan or other indole derivatives into a nitro-samine by treatment with nitrous acid followed by diazotization with N-l-naphthylethylene diamine dihydrochloride has been recently studied by Goswami (752). The method seems to be sensitive and to follow Beer s law over of wide range of concentrations of tryptophan. Selective nitrosation of tryptophan is achieved at room temperature in 1 M HCl and diazotization at 10° C or below. Sodium chloride was found to interfere with the assay. The temperature must be controlled with care, since the diazotization reaction is exothermic and diazonium compounds are stable only at low temperatures. This fact would explain the optimum temperature of 10 or 6° C in the diazotization reaction. 

Conversions of diazonium salts into halogenated derivatives have been reported for compounds of type 128 and 129 [73JCS(P1)2901 80JCS(P 1)2398], Although some 7-substituted pyrazolo[ 1,5-u]pyridines have been made from the lithiated precursors, no halogeno products have been reported (92JOC5538). 

The diazotization of amino derivatives of six-membered heteroaromatic ring systems, particularly that of aminopyridines and aminopyridine oxides, was studied in detail by Kalatzis and coworkers. Diazotization of 3-aminopyridine and its derivatives is similar to that of aromatic amines because of the formation of rather stable diazonium ions. 2- and 4-aminopyridines were considered to resist diazotization or to form mainly the corresponding hydroxy compounds. However, Kalatzis (1967 a) showed that true diazotization of these compounds proceeds in a similar way to that of the aromatic amines in 0,5-4.0 m hydrochloric, sulfuric, or perchloric acid, by mixing the solutions with aqueous sodium nitrite at 0 °C. However, the rapidly formed diazonium ion is hydrolyzed very easily within a few minutes (hydroxy-de-diazonia-tion). The diazonium ion must be used immediately after formation, e. g., for a diazo coupling reaction, or must be stabilized as the diazoate by prompt neutralization (after 45 s) to pH 10-11 with sodium hydroxide-borax buffer. All isomeric aminopyridine-1-oxides can be diazotized in the usual way (Kalatzis and Mastrokalos, 1977). The diazotization of 5-aminopyrimidines results in a complex ring opening and conversion into other heterocyclic systems (see Nemeryuk et al., 1985). 

Stannous chloride is used most frequently for the reduction of nitro compounds [177, 178, 179] and of quinones [180, 181], It is also suitable for conversion of imidoyl chlorides [182] and of nitriles [183] to aldehydes, for transformations of diazonium salts to hydrazines [184], for reduction of oximes [f[Pg.30]

Daidone and co-workers cyclized the diazonium salt derived from N-pyrazolylbenzamide 173 to obtain, in addition to other products, a small amount of pyrazolodiazocine, 174 (R = Ph) (80JHC1409). Rahman condensed 3-chloro-4-aryl-1,2,4-triazoles with N-methylanthranilic acid to afford triazoles 175 (R = H, Me R = Me). Conversion of this compound to the acid chloride, followed by cyclization with aluminum chloride,... 

Conversion of the diazonium salt to the diazohydroxide by means of alkali in the presence of a liquid aromatic compound with which the... 

Atomic motions involved in the conversion of a contact ion-pair between an aromatic diazonium ion and a nucleophile into the E and the Z-isomer of the covalent diazo-compound... 

A suspension of 2.10 g. of the freshly prepared diazonium salt and 50 ml. of ethanol is stirred in a 200-ml. Erlenmeyer flask and cooled to 0°C. while a solution of 4.7 g. of fcww-chloro-hydrido-bis(triethylphosphine) platinum (II) in 25 ml. of ethanol is added over a period of 10 minutes. The mixture becomes yellow immediately and is stirred at 0°C. for 10 minutes. At this point, yellow crystals of the aryldiimide complex usually separate. The mixture is filtered, and the filtrate is cooled to —78°C. to give a second crop of the diimide complex. Occasionally crystallization does not occur immediately. In this situation, the mixture is cooled to — 78°C. directly, and the crystals which form are filtered and washed with ether. In either case the total yield is about 4.9-5.4 g. (72-78%). (The checkers reported an 87% yield with a melting point of 105-108°C. with decomposition.) The purity of this material is adequate for most preparatory purposes. Further purification may be accomplished by conversion to the arylazoplatinum compound (Sec. D) followed by reprotonation with concentrated aqueous fluoroboric acid, HBF4. 

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