Diazotizing reagent

In most cases diazonium salts are not isolated, but are converted into products by reactions that can be carried out in situ. Moreover, it is actually recommended not to isolate these salts, not even for purification purposes, as many of them have a tendency to explode. In addition, the high solubility of most diazonium salts in water makes precipitation from this medium difficult. Therefore, to obtain solid diazonium salts the recommended method for many decades was to carry out diazotizations in ethanol followed by precipitation with ether. As inorganic salts of nitrous acid are scarely soluble in ethanol, Knoevenagel recommended alkyl nitrites (ethyl or isopentyl nitrite) as diazotization reagents as long ago as 1890. Various other solvents have subsequently been used for diazotizations with alkyl nitrites (see Saunders and Allen, 1985, p. 23 ff.), but as a method for obtaining solid diazonium salts this has been superseded by the isolation of diazonium tetrafluoroborates and, to a lesser degree, of hexafluorophosphates. 

Sulfanilic Acid, Diazotized Reagent Sulfanilic Acid, Diazotized Reagent 403 ... 

Although aryl halides are the substrates of choice for Heck transformations, dia-zonium salts have also gained great interest, due mainly to reasons of economy [478]. With this in mind, the group of Beller explored a domino diazotization/Heck sequence of substituted anilines 2-935 with ethylene (Scheme 2.209) [479]. The reaction proceeds best in the presence of Pd(OAc)2 and tBuONO as diazotization reagent in a mixture of acetic acid and CH2C12. Using these conditions, the desired styrenes 2-936 were isolated in yields up to 72 %. 

Nitrosyl halides, particularly NOCl and NOBr, can also be used as diazotization reagents undo" anhydrous conditions, as these gases (NOCl mp —59.6°C, bp —6.4°C NOBr bp 0°C) are readily soluble in many organic solvents. They can also be generated in situ in chlorinated hydrocarbons by reaction of trimethylsilyl halides with alkyl nitrites (equation 13) as shown by Weiss and Wagner . The group of Weiss found also that NW-bissUylated anilines react in aprotic dichloromethane with generation of diazonium salts and formation of the nonnucleophilic hexamethyldisiloxane (equation 14). 

The original Griess diazotization has been modified to use different diazotization reagents as noted in Section... 

Shul, G., R. Parent, H. A. Mosqueda, and D. Belanger. Localized in situ generation of diazonium cations by electrocatalytic formation of a diazotization reagent. ACS Appl. Mater. Interfaces 5, 2013 1468-1473. 

Diazotate reagent Cool 10 ml of a 0 06 per cent solution of -amino-acetophenone solution in 0 2N hydrochloric acid to 5°, add 3 ml of a 0-2 per cent sodium nitrite solution and mix. After three minutes add 3 ml of 2N sodium hydroxide and mix by shaking. Use between two and five minutes after preparation. 

For solutions Prepare a dilution of the sample to contain about 0 1 mg of aneurine hydrochloride per ml and having an acid concentration equivalent to O OIN. Transfer 5 ml to a 50-ml graduated flask, add 10 ml of 50 per cent ethanol, mix, add 5 ml of diazotate reagent and again mix. Place in a water-bath at 20° for twelve minutes and then dilute to 50 ml with wopropyl alcohol. Determine the extinction at 520 m u in a 1-cm cell, subtract the value of a reagent blank and read off the amount of aneurine from a calibration curve. 

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