Isopentyl nitrite, reagents

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nitrites (see Saunders and Allen, 1985, p. 23 ff.), but as a method for obtaining solid diazonium salts this has been superseded by the isolation of diazonium tetrafluoroborates and, to a lesser degree, of hexafluorophosphates. 

Nitrosyl formate may be generated in situ by treating isopentyl nitrite with anhydrous formic acid. This reagent evidently adds to olefins such as cyclohexene, styrene, norbomene, trans-3-hexene, and 2,3-dimethylbutene to give nitrosoformates. While the first three olefins were converted into dimeric products, 2,3-dimethylbutene produced a 50-50 mixture of the monomer and the dimer (as a blue oil). The product of the reaction with trans-3-hexene contained some of the corresponding oximino formate. 

Scheme 11. Reagents a, reflux in CH2C12 b, MCPBA c, H2/Pd-C/MeOH d, Ac20/Et3N e, H2/Pt02-Raney Ni/20 torr f, isopentyl nitrite/CH2Cl2 g, t-BuOK/DMSO/90°C h, H2/Raney Ni/30 torr i, KOH/aq MeOH j, TsOH/HC(OEt>, k, AlCl3/EtSH/CH2Cl2 1, 20% HCl/teflux.

Scheme 43. Synthesis of the esters of porphyrin octa-acetic acid [161]. Reagents (a) isopentyl nitrite. HCI (b) Zn, AcOH, 75 C (c) TKNOjlj/MeOH/ HCIO4 (d) Pb(OAc>4 (e) 20% HCI, reflux (f) O2 (g) ROH, H2SO4, 50 C (h) Zn(OAc>2, CHCl,/ MeOH, reflux.

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