152 Synthetic Routes to AromaticC-Nitro Compounds
protection as theirN-acetyl orN,N′-diacetyl derivatives. Thus, pentanitrotoluene (61) can be
prepared from 3,5-bis(diacetylamino)-2,4,6-trinitrotoluene (60) (Table 4.1, Entry 5).^139
4.7.1.2 Peroxymonosulfuric acid (Caro’s acid)
CH 3
NO 2NH 2
NO 2O 2 N O 2 NCH 3NO 2NO 2NO 256 57H 2 SO 5 , 100 °C74 %Figure 4.25Peroxymonosulfuric acid (H 2 SO 5 ) can be prepared by adding aqueous hydrogen peroxide,
or ammonium or alkali metal persulfates to sulfuric acid solutions of various concentrations.
The reagent is a weaker oxidant than peroxydisulfuric acid and often reacts with nitroani-
lines to give the corresponding nitroso compound.^156 ,^157 Nitro compounds can be formed un-
der more forcing conditions.^158 –^162 3-Amino-2,4,6-trinitrotoluene (56) is oxidized to 2,3,4,6-
tetranitrotoluene (57) in 74 % yield when heated to 100◦C with peroxymonosulfuric acid
prepared from potassium persulfate and sulfuric acid.^152 However, 2,4,6-trinitroaniline (pi-
cramide) remains unchanged on treatment with peroxymonosulfuric acid.
4.7.1.3 Peroxytriflic acid
NH 2NO 2NO 2O 2 N NO 2 O 2 NO 2 N O 2 NNO 2
NO 2NO 2
NO 2CF 3 SO 3 H,
90 % H 2 O 290 %31 55Figure 4.26Peroxytriflic acid (CF 3 SO 4 H) is preparedin situfrom the addition of 90–98 % hydrogen
peroxide to an excess of triflic acid. Peroxytriflic acid was first reported by Nielsen and
co-workers^139 and is possibly the most powerful peroxyacid known. The full potential of
peroxytriflic acid has not been explored but it is reported to oxidize the weakly basic amine
2,3,4,5,6-pentanitroaniline (31) to hexanitrobenzene (55) in 90 % yield; peroxydisulfuric acid
achieves the same conversion in only 58 % yield.^139
4.7.1.4 Peroxyacetic acid
Peroxyacetic acid (CH 3 CO 3 H) is a weak oxidant. Strong solutions are potentially explosive
and hazardous to store, although a 40 % solution in acetic acid is available commercially.
Emmons^164 prepared anhydrous solutions of peroxyacetic acid from the reaction of 90 %+
hydrogen peroxide with acetic anhydride in chloroform containing a trace of sulfuric acid.