ACIDITY AND BASICITY OF PRIMARY N-PHENYLNITRAMINES
117
The pKA values were measured using CI-316 pH-meter
(Elmetron). The aqueous solutions of nitramines
(1.377 Â 10À3 < c < 0.015 M) were triturated with
0.0542 M sodium hydroxide.
water (50 ml). The solution was cooled to 5°C and
diazotized with an excess of sodium nitrite (29.35 g,
0.28 mol) dissolved in a minimum amount of water
(30 ml).
Ammonium
tetrafluoroborate
(29.35 g,
0.28 mol), as a saturated aqueous solution, was added
and the precipitate of diazonium tetrafluoroborate was
collected by filtration. It was added to the cold (À5°C)
aqueous potassium hydroxide (60.0 g of 50% aq. KOH)
and the suspension was poured into potassium cyano-
ferrate(III) (200.0 g, 0.60 mol) dissolved in water
(1200 ml) containing potassium hydroxide (60.0 g). The
solution was stirred for 18 h at room temperature. A
yellow precipitate was collected by filtration, purified and
identified as 4,4'-azoxybenzene. The filtrate was cooled
in an ice bath and neutralized with 30% sulfuric acid.
Extraction with methylene chloride (3 Â 100 ml) gave a
multicomponent mixture, which was re-extracted with
1 M aq. KOH. The alkaline solution was neutralized as
before; the precipitate was collected by filtration, dried in
vacuum and crystallized from n-hexane. N-(4-Methoxy-
phenyl)-nitramine (13.45 g, 40%) was obtained as
colourless crystals melting at 77–79°C. MS, m/z (int.):
24'-Methanesulfonyl)-N-phenylnitramine 2proce-
dure A, 2b)
4-(Methanesulfonyl)-aniline (3.42 g, 0.02 mol) was dis-
solved in nitromethane (35 ml). Absolute nitric acid
(1.05 ml, 25 mmol) was added to cold acetic anhydride
(10 ml), the solution was maintained for 15 min at room
temperature and combined with the substrate solution.
The mixture was left for 0.5 h at room temperature and
cooled to À20°C. The crude product was collected by
filtration and crystallized twice from toluene, yielding
(4'-methanesulfonyl)-N-phenylnitramine (2.20 g, 51%)
as colourless prisms, m.p. 179–181°C. Calc. for
C7H8N2O4S (216.21): 38.88% C, 3.73% H. Found:
Á
39.11% C, 3.70% H. MS, m/z (int.): 216 (M , 26), 201
(2), 170 (69), 156 (26), 108 (100), 91 (40), 81 (53), 63
(72). IR (KBr): 1613, 1597, 1581, 1502, 1467, 1385,
1311, 1287.
Á
168 (M , 17), 153 (4), 122 (100), 107 (15), 95 (69), 80
(23), 79 (25), 65 (19), 52 (35). IR (KBr): 1592, 1581,
1512, 1466, 1436, 1396, 1327, 1306, 1252, 1220.
N-24-Fluorophenyl)-nitramine 2procedure B, 2d)
4-Fluoroaniline (3.33 g, 0.03 mol) was dissolved in dry
toluene (150 ml); methylmagnesium iodide in isoamyl
ether (3.5 ml of 1 M solution, 35 mmol) was added and
the mixture was stirred intensely at the boiling point for
3 h. It was cooled to room temperature and n-butyl nitrate
(4.00 g, 33 mmol) in toluene (4 ml) was added. The
mixture was stirred for 3 h at room temperature. Water
(30 ml) acidified with acetic acid (3 ml) was added
dropwise and the layers were separated. A toluene
solution was extracted (3 Â 30 ml) with 1 M aqueous
potassium hydroxide. The extract was neutralized with
4 M hydrochloric acid at 0°C; the crude product was
collected with methylene chloride. The solution was
dried over anhydrous sodium sulfate, filtered, diluted
with n-hexane and cooled. The crude product was
collected by filtration and crystallized from a mix-
ture of methylene chloride and n-hexane. N-(4-Fluoro-
phenyl)-nitramine (2.11 g, 45%) was obtained as white
leaflets, m.p. 100–101°C. Calc. for C6H5FN2O4 (156.12):
46.16% C, 3.23% H. Found: 46.25% C, 3.33% H. MS,
RESULTS AND DISCUSSION
We have prepared a series of para-substituted N-
phenylnitramines by nitration of corresponding anilines;
standard procedures were slightly modified to facilitate
isolation of the products in the pure state (scheme 3). The
derivatives containing electron-withdrawing substituents
were obtained in sulfolane or nitromethane solutions by
the action of acetyl nitrate (procedure A). The acetyl
group, as the electron acceptor, is not strong enough,
hence 4-aminoacetophenone cannot be N-nitrated in this
way. More basic anilines were nitrated with n-butyl
nitrate after pretreatment with a strong base (procedure
B); sodium hydride and Grignard reagents were alter-
natively employed. We could not find reaction conditions
(solvent, strong base) that were applicable in the
preparation of any primary nitramine. N-Phenylnitramine
was prepared from aniline by diazotation and oxidation
Á
m/z (int.): 156 (M , 14), 110 (100), 90 (6), 83 (92), 63
(14), 57 (34). IR (KBr): 1621, 1598, 1513, 1433, 1381,
1335, 1294, 1250, 1207.
N-24-Methoxyphenyl)-nitramine 2procedure C, 2g)
4-Anisidine (24.63 g, 0.20 mol) was dissolved in a
mixture of concentrated hydrochloric acid (50 ml) and
Scheme 3
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2002; 15: 115–122