Nitrosation of Tolazoline
Chem. Res. Toxicol., Vol. 21, No. 2, 2008 297
2 H), 2.03 (b, 1 H). 13C NMR: δ 175.8, 133.0, 129.5, 128.7,
bromide (30 wt % in acetic acid) at room temperature to a
solution of 17 (0.218 g, 1 mmol) in 2 mL. The oxime
(hydrobromide salt) precipitated. Recrystallization from ethanol
gave 0.179 g of 18 (95% yield) as a white solid; mp 230 –233
127.4, 59.3, 41.3, 40.9. IR (neat): 3399, 2919 (b), 1724 (s), 1496,
1368, 1024 cm-1
.
N-(2-Acetoxyethyl)phenylacetamide (12). N-(2-Acetoxy-
ethyl)phenylacetamide 12 was prepared from 13 by acetylation
with acetic anhydride followed by aqueous quenching, which
gave a crude solid. Recrystallization from ethanol gave 12 as
white solid (92% yield); mp 68–69 °C. 1H NMR: δ 7.32 (m, 5
H), 5.89 (b, 1 H), 4.09 (t, J ) 5.5 Hz, 2 H), 3.56 (s, 2 H), 3.49
(t, J ) 5.5 Hz, 2 H,), 2.03 (s, 3 H). 13C NMR: δ 171.1, 170.8,
134.7, 129.3, 128.8, 127.2, 62.8, 43.6, 38.6, 20.6. EIMS: 65,
88, 91, 92, 118, 130, 161, 179, 221. Anal calcd for C12H15NO3:
C, 65.14; H, 6.83; N, 6.33. Found: C, 65.05; H, 6.84; N, 6.25.
N-Nitroso-N-(2-acetoxyethyl)phenylacetamide (9). The ni-
trosamide 9 was prepared from 12 in a method similar to the
preparation of 10 (82% yield). The compound was too unstable
1
°C. H NMR (DMSO-d6): δ 12.92 (s, 1 H), 10.66 (s, 2 H),
7.54 (m, 5 H), 4.05 (s, 4 H). 13C NMR (DMSO-d6): δ 160.4,
142.3, 130.4, 129.1, 125.6, 44.8. The E isomer 19 of the title
compound was prepared by denitrosation of 17 with aqueous
hydrochloride acid. After 0.218 g of 17 (1 mmol) was stirred
in 2 M HCl for 12 h, the residue was evaporated to dryness
and purified by flash chromatography with CH2Cl2 and MeOH
as eluent solvent (9:1, v/v). Pure 19 (hydrochloride) was
obtained as a sticky oil with a yield of 82%. 1H NMR (DMSO-
d6): δ 13.44 (s, 1 H), 10.05 (s, 2 H), 7.49 (m, 5 H), 3.90 (s, 4
H). 13C NMR (DMSO-d6): δ 162.3, 143.1, 130.6, 129.3, 128.8,
127.5, 44.7.
1
for the determination of elemental composition. H NMR: δ
2-Methyl-4-phenyl-5-oxazolone-3-oxide (29). According to
the procedure reported by Seebach (25), 29, as a white solid,
was prepared from acetaldehyde and phenylglyoxylic acid oxime
7.31 (m, 5 H), 4.48 (s, 2 H), 4.03 (m, 4 H), 1.89 (s, 3 H). 13C
NMR: δ 174.9, 170.5, 133.1, 129.5, 128.7, 127.4, 59.9, 41.3,
37.3, 20.40. IR (neat): 3449 (w), 2912, 1736 (s), 1469, 1453,
1
30 in a yield of 83%; mp 72 -73 °C. H NMR (in CDCl3): δ
1364, 1221 (s), 1012 cm-1
.
8.63 (m, 2 H), 7.50 (m, 3 H), 5.96 (q, J ) 6.0 Hz, 1 H), 1.87
(d, J ) 6.0 Hz, 3 H). 13C NMR (in DMSO-d6): δ 164.1. 131.2,
128.6, 126.3, 125.2, 124.7, 94.5, 18.0. IR (KBr): 3409 (b), 1789
(s), 1576 (s), 1490, 1375, 1248, 1104, 786 cm-1. Anal. calcd
for C10H9NO3: C, 62.82; H, 4.74; N, 7.33. Found: C, 62.74; H,
4.78; N, 7.37.
N-Nitroso-N-(2-chloroethyl)phenylacetamide (11). The title
nitrosamide 11 was prepared from N-(2-chloroethyl)phenylac-
etamide (23) by a procedure similar to that used to prepare 10.
The pure product was obtained as pale yellow oil after
chromatography in a yield of 76%. 1H NMR: δ 7.31 (m, 5 H),
4.49 (s, 2 H), 4.09 (t, J ) 6.6 Hz, 2 H), 3.41 (t, J ) 6.6 Hz, 2
H). 13C NMR: δ 174.7, 129.5, 128.7, 127.5, 41.3, 39.3, 38.6.
IR (neat): 2919 (s), 1736 (s), 1507 (s), 1453, 1372, 1260, 1078,
N-Nitrosotolazoline (36). Tolazoline hydrochloride (1.96 g,
10 mmol) was dissolved in 20 mL of aqueous buffer (NaH2PO4,
0.5 M, pH 4). To this solution, NaNO2 (3.45 g, 50 mmol) in 20
mL of water was added slowly over a 2 h period while
constantly stirring at room temperature. Methylene chloride (2
mL) was added to the above reaction mixture every 5 min and
then removed with the replenishment of fresh solvent. Concen-
trated hydrochloric acid was added every few minutes to keep
the pH approximately 4. The combined CH2Cl2 extracts were
washed with NaHCO3-saturated solution and NaCl-saturated
solution and dried over Na2SO4. The solvent was then evapo-
rated, and the residue was chromatographed on silica gel flash
column with hexane and EtOAc as eluent solvents (1:2, v/v, Rf
) 0.6). Pure 36 was obtained as pale yellow oil (1.5 g, 79%
1028, 718 cm-1
.
N-Nitroso-2-imidazolinyl Phenyl Ketoxime (17) (Nitrosa-
tion of Tolazoline with Isopropyl Nitrite). A round-bottom
flask was charged with tolazoline free base (3.2 g, 20 mmol).
Isopropyl nitrite (17.8 g, 200 mmol) was added at room
temperature. The mixture was stirred at room temperature for
16 h. The excess isopropyl nitrite and 2-propanol were removed
using a rotary evaporator. The pure product 17 (3.18 g, 73%
yield) was obtained by recrystallization in a mixture of acetone
and acetonitrile; mp 93 – 95 °C. 1H NMR (acetone-d6): δ 11.39
(s, 1 H), 7.76 (m, 2 H), 7.42 (m, 3 H), 4.29 (t, J ) 7.2 Hz, 2
H), 3.97 (t, J ) 7.2 Hz, 2 H). 13C NMR (acetone-d6): δ 152.2,
147.8, 132.1, 130.5, 129.3, 126.7, 55.2, 43.8. MS (EI): 77, 103,
116, 129, 144, 159, 172, 188, 189, 218. IR (KBr): 2839 (b),
1662 (s), 1458 (s), 1204 (s), 1009 cm-1. HRMS (EI, protonated
molecular ion followed by loss of NO): m/z calcd for
C10H11N3O, 189.0902; found, 189.0892. Anal. calcd for
C10H10N4O2: C, 55.04; H, 4.62; N, 25.68. Found: C, 54.98; H,
4.60; N, 25.36.
1
yield). H NMR: δ 7.35 (m, 5 H), 4.26 (s, 2 H), 3.95 (t, J )
6.5 Hz, 2 H), 3.72 (t, J ) 6.5 Hz, 2 H). 13C NMR: δ 158.9,
133.9, 129.3, 128.6, 127.2, 52.8, 43.6, 34.2. IR (neat): 3031,
2877, 1684 (s), 1389 (s), 1277, 1200, 1024, 722 (s) cm-1
.
HRMS (EI): m/z calcd for C10H11N3O, 189.0902; found,
189.0898.
HPLC Quantification of UV-Absorbing Nitrosation
Products. A nitrosation mixture obtained as described above
was injected to the HPLC after dilution with CH3CN/H2O. Two
wavelengths, 220 and 254 nm, were set for the UV detection
of the eluting substances. A gradient program with two solvents
CH3CN (A) and NaH2PO4 buffer (0.025 M, pH 4.0) (B) was
utilized for the mobile phase. HPLC program (min, eluent) at
1 mL/min: 0–40, 10-90% A; 40–45, 90% A.
Quantification of Ethylene Glycol and Its Derivatives
in the Nitrosation Reaction Mixture. The ethylene glycol in
the reaction mixture was determined by a quantitative 13C NMR
spectral method. Generally, 400 µL of the nitrosation mixture
was mixed with 100 µL of CD3CN (for magnetic field locking
signal) and 50 µL of 0.6 M THF aqueous solution as an internal
standard. The 13C spectrum was collected for 30 min. The
concentration was calculated based on the methylene group peak
heights of ethylene glycol and THF (δ 62.73 and 67.51,
respectively). Ethylene glycol monoacetate and ethylene glycol
N-Nitroso-2-imidazolinyl Phenyl Ketone O-Phenylacetyl-
oxime (20). The title compound was prepared from 17 by
acylating it with phenylacetyl chloride. The product 20 is a
yellow solid (yield, 93%); mp 73–74 °C. 1H NMR: δ 7.79 (m,
2 H), 7.45 (m, 3 H), 7.27(m 3 H), 7.15(m, 2 H), 4.03 (t, J )
8.2 Hz, 2 H), 3.76 (s, 2 H), 3.60 (t, J ) 8.2 Hz, 2 H). 13C
NMR: δ 166.9, 154.2,151.3, 132.7, 132.2, 129.6, 129.2, 128.9,
128.5, 127.6, 127.1, 54.6, 43.1, 40.1. HRMS (EI, protonated
molecular ion followed by loss of NO): m/z calcd for
C18H17N3O2, 307.1320; found, 307.1316. IR (neat): 1785 (s),
1657,1604, 1450 (s), 1215 (b) cm-1. Anal. calcd for
C18H16N4O3: C, 64.28; H, 4.79; N, 16.66. Found: C, 64.21; H,
4.84; N, 16.35.
Z- and E-2-Imidazolinyl Phenyl Ketoximes: The Deni-
trosation of 17. The Z isomer of the title compound 18 was
prepared by the dropwise addition of 0.4 mL of hydrogen