ACID-BASE PROPERTIES OF 5-HYDROXY-1,3,6-TRIMETHYLURACIL
797
EXPERIMENTAL
purity of at least 95% (HPLC) dissolved in 7 mL of 24%
solution of NaOH. The reaction mixture was vigorously
stirred at 60°С during 4 h and then cooled. the crystals
were separated off and recrystallized from water. Yield
KOH (Sigma-Aldrich, 99%), D2O (DeuteroGmbH,
99%), and DMSO-d6 (DeuteroGmbH, 99%) were used
as received.
1
0.97 g (73%), white powder, mp 210°C. H NMR
The рKа1 values were determined via a conventional
procedure [17] by means of potentiometric titration in a
constant-temperature 25 mLvessel equipped with a reflux
condenser, at 20, 25, 35, and 45°С. Temperature was
maintained constant using an LOIP LT-205 thermostat.
The solution pH was measured using a рН-150MI
potentiometer equipped with an ESK-10307 combined
glass electrode calibrated using standard buffered
solutions. The solutions ionic strength was maintained
constant with 0.1 M. solution of KNO3. Freshly prepared
bidistilled water was used as the solvent. Concentration
of the freshly prepared KOH solution was determined
by acid-base titration with 0.01 М HCl standard solution
using phenolphthalein as indicator.
spectrum (DMSO-d6), δ, ppm: 2.54 s (3Н, СН3С6), 3.05 s
(3Н, N3СН3), 3.30 s (N1СН3), 7.01 s (4H, O3SOC5). 13С
NMR spectrum (D2О), δС, ppm: 13.81 (CН3С6), 27.31
(N3СН3), 30.27 (N1СН3), 126.39 (С5), 130.86 (С6),
154.50 (С2), 154.96 (С4).
5-Hydroxy-1,3,6-trimethyluracil (2). 1 g
(0.0037 mol) of 1,3,6-trimethyluracil-5-ammonium
sulfate was dissolved in 5 mL of water preheated to
80°С, and then 0.2 mL (0.0037 mol) of conc. H2SO4
was added dropwise. The obtained mixture was stirred
at 80°С during 1 h, and then cooled. The crystals were
filtered off and dried. Yield 0.63 g (88%), white powder,
mp185°C. UV spectrum, λmax, nm (ε, mol–1 L cm–1): 283
1
(7536). H NMR spectrum (D2O), δ, ppm: 2.22 s (3Н,
1Н, 13С, and 15N NMR spectra were recorded using
a Bruker Avance III impulse spectrometer operating
at 500.13 (1H), 125.47 (13C), and 50.58 MHz (15N)
(a 5 mm probe with Z-gradient PABBO, temperature
298 K, in D2O). Chemical shifts in the 1Н NMR spectra
were reported with respect to the residual signal of
water. The 13С NMR spectra with protons decoupling
(WALTZ-16) were recorded with the following settings:
spectral window 29.8 kHz, number of data points 64K,
exciting impulse duration (30°) 3.2 μs, relaxation delay
2 s, number of scans 2k. 2D spectra were recorded using
standard pulse sequences implemented in the instrument
software [18] (1H–13C HSQC) and [19, 20] (1H–13C
HMBC). Electronic absorption spectra were recorded
using a Shimadzu UV-1800 spectrophotometer (200–
350 nm, 1 cm quartz cell, concentration of the solutions
in bidistilled water 2×10–5 mol/L).
СН3С6), 3.23 s (3Н, N3СН3), 3.32 s (N1 СН3). 13С NMR
spectrum (D2О), δС, ppm: 12.36 (CН3С6), 27.4 (N3СН3),
31.194 (N1СН3), 127.41 (С5), 136.46 (С6), 150.76 (С2),
160.20 (С4). 15N NMR spectrum (D2О), δN, ppm: 125.38
(N1), 153.40 (N3).
FUNDING
This study was performed in the scope of
the State Task of the Ministry of Science and Higher
Education (no. AAAA-A20-120012090029-0 and
АААА-А19-119011790021-4) using the equipment of
“Chemistry” and “Agidel” Centers for Collective Usage of
Ufa Federal Research Center, Russian Academy of Sciences.
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
REFERENCES
1. Wempen, I. and Fox, J.J., J. Am. Chem. Soc., 1964,
vol. 86, p. 2474.
Preparation of the solutions. To record the NMR
spectra in neutral medium, dry specimens of compounds
1 and 2 (0.012 and 0.013 g, respectively) were diluted in
0.8 mLof D2O. To record the spectra in alkaline medium,
dry specimens of compounds 1 and 2 (0.012 and 0.013 g,
respectively) were added to a KOH solution (0.088 mol/L;
0.004 g in 0.8 mL of D2O). To record the NMR spectrum
of 1,3,6-trimethyluracil-5-ammonium sulfate, 0.018 g of
the dry sample was dissolved in 0.8 mL of DMSO-d6.
2. Ioffe, B.V., Kostikov, R.R., and Razin, V.V., Fizicheskie
metody opredeleniya stroeniya organicheskikh soedinenii
(Physical Methods for Determining the Structure of Or-
ganic Compounds), Moscow: Vysshaya Shkola, 1984.
3. Stimson, M.M., J. Am. Chem. Soc., 1949, vol. 71,
p. 1470.
4. Ilyina, M.G., Khamitov, E.M., Ivanov, S.P., and
Khursan, S.L., Comput. Theor. Chem., 2016, vol. 1078,
p. 81.
1,3,6-Trimethyluracil-5-ammonium sulfate. 1.68 g
(0.0075 mol) of dry ammonium persulfate was added
portionwise to 1 g (0.005 mol) of compound 3 [15] with
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 5 2020