J. Adamek et al. / Thermochimica Acta 512 (2011) 22–27
23
NMR) was obtained. After purification by column chromatography
and recrystallisation from CH2Cl2/Et2O (1:1, v/v) the pure product
was obtained.
2c: yield 71.5%, m.p. 227–229 ◦C, (lit. [5]: 234–236 ◦C). 1H NMR
(ı, ppm): 10.0 (t, 1H, J = 5.4 Hz, NH), 7.92–7.30 (m, 20H, arom.), 5.41
(dd, 2H, J1 = 5.8 Hz, J2 = 2.5 Hz, CH2P+Ph3); 13C NMR (ı, ppm): 168.1
(CONH), 134.9 (d, J = 3.0 Hz), 134.4 (d, J = 10.0 Hz), 129.9, 117.5 (d,
J = 83.9 Hz) (Ph3P+), 38.2 (d, J = 55.5 Hz, P+CH2), 132.0, 130.0, 128.3,
127.7 (Ph) lit. [5]: 1H NMR (ı, ppm): 9.96 (t, 1H), 8.0–7.5 (m, 17H),
7.40–7.28 (m, 3H), 5.41 (dd, 2H, J1 = 6.0 Hz, J2 = 3.0 Hz, CH2P+Ph3).
Scheme 1.
2.5. Synthesis of ˛-(N-acetylamino)methyltriphenyl-
phosphonium iodide 2d and its transformation to dimethyl
˛-(N-acetylamino)methylphosphonate 9
A mixture of methyl N-acetyl-␣-triphenylphosphoniumgly-
cinate iodide 1d (0.407 g, 0.783 mmol), triphenylphosphine
(0.102 g, 0.389 mmol) and triphenylphosphine hydroiodide
(0.337 g, 0.863 mmol) was dissolved in chloroform (1 cm3).
The solvent was then evaporated to dryness and the residue
was heated at 110 ◦C under reduced pressure (1–2 mm Hg) for
2 h. After recrystallisation of the residue using CH2Cl2/Et2O
Scheme 2.
UNITY INOVA-300 spectrometer at operating frequencies of 300
or 75.5 MHz, respectively, in the FT mode using TMS as an inter-
nal standard. Kieselgel 60 (Merck, 0.063–0.200 mm) was used for
column chromatography.
(1:2, v/v),
a crystalline substance (0.707 g) containing the
2.2. Thermogravimetric measurements
expected product 2d (0.322 g, 89%), methyltriphenylphospho-
nium iodide (0.348 g) and only 0.037 g of triphenylphosphine
(estimated by 1H NMR) was obtained. Synthesis of dimethyl ␣-(N-
acetylamino)methylphosphonate 9 was carried out in a glass vial
sealed with a screw-cap. Trimethylphosphite (0.061 cm3, 64.2 mg,
0.52 mmol) and (i-Pr)2EtN (0.006 cm3, 4.4 mg, 0.034 mmol) were
added to a solution of the crystalline substance obtained as
described above (0.349 g) in CH2Cl2 (0.6 cm3), contained ␣-(N-
acetylamino)methyltriphenylphosphonium iodide 2d (0.159 g,
0.345 mmol). The mixture was heated at 60 ◦C for 28 h, and the
solvent was then evaporated under reduced pressure. The residue
was extracted with toluene, and the toluene was subsequently
evaporated. The crude product (50 mg) was purified by column
chromatography (CH2Cl2/MeOH, 20:1) to obtain the pure product
as a thick oil (34.5 mg).
Thermogravimetric measurements were made with a Met-
tler Toledo thermobalance (Star 851, LF/1100) using standard
platinum crucibles (150 l) and sample size of 11–18 mg. Sam-
ples were heated at
a
rate of 5 ◦C min−1 from 25 to 200
Spectra of
or 300 ◦C with nitrogen flow of 50 ml min−1
a
.
gaseous products were recorded online in a Thermo Electron
Corporation FTIR spectrometer (Nicolet 6700) with external
interface module Nicolet X700 connected to the thermobal-
ance by a heated quartz capillary. Homogeneous mixtures of
N-acyl-␣-triphenylphosphonioglycinates, triphenylphosphine and
triphenylphosphine hydrohalides or tetrafluoroborates were pre-
pared by the dissolution of N-acyltriphenylphosphonioglycinate 1
(0.1 mmol) and other components in a proper ratio (see Table 2)
in chloroform (0.7 cm3). Evaporation of the solvent and the drying
of the residue were carried out at 25 ◦C under reduced pressure
(1–2 mm Hg) for 60 min.
9: yield 55%, oil. 1H NMR (␦, ppm): 6.71 (br, 1H, NH), 3.79 (d, 6H,
J = 5.4 Hz, OCH3), 3.74 (dd, 2H, J1 = 11.7 Hz, J2 = 5.7 Hz, CH2P), 2.04
(d, 3H, J = 0.9 Hz, CH3C O); 13C NMR (ı, ppm): 170.1 (CONH), 53.0
(OCH3), 33.7 (d, J = 157 Hz, PCH2), 22.8 (CH3C O) lit. [6]: 1H NMR
(ı, ppm): 7.60 (br, 1H, NH), 3.78 (d, 6H, J = 11.0 Hz, OCH3), 3.65 (d,
2H, J = 12.0 Hz, CH2P), 2.02 (s, 3H, CH3C O).
2.3. Dealkoxycarbonylations monitored by 1H NMR
N-acyl-␣-triphenylphosphonioglycinate
1 (0.05 mmol) or a
mixture of N-acyl-␣-triphenylphosphonioglycinate 1 (0.1 mmol)
tetrafluoroborates in a proper ratio (see Table 2) were dissolved
in chloroform (0.7 cm3). The solvent was then evaporated and the
residue was dried at 25 ◦C under reduced pressure (1–2 mm Hg) for
60 min. The dry residue was heated in an oil bath at reduced pres-
sure (see Table 2). The composition of the obtained mixture was
monitored using 1H NMR
3. Results and discussion
Fig. 1 shows TG, DTG and SDTA curves for demethoxycar-
bonylation of methyl N-acetyl-␣-triphenylphosphoniumglycinate
bromide 1a, methyl N-acetyl-␣-triphenylphosphoniumglycinate
iodide 1d and methyl N-acetyl-␣-triphenylphosphoniumglycinate
tetrafluoroborate 1g.
Thermogravimetrical experiments revealed that immediately
after the endothermic process of the melting of phosphonium salts,
started, which was accompanied by the release of CO2 and a loss of
9.5, 9.5, and 12.5% mass, respectively. The calculated values corre-
sponding to the loss of one CO2 molecule are equal to 9.3, 8.5 and
9.2%, respectively (see Fig. 1). The highest concentration of CO2 in
a nitrogen stream was detected almost exactly at the same time
as the DTG curves achieved the minimum value. The experiments
were repeated on a larger scale (0.1 mmol of salts 1a, 1d and 1 g) in a
glass flask. Samples of phosphonium salts were heated in an oil bath
at the temperature that produced the most rapid weight-loss (145,
135 and 215 ◦C, respectively) under reduced pressure (1 mm Hg) for
2.4. Synthesis and purification of ˛-(N-benzoylamino)
methyltriphenylphosphonium bromide 2c
A mixture of methyl N-benzoyl-␣-triphenylphosphoniumgly-
cinate bromide 1c (0.418 g, 0.781 mmol), triphenyphosphine
(0.102 g, 0.389 mmol) and triphenylphosphine hydrobromide
(0.295 g, 0.859 mmol) was dissolved in chloroform (1 cm3). The sol-
vent was evaporated to dryness and the residue was heated at
115 ◦C under reduced pressure (1–2 mm Hg) for 1.5 h. After crys-
tallisation using CH2Cl2/Et2O (1:2, v/v), a crystalline substance
containing 0.266 g of the expected product (71.5%) and about
0.030 g of methyltriphenylphosphonium bromide (estimated by 1H