Chemistry Letters Vol.33, No.3 (2004)
303
CH3OH þ HCl ꢀ CH3Cl þ H2O:
ð3Þ
800
The concentrations of CH3OH and CH3Cl reach a plateau at
190 min. At 70 min, glycolic acid emerges. With increasing time,
the concentration of glycolic acid increases as can be seen in
Figure 2. It is thus considered that the glycolic acid formation
occurs bimolecularly through
total C
CH2Cl2
600
400
200
0
CH2(OH)2
CH3OH
CH3Cl
HCOOH
HOCH2COOH
CH2(OH)2 þ HCOOH ! HOCH2COOH þ H2O:
ð4Þ
This reaction proceeds under acidic condition since dechlorina-
tion generates HCl and is enhanced by the concentration effect.
The concentration of HCOOH gets smaller than that of CH3OH
and decreases with time over 130 min because of the formation
of glycolic acid.
At the end of the reaction (CH2Cl2, 1 M), the yield of the
main product glycolic acid exceeds 50% at 225 and 250 ꢁC.
The yields (carbon atom %) at 225 ꢁC for 1 h are as follows:
53, 19, 16, 2, 3, and 1% for HOCH2COOH, CH3OH, CH3Cl,
HCOOH, CO2, and CO, respectively.
0
50 100 150 200 250 300 350
Time / min
Figure 2. Time evolution of the concentrations of reactant and
products treated at 200 ꢁC and quenched to room temperature.
In previous works,2,3,6 we have shown that HCOOH decom-
poses to CO and CO2 under hydrothermal conditions. To esti-
mate the concentrations of these gaseous products, we measured
1H and 13C spectra for the gas phase of the aqueous solution of
13C-enriched CH2Cl2 after the treatment at 225 ꢁC for 1 h. For
1H, the peak of CH3Cl was observed; the concentration was only
10 mM. For the 13C spectrum in Figure 1e, furthermore, the
peaks at 186 and 128 ppm are assigned to CO and CO2, respec-
tively. Their concentrations are 32 and 1 mM, respectively. We
consider that CO2 is a product of the cross disproportionation re-
action of formaldehyde (HCHO or CH2(OH)2) and formic acid.
In a previous work,2 we studied the reaction of 1,3,5-trioxane,
which is a trimer of HCHO, under hydrothermal condition with-
out catalysts. At 250 ꢁC, HCHO formed from trioxane yields
CH3OH and HCOOH through the disproportionation (reaction
scheme (2)). HCOOH further reacts with HCHO and yields
CH3OH and CO2 through the cross disproportionation reaction
of
From the 1H spectra, hydrogen-containing products were
identified. The peak of reactant CH2Cl2 is observed at
5.4 ppm. The peak at 4.8 ppm is assigned to methanediol,
CH2(OH)2, which is a hydrated form of formaldehyde. The
two peaks at 3.3 and 8.2 ppm are assigned to methanol (CH3OH)
and formic acid (HCOOH), respectively. The peak at 3.0 ppm is
assigned to methyl chloride (CH3Cl). The signal at 4.2 ppm is as-
signed to the methylene proton of glycolic acid.
To confirm the peak assignments, we measured 13C spectra
for aqueous solution of 13C-enriched CH2Cl2 after the treatment
at 225 ꢁC for 1 h. Glycolic acid is confirmed by the 13C spectrum
shown in Figure 1d; the doublet peaks at 59 and 176 ppm stand
for the methylene and carboxylic carbons in glycolic acid, re-
spectively. The peaks at 26, 49, and 166 ppm are assigned to
CH3Cl, CH3OH, and HCOOH, respectively. Glycolic acid was
1
also confirmed from the H and 13C chemical shifts of the au-
thentic compound.
HCHO þ HCOOH ! CH3OH þ CO2:
With respect to the CO formation, we reported that the dehydra-
tion of HCOOH occurs under hydrothermal conditions.2,3,6 In the
reaction studied here, however, this reaction path is minor.
ð5Þ
Figure 2 shows the time evolution of the reactant and prod-
ucts at 200 ꢁC. It indicates that the hydrothermal reaction of
CH2Cl2 is composed of the three steps. The concentration of
CH2Cl2 is kept constant at the saturated concentration of
220 mM up to 90 min; the total amount of CH2Cl2 added corre-
sponds to 1 M. The concentration of CH2(OH)2 increases with
time up to 70 min through the dechlorination of CH2Cl2 as fol-
lows:5,6
References
1
2
3
M. Nakahara, T. Tennoh, C. Wakai, E. Fujita, and H. Enomoto, Chem.
Lett., 1997, 163.
Y. Tsujino, C. Wakai, N. Matubayasi, and M. Nakahara, Chem. Lett.,
1999, 287.
Y. Nagai, C. Wakai, N. Matubayasi, and M. Nakahara, Chem. Lett.,
32, 310 (2003).
P. E. Savage, Chem. Rev., 99, 603 (1999), and cited there in.
Y. Yamasaki, H. Enomoto, N. Yamasaki, and N. Nakahara, Chem.
Lett., 1999, 83.
CH2Cl2 þ 2H2O ! CH2(OH)2 þ 2HCl:
ð1Þ
With increasing CH2(OH)2, the total carbon concentration also
increases because the reactant is initially added in excess of
the ambient solubility. Methanediol is active in hot water and re-
acts with itself even in the neutral or acidic condition
through2,3,5,6
4
5
6
7
Y. Yamasaki, H. Enomoto, N. Yamasaki, and M. Nakahara, Bull.
Chem. Soc. Jpn., 73, 2687 (2000).
M. Nakahara, C. Wakai, Y. Tsujino, and N. Matubayasi, in ‘‘Steam,
Water, and Hydrothermal Systems: Physics and Chemistry Meeting
the Needs of Industry,’’ ed. by P. R. Tremaine, D. E. Irish, and
P. V. Balakrishnan, NRC Press, Ottawa (2000), p 456.
J. H. Van Ness, in ‘‘Concise Encyclopedia of Chemical Technology,’’
3rd ed., ed. by M. Grayson, Wiley-Interscience, New York (1985),
p 631.
2CH2(OH)2 ! CH3OH þ HCOOH þ H2O:
ð2Þ
Methanol and formic acid were observed at 30 min and over. The
concentrations of CH3OH and HCOOH are almost the same up
to 70 min according to the stoichiometry of Eq. 2. After that,
CH3Cl was observed. As seen in Figure 2, the time dependence
of CH3Cl is very similar to that of CH3OH. CH3OH becomes at
equilibrium with CH3Cl under acidic condition by
8
9
J. S. Lee, J. C. Kim, and Y. G. Kim, Appl. Catal., 57, 1 (1990), and
cited there in.
Published on the web (Advance View) February 14, 2004; DOI 10.1246/cl.2004.302