482 Xue et al.
Asian J. Chem.
emptied after passing through the water, sodium bicarbonate
solution and concentrated sodium hydroxide solution.
The samples were gas chromatography analyzed as esters
using ethanol as esterification agent for the samples were
corrosive solutions. Then, the reaction yield was obtained by
computation.
onic anhydride was added 20 mol % of the propionic acid and
the promotive catalyst was added 0.1 g. In the presence of a
slight excess of chlorine, the effects of different types of Lewis
acid promotive catalysts and no promotive catalyst on the chlori-
nation of propionic acid were studied respectively.
The experimental results obtained with different promotive
effects on promotive catalytic activity selectivity with reaction
are depicted in Table-1. The experiments revealed that when
98 % H2SO4, FeCl3, FeCl3.6H2O, FeCl3/C and SbCl3 were
added in the chlorination reaction solution, the content of main
product α-monochloropropionic acid all increased. The results
showed that the 98 % H2SO4 got the best promotive effect, the
FeCl3 was second and the FeCl3·6H2O, FeCl3/C, SbCl3 also
demonstrate certain promotive effect. In the presence of 0.1 g
98 % H2SO4, the content of α-monochloropropionic acid
reached 91.08 % after 2.5 h. However, the activated carbon
got poor promotive catalytic activity and weak selectivity.
The experimental results obtained with different acids
effects on promotive catalytic activity selectivity are depicted
in Fig. 1. The results from our investigations are summarized
that a higher reaction rate was obtained with the addition of
98 % H2SO4, because the chlorination reaction is an acid-
catalyzed reaction. The reaction system got a raised acidity,
the reaction direction toward the positive reaction and the
reaction time was shortened at the same time. However, as a
porous material the activated carbon had no promotive catalytic
activity in the reaction system. This can be explained that the
acid-catalyzed enolization is the rate determining step in the
chlorination reaction and the activated carbon has no acidity.
Meanwhile, the byproduct α,α-dichloropropionic acid increased
due to chlorine adsorbed on the surface or pore structure of
activated carbon and caused deep chlorination. In the presence
of crystal water, FeCl3·6H2O would cause the main catalyst
propionic anhydride part decomposed, which is equivalent to
reducing the amount of the catalyst. Thereby, the catalysis
effect was lower than that of FeCl3. The catalysis activity of
SbCl3 was also lower than FeCl3, because Sb3+ has a larger
atomic radius than Fe atom and the ability of Sb3+ combining
with propionyl chloride is lower than Fe3+. SbCl3 is disadvanta-
geous to the improvement of the competitiveness of the product
for the high cost. So the promotive effect focused on 98 %
H2SO4 and FeCl3.
Preparation of promotive catalyst FeCl3/C: A solution
of FeCl3·6H2O (100 g) and activated carbon powder (50 g) in
ethanol (25 mL) was refluxed for 0.5 h at 80 ºC.After comple-
tion of the reaction, the product was filtrated and successively
washed with ethanol until the product became colourless. Then,
the product was filtered and activated in an oven for 2 h at
120 ºC, the product was taken in the dryer in the end of the
experiment9-12
.
Gas-chromatography analysis: In this paper, the corrected
area normalization method was used for the quantitative analysis,
the formula is as following:
FWi ×Ai ×100
W % =
i
ΣFWi ×Ai
In the formula: Wi % = the quality ratio of i component acid;
Fwi = the quality correction factor of i component acid; Ai =
the chromatographic peak area of i component acid.
Infrared spectroscopic analysis: Potassium bromide
semi-quantitative table method was used for infrared spectro-
scopic analysis. Due to the strong corrosion of α-monochloro-
propionic acid, so the best way to determine α-monochloropro-
pionic acid is to get it spreaded on KBr.
The group peak positions of sample (a) and α-chloropionic
acid (b) are identical. The stretching vibration peak of C-Cl
bond is observed at 700 cm-1.Another stretching vibration peak
at 1750 cm-1 is assigned to be acid monomer of C=O. Two
absorption peaks at 1440 and 920 cm-1, which are relatively
strong and wide, are bending vibration absorption peak due to
the -OH group of carboxylic acid. The stretching vibration
peak of methyl is at 2960 cm-1. The peak at 3000 cm-1, which
is wide and scattered, is the stretching vibration absorption
peak of O-H. Therefore, it was considered that the main product
was α-monochloropropionic acid. It implies that the product
synthesized by chlorination is relatively high without any
impurity peak.
RESULTS AND DISCUSSION
Influence of 98 % H2SO4 on chlorination: The chlori-
nation reactions were carried out at 130 ºC, the addition of
propionic acid was 14.9 g, the propionic anhydride was added
20 mol % of the propionic acid and the chlorine feed was 40
mL/min. In the presence of a slight excess of chlorine, the
Effect of different types of Lewis acid promotive cata-
lysts on the chlorination of propionic acid: The effect of
different types of Lewis acid was investigated were performed
at 130 ºC using a propionic acid addition of 14.9 g. The propi-
TABLE-1
COMPARISON OF DIFFERENT PROMOTIVE EFFECTS ON PROMOTIVE ACTIVITY SELECTIVITY WITH REACTION 2.5 h
Reaction
time (h)
α-Monochloropropionic
α,α-Dichloropropionic
acid (%)
β-Monochloropropionic
acid (%)
Catalyst
CA (%)
acid (%)
87.29
91.08
90.64
89.71
88.68
88.02
68.23
Blank
2.5
2.5
2.5
2.5
2.5
2.5
2.5
8.12
5.05
4.26
1.76
6.42
2.23
17.28
1.82
2.77
98 % H2SO4 (0.1 g)
FeCl3 (0.1 g)
2.01
1.76
2.19
2.91
FeCl3·6H2O (0.1 g)
FeCl3/C (0.1 g)
4.64
3.89
2.38
2.52
SbCl3 (0.1 g)
5.13
4.52
Activated carbon (0.1 g)
10.47
4.02
Note: The above percentage is the percentage of quality