Synthesis and thermal decomposition of zinc phthalate

Article abstract of DOI:10.1016/s0040-6031(99)00302-0

Zinc phthalate was synthesized by the rheological phase reaction method, and the crystal structure was determined. Its thermal decomposition in argon was investigated. The thermal decomposition products were characterized by IR, XRD and GC-MS methods. Benzophenone, anthraquinone and nanoscale zinc oxide were chiefly obtained when zinc phthalate was pyrolyzed at 400-450°C in argon atmosphere. The free radical reaction mechanism of zinc phthalate in the thermal decomposition process was proposed. Fresh nanoscale ZnO plays a role as catalyst for the forming of benzophenone and anthraquinone.

Full text of DOI:10.1016/s0040-6031(99)00302-0

Thermochimica Acta 343 (2000) 105±109
Synthesis and thermal decomposition of zinc phthalate
Jutang Sun, Liangjie Yuan, Keli Zhang*, Dongli Wang
Department of Chemistry, Wuhan University, Wuhan 430072, China
Received 5 July 1999; received in revised form 9 August 1999; accepted 17 August 1999
Abstract
Zinc phthalate was synthesized by the rheological phase reaction method, and the crystal structure was determined. Its
thermal decomposition in argon was investigated. The thermal decomposition products were characterized by IR, XRD and
GC±MS methods. Benzophenone, anthraquinone and nanoscale zinc oxide were chie¯y obtained when zinc phthalate was
pyrolyzed at 400±4508C in argon atmosphere. The free radical reaction mechanism of zinc phthalate in the thermal
decomposition process was proposed. Fresh nanoscale ZnO plays a role as catalyst for the forming of benzophenone and
anthraquinone. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structure; Phthalate; Rheological phase reaction; Thermal decomposition; Zinc
1. Introduction
In this paper, zinc phthalate was synthesized by the
rheological phase reaction method. The thermal
decomposition reaction mechanism is investigated
in inert atmosphere. The products of thermal decom-
position are characterized. It is expected to obtain a
new path of synthesizing anthraquinone.
The thermal behaviour of transition metal and rare
earth phthalates in air has been reported [1±5].
Brzyska et al. [6] have investigated the thermal
decomposition of zinc phthalate hydrate in air. The
thermal decomposition of the zinc phthalate hydrate
proceeded in two stages. In the ®rst step crystal water
was lost to yield anhydrous salt, then the anhydrous
salt was decomposed to zinc oxide in the second step.
However, no other detailed study has been reported on
the thermal decomposition reaction mechanism of
zinc phthalate in inert atmosphere. In our previous
works, xanthenone and dibenzofuran were obtained
by thermal decomposition of zinc monosalicylate in
argon. From the point of view of structure and com-
ponent, ZnC6H4(CO2)2 can be pyrolyzed accompany-
ing a decarboxylation to form the free radical
ÁC6H4(CO)Á and to assemble to anthraquinone.
The rheological phase reaction method is a process
of preparing compounds or materials from a solid±
liquid rheological mixture. The solid reactants were
fully mixed in the proper molar ratio, and made up by
adding a proper amount of water or other solvents to a
solid±liquid rheological body in which the solid par-
ticles and liquid substance were uniformly distributed.
After reaction under suitable experimental conditions
the product was obtained. There are many advantages
in the rheological phase system: the surface area of
solid particle can be ef®ciently utilized, the contact
between solid particle and ¯uid is close and uniform,
heat exchange is very good, local overheating can be
avoided, and the reaction temperature is easy to con-
trol. In addition, many substances exhibit new reaction
properties in this state.
* Corresponding author.
E-mail address: jtsun@whu.edu.cn (K. Zhang).
0040-6031/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ( 9 9 ) 0 0 3 0 2 - 0

106
J. Sun et al. / Thermochimica Acta 343 (2000) 105±109
2. Experimental
The collection of pyrolysis products: The sample
(2 g) was pyrolyzed by employing the apparatus
shown in the literature [7] in argon (¯ow rate
100 ml min 1) at 4508C for 7 h, and the condensate
of gas phase products was collected. Carbon dioxide
was determined with Ca(OH)2 solution.
Preparation of samples: The phthalic acid and zinc
oxide are of analytical reagent grade. The phthalic
acid and zinc oxide were fully mixed by grinding in
1 : 1 molar ratio, a proper amount of water was added,
and prepared to the solid±liquid rheological state
(semisolid state). Then the mixture was reacted for
2 h at 80±908C. Anhydrous zinc phthalate, ZnPht
[Pht ˆ C6H4(CO2)2], was obtained by drying at
1208C.
The contents of C, H and Zn were determined with a
Perkin-Elmer 240B analyzer and by the use of EDTA
titration, respectively. Elemental analysis found (cal-
culated): Zn 28.40 (28.49), C 41.96 (41.87), H 1.65
(1.76) %.
The GC±MS analysis was carried out with a VG
7070E-HF gas chromatography±mass spectrometer
(GC±MS), Beijing KYKY GC/MS-DS2 computer
data system, HP 5790A gas chromatograph and
OV1701 elastic quartz capillary column (0.32 mm
in inside diameter and 30 m in length). Gas chroma-
tography: the carrier gas was He, pre-column pressure
880 kPa, starting temperature 808C, heating rate
88C min 1, ®nal temperature 2808C, gasi®cation tem-
perature 2908C. Mass spectrometry: ionization man-
ner was EI, ion source temperature 2008C,
accelerating voltage 6 kV, electron energy 70 eV,
scanning range 45±800 m/z.
The infrared spectra of the samples in KBr pellets
were measured on a Nicolet 550 FT-IR spectrometer
in the range 4000±400 cm 1. The X-ray diffraction
patterns were obtained with a Rigaku D/MAX-
RA model X-ray diffractometer with a Ni-®lter and
graphite monochromator, and Cu Kꢀ radiation
3. Results and discussion
1
(ꢁ ˆ 0.15405 nm). The TG and DTA (5.1±9.8 mg
sample) curves of ZnPht were recorded with a Shi-
madzu DT-40 thermal analyzer in argon (¯ow rate
The powder X-ray diffraction data of ZnPht are
listed in Table 1. The result indicated that the crystal
structure of ZnPht is monoclinic, the calculated lattice
parameters are a ˆ 1.1048 Æ 0.0001, b ˆ 2.0057 Æ
1
40 ml min 1) at a heating rate of 208C min from
room temperature to 9008C.
Table 1
Powder X-ray diffraction data of ZnPhta
2ꢂ (deg)
dexpt (nm)
I/I1
dcalc (nm)
h
k
l
2ꢂ (deg)
dexpt (nm)
I/I1
dcalc (nm)
h
k
l
8.02
8.80
9.12
1.1014
1.0040
0.9688
100
20
1.1011
1.0029
0.9688
0.9652
0.7098
0.6994
0.6686
0.5505
0.5503
0.5309
0.5017
0.4844
0.4708
0.4626
0.4305
0.4162
0.4075
1
0
0
1
1
1
0
2
0
2
1
0
0
2
1
1
1
0
2
0
1
1
0
3
0
3
1
3
0
1
0
0
2
4
0
0
1
0
1
1
0
0
1
0
1
2
2
1
2
2
1
23.35
23.75
24.25
26.35
26.80
27.60
28.45
29.20
0.3806
0.3743
0.3667
0.3379
0.3324
0.3229
0.3135
0.3056
1
1
0.3804
0.3728
0.3670
0.3379
0.3329
0.3229
0.3131
0.3059
0.3048
0.2757
0.2753
0.2507
0.2504
0.2345
0.2265
0.2259
2
2
3
1
3
0
1
1
3
2
4
0
2
2
1
3
3
1
0
4
2
0
1
6
0
5
0
8
4
5
3
7
1
2
0
2
1
3
3
1
2
2
0
0
3
3
4
0
33
5
1
12.55
0.7047
1
1
< 1
2
13.25
16.10
0.6676
0.5500
3
1
< 1
16.60
17.65
18.30
18.85
19.25
20.70
21.40
21.75
0.5336
0.5021
0.4844
0.4704
0.4607
0.4287
0.4149
0.4083
1
32.45
35.82
0.2757
0.2505
< 1
1
< 1
6
11
< 1
2
38.35
39.80
0.2345
0.2263
< 1
1
2
2
a Monoclinic: a ˆ 1.1048, b ˆ 2.0057, c ˆ 0.9720 nm, ꢃ ˆ 94.718, V ˆ 2.1467 nm3.

J. Sun et al. / Thermochimica Acta 343 (2000) 105±109
107
(64.12%) at 4708C agreed with a calculated value
(64.54%) according to
ZnC8H4O4 ‡ 7:5O2 ˆ ZnO ‡ 8CO2 ‡ 2H2O
(1)
In argon atmosphere, ZnPht was decomposed
rapidly at 3758C. The mass loss is 48.85% at 375±
5158C, the solid residue was a black powder of zinc
oxide and carbon.
When ZnPht was decomposed at 4508C in argon,
CO2 was detected in the gas products by means of a
chemical method. The condensate of the gas phase
products is dark brown and sticky oily matter. The
results of GC±MS analysis are presented in Table 2.
The main products were benzophenone and anthra-
quinone. In addition, small amounts of diphenyl,
diphenylmethane, ¯uorene, ¯uorenone, triphenyl-
methane and 9-phenyl ¯uorene had been detected.
The infrared spectrum (Fig. 3) of light yellow crystals
separated from the condensate of the gas phase is
consistent with the standard IR spectrum of anthra-
quinone (Sadtler No. 297 K).
The powder X-ray diffraction data of the solid
residues are listed in Table 3. The re¯ections are in
agreement with zinc oxide of hexagonal wurtzite
structure (JCPDS card 5-0664). The lattice parameters
were slightly enlarged, with values of a ˆ 0.325,
c ˆ 0.523 nm and V ˆ 0.0478 nm3. By calculating
with line-width method, the particle size of zinc oxide
is about 5±10 nm.
Fig. 1. TG and DTA curves of ZnPht in air.
0.0001, c ˆ 0.9720 Æ 0.0001 nm, ꢃ ˆ 94.71 Æ 0.018,
V ˆ 2.1467 nm3. The intensity of strongest diffraction
peak in (100) plane (Table 1) is about three times that
of the second strongest peak. It indicates that the
structure of zinc phthalate is layered, zinc ions located
in the (100) plane and the benzene ring is situated on
two sides of the zinc ion plane.
Figs. 1 and 2 show the TG and DTA curves of ZnPht
in air and argon. ZnPht is stable below 3408C in air. On
the DTA curve, a strong exothermic peak is observed
at 4338C, which shows that decomposition and oxida-
tion reaction of ZnPht occurred in air. The mass loss
The above results revealed the thermal decomposi-
tion mechanism as follows:
During the thermal decomposition of zinc phtha-
late, the fracture of bonds occurred chie¯y in accor-
dance with Eqs. (2) and (3), to form the free radicals
ÁC6H4C(O)Á and :C6H4. Two ÁC6H4C(O)Á were reacted
to anthraquinone (see Eq. (4)).
(2)
Fig. 2. TG curve of ZnPht in argon.
(3)

108
J. Sun et al. / Thermochimica Acta 343 (2000) 105±109
Table 2
GC±MS results of condensate of gas phase products for the thermal decomposition of ZnPht at 4508C in argon
No.
Retention time (min)
Molecular weight
Compound
Peak area (%)
1
2
3
4
5
7
8
9
14.525
15.410
18.039
18.758
20.363
23.558
23.932
25.592
154
168
166
182
180
208
244
242
Diphenyl
Diphenylmethane
Fluorene
1.6
1.5
0.4
Benzophenone
Fluorenone
40.5
0.6
9,10-Anthraquinone
Triphenylmethane
9-Phenylfluorene
48.2
2.4
4.8
Fig. 3. The IR spectrum of thermal decomposition product (9,10-anthraquanone) of ZnPht at 4508C in argon.
Table 3
The powder X-ray diffraction data of ZnO from thermal decomposition of ZnPht at 4508C in argona
2ꢂ (deg)
dexpt (nm)
I/I1
Half-peak
dcalc (nm)
h
k
l
Grain size
breadth (deg)
(?hkl) (nm)
31.70
34.20
36.15
47.40
56.60
62.70
67.90
0.2820
0.2620
0.2483
0.1916
0.1625
0.1480
0.1379
83
100
92
9
1.0
1.8
1.3
1.4
1.0
1.4
1.4
0.2815
0.2615
0.2478
0.1916
0.1625
0.1482
0.138
1
0
1
1
1
1
1
0
0
0
0
1
0
1
0
2
1
2
0
3
2
9.2
5.1
7.1
6.9
47
11
30
10.0
7.4
7.6
a Hexagonal: a ˆ 0.325, c ˆ 0.523 nm.
to Eqs. (6) and (7), to produce C6H5C(O)Á and ÁC6H5,
and then benzophenone was obtained by Eq. (8).
(4)
: C6H4 ! 6C ‡ 4H
(5)
(6)
A part of :C6H4 was dehydrogenated easily to
elemental C (Eq. (5)). At the same time, the
ÁC6H4C(O)Á and :C6H4 were hydrogenated according
: C6H4 ‡ H ! ÁC6H5
(7)

J. Sun et al. / Thermochimica Acta 343 (2000) 105±109
109
reaction can be exactly controlled, the formations of
by-products can be avoided.
(8)
The presence of diphenyl and ¯uorenone in the
products proved further the formations of free radicals
described above.
Acknowledgements
This work was supported by The National Natural
Science Foundation of China.
2 Á C6H5 ! C6H5C6H5
(9)
References
(10)
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suggests that free radicals did not enter the gas phase,
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none proceeded on the surface of solid products. Fresh
nanoscale ZnO possesses probably very high catalytic
activity for the formation of anthraquinone and ben-
zophenone. If the condition of thermal decomposition
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