326 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 326^327y
Cyclodehydration of Some 1,n-Diols Catalysed by
Sulfated Zirconiay
Anil Wali and S. Muthukumaru Pillai*
Research Centre, Indian Petrochemicals Corporation Limited, Vadodara-391 346, India
Sulfated zirconia, a solid acid, is found to be a good catalyst in the cyclodehydration of several diols.
Cyclodehydration of diols is a useful method to obtain oxygen
heterocycles. In particular, the cyclodehydration of
butane-1,4-diol to tetrahydrofuran (THF) and of diethylene
glycol (DEG) to 1,4-dioxane are industrially important
reactions. Such reactions of diols are e¡ected in the liquid
or gas phase using mineral and organic acids,1 calcium
phosphate,2 HMPT,3 clay,4 alumina,5 PPh3 CCl4,6 Na¢on,7
etc. We have earlier reported the e¤cacy of group IV metal
halides and metallocenes8 and of H-ZSM59 in such
cyclodehydration reactions.
Some properties of the catalysts are given in Table 2.10 It
was of interest, to compare the catalytic features of
SO4 =ZrO2 with those of H-ZSM59 as both exhibit acidic
2
character.
Accordingly,
DEG
was
subjected
to
2
cyclodehydration over SO4 =ZrO2 at 200 8C similarly to
H-ZSM-5 (Table 3). While SO4 =ZrO2 could be easily
2
recycled six times, cyclodehydration over H-ZSM-5 did not
extend beyond the second cycle after 4 h. The results as
2
evident from Table 3 suggest that SO4 =ZrO2 is more
effective in the selective cyclodehydration of DEG to
1,4-dioxane. The relative ef®ciency of some catalyst systems
in the cyclodehydration of DEG to 1,4-dioxane is shown in
Herein, we report our results on the use of sulfated zir-
2
conia ꢀSO4 =ZrO2 in such reactions. The catalytic features
2
of H-ZSM5 and SO4 =ZrO2 are also compared. As is evi-
Table 4 which includes results with Na®on-H. The
dent from Table 1 butane-1,4-diol and pentane-1,5-diol furnish
the respective cyclic ethers, e.g. tetrahydrofuran and
tetrahydropyran in respectable conversion and high
selectivity. However, hexane-1,6-diol yields a mixture of
oxepine, tetrahydro-2-methyl-2H-pyran, 4-methyl-1-penten-
3-ol, hexenols and dienes in the proportion of 43:15:23:16:3.
Cyclohexane-1,4-diol also reacts similarly to give a mixture
of products that include oxabicylo[2.2.1]heptane and
cyclohexadienes. Both diethylene glycol (DEG) and
triethylene glycol (TEG) react to give 1,4-dioxane. TEG fur-
nishes 1,4-dioxane in 73.5% selectivity at 47% diol conversion.
The conversion of TEG to 1,4-dioxane may involve the
cyclodehydration of diols involves the Bronsted acid
sites of the catalyst.9 For hexane-1,6-diol and
cyclohexane-1,4-diol, 1,2-elimination appears to be respon-
sible for the formation of unsaturated alcohols and ole®ns
in the product mixtures. This alludes to the interaction of
both the OH groups of the diol with the catalyst surface in
the cyclodehydration mechanism. Interestingly, when
hexan-1-ol and cyclohexanol were similarly reacted over
2
SO4 =ZrO2, the former did not react even at 150 8C
whereas the latter was dehydrated to give a moderate
amount of cyclohexene. This shows that secondary hydroxy
group facilitates 1,2-elimination in cyclohexanol and
2
Ta b l e 1 Cyclodehydration of diols over SO4 =ZrO2 (catalyst : diol 1 : 25 w/w)
Entry
Substrate
t/min
T/ 8C
Conv.a(%)
Selectivityb
Yieldc(%)
Product(s)
1
2
3
4
Butane-1,4-diol
Pentane-1,5-diol
Hexane-1,6-diol
DEG (first cycle)
(av. three cycles)
Cyclohexane-1,4-diol
TEG
60
85
60
120
270
60
130
155
175
180
180
145
180
74
93
55
83
85
79
47
96
94
0.22
0.24
THF
THP
Mixtured
1,4-Dioxane
1,4-Dioxane
Mixturee
1,4-Dioxane
89.5
84.5
0.19
0.5
5
6
85
73.5
0.08
a Conversion of diol (total diol unreacted diol/total diol)Â 100. b Selectivity of product (moles of product obtained/moles of diol
converted) Â 100. c Yield of product (moles of product formed/weight of catalyst in g). d Oxepine, 2-methyl-2H-pyran,
4-methylpent-1-en-3-ol, hexenols, hexadienes. e Oxabicyclo[2.2.1]heptane, cyclohexadienes.
scission of TEG to 1,4-dioxane and ethylene glycol (EG)
and EG thus formed would react with another molecule
of TEG to give higher oligomers.9
Ta b l e 2 Properties of catalysts
Surface area/ Pore volume/ Density/ Aciditya=
1
1
3
1
Catalyst
m2 g
cm3 g
g cm
mol g
The reusability of this catalyst was examined for the
cyclodehydration of DEG with fresh DEG added to the
reaction £ask after completion of the ¢rst cycle. Three cycles
were carried out at 180 8C (Table 1). The DEG conversion
and 1,4-dioxane selectivity after the ®rst cycle were 83 and
89.5% while for the three cycles on average, values were 85
and 84.5%, respectively. At 200 8C (Table 3) the yield of
1,4-dioxane was higher than that obtained at 180 8C.
2
4
SO4 =ZrO2 16.8
8.76
1.24
0.8
9:48 Â 10
4
H-ZSM5
310
3:9 Â 10
a Determined by NH3 adsorption method. b Si=Al 40.
2
Ta b l e 3 Cyclodehydration of DEG over H-ZSM5 and SO4 =ZrO2
at 200 8C
2
H-ZSM5
SO4 =ZrO2
No of cycles
Total run time/h
1
4
6
4
* To receive any correspondence ( e-mail: ipcl@giasbm01.vsnl.net.in).
y IPCL Communication No. 337. This is a Short Paper as de¢ned in
the Instructions for Authors, Section 5.0 [see J. Chem. Research
(S), 1999, Issue 1]; there is therefore no corresponding material
in J. Chem. Research (M).
Total DEG conversion
1,4-Dioxane selectivity
Yield of 1,4-dioxane
(mole/g of catalyst)
63
67
0.16
86
85
0.82
Wali, Anil
