- Email: [email protected]
The molybdenum(V) complexes as the homogeneous and heterogenized catalysts in epoxidation reactions of olefins with the organic hydroperoxides
Journal of Molecular Catalysis, 3 (1977/78) 165 - 172 0 Elsevier Sequoia S-A., Lausanne -Printed in the Netherlands
THE MOLYBDENUM(V) COMPLEXES AS THE HOMOGENEOUS HETEROGENIZED CATALYSTS IN EPOXID,4TION REACTIONS OLEFINS WITH THE ORGANIC HYDROPEROXIDES
J. SOBCZAK Institute (Poland)
165
AND OF
and J. J_ ZI6EKOWSKI
of Chemistry,
University
of Wrodaw.
50 - 383 Wrocizzw. 14, Joliot-Curie
Street
Summary The catalytic properties of new MO(V) complexes with ligands such as ethylene gIyco1, lactic acid and amygdahc acid in homogeneous systems, as well as the properties of the heterogenized catalysts obtained in the ionic exchange reaction of the complex Naz[MoaO,(OX)z(HzO)a] -3HzO with Caste1 A-5OOp, Dowex 1X8, and Wofatit AD-41 anionites, were examined. The catalysts obtained are active in epoxidation reactions of olefins with organic hydroperoxides. The structure of the heterogenized catalysts is discussed, the catalyst changes during the epoxidation reaction are interpreted, and the correlation between the structure and reactivity of the homogeneous and heterogenized catalysts is considered on the basis of the i-r_ spectra-
Introduction Both the practicaI and theoretical aspects of the epoxidation reactions of olefins with organic hydroperoxides aroused great interest in studies on new catalytic systems for this process. Molybdenum complex compounds in the homogeneous phase are usually used as catalysts [l] _ Catalysts based upon molybdenum trioxide deposited on silica gel are examples of new heterogeneous catalytic systems [2 - 4]_ Synthesis of the heterogenized catalysts [5] was really progressive in the search for new catalytic systems. A polymeric catalyst supported on Amberlite IRA-45 anionite, modified by molybdenum hexacarbonyl is a good example- Its catalytic activity in the epoxidation reaction of propylene by the tert-butyl hydroperoxide is analogous to that of Mo(CO)s in the homogeneous phase [6] _ The homogeneous catalysts could be deposited on the appropriate carriers in several ways [‘I] . One of these methods is that of ionic exchange_ In this way we have obtained heterogenized catalysts by attachment of the [Mo&~(OX)&&O)~]~complex ion to one of the following anionites: Caste1 A-5OOp, Dowex 1X8 or Wofatit AD-41.
166
Experimental Cyclohexene (Fluka AG, Buchs S6) was distilled before use. Cumene hydroperoxide, approximately 70% in cumene (Suchardt, Munchen) Ethylene glycol, lactic and amygdahc acids, (POCh, Gliwice). MoO(OHs was prepared by a standard method as previously outlined IS]. Hs[MosO,(OX)a(H20)a] -3HaO was prepared by our own method [9] _ Preparation of the molybdenum(V) complexes Sodium-~-dioxo-bis(aquooxooxaZatooxomoiy~date(V)I 1Mo.zQ4(Ox)2(H.&).zI
3-hydrate
Nar
- 3Hz?o
To the H,[Mo~O~(OX),(H~O)~] - 3HsO complex dissolved in hot water, aqueous BaCls solution was added dropwise. The precipitated dark-red barium salt was filtered off, washed with acetone, and dried. An equimolar amount of an aqueous solution of sodium sulphate was then added dropwise to the hot, water slurry of the barium salt, Ba[MozO,(OX)z(HzO),l] -3HzO_ The barium suIphate precipitate was filtered off, and the sodium salt of the MO(V) complex was obtained under vacuum from the dark-red aqueous solution. The product was recrystallized from water-acetone solutionFound: C, 9-4; H, 2.2; MO, 32_9_ C&IIaMo201,Na2 requires C, S-45; H, 1.77; MO, 33.78%.
H,CMO~O~(C~H~O~)~(H~O)~I -2H20
0.02 Mol molybdenum(V) hydroxide, MoO(OH)s, was added to a 0.02 mol solution of ethylene glycol, under a neutral atmosphere. The solution was stirred vigorously and heated on a water bath. After the molybdenum(V) hydroxide had completeIy dissolved, the solution was evaporated under vacuum. The brown compound was crystallized from waterethanol solutionFound: C, 11.5; H, 3.0; MO, 42.7. C~H&Io2012 requires: C, 10.67; H, 4.03; MO, 42.64%_ Molybdenum/V) complex with lactic acid 0.055 Mol of molybdenum(V) hydroxide was dissolved
in 0.055 mol of an aqueous solution of lactic acid under the same conditions as above. Evaporation of the solution under vacuum produced a brown-green compound which was recrystallized from ethanol_ Found: C, 18-7; H, 3.8; MO, 34.4%. Molybdenum(V)
complex
with amygdaiic
acid
Ha[Mo204(C&&HOH-COO)4(H20)2] was obtained by dissolving MoO(OH)s in an aqueous solution of amygdalic acid. The brown-grey complex was crystallixed from ethanol-benzene solution_ Found: C, 435; H, 41; MO, 22.3, Cs2Hs.@0201s requires: C, 42.77; H, 3.81; MO, 21.96%. Synthesis The
of the heterogenized
heterogenixed
NazCModMOJQ&-W)2l-
catalysts
catalysts 3H~0
were obtained by ionic exchange of the complex and Na2Mo04 in aqueous solution,
167 TABLE
1
Concentration the anionites
of CMO~O~(OX)~(H~O)]~-
complex
Concentration
Anionite
ion and MoO+~-
of the complex
CMoz0&=)2U-C@)zl
2-
ion supported
in mole/g
anionite
1.34
Dowex
1x8
1.05
-
Wofatit
Ad-4 1
1.79
1.71
Epoxidation
x lo3
Mo042-
Caste1 A-500~
with the appropriate anionites. The concentrations appropriate anionites are given in Table l_
on
of the complexes
on the
reactions
Epoxidation was carried out, under nitrogen or argon atmosphere, in a system containing olefin, hydroperoxide, catalyst and a soIvent_ Reactions in homogeneous systems were studied using the apparatus described in ref_ [l] _ The heterogenized systems were examined in a thermostated glass reactor fitted with a porous glass filter (Gl) and with reflux. The reactor contents were mixed by passing argon in a closed circuit through the porous glass filter using a microdosing pump. Analysis
The reaction products were analysed as reported in ref. [l] _ The i.r_ spectra were recorded on a Perkin-Elmer Model 621 and Perkin Eimer 180 for the ranges 200 - 4 000 cm-l and 40 - 400 cm-‘, respectivelyResults We have described already the molybdenum(V) complexes with dicarboxylic acids and their cataIytic properties in the epoxidation reactions of oIefins [9] _ We now report some data obtained for the new homogeneous catalysts, their activity being examined in a model epoxidation reaction of cyclohexene with cumene hydroperoxide. The results for the molybdenum(V) complex with ethylene glycol and with lactic and amygdalic acids are shown in Table 2. The heterogenized catalysts were obtained by deposition of the [Mo20d(OX)2(H20)2]2complex ion on anionites, (Caste1 A-5OOp, Dowex 1X8 and Wofatit AD-41)_ For each anion& the total exchange capacity was attained_ Physicochemical examination of the heterogenized catalysts was limited to the analysis of their infrared spectra over the range 40 - 4 000 cm-‘. Consideration of the absorption bands arising from the exchanged anionites revealed that the spectrum of the deposited complex ion changed onIy slightly (Table 3)
TABLE
2
Epoxidation
of cyclohexene
with cumene
hydroperoxide
in trichloroethylene
at 85 OC*
Conversion of cumene hydroperoxide (%)
Conversion of cyclohexene
H2CMozO~(C,H,O2),(HZo)21-2H2O
54.2
96-7
87-6
84.7
MO(V)
57.8
97.2
87.9
85.5
56-S
88.7
75-5
66-9
Catalyst
+ lactic acid
H2[Mo204(C,H,CHOHCOO)4(H20)2]
Selectivity** (%)
Reaction yield (%)
(%I
*Reaction carried out under nitrogen atmosphere for 200 min, at cyciohexene: cumene hydroperoxider catalyst = 1 T 2 I O-002 molar ratio**Reaction
TABLE Some
selectivity
to epoxide,
calculated
according
to cyclohexene
used.
3 frequencies
observed
M[MO204(OX)2@320)21-=20*
160m
in i-r_ spectra
of the heterogenized
cataiysts
2-
CMo204(OX),(H,O),l ion on Caste1 A-500~ and Dowex 1x8 anionites
ion on Wofatit AD-41 anionite
-
-
-
260s
265w,sh/265m**
265w,sh
308m
305s
304s
795m
785s,sh;
950m,sh
955s
975s
965m,sh;
795s
785s,sh,
985w,sh
Frequency assignment
795s
a(OCO)
940m,sh
m(H20)
955s
vas(Mo0)
1280m
1280~~
1280m
vs(C0)
1415vs
1370s
1395s
UC021
*RI = Hz, Nan, Ba. **Observed for complex
ion on the Dowex
1X8
+ S(OC0)
anionite.
The reactivity of the heterogenized catalysts obtained was examined in the model epoxidation reaction of cyclohexene with cumene hydroperoxide at the following reagent concentrations: cyclohexene, 2.75 mol/l; cumene hydroperoxide, 1.25 moI/I; catalyst, 2-4 X 10e2 mol of a complex attached to the anionite/I. The reaction was carried out in trichloroethylene, under argon atmosphere, at 85 “C for 4 h. The results are given in Table 4. The catalytic activity of the binuclear complexes of the [Mo~O~(A-A)~(H~O)~]~type (A-A = chelating ligand) was confirmed by the eIectronic and crystal structures [l] _ The catalytic activity of such catalysts is changed after the complex ion is grafted on anionites, by comparison with the homogeneous
169
TABLE 4 Catalytic activity of [Mo~O~(OX)~(H~O)~]~-
-Ion in homogeneous
and heterogenized
systems* Selectivity***
Reaction
(%)
(%)
94.5
78.6
74-3
Heterogenized system on carriers: Caste1 A-500~ Dowex 1x8 Wofatit AD-41 _ _ Wofatit AD-41:’ Wofatit AD-41 ’
78-7 31.8 54-l 92.9 91.0
54-5 40-5 67-S 61.8 70.9
42.9 12.9 63.8 57-4 64.5
Wofatit
40.4
68.9
27.8
Conversion of cumene hydroperoxide
Catalyst**
yield
(%) Homogeneous
AD-41
system’,?
+ MoOa=
*Reaction conditions -see text. **Naa[MoaO4(OX)a(H20)2] -3HaO_ ***Reaction selectivity to epoxide cakulated per hydroperoxide _iCatalyst concentration: 2 X lob3 mol of complex per liter_
“After
trifold use of a cataIyst.
used-
I
catalyst. The change depends on the functional groups and the anion& structure_ The MO(V) complex on Wofatit AD-41 containing the -N(CH3)2 type coordination centres, exhibits the higher catalytic activity_ The catalysts on the other carriers (Caste1 A-500p and Dowex 1X8) containing the -N(CH&Cl function groups are less active_ The changes in the catalytic activity of the complex ions fixed on various anionites are analogous to the rate of the water substitution reaction by pyridine in the system (Table 6):
The reaction was carried out in ampouies in trichloroethylene solution at 75 “C for 1 h. The data in Table 4 indicate the dependence of the activity of the heterogenized catalyst on the effect of a carrier on the water fixation mode in the [Mo~O~(OX)~(H~O)~]~complex ion, The anaIysis of the i-r_ spectra for the heterogenized cataIysts before and after the reaction reveaied essential and identical changes of the complex ion attached to the Caste1 A-500~ and Wofatit AD-41 anionites- No changes were observed for the complex ion fixed on the Dowex 1X8 anio&e (Table 5). Discussion The fixation of the [Mo~O,(OX)~(H~O)~]~complex ion on anionites has only a slight effect on the i-r_ spectrum_ The changes are usually reflected
170 TABLE
5
Changes in the i-r_ spectrum of the [Mo20.&OX)2(H20)2J2Caste1 A-500~ and Wofatit AD-41 anion&s after epoxidation
CMO&LZ(OX)~(H~~)~I2- deposited Caste1 A-500~ before reaction
-
Caste1 A-500~ Wofatit AD-41 after reaction
265w,sh 305s 735m 755s,sh 795s
-
955s 965m,sh 985w,sh 128Ovw *Observed **Observed
-
on anionites and
265s 3oow 377w* ,- 3sow** 735w,sh 785s 805m,sh** 900s 940m*; 940s”* 965w*;
985vw*
1265w,sh for the complex for the complex
complex ion fiied reaction
ion settled ion settled
Wofatit AD-4 1 before reaction
-
-
on the
Vibration assignment
265w,sh 304s
-
735m 785s,sh 795s 9oow 940m,sh 955s
v(Mo02Mo) -
1280m
w.332)
-
%&Moo) %,(CO)
+ 6 w32)
on the Caste1 A-5OOp_ on the Wofatit AD-41.
in the lack of the band at 160 cm-‘, the appearance of a new band (shoulder) at 785 cm-‘, and the shift of the bands at 975 cm-’ (v,, (Mo=O) vibrations) to the asymmetric vibrations of the carboxyl and 1415 cm-‘, corresponding group IlO] towards Iower frequencies_ The spectrum of the complex ion on the Dower 1X8 anionite after epoxidation reaction shows no changes, whereas the cata!ysts on the Caste1 A-500~ and Wofatit AD-41 anion&s give spectra with essential and identical changes after epoxidation reaction_ Generally, these changes occur in the vibration range characteristic for the Mo-0 bonding. Their analysis allowed us to suppose that the formation of new bands at 380,900 and 940 cm-’ indicated the formation of a cis-cEoxo (Mo=O) arrangement [ 111. The cumene hydroperoxide molecule is responsible for these changes. The i-r. investigations of the H2[Mo204(OX)2(H@)2 Me2C0, 4H& complex with cumene and terf-butyl hydroperoxide indicated the same spectrum changes as those observed for the catalysts heterogenized with the Castel A-500~ and Wofatit AD-41 anionites [12] _ According to the epoxidation reaction mechanism of olefins by organic hydroperoxides proposed by us [l] the hydroperoxide molecule coordinates to molybdenum(V) by substitution for water (Scheme I, step A). This interaction is responsible for the formation of the molybdenum complex with hydroperoxide (Structure II). Due to this the electrophilic properties of oxygen atoms become stronger, which, in turn, facilitates the further reaction with olefm (step B) to form the epoxid,. 0 It could not be excIuded that the attack of the subsequent hydroperoxide molecule (step C) may cause the breaking of the oxygen bridges. That would lead to the cz?+dioxo system
171 Scheme
1.
TABLE
6
Substitution of water by pyridine in the [Mo~O~(OX)a(HaO)21*complex ion supported on anionites* [Mo204(OX),(H20)2 on the anionites
J2- supported
21-5
Caste1 A-500~
5.0
Dowex
1x8
Wofatit
AD-41
*Reaction **Pyridine
Amount of substituted water (%)**
conditions adsorption
39.9 -see text. for each anionite
were considered.
(structure IV) indicated by the intensity decay of the band at 735 cm-‘. The epoxidation reaction could proceed also in the monomeric complexes and the activity of the organic hydroperoxide could be realized by the formation of structure IV. That modification of a catalyst is not followed by its removal from the carrier is shown by the facts that the post-reaction solutions were not catalytically active and the multiple application of a catalyst changed its activity only slightly (Table 4). The observed differences in catalytic activity of the heterogenized catalysts are consistent with the results of the water substitution reaction by pyridine in the ]Mo~O~(OX),(H~O)~]*complex ion deposited on anionites, This revealed the essential role of the water molecule coordinated to molyb-
172
denum in the reaction mechanism_ The activity of a catalyst is determined by its lability and accessibility (Table 6).
References 1 J_ Sobczak and J. J. Ziakowski, Inorg. Chim. Acta, 19 (1976) 15, and references cited therein_ 2 L. Cerveny, A. Morhoul and V_ Ruiicka, Chem_ Prum., 23 (1973) 17. 3 F. Trifiro, P. Fonatti and J. Pasquon, Catalysis: Heterogeneous and Homogeneous. Proc_ Id_ SympRelations between Heterogeneous and Homogeneous Catalytic Phenomena, Brussels, BeIgium October, 1974, Elsevier, Amsterdam, 1975, p_ 5094 K_ B_ Jacimirskij, V_ M. BeIousov, A_ P_ Filipov. L_ A_ OIin, S. B_ Grinenko, G_ A_ Konis’evskaja, G. A. Sachovceva and B. E_ Krasotkina, Dokl_ Akad_ Nauk SSSR, 224 (1975) 1369_ 5 J_ C. Bailar, Jr., Catal_ Rev. Sci., 10 (1974) 17. 6 S. Ivanov, R. Boeva and S_ Tanielyan, React. Kinet_ Catal_ Lett_. 5 (1976) 297. 7 V_ A_ Licholobov, B_ N_ Kuznecov and Yu_ J_ Sermakov, Symp. Supported Metal Complex Catalysts, Liblice. Czechoslovakia. April 28 - 30, 1975_ 8 W_ G_ Palmer, Experimental Inorganic Chemistry, Cambridge University Press, Cambridge, 1962, p_ 406. 3 J. Sobczak and J_ J. Zio&owski, J_ Less-Common Met_. 54 (1977) 149_ 10 P. C_ H_ Mitchell, J_ Inorg_ NucI_ Chcm_, 26 (1964) 1967_ 11 W_ P_ Griffith and T_ D_ Wilkins, J_ Chem_ Sot. A, (1965) 400. 12 Unpublished results.
THE MOLYBDENUM(V) COMPLEXES AS THE HOMOGENEOUS HETEROGENIZED CATALYSTS IN EPOXID,4TION REACTIONS OLEFINS WITH THE ORGANIC HYDROPEROXIDES
J. SOBCZAK Institute (Poland)
165
AND OF
and J. J_ ZI6EKOWSKI
of Chemistry,
University
of Wrodaw.
50 - 383 Wrocizzw. 14, Joliot-Curie
Street
Summary The catalytic properties of new MO(V) complexes with ligands such as ethylene gIyco1, lactic acid and amygdahc acid in homogeneous systems, as well as the properties of the heterogenized catalysts obtained in the ionic exchange reaction of the complex Naz[MoaO,(OX)z(HzO)a] -3HzO with Caste1 A-5OOp, Dowex 1X8, and Wofatit AD-41 anionites, were examined. The catalysts obtained are active in epoxidation reactions of olefins with organic hydroperoxides. The structure of the heterogenized catalysts is discussed, the catalyst changes during the epoxidation reaction are interpreted, and the correlation between the structure and reactivity of the homogeneous and heterogenized catalysts is considered on the basis of the i-r_ spectra-
Introduction Both the practicaI and theoretical aspects of the epoxidation reactions of olefins with organic hydroperoxides aroused great interest in studies on new catalytic systems for this process. Molybdenum complex compounds in the homogeneous phase are usually used as catalysts [l] _ Catalysts based upon molybdenum trioxide deposited on silica gel are examples of new heterogeneous catalytic systems [2 - 4]_ Synthesis of the heterogenized catalysts [5] was really progressive in the search for new catalytic systems. A polymeric catalyst supported on Amberlite IRA-45 anionite, modified by molybdenum hexacarbonyl is a good example- Its catalytic activity in the epoxidation reaction of propylene by the tert-butyl hydroperoxide is analogous to that of Mo(CO)s in the homogeneous phase [6] _ The homogeneous catalysts could be deposited on the appropriate carriers in several ways [‘I] . One of these methods is that of ionic exchange_ In this way we have obtained heterogenized catalysts by attachment of the [Mo&~(OX)&&O)~]~complex ion to one of the following anionites: Caste1 A-5OOp, Dowex 1X8 or Wofatit AD-41.
166
Experimental Cyclohexene (Fluka AG, Buchs S6) was distilled before use. Cumene hydroperoxide, approximately 70% in cumene (Suchardt, Munchen) Ethylene glycol, lactic and amygdahc acids, (POCh, Gliwice). MoO(OHs was prepared by a standard method as previously outlined IS]. Hs[MosO,(OX)a(H20)a] -3HaO was prepared by our own method [9] _ Preparation of the molybdenum(V) complexes Sodium-~-dioxo-bis(aquooxooxaZatooxomoiy~date(V)I 1Mo.zQ4(Ox)2(H.&).zI
3-hydrate
Nar
- 3Hz?o
To the H,[Mo~O~(OX),(H~O)~] - 3HsO complex dissolved in hot water, aqueous BaCls solution was added dropwise. The precipitated dark-red barium salt was filtered off, washed with acetone, and dried. An equimolar amount of an aqueous solution of sodium sulphate was then added dropwise to the hot, water slurry of the barium salt, Ba[MozO,(OX)z(HzO),l] -3HzO_ The barium suIphate precipitate was filtered off, and the sodium salt of the MO(V) complex was obtained under vacuum from the dark-red aqueous solution. The product was recrystallized from water-acetone solutionFound: C, 9-4; H, 2.2; MO, 32_9_ C&IIaMo201,Na2 requires C, S-45; H, 1.77; MO, 33.78%.
H,CMO~O~(C~H~O~)~(H~O)~I -2H20
0.02 Mol molybdenum(V) hydroxide, MoO(OH)s, was added to a 0.02 mol solution of ethylene glycol, under a neutral atmosphere. The solution was stirred vigorously and heated on a water bath. After the molybdenum(V) hydroxide had completeIy dissolved, the solution was evaporated under vacuum. The brown compound was crystallized from waterethanol solutionFound: C, 11.5; H, 3.0; MO, 42.7. C~H&Io2012 requires: C, 10.67; H, 4.03; MO, 42.64%_ Molybdenum/V) complex with lactic acid 0.055 Mol of molybdenum(V) hydroxide was dissolved
in 0.055 mol of an aqueous solution of lactic acid under the same conditions as above. Evaporation of the solution under vacuum produced a brown-green compound which was recrystallized from ethanol_ Found: C, 18-7; H, 3.8; MO, 34.4%. Molybdenum(V)
complex
with amygdaiic
acid
Ha[Mo204(C&&HOH-COO)4(H20)2] was obtained by dissolving MoO(OH)s in an aqueous solution of amygdalic acid. The brown-grey complex was crystallixed from ethanol-benzene solution_ Found: C, 435; H, 41; MO, 22.3, Cs2Hs.@0201s requires: C, 42.77; H, 3.81; MO, 21.96%. Synthesis The
of the heterogenized
heterogenixed
NazCModMOJQ&-W)2l-
catalysts
catalysts 3H~0
were obtained by ionic exchange of the complex and Na2Mo04 in aqueous solution,
167 TABLE
1
Concentration the anionites
of CMO~O~(OX)~(H~O)]~-
complex
Concentration
Anionite
ion and MoO+~-
of the complex
CMoz0&=)2U-C@)zl
2-
ion supported
in mole/g
anionite
1.34
Dowex
1x8
1.05
-
Wofatit
Ad-4 1
1.79
1.71
Epoxidation
x lo3
Mo042-
Caste1 A-500~
with the appropriate anionites. The concentrations appropriate anionites are given in Table l_
on
of the complexes
on the
reactions
Epoxidation was carried out, under nitrogen or argon atmosphere, in a system containing olefin, hydroperoxide, catalyst and a soIvent_ Reactions in homogeneous systems were studied using the apparatus described in ref_ [l] _ The heterogenized systems were examined in a thermostated glass reactor fitted with a porous glass filter (Gl) and with reflux. The reactor contents were mixed by passing argon in a closed circuit through the porous glass filter using a microdosing pump. Analysis
The reaction products were analysed as reported in ref. [l] _ The i.r_ spectra were recorded on a Perkin-Elmer Model 621 and Perkin Eimer 180 for the ranges 200 - 4 000 cm-l and 40 - 400 cm-‘, respectivelyResults We have described already the molybdenum(V) complexes with dicarboxylic acids and their cataIytic properties in the epoxidation reactions of oIefins [9] _ We now report some data obtained for the new homogeneous catalysts, their activity being examined in a model epoxidation reaction of cyclohexene with cumene hydroperoxide. The results for the molybdenum(V) complex with ethylene glycol and with lactic and amygdalic acids are shown in Table 2. The heterogenized catalysts were obtained by deposition of the [Mo20d(OX)2(H20)2]2complex ion on anionites, (Caste1 A-5OOp, Dowex 1X8 and Wofatit AD-41)_ For each anion& the total exchange capacity was attained_ Physicochemical examination of the heterogenized catalysts was limited to the analysis of their infrared spectra over the range 40 - 4 000 cm-‘. Consideration of the absorption bands arising from the exchanged anionites revealed that the spectrum of the deposited complex ion changed onIy slightly (Table 3)
TABLE
2
Epoxidation
of cyclohexene
with cumene
hydroperoxide
in trichloroethylene
at 85 OC*
Conversion of cumene hydroperoxide (%)
Conversion of cyclohexene
H2CMozO~(C,H,O2),(HZo)21-2H2O
54.2
96-7
87-6
84.7
MO(V)
57.8
97.2
87.9
85.5
56-S
88.7
75-5
66-9
Catalyst
+ lactic acid
H2[Mo204(C,H,CHOHCOO)4(H20)2]
Selectivity** (%)
Reaction yield (%)
(%I
*Reaction carried out under nitrogen atmosphere for 200 min, at cyciohexene: cumene hydroperoxider catalyst = 1 T 2 I O-002 molar ratio**Reaction
TABLE Some
selectivity
to epoxide,
calculated
according
to cyclohexene
used.
3 frequencies
observed
M[MO204(OX)2@320)21-=20*
160m
in i-r_ spectra
of the heterogenized
cataiysts
2-
CMo204(OX),(H,O),l ion on Caste1 A-500~ and Dowex 1x8 anionites
ion on Wofatit AD-41 anionite
-
-
-
260s
265w,sh/265m**
265w,sh
308m
305s
304s
795m
785s,sh;
950m,sh
955s
975s
965m,sh;
795s
785s,sh,
985w,sh
Frequency assignment
795s
a(OCO)
940m,sh
m(H20)
955s
vas(Mo0)
1280m
1280~~
1280m
vs(C0)
1415vs
1370s
1395s
UC021
*RI = Hz, Nan, Ba. **Observed for complex
ion on the Dowex
1X8
+ S(OC0)
anionite.
The reactivity of the heterogenized catalysts obtained was examined in the model epoxidation reaction of cyclohexene with cumene hydroperoxide at the following reagent concentrations: cyclohexene, 2.75 mol/l; cumene hydroperoxide, 1.25 moI/I; catalyst, 2-4 X 10e2 mol of a complex attached to the anionite/I. The reaction was carried out in trichloroethylene, under argon atmosphere, at 85 “C for 4 h. The results are given in Table 4. The catalytic activity of the binuclear complexes of the [Mo~O~(A-A)~(H~O)~]~type (A-A = chelating ligand) was confirmed by the eIectronic and crystal structures [l] _ The catalytic activity of such catalysts is changed after the complex ion is grafted on anionites, by comparison with the homogeneous
169
TABLE 4 Catalytic activity of [Mo~O~(OX)~(H~O)~]~-
-Ion in homogeneous
and heterogenized
systems* Selectivity***
Reaction
(%)
(%)
94.5
78.6
74-3
Heterogenized system on carriers: Caste1 A-500~ Dowex 1x8 Wofatit AD-41 _ _ Wofatit AD-41:’ Wofatit AD-41 ’
78-7 31.8 54-l 92.9 91.0
54-5 40-5 67-S 61.8 70.9
42.9 12.9 63.8 57-4 64.5
Wofatit
40.4
68.9
27.8
Conversion of cumene hydroperoxide
Catalyst**
yield
(%) Homogeneous
AD-41
system’,?
+ MoOa=
*Reaction conditions -see text. **Naa[MoaO4(OX)a(H20)2] -3HaO_ ***Reaction selectivity to epoxide cakulated per hydroperoxide _iCatalyst concentration: 2 X lob3 mol of complex per liter_
“After
trifold use of a cataIyst.
used-
I
catalyst. The change depends on the functional groups and the anion& structure_ The MO(V) complex on Wofatit AD-41 containing the -N(CH3)2 type coordination centres, exhibits the higher catalytic activity_ The catalysts on the other carriers (Caste1 A-500p and Dowex 1X8) containing the -N(CH&Cl function groups are less active_ The changes in the catalytic activity of the complex ions fixed on various anionites are analogous to the rate of the water substitution reaction by pyridine in the system (Table 6):
The reaction was carried out in ampouies in trichloroethylene solution at 75 “C for 1 h. The data in Table 4 indicate the dependence of the activity of the heterogenized catalyst on the effect of a carrier on the water fixation mode in the [Mo~O~(OX)~(H~O)~]~complex ion, The anaIysis of the i-r_ spectra for the heterogenized cataIysts before and after the reaction reveaied essential and identical changes of the complex ion attached to the Caste1 A-500~ and Wofatit AD-41 anionites- No changes were observed for the complex ion fixed on the Dowex 1X8 anio&e (Table 5). Discussion The fixation of the [Mo~O,(OX)~(H~O)~]~complex ion on anionites has only a slight effect on the i-r_ spectrum_ The changes are usually reflected
170 TABLE
5
Changes in the i-r_ spectrum of the [Mo20.&OX)2(H20)2J2Caste1 A-500~ and Wofatit AD-41 anion&s after epoxidation
CMO&LZ(OX)~(H~~)~I2- deposited Caste1 A-500~ before reaction
-
Caste1 A-500~ Wofatit AD-41 after reaction
265w,sh 305s 735m 755s,sh 795s
-
955s 965m,sh 985w,sh 128Ovw *Observed **Observed
-
on anionites and
265s 3oow 377w* ,- 3sow** 735w,sh 785s 805m,sh** 900s 940m*; 940s”* 965w*;
985vw*
1265w,sh for the complex for the complex
complex ion fiied reaction
ion settled ion settled
Wofatit AD-4 1 before reaction
-
-
on the
Vibration assignment
265w,sh 304s
-
735m 785s,sh 795s 9oow 940m,sh 955s
v(Mo02Mo) -
1280m
w.332)
-
%&Moo) %,(CO)
+ 6 w32)
on the Caste1 A-5OOp_ on the Wofatit AD-41.
in the lack of the band at 160 cm-‘, the appearance of a new band (shoulder) at 785 cm-‘, and the shift of the bands at 975 cm-’ (v,, (Mo=O) vibrations) to the asymmetric vibrations of the carboxyl and 1415 cm-‘, corresponding group IlO] towards Iower frequencies_ The spectrum of the complex ion on the Dower 1X8 anionite after epoxidation reaction shows no changes, whereas the cata!ysts on the Caste1 A-500~ and Wofatit AD-41 anion&s give spectra with essential and identical changes after epoxidation reaction_ Generally, these changes occur in the vibration range characteristic for the Mo-0 bonding. Their analysis allowed us to suppose that the formation of new bands at 380,900 and 940 cm-’ indicated the formation of a cis-cEoxo (Mo=O) arrangement [ 111. The cumene hydroperoxide molecule is responsible for these changes. The i-r. investigations of the H2[Mo204(OX)2(H@)2 Me2C0, 4H& complex with cumene and terf-butyl hydroperoxide indicated the same spectrum changes as those observed for the catalysts heterogenized with the Castel A-500~ and Wofatit AD-41 anionites [12] _ According to the epoxidation reaction mechanism of olefins by organic hydroperoxides proposed by us [l] the hydroperoxide molecule coordinates to molybdenum(V) by substitution for water (Scheme I, step A). This interaction is responsible for the formation of the molybdenum complex with hydroperoxide (Structure II). Due to this the electrophilic properties of oxygen atoms become stronger, which, in turn, facilitates the further reaction with olefm (step B) to form the epoxid,. 0 It could not be excIuded that the attack of the subsequent hydroperoxide molecule (step C) may cause the breaking of the oxygen bridges. That would lead to the cz?+dioxo system
171 Scheme
1.
TABLE
6
Substitution of water by pyridine in the [Mo~O~(OX)a(HaO)21*complex ion supported on anionites* [Mo204(OX),(H20)2 on the anionites
J2- supported
21-5
Caste1 A-500~
5.0
Dowex
1x8
Wofatit
AD-41
*Reaction **Pyridine
Amount of substituted water (%)**
conditions adsorption
39.9 -see text. for each anionite
were considered.
(structure IV) indicated by the intensity decay of the band at 735 cm-‘. The epoxidation reaction could proceed also in the monomeric complexes and the activity of the organic hydroperoxide could be realized by the formation of structure IV. That modification of a catalyst is not followed by its removal from the carrier is shown by the facts that the post-reaction solutions were not catalytically active and the multiple application of a catalyst changed its activity only slightly (Table 4). The observed differences in catalytic activity of the heterogenized catalysts are consistent with the results of the water substitution reaction by pyridine in the ]Mo~O~(OX),(H~O)~]*complex ion deposited on anionites, This revealed the essential role of the water molecule coordinated to molyb-
172
denum in the reaction mechanism_ The activity of a catalyst is determined by its lability and accessibility (Table 6).
References 1 J_ Sobczak and J. J. Ziakowski, Inorg. Chim. Acta, 19 (1976) 15, and references cited therein_ 2 L. Cerveny, A. Morhoul and V_ Ruiicka, Chem_ Prum., 23 (1973) 17. 3 F. Trifiro, P. Fonatti and J. Pasquon, Catalysis: Heterogeneous and Homogeneous. Proc_ Id_ SympRelations between Heterogeneous and Homogeneous Catalytic Phenomena, Brussels, BeIgium October, 1974, Elsevier, Amsterdam, 1975, p_ 5094 K_ B_ Jacimirskij, V_ M. BeIousov, A_ P_ Filipov. L_ A_ OIin, S. B_ Grinenko, G_ A_ Konis’evskaja, G. A. Sachovceva and B. E_ Krasotkina, Dokl_ Akad_ Nauk SSSR, 224 (1975) 1369_ 5 J_ C. Bailar, Jr., Catal_ Rev. Sci., 10 (1974) 17. 6 S. Ivanov, R. Boeva and S_ Tanielyan, React. Kinet_ Catal_ Lett_. 5 (1976) 297. 7 V_ A_ Licholobov, B_ N_ Kuznecov and Yu_ J_ Sermakov, Symp. Supported Metal Complex Catalysts, Liblice. Czechoslovakia. April 28 - 30, 1975_ 8 W_ G_ Palmer, Experimental Inorganic Chemistry, Cambridge University Press, Cambridge, 1962, p_ 406. 3 J. Sobczak and J_ J. Zio&owski, J_ Less-Common Met_. 54 (1977) 149_ 10 P. C_ H_ Mitchell, J_ Inorg_ NucI_ Chcm_, 26 (1964) 1967_ 11 W_ P_ Griffith and T_ D_ Wilkins, J_ Chem_ Sot. A, (1965) 400. 12 Unpublished results.