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divinylbenzene copolymers
Reactive & Functional Polymers 68 (2008) 1207–1217
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Polymeric supports with amino groups from halogenoacetylated styrene/divinylbenzene copolymers _ Bozena N. Kolarz a, Anna Jakubiak a,*, Julia Jezierska b, Barbara Dach a a ´ skiego 27, Wrocław University of Technology, Faculty of Chemistry, Department of Polymer and Carbonaceous Materials, Wybrzez_ e Wyspian 50-370 Wrocław, Poland b University of Wrocław, Faculty of Chemistry, Joliot-Curie 14, 50-378 Wrocław, Poland
a r t i c l e
i n f o
Article history: Received 27 February 2008 Received in revised form 23 April 2008 Accepted 29 April 2008 Available online 4 May 2008
Keywords: Halogenoacetylation of styrene/ divinylbenzene copolymers Reductive amination Ethylenediamine Hydrazine Guanidyl ligands Oxidation catalysts
a b s t r a c t The introduction of amino groups to halogenoacetylated styrene/divinylbenzene (St/DVB) expanded gel or porous copolymer (2% or 10% DVB) with ethylenediamine (EtDA) or hydrazine (H) was carried out as a reductive or nonreductive amination. It has been found that the reductive amination in the presence of NaBH3CN is more effective than aminolysis without the reducing agent at room temperature. The amino groups were transformed to guanidyl ligands using thiourea/ethyl iodide mixture. Obtained supports with Schiff base bonds and guanidyl ligands after complexing Cu(II) ions are useful as oxidation catalysts. Their catalytic activity was tested in the model reaction – oxidation of hydroquinone to p-benzoquinone or 2,5-di-tert-butylhydroquinone to 2,5-di-tert-butylbenzoquinone. The expanded gel catalysts with guanidyl groups (ethylenediamine modification) showed the highest activity. EPR investigation on this group of catalysts indicated higher amounts of nitrogens in Cu(II) coordination sphere and formation of N3O complex between three amino nitrogens and water oxygen. The catalysts with aminoguanidyl groups (hydrazine modification) were characterized by low catalytic activity. It was a result of increase in intra and intermolecular crosslinking. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Chloromethyl ether is a common base product used to introduce exchangeable chlorine, which may be substituted for amines, in styrene/divinylbenzene copolymers (St/DVB). However, as strongly carcinogenic agent, its application is seriously restricted. Therefore better ways to insert exchangeable chlorine into macromolecules are searched. Well-known method of reactive and functional polymers synthesis is chloro- or bromoacetylation of styrene copolymers with acetyl chloride or halogenoacetyl chloride (Scheme 1.I) [1–4], but these processes are accompanied by side reactions resulting from the subsequent transformations [3]. The halogenoacetylation of 2 wt.% crosslinked gel or porous polystyrene beads with * Corresponding author. Tel.: +48 71 3203273; fax: +48 71 3202152. E-mail address: [email protected] (A. Jakubiak). 1381-5148/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.reactfunctpolym.2008.04.005
X(CH2)nCOCl carried out by Caze and Hodge [3] gave chlorine content about 2.75% for gel copolymers (yield of substitution 81%) and 2.23% (yield 71%) for porous ones. It was concluded that side reactions led to additional crosslinking, which was disadvantageous for the supports. Alexandratos and Hussain [4] introduced 3.11 mmol/g of chlorine into St/DVB copolymer using the reaction with chloroacetyl chloride in CS2 solution. It is also known that natural polymers with hydroxyl or carboxyl functional groups (cellulose, polysaccharides, dextrane, starch) reacted with halogenoacetyl chloride in different way [5–8]. In the next step of the transformation the chlorine in chloroacetylated copolymer can be exchanged by amine. Introduction of amino groups is possible by exchange of chlorine or by Schiff reaction with keto groups (Scheme 1.II). Chinese authors [9,10] investigated the reductive amination of acetylated St/DVB copolymer, i.e. treatment of
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P
+ CH2Cl
P
C Cl
C CH2Cl O
O I
+NH2CH2CH2NH2
P
C
CH2NHCH2CH2NH2
NCH2CH2NH2 +NH2C NH
II
+CH3C(=NOH)CCH3
SC2H5
P
O
C CH2NHCH2CH2NHC NH NCH2CH2NH2
C CH2NHCH2CH2N=C CH3
P
NCH2CH2NH2 HON CCH3
NH2
III
IV
Scheme 1. Modification of St/DVB copolymer. (I) Chloroacetylated support; (II) after aminolysis with EtDA; (III) after thiourea/ethyl iodide attachment; (IV) after DAMO attachment.
the acetylated St/DVB copolymer with ammonia or amines (methylamine, dimethylamine) in the presence of reducing agent, for example NaBH3CN in anhydrous methanol (65– 67 °C, 22 h). The optimal pH value for this reaction was generally about 6–8. When the molar ratio of acetylated groups to reducing agent was 1:1 and acetylated groups to methylamine was 1:8, the nitrogen content reached 6.65% and exchange capacity of resin was 4.67 mmol/g [10]. The reductive amination at temperature 25 °C caused decrease of nitrogen content to mere 1.5%. It should be noted that observed exchange capacities appeared to be, more or less, lower than the value calculated from the nitrogen content which is connected with the side reactions. The authors expected to find application for these anion exchangers [10]. However, since currently used reducing agent, i.e. NaBH3CN is expensive and modestly toxic, this new method cannot be applied in industry. Caze and co-worker [11] synthesized the chloroacetylated St/DVB supports that, after exchange of the chlorine for amino groups by potassium phtalimide, were used to enantioselective reduction of a-chloroacetophenone keto groups with NaBH4. The nitrogen content of supports was only about 0.6 mmol/g. The examples of chlorine exchange in chloroacetylated St/DVB with amine were shown in our paper [12]. Nowadays we know that this reaction, like the aminolysis of nitrile groups by hydrazine, is more complicated because the intramolecular and intermolecular reactions take place [13]. Zhang et al. [14] indicated a possibility of cycle forms creation during aminolysis with hydrazine. In case of our modifications the reactions become more complicated owing to Schiff base formation between amine and keto groups of chloroacetylated St/DVB copolymers. The aim of this work is to present the possibility of modifications of styrene/divinylbenzene copolymers with chloroacetyl chloride as ways to obtain the supports with sufficient amount of amino ligands after chlorine exchange with ethylenediamine or hydrazine. Our studies focused on the chlorine exchange at room temperature, when the
change of supramolecular structure was minimalized. After transformation of amino groups to guanidyl ligands and subsequent complexation with Cu(II) ions the supports were used as oxidation catalysts. 2. Experimental 2.1. Materials 2.1.1. Copolymers All starting styrene/divinylbenzene (St/DVB) copolymers were obtained using suspension polymerization method. The polymerization of expanded gel copolymer crosslinked with 2 wt.% of DVB was carried out in the presence of toluene (50 wt.% with respect to the monomer mixture) [15]. The porous copolymers were obtained with 10 wt.% of DVB in the presence of paraffin oil (80 wt.%). The porosity of copolymer was 0.6. The characteristics of porous structure of this copolymer were presented in [16]. 2.1.2. Acetylation of St/DVB copolymers St/DVB copolymers (4 g) were swollen in 16 cm3 of carbon tetrachloride. The next day 10 cm3 of acetyl chloride was added and 6 g of powdered anhydrous aluminium chloride was dosed in small portions. The mixture was conditioned for 24 h without air access and then refluxed for 15 min. The support was decomposed with 0.1 M HCl in dioxane and on the next day the beads were placed in column and washed with 0.2 M acetic acid, chloroform and methanol. Copolymer contained 5.9% of oxygen. Obtained acetylated copolymer (A) was treated as a blank sample for FTIR analysis. 2.1.3. Chloroacetylation or bromoacetylation of St/DVB copolymers St/DVB copolymers (4 g) were swollen in 50 cm3 of carbon disulfide and 8 cm3 of chloroacetyl chloride or 4.5 cm3 of bromoacetyl bromide. The mixture was cooled and 8 g of powdered anhydrous aluminium chloride was dosed.
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Copolymer
Diluent
1B 2B 3B 1 2 3 4 P5 P6
Gel Gel Gel Gel Gel Gel Gel Porous Porous
Carbon Carbon Carbon Carbon Carbon Carbon Carbon Carbon Carbon
tetrachloride disulfide disulfide tetrachloride tetrachloride disulfide disulfide tetrachloride disulfide
Timea (h)
Halogen (mmol/g)
a (%)
67 48 67 67 168 24 48 48 48
2.60 2.64 3.21 2.17 1.88 1.80 2.77 1.53 3.12
59.1 60.0 73.0 39.5 25.0 32.7 50.3 27.8 56.7
B – bromoacetylated; P – porous structure; a – degree of substitution. a Room temperature.
Whole mixture was conditioned for 48 h at room temperature without air access. Next it was processed as described above. The characteristics of halogenoacetylated copolymers are shown in Table 1. 2.1.4. Amination with ethylenediamine To 6 g of chloroacetylated copolymer swollen in 65 cm3 of dioxane 75.2 g of ethylenediamine (EtDA) was added. The mixture was stirred at 20 °C for 168 h. After reaction the mixture was acidified to pH 2 with 10% HCl and cyclized three times with 1% NaOH, water and 1% HCl. In case of reductive amination, 1 g of dry samples were swollen in 25 cm3 of anhydrous ethanol and NaBH3CN was added. The parameters of aminolysis are shown in Table 2 and characteristics of supports are presented in Table 3.
2.1.6. Modification of amino groups in supports The amino groups of supports were modified with thiourea in the presence of ethyl iodide to obtain ligands with guanidyl groups (G) (Scheme 1.III). The modification parameters were described in [12]. Another method of amino groups transformation to guanidyl ligands was reaction with cyanamide [17]. Primary amino groups of the supports were also modified with 2,3-butanedione monoxime (DAMO, Aldrich). The reaction route is shown in Scheme 1.IV. A 2.6 g of support with amino groups was swollen in 32 cm3 ethanol with 0.8 g DAMO. The mixture was refluxed for 4 h then washed with ethanol and water. The characteristics of support with guanidyl ligands and modified by DAMO are presented in Table 6. 2.2. Methods
2.1.5. Amination with hydrazine To 9 g of chloroacetylated copolymer swollen in 98 cm3 of dioxane 123 g of hydrazine (H) (80%) was added. The mixture was stirred at 20 °C for 168 h (Table 4). Further was proceeded as 2.1.4. The characteristics of supports are in Table 5.
2.2.1. Characteristics of supports Water regain was measured using a centrifugation technique (3000 rpm, 5 min). Nitrogen content was determined by Kjedahl’s method and amino groups were calculated (ZN). Anion exchange capacity was determined
Table 2 Parameters of halogenoacetylated St/DVB copolymers modification with ethylenediamine (EtDA) Symbol
Diluents
NaBH3CNa
Conditions
EtDA conc. (%)
b
N (mmol/g)
1B1 1B2 2B1 3B1 1E1 1E2 2E1 2E2 2E3 3E1 4E1 4E2 P5E1 P5E2 P5E3 P5E4 P6E1 P6E2
Dioxane Ethanol Dioxane Ethanol Dioxane Ethanol Dioxane Dioxane Dioxane Ethanol Dioxane Dioxane Dioxane without Dioxane Dioxane without Dioxane
+ + + + + + + +
4 h, ref. 4 h, ref. 24 h, room temperature 4 h, ref. 4 h, ref. 4 h, ref. 168 h, room temperature 168 h, room temperature 168 h, room temperature 4 h, ref. 168 h, room temperature 200 h, room temperature 168 h, room temperature 168 h, room temperature 2 h, ref. 2 h, ref. 168 h, room temperature 168 h, room temperature
19 6 28 6.7 32 6.6 100 50 27 6.6 36 36 100 100 3 11 100 53
24 18.5 24 8.2 27 13 136 136 153 15 39 39 109 109 6 12 67 67
4.42 5.17 2.57 5.65 2.28 2.78 2.77 2.58 2.66 3.27 4.23 4.40 3.12 3.48 3.24 3.51 4.32 4.27
X – Cl or Br; ref. – reflux; b – EtDA/X (molar ratio). a NaBH3CN:X (molar ratio) = 2.5:1.
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Table 3 Characteristics of supports with ethylenediamine ligands Symbol
Water regain (g/g)
ZN (mmol/g)
ZC (mmol/g)
Z NH2 (mmol/g)
Cu(II) sorption (mg/g)
1B1 1B2 2B1 3B1 1E1 1E2 2E1 2E2 2E3 3E1 4E1 4E2 P5E1 P5E2 P5E3 P5E4 P6E1 P6E2
2.35 3.52 2.10 2.71 2.14 1.05 0.71 1.32 1.60 1.08 1.28 1.73 1.25 1.25 1.20 1.22 1.33 1.31
1.1 2.6 1.3 2.8 1.1 1.4 1.4 1.3 1.3 1.6 2.0 2.2 1.5 1.7 1.6 1.8 2.2 2.1
1.1 2.4 0.9 2.6 1.0 1.3 0.5 0.5 0.3 1.5 1.6 2.2 1.1 0.5 0.5 0.6 1.6 1.6
0.8 1.0 0.6 2.0 0.5 0.9 0.4 0.5 0.3 1.2 1.4 2.2 1.1 0.5 0.5 0.6 1.6 1.6
5.36 11.96 3.37 8.55 2.73 2.40 1.62 1.46 1.46 3.87 5.18 9.25 2.14 1.47 1.17 1.52 – –
Table 4 Parameters of chloroacetylated St/DVB copolymer modification with hydrazine (H) Symbol
Diluent
Conditions
Hydrazine conc. (%)
b
N (mmol/g)
4H1 4H2 4H3 4H4 P6H1 P6H2 P6H3 P6H4 P6H5
Dioxane, NaBH3CNa Dioxane, NaBH3CNa Dioxane Dioxane, NaBH3CNa Dioxane Methanol, NaBH3CNa Dioxane Dioxane NaBH3CNa Dioxane
84 h, room temperature 168 h, room temperature 168 h, room temperature 132 h room temperature 48 h, room temperature 24 h, ref. 24 h, ref. 168 h, room temperature 168 h, room temperature
6 6 50 6 8 6 8 8 46
12 12 125 12 15 12 12 12 120
2.64 2.47 2.39 2.55 2.45 3.06 2.25 2.84 2.35
X – Cl or Br; b – hydrazine/X (molar ratio). a NaBH3CN:X (molar ratio) = 2.5:1.
Table 5 Characteristics of chloroacetylated St/DVB copolymer modified with hydrazine (H) Symbol
Water regain (g/g)
ZN (mmol/g)
ZC (mmol/g)
Z NH2 (mmol/g)
Cu(II) sorption (mg/g)
4H1 4H2 4H3 4H4 P6H1 P6H2 P6H3 P6H4 P6H5
2.23 2.02 1.51 1.93 1.33 1.31 1.31 1.24 1.31
1.3 1.5 1.2 1.2 1.2 1.5 1.1 1.4 1.2
1.0 1.2 1.5 0.9 0.8 1.2 0.9 0.9 0.7
0.3 0.4 1.0 0.3 0.2 0.8 0.7 0.4 0.4
3.46 1.62 4.06 2.43 2.68 2.73 1.21 1.09
Table 6 Characteristics of supports with guanidyl ligands Symbol
Water regain (g/g)
N (mmol/g)
ZN (mmol/g)
ZC (mmol/g)
Z NH2 (mmol/g)
Cu(II) sorption (mg/g)
4E2/G 4E2/DAMO P6E2/G P6E2/A 4H4/G P6H4/G P6H5/G P6H5/A
0.93 0.81 1.29 1.27 1.10 1.24 1.29 1.14
5.95 4.79 4.82 8.82 1.99 2.11 2.31 5.61
3.0 2.4 2.4 4.4 0.6 1.1 1.7 2.8
2.1 2.3 1.5 1.7 0.9 0.9 1.0 1.4
2.1 2.3 0.9 1.3 0.5 0.5 0.4 0.9
2.4 4.0 1.8 2.3 1.1 0.9 0.9 2.1
G – samples modified with thiourea; A – samples modified with cyanamide.
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by modified Colella-Siggia method [18]. A 0.5 g of support with amino groups was transformed to hydrochloride form by swelling in 0.1 M HCl (50 cm3) for 24 h. The sample was washed with anhydrous ethyl alcohol in column until chlorine was not detected. Then support was separated by centrifugation, carried into flask and 50 cm3 of 0.1 M NaOH was added. Concentration of basic and acidic groups (ZC) was calculated from the titration of solution from above the support. On the basis of chlorine concentration in this solution, amount of hydrogen chloride attached to reactive amino groups was determined by Volhard’s method ðZ NH2 Þ. }niger’s Chlorine and oxygen was measured using Scho method [19] and elemental analysis, respectively. Sorption of Cu(II) ions was determined by shaking of support samples with 104 M copper nitrate solution in 0.2 M acetate buffer (pH 5.6) at room temperature for 48 h. Then the supports were separated by filtration and metal concentration in solution was measured using atomic absorption spectroscopy (AAS) method on a Perkin–Elmer Analyst 100 spectrophotometer. Sorption of copper (mg/g, mmol/g) was calculated from the difference of Cu(II) concentration in solution before and after sorption. FTIR spectra in KBr pellets were recorded on Perkin–Elmer System 2000 FTIR spectrophotometer. The structure of Cu(II) active centres was studied by electron paramagnetic resonance (EPR) method at 77 K on the swollen samples, separated by filtration and air dried. The EPR spectra were recorded on a Bruker ESP 300E (Bruker, Germany) X-band spectrometer equipped with the Bruker NMR gaussmeter ER 035 M and the Hewlett-Packard microwave frequency counter HP 5350B. The EPR parameters were calculated by computer simulation using Bruker’s WIN-EPR SimFonia Software and are presented in Table 7. 2.2.2. Oxidation reaction Catalysts were swollen in 20 ml of hydrogen peroxide solution (5.6102 mol/l in acetate buffer pH 5.0) for
Table 7 Catalytic activity of samples Symbol
Cu(II) loading (mmol/g)
LH2 Q (%)
YQ (%)
LDTBH2 Q (%)
YDTBQ (%)
4E2
0.10 0.16 0.14 0.06 0.09 0.28 0.98 0.06 0.28 0.71 0.10 0.11 0.09 0.09 0.14 0.09 0.13 0.11 0.13
33.7
7.8
62.7 49.3
48 100
20.0 77.7 60.1 53.9 33.9
9.0 9.8 9.1 9.8 6.0 73.1 72.8 51.5
87 97 90.6
P6E2 4E2/G
4E2/DAMO P6E2/G2/G P6E2/A P6H5 4H4/G P6H5/G P6H5/A
43.0 20.5 22.0 23.7 18.6 59.5 22.4 22.1 16.7
9.3 9.6 11.3 14.0 10.2 48.5 13.6 10.1 7.1
LH2 Q , LDTBH2 Q – loss of hydroquinone or 2,5-di-tert-butylhydroquinone (%). YQ, YDTBQ – yield of p-benzoquinone or 2,5-di-tert-butylbenzoquinone (%).
30 min. Next, equal volume of 4103 mol/l hydroquinone (H2Q) or 1103 mol/l 2,5-di-tert-butylhydroquinone (DTBH2Q) was added in polyethylene flasks. The Cu(II) to substrate ratio was 1:10. Entire mixture was shaken (350 cycles/min) in desire time at 35 °C (H2Q) or at 22 °C (DTBH2Q). The concentrations of unreacted H2Q and pbenzoquinone (Q) or unreacted DTBH2Q and 2,5-di-tertbutylbenzoquinone (DTBQ) were determined by UV–vis spectrophotometry using JASCO 570c spectrophotometer at: k = 289 nm and k = 246 nm or k = 292 nm and k = 255 nm, respectively. Oxidation degree of H2Q (LH2 Q , %) or DTBH2Q (LDTBH2 Q , %) and yield of Q (YQ,%) or DTBQ (YDTBQ, %) after 60 min were calculated from following equations: LH2 Q = {D[H2Q]/[H2Q]0} 100% and YQ = {[Q]/[H2Q]0} 100%, respectively. The selectivity was defined as the ratio of main product concentration [Q] to the reacted substrate concentration [H2Q] [20,21]. The catalytic activity of samples is presented in Table 8. 3. Results and discussion 3.1. Supports synthesis Two types of St/DVB copolymers, one an expanded gel (2 wt.% DVB) [15] and another porous (10 wt.% DVB) [16], were halogenoacetylated with bromoacetyl bromide or chloroacetyl chloride. The yield of this reaction depended on the copolymer structure (expanded gel or porous) and solvent. The substitution degree was better when the reaction was carried out in the polar solvent such as carbon disulfide (Table 1). The yields of halogenoacetylated copolymers obtained in these reactions appeared to be similar. In the next syntheses chloroacetyl chloride has been used as cheaper and more useful compound. The FTIR spectra showed two carbonyl bands: one near 1700 cm1 due to chloroacetylated copolymer and second near 1680 cm1 ascribed to both chloroacetylated and crosslinked residues [3]. These peaks were related to vibration of arylketo groups (valence band) (Fig. 1. P6). Additionally, the band at 1286 cm1 assigned to –CH2– vibration in chloromethyl groups could be observed. The reaction of chlorine exchange in chloroacetylated copolymers by hydrazine (H) or ethylenediamine (EtDA) depended on various parameters like: time, temperature, kind of solvents, amine concentration and ratio of amine to Cl in chloroacetylated copolymers (b). The exchange of
Table 8 EPR parameters for Cu(II) complexes in prepared catalysts Catalyst
AII (104 cm1)
gII
g\
Complexes
4E2 4E2/G P6E2 P6E2/G P6E2/A 4H4/G P6H5 P6H5/G P6H5/A
184 184 185 184 185 167 157 162 192
2.236 2.236 2.255 2.277 2.250 2.310 2.336 2.310 2.233
2.050 2.055 2.050 2.069 2.066 2.066 2.070 2.065 2.070
N3O N3O N2O2 N2O2 N2O2 NO3 NO3 NO3 N3O
P – porous catalysts.
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100 P6 4E1 P6E2
80
%T
60
40
20
0 1800
1700
1600
1500
1400
1300
1200
Wavenumber, cm-1 Fig. 1. FTIR spectra of chloroacetylated St/DVB copolymer after EtDA amynolysis (—) P6; () 4E1; (– – – ) P6E2.
chlorine by these amines was possible due to long reaction time at room temperature or the reflux of solution. During the chlorine exchange a Schiff base creation between keto groups and amine took place (Scheme 1.II). Imine bonds formation was limited by the reaction conditions, e.g. temperature. Chinese authors [10] introduced into acetylated St/DVB copolymer about 3–4.8 mmol/g of nitrogen during the reductive amination with methylamine hydrochloride in the presence of NaBH3CN in boiling anhydrous methanol and only 1 mmol/g of the support at room temperature. To confirm the possibility of Schiff base formation we tested our acetylated gel copolymer (A) (degree of acetylation about 60%) modified with EtDA at room temperature (without NaBH3CN). After 168 h nitrogen content was about 1.1 mmol/g which indicates a Schiff base creation. It was additionally confirmed by the appearance of peak at 1634 cm1, corresponding to –CH@N–bond, close to the strong peak 1682 cm1 related to the nonreacted carbonyl groups (Fig. 2D). The introduction of amino groups into halogenoacetylated copolymers was carried out using reductive or nonreductive amination with EtDA [10]. During both modifications two kinds of reactions were possible: exchange of chlorine and Schiff base formation. However, when these transformations were carried out in anhydrous alcohol with reducing agent, the Schiff base was hydrogenated and stable amino bonds were created. Table 3 presents characteristics of bromoacetylated (B) and chloroacetylated St/DVB copolymers modified with EtDA in various reaction conditions. The unstable imine bonds were hydrogenated when the high amount of reducing agent, i.e. NaBH3CN was used. On the basis of valence vibrations m(N–H) and m(C@N) one can identify, with some restrictions, the kind of bonds. In
the interesting wavelength range FTIR spectra showed typical bands for the deformation vibration of N–H groups (1630–1530 cm1), vibration of C@N in Schiff base (1695–1585 cm1) [22], hydrazine groups (1658 cm1) [23] and guanidyl groups (1632, 1654 cm1) [24]. FTIR spectrum of supports aminolysed with EtDA indicated the disappearance of the bands at 1700 and 1680 cm1 characteristic for the arylketo groups absorption and peak at 1286 cm1 attributed to chloromethyl groups. At the same time appearance of wide bands at 1590–1670 cm1 was observed as the result of superimposing bands from primary amino groups and secondary amino groups (Fig. 1, 4E1). When aminolysis was carried out at room temperature without the reducing agent, more intensive peak at 1695–1655 cm1 attributed to superimposed bands from the amino groups vibration and stretching vibration of the imino groups in the Schiff base appeared (Fig. 1, P6E2). Additionally, after aminolysis, the intensity of peak 3420–3440 cm1 connected with the amino groups vibration increased. The samples with low degree of halogenoacetylation (3 and P5, Table 1) were characterized by low nitrogen content. For the bromoacetylated expanded gel copolymers the exchange of bromine by EtDA solution (in reflux) led to higher substitution degree than the aminolysis of chloroacetylated copolymers at room temperature. However, this degree of substitution by EtDA was sufficient for preparation of the supports useful in catalytic systems. The influence of the aminolysis time with EtDA on nitrogen content in chloroacetylated copolymer 4 at room temperature is presented in Fig. 3. The time of 168 h is enough to introduce about 4.23 mmol nitrogen per gram of the support 4E1 (Table 2). The samples with amino groups obtained from bromoacetylated copolymers were characterized by higher swell-
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100 A D 80
%T
60
40
20
0 1800
1700
1600
1500
1400
1300
1200
Wavenumber, cm-1 Fig. 2. FTIR spectra of acetylated St/DVB copolymers (A) and modified with EtDA (D).
N content (mmol/g)
5 4 3 2 1 0 2
4
72
168
200
Aminolysis time (h) Fig. 3. The influence of modification time on nitrogen content for support 4 (room temperature).
ing than chloroacetylated samples. Concentration of accessible amino groups determined by Colella-Siggia method (ZC) was similar to amount of these groups calculated from nitrogen content (ZN). The supports from chloroacetylated copolymers were characterized by lower free amino groups concentration than groups calculated from nitrogen content. Modification in boiling amine/solvent mixture or concentrated amine caused lower accessibility of amino groups as a result of intramolecular amino groups reactions (Tables 2 and 3). It has been found that the reductive amination is more effective than aminolysis at room temperature without the reducing agent. The hydrogenation stabilized unsaturated bonds and allowed to use these resins as anion exchangers in acidic and basic solutions. After Cu(II) ions complexation these supports with Schiff base bonds and others amino groups are also useful as catalysts.
The parameters of chloroacetylated St/DVB copolymers modification with hydrazine are presented in Table 4 (Scheme 2). In all cases the degree of modification by hydrazine (H) and amino groups concentration were smaller than after EtDA aminolysis. This transformation was independent of hydrazine concentration, hydrazine chlorine exchange ratio or presence of reducing agent. It ensued from the fact that the cyclization between amino groups described by Zhang et al. [14] was probably the main reaction. The possibility of cyclization or crosslinking with the emission of ammonia is showed in Scheme 2.II and III. FTIR spectrum for sample P6H5 (Fig. 4) is similar to that aminolysed with EtDA (Fig. 1), but the spectrum is less intensive, because of lower concentration of functional groups. The sorption of Cu(II) ions was carried out from diluted copper nitrate solution (104 M) in which the ratio of amino groups to Cu(II) ions was 10. Low concentration of Cu(II) ions in solution and amount of amino ligands higher than metal ions resulted in low sorption degree. However, the data in Tables 3 and 5 showed that all supports demonstrated ability for sorption of Cu(II) ions. 3.2. Catalytic activity We have published that supports with aminoguanidyl groups after Cu(II) ions sorption were better oxidation catalysts than supports with others amino groups [13,25–27]. Their catalytic activity was tested in two model reaction of hydroquinone (H2Q) to p-benzoquinone (Q) or 2,5-di-tertbutylhydroquinone (DTBH2Q) to 2,5-di-tert-butylbenzoquinone (DTBQ) oxidation using hydrogen peroxide (Scheme 3).
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P
C CH2Cl + NH2NH2
P
O
C
CH2 NH NH2
N
NH2
I
-NH3
-NH3
P
C
CH2 NH NH2
N P
C II
CH2
N
NH
NH
N
NH P
C
CH2 NH NH2
III Scheme 2. Modification of chloroacetylated St/DVB copolymers: (I) with hydrazine; (II) after intramolecular reaction; (III) after intermolecular reaction.
70 P6H5 P6H5/G P6H5/A
60
%T
50
40
30
20
10 1800
1700
1600
1500
1400
1300
1200
Wavenumber, cm-1 Fig. 4. FTIR spectra of modified St/DVB copolymers: (—) P6H5; () P6H5/G; (– – – ) P6H5/A.
O
OH R
R
H 2O 2
H 2 Q:
R
R
DT BH 2 Q:
OH
O
H2Q ( λ =289 nm)
Q ( λ = 246 nm)
DTBH2Q ( λ =292 nm)
R= -H R= -C(C H 3 ) 3
DTBQ ( λ =255 nm)
Scheme 3. Oxidation of hydroquinone (H2Q) or 2,5-di-tert-butylhydroquinone (DTBH2Q).
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100 80
LH 2Q (%)
One can see from our earlier investigation that there are two methods of introducing of guanidyl ligands to supports [13]. The first consists of direct exchange of chlorine in support with guanidine or aminoguanidine salts, or aminolysis of acrylonitrile groups in crosslinked acrylonitrile copolymers with these salts. The second one is based on indirect, several-step reactions. A few indirect ways of modification of amino groups to guanidyl ligands have been studied. After attaching thiourea/ethyl iodide to EtDA ligands the catalyst with guanidyl ligands was obtained (Scheme 1.III) [12]. In case of the support modified by hydrazine the aminoguanidyl ligands appeared, because amino groups are accessible to react with thiourea. The side reaction is crosslinking between amino groups with ammonia elimination. The next method of transformation is attaching cyanamide to amino groups [17]. Supports with ethylenediamine (E) or hydrazine (H) groups modified to guanidyl ligands in the reaction with thiourea (G) or cyanamide (A) are characterized in Table 6. In supports with EtDA ligands after modification with cyanamide, as well as with thiourea, the nitrogen content significantly increased. At the same time the concentration of free amino groups was in the same level. FTIR spectra of modified supports with guanidyl ligands are presented in Fig. 5. The superposition of characteristic peaks from amino groups was observed. The catalytic activity of all investigated catalysts in the model reaction of hydroquinone oxidation was above the average, but selectivity remained low. The expanded gel catalyst 4E2/G with guanidyl groups was better than catalyst 4E2 with ethylenediamine ligands (Table 7). Increase of Cu(II) complexes concentration led to the decrease of catalysts activity (Fig. 6).
60 40 20 0 A
B
C
Fig. 6. Catalytic activity of hydroquinone oxidation as a function of Cu(II) ions loading (sample 4E2/G) A – 0.06; B – 0.09; C – 0.28; D – 0.98 mmol/g.
The EPR investigation on gel catalysts (4E2 and 4E2/G) indicated higher amounts of nitrogen donors in copper coordination sphere and formation of N3O complexes between three amino nitrogens and water oxygen (Table 8). Polymer structure influenced also on the type of Cu(II) complexes. More rigid structure of porous copolymers (P6E2, P6E2/G and P6E2/A) and longer distance between reactive amino groups resulted in decrease of nitrogen amount around Cu(II) and the presence of N2O2 complexes (Table 8). During transformation of amino groups (P6E2) to guanidyl ligands (P6E2/G or P6E2/A), no change in complex type was observed. Comparing the results of catalytic activity one can see strong effect of polymer structure but no effect of Cu(II) complexes type on catalysts properties.
80 P6E4/G P6E4/A 4E2/DAMO
70 60
%T
50 40 30 20 10 0 1800
1700
1600
D
Cu (II) loading (mmol/g)
1500
Wavenumber, cm
1400
1300
1200
-1
Fig. 5. FTIR spectra of modified St/DVB copolymers: (—) P6E2/G; () P6E2/A; (– – – ) 4E2/DAMO.
B.N. Kolarz et al. / Reactive & Functional Polymers 68 (2008) 1207–1217
The supports modified with hydrazine and in the next step by thiourea/ethyl iodide (4H4/G, P6H4/G and P6H5/ G) showed low nitrogen content, lower than before transformation (Tables 5 and 6). It is due to the side reactions and ammonia elimination (Scheme 2). Along with increase in transformation degree, broad peak at the range 1660– 1615 cm1 associated with the presence of Schiff base and guanidyl groups appeared on FTIR spectra (Fig. 4, P6H5/A). The degree of modification of the supports aminolysed with hydrazine and transformed by thiourea to G was lower than that for modification with EtDA. Furthermore, catalytic activity of samples H/G was poor (Table 7). It may be caused by additional formation of stiff intramolecular 5cycle rings during aminolysis with hydrazine which make impossible effective Cu(II) complexation (Scheme 2). The supports with amino groups modified with cyanamide (P6E2/A and P6H5/A) are characterized by high degree of transformation (nitrogen content) and reveal higher Cu(II) ion sorption than those modified with thiourea, but no increase in catalytic activity (Table 7). Our earlier investigation indicated that only catalysts with aminoguanidyl ligand obtained in direct aminolysis of nitrile groups in acrylonitrile copolymers with aminoguanidine salts showed the highest activity and selectivity (about 100%) [13,25–27]. It results from possible formation of N2O2 complexes with two amino and two carboxyl groups around Cu(II) plane. The catalysts with aminoguanidyl ligands (obtained by indirect aminolysis with H of nitrile groups in acrylonitrile copolymer crosslinked with DVB or trimethylolpropane trimethacrylate (TMPMA)) had good catalytic activity but insufficient selectivity [13]. They were characterized by low carboxyl groups concentration. In currently investigated catalysts the carboxyl groups are absent and their involvement in Cu(II) coordination sphere is impossible. The values of EPR parameters (AII and gII) (Table 8) for copolymers modified with hydrazine gave evidence for NO3 type complex which indicate low efficiency of ligand-copper binding and the presence of three water molecules in Cu(II) plane. Further modification to aminoguanidyl group lead to elongation of the ligands but do not change Cu(II) complex type. The EPR parameters of the resulting catalysts suggest that in general NO3 type complexes are formed by Schiff base or guanidyl groups and water molecule. In one case (P6H5/A), when the support provides greater amount of the ligands, an involvement of more nitrogen donors in Cu(II) coordination is indicated by the EPR parameters (Table 8). A new way of amino groups modification was the attachment of DAMO (Scheme. 1. IV) leading to formation of the interesting multifunctional ligand which presence was confirmed by FTIR spectra. A characteristic broad peak at 1675–1630 cm1 indicated accumulation of amino groups (Fig. 5. 4E2/DAMO). The sorption of Cu(II) ions and catalytic activity of this modified support were low (Table 7). All the investigated catalysts were active in the oxidation of DTBH2Q (Table 7). The reaction was carried out at 22 °C and after 30 min their selectivity was about 100%. At 35 °C the reaction rate was very high and its exact mea-
100 80
L DTBH2Q (%)
1216
60 40 20 0 A
B
C
Cu(II) loading (mmol/g) Fig. 7. Catalytic activity of 2,5-di-tert-butylhydroquinone oxidation as a function of Cu(II) loading (sample 4E2/G) A – 0.06; B – 0.28; C – 0.71 mmol/g.
surement was impossible. It is well known, that substituted phenols undergo oxidation easier than phenol [2]. The guanidyl groups were more reactive than amino groups and the oxidation degree of DTBH2Q increased with decreasing Cu(II) ions loading (Fig. 7). As the result of our experiments we can conclude that model reaction, the oxidation hydroquinone to p-benzoquinone, is better to test the catalytic activity of the samples than substituted phenols. 4. Conclusion
1. It is possible to synthesize supports useful as catalysts for phenols oxidation using very simple method of chloroacetylation of St/DVB copolymer. 2. Oxidation of di-tert-butyl substituted hydroquinones occurred easier than hydroquinone. 3. The model reaction oxidation of hydroquinone to pbenzoquinone is better to test the catalytic activity of samples than substituted phenols. 4. The expanded gel catalysts have better catalytic activity than with porous structure.
Acknowledgement This work was supported by Ministry of Scientific Research and Information Technology, Grant 4T09B 014 24. References [1] P. Hodge, D.C. Sherrington (Eds.), Polymer-supported Reactions in Organic Synthesis, Wiley-Interscience, New York, 1980. [2] D.C. Sherrington, P. Hodge (Eds.), Synthesis and Separation Using Functional Polymers, Wiley, Chichester, 1988. [3] C. Caze, P. Hodge, Macromol. Chem. 191 (1991) 1633. [4] S.D. Alexandratos, L.A. Hussain, Macromolecules 31 (1998) 3235. [5] A. Nouvet, F. Lamaty, R. Lazare, Tetrahedron Lett. 39 (1998) 3469. [6] E.R. Kenawy, F.I. Abdel-Hay, A.E. Raheem, R.E. Shanshoury, M.H.E. Newehy, J. Control. Release 50 (1998) 145. [7] A.I. Martin, M. Sanchezchoves, F. Arronz, React. Funct. Polym. 39 (1999) 179. [8] S.A. Kim, C.Y. Won, C.C. Chu, Carbohydr. Polym. 40 (1999) 183. [9] H. Xu, X. Hu, J. Polym. Sci. Chem. 36 (1998) 2151.
B.N. Kolarz et al. / Reactive & Functional Polymers 68 (2008) 1207–1217 [10] H. Xu, X. Hu, React. Funct. Polym. 42 (1999) 235. [11] K. Adjidjonou, C. Caze, Eur. Polym. J. 31 (1995) 749. [12] B.N. Kolarz, D. Jermakowicz-Bartkowiak, I. Owsik, J. Jezierska, React. Funct. Polym. 61 (2004) 335. [13] B.N. Kolarz, A. Jakubiak, J. Jezierska, Polimery 51 (2006) 561. [14] B.W. Zhang, K. Fischer, D. Bieniek, A. Kettrup, React. Polym. 24 (1994) 49. [15] A. Trochimczuk, Eur. Polym. J. 34 (1998) 1657. [16] B.N. Kolarz, Chem. Stos. 20 (1976) 399. [17] D. Jermakowicz-Bartkowiak, B.N. Kolarz, W. Tylus, Polymer 44 (2003) 5797. [18] M.B. Colella, S. Siggia, R.M. Barnes, Anal. Chem. 52 (1980) 967.
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}niger, Microchim. Acta (1956) 869. [19] W. Scho [20] A. Jakubiak, B.N. Kolarz, J. Jezierska, e-Polymers 2005, Conferences, International Polymer Seminar, Gliwice, 2005, p. 016. [21] A. Jakubiak, B.N. Kolarz, J. Jezierska, Macromol. Symp. 235 (2006) 127. [22] M. Bocˇa, D. Valigura, W. Linert, Tetrahedron 56 (2000) 441. [23] K.Y. Lee, K.H. Bouhadir, D.J. Mooney, Biomaterials 25 (2004) 2461. [24] Y. Zhang, J. Jiang, Y. Chen, Polymer 40 (1999) 6189. [25] I. Owsik, B.N. Kolarz, J. Mol. Catal. A 178 (2002) 63. [26] I. Owsik, B.N. Kolarz, Catal. Today 91–92 (2004) 199. [27] A. Jakubiak, I. Owsik, B.N. Kolarz, Annal. Polish Chem. Soc. 3 (2004) 955.
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Reactive & Functional Polymers journal homepage: www.elsevier.com/locate/react
Polymeric supports with amino groups from halogenoacetylated styrene/divinylbenzene copolymers _ Bozena N. Kolarz a, Anna Jakubiak a,*, Julia Jezierska b, Barbara Dach a a ´ skiego 27, Wrocław University of Technology, Faculty of Chemistry, Department of Polymer and Carbonaceous Materials, Wybrzez_ e Wyspian 50-370 Wrocław, Poland b University of Wrocław, Faculty of Chemistry, Joliot-Curie 14, 50-378 Wrocław, Poland
a r t i c l e
i n f o
Article history: Received 27 February 2008 Received in revised form 23 April 2008 Accepted 29 April 2008 Available online 4 May 2008
Keywords: Halogenoacetylation of styrene/ divinylbenzene copolymers Reductive amination Ethylenediamine Hydrazine Guanidyl ligands Oxidation catalysts
a b s t r a c t The introduction of amino groups to halogenoacetylated styrene/divinylbenzene (St/DVB) expanded gel or porous copolymer (2% or 10% DVB) with ethylenediamine (EtDA) or hydrazine (H) was carried out as a reductive or nonreductive amination. It has been found that the reductive amination in the presence of NaBH3CN is more effective than aminolysis without the reducing agent at room temperature. The amino groups were transformed to guanidyl ligands using thiourea/ethyl iodide mixture. Obtained supports with Schiff base bonds and guanidyl ligands after complexing Cu(II) ions are useful as oxidation catalysts. Their catalytic activity was tested in the model reaction – oxidation of hydroquinone to p-benzoquinone or 2,5-di-tert-butylhydroquinone to 2,5-di-tert-butylbenzoquinone. The expanded gel catalysts with guanidyl groups (ethylenediamine modification) showed the highest activity. EPR investigation on this group of catalysts indicated higher amounts of nitrogens in Cu(II) coordination sphere and formation of N3O complex between three amino nitrogens and water oxygen. The catalysts with aminoguanidyl groups (hydrazine modification) were characterized by low catalytic activity. It was a result of increase in intra and intermolecular crosslinking. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Chloromethyl ether is a common base product used to introduce exchangeable chlorine, which may be substituted for amines, in styrene/divinylbenzene copolymers (St/DVB). However, as strongly carcinogenic agent, its application is seriously restricted. Therefore better ways to insert exchangeable chlorine into macromolecules are searched. Well-known method of reactive and functional polymers synthesis is chloro- or bromoacetylation of styrene copolymers with acetyl chloride or halogenoacetyl chloride (Scheme 1.I) [1–4], but these processes are accompanied by side reactions resulting from the subsequent transformations [3]. The halogenoacetylation of 2 wt.% crosslinked gel or porous polystyrene beads with * Corresponding author. Tel.: +48 71 3203273; fax: +48 71 3202152. E-mail address: [email protected] (A. Jakubiak). 1381-5148/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.reactfunctpolym.2008.04.005
X(CH2)nCOCl carried out by Caze and Hodge [3] gave chlorine content about 2.75% for gel copolymers (yield of substitution 81%) and 2.23% (yield 71%) for porous ones. It was concluded that side reactions led to additional crosslinking, which was disadvantageous for the supports. Alexandratos and Hussain [4] introduced 3.11 mmol/g of chlorine into St/DVB copolymer using the reaction with chloroacetyl chloride in CS2 solution. It is also known that natural polymers with hydroxyl or carboxyl functional groups (cellulose, polysaccharides, dextrane, starch) reacted with halogenoacetyl chloride in different way [5–8]. In the next step of the transformation the chlorine in chloroacetylated copolymer can be exchanged by amine. Introduction of amino groups is possible by exchange of chlorine or by Schiff reaction with keto groups (Scheme 1.II). Chinese authors [9,10] investigated the reductive amination of acetylated St/DVB copolymer, i.e. treatment of
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P
+ CH2Cl
P
C Cl
C CH2Cl O
O I
+NH2CH2CH2NH2
P
C
CH2NHCH2CH2NH2
NCH2CH2NH2 +NH2C NH
II
+CH3C(=NOH)CCH3
SC2H5
P
O
C CH2NHCH2CH2NHC NH NCH2CH2NH2
C CH2NHCH2CH2N=C CH3
P
NCH2CH2NH2 HON CCH3
NH2
III
IV
Scheme 1. Modification of St/DVB copolymer. (I) Chloroacetylated support; (II) after aminolysis with EtDA; (III) after thiourea/ethyl iodide attachment; (IV) after DAMO attachment.
the acetylated St/DVB copolymer with ammonia or amines (methylamine, dimethylamine) in the presence of reducing agent, for example NaBH3CN in anhydrous methanol (65– 67 °C, 22 h). The optimal pH value for this reaction was generally about 6–8. When the molar ratio of acetylated groups to reducing agent was 1:1 and acetylated groups to methylamine was 1:8, the nitrogen content reached 6.65% and exchange capacity of resin was 4.67 mmol/g [10]. The reductive amination at temperature 25 °C caused decrease of nitrogen content to mere 1.5%. It should be noted that observed exchange capacities appeared to be, more or less, lower than the value calculated from the nitrogen content which is connected with the side reactions. The authors expected to find application for these anion exchangers [10]. However, since currently used reducing agent, i.e. NaBH3CN is expensive and modestly toxic, this new method cannot be applied in industry. Caze and co-worker [11] synthesized the chloroacetylated St/DVB supports that, after exchange of the chlorine for amino groups by potassium phtalimide, were used to enantioselective reduction of a-chloroacetophenone keto groups with NaBH4. The nitrogen content of supports was only about 0.6 mmol/g. The examples of chlorine exchange in chloroacetylated St/DVB with amine were shown in our paper [12]. Nowadays we know that this reaction, like the aminolysis of nitrile groups by hydrazine, is more complicated because the intramolecular and intermolecular reactions take place [13]. Zhang et al. [14] indicated a possibility of cycle forms creation during aminolysis with hydrazine. In case of our modifications the reactions become more complicated owing to Schiff base formation between amine and keto groups of chloroacetylated St/DVB copolymers. The aim of this work is to present the possibility of modifications of styrene/divinylbenzene copolymers with chloroacetyl chloride as ways to obtain the supports with sufficient amount of amino ligands after chlorine exchange with ethylenediamine or hydrazine. Our studies focused on the chlorine exchange at room temperature, when the
change of supramolecular structure was minimalized. After transformation of amino groups to guanidyl ligands and subsequent complexation with Cu(II) ions the supports were used as oxidation catalysts. 2. Experimental 2.1. Materials 2.1.1. Copolymers All starting styrene/divinylbenzene (St/DVB) copolymers were obtained using suspension polymerization method. The polymerization of expanded gel copolymer crosslinked with 2 wt.% of DVB was carried out in the presence of toluene (50 wt.% with respect to the monomer mixture) [15]. The porous copolymers were obtained with 10 wt.% of DVB in the presence of paraffin oil (80 wt.%). The porosity of copolymer was 0.6. The characteristics of porous structure of this copolymer were presented in [16]. 2.1.2. Acetylation of St/DVB copolymers St/DVB copolymers (4 g) were swollen in 16 cm3 of carbon tetrachloride. The next day 10 cm3 of acetyl chloride was added and 6 g of powdered anhydrous aluminium chloride was dosed in small portions. The mixture was conditioned for 24 h without air access and then refluxed for 15 min. The support was decomposed with 0.1 M HCl in dioxane and on the next day the beads were placed in column and washed with 0.2 M acetic acid, chloroform and methanol. Copolymer contained 5.9% of oxygen. Obtained acetylated copolymer (A) was treated as a blank sample for FTIR analysis. 2.1.3. Chloroacetylation or bromoacetylation of St/DVB copolymers St/DVB copolymers (4 g) were swollen in 50 cm3 of carbon disulfide and 8 cm3 of chloroacetyl chloride or 4.5 cm3 of bromoacetyl bromide. The mixture was cooled and 8 g of powdered anhydrous aluminium chloride was dosed.
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B.N. Kolarz et al. / Reactive & Functional Polymers 68 (2008) 1207–1217 Table 1 Characteristics of halogenoacetylated styrene/divinylbenzene copolymers Symbol
Copolymer
Diluent
1B 2B 3B 1 2 3 4 P5 P6
Gel Gel Gel Gel Gel Gel Gel Porous Porous
Carbon Carbon Carbon Carbon Carbon Carbon Carbon Carbon Carbon
tetrachloride disulfide disulfide tetrachloride tetrachloride disulfide disulfide tetrachloride disulfide
Timea (h)
Halogen (mmol/g)
a (%)
67 48 67 67 168 24 48 48 48
2.60 2.64 3.21 2.17 1.88 1.80 2.77 1.53 3.12
59.1 60.0 73.0 39.5 25.0 32.7 50.3 27.8 56.7
B – bromoacetylated; P – porous structure; a – degree of substitution. a Room temperature.
Whole mixture was conditioned for 48 h at room temperature without air access. Next it was processed as described above. The characteristics of halogenoacetylated copolymers are shown in Table 1. 2.1.4. Amination with ethylenediamine To 6 g of chloroacetylated copolymer swollen in 65 cm3 of dioxane 75.2 g of ethylenediamine (EtDA) was added. The mixture was stirred at 20 °C for 168 h. After reaction the mixture was acidified to pH 2 with 10% HCl and cyclized three times with 1% NaOH, water and 1% HCl. In case of reductive amination, 1 g of dry samples were swollen in 25 cm3 of anhydrous ethanol and NaBH3CN was added. The parameters of aminolysis are shown in Table 2 and characteristics of supports are presented in Table 3.
2.1.6. Modification of amino groups in supports The amino groups of supports were modified with thiourea in the presence of ethyl iodide to obtain ligands with guanidyl groups (G) (Scheme 1.III). The modification parameters were described in [12]. Another method of amino groups transformation to guanidyl ligands was reaction with cyanamide [17]. Primary amino groups of the supports were also modified with 2,3-butanedione monoxime (DAMO, Aldrich). The reaction route is shown in Scheme 1.IV. A 2.6 g of support with amino groups was swollen in 32 cm3 ethanol with 0.8 g DAMO. The mixture was refluxed for 4 h then washed with ethanol and water. The characteristics of support with guanidyl ligands and modified by DAMO are presented in Table 6. 2.2. Methods
2.1.5. Amination with hydrazine To 9 g of chloroacetylated copolymer swollen in 98 cm3 of dioxane 123 g of hydrazine (H) (80%) was added. The mixture was stirred at 20 °C for 168 h (Table 4). Further was proceeded as 2.1.4. The characteristics of supports are in Table 5.
2.2.1. Characteristics of supports Water regain was measured using a centrifugation technique (3000 rpm, 5 min). Nitrogen content was determined by Kjedahl’s method and amino groups were calculated (ZN). Anion exchange capacity was determined
Table 2 Parameters of halogenoacetylated St/DVB copolymers modification with ethylenediamine (EtDA) Symbol
Diluents
NaBH3CNa
Conditions
EtDA conc. (%)
b
N (mmol/g)
1B1 1B2 2B1 3B1 1E1 1E2 2E1 2E2 2E3 3E1 4E1 4E2 P5E1 P5E2 P5E3 P5E4 P6E1 P6E2
Dioxane Ethanol Dioxane Ethanol Dioxane Ethanol Dioxane Dioxane Dioxane Ethanol Dioxane Dioxane Dioxane without Dioxane Dioxane without Dioxane
+ + + + + + + +
4 h, ref. 4 h, ref. 24 h, room temperature 4 h, ref. 4 h, ref. 4 h, ref. 168 h, room temperature 168 h, room temperature 168 h, room temperature 4 h, ref. 168 h, room temperature 200 h, room temperature 168 h, room temperature 168 h, room temperature 2 h, ref. 2 h, ref. 168 h, room temperature 168 h, room temperature
19 6 28 6.7 32 6.6 100 50 27 6.6 36 36 100 100 3 11 100 53
24 18.5 24 8.2 27 13 136 136 153 15 39 39 109 109 6 12 67 67
4.42 5.17 2.57 5.65 2.28 2.78 2.77 2.58 2.66 3.27 4.23 4.40 3.12 3.48 3.24 3.51 4.32 4.27
X – Cl or Br; ref. – reflux; b – EtDA/X (molar ratio). a NaBH3CN:X (molar ratio) = 2.5:1.
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Table 3 Characteristics of supports with ethylenediamine ligands Symbol
Water regain (g/g)
ZN (mmol/g)
ZC (mmol/g)
Z NH2 (mmol/g)
Cu(II) sorption (mg/g)
1B1 1B2 2B1 3B1 1E1 1E2 2E1 2E2 2E3 3E1 4E1 4E2 P5E1 P5E2 P5E3 P5E4 P6E1 P6E2
2.35 3.52 2.10 2.71 2.14 1.05 0.71 1.32 1.60 1.08 1.28 1.73 1.25 1.25 1.20 1.22 1.33 1.31
1.1 2.6 1.3 2.8 1.1 1.4 1.4 1.3 1.3 1.6 2.0 2.2 1.5 1.7 1.6 1.8 2.2 2.1
1.1 2.4 0.9 2.6 1.0 1.3 0.5 0.5 0.3 1.5 1.6 2.2 1.1 0.5 0.5 0.6 1.6 1.6
0.8 1.0 0.6 2.0 0.5 0.9 0.4 0.5 0.3 1.2 1.4 2.2 1.1 0.5 0.5 0.6 1.6 1.6
5.36 11.96 3.37 8.55 2.73 2.40 1.62 1.46 1.46 3.87 5.18 9.25 2.14 1.47 1.17 1.52 – –
Table 4 Parameters of chloroacetylated St/DVB copolymer modification with hydrazine (H) Symbol
Diluent
Conditions
Hydrazine conc. (%)
b
N (mmol/g)
4H1 4H2 4H3 4H4 P6H1 P6H2 P6H3 P6H4 P6H5
Dioxane, NaBH3CNa Dioxane, NaBH3CNa Dioxane Dioxane, NaBH3CNa Dioxane Methanol, NaBH3CNa Dioxane Dioxane NaBH3CNa Dioxane
84 h, room temperature 168 h, room temperature 168 h, room temperature 132 h room temperature 48 h, room temperature 24 h, ref. 24 h, ref. 168 h, room temperature 168 h, room temperature
6 6 50 6 8 6 8 8 46
12 12 125 12 15 12 12 12 120
2.64 2.47 2.39 2.55 2.45 3.06 2.25 2.84 2.35
X – Cl or Br; b – hydrazine/X (molar ratio). a NaBH3CN:X (molar ratio) = 2.5:1.
Table 5 Characteristics of chloroacetylated St/DVB copolymer modified with hydrazine (H) Symbol
Water regain (g/g)
ZN (mmol/g)
ZC (mmol/g)
Z NH2 (mmol/g)
Cu(II) sorption (mg/g)
4H1 4H2 4H3 4H4 P6H1 P6H2 P6H3 P6H4 P6H5
2.23 2.02 1.51 1.93 1.33 1.31 1.31 1.24 1.31
1.3 1.5 1.2 1.2 1.2 1.5 1.1 1.4 1.2
1.0 1.2 1.5 0.9 0.8 1.2 0.9 0.9 0.7
0.3 0.4 1.0 0.3 0.2 0.8 0.7 0.4 0.4
3.46 1.62 4.06 2.43 2.68 2.73 1.21 1.09
Table 6 Characteristics of supports with guanidyl ligands Symbol
Water regain (g/g)
N (mmol/g)
ZN (mmol/g)
ZC (mmol/g)
Z NH2 (mmol/g)
Cu(II) sorption (mg/g)
4E2/G 4E2/DAMO P6E2/G P6E2/A 4H4/G P6H4/G P6H5/G P6H5/A
0.93 0.81 1.29 1.27 1.10 1.24 1.29 1.14
5.95 4.79 4.82 8.82 1.99 2.11 2.31 5.61
3.0 2.4 2.4 4.4 0.6 1.1 1.7 2.8
2.1 2.3 1.5 1.7 0.9 0.9 1.0 1.4
2.1 2.3 0.9 1.3 0.5 0.5 0.4 0.9
2.4 4.0 1.8 2.3 1.1 0.9 0.9 2.1
G – samples modified with thiourea; A – samples modified with cyanamide.
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by modified Colella-Siggia method [18]. A 0.5 g of support with amino groups was transformed to hydrochloride form by swelling in 0.1 M HCl (50 cm3) for 24 h. The sample was washed with anhydrous ethyl alcohol in column until chlorine was not detected. Then support was separated by centrifugation, carried into flask and 50 cm3 of 0.1 M NaOH was added. Concentration of basic and acidic groups (ZC) was calculated from the titration of solution from above the support. On the basis of chlorine concentration in this solution, amount of hydrogen chloride attached to reactive amino groups was determined by Volhard’s method ðZ NH2 Þ. }niger’s Chlorine and oxygen was measured using Scho method [19] and elemental analysis, respectively. Sorption of Cu(II) ions was determined by shaking of support samples with 104 M copper nitrate solution in 0.2 M acetate buffer (pH 5.6) at room temperature for 48 h. Then the supports were separated by filtration and metal concentration in solution was measured using atomic absorption spectroscopy (AAS) method on a Perkin–Elmer Analyst 100 spectrophotometer. Sorption of copper (mg/g, mmol/g) was calculated from the difference of Cu(II) concentration in solution before and after sorption. FTIR spectra in KBr pellets were recorded on Perkin–Elmer System 2000 FTIR spectrophotometer. The structure of Cu(II) active centres was studied by electron paramagnetic resonance (EPR) method at 77 K on the swollen samples, separated by filtration and air dried. The EPR spectra were recorded on a Bruker ESP 300E (Bruker, Germany) X-band spectrometer equipped with the Bruker NMR gaussmeter ER 035 M and the Hewlett-Packard microwave frequency counter HP 5350B. The EPR parameters were calculated by computer simulation using Bruker’s WIN-EPR SimFonia Software and are presented in Table 7. 2.2.2. Oxidation reaction Catalysts were swollen in 20 ml of hydrogen peroxide solution (5.6102 mol/l in acetate buffer pH 5.0) for
Table 7 Catalytic activity of samples Symbol
Cu(II) loading (mmol/g)
LH2 Q (%)
YQ (%)
LDTBH2 Q (%)
YDTBQ (%)
4E2
0.10 0.16 0.14 0.06 0.09 0.28 0.98 0.06 0.28 0.71 0.10 0.11 0.09 0.09 0.14 0.09 0.13 0.11 0.13
33.7
7.8
62.7 49.3
48 100
20.0 77.7 60.1 53.9 33.9
9.0 9.8 9.1 9.8 6.0 73.1 72.8 51.5
87 97 90.6
P6E2 4E2/G
4E2/DAMO P6E2/G2/G P6E2/A P6H5 4H4/G P6H5/G P6H5/A
43.0 20.5 22.0 23.7 18.6 59.5 22.4 22.1 16.7
9.3 9.6 11.3 14.0 10.2 48.5 13.6 10.1 7.1
LH2 Q , LDTBH2 Q – loss of hydroquinone or 2,5-di-tert-butylhydroquinone (%). YQ, YDTBQ – yield of p-benzoquinone or 2,5-di-tert-butylbenzoquinone (%).
30 min. Next, equal volume of 4103 mol/l hydroquinone (H2Q) or 1103 mol/l 2,5-di-tert-butylhydroquinone (DTBH2Q) was added in polyethylene flasks. The Cu(II) to substrate ratio was 1:10. Entire mixture was shaken (350 cycles/min) in desire time at 35 °C (H2Q) or at 22 °C (DTBH2Q). The concentrations of unreacted H2Q and pbenzoquinone (Q) or unreacted DTBH2Q and 2,5-di-tertbutylbenzoquinone (DTBQ) were determined by UV–vis spectrophotometry using JASCO 570c spectrophotometer at: k = 289 nm and k = 246 nm or k = 292 nm and k = 255 nm, respectively. Oxidation degree of H2Q (LH2 Q , %) or DTBH2Q (LDTBH2 Q , %) and yield of Q (YQ,%) or DTBQ (YDTBQ, %) after 60 min were calculated from following equations: LH2 Q = {D[H2Q]/[H2Q]0} 100% and YQ = {[Q]/[H2Q]0} 100%, respectively. The selectivity was defined as the ratio of main product concentration [Q] to the reacted substrate concentration [H2Q] [20,21]. The catalytic activity of samples is presented in Table 8. 3. Results and discussion 3.1. Supports synthesis Two types of St/DVB copolymers, one an expanded gel (2 wt.% DVB) [15] and another porous (10 wt.% DVB) [16], were halogenoacetylated with bromoacetyl bromide or chloroacetyl chloride. The yield of this reaction depended on the copolymer structure (expanded gel or porous) and solvent. The substitution degree was better when the reaction was carried out in the polar solvent such as carbon disulfide (Table 1). The yields of halogenoacetylated copolymers obtained in these reactions appeared to be similar. In the next syntheses chloroacetyl chloride has been used as cheaper and more useful compound. The FTIR spectra showed two carbonyl bands: one near 1700 cm1 due to chloroacetylated copolymer and second near 1680 cm1 ascribed to both chloroacetylated and crosslinked residues [3]. These peaks were related to vibration of arylketo groups (valence band) (Fig. 1. P6). Additionally, the band at 1286 cm1 assigned to –CH2– vibration in chloromethyl groups could be observed. The reaction of chlorine exchange in chloroacetylated copolymers by hydrazine (H) or ethylenediamine (EtDA) depended on various parameters like: time, temperature, kind of solvents, amine concentration and ratio of amine to Cl in chloroacetylated copolymers (b). The exchange of
Table 8 EPR parameters for Cu(II) complexes in prepared catalysts Catalyst
AII (104 cm1)
gII
g\
Complexes
4E2 4E2/G P6E2 P6E2/G P6E2/A 4H4/G P6H5 P6H5/G P6H5/A
184 184 185 184 185 167 157 162 192
2.236 2.236 2.255 2.277 2.250 2.310 2.336 2.310 2.233
2.050 2.055 2.050 2.069 2.066 2.066 2.070 2.065 2.070
N3O N3O N2O2 N2O2 N2O2 NO3 NO3 NO3 N3O
P – porous catalysts.
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100 P6 4E1 P6E2
80
%T
60
40
20
0 1800
1700
1600
1500
1400
1300
1200
Wavenumber, cm-1 Fig. 1. FTIR spectra of chloroacetylated St/DVB copolymer after EtDA amynolysis (—) P6; () 4E1; (– – – ) P6E2.
chlorine by these amines was possible due to long reaction time at room temperature or the reflux of solution. During the chlorine exchange a Schiff base creation between keto groups and amine took place (Scheme 1.II). Imine bonds formation was limited by the reaction conditions, e.g. temperature. Chinese authors [10] introduced into acetylated St/DVB copolymer about 3–4.8 mmol/g of nitrogen during the reductive amination with methylamine hydrochloride in the presence of NaBH3CN in boiling anhydrous methanol and only 1 mmol/g of the support at room temperature. To confirm the possibility of Schiff base formation we tested our acetylated gel copolymer (A) (degree of acetylation about 60%) modified with EtDA at room temperature (without NaBH3CN). After 168 h nitrogen content was about 1.1 mmol/g which indicates a Schiff base creation. It was additionally confirmed by the appearance of peak at 1634 cm1, corresponding to –CH@N–bond, close to the strong peak 1682 cm1 related to the nonreacted carbonyl groups (Fig. 2D). The introduction of amino groups into halogenoacetylated copolymers was carried out using reductive or nonreductive amination with EtDA [10]. During both modifications two kinds of reactions were possible: exchange of chlorine and Schiff base formation. However, when these transformations were carried out in anhydrous alcohol with reducing agent, the Schiff base was hydrogenated and stable amino bonds were created. Table 3 presents characteristics of bromoacetylated (B) and chloroacetylated St/DVB copolymers modified with EtDA in various reaction conditions. The unstable imine bonds were hydrogenated when the high amount of reducing agent, i.e. NaBH3CN was used. On the basis of valence vibrations m(N–H) and m(C@N) one can identify, with some restrictions, the kind of bonds. In
the interesting wavelength range FTIR spectra showed typical bands for the deformation vibration of N–H groups (1630–1530 cm1), vibration of C@N in Schiff base (1695–1585 cm1) [22], hydrazine groups (1658 cm1) [23] and guanidyl groups (1632, 1654 cm1) [24]. FTIR spectrum of supports aminolysed with EtDA indicated the disappearance of the bands at 1700 and 1680 cm1 characteristic for the arylketo groups absorption and peak at 1286 cm1 attributed to chloromethyl groups. At the same time appearance of wide bands at 1590–1670 cm1 was observed as the result of superimposing bands from primary amino groups and secondary amino groups (Fig. 1, 4E1). When aminolysis was carried out at room temperature without the reducing agent, more intensive peak at 1695–1655 cm1 attributed to superimposed bands from the amino groups vibration and stretching vibration of the imino groups in the Schiff base appeared (Fig. 1, P6E2). Additionally, after aminolysis, the intensity of peak 3420–3440 cm1 connected with the amino groups vibration increased. The samples with low degree of halogenoacetylation (3 and P5, Table 1) were characterized by low nitrogen content. For the bromoacetylated expanded gel copolymers the exchange of bromine by EtDA solution (in reflux) led to higher substitution degree than the aminolysis of chloroacetylated copolymers at room temperature. However, this degree of substitution by EtDA was sufficient for preparation of the supports useful in catalytic systems. The influence of the aminolysis time with EtDA on nitrogen content in chloroacetylated copolymer 4 at room temperature is presented in Fig. 3. The time of 168 h is enough to introduce about 4.23 mmol nitrogen per gram of the support 4E1 (Table 2). The samples with amino groups obtained from bromoacetylated copolymers were characterized by higher swell-
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100 A D 80
%T
60
40
20
0 1800
1700
1600
1500
1400
1300
1200
Wavenumber, cm-1 Fig. 2. FTIR spectra of acetylated St/DVB copolymers (A) and modified with EtDA (D).
N content (mmol/g)
5 4 3 2 1 0 2
4
72
168
200
Aminolysis time (h) Fig. 3. The influence of modification time on nitrogen content for support 4 (room temperature).
ing than chloroacetylated samples. Concentration of accessible amino groups determined by Colella-Siggia method (ZC) was similar to amount of these groups calculated from nitrogen content (ZN). The supports from chloroacetylated copolymers were characterized by lower free amino groups concentration than groups calculated from nitrogen content. Modification in boiling amine/solvent mixture or concentrated amine caused lower accessibility of amino groups as a result of intramolecular amino groups reactions (Tables 2 and 3). It has been found that the reductive amination is more effective than aminolysis at room temperature without the reducing agent. The hydrogenation stabilized unsaturated bonds and allowed to use these resins as anion exchangers in acidic and basic solutions. After Cu(II) ions complexation these supports with Schiff base bonds and others amino groups are also useful as catalysts.
The parameters of chloroacetylated St/DVB copolymers modification with hydrazine are presented in Table 4 (Scheme 2). In all cases the degree of modification by hydrazine (H) and amino groups concentration were smaller than after EtDA aminolysis. This transformation was independent of hydrazine concentration, hydrazine chlorine exchange ratio or presence of reducing agent. It ensued from the fact that the cyclization between amino groups described by Zhang et al. [14] was probably the main reaction. The possibility of cyclization or crosslinking with the emission of ammonia is showed in Scheme 2.II and III. FTIR spectrum for sample P6H5 (Fig. 4) is similar to that aminolysed with EtDA (Fig. 1), but the spectrum is less intensive, because of lower concentration of functional groups. The sorption of Cu(II) ions was carried out from diluted copper nitrate solution (104 M) in which the ratio of amino groups to Cu(II) ions was 10. Low concentration of Cu(II) ions in solution and amount of amino ligands higher than metal ions resulted in low sorption degree. However, the data in Tables 3 and 5 showed that all supports demonstrated ability for sorption of Cu(II) ions. 3.2. Catalytic activity We have published that supports with aminoguanidyl groups after Cu(II) ions sorption were better oxidation catalysts than supports with others amino groups [13,25–27]. Their catalytic activity was tested in two model reaction of hydroquinone (H2Q) to p-benzoquinone (Q) or 2,5-di-tertbutylhydroquinone (DTBH2Q) to 2,5-di-tert-butylbenzoquinone (DTBQ) oxidation using hydrogen peroxide (Scheme 3).
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P
C CH2Cl + NH2NH2
P
O
C
CH2 NH NH2
N
NH2
I
-NH3
-NH3
P
C
CH2 NH NH2
N P
C II
CH2
N
NH
NH
N
NH P
C
CH2 NH NH2
III Scheme 2. Modification of chloroacetylated St/DVB copolymers: (I) with hydrazine; (II) after intramolecular reaction; (III) after intermolecular reaction.
70 P6H5 P6H5/G P6H5/A
60
%T
50
40
30
20
10 1800
1700
1600
1500
1400
1300
1200
Wavenumber, cm-1 Fig. 4. FTIR spectra of modified St/DVB copolymers: (—) P6H5; () P6H5/G; (– – – ) P6H5/A.
O
OH R
R
H 2O 2
H 2 Q:
R
R
DT BH 2 Q:
OH
O
H2Q ( λ =289 nm)
Q ( λ = 246 nm)
DTBH2Q ( λ =292 nm)
R= -H R= -C(C H 3 ) 3
DTBQ ( λ =255 nm)
Scheme 3. Oxidation of hydroquinone (H2Q) or 2,5-di-tert-butylhydroquinone (DTBH2Q).
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100 80
LH 2Q (%)
One can see from our earlier investigation that there are two methods of introducing of guanidyl ligands to supports [13]. The first consists of direct exchange of chlorine in support with guanidine or aminoguanidine salts, or aminolysis of acrylonitrile groups in crosslinked acrylonitrile copolymers with these salts. The second one is based on indirect, several-step reactions. A few indirect ways of modification of amino groups to guanidyl ligands have been studied. After attaching thiourea/ethyl iodide to EtDA ligands the catalyst with guanidyl ligands was obtained (Scheme 1.III) [12]. In case of the support modified by hydrazine the aminoguanidyl ligands appeared, because amino groups are accessible to react with thiourea. The side reaction is crosslinking between amino groups with ammonia elimination. The next method of transformation is attaching cyanamide to amino groups [17]. Supports with ethylenediamine (E) or hydrazine (H) groups modified to guanidyl ligands in the reaction with thiourea (G) or cyanamide (A) are characterized in Table 6. In supports with EtDA ligands after modification with cyanamide, as well as with thiourea, the nitrogen content significantly increased. At the same time the concentration of free amino groups was in the same level. FTIR spectra of modified supports with guanidyl ligands are presented in Fig. 5. The superposition of characteristic peaks from amino groups was observed. The catalytic activity of all investigated catalysts in the model reaction of hydroquinone oxidation was above the average, but selectivity remained low. The expanded gel catalyst 4E2/G with guanidyl groups was better than catalyst 4E2 with ethylenediamine ligands (Table 7). Increase of Cu(II) complexes concentration led to the decrease of catalysts activity (Fig. 6).
60 40 20 0 A
B
C
Fig. 6. Catalytic activity of hydroquinone oxidation as a function of Cu(II) ions loading (sample 4E2/G) A – 0.06; B – 0.09; C – 0.28; D – 0.98 mmol/g.
The EPR investigation on gel catalysts (4E2 and 4E2/G) indicated higher amounts of nitrogen donors in copper coordination sphere and formation of N3O complexes between three amino nitrogens and water oxygen (Table 8). Polymer structure influenced also on the type of Cu(II) complexes. More rigid structure of porous copolymers (P6E2, P6E2/G and P6E2/A) and longer distance between reactive amino groups resulted in decrease of nitrogen amount around Cu(II) and the presence of N2O2 complexes (Table 8). During transformation of amino groups (P6E2) to guanidyl ligands (P6E2/G or P6E2/A), no change in complex type was observed. Comparing the results of catalytic activity one can see strong effect of polymer structure but no effect of Cu(II) complexes type on catalysts properties.
80 P6E4/G P6E4/A 4E2/DAMO
70 60
%T
50 40 30 20 10 0 1800
1700
1600
D
Cu (II) loading (mmol/g)
1500
Wavenumber, cm
1400
1300
1200
-1
Fig. 5. FTIR spectra of modified St/DVB copolymers: (—) P6E2/G; () P6E2/A; (– – – ) 4E2/DAMO.
B.N. Kolarz et al. / Reactive & Functional Polymers 68 (2008) 1207–1217
The supports modified with hydrazine and in the next step by thiourea/ethyl iodide (4H4/G, P6H4/G and P6H5/ G) showed low nitrogen content, lower than before transformation (Tables 5 and 6). It is due to the side reactions and ammonia elimination (Scheme 2). Along with increase in transformation degree, broad peak at the range 1660– 1615 cm1 associated with the presence of Schiff base and guanidyl groups appeared on FTIR spectra (Fig. 4, P6H5/A). The degree of modification of the supports aminolysed with hydrazine and transformed by thiourea to G was lower than that for modification with EtDA. Furthermore, catalytic activity of samples H/G was poor (Table 7). It may be caused by additional formation of stiff intramolecular 5cycle rings during aminolysis with hydrazine which make impossible effective Cu(II) complexation (Scheme 2). The supports with amino groups modified with cyanamide (P6E2/A and P6H5/A) are characterized by high degree of transformation (nitrogen content) and reveal higher Cu(II) ion sorption than those modified with thiourea, but no increase in catalytic activity (Table 7). Our earlier investigation indicated that only catalysts with aminoguanidyl ligand obtained in direct aminolysis of nitrile groups in acrylonitrile copolymers with aminoguanidine salts showed the highest activity and selectivity (about 100%) [13,25–27]. It results from possible formation of N2O2 complexes with two amino and two carboxyl groups around Cu(II) plane. The catalysts with aminoguanidyl ligands (obtained by indirect aminolysis with H of nitrile groups in acrylonitrile copolymer crosslinked with DVB or trimethylolpropane trimethacrylate (TMPMA)) had good catalytic activity but insufficient selectivity [13]. They were characterized by low carboxyl groups concentration. In currently investigated catalysts the carboxyl groups are absent and their involvement in Cu(II) coordination sphere is impossible. The values of EPR parameters (AII and gII) (Table 8) for copolymers modified with hydrazine gave evidence for NO3 type complex which indicate low efficiency of ligand-copper binding and the presence of three water molecules in Cu(II) plane. Further modification to aminoguanidyl group lead to elongation of the ligands but do not change Cu(II) complex type. The EPR parameters of the resulting catalysts suggest that in general NO3 type complexes are formed by Schiff base or guanidyl groups and water molecule. In one case (P6H5/A), when the support provides greater amount of the ligands, an involvement of more nitrogen donors in Cu(II) coordination is indicated by the EPR parameters (Table 8). A new way of amino groups modification was the attachment of DAMO (Scheme. 1. IV) leading to formation of the interesting multifunctional ligand which presence was confirmed by FTIR spectra. A characteristic broad peak at 1675–1630 cm1 indicated accumulation of amino groups (Fig. 5. 4E2/DAMO). The sorption of Cu(II) ions and catalytic activity of this modified support were low (Table 7). All the investigated catalysts were active in the oxidation of DTBH2Q (Table 7). The reaction was carried out at 22 °C and after 30 min their selectivity was about 100%. At 35 °C the reaction rate was very high and its exact mea-
100 80
L DTBH2Q (%)
1216
60 40 20 0 A
B
C
Cu(II) loading (mmol/g) Fig. 7. Catalytic activity of 2,5-di-tert-butylhydroquinone oxidation as a function of Cu(II) loading (sample 4E2/G) A – 0.06; B – 0.28; C – 0.71 mmol/g.
surement was impossible. It is well known, that substituted phenols undergo oxidation easier than phenol [2]. The guanidyl groups were more reactive than amino groups and the oxidation degree of DTBH2Q increased with decreasing Cu(II) ions loading (Fig. 7). As the result of our experiments we can conclude that model reaction, the oxidation hydroquinone to p-benzoquinone, is better to test the catalytic activity of the samples than substituted phenols. 4. Conclusion
1. It is possible to synthesize supports useful as catalysts for phenols oxidation using very simple method of chloroacetylation of St/DVB copolymer. 2. Oxidation of di-tert-butyl substituted hydroquinones occurred easier than hydroquinone. 3. The model reaction oxidation of hydroquinone to pbenzoquinone is better to test the catalytic activity of samples than substituted phenols. 4. The expanded gel catalysts have better catalytic activity than with porous structure.
Acknowledgement This work was supported by Ministry of Scientific Research and Information Technology, Grant 4T09B 014 24. References [1] P. Hodge, D.C. Sherrington (Eds.), Polymer-supported Reactions in Organic Synthesis, Wiley-Interscience, New York, 1980. [2] D.C. Sherrington, P. Hodge (Eds.), Synthesis and Separation Using Functional Polymers, Wiley, Chichester, 1988. [3] C. Caze, P. Hodge, Macromol. Chem. 191 (1991) 1633. [4] S.D. Alexandratos, L.A. Hussain, Macromolecules 31 (1998) 3235. [5] A. Nouvet, F. Lamaty, R. Lazare, Tetrahedron Lett. 39 (1998) 3469. [6] E.R. Kenawy, F.I. Abdel-Hay, A.E. Raheem, R.E. Shanshoury, M.H.E. Newehy, J. Control. Release 50 (1998) 145. [7] A.I. Martin, M. Sanchezchoves, F. Arronz, React. Funct. Polym. 39 (1999) 179. [8] S.A. Kim, C.Y. Won, C.C. Chu, Carbohydr. Polym. 40 (1999) 183. [9] H. Xu, X. Hu, J. Polym. Sci. Chem. 36 (1998) 2151.
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