Solvent Effect on Complexation of Titanium

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13C-NMR, FT-IR spectroscopy and elemental analysis. The investigation shows ... The 13C NMR spectra were recorded on Bruker .... (enolic form; see Table I).
Journal of Inorganic and Organometallic Polymers and Materials, Vol. 15, No. 3, September 2005 ( 2005) DOI: 10.1007/s10904-005-7877-2

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Solvent Effect on Complexation of Titanium Tetraethoxide with Allylacetoacetate Asgar Kayan

The effect of the solvent butanol on the complexation reaction of allylacetoacetate (AAA) with titanium tetraethoxide. (Ti(OEt)4) in molar ratio Ti(OEt)4:AAA = 1:1 was investigated by 13 C-NMR, FT-IR spectroscopy and elemental analysis. The investigation shows that some ethoxy groups that are attached to the titanium are substituted with butoxy groups. The hydrolytic stability of the allylacetoacetate–Ti complex in a molar ratio Ti(OEt)4:H2O = 1:4 was also characterized by spectroscopic techniques and elemental analysis. The result of this characterization shows that almost 20% of the AAA and some ethoxy groups are released from the hydrolyzed product. KEY WORDS: Sol-gel; solvent effect; allylacetoacetate; hydrolysis; titanium tetraethoxide.

Organic solvents (i.e. alcohols) can substitute with alkoxy groups on the metal alkoxides to improve the properties of the products. The solvents are important to adjust steric balance, establish hydrophilic/hydrophobic balance, control porosity, direct chemical reactivity, and control hydrolysis and condensation [2,10]. Reactions of AAA with Ti(OEt)4 were studied in ethanol and ethyl methyl ketone [5,11]. However, the investigation of the reaction in the butanol, which is different from the alkoxy group of the precursor, has not been reported. This report is a study of the influence of solvent in the synthesis of complexes involving titanium and in the hydrolysis of the product.

1. INTRODUCTION The sol-gel process is a way to produce inorganic–organic hybrid polymers in a solvent. The properties of sol-gel products depend on (a) the precursors such as metal alkoxides, (b) the processing temperature, (c) the complexing ligands and (d) the organic solvents. The organic solvents and complexing ligands are the main chemical parameters [1,2]. Complexing ligands such as allylacetoacetate (AAA), cis-2-butene-1,4-diol, 3-pentenoic acid and methacrylic acid have been used in sol-gel processing to modify the reactivity of metal alkoxides and to control the processing of final gels or particles [3–9]. For example, reaction between metal alkoxides, where the metals are Ti, Zr, Sn and Al, and AAA (CH2 @CHCH2O(O@)CCH2C(@O)CH3) result in the transfer of an acidic proton from AAA to an alkoxy ligand, where alkoxy ligands are n-butoxide, n-propoxide, ethoxide, etc. to produce the organic–inorganic precursor and an alcohol.

2. EXPERIMENTAL 2.1. Methods and Materials The 13C NMR spectra were recorded on Bruker AC200 spectrometer at fields of 4.7 T. 13C NMR: inverse gated decoupling, repetition time: 10 s, pulse angle: 60, number of scans: 80–400. The Fourier

Department of Chemistry, Kocaeli University, Izmit, Turkey. E-mail: [email protected]

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Transform Infrared (FT-IR) spectra of products were recorded on a Bruker IFS-25 spectrometer. Elemental analyses were performed by The Institute for New Materials, Saarbruecken. Chemicals such as titanium tetraethoxide (Ti(OEt)4 (%95, Merck), allylacetoacetate (AAA) (98%, Aldrich), and butanol were used in the experiments without further purification. In order to examine the substitution reaction, Ti(OEt)4 was dissolved in butanol. n

2.2. Preparation of [Ti(OEt)3-x(OBu )x(AAA)]n (1) Ti(OEt)4 (0.01 mol) was stirred in butanol (10 g) for 2 min and AAA (0.01 mol) was added to the solution. The solution changed from cloudy to light yellow within a minute. The mixture was stirred for 2 h at room temperature. The solvent butanol and liberated ethanol were removed from the mixture under reduced pressure (5 mbar) at 60C and an orange viscous liquid was obtained. Peaks in the 13C NMR spectrum in CHCl3 (Fig. 2) that are attributable to coordinated AAA have the following chemical shifts (¶ ppm) and assignments: 25.0 (CH3, AAA, g¢), 65.2 (C(O)OCH2, c¢), 88.0 (C(O)CHC(O), e¢), 116.8–117.8 (CH2 @, doublet, a¢), 133.4–132.6 (CH=, doublet, b¢), 172.6–172.1 (C=C–O–Ti, doublet, f¢), 184.0–185.2 (CH2O–C=O–Ti, doublet, d¢). Peaks for coordinated OBun groups [Ti-(OCH12 CH22 CH32 CH43 )x] in ppm: 74.9 (OCH12 ), 35.0 (CH22 ), 19.2(CH32 ) 13.8 (CH43 ). Peaks for coordinated OEt groups [(TiOCH12 CH23 )3-x] in ppm: 71.0 (OCH12 ), 18.0 (CH23 ). FT-IR (in CH3Cl):lC@C : 1644 and 1618 cm)1 (enolic

form and free allyl group, respectively),lCAO : 1540 cm)1 (enolic form). Elemental analysis: Calculated for [Ti(OEt)3(AAA)]n (FW: 324 g/mol): C = 48.19%, H = 7.4%. Found: C = 52.31%, H = 8.38%. The considerable difference between the calculated and found percentages of carbon (viz. 4.21%) is a result of n-butoxy substitution for ethoxy groups on titanium. 2.3. Hydrolysis of [Ti(OEt)3-x(OBun)x(AAA)]n (2) Compound 1 was prepared as mentioned above. Before removing butanol, 4 moles of water per mole Ti(OEt)4 were added dropwise to the solution and the solution was stirred for 1 h at room temperature. Butanol and the liberated ethanol were removed from mixture under reduced pressure (5 mbar) at 60C and a light brown solid was obtained. Peaks in the 13C NMR spectrum (in CHCl3, Fig. 3) that are attributed to coordinated AAA appear as follows (¶ ppm): 25.4 (CH3, g¢), 65.4 (C(O)OCH2,c¢), 89.7 (C(O)CHC(O), e¢), 118.3 (CH2 @, a¢), 132.4 (CH=, b¢), 172.9 (C=C– O–Ti, broad, f¢), 185.7 (CH2O–C@O–Ti, broad, d¢). Peaks for coordinated OBun groups (¶ ppm): 75.0 (OCH12 Þ, 35.0 (CH22 ), 19.2 (CH32 ) 14.1 (CH43 ). Peaks for coordinated OEt groups (¶ ppm): 71.0 (OCH12 ), 19.2 (CH23 ). FT-IR (in CHCl3):lC@C : 1632 cm)1 (enolic form and free allyl group), lCAO : 1560 cm)1 (enolic form; see Table I). Elemental analysis: Found, C=35.98%, H=5.268%. The 13C NMR spectrum includes characteristic peaks for dissociated AAA from the hydrolyzed

Table I. FT-IR spectra of compounds 1 and 2 (cm)1) [13] Compound 1

2961 (CH3, asym str, s) 2934 (CH2, asym str, s) 2882 (CH3, sym str, s) 1644–1618 (C@C, enolic form and free allyl group, m) 1540 (COO asym str, m) 1472 (COO sym str, m) 1394 (CH3, asym bend, m) 1289 (CH2, out-of-plane bend, m) 1170–1034 (C–O str, C–C str, s) 998 (CH@CH, C–H out-of-plane bend, m) 966 (CH3 AC, str, m) 732–597 (chelate Ti–O, str, and Ti–O, br, m) 480 (Ti–O, str, br, m)

Spectra recorded in CHCl3: s, strong; m, medium; w, weak; br, broad; sh, shoulder.

Compound 2 3355 (O–H, str, br, m) 2974 (CH3, asym str, s) 2947 (CH2, asym str, s) 2882 (CH3 sym str, s) 1632 (C@C, enolic form and free allyl group, m) 1737 (C–O, small, free keto group) 1710 (C@O, small, free keto group) 1560 (COO asym str, m) 1460 (COO, sym str, m) 1395 (–CH3, asym bend, m) 1305 (O–H, in-plane bend, m) 1276 (CH2, out-of-plane bend, m) 1180–1040 (C–O and C–C str, s) 998 (CH@CH, C–H out-of-plane bend, m) 973 (CH3 AC, str, m) 737–597 (chelate Ti–O, str, and Ti–O, br, m) 478 (Ti–O, str, m)

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product. Data for dissociated AAA in the keto form in ppm appear at 25.4 (CH3, g), 50.1 (C(O)CH2C(O), e), 66.1 (OCH2, c), 119.0 (CH2 @, a), 131.7 (CH@, b), 167.0 (COO, d), and 200.7 (C@O, f) [7,8]. Almost 20% of the AAA, which is determined from signal intensity of coordinated COO to released COO from the titanium complex, was released from complex by hydrolysis. 3. RESULTS AND DISCUSSION Fig. 1. Complexation reaction of Ti(OEt)4 with AAA.

The reaction between AAA and Ti(OEt)4 in ethanol was studied and characterized spectroscopically [5]. The solvent butanol was used for comparing the degree complexation or substitution and the effect on stability of the titanium ethoxide complex. 13C NMR and FT-IR spectra and elemental analyses were used to show the changes in the complexation reaction in the presence of solvent butanol. The 13C NMR spectrum of free AAA shows that the reagent is in the keto–enol form in the ratio of 9:1 [5, 12]. The carbon atom signals (Fig. 1) of AAA appear at 21.1 (g¢), 30.0 (g), 49.9 (e), 64.5 (c¢), 65.7 (c), 89.5 (e¢), 118.0 (a¢), 118.5 (a), 132.0 (b), 132.4 (b¢), 166.9 (d), 172.3 (f¢), 176.0 (d¢) and 200.5 (f) ppm [7, 8]. When AAA is coordinated to titanium ethoxide, the 13 C NMR chemical shift of the carbonyl carbons of the AAA moiety shifts to a different region in the spectrum; e.g. for [Ti(OEt)3-x(OBun)x(AAA)]n

Fig. 2.

13

¶ = 172.6–172.1 ppm for C@C–O–Ti (doublet, f¢) and 184.0–185.2 ppm for CH2O–C@O–Ti (doublet, d¢) (Fig. 2). These values indicate complexation with the enolic form of AAA. In addition, peaks at 74.9 (OCH12 ), 35.0 (CH22 ), 19.2 (CH32 ) 13.8 ppm (CH43 ) (i.e. Ti–OCH12 CH22 CH32 CH43 ) for 1 show that the n-butoxy groups are substituted with ethoxy groups and coordinated to titanium. The signals at 71.0 ppm (OCH12 ) and 18.0 ppm (CH23 , TiAOCH12 CH23 ) are evidence for the presence of ethoxy groups on titanium. Four bands in the FT-IR spectrum of uncoordinated AAA were observed at 1740 cm)1 (lC A OðKÞ ), 1715 cm)1 (lC@OðKÞ ), 1650 cm)1 (lCAO;C@ðEÞ ) and 1633 cm)1 (lC@C Þof the allyl group. No bands are seen in the carbonyl region (1740–1715 cm)1) of compound 1, which was prepared in 1:1 ratio.

C NMR spectrum of [Ti(OEt)3-x(OBun)x(AAA)]n (1).

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Fig. 3.

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C NMR spectrum of hydrolyzed product [Ti(OEt)3-x(OBun)x(AAA)]n (2).

Therefore, two carbonyl groups of AAA must be in a chelating coordination mode [5,8]. In other words, AAA coordinates to titanium in the enolic form. A band at approximately 1644 cm)1 indicates the presence of the uncoordinated double bond of the allyl group. Additional peaks and assignments are summarized in Table I. Elemental analysis provides added evidence for the formation of [Ti(OEt)3-x(OBun)x (AAA)]n. The calculated percentages of C and H for [Ti(OEt)3(AAA)]n are 48.1% and 7.4%, respectively; however, the percentages from elemental analysis are 52.31 and 8.38. This indicates a partial substitution of ethoxy groups on titanium with n-butoxy groups to form [Ti(OEt)3-x(OBun)x(AAA)]n. The hydrolysis of compound 1 was also investigated. For example, the 13C NMR spectrum of the hydrolyzed product of [Ti(OEt)3-x(OBun)x(AAA)]n (Fig. 3) displays an intensity ratio of free carbon (COO) to bonded carbon of AAA of 0.76/3.7, which indicates that almost 20% AAA is freed from the titanium complex. The shifts and assignments of dissociated AAA (in the keto form) are ¶ = 25.4 (CH3, g), 50.1 (C(O)CH2C(O), e), 66.1 (OCH2, c), 119.0 (CH2 @, a), 131.7 (CH=, b), 167.0 (COO, d), and 200.7 (C=O, f) ppm. The 13C NMR spectrum of hydrolyzed product also shows characteristic peaks at 75.0 (OCH12 ), 35.0 (CH22 ), 19.2 (CH32 ), and 14.1 ppm (CH43 ) for the butoxy groups coordinated to titanium.

The salient bands in the FT-IR spectrum of [Ti(OEt)3-x(OBun)x(AAA)]n-hydrolysate are summarized in Table I. The spectrum exhibits a prominent OAH stretching band at 3355 cm)1. The presence of an OH band confirms that some of the alkoxy groups in 1 are removed by hydrolysis–condensation. Elemental analysis provides additional evidence for hydrolysis–condensation reactions. The percentages of C and H for the [Ti(OEt)3-x(OBun)x(AAA)]nhydrolysate are 35.98% and 5.26%, respectively which are reduced from 52.31% and 8.38% in 1. Thus, the number of ethoxy and butoxy groups bonded to titanium decreases and number of OH groups and oxy groups increases on hydrolysis and condensation.

4. CONCLUSIONS An inorganic–organic hybrid titanium compound and its hydrolyzed product were synthesized in butanol by the sol-gel process. The complexation reaction between titanium tetraethoxide and AAA using 1:1 mole ratio of reactants is complete. A substitution reaction occurs between ethoxy and butoxy groups i.e., the formation of [Ti(OEt)3-x(OBun)x(AAA)]n. The product 1 is suitable for additional polymerization and addition reactions due to the presence of an

Solvent Effect on Complexation of Titanium Tetraethoxide uncoordinated double bond [5]. Hydrolysis of 1 liberates 20% AAA from the complex under the reaction conditions. This result is supported by the 13C NMR spectra. After hydrolysis, some ethoxy and butoxy groups remain bonded to titanium.

REFERENCES 1. M. J. Percy, J. R. Bartlett, J. L. Woolfrey, L. Spiccia, and B. O. West, J. Mater.Chem. 9, 499 (1999). 2. C. Sanchez and F. Ribot, New J. Chem. 18, 1007 (1994). 3. J. C. Debsikdar, J. Non-Cryst. Solids 86, 231 (1986). 4. A. Kayan, J. Inorg. Organomet. Polym. 13, 29 (2003).

365 5. A. Kayan, D. Hoebbel, and H. Schmidt, J. Appl. Polym. Sci. 95, 790 (2005). 6. G. Bulut, E. Mercanci, and A. Kayan, J. Inorg. Organomet. Polym. 3, 191 (2004). 7. D. Hoebbel, T. Reinert, and K. Endres, H. Schmidt, A. Kayan, and E. Arpac, Proc. First Europe Workshop on Hybrid OrganicInorganic Materials, Bierville, France, pp. 319–323. 8. D. Hoebbel, T. Reinert, H. Schmidt, and E. Arpac, J. Sol-Gel Sci. Technol. 10, 115 (1997). 9. U. Schubert, E. Arpac, W. Glaubitt, A. Helmerich, and C. Chau, Chem. Mater. 4, 291 (1992). 10. Y. Chujo and T. Saegusa, Adv. Polym. Sci. 100, 12 (1992). 11. A. Kayan, Master’s thesis (Inonu¨ University, Malatya, 1992). 12. E. Breitmeier and W. Voelter, Carbon-13 NMR Spectroskopie (VCH Verlagsgesellschaft, Weinheim, 1990) 232. 13. P. Crews, J. Rodriguez, and M. Jaspars, Organic Structure Analysis (Oxford University Press, Oxford, 1998).