Polymer Journal, Vol. 29, No. 3, pp 261-268 (1997) Synthesis of Polyesters from Terephthalaldehyde and Isophthalaldehyde through Tishchenko Reaction Catalyzed by the Ethylmagnesium Bromide-(- )-Sparteine Complex and Aluminum Alkoxides Seong-Ho CHOI, Eiji YASHIMA, and Yoshio 0KAMOTOt Department of Applied Chemistry, School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-{)J, Japan (Received September 13, 1996) ABSTRACT: Terephthalaldehyde (TPA) and isophthalaldehyde (IPA) were polymerized with the ethylmagnesium bromide-(-)-sparteine (EtMgBr-Sp) complex and aluminum alkoxides as catalysts to obtain polyesters through the Tishchenko reaction. The polyester prepared from TPA with the EtMgBr-Sp complex was characterized by IR, FD mass, 1H and 13C NMR spectroscopies, and was found to be a random copolymer composed of oxycarbonyl-1,4-phenylenemethylene and terephthaloyloxymethylene-1 ,4-phenylenemethyleneoxy units. The polyesters possessed terminal formyl groups and were further polymerized with the EtMgBr-Sp complex. On the basis of the results, a possible mechanism for the polymerization is discussed. KEY WORDS Terephthalaldehyde I Isophthalaldehyde I Tishchenko Reaction I Sparteine I Polyester I Aluminum Alkoxides Condensation reactions of aldehydes to produce es­ with 3-phenylpropoxymagnesium bromide and terminat­ ters are known as the Tishchenko reaction, 1 which are ed by the Tishchenko reaction to afford the polymer catalyzed by various metal complexes2 including alumi­ having an ester terminal at w-end. In the polymerization, num alkoxides, 3 lanthanoid complexes, 4 and ruthenium a large amount of 3-phenylpropyl 3-phenylpropanoate complexes. 5 The metal complexes may be used as the was produced as a side product through the Tishchenko catalysts for the syntheses of polyesters from dialdehydes reaction. These results indicate that the EtMgBr-Sp such as terephthalaldehyde (TPA) through the Tish­ complex can be used as a novel catalyst for the en­ chenko reaction. However, a few papers describe the antioselective Tishchenko reaction of racemic alde­ polyester syntheses using the metal complexes. Mitin hydes such as (±)-2-phenylpropanal (2-PPA). Actually, et al. 6 and later, Sweeny 7 reported the polymerization the EtMgBr-Sp complex catalyzed the enantioselective of TPA to polyesters by means of the Tishchenko reac­ Tishchenko reaction to afford optically active 2-phenyl­ tion with aluminum ethoxide and alkylaluminums, re­ propyl 2-phenylpropanoate. Enantiomeric excess of op­ spectively. The polyesters were examined by IR, X-ray tically active 2-phenylpropyl2-phenylpropanoate obtain­ diffraction patterns, and differential thermal analysis ed achieved up to 65%. 10 In both reactions, 3-phenyl- or (DSC), and their structures were postulated to be not 2-phenylpropoxymagnesium bromide-Sp complex is a pure poly(oxycarbonyl-1,4-phenylenemethylene) (1), but real intermediate and further reacts with 3-PPA or 2-PPA a random copolymer composed of oxycarbonyl-1 ,4- followed by the Tishchenko-type termination again with phenylenemethylene and terephthaloyloxymethylene- the aldehydes to afford the optically active poly(3-PPA) 1,4-phenylenemethyleneoxy ( 4-xylyleneterephthalate) having an ester terminal at w-end and 2-phenylpropyl units (2). Very recently, Yamamoto and co-workers also 2-phenylpropanoate, respectively, as a cyclic mecha­ prepared polyesters with ruthenium complexes similar nism.9·10 These results led us to apply our system to in structures to those reported by Sweeny from TPA prepare polyesters from dialdehydes such as TPA and through the Tishchenko reaction. 8 isophthalaldehyde (IPA) through the Tishchenko reac­ tion. (-)-Sparteine is a commercially available chiral diamine and has been widely used for asymmetric sy­ 11 12 OHC-o-CHO nthesis, helix-sense-selective polymerization, and en­ antiomer-selective polymerization of racemic methac­ TPA IPA Sp rylates.13 In the present study, we performed the polymerization of TPA and IPA with the EtMgBr-Sp complex and aluminum alkoxides through the Tishchenko reaction. The structures of polyesters and the mechanism of the Previously, we found that an optically active poly(3- polymerization were elucidated on the basis of IR, 1D phenylpropanal) with a predominant one-handed helical and 2D NMR, and FD-mass spectroscopies. structure could be obtained by the asymmetric polymer­ ization of 3-phenylpropanal (3-PPA) with the ethylmag­ EXPERIMENTAL nesium bromide-(-)-sparteine (EtMgBr-Sp) complex in toluene at - 78°C. 9 The polymerization was also initiated Materials TPA, IPA, terephthalic acid, and 4-carboxybenzalde­ t To whom correspondence should be addressed. hyde were purchased from Tokyo Kasei and used as 261 S.-H. CHOI, E. YASHIMA, andY. OKAMOTO received. 1,4- Bis(hydroxymethyl)benzene, 4-( chlorometh­ was stirred at 40oC for 3 h, it was cooled to room yl)benzoic acid, and Me3Al in toluene (2M) were ob­ temperature and poured into methanol (200 ml). The tained from Aldrich. (R)-( + )-1, 11-Bi-2-naphthol ([ocJ55 polymer precipitated was separated by centrifugation, + 32°, c 1.5 g dl- 1, tetrahydrofuran (THF)) was obtained washed with methanol, and dried in vacuo at 50°C for from Kankyo Kagaku Center. EtMgBr was prepared by 3 h. The polymer obtained was not soluble in common the usual method using magnesium and ethyl bromide organic solvents. The yield of the polymer was 2.6 g in dry ether under nitrogen atmosphere and its con­ (98%). IR (KBr): 1717cm-1 (C=O), 1272, 1102cm-1 centration was determined to be 0.92 M by acid and (C-O). base titration. Toluene was purified in the usual manner, Poly( oxycarbonyl-1 ,4-phenylenemethylene) (1 ). This mixed with a small amount of butyllithium, and distilled polymer was prepared according to the reported pro­ under high vacuum just before use. THF was dried over cedure14 by the polymerization of 4-(chloromethyl)ben­ sodium benzophenone ketyl before distillation and fur­ zoic acid in the presence of triethylamine in THF under ther distilled over LiAIH4 under high vacuum just before reflux. IR (KBr): 1717 em - 1 (C = 0), 1272, 1102 em - 1 use. Dichloromethane and chloroform were dried over (C-O). CaH2 and distilled under high vacuum just before use. Model compounds, dimethyl terephthalate (3), 1,4- (-)-Sparteine (Sigma) was dried over CaH2 for 2 h with bis(acetyloxymethyl)benzene (4), and 4-(hydroxymeth­ stirring and distilled under reduced pressure (bp 92.0- yl)benzoic acid (5) were prepared by usual methods or 93SC/0.06 mmHg). Aluminum isopropoxide was from according to the reported procedure. Tokyo Kasei and used as a toluene solution (2M). (3): mp 140-142oC; 1H NMR (CDC13): b 3.95 (s, 3H, -CH3), b 8.10 (s, 4H, -Ph); 13C NMR (CDC13): 166.29, Preparation of Catalysts 133.92, 129.54, 52.35; IR (KBr): 1721 cm- 1 (C=O); The EtMgBr-Sp complex was prepared by mlXlng El-MS: 194 (M+). EtMgBr with 1.2 equivalent (-)-Sp in toluene at room (4): mp 42--43oC; 1H NMR (CDC13) b 2.10 (s, 3H, temperature under dry nitrogen, and the concentration -CH3), b 5.10 (s, 4H, -CH2-Ph), b 8.10 (s, 4H, -Ph); of the complex was adjusted to 0.30 M. The complex 13C NMR (CDC13) 170.85, 136.04, 128.45, 65.85, 20.89; ((R)-BIN-Al) of (R)-( + )-1,1 1-bi-2-naphthol with Me3Al IR (KBr) 1723cm-1 (C=O); El-MS: 222 (M+). was prepared by mixing (R)-( + )-1, 11 -bi-2-naphthol in (5): mp 175-l77°C (lit. 15 174-180°C); 1 H NMR dry toluene with 1 equivalent Me3Al in toluene at (dimethyl sulfoxide (DMSO)-d6): b 3.38 (s, 2H, -CH20H), room temperature under dry nitrogen. Methane gas was b 5.20 (s (broad), lH, -OH), b 7.44-7.92 (d, -Ph, 4H); produced immediately. The mixture was stirred for 1 h 13 C NMR (DMSO-d6 ): 167.59, 148.04, 129.46, 129.36, at room temperature and used as a catalyst for the 126.46; IR (KBr): 3420 (-OH), 1720cm-1 (C=O); El­ polymerization. MS: 152 (M+). Polymerization Procedure Alkaline Hydrolysis of the Polyester Obtained with the Polymerization was carried out in a glass ampule EtMgBr-Sp Complex under dry nitrogen atmosphere. A typical polymerization Poly(TPA) (0.50 g, run 4 in Table I) was dispersed in procedure is described below. TPA (l.Og, 7.5mmol) was ethanol (15ml) containing KOH (1 g) at room tem­ placed in an ampule, and was dried on a vacuum line. perature. After 6 h stirring, the solution was poured into After the ampule was flushed with dry nitrogen, a three­ H 2 0, and then extracted with ether. The ether solution way stopcock was attached to the ampule. Chloroform was dried over Mg2 S04, and the ether was removed by (1 0 ml) was then added with a hypodermic syringe. The evaporation, yielding oily residues (ca. 0.06 g, ca. 10% monomer solution was cooled to 0°C, and the prescribed yield based on the poly(TPA)). The aqueous layer was initiator solution was added to the mixture to initiate the acidified with IN HCl solution and the mixture was polymerization with a syringe. After 30 min, the ampule extracted with ether. The ether solution was dried over was placed in a water bath at 30oC or 50°C. The molar Mg2 S04, and the ether was removed by evaporation, ratio of monomer to EtMgBr or aluminum alkoxide was giving a crystalline residue (ca. 0.5 g, ca. 88%). Each 50 unless otherwise noted. The reaction was terminated product obtained from the ether layer and aqueous layer with a few drops of methanol containing a small amount was dissolved in DMSO-d6 , and 1H, 13C NMR, and of HCI. The polymer was precipitated in a large amount electron impact (EI) mass spectra were measured. The of methanol, separated by centrifugation, and dried in data are given in Figure 3. vacuo at 50°C for 3 h.