Polymerization of Aromatic Aldehydes. VII. Cyclopolymerization of O-Formylphenylacetaldehyde and Formation of a Cyclic Trimer
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Polymer Journal, Vol. 2, No. 1, pp 101-108 (1971) Polymerization of Aromatic Aldehydes. VII. Cyclopolymerization of o-Formylphenylacetaldehyde and Formation of a Cyclic Trimer Sanae TAGAMI, Takashi KAGIYAMA, and Chuji Aso Department of Organic Synthesis, Faculty of Engineering, Kyushu University, Fukuoka, 812, Japan. (Received October 19, 1970) ABSTRACT: Polymerization of o-formylpheny1acetaldehyde was carried out with various catalysts. The polymer obtained below -60°C with BFsOEt2 catalyst was soluble in common organic solvents and was confirmed as a cyclopolymer composed of 6-membered cyclized units. The cationic cyclization step in the cyclopolymerization of o-formylphenylacetaldehyde was inferred to proceed through a intermediate or con certed scheme similar to those proposed for the cationic propagation of o-phthalalde hyde. On the other hand, under cationic polymerization conditions over -40°C o-formyl phenylacetaldehyde gave a cyclic trimer (mp 284-285°C) possessing fused ring ether, which had no aldehyde group. Interestingly, the cyclic trimer was also produced from the polymer by treatment with BFsOEt2 in methylene dichloride. Cyclopolymers of o-formylphenylacetaldehyde were also obtained with Ziegler cata lyst at 0 and -78°C, and with t-BuOLi catalyst at -78°C. KEY WORDS CyclopolymerizationjCationic Polymerization/Ring Forma tion I Cyclooligomerization I o-Formy lphenylacetaldehyde j Dialdehyde j Cyclopolymer I Cyclic Trimer/Poly (o-Formylphenylacetaldehyde) I Polyacetal In contrast to the difficulty in obtaining poly formation of the six-membered ring unit. It mers from benzaldehyde and its derivatives, was of particular interest to compare the re o-phthalaldehyde was found to give a cyclo activities of these aldehyde groups. The isola polymer readily, as shown in eq 1. 1 •2 tion of o-formylphenylacetaldehyde was not reported, though synthesis of isobenzpyrylium ferric chloride without isolation of this dialde hyde was reported by Blount and Robinson.4 This paper describes the polymerization of o formylphenylacetaldehyde with various catalysts The driving force for the polymerization and the formation of a cyclic trimer under was ascribed to the ease of intramolecular cationic conditions. cyclization, and it was emphasized that the aromatic aldehyde group could participate in polymerization when ready formation of the EXPERIMENTAL cyclic unit by cyclopolymerization was expect Materials ed. This presumption was substantiated by the o-Formylphenylacetaldehyde was prepared from fact that o-vinylbenzaldehyde gave a cyclo indene as follows polymer with cationic catalysts. 3 That investigation is now extended to the polymerization of o-formylphenylacetaldehyde, a monomer which possesses aromatic and aliphatic aldehyde groups, and is believed to undergo 101 S. TAGAMI, T. KAGIYAMA, and C. Aso The cleavage reaction of trans-indane-1, 2-diol Anal. Calcd for C 9H 80 2: C, 72.95; H, 5.44. to dialdehyde was carried out in accordance Found: C, 72.70; H, 5.45. with the procedure reported by Blount and 2, 4-Dinitrophenylhydrazone of the dialdehyde, Robinson,4 and o-formylphenylacetaldehyde was consisting of orange-colored needles, was recrys tallized from dimethylformamide, mp 259- able to be isolated at relatively high yield. 260oC (decomposed). trans-Indane-1, 2-diol. To a mixture of 500 ml Anal. Calcd for C H N 0 : C, 49.61; H, of 85% formic acid and 50 ml of an aqueous 21 15 8 8 3.17; N, 20.03. solution of 30% hydrogen peroxide was added Found: C, 50.77; H, 3.47; N, 20.12. dropwise 58 g (0.5 mol) of indene over a period BFa0Et 2 was purified by distillation under ·of 30 min at a temperature below30°C. The nitrogen. TiC1 4 was heated at 100°C with reaction mixture was then stirred at room tem copper powder and distilled. AlEta (Ethyl Corp., perature for 3 hr, and approximately 1 kg of U.S.A.) was used without further purification. <:racked ice and 0.5 kg of anhydrous potassium t-BuOLi was prepared by the reaction of dry t carbonate were added. The yellowish white butyl alcohol with lithium in benzene under precipitate was filtered and the solid product nitrogen. The reaction mixture was filtered and was saponified in 200 ml of 5% aqueous sodi the benzene was evaporated. Solvents were um hydroxide at 50°C for 30 min. The brown purified by the usual methods. ish crude dio1 product, which was separated by cooling the solution to ooc, was collected by Cationic Polymerization filtration and recrystallized from benzene: Polymerizations were carried out in Schlenk yield, 25%; mp 100-101.5°C (lit. 5 mp 102- type ampoules. Monomer and solvent were 1040C). placed in the ampoule, which was then purged o-Formylphenylacetaldehyde. To a solution of with dry nitrogen and cooled to the given poly merization temperature. A precooled catalyst 25 g (0.17 mol) of indane-1, 2-diol in 300 ml of solution was added. After a given period the dry benzene containing 2 ml of pyridine was polymerization was terminated by adding pyri added 80 g (0.18 mol) of lead tetraacetate at 20- dine or methanol, and the mixture poured into 25oC over a period of 10 min while stirring. excess methanol. The white powdery polymer The reaction mixture was stirred for an additio obtained was purified by reprecipitation from nal 10 min and then filtered. The filtrate was benzene and methanol and then dried in vacuo washed with an aqueous solution of sodium at room temperature for one day. chloride and then with 5% aqueous potassium carbonate, and dried over anhydrous sodium When cationic polymerization was carried sulfate. Benzene was evaporated in vacuo and out at temperatures above -40°C, an insoluble the residual colorless liquid was purified by cyclic trimer precipitated during polymerization, fractional distillation in a high vacuum: yield, as shown later in this paper. It was separated 64%; bp 77-78°C (0.03 mm); mp ca. 24°C. from the reaction mixture by filtration and then The IR spectrum showed peaks at 2830 (weak, the filtrate was poured into excess methanol to vcH of aliphatic aldehyde), 2760 (weak, vcH of recover the soluble polymeric product. Charac aromatic aldehyde), 1730 (strong, vc=o of ali teristics of the cyclic trimer are given later. phatsc aldehyde), 1700 (strong, vc=o of aroma Other Polymerization Procedures tic aldehyde), 1600 (weak, phenyl), 1582 (medi The procedures are basically similar to that um, phenyl), and 750 cm-1 (strong, phenyl). of cationic polymerization. Ziegler-type catalysts The NMR spectrum (CC1 4) exhibited peaks at were prepared in toluene and aged at room 10.05 (aromatic aldehyde proton, singlet), 9. 76 temperature before polymerization. AlEta (aliphatic aldehyde p.roton, triplet), 7.0-7.8 PhNHCOCHa catalyst was prepared by the re (phenyl proton, multiplet), and 3.96 ppm action of AlEta with an equimolar amount of (methylene proton, doublet). The area ratio of acetanilide at 20°C in toluene, according to the these peaks (1.0: 1.1 : 4.0: 1.9) was close to the method of Tani, et al. 6 Coordination polymer theoretical value ( 1:1 : 4:2). izations were terminated by pouring the reaction 102 Polymer J., Vol. 2, No. 1, 1971 Cyclopolymerization, Trimer of o-Formylphenylacetaldehyde mixture into methanol and the polymer was trimer was obtained by connecting a spectro zecovered. Anionic p.olymerizations were termi accumulator. An X-ray powder spectrum was nated by adding a THF solution of acetic an taken with a Norelco (North American Phillips hydride. Co.). The molecular weights of the polymer Formation and Characteristics of the Cyclic and the trimer were measured with a vapor Trimer pressure osmometer (Mechrolab Model 301 A) The following is one example of formation of in benzene and chloroform, respectively, at 37°C. a cyclic trimer. To a solution of I g of mono mer in 5 ml of methylene dichloride was added RESULTS BF30Et3 (1 mol% of monomer) in methylene dichloride at 20°C in a Schlenk-type ampoule. Cyclopolymerization and Cyclooligomerization with Immediately a white product began to precipi BF30Et2 Catalyst tate. The reaction mixture was kept at 20°C When a BF30Et2 solution was added to a for 12 min. Then the precipitate was filtered solution of o-formylphenylacetaldehyde below and washed with benzene and dried in vacuo. -60°C, the polymerization system immediately The filtrate and the benzene washings were turned pale yellow and then became colorless. combined and poured into excess methanol, but Pertinent data (runs no. 1 to no. 4) are sum the polymer was not recovered in any appreci marized in Table I. The polymer obtained was able quantity. The precipitate was insoluble soluble in common organic solvents, such as in benzene and carbon tetrachloride, and slight benzene and chloroform, and softened at tem ly soluble in chloroform (solubility, ca. 5 mgjl peratures below 140°C. The molecular weights ml at 50°C). Recrystallization from chloroform of the polymers were rather low and the ele gave colorless needles: yield, 26%; mp 284- mental analysis data were in accord with the 2850C. calculated value. Anal. Calcd for (C 9H 80 2) 3 : C, 72.95; H, Figure 1 a shows an IR spectrum of the 5.44; mol wt, 444. polymer. Absorption peaks caracteristic of the Found: C, 72.78; H, 5.42; mol wt, 442. acetal linkage are seen in the 930-1130cm-1 region and the carbonyl groups disappears. Attempted Copolymerization of Benzaldehyde and Phenylacetaldehyde A portion of 2g (0.019 mol) of benzaldehyde and 2 g (0.017 mol) of phenylacetaldehyde in 10 ml of toluene was placed in a Schlenk-type ampoule, and BF30Et2 catalyst (5 mol % to monomer) was added at -78°C. When the reaction mixture was poured into excess metha nol after 20 hr, only a trace amount of the re sultant product was obtained.