Synthesis and Polymerization Behavior of 7-Cyano-7-(phenyl

A novel captodatively substituted benzoquinone methide, 7-cyano-7-(phenyl)benzoquinone methide (3), was synthesized successfully as an isolable crysta...
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Macromolecules 2000, 33, 269-277

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Synthesis and Polymerization Behavior of 7-Cyano-7-(phenyl)benzoquinone Methide Takahito Itoh,* Eriko Nakanishi, Masayuki Okayama, and Masataka Kubo Department of Chemistry for Materials, Faculty of Engineering, Mie University, 1515 Kamihama-cho, Tsu-shi, Mie 514-8507, Japan Received June 29, 1999; Revised Manuscript Received November 12, 1999 ABSTRACT: A novel captodatively substituted benzoquinone methide, 7-cyano-7-(phenyl)benzoquinone methide (3), was synthesized successfully as an isolable crystal at room temperature. 3 polymerized spontaneously on dissolving it in highly polar, basic solvents such as DMSO and DMF. The acid-catalyzed 1,6-addition reaction of 3 was investigated. Acid-catalyzed 1,6-addition reactions of 3 with phenol and N,N-dimethylaniline afforded 1:1 adducts. In the reaction with hydrogen chloride, a 1,6-addition adduct was also formed. Homopolymerizations of 3 and 7,7-di(cyano)benzoquinone methide (1a) with radical, anionic, and cationic initiators were investigated. 3 and 1a are homopolymerizable with an anionic initiator but not with radical and cationic ones. 3 is copolymerizable spontaneously with styrene in an alternating fashion. The copolymer structure of 3 with styrene was determined on the basis of the spectral data of model compounds and the polymerization mechanism was discussed.

Introduction Unsubstituted quinodimethane is unstable to give its polymer spontaneously at room temperature.1 However, captive substitution on exocyclic methylenes in the highly reactive unsubstituted quinodimethane with electron-withdrawing substituents such as cyano, ester, and acyl groups lowers its reactivity (polymerizability), resulting in highly electron-accepting substituted quinodimethanes2-10 isolable as crystals at room temperature. Captodative substitution on exocyclic methylenes in the quinodimethane structure with both electron-withdrawing substituents and electron-donating substituents such as alkylthio and phenyl groups also affords isolable substituted quinodimethanes, being close to neutral in polarity.11-13 We have studied the polymerization behaviors of these isolable and treatable substituted quinodimethanes.3-5,7-13 Interesting polymerization behaviors such as equilibrium polymerizations, alternating copolymerizations, and changes in the polymerization mode from random to alternating copolymerization, according to its substitution mode and bulkiness of substituents, were found for the substituted quinodimethanes, and it was proven that they are a new class of monomers different from vinyl and related compounds.14 Unsubstituted benzoquinone methide,15 being a member of the quinonoid family, is unstable, giving dimeric compounds and oligomers at room temperature like an unsubstituted quinodimethane. Substitution of hydrogen atoms on exocyclic methylene with electron-withdrawing substituents such as cyano and/or ester groups or with electron-donating substituents such as phenyl and dithioethylene groups afforded the corresponding substituted benzoquinone methides as isolable crystals at room temperature because of reduced polymerizability: e.g., 7,7-di(cyano)benzoquinone methide (1a),16 7-(alkoxycarbonyl)-7-cyanobenzoquinonemethides(1b),17,18 7,7-bis(alkoxycarbonyl)benzoquinone methides (1c),19 7,7-di(phenyl)benzoquinone methide (2a),20 and 4-(1′,3′* Corresponding Author. Telephone: +81(Japan)-59-231-9410. Fax: +81(Japan)-59-231-9410. E-mail: [email protected].

dithiolan-2′-ylidene)-2,5-cyclohexadien-1-one (2b).21 Polymerization behaviors of these captively substituted benzoquinone methides 1a-c, have been investigated.17-19,22 It was found that 1a is not homopolymerizable with radical initiator, but copolymerizable with styrene in an alternating fashion, and both 1b and 1c are homopolymerizable with radical and anionic initiators and copolymerizable with styrene and p-methoxystyrene in a random fashion except for 1c with a bulky isopropyl group, which exhibited a polymerization behavior similar to 1a. In analogy with captodatively substituted quinodimethanes, captodative substitution on the exocyclic methylene in the reactive unsubstituted benzoquinone methide is expected to afford the substituted benzoquinone methide isolable as crystals at room temperature. Captodatively substituted benzoquinone methides have not been synthesized yet, and also their polymerization behaviors are of interest in comparison with those of captively substituted benzoquinone methides. In this work, 7-cyano-7-(phenyl)benzoquinone methide (3) as one of the novel captodatively substituted benzoquinone methides was successfully synthesized as an isolable crystal, and some of its chemical properties and polymerizations were investigated.

Experimental Section Monomer Synthesis. 4-[1′-Cyano-1′-(phenyl)methylene]-1,4-dioxaspiro[4.5]decane (4). 1,4-Cyclohexanedione monoethylene ketal (11.84 g, 75.8 mmol) and phenylacetonitrile (8.88 g, 75.8 mmol) were dissolved in 120 mL of ethanol, and to the resulting solution was added 7.58 g (75.8 mmol) of

10.1021/ma9910540 CCC: $19.00 © 2000 American Chemical Society Published on Web 01/06/2000

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a 40% sodium hydroxide aqueous solution, and then the mixture was stirred for at room temperature for 3 days. A 200 mL aliquot of water was added to the reaction mixture, and the resulting solution was extracted with 100 mL of diethyl ether three times. The extracts were combined, washed with 100 mL of water, and dried over anhydrous magnesium sulfate. The filtrate was placed under reduced pressure to remove solvents to afford a pale yellow solid, which was recrystallized from hexane to give 15.92 g (82.2% yield) of 4 as white needles: mp 63.4-65.4 °C; IR (KBr) νCH 3018-2990, νCH 2922-2858, νCN 2182, νCdC 1594, νC-O 1115, 1085 cm-1; 1 H NMR (CDCl3) δ 7.40-7.35 (m, 3H), 7.30-7.27 (m, 2H), 4.00 (s, 2H), 3.99 (s, 2H), 2.87 (t, J ) 6.60 Hz, 4H), 2.50 (t, J ) 6.60 Hz, 2H), 1.89 (t, J ) 6.60 Hz, 2H), 1.70 (t, J ) 6.60 Hz, 2H). Anal. Calcd for C16H17NO2: H, 6.72; C, 75.27; N, 5.48; O, 12.53. Found: H, 6.84; C, 75.33; N, 5.27; O, 12.56. 4-[1′-Cyano-1′-(phenyl)methylene]cyclohexanone (5). 4 (12.68 g, 62.1 mmol) was added to 240 mL of a 2% aqueous sulfuric acid solution, and the resulting suspension was refluxed for 1 h and then, after cooling, extracted with four times with 100 mL of chloroform. The extracts were combined, washed with 100 mL of water and 100 mL of saturated sodium carbonate aqueous solution, and dried over anhydrous magnesium sulfate and then placed under reduced pressure to remove solvent to give a pale yellow oil, which was dissolved in a small amount of benzene. The resulting solution was passed through a silica gel column by using benzene as an eluent. The yellow elution band was collected and placed under reduced pressure to remove solvent to obtain 10.2 g (83% yield) of 5 as a yellow oil: IR (NaCl) νCH 3016-2986, νCH 2926-2868, νCN 2190, νCdO 1681, νCdC 1588, νCdC 1466 cm-1; 1H NMR (CDCl3) δ 7.44-7.33 (m, 3H), 7.32-7.31 (m, 2H), 3.10 (t, J ) 6.60 Hz, 2H), 2.76 (t, J ) 6.60 Hz, 2H), 2.62 (t, J ) 6.60 Hz, 2H), 2.44 (t, J ) 6.60 Hz, 2H). Anal. Calcd for C14H13NO: H, 6.21; C, 79.59; N, 6.63; O, 7.57. Found: H, 6.34; C, 79.36; N, 6.64; O, 7.66. 7-Cyano-7-(phenyl)benzoquinone Methide (3). 5 (3.41 g, 16.7 mmol) was dissolved in 100 mL of benzene and then into the resulting solution were added 14.5 g (167 mmol) of activated manganese dioxide and 14.5 g of 3A molecular sieves. The mixture was refluxed with stirring for 24 h, cooled, and then filtered. The orange filtrate was placed under reduced pressure to remove solvent to give a dark orange solid, which was dissolved in a small amount of benzene. The resulting solution was passed through a silica gel column by using benzene as an eluent. The orange elution band was collected and placed under reduced pressure to remove solvent to obtain an orange solid, which was recrystallized from a mixed solution of hexane and dichloromethane to give 0.67 g (20% yield) of 3 as orange needles: mp 113.0-114.0 °C; IR (KBr) νCH 3020, νCN 2184, νCdO 1598, νCdC 1581, νCdC 1534, νCdC 1486 cm-1; 1H NMR (CDCl3) δ 7.85 (dd, J ) 9.89 and 2.64 Hz, 1H), 7.54 (s, 5H), 7.48 (dd, J ) 10.23 and 2.64 Hz, 1H), 6.62 (dd, J ) 9.89 and 1.98 Hz, 1H), 6.49 (dd, J ) 10.23 and 1.98 Hz, 1H); 13C NMR (CDCl3) δ 186.4 (CdO), 139.6 (Ar), 136.9, 134.4, 131.9 (>Cd), 131.4, 131.3, 131.2 (Ar), 130.4 (Ar), 129.3 (Ar), 124.0 (>Cd), 117.1 (CN); UV-vis (CHCl3) λmax ) 362 ( ) 2.48 × 104) nm. Anal. Calcd for C14H9NO: H, 4.39; C, 81.14; N, 6.76; O, 7.71. Found: H, 4.52; C, 80.83; N, 6.72; O, 7.93. Adduct Formation of 3. With Phenol. 3 (100.8 mg, 0.486 mmol) and phenol (102.0 mg, 1.084 mmol) were dissolved in 10 mL of tetrahydrofuran (THF), and then 3 drops of acetic acid were added. The orange color changed to pale yellow color immediately. After being allowed to stand at room temperature for 13 h, the reaction mixture was placed under reduced pressure to remove solvent to give a viscous pale yellow oil, which was dissolved in a small amount of dichloromethane. The resulting solution was passed through a silica gel column by using dichloromethane as an eluent. The pale yellow elution band was collected and placed under reduced pressure to remove solvent to afford a pale yellow solid, which was recrystallized from toluene to give 132.5 mg (90.4% yield) of 1-cyano-1-phenyl-1,1-di(4-hydroxyphenyl)methane (6) as white needles: mp 168-169.5 °C; IR (KBr) νOH 3298, νCH 3020, νCH 2988, νCN 2226, νCdC 1670, νCdC 1582, νCdC 1565, νCdC 1485

Macromolecules, Vol. 33, No. 2, 2000 cm-1; 1H NMR (CDCl3) δ 7.35-7.32 (m, 3H), 7.23-7.20 (m, 2H), 7.06 (d, J ) 8.91 Hz, 4H), 6.79 (d, J ) 8.91 Hz, 4H), 4.91 (s, 2H). Anal. Calcd for C20H15NO2: H, 5.02; C, 79.71; N, 4.65; O, 10.62. Found: H, 5.09; C, 80.07; N, 4.55; O, 10.29. With N,N-Dimethylaniline. 3 (101.2 mg, 0.488 mmol) and phenol (500.1 mg, 4.13 mmol) were dissolved in 10 mL of THF, and then 507.7 mg (8.45 mmol) of acetic acid was added. After being allowed to stand at room temperature for 4.5 h, the reaction mixture was poured into 50 mL of ice-water and then extracted three times with 50 mL of chloroform. The extracts were combined, washed with water and dried over anhydrous magnesium sulfate, and then placed under reduced pressure to remove solvent to give a brown solid, which was dissolved in a small amount of dichloromethane. The resulting solution was passed through a silica gel column by using dichloromethane as an eluent. The yellow elution band was collected and placed under reduced pressure to remove solvent to afford 65.6 mg (40.9% yield) of 1-cyano-1-phenyl-1-(4′-hydroxyphenyl)-1-[4′′-(N,N-dimethylamino)phenyl]methane (7) as yellow solids: mp 226.0-228.6 °C; IR (KBr) νOH 3336, νCH 3040, νCH 2880, νCN 2220, νCdC 1578, νCdC 1485, νCdC 1421 cm-1; 1H NMR (CDCl3) δ 7.34-7.30 (m, 3H), 7.25-7.21 (m, 2H), 7.02 (d, J ) 8.9 Hz, 2H), 6.90 (d, J ) 8.9 Hz, 2H), 6.79 (d, J ) 8.9 Hz, 2H), 6.66 (d, J ) 8.9 Hz, 2H), 2.95 (s, 6H). Anal. Calcd for C22H20N2O: H, 6.14; C, 80.46; N, 8.53; O, 4.87. Found: H, 5.97; C, 80.09; N, 8.59; O, 5.35. With Hydrogen Chloride. 3 (109.6 mg, 0.529 mmol) was dissolved in 10 mL of dichloromethane, and then dry hydrogen chloride was bubbled through the resulting solution for 30 min. The orange color of the solution changed to yellow gradually on bubbling. The yellow solution was concentrated to about 1 mL in volume and passed through a silica gel column by using dichloromethane as an eluent. The yellow band was collected and placed under reduced pressure to remve solvent to obtain 85.8 mg (66.6% yield) of 1-cyano-1-chloro-1-phenyl-1-(hydroxyphenyl)methane (8) as a yellow oil: IR (NaCl) νOH 3374, νCH 3020-2990, νCN 2220, νC-Cl 631 cm-1; 1H NMR (CDCl3) δ 7.45 (s, 2H), 7.36 (d, J ) 5.9 Hz, 3H), 7.29 (d, J ) 8.9 Hz, 2H), 6.81 (d, J ) 8.9 Hz, 2H), 6.33 (s, 1H). Anal. Calcd for C14H10NOCl: H, 4.14; C, 69.00; N, 5.75; O, 6.56; Cl 14.55. Found: H, 4.25; C, 69.13; N, 5.91; O, 6.25; Cl, 14.46. Model Compounds. 1-Phenyl-1-phenoxyethane (12). Sodium metal (0.10 g, 4.35 mmol) was dissolved in 30 mL of ethanol, and into the resulting solution was dissolved 0.41 g (4.36 mmol) of phenol and then 0.80 g (4.32 mmol) of R-bromoethylbenzene was added and the mixture refluxed for 2 h. The reaction mixture was placed under reduced pressure to remove solvents to give a solid and a viscous oil, to which was added 30 mL of water. The resulting solution was extracted three times with 30 mL of chloroform, and the extracts were dried over anhydrous magnesium sulfate. The filtrate was placed under reduced pressure to afford a pale yellow oil, which was dissolved in a small amount of chloroform. The resulting solution was passed through a silica gel column by using chloroform as an eluent. The second elution band was collected and placed under reduced pressure to remove solvent to give 246.2 mg (28.4% yield) of 12 as a colorless oil: IR (NaCl): νCH 3018-2936, νCH 2886, νCdC 1567, νCdC 1466, νCdC 1426, νC-O 1220 and 1071, σC-H 739 and 687 cm-1; 1H NMR (CDCl3) δ 7.27-6.73 (m, 10H), 5.17 (q, J ) 6.60 Hz, 1H), 1.51 (d, J ) 6.60 Hz, 3H); 13C NMR (CDCl3) δ 158.0 (Ar), 143.2 (Ar), 128.5 (Ar), 127.3 (Ar), 125.5 (Ar), 120.6 (Ar), 115.9 (Ar), 75.8 (CH), 24.4 (CH3). Anal. Calcd for C14H14O: C, 84.80; H, 7.13; O, 8.07. Found: C, 84.51; H, 7.20; O, 8.29. 1-Phenyl-2-phenoxyethane (13). 13 was obtained as a colorless oil in 19.5% yield from β-bromoethylbenzene in a process similar to that for 12: IR (NaCl) νCH 3016-2904, νCH 2832, νCdC 1568, νCdC 1470, νCdC 1420, νC-O 1225 and 1025, σC-H 737 and 683 cm-1; 1H NMR (CDCl3) δ 7.34-6.87 (m, 10H), 4.14 (t, J ) 6.60 Hz, 2H), 3.09 (t, J ) 6.60 Hz, 2H); 13C NMR (CDCl3) δ 158.8 (Ar), 138.3 (Ar), 129.4 (Ar), 129.0 (Ar), 128.5 (Ar), 120.7 (Ar), 114.5 (Ar), 68.5 (CH2), 35.8 (CH2). Anal. Calcd for C14H14O: C, 84.80; H, 7.13; O, 8.07. Found: C, 84.60; H, 7.23; O, 8.17.

Macromolecules, Vol. 33, No. 2, 2000 1-Cyano-1,1,2-triphenylpropane (14). Commercial sodium hydride (60% in oil) was washed twice with hexane and dried reduced pressure to obtain 0.37 g (15.4 mmol) of sodium hydride in a powder state, to which 50 mL of THF was added under nitrogen. Into this mixture was added 0.50 g (2.59 mmol) of phenylacetonitrile and the resulting mixture refluxed for 30 min. Into the resulting solution was added 0.48 g (2.59 mmol) of R-bromoethylbenzene and the resulting mixture refluxed for 4 h. The reaction mixture was cooled to room temperature and placed under reduced pressure to remove solvents to give white solids, to which was added 30 mL of water. The resulting solution was extracted three times with 30 mL of chloroform, and the extracts were combined, washed with water, and dried over anhydrous magnesium sulfate. The filtrate was placed under reduced pressure to afford a white solid, which was dissolved in a small amount of chloroform. The resulting solution was passed through a silica gel column by using chloroform as an eluent. The first elution band was collected and placed under reduced pressure to remove solvent to give 348.4 mg (35.5% yield) of 14 as white needles: mp 89.5-91.0 °C; IR (KBr) νCH 3018-2990, νCH 2938, νCN 2214, νCdC 1570, νCdC 1468, νCdC 1426, σC-H 737 and 688 cm-1; 1H NMR (CDCl3) δ 7.67-7.02 (m, 15H), 3.88 (q, J ) 6.90 Hz, 1H), 1.57 (d, J ) 6.90 Hz, 1H); 13C NMR (CDCl3) δ 140.4 (Ar), 139.4 (Ar), 138.8 (Ar), 128.8 (Ar), 128.5 (Ar), 128.3 (Ar), 128.2 (Ar), 128.0 (Ar), 127.8 (Ar), 127.8 (Ar), 127.4 (Ar), 127.0 (Ar), 126.8 (Ar), 126.7 (Ar), 121.3 (CN), 58.9 (>CC