Nitro Displacement Reactions in Aromatic Ether Synthesis, Study notes of Analytical Chemistry

Download Nitro Displacement Reactions in Aromatic Ether Synthesis and more Study notes Analytical Chemistry in PDF only on Docsity! Polymer Journal, Vol. 19, No. 1, pp 191-202 (1987) Synthesis of High Performance Aromatic Polymers via Nucleophilic Nitro Displacement Reaction T. TAKEKOSHI General Electric Company. Research and Development Center, Schenectady, New York 12301, U.S.A. (Received August 17, 1986) ABSTRACT: Nucleophilic displacement reaction of activated aromatic nitro groups with various nucleophiles is a useful and versatile method for the synthesis of aromatic compounds such as ethers, thioethers and other functionalized intermediates and polymers. Various strong electron withdrawing groups can activate aromatic nitro groups. Effective activating groups include cyano, nitro, sulfone and carbonyl groups such as ester, ketone, anhydride, imide, etc. The reaction of activated nitro compounds with bisphenols and bisthiophenols yields bisethers and bisthioethers from which various aromatic polymers containing ether and sulfide groups can be derived. In many cases, nitro displacement reactions are essentially quantitative so that high molecular weight polymers are directly prepared by the displacement reaction of difunctional nitro compounds with bisphenols or bisthiophenols. Another type of unique nitro displacement occurs in the presence of catalytic amount of a nucleophile at higher temperatures resulting de-nitro coupling of two molecules of nitro compound to form substituted diarylethers. KEY WORDS Nitro Displacement I Aromatic Ether I Dianhydride Polyarylene Ether I Polyetherimide I Phthalonitrile Ether I Intensive investigations on high temperature polymers in recent decades have lead to de­ velopment of a large number of thermo­ oxidatively stable polymers. Basic structures of these polymers are composed of difficult-to­ oxidize "electron sink" such as aromatic rings with electron-withdrawing groups and het­ eroaromatic system. Polar and rigid struc­ tures of high symmetry associated with such aromatic ring systems are responsible for gen­ eral lack of adequate processability of these polymers. More recently, greater efforts have been made by many researchers in improving processability of high temperature polymers. One of the effective approaches toward such goal is to insert aromatic ether linkages in the main chains of heteroaromatic systems. In general, such a structural modification lead to reduction of energy of internal rotation of the chains, resulting in lowering glass transition temperatures and crystalline melting tempera­ tures. As a result the process characteristics of polymers are significantly improved without greatly sacrificing their thermal stability. However, few convenient synthetic methods have been available for the formation of aro­ matic ether bonds in high yields. Recently, it has been shown that certain activated aromatic nitro groups can be readily displaced by phenolate and thiophenolate anions to form various aromatic ethers and thioethers.1.2 In this article we wish to review recent develop­ ment of nitro displacement reaction in the synthesis of ether-containing aromatic mono­ mers and polymers. Nucleophilic displacement reactions of aro­ matic nitro groups have been known for many years. 3 Laubenheimer4 •5 described displace­ ment of the nitro group of 3,4-dinitrochloro­ benzene by aniline to form 2-nitro-5- 191 T. T AKEKOSHI chlorodiphenylamine. The presence of co­ product, nitrile ion was also confirmed by iso­ lation of 4-aminoazobenzene which was the coupling product of aniline and benzene­ diazonium cation, the latter was in turn for­ med by the reaction of aniline and nitrous acid. Interestingly, very little had been de­ scribed on the application of nitro displace­ ment reaction unit! Gorvin6 demonstrated the reaction of 2,2' -dibromo-4,4' -dinitrobenzo­ phenone (I) and methoxide as shown in eq 1. The reaction was nearly quantitative, indicat­ ing that the nitro groups were far more re­ active than the bromo groups. The successful result of Gorvin was attrib­ uted to the use of a dipolar aprotic solvent for the first time. In general, use of dipolar sol­ vents is required in order to attain high yield of the product at moderate temperatures. Caswell/ Beck,8 - 10 Wirth/1- 13 Korn­ blum,14 and Williams15 - 17 have since shown that nitrobenzene derivatives with other strong electron-withdrawing groups undergo nitro displacement reactions. Among the acti- vating groups, cyano group was the most effective followed by N-substituted imide, keto, and ester groups. Generally, phenolates used for nitro displacement reactions are re­ quired to be substantially anhydrous. In the presence of water, the ester and imide de­ rivatives are readily deactivated by hydrolysis and ring-opening reaction, respectively. However, cyano and ketone derivatives are less sensitive to the presence of minor amount of water. In those cases, free phenols can be used in the presence of alkali carbonates or hydroxides. Under normal conditions, the coproduct, alkali nitrite does not undergo undesirable side reaction. However, during a prolonged reaction particularly at elevated temperatures, nitrite ions may attack other nucleophilic sites of the starting compounds or products. 17 •18 DISPLACEMENT ON NITRO DE­ RIVATIVES OF AROMA TIC KETONES Radlmann1 demonstrated for the first time that nitro displacement reactions were quanti­ tative enough to form high molecular weight aromatic polyethers. Various polyetherketones were synthesized by the reaction of 4,4 '-di­ nitrobenzophenone and bisphenols as shown in Table I. ()(,{j-Diketo groups can also activate aro­ matic nitro groups. Bis(bibenzyl)ethers (IV) were synthesized from 4-nitrobenzyl (III) and Table I. Polyetherketones via nitro displacement' HO-Ar-OH Bisphenol A 4,4' -Dihydroxybiphenyl 4,4' -Dihydroxydiphenylsulfone 192 Polym. temp 65 145 140 tire I Polymer Polym. inNMP melt temp solvents at 0.2% oc DMSO/PhCl 1.32 195-220 DMSO 1.18 236-255 DMSO 1.07 201-228 Polymer J., Vol. 19, No. I, 1987 Aromatic Polymers via Nitro Displacement Reaction Table V. Nitro diplacement reaction on dinitrobenzonitriles with aminophenols Reactants Solv./temp, "C Phenols Benzonitriles 2-APa 2,6-DBNb DMS0/50 3-AP 2,6-DBN DMS0/115 4-AP 2,4-DBN DMSOj75 4-AP 2,6-DBN DMS0/115 4-AP+3-APd 2,6-CNBW DMS0/50/120 a AP, aminophenol. b DBN, dinitrobenzonitrile. ' 2,6-CNBN, 2-chloro-6-nitrobenzonitrile. d 4-AP (0.5 part) was added at 50oc and then 3-AP (0.5 part) at I20°C. ' The product was 2-(3-aminophenoxy)-6-(4-aminophenoxy)benzonitrile. Bis(aminophenoxy)benzonitriles Yield/% mp;oc 88 167-169 88-90 91.5 193-195 55 211-212 76'· 169-171 Table VI. Nitro displacement polymerization of dinitrobenzonitriles and bisphenol salts40 Polymers React. condtn. Dinitroa BisphenoJsh Yield [IJ] T' TGAd;oc cpds. g Solv./temp, cc % dlg- 1 oc Air N 2,4-DBN BPA DMS0/115 81 0.68 141 430 430 2,6-DBN BPA DMS0/145 75 0.51 173 385 420 2,4- and 2,6- BPA DMS0/140 89 0.60 160 420 425 DBN (I: I) 2,4-DBN 4,4'-DDE DMS0/140 79 0.24 136 360 380 2,6-DBN 4,4'-DDS DMS0/115 77 0.40 147 450 450 2,4-DBN 4,4'-DDS DMS0/115 85 0.32 134 450 2,6-DBN Resorcinol+ BP A DMS0/115 75 0.34 155 390 400 (I : I) 2,6-DBN HQ+BPA DMS0/114 0.55 176 415 430 (I : 9) 2,6-DBN 2-CI-HQ+BPA DMS0/115 88 0.50 174 430 410 (I : I) 2,6-DBN + DDSO BPA DMS0/150 91 0.38 178 430 420 (I : I) a DBN, dinitrobenzonitrile; DDSO, 4,4-dichlorodiphenylsulfone. b DDE, dihydroxydiphenyl ether; DDS, dihydroxydiphenylsulfide; HQ, hydroquinone. ' Measured by DSC. d Temperature at which I% of weight loss was observed. Polyetheramides with pendant cyano groups have been synthesized from IX. 25 Similarly, 4-(3-aminophenoxy)phthalo­ nitrile (X) have been obtained from 3-amino­ phenol and nitrophthalonitrile.26 Recent literatures27 - 30 indicated that 1 ,2-dicyano compounds such as succinonitrile, phthalo­ nitrile and 1,2,4,5-tetracyanobenzene under- went cyclopolycondensation with various di­ amines to form thermally stable cross-linked polymers. We have shown that phthalo­ nitrile moieties can be incorporated at the end groups of thermally stable and readily processable polyetherimides (XI) by using (X) as a chain capping agent. 26 Polymer J., Vol. 19, No. I, 1987 195 T. T AKEKOSHI XI Similarly, phthalonitrile end groups have been also incorporated into polyethersulfones (XII).z6 NCU I .lO:tN '-/ -N XII The above phthalonitrile terminated oligo­ mers were cured effectively when they were heated at 200-250°C in the presence of tetra­ amines such as 3,3',4,4'-tetraaminobenzo­ phenone. The crosslink density could be in­ creased by addition of bisphthalonitrile ethers listed in Table IV. The crosslinking was found to be the result of the formation of I ,2- bisbenzimidazole (Xlll) moiety as illustrated by the following model reaction of phthalo­ nitrile and o-phenylenediamine.26 rA'fN + 2 H,Nu (6) More recently, comparable phtharonitrile resin systems were also described by Keller et a/.31.32 Interestingly, 4,4' -bis(3,4-dicyano­ phenoxy)biphenyl was reported to give an electrically conductive substance when it was cured at 450°C under inert atmosphere. 33 NITRO DISPLACEMENT POL YM­ ERIZATION ON DINITRO­ BENZONITRILES Because of extremely strong activation by the cyano group, the two nitro groups of 2,4- and 2,6-dinitrobenzonitriles (XIV) were both 196 readily displaced. High molecular weight aro­ matic polyethers containing pendant cyano groups were prepared by nitro displacement polymerization of XIV with various bisphenol salts as shown in Table VI. 11 XIV XV The majority of polyethernitriles were soluble in chlorinated hydrocarbons and tough flexible films were obtained from the solutions. High glass transition temperatures and excellent thermal stabilities of polyethernitriles were at­ tributed to their aromatic structures and high polarity of cyano groups. NITRO DISPLACEMENT ON NITROPHTHALIMIDES Nitro groups activated by two carbonyl groups are very labile to nucleophilic displace­ ment.11·16·34-36 In particular, activation by cyclic imide groups is prominent. The high reactivity of N-substituted nitrophthalimides (XVI) is attributed to the "locked" confor­ mation of two carbonyl groups in relation to the plane of the benzene ring as well as their strong electron-withdrawing effect. The neg- Polymer J., Vol. 19, No. I, 1987 Aromatic Polymers via Nitro Displacement Reaction Table VII. Bis(ether anhydride)s36 }Qo_.,J9Q Yield mp -Ar- Isomer % 'C 1Qr 3,3'- 100 228-229.5 4,4'- 89.9 284.5-286 --@- 3,3'- 98.0 306-307 4,4'- 91.2 265-266 --<QKQ)- 3,3'- 88.9 280-281 4,4'- 100 285-286.5 --(Q\-o-<0)- 3,3'- 97.0 186.5-187.5 4,4'- 85.0 189-190 3,3'- 98.9 254-255.5 4,4' 100 238-239 --(Q\-s-<0)- 3,3'- 46.6 257-257.5 4,4'- 97.0 189-190 -@-so,-<Q)- 3,3'- 57.9 230.5-231.5 4,4'- 99.6 251.5-252 3,3'- 59.0 278-279 4,4'- 70.5 215-216 ative charge on the expected Meisenheimer intermediate is, therefore, well delocalized by the contribution of the following resonance structures (XVI a and XVIb ): XVI a XVIb N-substituted 3- and 4-nitrophthalimides (XVI) were readily converted to bisetherimides (XVII) by nitro displacement reaction with various bisphenolate salts. Polymer J., Vol. 19, No. I, 1987 (8) XVII Hydrolysis of XVII, followed by cyclodehy­ dration of the resulting tetraacids, afforded bisetheranhydrides (VIII), which are listed in Table Vll. 35 •36 XVII VIII In contrast to dianhydrides presently available from commercial sources, bisetheranhydrides shown in Table VII were hydrolytically stable in the presence of atmospheric moisture and readily dissolved in conventional solvents. The moderate reactivity of the anhydride groups was attributed to the electro-donating effect of the aryloxy substitutions. A wide variety of polyetherimides (XVIII) were prepared by the reaction of bisetheranhydrides and various aromatic diamines.37 VIII + --r»M*f1 (10) XVIII Polyetherimides (XVIII) were thermally very stable as shown by the thermogravimetric re­ sults in Tables VIlla and Vlllb. In addition, polyetherimides were soluble in completely imidized forms in various solvents such as chlorinated hydrocarbons, phenolic solvents and dipolar aprotic solvents. Because of flex­ ible ether linkages, glass transition tempera­ tures of polyetherimides were in a moderate range of 180 to 280cc which provided good thermal processing characteristics. The above unique combination of properties made it 197 T. T AKEKOSHI IX. The thermal properties of ULTEM® resin are also listed in Table IX. High heat distor­ tion temperature, excellent flame resistance and nonsmoking property are some of the important characteristics of this resin. COUPLING REACTION OF AC­ TIVATED AROMATIC NITRO COMPOUNDS When solutions of N-methyl-4-nitro­ phthalimide in dipolar aprotic solvents were heated above 140°C in the presence of potas­ sium nitrite or fluoride, bis(phthalimido )­ ether (XXI) was obtained in good yield.44 2 Mo N-R NO?, 140 • NA (13) XXI Similar reaction has been reported in which p­ nitrobenzonitrile and p-chlorobenzonitrile were converted to 4,4' -dicyanodiphenylether by the action of stoichiometric amount of sodium nitrite in N-methylpyrrolidone.45 The initial di.splacement of nitro group by an in­ itiating nucleophile (nitrite or fluoride) pro­ duces unstable nitrite ester of 4-hydroxy­ phthalimide (XXII) which reacts with the co­ product nitrite ion to produce phthalimido­ xylate (XXIII) and nitrous anhydride. The latter presumably decomposes to nitrogen oxides. Table IX. Properties of UL TEM® polyetherimide Mechanical properties Tensile strength at yield Tensile modulus Tensile elongation, ultimate Flexural strength Flexural modulus Compressive strength Compressive modulus Gardner impact strength Izod impact strength Notched Unnotched Thermal properties Glass transition Heat deflection temp at 264psi at 66 psi Flammability Limited oxygen index UL 94 vertical burn NBS smoke density D, at 4min Dm., at 20min IOSNmm- 2 3,000Nmm- 2 60-80% 145Nmm-2 3,300Nmm- 2 140Nmm- 2 2,900Nmm- 2 36N·m SOJm- 1 1,300Jm- 1 47 V-0 at 0.64mm 0.7 30 The phthalimidoxylate then undergoes nitro displacement to form the ether XXI and re­ generates new nitrite ion. Therefore, entire cycle is repeated with nitrite ion as a catalyst. •q• XXI (15) 4,4' -Bis(phthalimido)ether can be converted to diphenylether-3,3' ,4,4' -tetracarboxylic dian­ hydride by hydrolysis followed by cyclodehyd­ ration. The dianhydride has been synthesized by Kolesnikov et a/.46 by oxidation of tetra­ methyldiphenylether. Polyimides have been also prepared from the dianhydride and vari­ ous diamines.46 * ULTEM® is a registered trademark of General Electric Co. 200 Polymer J., Vol. 19, No. I, 1987 Aromatic Polymers via Nitro Displacement Reaction Similar coupling reactions were observed when molten 3-nitrophthalic anhydride was reacted with a catalytic quantity of alkali mtntes. 2,2 ',3,3 '-Tetracarboxydiphenylether dianhydride was formed in good yields at moderate conversion rates.47 ·9i KN02 ) XXIV N,o, (16) XXV The major side reaction was catalyst deacti­ vation by the following ring-opening reaction with the nitrite. XXIV + 2 KN0 2 (17) Unlike the coupling reaction of 4-nitrophthal­ imide, the use of dipolar solvents was detri­ mental, presumably the ring-opening reaction predominated. On the other hand the use of nonpolar inert solvents such as trichloroben­ zene was beneficial to moderate otherwise po­ tentially dangerous exotherm. Thermally stable polyimides have been also prepared from 2,2' ,3,3 '-tetracarboxydiphenyl­ ether dianhydride with various diamines.48 REFERENCES I. E. Radlmann, W. Schmidt, and G. E. Nischk, Maklomol. Chern., 130, 45 (1969). 2. D. R. Heath and J. G. Wirth, U.S. Patent 3,763,210 (1973). 3. J. F. Bennett and R. E. Zahler, Chern. Rev., 49, 273 (1951). 4. A. Laubenheimer, Chern. Ber., 9, 768 (1876). 5. A. Laubenheimer, Chern. Ber., 9, 1826 (1876). 6. J. H. Gorvin, Chern. Ind. (London), 36, 1525 (1969). 7. L. Caswell and T. Kao, J. Heterocyc/. Chern., 3, 333 (1966). 8. J. R. Beck, J. Org. Chern., 37, 3224 (1972). 9. J. R. Beck, J. Org. Chern., 38, 4086 (1973). Polymer J., Vol. 19, No. I, 1987 10. J. R. Beck, R. L. Sobczak, R. G. Suhr, and J. A. Yahner, J. Org. Chern., 39, 1839 (1974). II. D. R. Heath and J. G. Wirth, U. S. Patent 3, 730,946 (1973). 12. D. R. Heath and J. G. Wirth, U.S. Patent 3,787,475 (1974). 13. J. G. Wirth and D. R. Heath, U.S. Patent 3,838,097 (1974). 14. N. Kornblum, L. Cheng, R. C. Kerber, M. M. Kestner, B. N. Newton, H. W. Pinnick, R. G. Smith, and P. A. Wade, J. Org. Chern., 41, 1560 (1976). 15. F. J. Williams, U.S. Patent 3,933,862 (1976). 16. F. J. Williams and P. E. Donahue, J. Org. Chern., 42, 3414 (1977). 17. F. J. Williams, H. M. Relies, J. S. Manello, and P. E. Donahue, J. Org. Chern., 42, 3419 (1977). 18. R. L. Markezich, 0. S. Zamek, P. E. Donahue, and F. J. Williams, J. Org. Chern., 42, 3435 (1977). 19. H. M. Relies, C. M. Orlando, D. R. Heath, R. W. Schluenz, J. S. Manello, and S. Hoff, J. Polym. Sci., Polym. Chern. Ed., 15, 2441 (1977). 20. A. K. St. Clair and N. J. Johnston, J. Polym. Sci., Polym. Chern. Ed., 15, 3009 (1977). 21. W. Reinders and W. E. Ringer, Rec. Trav. Chim., 18, 326 (1899). 22. W. E. Ringer, Rec. Trav. Chim., 18, 330 (1899). 23. R. D. Knudsen and H. R. Snyder, J. Org. Chern., 39, 3343 (1974). 24. D. R. Heath and J. G. Wirth, U.S. Patent 3,869,499 (1975). 25. D. R. Heath and J. G. Wirth, U.S. Patent 3,763,211 (1973). 26. T. Takekoshi, W. B. Hillig, G. A. Mellinger, J. E. Kochanowski, J. S. Manello, M. J. Webber, R. W. Bulson, and J. W. Nehrich, NASA Contract Report, NASA CR-145007 (1975). 27. D. I. Packham and F. A. Rackley, Polymer, 10, 559 (1969). 28. D. I. Packham and J. C. Haydon, Polymer, 11, 385 (1970). 29. R. J. Gaymans, K. A. Hodd, and W. A. Holmes­ Walker, Polymer, 12, 400 (1971). 30. E. Woehrle, Makromol. Chern., 160, 83 (1972); ibid., 160, 99 ( 1972). 31. T. M. Keller and J. R. Griffith, "Resins for Aerospace," Am. Chern. Soc. Symp. Ser., 132, 25 (1980). 32. T. M. Keller and T. R. Price, J. Macromol. Sci., Chern., A18, 931 (1982). 33. T. M. Keller, Polym. Mater. Sci. Eng., 52, 192 (1985). 34. J. G. Wirth and D. R. Heath, U. S. Patent 3,838,097 (1974). 35. D. R. Heath and T. Takekoshi, U. S. Patent 3,879,428 (1975). 36. T. Takekoshi, J. E. Kochanowski, J. S. Manello, and M. J. Webber, J. Polym. Sci., Polym. Chern. Ed., 23, 1759 (.1985). 201 T. TAKEKOSHI 37. T. Takekoshi, 1. E. Kochanowski, 1. S. Manello, and M. 1. Webber, J. Polyrn. Sci., Polyrn. Syrnp., 74, 93 ( 1986). 38. T. Takekoshi and 1. E. Kochanowski, U. S. Patent 3,991,004 (1976). 39. T. Takekoshi and 1. E. Kochanowski, U. S. Patent 3,803,085 ( 1974). 40. T. Takekoshi, 1. G. Wirth, D. R. Heath, 1. E. Kochanowski, 1. S. Manello, and M. 1. Webber, J. Polyrn. Sci., Po/yrn. Chern. Ed., 18, 3069 (1980). 41. D. M. White, T. Takekoshi, F. 1. Williams, H. M. 202 Relies, P. E. Donahue, H. 1. Klopfer, G. R. Louks, 1. S. Manello, R. 0. Matthews, and R. W. Schluenz, J. Polyrn. Sci., Polyrn. Chern. Ed., 19, 1635 (1981). 42. F. 1. Williams, U. S. Patent 3,933,862 (1976). 43. F. 1. Williams, U. S. Patent 3,933,749 (1976). 44. R. L. Markezich and 0. S. Zamek, J. Org. Chern., 42, 3431 (1977). 45. H. Eilingsfeld and E. Schaffner, Ger. Patent 2,037,781 (1972). 46. G. S. Kolesnikov, 0. Ya. Fedotova, E. I. Hofbauer, and V. G. Shelgayeva, Vysokornol. Soyed., Ser. A, 9, 612 (1967). 47. A. S. Hay and T. Takekoshi, Br. Patent 1,467,275 (1977). 48. T. Takekoshi, U.S. Patent 4,048,142 (1977). Polymer 1., Vol. 19, No. I, 1987