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1977 1705Organic Reactions in Melts and Solids. Part 10.l Reactions of Carb-oxylic Acids and Anhydrides with CarbarnatesBy Michael Michman," Saul Patai, and Yitshak Wiesel, Department of Organic Chemistry, The HebrewUniversity of Jerusalem, Jerusalem, IsraelTransacylation reactions have been carried out in melts between carboxylic acids and ethyl carbarnate, rnono-N-substituted carbarnates, and di-A/-substituted derivatives a t 1 50-1 80 "C. Phthalic acid, pyrornellitic acid, andphthalic anhydride reacted with ethyl carbarnate and N-substituted ethyl carbarnates to give the correspondingarnides and irnides, carbon dioxide, and ethanol in high yields. Benzoic acid. 4-rnethoxy- and 4-nitro-benzoic acid,and acetic acid gave with ethyl carbarnate mono-N-substituted ethyl carbamates and phenyl N-phenylcarbarnategave arnides in low yields. Ethyl NN-diethyl- and NN-diphenyl-carbamate did not react with either phthalic acidor the rnonocarboxylic acids mentioned.In the case of phthalic acid the rates of reactions and overall kineticorder are similar to those found for transacylations with amides. Two examples of the preparation of thermallystable polyirnide oligorners are given.TRANSACYLATION reactions in melts between acids andamides have been described in preceding publications ofthis series1 We now describe transacylation reactionsinvolving carbamates instead of amides. Carbamatescarry amide function which can be acylated by agentssuch as ester^,^^^ carboxylic anhydride^,^, acyland k e t e n ~ .~ , ~ ~ Carboxylic acids are generally known toacylate the nitrogen atom of carbamates in the presenceof additives such as phosphoryl chloride or acetic an-hydride. 11-13The reaction of carbamates is of interest since it is notReactions were carried out with 8 : 1 to 4 : 1 molarratios of carbamate to acid or anhydride in order toobtain homogeneous melts, but yields were not decreasedwith lower ratios and heterogeneous environments.With phthalic acid and ethyl carbamate a 90% yield ofphthalimide was obtained (150 "C; 12 h). Reactionswere slower at 130 "C and hardly discernible at lowertemperatures. With phthalic anhydride at 150 "C for40 h, a 75% yield of phthalimide was obtained. This isin contrast with previously studied reactions with amidesin which the anhydride did not react unless catalystsa c > O + H,N.C02Et - a > N H t CO, + EtOHcoSCHEME 1 R = H, Ph, 4-MeC,H4, 2-ClC,H4, 3-C1C,H4, 4-C1C,H4, 4-Me0*C,H4, or 4-0,NC,H4possible to predict with certainty the behaviour of theester moiety, which may decompose during the reactionto carbon dioxide and an alcohol or may be incorporatedinto the products in various ways, e.g.to yield hetero-cyclic compounds.14RESULTSWe have studied the reactions of carboxylic acids andan anhydride with carbamates RNH*CO*OR', in whichcarbon dioxide and the alcohol R'OH are formed asvolatile products, and the resulting amide or imide canbe isolated easily. Reactions were carried out mostlywith phthalic acid and phthalic anhydride so as to obtainresults comparable with previous work 15-17 (Scheme 1).Part 9, M.Michman and D. Meidar, J.C.S. Perkin 11, 1972,0. Diels and H. Heintzel, Ber., 1905, 38, 297.A. Hantzsch, Ber., 1894, 27, 1248.D. M'Creath, Ber., 1875, 8, 1181.R. H. F. Manske, J . Amer. Chem. SOC., 1929, 51, 1202.W. Traub, Ger. Pat., 179,946, Chem. Zentr., 1907, I, 433.G. H. L. Nefkens, Nature, 1960, 185, 309.D. Ben Ishai and E. Katchalski, J . Org. Chem., 1951, 16,1026.@ N. V. Smirnova, A. P. Skoldinov, and K. A. Koscheshkov,Doklady Akad. Nauk, S . S . S . R . , 1952, 84, 737 (Chem. Abs., 1953,47. 3233b).300.were added, but in agreement with an early report byMan~ke.~Similar high yields were obtained in the reactions ofphthalic acid with a series of N-aryl carbamates (Scheme1). Monocarboxylic acids RC02H (R = 4-O2N*C6H4,4-MeO*C,H4, Ph, or Me) gave with ethyl carbamate thecorresponding amides in low yields : 4-nitrobenzamide(25%; 160 "C; 24 h), 4-methoxybenzamide (ca.5%;160 "C; 24 h), benzamide (nil; 160 "C; 24 h). Benzoicacid yielded benzanilide (10%; 160 "C; 24 h) in itsreaction with phenyl N-phenylcarbamate. Boiling aceticacid gave acetanilide with phenyl N-phenylcarbamate(5%; 42 h) despite the low temperature. Attemptedreactions of ethyl carbamate with succinic, adipic, andpyridine-2,3-dicarboxylic acids failed. Ethyl NN-di-10 L. I . Smith and 0. H. Emerson, Org. Synth., Coll. Vol. 111,1955, p. 151.11 P. Adams and F. A. Baron, Chem. Rev., 1965,65, 576.12 M. Conrad and K.Hock, 1903, 36, 2206.l 3 M. Conrad and A. Schultze, Ber., 1909,42, 734.14 Y. Wiesel, S. Patai, M. Michman, Proc. XLII Meeting, Israell5 M. Michman, S. Patai, and I . Shenfield, J . Chem. SOC. ( C ) ,16 M. Krasnoselsky and S. Patai, J . Chem. SOC. ( B ) , 1969, 24.17 M. Michman and M. Frenkel, J . Chem. SOC. ( C ) , 1971, 3856.Chem. SOC., 1972, p. 5.1967, 13371706 J.C.S. Perkin Iphenyl- and NN-diethyl-carbamate did not react withphthalic acid or with benzoic, 4-nitrobenzoic, or 4-methoxybenzoic acid. However di-N-alkyl amides doreact with phthalic acid.15 For the syntheses of phthal-imides, the present method is more simple and convenientthan traditional methods such as reactions of amineswith phthalic anhydride or phthaloyl chloride, or theGabriel method.Similarly, pyromellitic di-imides were prepared frompyromellitic acid and carbamates.With ethyl carba-mate the yield is nearly quantitative (160 "C; 24 h);hence this method is straightforward and simpler thanothers.lB Pyromellitimide is the building block of severaltypes of specialty polyimide p01ymers.l~ NN'-Diaryl-pyromellitimides, some of which have not been previouslyreported, are high-melting powders of low solubility inmost organic solvents.Two attempts were made to prepare polyimide poly-mers with the use of bifunctional reagents. From thereactions of pyromellitic acid with diethyl m- and p-phenylenebiscarbamate at 200-220 "C in melts, apolymeric product precipitated after 15 min. Thepowder obtained was slightly soluble in concentratedsulphuric acid but almost insoluble in many commonTABLE 1Reactions of carbarnates with phthalic acid and anhydrideat 150 & 1 "C; values of rate constant k according tosecond-order equationConc.Conc. lo-%/Cdrbamate (moll-l) (mol 1-1) 1 ino1-l s.-lEthyl 8.12 phthdlic 2.03 4.2acidEthyl 9.4 Phthalic 1.17 4.3acidEthyl 9.94 Phthalic 0.62 5.4acidEthyl 8.24 Phthalic 2.06 2.7anhydrideEthyl N-phenyl 5.4 Phthalic 0.68 13.0acidEthyl N-p-tolyl 5.2 Phthalic 0.65 12.0acidEthyl N-P- 4.9 Phthalic 0.61 11.6methoxyphenyl acidorganic solvents. Differential thermal analysis showedthermal stability up to 300 "C (in air or nitrogen) anddecomposition (ca. 22% in 1 h) at a higher temperature(320 "C) .p-Ethoxycarbonylaminobenzoic acid washeated above its m.p. and gave an immediate precipitateof an impure and intractable product. However 72 hin boiling m-cresol yielded polybenzamide, soluble inconcentrated sulphuric acid. Solutions (5%) in thissolvent showed relative viscosity (ut,,l.) 0.1, indicatinga polymer with molecular weight ca. 210. Thermo-gravimetric analysis showed the material to be stable upto 320 "C in air and 360 "C in nitrogen.Rates of the reaction of phthalic acid and anhydridewith several carbamates have been measured by meas-uring the volume of carbon dioxide evolved (Table 1).S. S . Gitis, V. M. Ivanova, S. A. Nemleva, Z . N. Seina, andA. V. Ivanov, U.S.S.R. P. 187006 (Cl.C.07~) 1966 (Chem. Abs.,1967, 67, 64074t, 116726d).Such measurements in melts have their limitationssince comparison of k values for different materials musttake into account that, in the absence of solvent, equi-molecular quantities of different materials representdifferent concentrations and that effects due to polarity,dipole-dipole interaction, etc., are not buffered by largeamounts of solvent, as is usually the case.The resultsindicate a reaction of overall second order, first orderTABLE 2Rate measurement of the reaction of phthalic acid and ethylcarbamate a t 150 "C. Initial concentrations: phthalicacid (a) 2 . 0 3 0 ~ ; ethyl carbamate (b) 8.120111. Initialdensity of melt 1.060Temperature of gaspressure 0.908 atm.Vol .evolvedTime (ml corr. Xof co,(102t/s) t o S.T.P.) mmol l-'3 4.9 0.066 7.95 0.09515 13.1 0.1621 15.7 0.1924 17.5 0.2130 20.85 0.2542 26.5 0.3248 29.5 0.3557 33.6 0.4063 36.1 0.4372 39.4 0.4779 42.2 0.5084 44.0 0.5396 47.7 0.57g ml-l. Sample weight 3.94 g.burette 299.5 K ; barometrickt -0.003 6940.006 2590.010 0560.012 7190.013 6210.017 0950.021 0380.024 3090.028 1660.029 9380.032 7160.036 2170.038 3550.042 4431Ou6K/mob1 s-l12.310.46.76.05.65.65.05.04.94.74.54.54.54.4k 4.17 x 10 ' 1 mol-' s - ~ .in each phthalic acid (or anhydride) and carbamate.Thekinetic behaviour is similar to that of previously studiedtransacylation reactions.1p16 The effect of para-substi-tuents on the phenyl group in the three N-arylcarbamatesstudied is small, but all three react three times as fast asethyl carbamate (Table 1).A typical sample run isgiven (Table 2). At 160 "C phthalic acid reacts 1.6 timesfaster than the anhydride.DISCUSSIONScheme 2 represents some possible sequences for thereaction. These may involve three main types of process :(1) acyl group transfer; (2) acyl group transfer accom-panied by cyclisation and formation of water; (3)hydrolysis by water formed in the melt. The reaction ofphthalic acid with cthyl carbamate (1) may yield eitherphthalamic acid (2) or N-ethoxycarbonylphthalamicacid (3). Only the second possibility is reasonable in thecase of phthalic anhydride since for the first case thepresence of water would be needed. For the formationof products from N-ethoxycarbonylphthalamic acid,again two routes are possible.Route (A) is hydrolysisleading to phthalamic acid and route (B) is an intra-molecular cyclisation. Amide hydrolysis is not easilyachieved. Experience accumulated in the studies oftransacylations in melts does not support the possibilityl* R. M. Campbell, jun., ' Modern Plastics Encyclopedia,'McGraw-Hill, New York, 1970-1971, vol. 41, p. 207; N. C. W.Judd and W. W. Wright, Refiorts Progr. Appl. Chem., 1974,50,871977 1707that water obtained in situ by anhydride formation or at what stage during the transacylation of phthalic acidother cyclisations will be an effective hydrolytic agent.Thus, phthalic acid did not hydrolyse amides with whichit was mixed in melts at 180 OC.15 The alternative route(B) (transacylation followed by cyclization) does notinvolve hydrolysis and is a more direct and simple one.Examples of such processes are known, e.g.1,kbenzdi-azapine (the first to be described) was obtained by asimilar (not identical) cyclic dehydration.20 Davidsonand his co-workers have reaced similar conclusions 21-23in regard to reactions between acids and amides. Finally,the likelihood that N-ethoxycarbonylphthalamic acidis an intermediate is demonstrated by its decompositionat 150 "C to phthalic anhydride (76%), ethyl carbamate,and phthalimide (23y0), when melted alone but itsdecomposition to phthalimide in 87% yield when meltedin the presence of an excess of ethyl carbamate at thesame temperature. Therefore, the route from (1) to(4) through (3) via (B) fits well with experimental data.U C ' N H + H2OC'I10SCHEME 2Hydrolysis of N-ethoxycarbonylphthalamic acid yieldsphthalic acid.The case of phthalic acid must be further considered.The reaction does not seem to involve phthalic anhydrideas an intermediate since, as the rate measurementsshow, it reacts 1.6 times faster than the latter.Form-ation of phthalamic acid would be analogous to theformation of amides from monocarboxylic acids and topreviously studied tran~acy1ations.l~ As it is not known2o S. Gartner, Annalen, 1904, 882, 226.21 D. Davidson and H. Skovronek, J. Amer. Chem. SOC., 1958,22 R. N. King, J . G. Sharefkin, and D. Davidson, J. Org. Chem.,23 D.Davidson and M. Karten, J . Amev. Chem. SOC., 1956, 78,80, 376.1962, 27, 2428.1066.the losses of carbon- dioxide, water, and ethanol occur,both pht halamic and et hox ycarbonylphthalamic acidscan equally be the intermediates. It is interesting thatphthalic anhydride is only a slightly slower transacylatingagent than phthalic acid, whereas in the case of amidesthe anhydride did not react at all in the absence ofcatalysts. As carbamates are not expected to differmuch in nucleophilicity from the amides studied, thisdifference is striking.The rate measurements (Table 1) indicate almost nosubstituent effect with different aryl groups attached tothe nitrogen atom, and the rate differences betweenunsubstituted and aryl-substituted carbamates are small.0II H0II0 U UI0 0SCHEME 3We believe that since the reaction involves both astronglydeveloped electrophilic centre (i.e.the carbonyl carbonatom of either a carboxy or a carbamoyl group) and aninherently strong nucleophilic centre (i.e. the amidenitrogen atom), the small sensitivity to aryl substitutionon the nitrogen atom, let alone to further substitution onthe para-carbon atom of the aryl group, can be reasonablyaccepted, even if one could not have predicted it (Scheme3). These conclusions as summarized in pathway (B) inScheme 3 are related to our previously suggested mech-.anisms for the transcylation of amides in which acyliumions or their precursors were assumed to have a significantrole.1915-17 However there are still widely differingideas as to the detailed mechanisms of transacylations,some of which have recently been re~iewed.2~The possibility that decomposition of ethyl carbamateto alcohol and isocyanate plays an important role insuch reactions as assumed by Mukaiyama et ~ 1 .~ ~ seemsunsupported by our control experiments, which showedthe carbamates to be thermally stable at 150-160" andup to 180 "C. Since the kinetics are first order in acidand in carbamates, it can a t least be stated that suchdecomposition of the carbarnate, if it takes place at all,is not a rate-controlling step.Transacylations with amides have been shown to bereversible reactions 15924 reaching completion in the case of24 R. Puffr and J . Sebenda, Coll.Czech. Chem. Comm., 1975,40,3339.25 T. Hoshino, T. Mukaiyama, and H. Hoshino, Bull. Chem.SOC. Japan, 1952, 25, 392; T. Mukaiyama, S. Motogi, and Y.Hamada, ibid., 1953, 26, 49; T. Mukaiyama and Y. Hoshino, J.Amer. Chem. Soc., 1956, 78, 19461708 J.C.S. Perkin Iphthalic acid owing to the consecutive and irreversiblecyclisation to phthalimide.15917 It was therefore ex-pected that with carbamates the irreversible evolutionof carbon dioxide, water, and alcohol would offer anefficient transacylation procedure. In fact monobasicacids are recovered in high yields, indicating a low re-activity of the system, leaving as its main asset the factthat the transacylation product is obtained alone, theother products being evolved as gases. These advantagesare demonstrated by the straightforward preparation ofpyromellitic acid imides, and by the two types of poly-merizat ion described.EXPERIMENTALN-Arylcarbarnates.ll-(i) Alkyl chloroformate (0.22 mol)was added with stirring a t room temperature to a solutionof an amine (0.2 mol) in pyridine (250 ml) during 1 h.After an additional 15 min the liquid was concentrated tohalf its volume and poured on ice (500 g).The product wasextracted with methylene chloride and the extract washedwith 10% hydrochloric acid and water, dried (MgSO,), andevaporated. The residue was crystallized from lightpetroleum or purified by distillation.(ii) Alkyl chloroformate (0.11 mol) was added to the amine(0.1 mol) and NN-dimethylaniline (1.0 mol) in dry benzene(150 ml) and the mixture worked up as above.The following carbamates were prepared and identified byelemental analysis, n.m.r. spectra, and m.p.or b.p.: 4-Me-C,H4*NH*C02Et, m.p. 46 "C (lit.,26 51 "C) ; 4-MeO*C,H4.NH.CO,Et, m.p. 56 "C (lit.,27 56 "C) ; 4-ClC6H,*NH*C0,Et, m.p.67 "C (lit.,27 69 "C; 3-C1CGH4*NH*C0,Et, b.p. 130 "Ca t 3 mmHg (lit.,28 95 "C a t 0.5 mmHg) ; 2-ClC,H4*NH*C0,-Et, b.p. 92 "C at 2 mmHg (Found: C, 54.2; H, 5.1;N, 7.2. C,Hl,CINO, requires C, 54.1; H, 5.05; N,7.0%), &(neat) 1.02 (3 H, t), 3.92 (4 H, q), 6.35-7.10(4 H, m), 4-N0,*C,H4*NH*C0,Et, m.p. 125 "C (lit.,2632B129 "C); PhNMe*CO,Et, b.p. 127 "C at 3 mmHg (lit.,30127 "C) ; PhNEt*CO,Et, b.p. 60 "C at 3 mmHg (lit.,31 63 "Ca t 14 mmHg); PhNMe*CO,Ph, m.p.57 "C (lit.,32 57 "C);PhNH-CO,Et, m.p. 52 "C (lit.,33 52 "C).Ethyl NN-diphenylcarbarnate. Diphenylamine and ethylchloroformate were heated without solvent according to themethod of Hager,34 to yield the product, m.p. 72 "C, whichwas dried in vacuum (P,O,) to eliminate traces of pentylalcohol used for crystallization; G(CDC1,) 1.2 (3 H, t), 4.2(2 H, q), and 7.0br (10 H, s) (Found: C, 74.7; H, 6.3;N, 5.8. C,,H,,NO, requires C, 74.7; H, 6.2; N, 5.8%).Stability of Carbarnates under Reaction Conditions.-Ethyl carbamate (5 g) was heated for 24 h a t 150, 160, or180 "C; it was unchanged in the first two cases. In thethird case about 2% of high-melting material was formed-possibly by self condensation. Ethyl N-4-nitrophenyl-carbamate (0.18 g) partially sublimed (0.16 g) when heatedfor 24 h a t 150 "C.The sublimate as well as the residue wereidentical with the starting material. Other carbamateswere similarly stable at 150 "C.26 G. M. Dyson and T. Harrington, J . Chem. Soc., 1942, 150.27 C. W. Whitehead and J. J. Traverso, J . Amer. Chem. SOC.,28 S. L. Shapiro, V. Bandurco, and L. Freedman, J . Org. Chem.,29 R. L. Shriner and R. F. B. Cox, J . Amer. Chem. Soc., 1931,3O W. Gebhardt, B e y . , 1884, 17, 3042.31 J. von Braun, Ber., 1903, 36, 2287.32 E. Lellmann and E. Benz, Bey., 1891, 24, 2108.1955, 77, 5872.1961, 26, 3710.53, 1601.Reactions of Ethyl Carbamate and Ethyl N-Phenylcarb-amate with Phthalic Acid and Phthalic Anhydride.-(i) Amixture of phthalic acid (0.02 mol) and ethyl carbarnate(5.34 g, 0.06 mol) in a flask equipped with a distillationhead and condenser was flushed with dry nitrogen andheated in an oil-bath a t 150 "C for 12 h.Volatile productssuch as water and ethanol were collected in a cold trap,dissolved in deuterium oxide (1-2 ml) (Merck Uvasol99.750/,), and analysed by n.m.r. to show the presence ofequivalent amounts of water and ethanol. Carbon dioxidewas trapped in a clear barium hydroxide solution and yieldedbarium carbonate.The residue was washed with saturated aqueous sodiumhydrogen carbonate and recrystallized from ethanol.Phthalimide (2.65 g, 90%) formed was identical withauthentic samples (m.p. and mixed m.p. 235 "C; i.r. spec-trum). Alternatively the residual mixture was trituratedwith cold diethyl ether and filtered.The insoluble phthal-imide was crystallized from ethanol. The filtrate containedethyl carbamate.(ii) The reactions with phthalic anhydride were run forlonger periods (40 h). The volatile products consistedsolely of ethanol and carbon dioxide. The residue wastreated with sodium hydrogen carbonate for 24 h to ensurecomplete extraction of residual anhydride. The singleproduct was phthalimide (2.24 g, 750,/,).(iii) The reaction of phthalic acid (0.50, 0.003 mol) andethyl N-phenylcarbamate (1.5 g, 0.01 mol) (150 "C; 24 h)yielded carbon dioxide and equimolar amounts of water andethanol. Phthalanil was obtained as above, identical(m.p. 217 "C and i.r.) with an authentic sample.Mixtures of phthalic acid or anhydridewith the carbamate were prepared by grinding the consti-tuents together, and kept in a desiccator (CaCl,).Samplesof 4 g were used in a 50 ml flask equipped with a refluxcondenser (air-cooled), which was in turn connected to agas burette containing 10% hydrochloric acid previouslysaturated with carbon dioxide. To start a reaction, theflask was dipped into an oil bath a t 150 "C, and measure-ments were started exactly 5 min later, by which time ahomogeneous melt had been obtained. The volume ofcarbon dioxide formed was measured at 5 min intervals for30 min, and 15 or 30 min intervals thereafter. Volumefluctuations due to temperature fluctuations in the oil-bathand reaction apparatus were &l ml. The initial densitiesof the mixtures were determined as described previously,'and concentrations of reactants were calculated accordingly.Reactions of Phthalic Acid with N-A ry1carbamates.-N-Arylphthalimides were prepared by melting a mixture ofphthalic acid (3.32 g, 0.02 mol) and the corresponding car-bamate (0.04 mol) at 180 "C for 24 h . After cooling, un-changed carbamate and acid were removed by grinding theresidue in cold ethanol and recrystallizing the solids fromethanol.N-Arylphthalimides [C,H,(CO),NAr] were identi-fied by elemental analysis, i.r., and n.m.r. spectra, and m.p.Yields were as follows: Ar = Ph, m.p. 317 "C (lit.,36a 211 "C),(iv) Kinetic runs.33 T. Wilm and G. Whischin, Annalen, 1868,147, 157.34 H. Hager, B e y . , 1885, 18, 2573.35 ( a ) M.L. Sherrill, F. L. Schaeffer, and E. P. Shoyer, J .Amer. Chem. SOC., 1928, 50. 474; (b) 0. L. Brady, W. G. E.Quick, and W. F. Welling, J . Chem. Soc., 1925, 127, 2264; (c) S.Gabriel, Ber., 1878, 11, 2260; ( d ) ' Dictionary of Organic Chem-istry,' eds. J. R. A. Pollock and R. Stevens, 4th edn., OxfordUniversity Press, New York. vol. 5, p. 2742; (e) A. Piutti and G.Abbatti, Bey., 1903,36, 1000; (f) C . I,. Riitlcr. jun., and R. Adams,J . Amer. Chem. SOC., 1925, 47, 26101977 170966%; 4-MeC,H4, m.p. 209 "C (lit.,356 204 "C), Wy0; 4-ClC,H,, m.p. 196 "C (lit.,Ssc 194-195 "C), 77% ; 3-C1C,H4,m.p. 163 "C (lit.,35a 163-164 "C), 84%; 2-ClC,H4, m.p.143 "C (lit.,35a 132-140 "C; lit.,35d 143 "C), 61%; 4-MeO.C,H,, m.p. 159 "C (lit.,35e 161-162 "C), 60%; 4-N0,C,H4,m.p.274 "C (lit.,,%! 271-272 "C), 80%.Reaction of Ethyl Carbamate with 4-Nitrobenzoic A czd .-Amixture (4 g) of ethyl carbamate and 4-nitrobenzoic acid in8 : 1 molar ratio was heated in an evacuated sealed ampoule(20 ml) at 160 "C for 24 h. The ampoule was opened andthe residue treated with sodium hydrogen carbonate solutionand recrystallized from water to yield 4-nitrobenzanilide,m.p. 201 "C (25%) (Found: C, 50.35; H, 4.15; N, 16.9.C,H,N203 requires C, 50.6; H, 3.65; N, 16.9%).Reaction of Ethyl Carbamate with 4-Methoxybenzoic Acid.-The procedure was as above except for crystaliizing theresidue from diethyl ether after the hydrogen carbonatetreatment. The 4-methoxybenzamide obtained was re-crystallized from water (yield 5 % ) , m.p.163 "C (lit.,:,163 "C).Reaction between Ethyl N-Phenylcarbamate and AceticAcid.-Ethyl N-phenylcarbamate (0.05 mol) was dissolvedin acetic acid (30 g, 0.6 mol) and the solution refluxed for42 h. After cooling and neutralization with 10% sodiumcarbonate solution the mixture was extracted with chloro-form; the extract was dried (MgSO,) and evaporated.The residue was boiled several times in light petroleum toremove unchanged carbamate and the acetanilide wasrecrystallized from benzene (yield 0.286 g, 4.2y0), n1.p.116 "C, mixed m.p. 115 "C.Attempted Reactions with Other Acids and with NN-Dialky1carbamates.-An attempted reaction of ethyl carb-amate with pyridine-2,3-dicarboxylic acid yielded un-changed ethyl carbamate, carbon dioxide, and nicotinicacid, m.p.236 "C. Attempted reactions of NN-diphenyl-carbamates., ethyl NN-diethylcarbamate (170 "C, 24 h), andethyl N-methyl-N-phenylcarbonate (150 "C; 24 h) withphthalic acid, and attempted reactions of ethyl NN-diethylcarbamate with benzoic, 4-methoxybenzoic, and4-nitrobenzoic acids (170 "C; 24 h) left the starting materialsessentially unchanged. Phthalic acid was recovered (90%)as the anhydride.N-Ethoxycarbonylphthalamic A cid.-A suspension of N -ethoxycarbonylphthalimide (Fluka) (20 g) in distilledwater was warmed to 70 "C until most of the material haddissolved, quickly filtered, and cooled. The precipitate wasrecrystallized from chloroform or light petroleum (b.p.40-60 "C); yield 12 g, m.p. 55-70 "C (lit.,,' 40-50 "C),G(CDC1,) 1.23 (3 H, t, CH,*CH,*O), 4.20 (2 H, q, CH,*CH,*O),7.41-7.82 (3 H, m, arom.), 8.10-8.25 (1 H, m, arom.),8.65 (1 H, s, CO,H), and 9.3 (1 H, s, CO-NH-CO).Pro-longed treatment with hot water yields phthalic acid.Pyrolysis of N-Ethoxycarbonylphthalarnic Acid at 150 "C.-N-Ethoxycarbonylphthalamic acid (2.3 g, 0.01 mol) washeated (150 "C ; 12 h) under a slow stream of dry nitrogenin a distillation system. Small amounts of carbon dioxideformed were trapped in barium hydroxide solution. Somesolid material sublimed into the condenser and after separ-ation with dry ether was identified as a mixture of phthalicanhydride (1.1 g, 74%) and ethyl carbamate. The residuein the distillation flask was recrystallized from ether to yieldphthalimide (0.34 g, 23%).The same procedure wasrepeated with a mixture of N-ethoxycarbonylphthalamic36 L. Gattermann, Annalen. 1888, 244, 62.37 G. Heller and P. Jacobsohn, Ber., 1921,54, 1112.acid (2.3 g, 0.01 mol) and ethyl carbamate (0.04 mol).After heating (150 "C; 10 h) the residue in the distillationflask yielded phthalimide (washed with aq. NaHCO,)(1.27 g, 86.5%).Pyromel1itimides.-Well ground mixtures of pyromelliticacid (5.08 g, 0.02 mol) and the appropriate carbamate(0.OP-0.08 mol) were heated for 24 h, at 160 "C (with ethylcarbamate) or 180 "C (with N-phenylcarbamates) . Evolu-tion of carbon dioxide and precipitation in the initiallyhomogenous melt were observed. After cooling, the solidmass was ground, the residual acid removed with aqueous10% sodium carbonate, and the carbamate extracted withether or with boiling ethanol.Usually, no solvent forrecrystallization was found ; some products were purifiedby boiling in pyridine or dimethylformamide (DMF) .None of the products melted below 300 "C. The followingNN-diaryl~yromellitimides were prepared : Ar = Ph, yield707A (Found: C, 71.8; H, 3.35. C,,H,,N,O, requiresC, 71.75; H, 3.25y0), Amax. 257 nm (log E 4.4); Ar = 4-Me-C,H,, 42% (Found: C, 72.05; H, 3.95; N, 7.05. C,,H,,-N,O, requires C, 72.7; H, 4.05; N, 7.05y0), crystallizedfrom DMF, Amax. 267 nm (log E 4.7); Ar = 4-C1C6H,, 65%(Found: C, 59.75; H, 2.4; C1, 15.5; N, 5.9. C,,HloC1,N,O,requiresC, 60.4; H, 2.3; C1, 16.25; N, 6.4y0), A,,,. 267 nm(log E 4.7); Ar = 2-C1C,H4, 76% (Found: C, 60.35; H,2.6; C1, 15.6; N, 6.4%), washed with pyridine, A,.312(log E 3.42); Ar = 3-C1C6H,, 65% (Found: C, 60.55; H,2.7; C1, 15.7; N, 6.35y0), washed with boiling pyridine,A,,,. 257 (log E 4.57); Ar = 4-MeO*C,H4, 82% (Found:C, 67.05; H, 3.75; N, 6.35. C,,H,,N,O, requires C, 67.3;H, 3.75; N, 6.55y0), washed with pyridine, Amax. 282 nm(log E 4.23); Ar = 4-NO2*C,H,, 41% (Found: C, 57.4;H, 2.05; N, 12.0. C,,H,,N,O, requires C, 57.65; H, 2.2;N, 12.2%), washed in pyridine, A,. 288 nm (log E 4.75).Typical i.r. absorptions (1 7 15 and 1 735 cm-l) were observedin all cases.Diethyl m- and p-Phenylenebiscarbamates.38-These wereprepared by the dropwise addition with stirring, of ethylchloroformate (Fluka purum; 25 g, 0.25 mol) to a solutionof the appropriate phenylenediamine (10.8 g, 0.1 mol) inpyridine ( 100 ml) .The mixture was left to cool and pouredon crushed ice. The precipitate was filtered off, dried, andrecrystallized from ethanol-water or from ether. Thepara-isomer, n1.p. 195 "C (lit.,38 195 "C), was recrystallizedfrom ethanol. The meta-isomer had m.p. 143 "C (lit.,38Reactions of Phenylenebiscarbamates with PyromelliticAcid.-A mixture (10 g) of the biscarbamate and acid in3 : 1 molar ratio was heated in a distillation apparatus at160-180 "C. Carbon dioxide was evolved along withethanol and water, detected as above. After several hoursthe mixture was cooled, crushed, and treated with an excessof sodium hydrogen carbonate (until no more carbon dioxidewas evolved). Repeated washings with boiling ethanolleft a yellowish amorphous solid, m.p. >300 "C, insoluble inall solvents tried. The i.r. spectrum displayed aromaticabsorptions a t ca. 800 cm-l and carbonyl bands similar tothose of pyromellitimide [Found (impure powder) :C, 63.1; H, 3.4; N, 9.95. Calc. for C,,H,N,O,,: C, 66.2;H, 2.05; N, 9.65%].Polymerization of p-Ethoxycarbonylaminobenzoic A cad .-The acid 39 [m.p. 208 "C (lit.,39 208-209 "C] (4.13 g, 0.02 mol)in m-cresol (150 ml) was refluxed for 72 h. While still hot,38 E. Davidis, J . prakt. Chem., 1896, 54, 66.39 H. King and W. 0. Murch, J . Chem. SOC., 1924, 125, 2595.143-145 "C)1710 J.C.S. Perkin Ithe solvent was removed by filtration and the solid was then 'l'his research was sponsored by a grant in aid from theboiled in ethanol (200 ml), filtered off, and washed with European Research Office of the United States Army,acetone [Found (impure powder) : C, 70.9; H, 4.75; N, London.12.0. Calc. for (C,H,NO),: C, 70.6; H, 4.2; N, 11.750/,].The i.r. spectrum showed carbonyl absorptions.Viscosity was determined in concentrated sulphuric acid(AnalaR) a t 25 & 0.1 "C with an IJbbelohde Viscometer at0.5% concentration; 40 the value Of Was 0.1, corres-ponding to ca. 10 units per chain ( M 210).[6/1973 Received, 25th Octobev. 1976140 F. w. Billmeyer, jun., ' Textbook of Polymer Science,'Wiley, New York, 1971, 2nd edn., p. 84

ISSN:1472-7781    

DOI:10.1039/P19770001705

出版商:RSC    

年代:1977

数据来源: RSC