1976 1827Behaviour of Nitrile Oxides towards Nucleophiles. Part 1V.l Hetero-macrocycles from Acetonitrile OxideBy Alberto Brandi, Francesco De Sarlo,' and Antonio Guarna, Centro di studio sulla chimica e la strutturadei composti eterociclici e loro applicazioni, C.N.R., lstituto di Chirnica organica, UniversitB di Firenze,ItalySeveral polymers of acetonitrile oxide have been obtained by treatment of the pure monomer with pyridine or tri-methylamine. Spectroscopic properties of dimer, hexamer, heptamer, and octamer support stereoregular un-saturated monocyclic structures ; this has been confirmed, for one of them, by crystallographic analysis. Anotherpolymer, which is the main product from very concentrated solutions of acetonitrile oxide and trimethylamine, isbelieved to have a linear structure.A polymerization mechanism is suggested.ethanol as solvent. Acetonitrile oxide exhibits a strongvEN band at 2 315 cm-l (in ethanol) and a singlet atTHE isolation of acetonitrile oxide has been reportedbriefly,2 but the experimental procedure was not de-scribed. The preparation and purification of aceto-nitrile oxide reported here allowed us to examine itsreactivity with trimethylamine and with pyridine, in FgE:;:;g pgsE$ A G ~ ~ ~ ~ 1964. 3, 3831828 J.C.S. Perkin I6 2.25 in the lH n.m.r. spectrum (in ethanol). Dimeris-ation to dimet hylfurazan N-oxide requires several hoursfor completion: this is shown by i.r. spectroscopy(disappearance of the u s = band) or by the replacement ofthe n.m.r. signal at 6 2.25 by two singlets at 6 2.19 and2.38.Earlier reports on the low stability of this nitrileoxide are considered to refer to the pure substance aboveits m.p.The high solubility of acetonitrile oxide in ethanolallows reactions with nucleophiles to be performed inmuch more concentrated solutions than those attainablewith aromatic nitrile oxides.lJ In this way, higherpolymers are easily obtained, as well as some dimersanalogous to those from aromatic nitrile oxides. Men-tion has been made, among othersJ4 of polymers ofacetonitrile oxide and of benzonitrile oxide, the lasthaving been obtained from benzonitrile oxide withtrimethylamine as catalyst.6With pyridine in ethanol, acetonitrile oxide givesmainly a dimer in dilute solution.At higher aceto-nitrile oxide concentration a precipitate of molecularformula (C,H,NO), is also obtained, soluble in chloroform,which does not melt below 320 "C, but decomposes slowlyabove 250 "C. In very concentrated solution, the samepolymers prepared with trimethylamine can be identified,in addition to the dimer.With alcoholic trimethylamine, the same hexamer asproduced with pyridine is obtained in moderatelydilute solution ; another polymer, insoluble in commonorganic solvents, precipitates from a concentrated solu-tion. The mother liquor from the latter reaction gives,on concentration in vacuo, more precipitate, soluble inchloroform and in ethanol, containing two main con-stituents (t.l.c.), a heptamer and an octamer, whichhave been isolated by column chromatography.Fromall the above reactions some 3,4-dimethylfurazan N-oxide was detected in solution by g.1.c.Yields of polymers generally increase with the con-centr at ions of both ace t oni t rile oxide and trime thylamine.At high reagent concentration (ca. 31bsol;11 in nitrile oxide and2.5 or IM in nucleophile) the insoluble polymer is pre-valent among the products, whereas the hexamer, theheptamer, and the octamer predominate at lowerconcentrations (ca. IM in each reagent); in more dilutesolution (ca. 0 . 1 ~ in nitrile oxide and 0 . 2 ~ in nucleophile)only 3,4-dime thylf urazan N-oxide is detected, toget herwith unidentified by-products.Spectral properties of the polymers are collected inTables 1 and 2.On the basis of spectroscopic evidence, the dimerobtained with pyridine can be identified as 3,6-dimethyl-lJ4,2,5-dioxadiazine (1; R = Me) analogous to thedimers obtained from aromatic nitrile oxides and pyri-dine.3 Only one signal, at 6 1.97, appears in its lH n.m.r.spectrum (Table l), indicating that the two methylgroups are equivalent; no U.V.absorption maximumF. De Sarlo, J.C.S. Perkin I, 1974, 1951.References in Ch. Grundmann and P. Griinanger, 'TheNitrile Oxides,' Springer-Verlag, New York, 1971, p. 83.5 H. Wieland, Ber., 1909, 42, 816.occurs above 200 nm (in ethanol) (thus conjugated doublebonds can be excluded); and finally the mass spectralfragmentation (Table 3) closely resembles that for aryl-substituted dioxadiazines (1 ; R = Ar).TABLE 1U.V.and n.m.r. spectra of polymers of acetonitrile oxideN. m.r.bPolymer U,v.a ' 1H 13CH3 1 3 e 'Dimer (1; R = Me) ZOO 1.97(s) 15.1 161.3Hexamer 208 2.14(s) 15.4 160.3Heptamer 217 (4.708) 2.10(s) 15.6 161.3Octamer 217 (4.716) 2.06(s) 15.5 162.4hmsx./nm (log e) ; solvent methanol. 6 Values : solventdeuteriochloroform. 13C Spectra are decoupled. c Qualitativespectrum, owing to low solubility.We will discuss the structures of the hexamer, theheptamer, and the octamer together. In the massspectra, the molecular ion peaks, though not veryintense, confirm the molecular weights found in solution;among other fragments, the dimer and the monomer wereprominent, in addition to those produced by furtherbreakdown of the dimer (1; R = Me).U.V. spectra(Table 1) indicate the absence of conjugated doublebonds; therefore the monomer units must be linked, asin the dimer (1; R = Me), via 0-C bonds. Eachpolymer gives, in the n.m.r. spectra, only a singlet lHsignal and two 13C signals (decoupled spectra) (Table 1) ;this means that all monomeric units are in equivalentpositions, and cyclic structures must therefore be con-sidered. Raman and i.r. spectra (Table 2), indicatingC=N and N-O-C linkages, confirm the postulated mode oflinkage; moreover, the great similarity of the spectraof the hexamer, the heptamer, and the octamer suggeststhat their structures are strictly analogous. In view ofthe equivalence of the monomeric units, each structuremust contain all double bond systems in the same geo-metrical configuration, i.e.either all syn- or all anti-methyl. In conclusion, the hexamer has to be formulatedas 3,6,9,12,15,18-hexamethy1-lJ4,7 ,lo, 13 , 16-hexaoxa-2,5,8 , 1 1 , 14,17-hexa-azacyclo-octadeca-2,5,8 , 1 1 , 14 , 17-hexaene, either syn (2) or anti (3); the analogouspossible structures for the heptamer and the octamerare not illustrated.The geometrical configuration of these heteromacro-cycles was established by X-ray crystallographic analysisof the octamer; the results confirm the proposed cyclicstructure , in the anti-methyl configuration.' Thisconclusion can be extended with confidence to thehexamer structure (2) is rejected in favour of (3) andto the heptamer, in view of the similarity of 13C n.m.r.data (Table 1) and of the mode of formation (see later).The so-called ' insoluble polymer ' exhibits the samekind of vibrational spectra as the other polymers (Table2).However, its behaviour is otherwise unusual: itundergoes deflagration on heating; it exploded underlaser irradiation during an attempt to obtain a Raman8 G. Speroni and M. Bartoli, ' Sopra gli ossidi di benzonitrile,'nota VIII, Stabilimento tipografico Marzocco, Firenze, 1952 ;quoted in ref. 4, p. 82.7 S. Menchetti and C. Sabelli, J.C.S. Perkin 11, in the press1976spectrum; in the high vacuum of the mass spectrometer, tions are dilute, both nucleophile release and isomeriz-at 50 "C, it produces repeatedly sudden pressure rises. ation to the syn-methyl configuration are slower thanIn the mass spectrum the most intense peak corresponds further nucleophilic attack on more acetonitrile oxide.to the monomer; no appreciable fragments corresponding This process leads to stereoregular intermediates (6;to a dimer or at higher mle values were observed. Nu = NMe,); at very high nitrile oxide concentration,These facts lead to the assignment of a linear structure the chain in the intermediates (6; Nu = NMe,) isof the type : -C(Me)=N-O-C(Me)=N-O-C(Me)=N-O-, rapidly lengthened so that the insoluble polymer is theRamanTABLE 2Raman and i.r.spectra of polymers of acetonitrile oxide aDimer2 983w2 931s1 663w1428w1 386w908w805vs595w480vsHexamer3 012m2 988m2 936vs1 662vs1 644s1430s1394w1225w1 044m1017w971w872m593s414w,I In cm-1.RMePh I,4-MeC6H,4-Me0.C,H42,4,6-Me3C,H, b4-ClC6H44-N02*C6H4Heptamer3 005sh2 990m2 937vs1 659vs1430s1387m1230w1038m1 020w963w847w820s621m574m415wOctamer3 OOOm2 984w2 932vs1 676m1655vs1 430s1 380m1227w1040m1025w957m837w814m620w584m512wI.r.=L cDimer3 004w2 935w1658s1 639m1 445w1 423m1415m1382vs1 293vs1240w1071w1 063w1039w988vs811s731s543w480wHexamer Heptamer Octamer30lOw 3000w 3008w2988w 2990w 2982w2937w 2938w 2936w1675m 1670vs 1662vs1 655vs 1 650vs 1 645vs1427m 1424s 1418s1378vs 1380s 1374s1340w 1324w1318m 1294s1282vs 1270vs 1254vs1 045sh1033vs 1038sh 03"1028vs 022s969vs 970vs 965vs945sh850s 842s 852w832s647w 640w614m 630m 625w618sh 610sh585w 581w 591w585w565wInsoluble'polymer3 ooow2 99ow2 933w1 656vs1422w1380vs1310vs1248w1041s980s861w830w61 lw592wApprox.description } VC-HVC=N } 8OHa} w-0-0b Powdered samples.C KBr pellets, except for the dimer (solid film at liquid N, temperature).TABLE 3Mass spectra of substituted 1,4,2,5-dioxadiazines ( 1) aFragments : M M + 1 M - 1 6 RCNO RCO RCN15.6 1 1 2.2 21 10012 2 1 9 40 10032 6 1 25 100 8611 2.5 4 24 47 10010 1.7 0.8 9 60 10026 5 1 5.5 100 451.5 0.3 0.5 30 40 70Relative abundances of the main fragments (yo); spectra were taken at 70 eV by direct insertion, except for compound(l;R=Me), injected by g.1.c.S. Morrocchi, A. Ricca, A. Selva, and A. Zanarotti, Gazzefta, 1969, 99, 165.analogous to the structure postulated for an explosivepolymer obtained from benzonitrile oxide.6In the light of our previous results on aromatic nitrileoxides ,l* we tentatively rationalize the polymerizationof acetonitrile oxide in terms of the illustrated reactionscheme. With trimethylamine as nucleophile, twosuccessive nucleophilic additions afford the intermediate(5; Nu = NMe,). Then, unless the nitrile oxide solu-main product. At low reagent concentrations, otherprocesses are prevalent, but these have not yet beenexamined. At intermediate concentrations, chain growthleading to the intermediates (6; Nu = NMe,) occurs atsuch a rate that ring closure, when n = 4, 5, or 6, isprevalent over further linear polymerization.Ringclosure of the intermediates (6) can occur via C-0 bonds* F. De Sarlo and A. Guarna, J.C.S. Perkin 11, 1976, 6261830 J.C.S. Perkin Iwith either nucleophile, without steric hindrance ;suitable conformations can be attained with chains ofthis length. The formation of small amounts of poly-mers of molecular weight intermediate between thedimer and the hexamer cannot be excluded. Likewise,we cannot exclude the production of some 3,5-dimethyl-1,2,4-oxadiazole 4-oxide from the intermediate ( 5 ; Nu =NMe,) by loss of nucleophile followed by ring closure.On the other hand, higher polymers are formed frombenzonitrile oxide under similar reaction conditions,6 asalready mentioned.MeMeMebonds : the nucleophilic centre binds to the carbon atomof the nitrile oxide triple bond, and the lone pair settleson the nitrogen atom in the trans orientation.Thisfeature has already been observed in the addition ofhydrochloric acid to nitrile oxide~.~J*EXPERIMENTALInstruments used were : Perkin-Elmer F 21 preparativegas chromatograph ; Hitachi-Perkin-Elmer 11 5 osmometer(for molecular weights) ; Perkin-Elmer 270 spectrometer(for mass spectra) ; Perkin-Elmer 42 1 spectrophotometerMebsol;MeMeJ( 5 )L(6 1SCHEMEWith pyridine as nucleophile, the main reaction pathin dilute solution is dimerization to (1 ; R = Me) throughthe intermediate (5; Nu = pyridine), as for aromaticnitrile oxidess However, at high acetonitrile oxideconcentration, chain growth to give the intermediates(6; Nu = pyridine) is also possible, and all the describedpolymers have been found amongst the reaction products.The stereochemical course of acetonitrile oxide poly-merizations, leading to anti-methyl cyclic polymers, is inagreement with the usual trans-addition to unsaturatedH.E. Ungnade, G. Fritz, and L. W. Kissinger, Tetrahedron,1963, 19, Suppl. 1, 235.(for i.r. spectra); Cary 81 spectrometer equipped with anAr+ laser source selecting the 4 880 line as exciting light(for Raman spectra) ; Cary 14 spectrophotorneter (for U.V.spectra) ; Perkin-Elmer R 32 spectrometer (for 1H n.m.r.spectra) ; Bruker W H-90 PFT spectrometer (for 13C n.rn.r.spectra).Acetohydroxamoyl Chloride.-The crude material, pre-pared as reported,Il was recrystallized from petroleum a t-60 OC, filtered off quickly in a dry-box at - 5 "C, andstored in solid carbon dioxide.10 J.P. GuettC, J. Armand, and L. Lacombe, Compt. rend.,1967, 264C, 1509.l1 H. Wieland, Ber., 1907, 40, 16771976 1831A cetonitrile Oxide.-Acetohydroxamoyl chloride (2 g) wasdissolved in petroleum (250 ml), and triethylamine (3 ml;slight excess) was added to the cold solution. After removalof the precipitated hydrochloride, the solution was shakenwith solid potassium hydrogen sulphate, decanted, andcooled at -60 "C. The precipitated product was collectedin a cooled dry-box and immediately dissolved for use;yield 43 (from integrated n.m.r. spectrum; referenceethanol).AcetonitriZe Oxide and Trirnethylarnine ; the Hexamer (3),the Heptamer, the Octamer, and the Insoluble Polymer.-Theacetonitrile oxide prepared from 4 g of acetohydroxamoylchloride was dissolved in ethanol a t ca.0 "C, then added toconcentrated ethanolic trimethylamine to give 6 ml ofsolution (ca. 3~ in nitrile oxide * and ca. 2 . 5 ~ in nucleophile).The precipitate was collected and washed with ethanol, thenwith chloroform to give insoluble polymer (0.52 g, 50),which darkens near 150 "C and deflagrates a t 180-183 "CFound: C, 42.0; H, 5.35; N, 24.8. Calc. for (C,H,NO),:C, 42.1; H, 5.3; N, 24.55. The chloroform solutionafforded, on dilution with ethanol, the hexarnev (26 mg);this product becomes dark above 250 OC, but does not meltbelow 320 "C Found: C, 42.0; H, 5.3; N, 24.8; M , 363,334, 342.(C,H,NO)6 requires C , 42.1; H, 5.3; N, 24.55;M , 342.31.From the mother liquor, combined with ethanol washings,a mixture of heptamer and octamer precipitated on partialconcentration (60 mg): more of these polymers werecontained in the residue obtained by complete evaporation,together with unidentified by-products. On t.1.c. silicagel (Il/lerck FfB4, 0.25 mm thickness); eluant 1 : 1 chloro-form- diethyl ether the heptamer and the octamer gaveRF values of 0.81 and 0.66, respectively; they were isolatedby column chromatography with silica gel (Merck 70-325mesh ASTM; same eluant). The heptarnev was recrystal-ized from methanol; m.p. 174-176 "C (decomp.) Found:C, 42.2; H, 5.3; N, 25.4; M , 378, 408, 396. (C,H,NO),* Concentrations and yields are calculated on the assumptionthat 1.05 g of acetonitrile oxide are produced from 4 g of aceto-hydroxamoyl chloride.requires C, 42.1; H, 5.3; N, 24.55; M , 399.351.Theoctamer was also recrystallized from methanol; m.p. 171 "C(decomp.) Found: C , 42.2; H, 5.4; N, 24.9; M , 444,451, 466. (C,H,NO), requires C, 42.1; H, 5.3; N, 24.55;M , 456.41.With lwtrimethylamine and the same nitrile oxide con-centration, a decrease in the yields of the above products wasobserved. At lower trimethylamine concentration ( 0 . 2 ~ )the yield of insoluble polymer was more severely reduced(ca. 5) and those of the other polymers were scarcelyaffected.Reactions of 0.6~-acetonitrile oxide gave, with concen-trated trimethylamine (ca.3 ~ ) , ca. 10 yield of insolublepolymer and smaller amounts of the other polymers; withlwtrimethylamine only 15 mg of insoluble polymer butincreased yields of the other polymers (10 of isolatedhexamer) were obtained ; with 0 . 2 ~ trimethylamine, 5 ofthe hexamer and smaller amounts of heptamer and octamerwere isolated, but no insoluble polymer.At lower acetonitrile oxide concentration (0.06~) nosuch polymers were obtained, whatever the trimethylamineconcentration.Acetonitrile Oxide and Pyridine; the Dirner (1; R = Me).-The nitrile oxide obtained from 4 g of acetohydroxamoylchloride was dissolved in ethanol (70 ml) and added topyridine (12 ml). The hexamer (3) (50 mg) precipitatedfrom the yellow mixture : the clear solution was concentratedwith a fractionating column at atmospheric pressure. Thedimer, 3,6-dimethyZ- 1,4,2,5-dioxadiazine (1 ; R = Me) couldthen be isolated by preparative g.1.c. 2 m column packedwith OV 17 (10) on Chromosorb A; constant temp. 100 "Cor by concentrating a solution in chloroform washed withdilute sulphuric acid; m.p. 61" (sublimed) (Found: C, 42.6;H, 5.3; N, 24.8. C,H,NO requires C, 42.1; H, 5.3; N,24.55). The molecular weight could not be measured bythe isopiestic method owing to the high vapour pressure ofthe compound.In very concentrated solution, acetonitrile oxide andpyridine produced all the polymers described above.6/131 Received, 20th January, 1976
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