Elektrocyclische Ringöffnungen von Ethylenoxiden

Huisgen, Rolf

doi:10.1002/ange.19770890905

Cited by 56 publications

(5 citation statements)

References 56 publications

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“…These data are in agreement with the conformational study of the lactams, where it was shown that dodecalactam or its dimer 39 are more thermally stable that enantholactam or undecalactam or their dimers. 23,24,40 Thermogravimetric curves of nylon 11 and nylon 12, 32 are shown in Fig 1. In terms of weight loss, both of these nylons decompose very similarly. As expected, they are more stable than nylon 6 because they contain a lower concentration of amide groups.…”

Section: Nylons 7 11 and 12mentioning

confidence: 99%

Thermal decomposition of aliphatic nylons

Levchik¹,

Weil²,

Lewin³

1999

Polym. Int.

358

250

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An overview of the literature together with selected authors' data on thermal and thermo‐oxidative decomposition of commercial aliphatic nylons (nylon 6, nylon 7, nylon 11, nylon 12, nylon 6.6, nylon 6.10, nylon 6.12) is presented. Despite the high level of research activity and the large number of publications in the field, there is no generally accepted mechanism for the thermal decomposition of aliphatic nylons. Polylactams (nylon 6, nylon 11 and nylon 12) tend to re‐equilibrate to monomeric or oligomeric cyclic products. Diacid–diamine type nylons (nylon 6.6, nylon 6.10 and nylon 6.12) produce mostly linear or cyclic oligomeric fragments and monomeric units. Because of the tendency of adipic acid to fragment with elimination of CO and H2O and to undergo cyclization, significant amounts of secondary products from nylon 6.6 are reported in some papers. Many authors have shown that the primary polyamide chain scission occurs either at the peptide C(O)NH or at adjacent bonds, most probably at the alkyl–amide NHCH2 bond which is relatively the weakest in the aliphatic chain. Hydrolysis, homolytic scission, intramolecular CH transfer and cis‐elimination (a particular case of CH transfer) are all suggested as possible primary chain‐scission mechanisms. There are no convincing results reported which tend to generally support one of these mechanisms relative to the others; rather, it seems that the contribution of each mechanism depends on experimental conditions. This conclusion is also supported by the wide spread of kinetic parameters measured under the different experimental conditions. More uniform results are observed in the literature regarding the mechanism of thermo‐oxidative decomposition of aliphatic nylons. Most authors agree that oxygen first attacks the N‐vicinal methylene group, which is followed by the scission of alkyl–amide NC or vicinal CC bond. Alternatively, it is suggested that any methylene group which is β‐positioned to the amide group methylene can be initially oxidized. There are few mechanisms in the literature which explain discoloration (yellowing) of nylons. UV/visible active chromophores are attributed either to pyrrole type structures, to conjugated acylamides or to conjugated azomethines. Some secondary reactions occurring during the thermal or thermo‐oxidative decomposition lead to crosslinking of nylons. Nylon 6.6 crosslinks relatively easily, especially in the presence of air, whereas nylon 11 and nylon 12 crosslink very little. Strong mineral acids, strong bases, and some oxides or salts of transition metals catalyse the thermal decomposition of nylons, but minimize crosslinking. In contrast, many fire retardant additives promote secondary reactions, crosslinking and charring of aliphatic nylons. © 1999 Society of Chemical Industry

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Section: Nylons 7 11 and 12mentioning

confidence: 99%

Thermal decomposition of aliphatic nylons

Levchik¹,

Weil²,

Lewin³

1999

Polym. Int.

358

250

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“…17 This was demonstrated by the enantiomer separation of 1-chloroaziridines, [11][12][13]18 1-alkoxyoxazolidines 19 and by the enantiomeric or diastereomeric enrichment of dialkoxyamines, containing the asymmetric nitrogen solely in the open chain. Despite these efforts, the nature of the interconversion process in aziridines and diaziridines via nitrogen inversion [20][21][22][23] as in ammonia, or electrocyclic ring opening ring closure as in oxiranes [24][25][26] is still unknown (cf. Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

The stereodynamics of 1,2‐dipropyldiaziridines

et al. 2009

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N-alkylated trans-diaziridines are an intriguing class of compounds with two stereogenic nitrogen atoms which easily interconvert. In the course of our investigations of the nature of the interconversion process via nitrogen inversion or electrocyclic ring opening ring closure, we synthesized and characterized the three constitutionally isomeric diaziridines 1,2-di-n-propyldiaziridine 1, 1-isopropyl-2-n-propyldiaziridine 2, and 1,2-diisopropyldiaziridine 3 to study the influence of the substituents on the interconversion barriers. Enantiomer separation was achieved by enantioselective gas chromatography on the chiral stationary phase Chirasil-beta-Dex with high separation factors alpha (1-isopropyl-2-n-propyldiaziridine: 1.18; 1, 2-diisopropyldiaziridine: 1.24; 100 degrees C 50 kPa He) for the isopropyl substituted diaziridines. These compounds showed pronounced plateau formation between 100 and 150 degrees C, and peak coalescence at elevated temperatures. The enantiomerization barriers DeltaG(double dagger) and activation parameters DeltaH(double dagger) and DeltaS(double dagger) were determined by enantioselective dynamic gas chromatography (DGC) and direct evaluation of the elution profiles using the unified equation implemented in the software DCXplorer. Interestingly, 1-isopropyl-2-n-propyldiaziridine and 1,2-diisopropyldiaziridine exhibit similar high interconversion barriers DeltaG(double dagger) (100 degrees C) of 128.3 +/- 0.4 kJ mol(-1) and 129.8 +/- 0.4 kJ mol(-1), respectively, which indicates that two sterically demanding substituents do not substantially increase the barrier as expected for a distinct nitrogen inversion process.

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“…Intramolekulare Cycloadditionen. -Die C/C-Ringoffnung von substituierten Aziridinen erfolgt im Gegensatz zu der von Oxiranen [6c] [12] schon bei relativ niedrigen Temperaturen [7] [ 131. Im Einklang mit Ergebnissen ahnlich aktivierter Derivate bei bimolekularen Cycloadditionen [ 13a-c] Wie die Produktverteilung (Tab.…”

Section: Intramolecular Cycloaddition Reactions With Azomethine Ylideunclassified

“…IR (KBr): 2930(KBr): ,2860(KBr): , 1730(KBr): , 1610(KBr): , 1270(KBr): , 1200(KBr): , 1170(KBr): , 1100. -1,2a, 3~.3aa,4, 6.7.8,9,IO.II,12.13,14,15,17,18]- [ 1,12]dioxacyclononadeca [ 15,14-b]pyrrolidin-2~,3a-dicarbonsaure-dimethylester (16d) und das 1,2a,3a,3ajl,4, 6,7, 8,9,10,ll,12,13,14,15,20ba-Hexadecahydro-Isomere 17d. Aus 850 mg 4d wurden 530 mg (61 %) 16d/17d (ca.…”

Section: I520ba-hexade~ahydro-l7h-benzo[lbl718]-[i 12]-dioxacycunclassified

Intramolekulare Cycloadditionen Mit Azomethin‐Yliden: Synthese und NMR‐Untersuchungen einiger Paracyclophan‐Derivate vom Makrolid‐Typ

Eberbach¹,

Heinze²,

Knoll³

et al. 1988

Helvetica Chimica Acta

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2 n = 11) sondern auch die gespannten Derivate rnit n = 2 und 3 zuganglich sind (als Barrieren der Konforrnationsanderungen der Brucke wurden fur die letzteren Verbindungen AG +-Werte von ca. 12 b m . 20 kcal/mol ermittelt).Zur Bildung von Verbindungen des Paracyclophan-Typs sind die geometrischen Voraussetzungen einer intramolekularen Cycloaddition sehr vie1 ungiinstiger. Unsere Untersuchungen galten deshalb zunachst praparativen Aspekten und insbesondere der Frage, ob so auch Derivate rnit kleinen 'Henkeln' zuganglich sind. Solche Reaktionen sind interessant fur Synthesen von Modellverbindungen fur Peptid-Alkaloide [8], die zehn-und mehrgliedrig verbruckte Meta-bzw. Paracyclophan-Einheiten enthalten [8] [9].Wir haben deshalb einige Arylaziridine der Struktur 3 und 4 mit para-Substituenten unterschiedlicher Kettenlange als Vorstufen der Azomethin-ylid-Zwischenstufen synthetisiert und die Ringschluss-Reaktionen dieser Dipole studiert.Die fur die Konstitutions-und Konfigurationszuordnung der Cycloaddukte notwendigen, aus detaillierten 'Hund I3C-NMR-Experimenten gewonnenen Daten werden auch im Hinblick auf das dynamische Verhalten der Bruckeneinheiten in den Cyclophan-Derivaten ausfuhrlich diskutiert. 0 3 (cis-Aziridin) 4 (trans-Aziridin) E = CO,CH,, R = CH,PhSynthese der Aziridine 314. -Fur den Aufbau der Aziridin-Ringe hat sich die Methode von Cromwell und Mitarbeitern bewahrt [ lo], bei der das Zimtsaureester-Derivat 8 in das Dibromid 9 ubergefuhrt und dieses anschliessend rnit Benzylamin/MeOH zu einem (3 : 1)-Gemisch der cisltrans-Aziridine 10/11 umgewandelt wird (vgl. Schema I). Als Ausgangssubstanz diente in allen Fallen das aus p -Formylbenzoesaure uber 5 leicht zugangliche Acyl-chlorid 6, welches ohne weitere Reinigung mit den entsprechenden mono-THP-geschutzten Diolen (THP = 3,4,5,6-Tetrahydro-2H-pyran-2-yl) verestert wurde. Abschliessende Umsetzung von l O / l l rnit (E)-3-(Chloroformyl)-2-propensauremethylester fuhrte zu den gewunschten, saulenchromatographisch auftrennbaren En-Aziridinen 3 und 4.

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Elektrocyclische Ringöffnungen von Ethylenoxiden

Cited by 56 publications

References 56 publications

Thermal decomposition of aliphatic nylons

Thermal decomposition of aliphatic nylons

The stereodynamics of 1,2‐dipropyldiaziridines

Intramolekulare Cycloadditionen Mit Azomethin‐Yliden: Synthese und NMR‐Untersuchungen einiger Paracyclophan‐Derivate vom Makrolid‐Typ

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