Cyclotrimerization Of Isocyanates Research Articles

ChemInform Abstract: Cyclodimerization and Cyclotrimerization of Isocyanates Promoted by One Praseodymium Benzenethiolate Complex [Pr(SPh)3(THF)3

AbstractTitle praseodymium complex efficiently catalyzes the cyclotrimerization of aryl isocyanates (I) to give sym‐triazines (II) in excellent yields.

Cyclodimerization and cyclotrimerization of isocyanates promoted by one praseodymium benzenethiolate complex [Pr(SPh) 3(THF) 3

The cyclotrimerization of aryl isocyanates and the cyclodimerization of alkyl isocyanates initiated by one praseodymium benzenethiolate complex [Pr(SPh) 3(THF) 3] were investigated. Comparative runs with [Pr(SPh) 3(THF) 3] and its precursor Pr[(Me 3Si) 2N] 3 showed that the former has the advantages of a higher selectivity toward isocyanates, easy preparation, low catalyst loading, high conversion as well as mild reaction conditions.

Organocatalytic, rapid and facile cyclotrimerization of isocyanates using tetrabutylammonium phthalimide-N-oxyl and tetraethylammonium 2-(carbamoyl)benzoate under solvent-free conditions

Tetrabutylammonium phthalimide-N-oxyl and tetraethylammonium 2-(carbamoyl)benzoate were found to be effective and easily accessible organocatalysts for selective cylotrimerization of aryl and alkyl isocyanates under mild reaction conditions. The reaction proceeds smoothly using very low catalyst loadings of these metal-free organocatalysts (0.025 and 0.25 mol%, respectively) under solvent-free conditions at room temperature within a very short reaction time.

Polyisocyanurates as Catalyst Support Systems

N-heterocyclic carbenes (NHCs) are known to catalyze the cyclotrimerization of isocyanates (1 → 2). The authors used this reaction to develop the synthesis of a microporous covalent network (4) from a diisocyanate (3). By absorbing FeCl2 onto 4 a heterogeneous oxidation catalyst was formed, which could be recycled numerous times without loss of activity, and was generally a superior oxidant of benzyl alcohol than FeCl2 by itself. The absorption of benzyl alcohol by the porous framework, thereby increasing the exposure of the reagent to the catalyst, was offered as an explanation for the increased catalyst activity.

N‐Heterocyclic Carbenes as Highly Efficient Catalysts for the Cyclotrimerization of Isocyanates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

N-Heterocyclic Carbenes as Highly Efficient Catalysts for the Cyclotrimerization of Isocyanates

[reaction: see text] A series of N-heterocyclic carbenes (NHCs) were evaluated as potential catalysts for the cyclotrimerization of isocyanates to afford isocyanurates. 1,3-Bis-(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) was found to be a highly efficient catalyst for the cyclotrimerization of a variety of isocyanates.

ChemInform Abstract: Solvent‐Free Cyclotrimerization of Isocyanates Catalyzed by Sodium or Potassium Piperidinedithiocarbamate or Nitrite under Conventional or Microwave Heating: Preparation of Aryl or Alkyl Isocyanurates.

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Solvent-free Cyclotrimerization of Isocyanates Catalysed by Sodium or Potassium Piperidinedithiocarbamate or Nitrite under Conventional or Microwave Heating: Preparation of Aryl or Alkyl Isocyanurates

A solvent-free method for the efficient preparation of symmetrically trisubstituted aryl or alkyl isocyanurates from isocyanates catalysed by sodium or potassium piperidinedithiocarbamate or the readily available sodium or potassium nitrite under conventional or microwave heating is described.

Synthesis and thermotropic properties of new discotic 1,3,5-trisubstituteds-triazinetriones obtained by cyclotrimerization of isocyanates

Abstract The synthesis of a number of s-triazine-2,4,6-triones (isocyanurates) by cyclotrimerization of 4-monoalkoxy-, 3,4-dialkoxy-, or 3,4,5-trialkoxyphenyl-, benzyl-, or styryl-isocyanates is reported. The thermal and phase behaviour of the novel compounds were investigated by optical polarized light microscopy and thermal analysis. No mesophase could be observed for any of the precursors except 4-decyloxybenzoic acid. Mesophases of the isocyanurates were observed only in the series containing 3,4-dialkoxyphenyl moieties. A vinylene group between the inner s-triazine ring and the outer phenylene rings gives low melting points and enantiotropic mesophases for C8 and longer alkyl chains. The phenylisocyanurates may exhibit a monotropic mesophase and normally have the highest melting points of the three types, whereas a methylene spacer suppresses formation of a mesophase. According to the textures observed, the mesophases are hexagonal columnar. This will have to be confirmed by X-ray scattering techniques.

Nature of the active center in the cyclotrimerization of isocyanates catalyzed by the tertiary amine??-oxide?protondonor system

The structure of the dimethylbenzylamine (DMBA)—phenylglyc idyl ether (PGE)—phenol complex was studied by IR and1H NMR spectroscopy under various conditions of its formation. The active catalyst in the cyclotrimerization of isocyanates is a complex of composition DMBA : PGE : PhOH = 1 : 1 : 2, in which the oxygen atom of the zwitter-ion PhCH2N+Me2CH2CH(O−)CH2OPh that forms after opening, of the epoxide cycle is bound to two phenol molecules by a very strong hydrogen bonds. In this complex, the oxygen atom of both the zwitter-ion and the phenolate anion can be catalytic centers. Two schemes of the cyclotrimerization of isocyanate in the presence of the aforementioned catalytic system are suggested, depending on whether the catalytic complex has time to form or not.

The nature of active centers in cyclotrimerization of isocyanates catalyzed by the tertiary amine??-oxide?proton donor system 1. The role of the proton donor

The rate of cyclotrimerization of phenyl isocyanate in chlorobenzene at 120 °C in the presence of the tertiary amine-α-oxide-proton donor (PD) ternary catalytic system has been studied using a dual calorimeter and a series of phenols with various acidities as the PD. In the presence of weakly acidic phenols, complexes of quaternary ammonium type bases are formed in the ternary catalytic systems. Acidic phenols afford salt complexes with the transfer or a proton from phenol to the tertiary amine in a quantitative yield, while the α-oxide present remains unaffected. The structures of the complexes were studied by IR and by IR and1H NMR spectroscopy.

Cyclotrimerization of isocyanate groups. I. Catalyzed reactions of phenyl isocyanate

AbstractCyclotrimerization of phenyl isocyanate in the presence of various catalysts was studied. All reactions were carried out in 1,4‐dioxane at 30–50°C. Reaction products were determined by reverse‐phase liquid chromatography. 1,3,5‐Triphenyl isocyanurate was formed and also traces of 1,3‐diphenylurea and 1,3,5‐triphenylbiuret were found. The catalytic activity decreased in the following series: quaternary ammonium salt > organic acid salt ≫ tertiary amine. Apparent rate constants of cyclotrimerization were calculated and the overall reaction order is discussed. © 1994 John Wiley & Sons, Inc.

The preparation and X-ray structural study of complexes that catalyze isocyanate cyclotrimerization

A 1∶1-complex of trinitrophenol with benzyldimethylamine (1) and a 1∶1∶1-complex, the product of the interaction of benzyldimethylamine, glycidyl phenyl ether, and phenol (2), have been synthesized and characterized by means of X-ray analysis. Complex1 is a precursor for the catalysts of selective isocyanate cyclotrimerization, while complex2 is one of those catalysts. In the crystal structure complex1 forms H-bonded cationic-anionic aggregates with proton transfer from phenol to the N-atom of the tertiary amine. Complex2 crystallizes as a monohydrate (2a) with a strong H-bond between the quaternary ammonium and phenolic components, and exists in crystals in the form of globular H-bonded dimeric hydrates. Possible pathways of dissociation of complex2a are discussed. The data obtained may be used as a basis for further interpretation of the regularities of cyclotrimerization of isocyanates catalyzed by complexes of this type.

Cyclotrimerization of butyl and cyclohexyl isocyanate—catalysis and kinetics

AbstractThe cyclotrimerization of model aliphatic and cycloaliphatic isocyanates (butyl and cyclohexyl isocyanate) was carried out using an ammonium carboxylate and a salicylaldehyde‐potassium complex as catalysts. The kinetics of the cyclotrimerization of butyl isocyanate in both 2‐ethoxyethyl acetate and dimethylformamide (DMF) using the 2‐ethylhexanoate salt of trimethylaminopropanol‐2 was found to be of first order with respect to the isocyanate and also of first order with respect to the catalyst. The reaction rate in DMF was considerably greater than in 2‐ethoxyethyl acetate, as could be expected. Employing the salicylaldehyde‐potassium catalyst, the cyclotrimerization of butyl isocyanate followed second‐order kinetics with respect to the isocyanate and first order with regard to the catalyst. Due to the fact that the cyclotrimerization of cyclohexyl isocyanate was found to be slower than that of butyl isocyanate, the cyclotrimerization of this isocyanate was carried out only in DMF using the 2‐ethylhexanoate salt of trimethylaminopropanol‐2 as the catalyst. The kinetics of this reaction was found to follow second order with respect to the isocyanate and first order with regard to the catalyst. The products of the reactions were identified by IR, 1H‐NMR, and mass spectrometry.

Analysis of the possibility of anionic homoaddition of isocyanates to zwitterionic active centers

An investigation of the complexation of an R3+NCH2CH2O− zwitterion with HNCO and the subsequent interaction of the complex formed with a second molecule of HNCO has been carried out by the CNDO/2 method. It has been shown on the basis of an analysis of the structure of the frontier MO's of the reactants and their electronic structure that the successive homoaddition of isocyanates is unlikely. This raises some question as to the possibility of the anionic mechanism of the cyclotrimerization of isocyanates in the presence of zwitterions.

Activation of molecules of proton donors in the catalytic system amine-epoxide-proton donor

We present the results of a quantum-chemical study by the CNDO/2 method of the system trimethylamine-ethylene oxide-proton donor (water, alcohol, carbamide, carbamate, biuret, allophanate) and we consider the nature of the activation of the proton donor on complex formation. The results of the calculations are analyzed from the point of view of the catalytic activity of the system in the cyclotrimerization of isocyanates.

Special features of the catalysis of cyclotrimerization of isocyanates in the presence of o-aminophenols and reasons for the “autoinhibition” of this reaction

It is established that the reason for the catalytic activity of o-aminophenols in the cyclotrimerization of isocyanates is the presence in the catalyst molecule of intramolecular hydrogen bonds O - H…N. The activation of the phenyl hydroxyl group due to this results in consumption of the catalyst in the formation of the corresponding urethane, which is reflected in the kinetics in the form of “autoinhibition” of cyclotrimerzation.

The role of proton-donors in cyclotrimerization of isocyanates by the action of an amine-epoxide catalytic system

A kinetic study was made of cyclotrimerization of phenylisocyanate by the action of a 2-methyl-diazabicyclooctane-phenylglycidyl ether catalytic system in the presence of proton-donors and of variations taking place in the catalytic system itself over a period of time. Water, methanol, phenol, diphenylurea, methyl-N-phenyl-urethane and methyl-α, γ-diphenylallophanate were used as porton-donors. It was shown that during the interaction of all three components of the catalytic system products of quaternary ammonium bases are formed with high basicity and much higher catalytic activity in the process examined than the amine-epoxide binary system. Diphenylurea has the highest activity as proton-donor. A proportionality was established between the rate of cyclotrimetrization and the concentration of active adduct formed in the ternary system.

Cyclotrimerization of isocyanates catalyzed by aminimides

Die Makromolekulare ChemieVolume 180, Issue 4 p. 1081-1084 Short Communication Cyclotrimerization of isocyanates catalyzed by aminimides Jiři E. Kresta, Jiři E. Kresta Polymer Institute, University of Detroit, Detroit, Michigan, 48221, U.S.A.Search for more papers by this authorRong J. Chang, Rong J. Chang Polymer Institute, University of Detroit, Detroit, Michigan, 48221, U.S.A.Search for more papers by this authorShiraz Kathiriya, Shiraz Kathiriya Polymer Institute, University of Detroit, Detroit, Michigan, 48221, U.S.A.Search for more papers by this authorKurt C. Frisch, Kurt C. Frisch Polymer Institute, University of Detroit, Detroit, Michigan, 48221, U.S.A.Search for more papers by this author Jiři E. Kresta, Jiři E. Kresta Polymer Institute, University of Detroit, Detroit, Michigan, 48221, U.S.A.Search for more papers by this authorRong J. Chang, Rong J. Chang Polymer Institute, University of Detroit, Detroit, Michigan, 48221, U.S.A.Search for more papers by this authorShiraz Kathiriya, Shiraz Kathiriya Polymer Institute, University of Detroit, Detroit, Michigan, 48221, U.S.A.Search for more papers by this authorKurt C. Frisch, Kurt C. Frisch Polymer Institute, University of Detroit, Detroit, Michigan, 48221, U.S.A.Search for more papers by this author First published: 5 April 1979 https://doi.org/10.1002/macp.1979.021800429Citations: 8AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume180, Issue45 April 1979Pages 1081-1084 RelatedInformation

Oligomerization of isocyanates by cyclic sulfonium zwitterions

The cyclic sulfonium zwitterions (I) are very effective catalysts for the cyclotrimerization of isocyanates. Under certain conditions (high concentration of isocyanate in the reaction system or high reaction temperature) cyclic sulfonium zwitterions act as anionic initiators. This behavior is due to the reaction of the isocyanate with stabilizing molecules of water of cyclic sulfonium zwitterions followed by rapid polymerization of the initiator. This phenomenon can be easily utilized in the one-step preparation of stable NCO-terminated oligomers of difunctional isocyanates.