Kinetics and mechanism of isocyanate reactions. II. Reactions of Aryl Isocyanates with Alcohols in the presence ob tertiary amines

Bacaloglu, R.; Cotarca, Livius; Marcu, N.; Tölgyi, St

doi:10.1002/prac.19883300406

Cited by 13 publications

(13 citation statements)

References 11 publications

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“…For instance, 1 H NMR of an equimolar mixture of this alcohol model and 2b revealed proton chemical shifts for the alcohol hydrogen, which indicates that hydrogen bonded complex MTBD-2,3-dimethoxyphenethyl alcohol might be involved at some stage (Supporting Information). , However, activation through general base catalysis should also imply that the reaction rate increases with the basicity of the catalyst . As shown above, catalytic activities of organocatalysts follow the order: DABCO 6 < DMAP 5 (17.95) < TBD 2a (26.03) < TMGN 3 (25.4) < BEMP 11 (27,5) < TMG 7a (23.3) ∼ BnTMG 7b < MTBD 2b (25.43) ∼ DBU 4b (24.33), which does not fit with the corresponding p K a ’s (in CH 3 CN). , It is thus worthy of note that bis-guanidine 3 (TMGN) and phosphazene 11 led to poor activity despite their strong basicity (Figure ).…”

Section: Resultsmentioning

confidence: 91%

“… , However, activation through general base catalysis should also imply that the reaction rate increases with the basicity of the catalyst . As shown above, catalytic activities of organocatalysts follow the order: DABCO 6 < DMAP 5 (17.95) < TBD 2a (26.03) < TMGN 3 (25.4) < BEMP 11 (27,5) < TMG 7a (23.3) ∼ BnTMG 7b < MTBD 2b (25.43) ∼ DBU 4b (24.33), which does not fit with the corresponding p K a ’s (in CH 3 CN). , It is thus worthy of note that bis-guanidine 3 (TMGN) and phosphazene 11 led to poor activity despite their strong basicity (Figure ). The difference in catalytic activity between TMGN 3 and MTBD 2b, which exhibit similar p K a ’s (25.4 and 25.43 respectively) during polymerization of IPDI and PTMO-650 (Figure ), is also striking, suggesting that other mechanism(s) than general base catalysis may operate .…”

Section: Resultsmentioning

confidence: 91%

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Cyclic Guanidines as Efficient Organocatalysts for the Synthesis of Polyurethanes

et al. 2012

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International audienceA systematic survey of basic/nucleophilic organocatalysts for the polyaddition in bulk of polyols, PEG-600, and PTMO-650, to isophorone diisocyanate (IPDI) has been performed. Guanidines were shown to be very efficient catalysts for the urethane linkage formation. Bicyclic penta-alkylated guanidines such as MTBD led to polyurethane molecular weight and dispersity that are in the range of those observed with tin-based catalysts such as DBTDL. Tetra-alkylated guanidine such as TBD was shown to be a weaker catalyst as compared to pentaalkylated guanidines, as a result of its high reactivity toward isocyanate, resulting in the formation of a less nucleophilic urea. Although the mechanism has not yet been firmly established, these experiments suggest that a nucleophilic-catalysis mechanism, involving the attack of one of the nitrogen of the guanidine onto the unsaturated system of the isocyanate, should not be totally ruled out with such strong Bronsted base catalysts

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Section: Resultsmentioning

confidence: 91%

Section: Resultsmentioning

confidence: 91%

Cyclic Guanidines as Efficient Organocatalysts for the Synthesis of Polyurethanes

et al. 2012

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“…The authors also investigated acyclic guanidines as catalysts (Scheme b). Activation through a general basic catalysis should imply that the reaction rate should increase with the basicity of the catalyst . Thus, comparing acyclic guanidine, naphthyl bis guanidine, and cyclic guanidine, N -methyl-1,5,7-triazabicyclododecene, which exhibit similar p K a values (25.4 and 25.43, respectively, in CH 3 CN), , similar catalytic activities were expected.…”

Section: Organocatalyzed Step-growth Polyaddition Of Diols and Diisoc...mentioning

confidence: 81%

“…Activation through a general basic catalysis should imply that the reaction rate should increase with the basicity of the catalyst. 41 Thus, comparing acyclic guanidine, naphthyl bis guanidine, and cyclic guanidine, N-methyl-1,5,7-triazabicyclododecene, which exhibit similar pK a values (25.4 and 25.43, respectively, in CH 3 CN), 38,39 similar catalytic activities were expected. Nevertheless, cyclic guanidines were found more active than the acyclic analogous, suggesting that another mechanism might operate in the isocyanate−alcohol polymerization process.…”

Section: Introductionmentioning

confidence: 82%

Synthesis of Polyurethanes Using Organocatalysis: A Perspective

et al. 2015

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International audienceOrganocatalysis has become an invaluable tool for polymer synthesis, and its utility has been demonstrated in ring-opening, anionic, zwitterionic, and group-transfer polymerizations. Despite this, the use of organocatalysis in other polymerization reactions such as step-growth polymerizations remains underexplored, relative to more traditional metal-based polymerizations. Recently, the use of organic bases such as guanidines, amidines, N-heterocyclic carbenes, and organic "strong or super-strong" Bronsted acids to catalyze the synthesis of metal-free polyurethanes has shown to be competitive to commercially widely used dibutyltin dilaurate and dibutyltin diacetate catalysts. This Perspective article highlights recent advances in organocatalyst design for isocyanate-based polyurethane synthesis with the aim of comparing the activity and selectivity of each of the new catalytic reactions to each other and the traditional metal-based catalysts. The article also draws attention to new trends in isocyanate-free polyurethane synthesis and the key role that organocatalysis is playing in these innovative polymerization processes

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“…These data are consistent with the experimentally observed pattern of the effect of sybstituents in the aryl isocyanates in the reactions with alcohols. For instance, the value of the reaction constants ρ in the interaction of aryl isocyanates with 2-ethylhexanol at 28°С in benzene is equal to 1.976 [9], with 1-butanol in tetrachloromethane at 32°С, 1.852 [10], with ethanol in toluene at 30°С, 1.69 [11].…”

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confidence: 99%

Quantum-chemical investigation of isocyanate reactions with linear methanol associates: V. Aryl isocyanate reactions with linear methanol associates

et al. 2012

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The mechanism of addition of linear methanol associates (monomer, dimer, trimer) to aryl isocyanates at their C=N and С=О bonds was investigated applying the quantum-chemical method B3LYP/6-311++G(df,p). Notwithstanding the electronic character of substituents in the aromatic ring of the isocyanates all reactions proceed through concerted asymmetric late transition states. The addition to the C=N bond is considerably more preferable than to the С=О bond. In the transformations under consideration the intermolecular donor-acceptor interactions between the reagents result in the appearance of abnormal selectivity.Formerly we carried out a quantum-chemical investigation of the reaction mechanism between phenyl isocyanate with methanol linear associates (monomer, dimer, trimer) [2, 3]. It was established that the reactions proceeded through concerted cyclic asymmetric late transition states. With the growing degree of the alcohol association the activation barriers on the conversion route decrease due to the growing electron-donor property of the alcohol, and increases the thermodynamic feasibility of their reaction with isocyanates [1,4].In order to reveal whether the mechanism of the alcohol reaction with isocyanates might change with the change of the electronic character of substituents in the isocyanates we supplementary to the previously obtained data [2-4] investigated reactions of p-nitro-and ----------------*For Communication IV, see [1].p-methoxyphenyl isocyanate with the methanol linear associates.The electronic character of the substituents in the aryl isocyanates in question is essentially different. It was therefore expectable that if the substituents in the aromatic ring of isocyanates might cause a change in the reaction mechanism, it would be observed in the reactions under study.Quantum-chemical calculations were performed by the method B3LYP/6-311++G(df,p) employing the package of the applied programs GAUSSIAN 03 [5,6]. The preliminary geometry optimization was carried out by the density functional method with the help of PRIRODA 6 program [7] using the basic L11 (analog of cc-pCVDZ [8]). The search for the transition state was fulfi lled with respect to the fi rst negative oscillation frequency in the Hesse matrix. The verity of the transition state was determined by the procedure of the decent from the transition state point in two directions using the IRC procedure with the subsequent geometry optimization of the obtained prereaction and postreaction complexes. The principles of the estimation of conformer structures corresponding to the minimal energy are described in [2].

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Kinetics and mechanism of isocyanate reactions. II. Reactions of Aryl Isocyanates with Alcohols in the presence ob tertiary amines

Cited by 13 publications

References 11 publications

Cyclic Guanidines as Efficient Organocatalysts for the Synthesis of Polyurethanes

Cyclic Guanidines as Efficient Organocatalysts for the Synthesis of Polyurethanes

Synthesis of Polyurethanes Using Organocatalysis: A Perspective

Quantum-chemical investigation of isocyanate reactions with linear methanol associates: V. Aryl isocyanate reactions with linear methanol associates

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