An Ab Initio Investigation of the 4,4′-Methlylene Diphenyl Diamine (4,4′-MDA) Formation from the Reaction of Aniline with Formaldehyde
| Autor: | Béla Viskolcz, Milán Szőri, Károly Nehéz, R. Zsanett Boros, László Farkas |
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| Jazyk: | angličtina |
| Rok vydání: | 2019 |
| Předmět: |
Reaction mechanism
Polymers and Plastics MDA water Formaldehyde Article PABA lcsh:QD241-441 chemistry.chemical_compound Aniline lcsh:Organic chemistry standard enthalpy of formation Computational chemistry Diamine Elementary reaction pKa aniline Methylene bis(4-aminophenyl)methane ab initio General Chemistry transition state Standard enthalpy of formation chemistry Aminal reaction mechanism G3MP2B3 |
| Zdroj: | Polymers Polymers, Vol 11, Iss 3, p 398 (2019) Volume 11 Issue 3 |
| ISSN: | 2073-4360 |
| Popis: | The most commonly applied industrial synthesis of 4,4&prime methylene diphenyl diamine (4,4&prime MDA), an important polyurethane intermediate, is the reaction of aniline and formaldehyde. Molecular understanding of the 4,4&prime MDA formation can provide strategy to prevent from side reactions. In this work, a molecular mechanism consisted of eight consecutive, elementary reaction steps from anilines and formaldehyde to the formation of 4,4&prime MDA in acidic media is proposed using accurate G3MP2B3 composite quantum chemical method. Then G3MP2B3-SMD results in aqueous and aniline solutions were compared to the gas phase mechanism. Based on the gas phase calculations standard enthalpy of formation, entropy and heat capacity values were evaluated using G3MP2B3 results for intermediates The proposed mechanism was critically evaluated and important side reactions are considered: the competition of formation of protonated p-aminobenzylaniline (PABAH+), protonated aminal (AMH+) and o-aminobenzylaniline (OABAH+). Competing reactions of the 4,4&prime MDA formation is also thermodynamically analyzed such as the formation of 2,4-MDAH+, 3,4-MDAH+. AMH+ can be formed through loose transition state, but it becomes kinetic dead-end, while formation of significant amount of 2,4-MDA is plausible through low-lying transition state. The acid strength of the key intermediates such as N-methylenebenzeneanilium, PABAH+, 4-methylidenecyclohexa-2,5-diene-1-iminium, and AMH+ was estimated by relative pKa calculation. |
| Databáze: | OpenAIRE |
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