Reductive Methylation of Homogeneous Primary β-Lauryl/myristyl 7/3 Polyethyleneoxy n = 3-18 Ethylamines under Phase-Transfer Catalysis Conditions.

Călin Jianu

doi:10.3390/molecules26154612

Abstract

Homogeneous tertiary N,N-dimethyl-N-β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylamines, LM(EO)nAT, are niche intermediates in the synthesis of homogeneous N-alkyl (C1–C18)-N,N-dimethyl-N-β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylammonium chlorides (unitary degree of oligomerization of ethylene oxide in the polyoxyethylene chain). This paper synthetically presents the dependence of the reductive methylation yields of homogeneous primary β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylamines, LM(EO)nAP, on the reaction time (10–90 min), the temperature (70 °C), the molar ratio formic aldehyde /LM(EO)nAP (1.1/1–2.5/1), the molar ratio HCOOH/LM(EO)nAP (5/1), the degree of oligomerization of ethylene oxide in the homogeneous polyoxyethylene chain in the 3,6,9,12,18 series, and the structure of the phase-transfer catalysts. The steric effects of hydrophobic groups CH3 and C18H37 grafted onto the ammonium function, and the micellar phenomena in the vicinity of their critical micellar concentration, directly proportional to the homogeneous degree of oligomerization, were highlighted. In all cases, a steady increase in reductive methylation yields was observed, with even quantitative values obtained. The high purity of the homologous series LM(EO)nAT will allow their personalization as reference structures for the study of the evolution of basic colloidal characteristics useful in forecasting technological applications. LM(EO)nAP were obtained either by direct amidoethylation (nucleophilic addition under basic catalysis of homogeneous lauryl/myristyl 7/3 polyethoxylated n = 3, 6, 9, 12, 18 alcohols, LM(EO)nOH, to acrylamide monomer) or by cyanoethylation of LM(EO)nOH under basic catalysis at 25–50 °C, in the presence of Fe2+ cations as oligomerization/polymerization inhibitor, followed by partial acid hydrolysis of homogeneous β-alkyl (C12H25/C14H29) 7/3 polyethyleneoxy n = 3, 6, 9, 12, 18 propionitriles, LM(EO)nPN, to β-alkyl (C12H25/C14H29) 7/3 polyethyleneoxy n = 3, 6, 9, 12, 18 propionamides, LM(EO)nPD, which led to LM(EO)nAP by Hoffmann degradation. Homogeneous higher tertiary polyetheramines LM(EO)nAT were structurally characterized.

Highlights

Reductive amination, known as “aminative reduction” or “reductive alkylation” for almost 150 years [1,2], is an oxidation-reduction process for grafting alkyl, alkylaryl, aryl, hetaryl, etc. radicals to the primary/secondary amino functional group
This paper synthetically presents the dependence of the reductive methylation yields of homogeneous primary β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylamines, LM(EO)nAP, on the reaction time (10–90 min), the temperature (70 ◦C), the molar ratio formic aldehyde /LM(EO)nAP (1.1/1–2.5/1), the molar ratio HCOOH/LM(EO)nAP (5/1), the degree of oligomerization of ethylene oxide in the homogeneous polyoxyethylene chain in the 3,6,9,12,18 series, and the structure of the phase-transfer catalysts
Known as “aminative reduction” or “reductive alkylation” for almost 150 years [1,2], is an oxidation-reduction process for grafting alkyl, alkylaryl, aryl, hetaryl, etc. radicals to the primary/secondary amino functional group. It is a process appreciated in organic synthesis for the formation of new C–N covalent bonds, based on the affinity of carbonyl compounds towards nucleophilic addition and the reducing action of formic acid [3], formates [4], silanes [5], and borohydrides [6] such as: NaBH3CN—sodium cyanoborohydride; NaBH(OAc)3—sodium triacetoxyborohydride etc.; or formamide

Summary

Introduction

Known as “aminative reduction” or “reductive alkylation” for almost 150 years [1,2], is an oxidation-reduction process (mostly heterogeneous with a pronounced ionic character) for grafting alkyl (including methyl), alkylaryl, aryl, hetaryl, etc. radicals to the primary/secondary amino functional group. If formic acid is used as a reducer, we can distinguish the Wallach reaction [1], and if we additivate the alkylation process with ammonium salts of formic acid, ammonium tetrafluoroborate (NH4BF4), ammonium perchlorate (NH4ClO4), ammonium hexafluorophosphate (NH4PF6), or formamide, we distinguish the Leuckart reaction [2]. Both processes in the original (classic) version have major disadvantages (average yields, mixtures of secondary and tertiary amines along with non-alkylated primary ones, formation of N-formyl derivatives above 180 ◦C), which limited the generalization of these processes. The reactivity of aldehydes and ketones is due to the advanced polarization of the electron cloud in the C=O double bonds by -Is; -Es effects [11,12]

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