A cautionary note on “exothermic events” upon contact of carbodiimide coupling agents and the cellulose solvent N-methylmorpholine-N-oxide

Abstract

The cellulose solvent N-methylmorpholine-N-oxide monohydrate (NMMO) reacts violently with carbodiimide coupling agents, such as the widely used DCC (dicyclohexylcarbodiimide) and EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide), which can cause explosions, heavy smoke generation and complete charring of the reaction mixtures. For this reason it is clear that cellulose or other carbohydrates dissolved in NMMO (“Lyocell conditions”) cannot be safely esterified or amidified under DCC/EDC conditions. It is important to note that cellulosic material regenerated from NMMO solutions also poses a risk if it contains residual NMMO, which can then come into contact with DCC-type coupling agents in non-aqueous media, as recent accidents have unfortunately shown. Similarly, EDC/DCC traces in cellulose can have detrimental effects when trying to dissolve the material in NMMO. Working in aqueous systems generally reduces the risk of uncontrolled reactions, while alcohols or aprotic solvents are not very effective in this regard. Washing for NMMO removal or EDC/DCC removal should therefore always be carried out by aqueous media, if any possible, if there is a potential risk that the reagents might come into contact later. This warning describes the potential hazards of the reagent combination, highlights the underlying degradation mechanism and explains the precautions to be taken to avoid any “exothermic events”. Graphic abstract

Superbase-based protic ionic liquids for cellulose filament spinning

“…The continuous expansion of the global lyocell capacity reflects the increasing demand for sustainably produced bio-based fibers. This and certain stability issues associated with NMMO (Buijtenhuijs et al 1986;Rosenau et al 2001;Jusner et al 2020), have motivated research on other cellulose solvents that allow for direct dissolution and subsequent fiber spinning. Meanwhile, a wide spectrum of cellulose solvent systems is known, including electrolyte solutions [DMAc/LiCl (Hansen and Björkman 1998), DMSO/TBAF (Heinze et al 2000;Köhler and Heinze 2007), ammonia or amine/thiocyanate (Hattori et al 2002(Hattori et al , 2004, [BMIM]Cl/DMI (Rinaldi 2011)], phosphoric acids (Bredereck and Hermanutz 2005;Liebert 2010), metal complex-based solvents (Horvath 2006;Liebert 2010), and aqueous sodium hydroxide (with and without additives) (Budtova and Navard 2016;Kamida et al 1984;Kamide et al 1992;Yamashiki et al 1992).…”

Medicinal Chemistry of Drugs with N-Oxide Functionalities

“…Residual NMO can therefore induce an autocatalytic decomposition if carbodiimides are used for acylation of cellulose. 40 Nonclassical Polonovski reactions are initiated by metal cations and have been used for the dealkylation of tertiary amines to secondary amines. 41 Aromatic N-oxides are typically more stable and cannot undergo the aforementioned rearrangements or eliminations.…”

“…This reaction has led to a number of industrial accidents where NMO is used as a solvent in the Lyocell process in cellulose manufacture. Residual NMO can therefore induce an autocatalytic decomposition if carbodiimides are used for acylation of cellulose . Nonclassical Polonovski reactions are initiated by metal cations and have been used for the dealkylation of tertiary amines to secondary amines …”

A Review on the Modification of Cellulose and Its Applications

“…Drozd et al developed a platform for the immobilization of enzymes [ 224 ]. They conjugated cyclodextrin glycosyltransferase (CGTase) and alcohol oxidase as an active matrix [ 225 ].…”