Cellulose acetate (CA) is one on the most important cellulose derivatives. The use of ionic liquids in cellulose processing was recently discovered to not exclusively act as a solvent but also as a reagent. Recent studies showed that bulky chlorides as well as acetyl chloride mixed with ionic liquids can facilitate cellulose acetylation. This work focused on a simple chloro-organic cosolvent, dichloromethane (DCM), and showed the ability of this relatively small molecule, mixed with the ionic liquid, to facilitate homogenous acetylation by displacement of the acetate ion of the ionic liquid with a chloride ion. Maximal acetylation achieved by this method was a degree of substitution (DS) of 1.9, were only a small fraction of DCM was utilized for acetylation, well below even that expected for equimolar reaction. The degree of substitution was controlled by the dichloromethane content, thus controlling its solubility in water. (c) 2018 Wiley Periodicals, Inc.