A method of removing a carboxylic acid from a liquid including a tertiary amide solvent includes: forming an extraction medium including an acid-extracting tin species and an extraction solvent that is immiscible with the tertiary amide solvent; subsequently contacting the liquid with the extraction medium, forming a phase including a de-acidified tertiary amide solvent and a phase including the extraction solvent; and removing the phase including the extraction solvent, to afford a liquid including the de-acidified tertiary amide solvent. The acid-extracting tin species is one or more tin species obtained by reaction of a di(hydrocarbyl) tin oxide with less than one equivalent of a carboxylic acid, or tin species obtainable by reaction of a 1,3-diacyloxy-1,1,3,3-tetra-(hydrocarbyl)distannoxane with an aqueous base. A method of preparing a sucralose-6-acylate includes uses the foregoing method to remove a carboxylic acid from a liquid including a tertiary amide solvent and the sucralose-6-acylate.