2-Butoxyethanol-d4 is the isotope labelled analog of 2-Butoxyethanol; a reagent in the synthesis of 4-butoxyethoxy-N-octadecyl-1,8-naphthalimide as a new fluorescent probe for the determination of proteins. Also used as a reagent in the synthesis of 4-hydroxybenzaldehyde derivatives as tyrosinase inhibitors.