Empirical Formula (Hill Notation): C6H5N3O · xH2O Molecular Weight: 135.12 (anhydrous basis) CAS Number: 123333-53-9 Hydroxybenzotriazole (abbreviated HOBt) is an organic compound that is a derivative of benzotriazole. It is a white crystalline powder, which as a commercial product contains some water (~11.7% wt as the HOBt monohydrate crystal). Anhydrous HOBt is explosive. It is mainly used to suppress the racemization of single-enantiomer chiral molecules and to improve the efficiency of peptide synthesis.