Despite the rapid advancements of databases, data quality remains a significant issue in particular for machine learning applications in chemistry . A particularly serious problem is that omission of co-reactants or co-products. For example, less than 12% of the single step reactions in Reaxys analyzed to study the exploration history of chemical space were balanced. This problem has multiple roots, including historical and procedural practices. These deficiencies are attributed to the limitations of text mining, which struggles with the variability of publication formats , and to errors introduced during manual data curation .