In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Fifty - eight percent of group 1 patients , 33 % of group 2 , and 26 % of group 3 had reactions to TDI .
### Output Text:
Fifty - eight percent of group 1 patients , 33 % of group 2 , and 26 % of group 3 had reactions to TDI . 