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: Skin rash is a well - known complication of diphenylhydantoin treatment as is benign and malignant lymphadenopathy .
### Output Text:
Skin rash is a well - known complication of <span class="chemical">diphenylhydantoin</span> treatment as is benign and malignant lymphadenopathy . 