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: Patients tapped faster after propranolol than diazepam and they were more sedated after diazepam than propranolol .
### Output Text:
Patients tapped faster after <span class="chemical">propranolol</span> than <span class="chemical">diazepam</span> and they were more sedated after <span class="chemical">diazepam</span> than <span class="chemical">propranolol</span> . 