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: A 69 - year - old man operated for acute cholecystitis under methoxyflurane anesthesia developed postoperatively a hepatic insufficiency syndrome and renal tubular acidosis .
### Output Text:
A 69 - year - old man operated for acute cholecystitis under <span class="chemical">methoxyflurane</span> anesthesia developed postoperatively a hepatic insufficiency syndrome and renal tubular acidosis . 