Table 2.

Newly developed laboratory synthesis methods of lactide.

Catalyst	Set up/Equipment	T (°C)	P (kPa)	Duration (h)	Yield (%)	Ref.
Acidified chloride catalyst supported on silica gel	Silica gel catalyst system with nitrogen gas flow	170–260	0.08–10	4–12	60	[18]
Stannous octoate (3 wt %)	Short path distillation	170–250	0.5	-	95–97	[19]
Zinc oxide (1 wt %)	Heating gas stream	230–240	1.33–26.6	-	72	[20]
Stannous octoate-toluene (0.04 wt %)	Oil bath with nitrogen gas flow	220–240	11.3	6–8	80	[21]
Zinc oxide-stannous octoate	Constant temperature heating device	180–206	95	7	86.4	[22]
Stannous oxide (0.1 wt %)	Oil bath	220	2.67	>8	77	[23]
Zinc powder (1.2 wt %)	Modified domestic microwave oven	170–180	3.99	3–5	40.3	[24]
Stannous octoate (1 wt %)	Oil bath and ice bath	180–210	1.33	16	41.3	[25]