Table 4.

A comparison of the methods used in the articles and the method used in this work.

Entry	Catalyst	Conditions	Reaction time (min)	Yields%	Ref.
1	PEG	H2O/reflux	∼ 180	∼ 90	[39]
2	activated zinc metal and solid NH4C	Solvent free /MW	∼ 50	∼ 90	[40]
3	1-butyl-3-methylimidazoliumtetrafluoroborate (BMIF)	solvent free/∼200 ˚C	∼ 60	∼ 90	[41]
4	Fe nanoparticles loaded in zeolite X (Fe-X)	Solvent-free, 90°C	∼ 40	∼ 90	[42]
5	SO3H@Fe3O4 magnetic nanocatalyst	Solvent-free, 80 ˚C	∼ 20	∼ 90	[43]
6	Zr(HSO4)4	Solvent-free, 110°C	35-60	72-95	This work