Table 2.

The reaction yield (%) of the products that formed from glycine at temperatures of 50°, 90°, and 120 °C for 35 days in the presence of metal ferrites.

Catalyst	% Yield of the Products Formed When Glycine Was Heated at 50, 90, and 120 °C for 35 Days
	DKP (Diketopiperazine) (Gly)			(Gly)2			(Gly)3
	50 °C	90 °C	120 °C	50 °C	90 °C	120 °C	50 °C	90 °C	120 °C
No catalyst	0.05	0.12	0.43	n.d	0.40	0.20	n.d	n.d	n.d
NiFe2O4	4.50	17.15	22.01	14.71	25.70	20.10	trace	14.2	3.10
CoFe2O4	3.30	16.13	20.84	10.91	22.98	16.01	* n.d	6.30	1.40
CuFe2O4	1.78	13.89	17.23	7.11	19.72	12.71	n.d	2.47	0.71
ZnFe2O4	1.41	12.01	15.67	4.07	18.70	11.11	n.d	1.23	0.15
MnFe2O4	0.31	9.80	12.45	0.41	15.01	8.90	n.d	n.d	n.d

* n.d = not detected.