Mesoporous titania–ceria mixed oxide (MTCMO): a highly efficient and reusable heterogeneous nanocatalyst for one-pot synthesis of β-phosphonomalonates via a cascade Knoevenagel–phospha-Michael addition reaction

Figures & data

Scheme 1. Synthesis of β-phosphonomalonates using MTCMO.

Figure 1. FT-IR spectra of MTCMO (a), CeO₂ (b) and TiO₂ (c).

Figure 2. XRD pattern of MTCMO (a), CeO₂ (b) and TiO₂ (c).

Figure 3. SEM micrograph of the calcined MTCMO.

Figure 4. TEM micrograph of the calcined MTCMO.

Figure 5. The EDX pattern of MTCMO.

Table 1. The EDX data of MTCMO.

Element	Weight%	Atomic%
O	56.40	76.59
Ti	28.48	12.97
Ce	15.12	10.44
Totals	100.00	100.00

Figure 6. N₂ adsorption–desorption isotherms of MTCMO at 77 K. The pore size distribution curve using BJH method is shown in the inset.

Table 2. Screening of different catalysts for a model reaction between benzaldehyde, malonitrile and triethylphosphite.^a

Entry	Catalyst	Conversion (%)	Yield (%)^b
1	–	20	15
2	TiO2 NPs	55	40
3	CeO2 NPs	66	55
4^c	TiO2 +CeO2	70	65
5	TCMO	40	35
6	MTCMO	80	75

^a Reaction conditions: Benzaldehyde (1 mmol), malononitrile (1 mmol), triethylphosphite (1 mmol), solvent-free, 50 °C, 2 h.

^b Isolated yield.

^c The reaction was carried out with 2 mol% of TiO₂ and 2 mol% of CeO₂.

Table 3. Optimisation of the reaction conditions.^a

Entry	MTCMO (mol%)	Solvent	Temperature (^οC)	Yield (%)^b
1	2	–	50	75
2	2	MeOH	50	80
3	2	Toluene	50	50
4	2	CH2Cl2	50	60
5	2	CH3CN	50	72
6	2	EtOH	50	85
7	3	EtOH	50	90
8	3	EtOH	60	95

^a Reaction conditions: Benzaldehyde (1 mmol), malononitrile (1 mmol), triethylphosphite (1 mmol) solvent (5 mL), 2 h.

^b Isolated yields.

Table 4. One-pot synthesis of β-phosphonomalonates catalysed by MTCMO.^a

Entry	R-	Time (h)	Yield (%)^b	Mp (Lit.)^Ref./°C
1		2	95	54 (53–54)^[^66^]
2		1	92	94–96 (93–95)^[^66^]
3		1.5	90	94 (95–96)^[^66^]
4		0.5	95	120 (119–120)^[^67^]
5		0.5	96	104 (104–105)^[^66^]
6		4	96	61–63 (60–62)^[^66^]
7		3.5	95	94–95 (93–95)^[^66^]
8		3	90	131 (129–131)^[^40^]
9		2.5	96	Oil (oil)^[^66^]
10		3	95	Oil (oil)^[^66^]

^a Reaction conditions: Aldehyde (1 mmol), malononitrile (1 mmol, 0.06 g), triethylphosphite (1.5 mmol) and MTCMO (3 mol%) at 60 ^οC in ethanol (5 mL).

^b Isolated yields.

Table 5. Comparison of catalytic activity of the MTCMO with some of the recently reported systems.

Entry	Reaction conditions	Catalyst loading (mol%)	Time	Yield (%)^Ref.
1	DMAP, H2O, MW/Reflux	20	12 min/8 h	95/90^[^68^]
2	HClO4-SiO2, Solvent-free	3	3 h	83^[^38^]
3	Silica-bonded 2-HEEA, r.t.	1	15 min	88^[^69^]
4	γ-Fe2O3@SiO2–La(OTf)2, Solvent-free, r.t.	1	3 h	83^[^70^]
5	This work	3	4.5 h	96

Table 6. Comparison of the BET surface area between MTCMO and some of similar oxides and mixed oxides.

Entry	Oxide/mixed oxide^Ref.	Surface area (m^2/g)
1	TiO2–Fe2O3^[^71^]	367
2	TiO2–ZrO2 (95:5 mol%)^[^72^]	109
3	CeO2–ZrO2 (50:50 mol%)^[^73^]	309
4	TiO2^[^74^]	58.9
5	ZrO2^[^74^]	31.3
6	Nano ceria^[^75^]	214
7	This work (TiO2–CeO2)	445.73

Figure 7. Reusability of MTCMO in a model reaction between malonitrile, triethylphosphite and benzaldehyde.

Scheme 2. Possible reaction mechanism for the preparation of β-phosphonomalonates over MTCMO.

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