Solar-Driven Thermocatalytic Synthesis of Octahydroquinazolinone Using Novel Polyvinylchloride (PVC)-Supported Aluminum Oxide (Al2O3) Catalysts

The chemical industry is one of the main fossil fuel consumers, so its reliance on sustainable and renewable resources such as wind and solar energy should be increased to protect the environment. Accordingly, solar-driven thermocatalytic synthesis of octahydroquinazolinone using polyvinylchloride (PVC)-supported aluminum oxide (Al2O3) as a catalyst under natural sunlight is proposed in this work. The Al2O3/PVC catalysts were characterized by FT-IR, SEM, BET, XRD, and XPS techniques. The obtained results indicate that the yield and reaction time can be modified by adjusting the molar ratio of the catalyst. To investigate the stability of the catalyst, the spent catalyst was reused in several reactions. The results indicated that, when a 50% Al2O3 catalyst is employed in an absolute solar heat, it performs exceptionally well in terms of yield (98%) and reaction time (35 min). Furthermore, the reaction times and yield of octahydroquinazolinone derivatives with an aryl moiety were superior to those of heteroaryl. All the synthesized compounds were well characterized by FT-IR, 1H-NMR, and 13C-NMR. The current work introduces a new strategy to use solar heat for energy-efficient chemical reactions using a cost-effective, recyclable environmentally friendly PVC/Al2O3 catalyst that produces a high yield.


Introduction
As the chemical industry requires considerable amounts of energy, its reliance on fossil fuels needs to be reduced to protect the environment. As solar energy is readily available and does not generate any harmful byproducts, it is a viable alternative [1]. In extant studies, chemical reactions induced by solar radiation have already been explored [2,3], indicating that different reagents can be successfully activated by specific wavelengths in the solar spectrum. However, the mechanisms currently employed for this purpose are complex, expensive, difficult to monitor, and insufficiently selective [4]. Moreover, in most cases, useful molecules can only be synthesized if the incident radiation can be tuned to be efficiently absorbed by the materials being used. Since many substances do not absorb radiation in the visible part of the solar spectrum, or require specific wavelengths from the UV region, the use of natural light for chemical processes is often impractical. Nonetheless, as sunlight generates considerable heat, it can promote dependable and sustainable chemical synthesis [5] without generating any harmful byproducts [6]. These

Catalyst Characterization
Thermo Science's iD5 ATR diamond Nicolet is 5 FT-IR Spectrometer was used to record the Fourier transform infrared (FT-IR) spectra, while Cu Kα radiation (λ = 1.543 Å) provided by an X-ray diffractometer (Ultima IV, Rigaku, Japan) in the 10°−80° 2θ range was used to capture X-ray diffraction (XRD) spectra to define the phase composition of produced catalysts. The morphological properties of all studied samples were assessed using a field emission scanning electron microscope (FESEM, Model: Quanta FEG 250, Thermo Fisher Scientific, Amsterdam, The Netherland), and their chemical composition was characterized using Thermo scientific K-alpha X-ray photoelectron spectrometer (XPS) Waltham, MA, USA with a characteristic energy of 1486.6 eV generated by a monochromic Al Kα source. Throughout the XPS measurements, a pressure of approximately 10 −8 m bar, room temperature (RT), and 400 μm spot size were maintained. XPS survey scans used for elemental identification were obtained at 200 eV pass energy and 1 eV step size, while 50 eV and 0.1 eV were employed for capturing high-resolution XPS images.

Materials
Aluminum oxide was purchased from Loba Chemie (Mumbai, India), while a fine PVC (Polyvinyl Chloride) powder with a 36 µm particle diameter was supplied from SABIC corporation (Riyadh, Saudi Arabia) as a support material for the catalyst. Dimedone

Catalyst Characterization
Thermo Science's iD5 ATR diamond Nicolet is 5 FT-IR Spectrometer was used to record the Fourier transform infrared (FT-IR) spectra, while Cu Kα radiation (λ = 1.543 Å) provided by an X-ray diffractometer (Ultima IV, Rigaku, Japan) in the 10 • −80 • 2θ range was used to capture X-ray diffraction (XRD) spectra to define the phase composition of produced catalysts. The morphological properties of all studied samples were assessed using a field emission scanning electron microscope (FESEM, Model: Quanta FEG 250, Thermo Fisher Scientific, Amsterdam, The Netherland), and their chemical composition was characterized using Thermo scientific K-alpha X-ray photoelectron spectrometer (XPS) Waltham, MA, USA with a characteristic energy of 1486.6 eV generated by a monochromic Al Kα source. Throughout the XPS measurements, a pressure of approximately 10 −8 m bar, room temperature (RT), and 400 µm spot size were maintained. XPS survey scans used for elemental identification were obtained at 200 eV pass energy and 1 eV step size, while 50 eV and 0.1 eV were employed for capturing high-resolution XPS images. The catalyst's BET surface area, pore radius, and pore volume were estimated by N 2physisorption at 77 K using Quantachrome ASiQwin software, version 5.2. Finally, Bruker-Plus (400 MHz) nuclear magnetic resonance (NMR) apparatus was used to record the 1 H-NMR and 13 C spectra of synthetic octahydroquinazolinones with tetramethylsilane serving as an internal reference.

Al 2 O 3 /PVC Catalyst Preparation
Catalysts were prepared by the wet impregnation method. For the preparation of a 5% Al 2 O 3 catalyst, 50 mL of distilled water was mixed with Al 2 O 3 and PVC (at 5:95 wt. ratio) in a 100 mL beaker and the contents were rapidly agitated at 100 • C for up to one hour. The resulting catalyst was then stored inside a hot air oven overnight at 90 • C. The same process was adopted to obtain Al 2 O 3 /PVC catalysts containing 25%, 50%, 60%, and 75% Al 2 O 3 (henceforth denoted as 25% Al 2 O 3 , 50% Al 2 O 3 , 60% Al 2 O 3 , and 75% Al 2 O 3 ) all of which subjected to XRD, FT-IR, Brunauer-Emmett-Teller (BET), and scanning electron microscopy (SEM) analyses, along with pure PVC and Al 2 O 3 samples to facilitate comparisons.

Generalized Method for the Synthesis of Octahydrquinazolinone Derivatives
For the synthesis of octahydroquinazolinone derivatives, dimedone, urea/thiourea, and various aldehydes were mixed with an optimized amount of ethanol and 100 mg of Al 2 O 3 /PVC catalyst in a 100 mL beaker placed on a magnetic stirrer. Heat (75-80 • C) generated by sunlight was regularly measured a by thermometer and slight solvent evaporation was compensated for during the reaction. Before its use, the beaker was painted black to facilitate the absorption of the heat generated by sunlight. Once the beaker was painted can be reused many times in several reactions. Mixtures in a ratio of 7:3 of acetone and ethyl acetate were used as the solvent, and the reaction progress was regularly monitored. As the aim was to reuse the solid catalyst in subsequent reactions, the organic layer was separated by centrifugation, after which the solid product was purified by evaporation and recrystallization with ethanol. The final compounds were characterized by determining the melting point, as well as by analyzing the FT-IR, 1 H NMR, and 13 C NMR spectra.

Results and Discussion
3.1. Characterization 3.1.1. X-ray Diffraction (XRD) Measurements Figure 2 shows the XRD patterns of raw PVC, Al 2 O 3, and prepared Al 2 O 3 /PVC catalysts. The XRD pattern of PVC powder displays relatively broad peaks, indicating its amorphous character [41]. However, crystallinity starts to emerge as the Al 2 O 3 content in the Al 2 O 3 /PVC catalyst increases from 25% to 75%. The XRD patterns of the prepared samples, Al 2 O 3 /PVC catalysts, demonstrate that a mixture comprising 67.3% aluminum oxide, 16.7% bassanite (2CaSO 4 ·H 2 O), 2.5% calcium sulfate, 10.3% aluminum oxide hydroxide (boehmite), and 3.2% aluminum hydroxide oxide hydrate (nordstrandite) as the raw material reacts with water molecules from the air or the aqueous medium used in sample preparation.

Fourier Transform Infrared (FT-IR) Measurements
The FT-IR spectra of aluminum oxide, polyvinyl chloride, and Al2O3/PVC catalyst with different aluminum oxide ratios are displayed in Figure 3. As can be seen from the graph, the main infrared peaks produced by the aluminum powder are located at ~594 and ~465 cm −1 , which corresponds to the Al−O bending vibration of Al-OH groups. In addition, the peak at 652 cm −1 represents Al−O stretching vibration.
Al2O3 FT-IR spectra show bands of absorption at 3606 cm −1 that are corresponding to the stretching vibrations of the О-Н groups and water [42]. On the other hand, PVC produces peaks at 2913 cm −1 , ~1425 cm −1 , 1324 cm −1 , 1088 cm −1 , 957 cm −1 and 614 cm −1 , respectively, reflecting the -CH2-asymmetric stretching vibration, wagging -CH2, CH2 deformation, C−H stretching from CH−Cl, rocking CH2, and C−Cl stretching [43]. The obtained spectra further reveal that, as the Al2O3 content in the sample increases from 5% to 75%, several PVC peaks diminish and can no longer be discerned might be due to Al2O3 concentration overlapping the PVC peaks.

Fourier Transform Infrared (FT-IR) Measurements
The FT-IR spectra of aluminum oxide, polyvinyl chloride, and Al 2 O 3 /PVC catalyst with different aluminum oxide ratios are displayed in Figure 3. As can be seen from the graph, the main infrared peaks produced by the aluminum powder are located at~594 and~465 cm −1 , which corresponds to the Al−O bending vibration of Al-OH groups. In addition, the peak at 652 cm −1 represents Al−O stretching vibration.  Table 1 displays the surface area analysis of the pure PVC, Al2O3, and Al2O3/PVC catalysts with different amounts of Al2O3 in the range of 5-75 wt.%. It can be noted that pure PVC has a very low surface area of 3.70 m 2 /g, whereas pure Al2O3 has a high surface   [42]. On the other hand, PVC produces peaks at 2913 cm −1 ,~1425 cm −1 , 1324 cm −1 , 1088 cm −1 , 957 cm −1 and 614 cm −1 , respectively, reflecting the -CH 2 -asymmetric stretching vibration, wagging -CH 2 , CH 2 deformation, C−H stretching from CH−Cl, rocking CH 2 , and C−Cl stretching [43]. The obtained spectra further reveal that, as the Al 2 O 3 content in the sample increases from 5% to 75%, several PVC peaks diminish and can no longer be discerned might be due to Al 2 O 3 concentration overlapping the PVC peaks. Table 1 displays the surface area analysis of the pure PVC, Al 2 O 3 , and Al 2 O 3 /PVC catalysts with different amounts of Al 2 O 3 in the range of 5-75 wt.%. It can be noted that pure PVC has a very low surface area of 3.70 m 2 /g, whereas pure Al 2 O 3 has a high surface area of 105.40 m 2 /g. In addition, it can be seen that increasing the amount of Al 2 O 3 in Al 2 O 3 /PVC catalyst enhances the surface area of the catalyst and pore volume where they increased from 7.30 up to 76.50 m 2 /g and from 0.017 up to 0.182 cc/g, respectively. Additionally, the pore radius was observed to increase with increasing the amount of Al 2 O 3 to 50 wt.% and then decreased with 60 and 75 wt.% of Al 2 O 3 . The maximum pore radius was noted using a 50 wt.% Al 2 O 3 /PVC catalyst where it was 32.70 Å. However, it seems that there is an integration between Al 2 O 3 and PVC that has led to an increase in the surface area, as Al 2 O 3 has a higher surface area than PVC.  Figure 4a,b presents the N 2 adsorption-desorption isotherms and pore size distributions of the catalysts. According to the IUPAC standard, all catalysts exhibited a type V isotherm with an H3 hysteresis loop as shown in Figure 4a. This type of hysteresis revealed that the catalysts have mesoporous structures. However, type H3 hysteresis is generally found on solid materials that consist of aggregates or agglomerates of particles forming slit-shaped pores (plates or edged particles such as cubes), with irregular size and/or shape [44]. Moreover, it can be seen that the increase in the amount of Al 2 O 3 added to the PVC led to higher N 2 adsorbed volume in the p/p • range of 0.49 to 0.95. This finding is consistent with the results shown in Table 1, where the surface area and pore volume increased with increasing the amount of Al 2 O 3 . Figure 4b illustrates the pore size distributions. It was reported that solid materials which have pore sizes in the range from 2 to 50 nm classify as mesoporous [44]. From Figure 4b, it can be noted that increasing the Al 2 O 3 content produced pore sizes well within the mesoporous range, where the pore size distribution was with a peak at 40 nm. The pure PVC sample showed a very low number of pores, and they increased as a result of the addition of Al 2 O 3 . Therefore, it seems that the Al 2 O 3 content in the samples plays a significant role in changing the textural properties of the Al 2 O 3 PVC catalysts.

Structural Properties
tions. It was reported that solid materials which have pore sizes in the range from 2 to 50 nm classify as mesoporous [44]. From Figure 4b, it can be noted that increasing the Al2O3 content produced pore sizes well within the mesoporous range, where the pore size distribution was with a peak at 40 nm. The pure PVC sample showed a very low number of pores, and they increased as a result of the addition of Al2O3. Therefore, it seems that the Al2O3 content in the samples plays a significant role in changing the textural properties of the Al2O3 PVC catalysts.

Scanning Electron Microscopy (SEM) Analysis
The morphology of Al2O3, PVC, and Al2O3/PVC samples with different molar ratios of Al2O3 was analyzed using SEM at different magnifications and the obtained images are shown in Figure 5. As can be seen from Figure 5a,g, PVC comprises sporadic mushroom cap spores, while the Al2O3 structure is characterized by the agglomeration of fine particles of various shapes (rectangles, oval bars, and cubes) and sizes. It is also apparent that the Al2O3 particle size is smaller than that of pure PVC. Consequently, the Al2O3/PVC catalysts with 5 to 75% Al2O3 content exhibit a gradual shift in morphology, becoming progressively more similar to Al2O3, as shown in Figure 5c−f. As surface area is inversely proportional to the particle size [45], increasing the amount of Al2O3 in the Al2O3/PVC catalyst increases the surface available for chemical reaction. This is well-aligned with the BET surface area results, in Table 1.

Scanning Electron Microscopy (SEM) Analysis
The morphology of Al 2 O 3 , PVC, and Al 2 O 3 /PVC samples with different molar ratios of Al 2 O 3 was analyzed using SEM at different magnifications and the obtained images are shown in Figure 5. As can be seen from Figure 5a,g, PVC comprises sporadic mushroom cap spores, while the Al 2 O 3 structure is characterized by the agglomeration of fine particles of various shapes (rectangles, oval bars, and cubes) and sizes. It is also apparent that the Al 2 O 3 particle size is smaller than that of pure PVC. Consequently, the Al 2 O 3 /PVC catalysts with 5 to 75% Al 2 O 3 content exhibit a gradual shift in morphology, becoming progressively more similar to Al 2 O 3 , as shown in Figure 5c−f. As surface area is inversely proportional to the particle size [45], increasing the amount of Al 2 O 3 in the Al 2 O 3 /PVC catalyst increases the surface available for chemical reaction. This is well-aligned with the BET surface area results, in Table 1. 3.1.5. X-ray Photoelectron Spectrometry (XPS) Analysis XPS survey spectra were captured to study the surface chemistry and the chemical composition of PVC, Al 2 O 3, and Al 2 O 3 /PVC catalysts with different Al 2 O 3 amounts, as indicated in Figure 6a. It is evident that both PVC and Al 2 O 3 /PVC contain C, Cl, and O. Additionally, the Al 2 O 3 /PVC catalysts contain Al, Ca, and S. However, the Al 2 O 3 sample comprises C, O, Al, Ca, and S. The presence of oxygen in the XPS survey spectra of PVC might be ascribed to contamination or polymer chain oxidation [46]. Similarly, the presence of both Ca and S in the Al 2 O 3 /PVC spectra is expected, because the Al 2 O 3 sample contains CaSO 4 ·H 2 O. The high-resolution C 1s spectra produced by PVC, Al 2 O 3 /PVC catalysts, and Al 2 O 3 are shown in Figure 6b, respectively. The PVC sample comprises three kinds of carbon, which produce peaks at 287.13 eV, 288.52 eV, and 289.54 eV binding energies that correspond to the C-C and C-H and the C-Cl bonds and O=C−O bonds, respectively [46,47]. Additionally, catalysts containing smaller amounts of Al 2 O 3 exhibit three peaks at around 285.5, 287.5, and 289.6 eV, reflecting the presence of C−C, C−Cl, and O=C−O bonds. However, as the Al 2 O 3 content in the Al 2 O 3 /PVC catalyst increases, C-C and C-Cl peaks decrease in amplitude, while the magnitude of O-C=O peaks increases. The C 1s XPS spectra of the 75% Al 2 O 3 catalyst and Al 2 O 3 samples can be deconvoluted into two peak components at around 286.6 and 289.7 eV binding energies, which are attributed to the C−C and O=C−O species, respectively.

X-ray Photoelectron Spectrometry (XPS) Analysis
XPS survey spectra were captured to study the surface chemistry and the chemica composition of PVC, Al2O3, and Al2O3/PVC catalysts with different Al2O3 amounts, as indicated in Figure 6a. It is evident that both PVC and Al2O3/PVC contain C, Cl, and O Additionally, the Al2O3/PVC catalysts contain Al, Ca, and S. However, the Al2O3 sample comprises C, O, Al, Ca, and S. The presence of oxygen in the XPS survey spectra of PVC might be ascribed to contamination or polymer chain oxidation [46]. Similarly, the presence of both Ca and S in the Al2O3/PVC spectra is expected, because the Al2O3 sample contains CaSO4·H2O. The high-resolution C 1s spectra produced by PVC, Al2O3/PVC catalysts, and Al2O3 are shown in Figure 6b, respectively. The PVC sample comprises three kinds of carbon, which produce peaks at 287.13 eV, 288.52 eV, and 289.54 eV binding en-   Figure 6c shows high-resolution C1 2p spectra produced by PVC, Al 2 O 3 /PVC catalysts, and Al 2 O 3 . The PVC spectrum can be decomposed into three peaks, namely Cl 2p 1/2 at 204.7 eV and peak Cl 2p 3/2 at 202.6 eV representing organic chlorine atoms covalently bounded sp2 carbon [46,47], whereby the latter is assigned to the chloride ion and the hydrogen bonds [48]. On the other hand, Cl 2p spectra produced by most Al 2 O 3 /PVC catalysts contain two peaks of high intensity with a maximum of 203.2 eV (Cl 2p 1/2 ) and 200.1 eV (Cl 2p 3/2 ), which are attributed to the C-Cl bonds. The oxygen O 1s spectra of the PVC, Al 2 O 3 /PVC catalysts, and Al 2 O 3 sample are also presented in Figure S1a (S = Supplementary) where the two peaks at 533.1 and 535.2 eV, which are attributed to the C-C=O and C-O-H bonds, respectively, characterize the XPS O 1s spectrum produced by PVC [46]. On the other hand, the O 1s peak produced by most of the Al 2 O 3 /PVC catalyst samples can be decomposed into three peaks located at around 532 and 534 eV, corresponding to O bound to the Al lattice (Al−O−Al bonds) and OH/COO bonds, respectively [49]. The evidence of OH/COO bonds in the Al 2 O 3 spectra is attributed to the use of H 2 O as the reaction medium in the present study and is consistent with the findings reported by other authors [50,51]. Similarly, the peak at 536 eV arises due to the adsorption of free water molecules. As noted above, the intensity and number of O 1s peaks increase, while the intensity and number of C 1s and Cl 2p peaks decrease with the increase in Al 2 O 3 content in the Al 2 O 3 /PVC catalysts, confirming that adding Al 2 O 3 introduces abundant oxygen atoms into the PVC chain. Figure S1b shows the Al 2p spectra produced by Al 2 O 3 , Al 2 O 3 /PVC catalysts, and PVC. The Al 2 O 3 /PVC samples contain the two peaks produced by Al 2p of Al 2 O 3 (at around 77 and 79 eV) confirming the presence of Al-O and Al-OH bonds, respectively [52]. Additionally, the peak located at around 75 eV is attributed to the AlO(OH) bond. In the spectrum produced by the 50% Al 2 O 3 catalyst sample, a greater contribution from the OH groups is evident [50,51]. Thus, as demonstrated by the XPS results, which are in good agreement with the XRD and FT-IR data, Al 2 O 3 was successfully mixed and dispersed inside the PVC matrix to create Al 2 O 3 /PVC catalysts. Furthermore, Table S1 with the ratios of the electronic state of the elements for the as-prepared Al 2 O 3 /PVC catalysts was displayed in the supplementary file.

Catalytic Activity
To achieve optimized reaction conditions, the catalyst and solvent amounts, as well as the reaction, were modified, and the findings are reported in Tables 2-6. When ethanol was used without a catalyst, no reaction was observed after 12 h. Moreover, experiments conducted with different Al 2 O 3 amounts revealed that the reaction involving 50% Al 2 O 3 resulted in the highest (98%) yield while requiring only 35 min to complete, which could be attributed to the sufficient number of Brönsted and Lewis acid sites [3], as reflected in a greater pore radius, Table 1. Thus, as this Al 2 O 3 quantity in the PVC matrix may be led to the optimal development of Lewis acid-base interactions between the polar surface group of the Al 2 O 3 and the ionic species of the PVC, it can be adopted to improve the ionic conductivity, thermal conductivity, and mechanical stability of the 50% Al 2 O 3 catalyst. Consequently, in the subsequent experiments, 50% Al 2 O 3 was used as a catalyst, but its quantity was varied in the 20-120 mg range, to assess the influence of these factors on the reaction efficiency. As can be seen from Table 3, 100 mg of catalyst yields the most optimal results. Next, 100 mg of 50% Al 2 O 3 catalyst was used while varying the solvent type to assess its influence on the reaction efficiency. As can be seen from Table 4, ethanol is most conducive for high yields, as the values obtained for CH 2 Cl 2 , DMF, MeOH, EtOH, H 2 O, and EtOH/H 2 O are much lower and the reactions took longer time to complete, and also the amount of solvent in mL was also wasted in each type during sunlight irradiation depending upon the boiling point of solvents. Therefore, each solvent was continuously added as required during the course of the reaction. To ensure that 50% Al 2 O 3 is the most beneficial catalyst, additional experiments were conducted using HCl (Conc.), H 2 SO 4 (Conc.), P-TsOH, Al 2 O 3, and PVC and the results are presented in Table 5. The reactions based on the 50% Al 2 O 3 catalyst require the shortest time to complete while producing the highest yield, confirming that Al 2 O 3 /PVC has superior catalytic potential compared to all other tested compounds, including aluminum oxide and polyvinyl chloride (PVC).
Finally, the optimal conditions established through previous experiments (100 mg of 50% Al 2 O 3 as a catalyst, optimized amount of ethanol) were adopted for the synthesis of 4-(substituted)-7,7-dimethyl-1,2,3,4,5,6,7,8-octahydroquinazoline-2,5-dione to assess the adaptability of the proposed protocol to other processes. Various substituents on aldehyde including Cl, F, OCH 3 , OH, and Furan moieties were used for this purpose and the obtained results are reported in Table 6.  As evident from the tabulated results, 50% Al2O3 outperformed all considered compounds in terms of both generated yield and reaction time.

Plausible Octahydroquinazolinone Production Mechanism Using Al2O3/PVC as a Catalyst
As shown in Figure 7, Al2O3/PVC activates the carbonyl group of the aldehyde to produce Intermediate I under the influence of solar heat. This is followed by condensation with urea/thiourea (Intermediate II) and subsequent dehydration, resulting in Intermediate III, which reacts with dimedone to produce Intermediate IV. Finally, cyclization with the removal of water yields the desired octahydroquinazolinones. As evident from the tabulated results, 50% Al 2 O 3 outperformed all considered compounds in terms of both generated yield and reaction time.

Plausible Octahydroquinazolinone Production Mechanism Using Al 2 O 3 /PVC as a Catalyst
As shown in Figure 7, Al 2 O 3 /PVC activates the carbonyl group of the aldehyde to produce Intermediate I under the influence of solar heat. This is followed by condensation with urea/thiourea (Intermediate II) and subsequent dehydration, resulting in Intermediate III, which reacts with dimedone to produce Intermediate IV. Finally, cyclization with the removal of water yields the desired octahydroquinazolinones. Materials 2023, 16, x FOR PEER REVIEW 14 of 17 Figure 7. A proposed mechanism for the synthesis of octahydroquinazolinone derivatives using Al2O3/PVC catalyst.

Recyclability of the Al2O3/PVC
As sufficient catalyst reusability and recovery are crucial for obtaining sustainable and environmentally friendly synthesis methods that can be adopted in practice, these aspects were also considered in the present study, and the findings are reported in Table  7. The catalyst can be reused up to four times without a significant loss in yield and most of its original mass can be recovered by centrifugation.

Conclusions
In this work, functionalized 1,2,3,4,5,6,7,8-octahydroquinazolinone derivatives were successfully synthesized through an affordable process that relies on polyvinylchloridesupported aluminum oxide through sunlight exposure as a free source of heat. As the catalyst can be reused, this environmentally friendly method can be adopted in a wide

Recyclability of the Al 2 O 3 /PVC
As sufficient catalyst reusability and recovery are crucial for obtaining sustainable and environmentally friendly synthesis methods that can be adopted in practice, these aspects were also considered in the present study, and the findings are reported in Table 7. The catalyst can be reused up to four times without a significant loss in yield and most of its original mass can be recovered by centrifugation.

Conclusions
In this work, functionalized 1,2,3,4,5,6,7,8-octahydroquinazolinone derivatives were successfully synthesized through an affordable process that relies on polyvinylchloridesupported aluminum oxide through sunlight exposure as a free source of heat. As the catalyst can be reused, this environmentally friendly method can be adopted in a wide range of processes, given that it produces a higher yield in a shorter time compared to the previously reported conventional thermal technique. The FT-IR and XRD results indicated the formation of the Al 2 O 3 /PVC catalysts. Additionally, the obtained results indicate that the yield and reaction time can be modified by adjusting the molar ratio of the catalyst. A total of 50% Al 2 O 3 /PVC catalyst performed better than any other alternative under solar heat in terms of yield and reaction time. Additionally, under solar heat, arylmodified octahydroquinazolinone performed much better than heteroaryl when compared to reaction times and yield. In the context of green chemistry, this study introduces a new strategy towards the use of abundant solar energy for a cost-effective, energy-efficient, and environmentally friendly chemical industry.