PROGRAMA ASISTENCIA BIOPSICOSOCIAL

Prins condensation was carried out with β-pinene and paraformaldehyde at 90 °C using tin (II) hydroxychloride and toluene as solvent. In this reaction, Sn(OH)Cl achieved 99% of nopol selectivity at 98% conversion, while SnO and SnO2 showed lower activity under the same conditions. Sn(OH)Cl2 was prepared by co-precipitation and characterised by techniques such as FTIR, XRD, 1H MAS NMR, TG-DTA, SEM, BET surface area and porosity. FTIR-pyridine showed that Sn(OH)Cl had a very large number of Brønsted acid sites on the catalyst surface compared with SnO and SnO2. The acidity of Sn(OH)Cl was also confirmed by 1H MAS NMR. The catalyst was efficient and had good recyclability, maintaining activity for at least three cycles.147

Opanasenko et al.150 investigated some metal organic frameworks over zeolite in the Prins condensation of β-pinene and paraformaldehyde in the liquid phase at 80-120 °C under atmospheric pressure.140 MIL-100(Fe) was the most active catalyst, giving 82% nopol yield in the presence of acetonitrile as solvent. However, at 120 °C, the yield of nopol increased to 87% with p-xylene as solvent. The researchers found that the β- pinene/catalyst ratio affected nopol yield, which also increased as solvent polarity increased. The catalysts were used at least three times without any observed loss in activity.

Do and co-workers146 studied mesoporous catalyst Zr-SBA-15 platelets with 4-8 nm pore size distribution as a catalyst for Prins condensation of β-pinene and paraformaldehyde in the liquid phase. The reaction conditions were 0.5 g of catalyst, 1 mmol of β-pinene, 2 mmol of paraformaldehyde and 5 ml of toluene as solvent at 80-110 °C. The catalyst was characterised by N2 adsorption, TGA analysis, SEM and TPD ammonia. The results showed that the catalyst had strong Lewis sites and weak Brønsted acidity, which affected its activity and selectivity. Zr-SBA-15 showed 100%

nopol selectivity in 6 h reaction time. H-beta catalyst was also tested in the reaction and found to have only 4% nopol selectivity, because this catalyst has too strong Brønsted acidity. Therefore, Zr-SBA-15 has excellent selectivity probably because of an appropriate combination of Lewis and Brønsted sites on its surface. The used catalyst was regenerated by solvent washing and a hydrothermal H2O2 wash at 40 °C, after which it had 100% nopol selectivity at > 95% conversion.

Extra-large pore UTL zeolite, large-pore aluminosilicate zeolite beta and metal- organic-framework Cu3(BETC)2 and Fe(BTC) were tested in the Prins reaction to produce nopol. X-ray diffraction and N2 (-196 °C) adsorption were used to determine the crystallinity, porosity and surface area of the catalysts, while pyridine adsorption and FTIR spectroscopy were used to determine properties such as the concentration of Lewis and Brønsted acid sites. The Prins reaction was carried out in the liquid phase with 0.2 g of catalyst at 80 °C. Typically, 4 mmol of β-pinene and 8 mmol of paraformaldehyde were added to 0.4 g of internal standard (mesitylene) and 10 ml of acetonitrile as solvent. Cu3(BETC)2 was the catalyst with the greatest surface area (1500 m2g-1), while Fe(BTC) had a surface area of 1060 m2g-1 and contained a larger number of accessible active sites within MOF at the appropriate strength.155

Jadhav et al.151 studied nanosized sulfated zinc ferrite (SZF) to catalyse the synthesis of nopol from β-pinene and paraformaldehyde. Zinc ferrite was prepared by simple co- precipitation, then sulphated by impregnating it with ammonium sulfate. The resulting catalyst was calcined at 470 °C, then characterised by techniques such as FTIR-pyridine and ammonia TPD to measure the acid sites. The catalyst was pre-treated at 200 °C for 1 h, then the reaction was carried out in the liquid phase for 12 h. Five mmol of β- pinene and 15 mmol of paraformaldehyde were added to 4 ml of toluene solvent and 0.14 g of catalyst, then refluxed at 95 °C. The catalyst showed good activity and

selectivity, converting 70% β-pinene with 88% nopol selectivity. It is reported that increasing the reaction temperature to 110 °C improved conversion, but the selectivity decreased to 57%. The catalyst was recycled four times and no significant loss in the performance was observed.

Sn-MCM-41 was characterised by BET, XPS and H2-TPR and tested for nopol synthesis from β-pinene and paraformaldehyde by Prins condensation. The reaction was affected by various parameters. It was found that increasing catalyst concentration increased the rate of conversion but reduced the selectivity. The catalyst showed 95% selectivity of nopol after 6 h using ethyl acetate as solvent instead of toluene. The catalyst was regenerated twice by washing with acetone.161

Yadav et al.145 prepared ZnCl2-impregnated montmorillonite and tested it in the Prins reaction to obtain nopol. Prior to use, the catalyst was heated at 120 °C for 2 h. The reaction was affected by catalyst amount, reaction time, reaction temperature, β-pinene/ PF molar ratio and the type and amount of solvent. It was found that using acetonitrile gave a better conversion compared with toluene, because the polarity of the solvent affected the activity of the catalyst. The reaction was run at temperatures ranging from 60 to 100 °C. At 80 °C, with a 1:2 molar ratio of β-pinene/PF and 0.1 g of catalyst, there was 75% β-pinene conversion. This fell to 64% when the temperature was increased to 100 °C. Under the same conditions, the amount of catalyst was increased to 0.4 g and conversion was observed to increase from 75% to 90% with the same selectivity (97%).

Finally, mesoporous FePO4 was used in the Prins condensation of β-pinene and paraformaldehyde in the liquid phase to produce nopol. The catalyst was found to be active, environmentally benign and without toxic constituents. Acetonitrile was used as solvent under different conditions of temperature and amount of catalyst: temperature was varied in the range of 30-80 °C, with 0.01-1 g of catalyst. The ratio of β-pinene to

paraformaldehyde and reaction time were also studied. Under optimised conditions (5 mmol of β-pinene, 10 mmol of PF, 10 mL of acetonitrile and 1 g of catalyst at 80 °C) nopol yield reached 100% after 4 h and was stable for at least 6 h. The catalyst was reused five times and showed no loss in activity or nopol selectivity.148