Development of the solar heat source
The same design for the solar reflector was used as the reflector in our previous publications [9–11]. The solar reflector was developed through the repurposing of a satellite dish into a reflective parabolic mirror (Fig. 3). The satellite dish was completely covered with metalized Mylar® tape to attain the reflective properties needed to generate heat. Since the feed horn of the dish is located at the focal point, it was removed and reaction flasks were placed in this position in order to achieve maximum intensity from the sunlight. Round bottom flasks that were used as the reaction vessels were painted black up to approximately half-way up the flask using VHT® Flame Proof paint, which can withstand intermittent temperatures up to 1093 °C. The round bottom flasks were painted to prevent photochemical side reactions and allow for an efficient heating process. The synthesis consists of five steps, beginning with the Friedel–Crafts acylation of benzene (Fig. 4).
Isobutyrophenone synthesis
The synthetic procedure for this step has been published in a previous manuscript [9]. Benzene underwent a Friedel–Crafts acylation with isobutyryl chloride to synthesize isobutyrophenone. The reaction was performed using excess benzene as a replacement for a typical solvent and heat to reflux (88 °C) for a period of 3 hours. Any unreacted benzene was recovered after the reaction during the distillation process. A 66 % yield of isobutyrophenone was obtained from the solar synthesis, compared to a 44 % yield from an in-lab, electrical heating analysis.
Isobutylbenzene synthesis
The synthetic procedure for this step has been published in a previous manuscript [10, 11]. Isobutyrophenone, from the previous reaction, underwent a Wolff–Kishner reduction using hydrazine hydrate and strong base conditions to synthesize isobutyl benzene. The solvent for this reaction was replaced with the more sustainable solvent glycerol. The glycerol for this reaction was obtained from the synthesis of biodiesel. The reaction was allowed to heat at reflux (149–155 °C) for a period of three hours. An average 51 % yield of isobutyl benzene was obtained from the solar synthesis, compared to a 55 % yield from an in-lab, electrical heating analysis.
Isobutylacetophenone synthesis
A solution of isobutyl benzene (61.4 mmol), acetyl chloride (57.3 mmol), and aluminum chloride (25.1 mmol) was placed into a 25 mL round bottom flask. The flask was then placed in an aluminum heating block that was attached to the solar heat source near the point at which the focal point was going to be located. Because the reaction was required to reflux for a certain amount of time, a condenser was filled with cold water and capped with pipet bulbs to ensure that the water stayed in the condenser (Fig. 5). The same procedure as used in the synthesis of isobutyrophenone was incorporated into this synthetic procedure. The solar heat source was then moved into a position in which it was reflecting sunlight such that the focal point of the sunlight was directed at the bottom of the aluminum block. The solution was allowed to reflux at a temperature of 49–58 °C for a period of three hours. After reflux period was complete, the solution was washed with methanol and poured over ice. The product was extracted using dichloromethane and dried over calcium chloride. Pure isobutylacetophenone was obtained via vacuum distillation. The in-lab study of this chemical reaction was conducted using the same molar amounts of each reactant, but the reaction was heated using a Fisher Scientific hotplate.
A 60 % yield (6.015 g) of isobutylacetophenone was obtained when the Friedel–Crafts acylation of benzene was performed with the solar reflector, while a comparative study using an electric heat source only had a 51 % yield (5.113 g) of isobutylacetophenone. Spectral analysis using 1H and 13C NMR identified the products. 1H NMR (300 MHz, CDCl3): δ7.893 (2H, m, J = 5.4 Hz), δ7.313 (2H, m, J = 5.8 Hz), δ2.581 (3H, s, J = 2.1 Hz), δ2.522 (2H, t, J = 5.4 Hz), δ1.874 (1H, m, J = 5.1 Hz, 10.2 Hz), δ0.913 (6H, q, J = 4.5 Hz). 13C NMR (300 MHz, CDCl3): δ197.002, δ146.36, δ135.169, δ129.509, δ128.224, δ45.227, δ30.76, δ25.757, δ23.337.
1-(4-isobutylphenyl)ethanol synthesis
The synthetic procedure for this step was a modification of the synthesis previously published by Kjonaas et al. [14]. A solution of p-isobutylacetophenone (1.20 mL), methanol (3.00 mL), and sodium borohydride (0.2509 g) was mixed in a separatory funnel and allowed to sit for 10 min. After the standing time period, a 10 % HCl solution (10.0 mL) was added to remove any unreacted sodium borohydride, and the product was extracted using petroleum ether. 1-(4-isobutylphenyl)ethanol product (1.002 g, 87.2 %) was collected and dried using anhydrous sodium sulfate. 1H NMR (300 MHz, CDCl3): δ7.281 (2H, m, J = 4.0 Hz), δ7.174 (2H, m, J = 4.0 Hz), δ4.855 (1H, s, J = 0.92 Hz), δ2.714 (3H, q, J = 2.2 Hz), δ2.554 (2H, t, J = 2.8 Hz), δ1.795 (1H, q, J = 2.7 Hz), δ1.484 (1H, m, J = 2.8 Hz), δ0.976 (6H, q, J = 6.1 Hz). 13C NMR (300 MHz, CDCl3): 143.325, 140.684, 129.143, 125.357, 70.034, 45.196, 30.343, 25.076, 22.725, 22.465.
1-chloro-1-(4-isobutylphenyl)ethane synthesis
The synthetic procedure for this step was a modification of the synthesis previously published by Kjonaas et al. [14]. A solution of 1-(4-isobutylphenyl)ethanol (1.10 mL) was placed into a separatory funnel and mixed with 12.0 M HCl (10.0 mL) for a period of 5 min. The product of the reaction was extracted using petroleum ether. 1-chloro-1-(4-isobutylphenyl)ethane product (0.860 g, 78.8 %) was collected and dried using anhydrous sodium sulfate. 1H NMR (300 MHz, CDCl3): δ7.111 (2H, m, J = 4.0 Hz), δ7.104 (2H, m, J = 4.0 Hz), δ5.985 (1H, q, J = 0.94 Hz), δ3.341 (3H, q, J = 2.0 Hz), δ2.701 (2H, t, J = 3.1 Hz), δ1.761 (1H, m, J = 2.1 Hz), δ0.996 (6H, q, J = 6.1 Hz). 13C NMR (300 MHz, CDCl3): δ197.002, δ146.36, δ135.169, δ129.509, δ128.224, δ45.227, δ30.76, δ25.757, δ23.337.
Ibuprofen synthesis via Grignard reaction using solar heat source
The synthetic procedure for this step was a modification of the synthesis previously published by Kjonaas et al. [14]. A solution of 1-chloro-1-(4-isobutylphenyl)ethane (0.25 mL), magnesium (0.507 g), THF (10.00 mL) and 1,2-dibromoethane (4 drops) was placed in a dry 50-mL round bottom flask that had been painted black using VHT® Flame Proof paint. No stir-bar was placed into the round bottom flask because refluxing liquid was sufficient to mix the solutions. The flask was attached to the solar reflector in the position that the feed horn of the satellite dish was located to provide the best location for the directed focal point of sunlight (Fig. 6).
A modified Baum et al. [15] Allign-type condenser, filled with propylene glycol and capped with pipet bulbs to insure that the propylene glycol stayed in the condenser, was attached to the round bottom flask. To ensure that the reaction stayed moisture free, a drying tube filled with calcium chloride was attached to the top of the condenser. The solar heat source was then moved into a position in which it was reflecting sunlight onto the bottom of the round bottom flask. The solution was allowed to heat at reflux temperature (65 °C) for 30 min once there was evidence that the Grignard formation had begun (large amount of foaming present) (Fig. 7). After 30 min of reflux, the solution was moved out of the focal point and the solution was allowed to cool to ambient temperature. Carbon dioxide was bubbled into the reaction mixture for a period of 15 min. This solution was then decanted into a separatory funnel and washed with diethyl ether. The solution was then washed with 10 % HCl (8.00 mL) and mixed for a period of 5 minutes. The aqueous phase was then extracted using diethyl ether and combined with the organic phase. This new organic phase was then washed with 5 % NaOH solution. The aqueous layer from this wash was acidified using 10 % HCl until the solution was acidic to litmus. The aqueous layer was washed with diethyl ether to extract the product. Ibuprofen product (37 mg, 27.2 %) was collected. 1H NMR (300 MHz, CDCl3): δ12.22 (1H, s, J = 3.1 Hz), δ7.22 (2H, m, J = 8.1 Hz), δ7.10 (2H, m, J = 7.9 Hz), δ3.71 (1H, q, J = 7.2 Hz), δ2.44 (2H, t, J = 7.2 Hz), δ1.84 (3H, q, J = 6.7 Hz), δ1.50 (1H, m, J = 7.2 Hz), δ0.89 (6H, q, J = 6.6 Hz). 13C NMR (300 MHz, CDCl3): 180.21, 140.77, 136.95, 129.41, 127.22, 45.03, 44.70, 33.13, 22.37, 17.98.
Ibuprofen synthesis via Grignard reaction using electrical heat source
The synthetic procedure for this step was a duplicate of the synthesis previously published by Kjonaas et al. [14]. A solution of 1-chloro-1-(4-isobutylphenyl)ethane (0.25 mL), magnesium (0.510 g), THF (10.00 mL), and 1,2-dibromoethane (4 drops) was placed in a dry 50-mL round bottom flask. The flask was heat using an electric heating mantle. To ensure that the reaction stayed moisture free, a drying tube filled with calcium chloride was attached to the top of the condenser. The solution was allowed to heat at reflux temperature (65 °C) for 30 min once there was evidence that the Grignard formation had begun (large amount of foaming present). After 30 min of reflux, heat was removed and the solution was allowed to cool to ambient temperature. Carbon dioxide was bubbled into the reaction mixture for a period of 15 min. This solution was then decanted into a separatory funnel and washed with diethyl ether. The solution was then washed with 10 % HCl (8.00 mL) and mixed for a period of 5 minutes. The aqueous phase was then extracted using diethyl ether and combined with the organic phase. This new organic phase was then washed with 5 % NaOH solution. The aqueous layer from this wash was acidified using 10 % HCl until the solution was acidic to litmus. The aqueous layer was washed with diethyl ether to extract the product. Ibuprofen product (48 mg, 35.1 %) was collected.. 1H NMR (300 MHz, CDCl3): δ12.52 (1H, s, J = 3.1 Hz), δ7.28 (2H, m, J = 8.0 Hz), δ7.17 (2H, m, J = 8.0 Hz), δ3.65 (1H, q, J = 7.1 Hz), δ2.47 (2H, t, J = 7.0 Hz), δ1.89 (3H, q, J = 6.9 Hz), δ1.55 (1H, m, J = 7.2 Hz), δ0.91 (6H, q, J = 6.6 Hz). 13C NMR (300 MHz, CDCl3): 180.45, 140.77, 136.50, 129.45, 127.25, 45.01, 44.62, 33.19, 22.17, 17.78.