Synthesis of 2-Alkynyl-1,4-cyclohexadienes via a Diels–Alder Reaction of Conjugated 2,4-Diynones

Abstract

General Methods. All reactions were performed in flame-dried glassware under a N 2 atmosphere. Solvents were degassed and dried by standard methods before use. Purification of the crude products was carried out by column chromatography using silica gel. Analytical TLC was performed on a silica gel GF 254 plate. The TLC plates were visualized under ultraviolet (UV, 254 nm) light or by staining with PMA or CAM. NMR spectra were recorded on a 400 or 500 MHz NMR spectrometer in CDCl 3. Proton chemical shifts are expressed in parts per million (ppm, δ scale) and are referenced to residual protium in the NMR solvent (CDCl 3 , δ 7.26). Data for 1 H NMR are reported as follows: chemical shift, multiplicity (s=singlet, d=doublet, t=triplet, q=quartet, m= multiplet, br=broad), coupling constant (J) in Hertz, and integration. Carbon chemical shifts are expressed in parts per million (ppm, δ scale) and are referenced to the carbon resonance of the NMR solvent (CDCl 3 , δ 77.16). Infrared (IR) spectra were recorded on an ATR/FTIR spectrometer as a thin film on a composite of zinc selenide and diamond crystal and only major functional group peaks are reported in cm-1. High-resolution mass spectra (HRMS) were obtained on a high-resolution Q-TOF mass spectrometer (ionization mode: ESI). Commercially available reagents and solvents were used without further purification. Diynones 1a-1f 1,2 and 1g-1h, 3 as well as diene 2d 4 were synthesized according to reported procedures. S3 General Procedure for Diels-Alder reaction of diynones: To a solution of diynone 1 (1.0 equiv.) and diene 2 (5.0 equiv.) in dichloromethane (ca. 0.05-0.15 M) was added dimethylaluminum chloride (1.0 M in hexanes, 1.0 equiv.) slowly over 10 minutes. The reaction mixture was stirred at room temperature for 1-5 h, quenched with dilute aq. NaHCO 3 , dried over anhydrous MgSO 4 and filtered. The solvent was removed in vacuo and the crude product was purified by column chromatography (silica gel).

Vapor-fed microfluidic hydrogen generator

“…In the case of the devices presented in this study, the crossover of oxygen is expected to be lower than that measured for H 2 , as its permeability in Nafion is lower. 40,41 …”

Gas Sorption, Diffusion, and Permeation in Nafion

“…[22][23][24][25] Surprisingly, only very limited pure-gas transport data have been reported for Nafion ® . [26][27][28][29][30][31] The first comprehensive study on the gas permeation properties of dry Nafion ® was reported by Chiou and Paul using the constant volume/variable pressure technique. 29 The gas diffusion coefficients were then deduced from the time-lag method.…”

“…[26][27][28][29][30][31] The first comprehensive study on the gas permeation properties of dry Nafion ® was reported by Chiou and Paul using the constant volume/variable pressure technique. 29 The gas diffusion coefficients were then deduced from the time-lag method. Their study indicated low permeability in dry Nafion ® for all gases other than He and H 2 .…”

“…33 Chiou and Paul showed that the CO 2 permeability increased with pressure, a typical behavior observed in rubbers, and suggested that this could possibly indicate that the rubbery phase dominates gas transport. 29 It was concluded that direct gas sorption measurements are necessary to gain more definitive insight into the role of the rubbery phase and the ionic cluster domains with respect to gas permeation in Nafion ® . To date, to the best of our knowledge, only one study has reported directly measured gas sorption isotherms in Nafion ® , and was limited to He and H 2 .…”

“…In this study, the gas solubilities were directly measured using barometric and gravimetric methods and are generally in good agreement. Previously reported solubility values by Chiou et al 29 and Fan et al 30 were calculated from the diffusion time-lag method, which is prone to errors especially for polymers with low gas solubility. 51 The solubility data for He and H 2 , measured using the barometric method in this study agree reasonably well with the gravimetrically measured values reported by Smith et al polymers.…”