STEP 1: Place 100 mg of Adams' platinum dioxide catalyst and 9.8 g (0.14 mol) of 2-methylbut-2-ene in a 100-m1 hydrogenation flask.
STEP 2: Attach the flask to the adapter of the atmospheric hydrogenation apparatus and cool the lower part in an ice-water bath.
STEP 3: Fill the flask and gas burettes with hydrogen by the hydrogenation procedure; note the volumes in the gas burettes, remove the cooling bath and gently agitate the flask.
STEP 5: Cool the flask contents and follow the procedure for replacing the hydrogen in the apparatus with air.
STEP 6: Disconnect the hydrogenation flask and with a suitably sized dropper pipette transfer the liquid to a small distillation flask leaving the catalyst in the hydrogenation flask (1).
STEP 7: Distil the 2-methylbutane (b.p. 30 °C) using a small ice-cooled water condenser with the receiver flask immersed in an ice-salt cooling bath (2).
STEP 8: The yield is 7 g (70%). Record the i.r. spectrum and compare it with the spectrum of the starting material (3).
STEP 9: Note (a) the disappearance upon hydrogenation of the absorption bands at 810 and 1675 cm -1 (due to the out-of-plane deformation of the =C—H bond and the stretching of the carbon-carbon double bond respectively) in the alkene, and (b) the replacement of the peak at 1380 cm -1 in the alkene (—CH3 bending mode) by a doublet at 1385 and 1375 cm -1 ((CH3)2C— plus terminal —CH3).
STEP 10: The m.s. shows principal fragment ions at m/z 72 (M), 57 (M—CH3), 43 (M—C2115, base peak) and at 29(C2 H5 GI).
Notes to keep in mind:
1. This technique, rather than conventional filtration, is to be preferred in this case owing to the high volatility of the hydrocarbon. For more details you can refer disposal and recovery of the catalyst, Hydrogenation at atmospheric pressure(12).
2. An alternative and convenient arrangement is to supply the condenser with cooled water from an ice/water reservoir by means of a peristatic pump.
3. In both cases a fixed path length cell (0.025 mm) should be employed.
3. In both cases a fixed path length cell (0.025 mm) should be employed.
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