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Reduced chromium residues can be removed from glassware with concentrated HCl or 10-15% aqueous HF. Solid chromium waste should never be thrown away, as residual CrO<sub>3</sub> may ignite. Chromium(VI) reagents are toxic and should be handled with care in a well-ventilated fume hood.
===Example Procedure<ref>Guziec, F. S., Jr.; Luzzio, F. A. ''J. Org. Chem.'', '''1982''', ''47'', 1787.</ref>===
<span style="float:right;padding-right:50px;padding-top:10px;">'''''(10)'''''</span><center>[[File:ChroEx.png]]</center>
To a solution of ''p''-(3-hydroxypropyl)benzyl alcohol (165 mg, 1 mmol) in N,N-dimethylformamide (3 mL) was added imidazolium dichromate (705 mg, 2 mmol) and the mixture was stirred at room temperature (4 hours). After completion of the reaction, water (30 mL) was added to the reaction mixture and the product was extracted three times with diethyl ether. The ether extracts were washed with water and aqueous NaHCO<sub>3</sub>, dried over anhydrous MgSO<sub>4</sub>, and evaporated to dryness. The crude product was subjected to silica gel column chromatography with dichloromethane-ethyl acetate (4:1) as eluent to yield ''p''-(3-hydroxypropyl)benzaldehyde (112 mg, 68%): <sup>1</sup>H NMR (CDCl<sub>3</sub>): δ 1.8–2.3 (m, 2 H), 2.77 (s, 1 H), 2.93 (t, 2 H, J = 6 Hz), 3.80 (t, 2 H, J = 6 Hz), 7.4–7.98 (m, 4 H), 10.10 (s, 1 H). IR (film) 1700 cm<sup>–1</sup>. and 3-(4-formylphenyl)propanal (4 mg, 3%): <sup>1</sup>H NMR (CDCl<sub>3</sub>): δ 2.45–3.21 (m, 4 H), 7.31–7.85 (m, 4 H), 9.81 (s, 1 H), 9.95 (s, 1 H).
==References==
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