Organic 2 Review Problem 270

Organic 2 Review Problem 270 - + CH 8 COCl -f AlCl...

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254 PRACTICAL ORGANIC CHEMISTRY acetic acid. For this purpose, a solution of a known quantity of chloramine-T in water containing acetic acid, or dichloramine-T in acetic acid itself, is diluted with an excess of potassium iodide solution, and the iodine is then estimated by direct titration with standard sodium thiosulphate solution. Aromatic Ketones. Aromatic ketones may be divided into two classes: (1) The true ketones, in which the >CO group is in the side chain, the most common examples being acetophenone or methyl phenyl ketone, C 6 H 8 COCH 3 , and benzophenone or diphenyl ketone, C 4 H 6 COC 6 H 5 . These ketones are usually prepared by a modification of the Friedel-Crafts* reaction, an aromatic hydrocarbon being treated with an acyl chloride (either aliphatic or aromatic) in the presence of aluminium chloride. Thus benzene reacts with acetyl chloride C 6 H 5 H + ClCOCH 3 -> C 6 H 5 COCH 3 -f HCl readily in these circumstances to give acetophenone. A probable mechanism of the reaction is as follows:
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Unformatted text preview: + CH 8 COCl -f AlCl 8-> CH 3 CO + AlCl 4 (I) The benzene nucleus is then attacked by the carbonium ion (I) (cf. attack by + NO a ion, p. 157): + + C 6 H 5 H -f CH 8 CO -> CeH 8 COCH 3 + H followed by: + H -f AlCl 4-> HCl -f AlCl 8 . (2) The quinones, in which the carbon of the >CO group is part of the ring; for this reason, the properties of the >CO group are sufficiently modified to make the quinones quite distinct from the true ketones of class (i). Quinones may often be prepared by direct oxidation of the corresponding hydrocarbon: thus anthracene (A) on oxidation gives anthraquinone (B) whilst phenanthrene (C) gives phenanthraquinone (D), these quinones being examples of para and ortho quinones respectively. The specific term quinone is usually applied to />-benzoquinone (F) which cannot easily be prepared by the direct oxidation of benzene on a laboratory scale. It can, however, be readily...
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This note was uploaded on 09/19/2011 for the course CHM 2211 taught by Professor Castalleano during the Fall '06 term at University of Florida.

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