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Organic Lab Reactions 193

Organic Lab Reactions 193 - example d-pulegone(XXVIII upon...

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188 REDUCTION WITH ALUMINUM ALKOXIDES xylene as a solvent, increase the amount of polymerization and conden- sation of unsaturated aldehydes such as crotonaldehyde. In addition, the Tishchenko reaction can occur to produce the ester, RCOOCH2R: 27 2RQH0 -^5 * BCOOCH.R This reaction occurs to a greater extent in benzene than in isopropyl alcohol. 13 - 27 ° It appears that an excess of aluminum isopropoxide has "the desired effect of speeding up the reduction reaction and thus min- imizing side reactions in the case of aliphatic aldehydes. 13 The excess, however, is disadvantageous with aromatic aldehydes (see p. 195). Dehydration of the Alcohol. Several investigators have reported that dehydration sometimes accompanies reduction of a ketone and that an olefin is obtained as the major product. Usually, but not always, an
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Unformatted text preview: example, d-pulegone (XXVIII) upon reduction at 120 to 170° for twenty hours gave over 40% of a mixture of menthadienes (XXX) and only 5 to 10% of the carbinols (XXIX). 28-29 ' 80 Even under these drastic conditions unreduced ketone was present. In the reduction of 4-ketotetrahydrochrysene (XXII) 23 the replacement of toluene by xylene as a solvent usually resulted in the formation of the hydrocarbon XXXII instead of the carbinol XXXI. OH XXXI 27 Tishchenko, J. BiMS.Phya. Chem. Soc., 38,355,482 (1906) [Chem. Zentr., 77, (II), 1309 1552 (1906)]. »»» Child and Adkins, J. Am. Chem. Soc., 45, 3013 (1923). 28 Doeuvre and Perret, BvU. soc. chim., [5] 2, 298 (1935). 29 Grubb and Read, / . Chem. Soc., 1934, 242. 80 Short and Read, J. Chem. Soc., 1939, 1306....
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