US EPA

8310263 

Journal Article 

Platinum oxide as a catalyst in the reduction of organic compounds. II. Reduction of aldehydes. Activation of the catalyst by the salts of certain metals 

Carothers, WH; Adams, R 

1923 

Yes 

Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 

45 

4 

1071-1086 

English 

10.1021/ja01657a031 

1. Platinum black from platinum oxide prepared from absolutely pure chloroplatinic acid becomes very quickly inactive when shaken with an aldehyde in an atmosphere of hydrogen; only by frequent re-activation can the reduction be carried to completion. 2. The addition of as much as 4 parts per million of iron in the form of ferrous or ferric chloride greatly accelerates the rate of the reduction. 3. A systematic study has been made of the effects of various amounts of ferrous and ferric chloride on the catalytic reduction of benzaldehyde, and of ferrous chloride on the catalytic reduction of heptaldehyde, using the platinum oxide catalyst described in a previous paper. In all cases an optimum effect is observed when the amount of iron chloride present corresponds to a concentration of approximately 0.0001 mole in 100 cc. of the reaction mixture. 4. When higher concentrations of ferrous chloride are used the only additional effect observed is a very slight diminution in the rate of reduction and a tendency for the reduction to proceed beyond the alcohol stage. 5. When ferric chloride is used it is first reduced to ferrous chloride. With amounts of ferric chloride not greater than 0.0001 mole the effect is quite similar to that produced by ferrous chloride. With larger amounts an induction period appears and the reduction becomes slower because of the hydrogen chloride set free in the reduction of the ferric chloride. The reduction proceeds beyond the formation of benzyl alcohol to toluene and even further. 6. It is shown that foreign materials sufficient to increase the activity of the catalyst appreciably are accumulated during its recovery even when c. p. reagents are used and every precaution is taken to guard against the entrance of accidental impurity. 7. Evidence is given for the following interpretation of the effect of the ferrous salt. The inactivity of the pure platinum black is due to the fact that it is deprived of the oxygen necessary for its activity by the readily oxidizable aldehyde. The iron salt specifically inhibits this reaction and so prolongs the active life of the catalyst. 8. Using appropriate amounts of ferrous chloride and 0.23 g. of catalyst, it is shown that 21.2 g. of benzaldehyde may be smoothly reduced to the alcohol in 20 to 25 minutes. The reaction then stops and no further reduction takes place. A method is described for reducing 100 g. of benzaldehyde in 4 hours with 0.025 g. of catalyst. © 1923, American Chemical Society. All rights reserved.