Bifunktionelle Katalyse und Mechanismus der Monomethylol-Bildung aus Harnstoff und Formaldehyd in Wasser

✍ Scribed by P. Eugster; H. Zollinger

• Publisher: John Wiley and Sons
• Year: 1969
• Tongue: German
• Weight: 753 KB
• Volume: 52
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19690520723

✦ Synopsis

1. The thirtl-ortlcr catalytic rate constants of the reaction of formaldehyde with urea with 5 gcncral acid-base catalysts in aqucous solution wcrc mcasurcd polarographically in the temperaturc range 30 -45 '.

(2) T h e catalytic constants obtained with hytlrogcncarbonatc, primary and secondary phosphate arc higher than expcctcd on the basis of the BRONSTED relationship. The activation entropies for the reactions with these catalysts are 15 to 20 entropy units lower than those with the water molecule and thc hydroxyl ion as catalysts.

(3) These observations indicate a bifunctional catalysis with a cyclic rate-dctermining transition state by the three firstmentioned catalysts. It is postulated that with mono-and bifunctional catalysts no tcrmolecular collison step takes place, but first a hydrogen-bonded complex of thc general acid catalyst with formaldehyde or the gcncral basc with urca is formed. B , ,L)ie in dicser Arbeit (S. 1990) diskutiertc Moglichkcit dcs Aufti-etcns weitcrer, inctastabiler Z?;ischciiprotfukte ist in der Figur vzzrht berucksichtigt.