Beiträge zur Reaktionskinetik der Cannizzaro‐Reaktion

Abstract

Ein Vergleich der 14C‐Isotopeneffekte bei der Verseifung von Benzoesäure‐benzylester und der Cannizzaro‐Reaktion mit Benzaldehyd führt zur Ablehnung eines intramolekularen Reaktions‐mechanismus. Für die Cannizzaro‐Reaktion des Benzaldehyds, p‐Chlor‐benzaldehyds und Thiophen‐aldehyds‐(2) wird der kinetische 3H‐Isotopeneffekt bestimmt. Die Reaktionsge‐schwindigkeit der Cannizzaro‐Reaktion des Benzaldehyds erhöht sich vom Lithiumhydroxid zum Cäsiumhydroxid. Für den Ablauf der Cannizzaro‐Reaktion nach III. Ordnung wird ein Chelatmechanismus vorgeschlagen.

Quantitative and qualitative 1H, 13C, and 15N NMR spectroscopic investigation of the urea–formaldehyde resin synthesis

“…There are several possible side reactions in the formaldehyde–water system of which the Cannizzaro reaction, yielding formic acid and methanol, is the most important (Section on Side Reactions in the UF System). Remaining from the production process and added as a stabilizer, aqueous formaldehyde solutions often also contain methanol. With methanol, formaldehyde forms the hemiformals of the oligomeric polyoxymethylene glycols.…”

The intramolecular Cannizzaro reaction of phthalaldehyde

“…[I], = [3] The activation parameter plot (of In k,T-l vs. T-') vielded values for AH* and AS* of 19.0 0.5 kcal + [4]). ' NO significant reaction of the monoanion -mO1-' and -1 1.4 f: 1.6 cal K-' mol-', respectively.…”

“…2 (see Scheme 1) can be detected under our condit i o n~.~ If the internal hydride transfer step in 5 is rate-limiting (with a first-order rate constant, k), then the rate of appearance of product is given by eq. [4] where K-, is the equilibrium constant for the very unfavorable ring opening of the cyclic hydrate [4] dianion. The rate is also given by equation [5] where kobs is the pseudo-first-order rate constant s-I, respectively.…”