Reactivity of glycerol/acetone ketal (solketal) and glycerol/formaldehyde acetals toward acid-catalyzed hydrolysis

• Autor(a) principal: Ozorio,Leonardo P.
• Data de Publicação: 2012
• Outros Autores: Pianzolli,Rafael, Mota,Maria Beatriz S., Mota,Claudio J. A.
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Journal of the Brazilian Chemical Society (Online)
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532012000500019
• topic: glycerol; biodiesel; hydrolysis; solketal; acetals

The effect of temperature, molar ratio and catalyst loading on the acid-catalyzed hydrolysis of glycerol/acetone ketal (solketal) and glycerol/formaldehyde acetals was studied. The reactivity of the solketal was significantly higher than the glycerol/formaldehyde acetals. At 80 ºC, 5:1 water/ketal molar ratio and 3.0 mmol of catalyst loading (amberlyst-15) the hydrolysis of the solketal was almost complete, whereas the glycerol/formaldehyde acetals showed around 40% conversion. The higher reactivity of solketal toward hydrolysis is associated with the formation of a tertiary carbocation intermediate, whereas in the case of glycerol/formaldehyde acetals hydrolysis takes place through direct nucleophilic displacement. DFT theoretical calculations of the relative stability of the ketal and acetal isomers, having five and six-membered rings, explain the experimental distribution.