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

Abstract

Foi investigado o efeito da temperatura, razão molar e quantidade de catalisador na hidrólise ácida do cetal de glicerol/acetona (solketal) e acetais de glicerol/formaldeído. A reatividade do solketal foi bem maior que a dos acetais de glicerol/formaldeído. A 80 o C, 5:1 de razão molar água/ cetal e uma quantidade de catalisador correspondendo a 3.0 mmol de sítios ácidos (amberlyst-15), a hidrólise do solketal foi praticamente quantitativa, enquanto os acetais de glicerol/formaldeído apresentaram cerca de 40% de conversão. A maior reatividade do solketal para hidrólise pode ser associada à formação de um carbocátion terciário como intermediário, enquanto no caso dos acetais de glicerol/formaldeído a hidrólise acontece via deslocamento nucleofílico direto. Cálculos teóricos no nível DFT sobre a estabilidade relativa dos acetais e cetais com anéis de cinco e seis membros explicam a distribuição experimental dos isômeros.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 o C, 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. Keywords: glycerol, biodiesel, hydrolysis, solketal, acetals IntroductionBiodiesel is one of the main biofuels used worldwide. It is produced through the transesterification of vegetable oils or animal fat with methanol, under base catalysis conditions.1 In this process, glycerol or glycerin is formed as byproduct in approximately 10 wt%. The overall world production of glycerin from biodiesel processing is estimated to reach 1.2 million tons by 2012, 2 but the forecast points to a much higher value in the future, due to the widespread production of this biofuel.In Brazil, biodiesel is presently blended with the petrodiesel in 5% (v/v), yielding approximately 250 thousand tons of glycerin per year. This value is much higher than the glycerin market in Brazil, in the order of 30 thousand tons per year, and it is imperative to the economical feasibility of the biodiesel program to drain this excess of glycerin. Personal care products, soaps, pharmaceuticals and foods are the main sectors that make regular use of glycerin. However, they cannot absorb, alone, all the glycerin produced from the biodiesel industry. Thus, it is necessary to find new applications for this excess of glycerin produced by the biodiesel industry.The use ...

Synthesis, Characterization and Catalytic Performance of a Novel Picolinic Acid-12-Molybdophosphoric Acid Hybrid Catalyst

“…In PI-HPM, there exists one classical Keggin 2 ] coordination moiety, each molybdenum cation was coordinated by two terminal oxygen atoms, one oxygen atom from one water molecule, one bridging oxygen atom, and finally chelated by one PI anion through its nitrogen and carboxylate oxygen atoms. These two molybdenum centers were linked to each other by the bridging oxygen atom to form a dinuclear coordination moiety.…”

“…[1][2][3][4][5] Conventional acid catalysts that are widely used in industries are mineral acids, such as H 2 SO 4 , H 3 PO 4 , HCl, CF 3 COOH and ClSO 2 OH. 6,7 These liquid acids have excellent catalytic activities, but they suffer from several drawbacks, such as the corrosiveness, the existence of side reactions and difficulty of separation from the reaction mixtures.…”

“…17,18 Therefore, supported HPAs and salts of HPAs are developed to overcome the abovementioned problems. [2][3][4][17][18][19][20] Although these technologies can obviously improve the separation problem of HPAs from reaction system, the acid strength of supported HPAs and salts of HPAs was commonly lower than that of bulk HPAs. 21 The supported HPAs materials also suffered from the leaching of HPAs active species in polar reaction media.…”

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2 ] coordination moiety, the protonated HPI and the lattice water molecules. Then PI-HPM was employed as heterogeneous catalyst for esterification reaction to evaluate its acid-catalytic activity.

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Atmospheric Pressure Continuous Production of Solketal from the Acid-Catalyzed Reaction of Glycerol with Acetone

“…Therefore, it can be a potential oxygenated gasoline additive, reducing gum formation and improving the octane number. In addition, solketal is easily hydrolyzed in excess water, 24 indicating that it will not contaminate water sources, as methyl-tert-butyl ether (MTBE) does, and this has been the main reason for this additive to be phased out, because it shows carcinogenic properties. 25 Continuing our interest on the development of continuous-flow protocols, 26 we wish to report an atmospheric pressure continuous flow study for the production of solketal, by the acid-catalyzed ketalization of glycerol (Scheme 1).…”