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Propanediol Production from Glycerol
Published in Ozcan Konur, Biodiesel Fuels, 2021
Akiyama et al. (2009) study the vapor-phase reaction of glycerol over copper metal catalysts at an ambient hydrogen pressure in a paper with 133 citations. They convert glycerol into 1,2-PD through dehydration into hydroxyacetone, followed by hydrogenation into 1,2-PD. The yield of 1,2-PD was limited up to 80% at a constant temperature of 190°C because of a trade-off problem between the dehydration and the hydrogenation. Dehydration needs relatively high reaction temperatures, whereas hydrogenation favors low temperatures and a high hydrogen concentration. They developed an efficient process during which glycerol was converted into 1,2-PD with a yield higher than 96% in the hydrogen flow at gradient temperatures; the dehydration into hydroxyacetone was catalyzed at ca. 200°C, and the following hydrogenation into 1,2-PD was completed at ca. 120°C. The developed process controls the thermodynamic equilibrium of second-step hydrogenation.
Catalytic Hydrothermal Reactions for Small Molecules Activation
Published in Fangming Jin, Hydrothermal Reduction of Carbon Dioxide to Low- Carbon Fuels, 2017
Further quantum chemistry calculations reveal that the key step in the whole process [51–53], from hydroxyacetone and bicarbonate to pyruvaldehyde and formate, is composed of two elementary steps (see Figure 2.2). The first step (step 1) is the deprotonation of the –OH group in hydroxyacetone by bicarbonate. This step would produce CH3COCH2O− and release CO2 molecules. The second step (step 2) proceeds in a way that one hydrogen in the –CH2O− group attacks the carbon on CO2 by nucleophilic addition to form pyruvaldehyde and formate. CH3COCH2O− is first suggested by theoretical calculation to be the key intermediate of reducing CO2. The role of bicarbonate can be concluded into two aspects: (1) to deprotonate the –OH group in hydroxyacetone as a base and (2) to release CO2 molecules to be reduced in the second step. As can be seen from Figure 2.2, the estimated activation barriers (13.2 and 18.0 kcal/mol) are easy to overcome under hydrothermal conditions and are quite different from the apparent activation energy (41 kcal/mol). This result suggests that the rate-determining step of this process is some step before hydroxyacetone reduction or after pyruvaldehyde formation. Therefore, the optimal catalyst (base) should be searched to accelerate the conversion of glycerol to hydroxyacetone or pyruvaldehyde to lactate. Principally, the basicity of medium is critical to determine the selectivity. If the base is too strong, another pathway will be favored more [52]. If the base is too weak, hydroxyacetone or lactate may not be formed readily.
Biocatalysts: The Different Classes and Applications for Synthesis of APIs
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
As many aldolases are strictly dependent on the rather costly and instable donor DAHP (see, e.g., Suau et al., 2006), alternatives have been looked for. Examples are a phosphorothioate analogue (Duncan and Drueckhammer, 1996) or an in situ generation of DAHP starting from inexpensive and commercially available rac-glycidol epoxide (Charmantray et al., 2006); in some cases, it could be demonstrated that DHAP-dependent aldolases accept dihydroxyaceton instead of DHAP as a donor substrate in case that borate (Sugiyama et al., 2006) or arsenate arsenate (Schoevaart et al., 2001) were present. A breakthrough came with the detection of fructose-6(six)-phosphate aldolase (FSA) through an investigation of the open reading frames of E. coli by Schürmann and Sprenger (2001). FSA consists of 10 identical subunits each with 220 aa residues, forming ring-like pentamers, that are arranged to a decameric structure. The subunits fold into an α/β barrel with the catalytic Lys85 residue located on a barrel strand β4; Thorell et al. (2002) solved the crystal structure at 1.93 Å resolution. The enzyme uses dihydroxyacetone (DHA) as donor but hydroxyacetone (HA), 1-hydroxy-2-butanone (HB), glycolaldehyde (GA) and acetone are also accepted with HA showing the best performance. For a recent review, see Samland and Sprenger (2014). FSAs are evolutionary closer related to transaldolases belonging to the enzyme class of transferases, than to DHAP-dependent aldolases. Furthermore, glycine-dependent aldolases are known and 2-deoxyribose-5-phosphate aldolases (DERAs) that work with acetaldehyde as donor are able to catalyze a sequential aldol reaction resulting, e.g., in the formation of 2,4-dideoxyhexose derivatives (see below).
Chemical characterization of nanoparticles and volatiles present in mainstream hookah smoke
Published in Aerosol Science and Technology, 2019
Véronique Perraud, Michael J. Lawler, Kurtis T. Malecha, Rebecca M. Johnson, David A. Herman, Norbert Staimer, Michael T. Kleinman, Sergey A. Nizkorodov, James N. Smith
Mass spectra from control experiments, which include experiments performed without any tobacco (charcoal + water only), with the conventional tobacco but no charcoal (no heat) and only glycerol (replacing the tobacco) are given in SI Figure S8. The major common ions (nominal m/z 43, 45, 57, 61, and 75) observed in the waterpipe mainstream smoke were common to all spectra, including that of glycerol (propane-1,2,3-triol). Upon thermal decomposition, glycerol has been reported to form not only two major products, namely acetaldehyde (C2H4O, MW = 44 g mol−1) and acrolein (C3H4O, MW = 56 g mol−1), but also 3-hydroxypropanal (C3H6O2, MW = 74 g mol−1), 1-hydroxypropan-2-one (C3H6O2, MW = 74 g mol−1), hydroxyacetone (or acetol; C3H6O2, MW = 74 g mol−1), glycolaldehyde (C2H4O2, MW = 60 g mol−1), and acetic acid (C2H4O2, MW = 60 g mol−1) (Corma et al. 2008; Hemings et al. 2012; Jensen, Strongin, and Peyton 2017; Katryniok et al. 2010; Martinuzzi et al. 2014; Nimlos et al. 2006). Ionization of these compounds in the PTR-ToF-MS ion source would give the observed [M + H]+ ions. Both acetic acid and glycolaldehyde are known to fragment under typical PTR-MS conditions such as the ones applied here, to give an additional fragment at m/z 43.018 (C2H3O+) (Baasandorj et al. 2015). Though, acetic acid is thought to be formed from secondary oxidation process (Jensen, Strongin, and Peyton 2017; Katryniok et al. 2010), it is more likely that the peaks at m/z 61/43 are due to glycolaldehyde instead. Further evidence for this assignment is the presence of a minor peak at m/z 91.039 attributed to glyceraldehyde (SI Figure S7), which was previously proposed as an intermediate in the decomposition process of glycerol leading to glycolaldehyde. (Jensen, Strongin, and Peyton 2017).