Oxidation glycerol

B) A solution of 1 g. of dimedone (preparation, p. 277) in 10 ml, of ethanol. This solution will be required only for the glycerol oxidation experiment. 

Figure 3. Product composition vs. time Figure 4. Product composition vs. time for glycerol oxidation under basic for glycerol oxidation under acidic conditions on 5%Pd/C. conditions on 7%Pt3%Bi/C.

Figure 5. Composition vs. contact time for glycerol oxidation to dihydroxyacetone on 4%Ptl%Bi/C in a continuous reactor.

Au/C was established to be a good candidate for selective oxidation carried out in liquid phase showing a higher resistance to poisoning with respect to classical Pd-or Pt-based catalysts [40]. The reaction pathway for glycerol oxidation (Scheme 1) is complicated as consecutive or parallel reactions could take place. Moreover, in the presence of a base interconversion between different products through keto-enolic equilibria could be possible. 

Scheme 1. Reaction pathways for glycerol oxidation with Au/C in the presence of a base. (Reprinted from Ref. [40], 2004, with permission from Elsevier.)...

Ethyl sulfate Flammable liquids Fluorine Formamide Freon 113 Glycerol Oxidizing materials, water Ammonium nitrate, chromic acid, the halogens, hydrogen peroxide, nitric acid Isolate from everything only lead and nickel resist prolonged attack Iodine, pyridine, sulfur trioxide Aluminum, barium, lithium, samarium, NaK alloy, titanium Acetic anhydride, hypochlorites, chromium(VI) oxide, perchlorates, alkali peroxides, sodium hydride... 

In view of the use of glycerol as a chemical commodity for the production of chemical intermediates, an overview will be made of existing catalytic knowledge. More specifically, glycerol oxidation, dehydration, hydrogenolysis, oligomerization/polymerization, polyol formation, and formation of a few miscellaneous products will be dealt with. 

The aqueous phase air oxidation of glycerol with supported noble metal catalysts occurs under mild conditions (60 °C), but is very dependant on the pH of the reaction medium. Relevant data are shown in Fig. 11.3 [48], For Pd, Pt and Bi-promoted Pt the glycerol oxidation rate increases significantly with the pH of the medium, with Pd showing the lower activity. 

The Pt/C catalyst, compared with Pd/C, showed not only enhanced activity (vide supra) but also reduced selectivity for glyceric acid (only 55% at 90% conversion), favoring dihydroxyacetone formation up to 12%, compared with 8% for the Pd case [48]. The Pt/C catalyst promoted with Bi showed superior yields of dihydroxyacetone (up to 33%), at lower pHs. Glyceric and hydroxypyruvic acids, apparently, are formed as by-product and secondary product, respectively [48], The addition of Bi seems to switch the susceptibility of glycerol oxidation from the primary towards the secondary carbon atoms. 

In a second wave of activity in the area of glycerol oxidation with Pt or Pd-on-carbon catalysts, the high yields for glyceric add at 60 °C and atmospheric pressure described earlier, were initially no longer obtained by other authors. It seems that there is appreciable formation of compounds other than C3 and C2 oxidized... 

Scheme 11.11 Reaction scheme for glycerol oxidation with dioxygen on Au/C catalysts. (After [84]).

With aqueous H202, catalyzed glycerol oxidation has also been examined [52], With Ti, V- and Fe-substituted silicalite (TS-1, VS-1, FeSl) low conversion was obtained from 70 °C on. Formate esters of glycerol were dominant (60-80% selectivity) (Scheme 11.13), along with some hydroxyethanoic acid. 

As shown in Scheme 3.4, there are several reaction pathways of glycerol oxidation to form dihydroxyacetone, glyceric acid, hydroxypyruvic acid, mesoxalic acid, and so on. Dihydroxyacetone is formed by the oxidation of a secondary hydroxy group under... 

The Au-catalyzed glycerol oxidation was influenced by the kind of support, the size of Au particles and the reaction conditions such as concentration of glycerol, p02 and molar ratio of NaOH to glycerol. As metal oxide supports showed inferior selectivity to glyceric acid compared to carbons, due to successive oxidation and C—C bond cleavage to form di-adds such as tartronic acid and glycolic acid, research has focused on Au NPs supported on carbon, as in the case of ethylene glycol oxidation [182]. Indeed, the catalytic activity was influenced by the kind of carbon support in terms of porous texture [183]. 

Most recently, Taarning et al. reported that the fully oxidized ester dimethyl mesoxalate, which can be used as a monomer to yield poly(ketomalonate) [190], was produced by glycerol oxidation over Au/Ti02 and Au/Fe203 with 10% NaOCH3 in methanol with a seledivity of 89% at a full conversion [177]. Alcoholic media... 

Thus, the volume of water produced (ignoring the contribution of glycerol oxidation) is... 

Figure 2.2.12 Reaction network of glycerol oxidation (GLY, glycerol DHA, dihydroxyace-tone GLA, glyceric aldehyde GLS, glyceric acid HBT, hydroxypyruvic acid MOS, mesoxalic acid TS, tartronic acid GOX, glyoxal GOS, glycolic acid GYS, glyoxylic acid OS, oxalic acid).

Demirel S, Lehnert K, Lucas M, Claus P. Use of renewables for the production of chemicals glycerol oxidation over carbon supported gold catalysts. Appl Catal B Environ. 2007 70 637-43. 

Fig. 6.14. Selected reactions of network of the glycerol oxidation (adapted from...

VI, V2), for removal of phospholipids. The extracts are then introduced into the automated analsrtical system for carrying out saponification of triglycerides to glycerol, oxidation to formaldehyde, followed by condensation with diacetylacetone and ammonia to give a fluorescent product, 3,5-diacetyl-1,4-dihydrolutidine. 

The reaction pathway for glycerol oxidation, shown in Fig. 9.7 is complex and a considerable challenge exists if high selectivities to glyceric acid are to be obtained. 

---