Dehydration of glycerol

Dijbner-von Miller Synthesis. A much less violent synthetic pathway, the Dn bner-von Miller, uses hydrochloric acid or 2inc chloride as the catalyst (43). As in the modified Skraup, a,P-unsaturated aldehydes and ketones make the dehydration of glycerol uimecessary, and allow a wider variety of substitution patterns. No added oxidant is required. With excess aniline the reaction proceeds as follows ... 

Polyglycerols obtained by the dehydration of glycerol (Scheme 3.7) are employed as surfactants, lubricants, cosmetic, food additives, etc. Their esterification with fatty acids leads also to valuable emulsifiers or metal-working fluids. Zeolites have been used to take advantage of their shape selectivity effect to minimize oligomer formation, as described in two patents [61, 62]. A fair compromise between activity and selectivity has been obtained by Clacens et al. [63] using cesium-impregnated mesoporous MCM-41. 

Scheme 3 Acrolein can be obtained by dehydration of glycerol. The reaction was reported many years ago using powdered KHSO4/K2SO4 as catalyst. Recently, the use of silica-supported heteropolyacids has also been described, notably with silicotungstic acid as catalyst.

Shigematsu et al. (3) prepared aliphatic polymers containing ketone and ether components in the main chain, (III), by the dehydration of glycerol followed by treatment with 1,10-decane diol and sulfuric acid at 165°C. 

Gas-phase oxidation of glycerol has been less investigated than liquid-phase oxidation it occurs via a two-step catalyzed reaction involving first the dehydration of glycerol into acrolein, catalyzed by an acid, and then its oxidation. The same reactions can be conducted in two distinct reactors, in which the first step can be carried out with an acid catalyst such as phosphoric acid over alumina [107]. Then acrolein is oxidized to acrylic acid with a conventional alumina-supported Mo/V/Cu/O catalyst. 

Arkema has recently issued patents on the gas-phase dehydration of glycerol to acrolein and on the oxidation of glycerol to acrylic acid [ 107]. The dehydration can be carried out at 300 ° C, with a Zr02/W03 catalyst the conversion of glycerol is total, and the yield to acrolein is 72%, when a feed made of an aqueous solution of glycerol (20%) is used. The addition of 02 in the feed stream has the effect of yielding also the formation of acrylic acid (4.5%), and of lowering the yield to acrolein. 

The penultimate enzyme in the pathway, glycerol dehydratase (E. C. 4.2.1.30), catalyzing the dehydration of glycerol to 3-hydroxypropionaldehyde, is a vitamin B12-dependent, cyanocobalamin-containing enzyme, which employs a radical... 

Another important bulk chemical that could be derived from glycerol is acrylic acid (Craciun et al., 2005 Shima and Takahashi, 2006 Dubois et al., 2006). Shima and Takahashi (2006) reported a complete process for acrylic acid production involving the steps of glycerol dehydration in a gas phase followed by the application of a gas phase oxidation reaction to a gaseous reaction product formed by the dehydration reaction. Dehydration of glycerol could lead to commercially viable production of acrolein, which is an important and versatile intermediate for the production of acrylic acid esters, superabsorber polymers or detergents (Ott et al., 2006). Sub- and supercritical water have been applied by Ott et al. (2006) as the reaction media for glycerol dehydration, but the conversion and acrolein selectivities that have been achieved so far are not satisfactory for an economical process. 

Ott, L., Bicker, M. and Vogel, H. 2006. Catalytic Dehydration of Glycerol in Sub- and Supercritical Water A New Chemical Process for Acrolein Production. Green Chem., 8, 214-220. 

Acrolein Zirconium and niobium mixed oxides have been shown to catalyze the dehydration of glycerol to acrolein, at 300°C in the presence of water with high selectivity (72%) at nearly total glycerol conversion [50]. Silica-supported niobia catalysts can also be used with similar catalytic performance [51]. Catalytic results for small-sized H-ZSM 5 zeolites showed that the high density of Bronsted acid sites favors acrolein production [52]. Acrolein production from glycerol has also been carried out in subcritical water at 360°C and 34 MPa with catalytic quantities of ZnS04 (791 ppm [g/g]) [52],... 

Jia CJ, Liu Y, Schmidt W, Lu AH, Schiith F. Small-sized HZSM-5 zeolite as highly active catalyst for gas phase dehydration of glycerol to acrolein. J Catal. 2010 269 71-9. 

Dehydration of glycerol by hot sulfuric acid to yield the unsaturated aldehyde acrolein ... 

Problem 31.22 The dehydration of glycerol to yield acrolein involves acid-catalyzed dehydration and keto-enol tautomerization. Outline the possible steps in the dehydration. (// / / Which OH is easier to eliminate, a primary or a secondary )... 

Quinolines are commonly synthesized by a method known as the Skraup synthesis, which involves the reaction of aniline with glycerol under acidic conditions. Nitrobenzene is added to the reaction mixture to serve as an oxidizing agent. The first step in the synthesis is the dehydration of glycerol to propenal. 

Fig. 2.6. Mechanism for the formation of acrolein by double dehydration of glycerol...

Catalytic dehydration of glycerol to acrolein in gas phase (precursor of acrylic acid) H-ZSM-5, H-ZSM-11, H-P Glycerol conversions of 100% and selectivities in the range of 80% at temperatures 330-360 C [61]... 

Diol dehydratase (DD) and glycerol dehydrates (GD) are isofunctional enzymes that catalyze the dehydration of glycerol, ethane-1,2-diol and propane-1,2-diol to 3-hydroxypropanal, acetaldehyde and propanal, respectively (other glycols can be dehydrated in an analogous fashion) [210] (see Fig. 19). DD has about a twofold preference for propane-1,2-diol to glycerol, whereas GD prefers glycerol to propane-1,2-diol as a substrate [178]. Conversion of glyc-... 

Dehydration of glycerol with KHSO4, AI2O3, or H3PO4 at about 190°C (obsolete method). 

Scheme 4.34 Reaction mechanism for the catalytic dehydration of glycerol to...

A multi-bed catalytic reactor is also claimed for the production of acrylic acid in which propene, glycerol and air are co-fed to the reactor. The first bed serves for the dehydration of glycerol to acrolein, the second bed for the oxidation of propene to acrolein, and the third bed for the oxidation of acrolein to acrylic acid [108c, e]. 

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