Glycerol dehydration

Therefore, the observed process (I) could be related to the cooperative dynamics of glycerol in the supercooled phase, while process (II) is most likely related to the crystalline phase of glycerol and is the result, similar to water, of the mobility of defects in the crystalline lattice [200]. The temperature dependence of the relaxation time for dehydrated glycerol is compared in Fig. 23 with those for the usual behavior of glycerol, which has absorbed some water from the atmosphere. 

The application of glycerol is based on the hygroscopic properties. The suggested pharmacotherapeutic action is by the lowering of the pressure in the middle ear by dehydration. Glycerol has preservative properties at concentrations >30 %. 

Dubois JL, Duquenne C, Hoelderlich W. Process for dehydrating glycerol to acrolein. WO 2006087083 2006. 

When a mixture of aniline, nitrobenzene, glycerol and concentrated sulphuric acid is heated, a vigorous reaction occurs with the formation of quinoline. It is probable that the sulphuric acid first dehydrates the glycerol giving acrolein or acraldehyde (A), which then condenses at its double bond with the amino group of the aniline to give acrolein-aniline (B), The latter in its enol... 

Place 24 ml. (24 5 g.) of aniline, 13 ml. (15 5 g.) of nitro-benzene,t and 62 ml. (75 g.) of the anhydrous glycerol in the flask and mix thoroughly. (If the glycerol is still warm from the dehydration, cool the mixture in water.) Now add slowly 36 ml. (66 g.) of concentrated sulphuric acid, shaking the mixture thoroughly during the addition. The mixture at first... 

I. Acrolein test. Heat 0-5 ml. with about i g. of finely powdered KHSO4. Acrolein, CH2 CH CHO, produced by dehydration of the glycerol, is readily detected by its characteristic and irritating odour smell cautiously). 

If the approximate water content of commercial glycerol is known, the above dehydration may be avoided by adding sufficient SO, in the form of oleum to the concentrated sulphuric acid employed in the Skraup reaction to combine with all the water present. 

By substituting paraldehyde for glycerol, 2-methylquinoline [27601-00-9] may be synthesized. The Skraup synthesis is regarded as an example of the broader Doebner-von Miller synthesis. In the case of the Skraup synthesis, the glycerol undergoes an acid-catalyzed dehydration to provide a small concentration of acrolein that is the reactive species. If acrolein itself is used as a reactant, it would polymerize. Crotonaldehyde is the reactive intermediate in the Doebner-von Miller synthesis (28). 

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 ... 

The acid occurs both as colorless triclinic prisms (a-form) and as monoclinic prisms ( 3-form) (8). The P-form is triboluminescent and is stable up to 137°C the a-form is stable above this temperature. Both forms dissolve in water, alcohol, diethyl ether, glacial acetic acid, anhydrous glycerol, acetone, and various aqueous mixtures of the last two solvents. Succinic acid sublimes with partial dehydration to the anhydride when heated near its melting point. 

The glycerol is dehydrated by heating slowly in an an open dish in a hood until the temperature of the liquid is 170°. A... 

For the Skraup synthesis, glycerol 2 is used as starting material in the presence of concentrated sulfuric acid (see scheme above) it is dehydrated to acrolein 6. Although it is assumed that the reactive carbonyl component in the Skraup reaction actually is acrolein, attempts to use acrolein directly, instead of glycerol, proved to be unsuccessful." ... 

Several methods and reaction pathways have been reported for the conversion of glycerol in the literature, such as etherification, esterification [1], and oxidation [2], Via ionic dehydration acetol [3] and acrolein can be produced. The radical steps result in aldehydes, allyl alcohol, etc. [4], If the dehydration is followed by a hydrogenation step, propanediols (1,2- or 1,3-) can be obtained [5-6]. 

Van Ruymbeke (2) A process for dehydrating 95 percent aqueous ethanol by counter-current extraction of the vapor with glycerol. 

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. 

Acrolein has been obtained in 38% yield by glycerol dehydration at 360 °C, 25 MPa in the presence of zinc sulfate [64]. 

TBA and isobutene have been compared as the etherifying agent at 60 °C. The initial molar ratio of isobutene to glycerol was 4.0 with Amberlyst A35 as the catalyst. The conversion of glycerol is lower when etherified with TBA than when etherified with isobutene. More hydrocarbons are formed with isobutene than with TBA. But, with TBA, mainly monoethers are formed and valuable triethers are formed only in small amounts. In addition, TBA dehydrates to water, which has an inhibition effect on ion-exchange resin catalysts [23],... 

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. 

Some homogeneous metal catalysts have been examined in the production of acrolein from glycerol [20], However, considering all reaction components present, it is more likely that soluble acids, such as HC1 and CF3SO3H, are responsible for glycerol dehydration instead of Pt and Pd phosphine complexes. 

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