Polyglycerols

Mixtures of glycerol with other substances are often named as if they were derivatives of glycerol eg, boroglycetides (also called glyceryl borates) are mixtures of boric acid and glycerol. Derivatives, such as acetals, ketals, chlorohydrins, and ethers, can be prepared but are not made commercially, with the exception of polyglycerols. 

By the enzymatic esterification of diglycerol with lauric acid, the corresponding monolaurate ester is obtained [84]. This is an important industrial reaction for the cosmetic, pharmaceutical and feed industries, since this ester is used as biodegradable non-ionic surfactant. In recent years, the synthesis of this and other polyglycerols with fatty acids has attracted growing interest in industry, leading also to a demand for enantiomerically and isomerically pure products. 

Fig. 11 Structures of three polyglycerol-based nonionic surfactants used in the preparation of nionsomes ( represents an average number value of glycerol units).

The Clauson-Kaas pyrrole synthesis was adapted to a soluble polyglycerol (PG) support <060L403>. Electrochemical oxidation of furan 33 in the presence of methanol followed by hydrogenation gave 2,5-dimethoxytetrahydrofuran 34. Cyclocondensation with primary arylamines gave A-arylpyrroles 35. Removal from the PG support was then accomplished by treatment of 35 with LiOH which gave 2-pyrrolepropanoic acids 36. 

Scheme 9. (A) Different dendrimers as macromolecular scaffolds for MRI contrast agents ethylenediamine cored polyamido amine, generation 4 (PAMAM G4), top hyperbranched, ethylenediamine cored polyethylene imine (HB-PEI), bottom left hyperbranched, amino functionalized polyglycerol (HB-PG), bottom right. (B) Different moieties attached to the respective dendrimers via amide or thiourea bonds.

E 475 Polyglycerol esters of fatty acids E 476 Polyglycerol polyricinoleate E 477 Propane-1,2-diol esters of fatty acids E 479b Thermally oxidised soya bean oil interacted with mono- and diglycerides of fatty acids E 481 Sodium stearoyl-2-lactylate... 

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. 

Table 4.6 Properties of selected polyglycerol esters as emulsifiers for personal care and food technology.

Polyglycerol polyridnoleate (E 476) Polymuls PGPR Food — emulsifier... 

Today, glycerol has over 2000 different applications, in cosmetics, pharmaceutics, foods and drinks, tobacco, paper, inks and printing colors, the production of phthalic and maleic alkyd resins and crosslinked polyesters, and as a hydraulic agent. Polyglycerols have a wide range of applications as emulsifiers, and technical esters of glycerol with fatty acids are used as synthetic lubricants [4]. 

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