Formation of polyols

The reaction of inulin with hydrogen gas in the presence of a catalyst results in cleavage, similar to the role of water in hydrolysis, and the formation of polyols such as glycerol, 1,2-propanediol, and ethylene glycol. Yields of up to 60% glycerol have been achieved (Fuchs, 1987). 

Reductions catalyzed by glycerol dehydrogenase, sorbitol dehydrogenase, mannitol dehydrogenase, and aldose reductases formation of polyols from carbohydrates. 

By the reaction of epoxidised vegetable oils with HCl, HBr or various organic acids (R-COOH), the epoxidic ring is opened with the formation of polyols having chlorohydrin, bromohydrin or hydroxyalkyl esters structures (reactions 17.17, 17.18 and 17.19) [31-34]. 

Polyurethane chemolysis can be performed by processes similar to those applied to PET. Thus, polyurethane glycolysis yields a mixture of polyols, which can be reused in the formulation of new polyurethanes. Likewise, polyurethane hydrolysis leads to the formation of polyols, diamines and carbon dioxide. The diamine can be subsequently transformed into the corresponding isocyanate by reaction with phosgene, whereas the polymer-... 

S. R. Sarfati and P. Szabo, Quantitative determination with periodate of compounds subject to non-Malapradian oxidation. Part III. Cyclohexanehexols, Carbohydr. Res., 11 (1969) 571-573. S. J. Angyal, D. Greeves, and V. A. Pickles, The stereochemistry of complex formation of polyols with borate and periodate anions, and with metal cations, Carbohydr. Res., 35 (1974) 165-173. 

Leino and Vogt [70] studied the hydroformylation-hemiacetal formation of polyols in an aqueous medium (Scheme 5.79). For example, the reaction with a rhodium catalyst based on Sulfoxantphos gave in water almost full conversion and excellent yield of the hemiacetal. The intermediary aldehyde could not be detected. Extraordinary results were likewise noted with a Xantphos catalyst under these conditions. 

The anionic forms of polyol complexes (derived from alcohob bearing three or more OH groups) are stabilized thermodynamically and are not prone to hydrolysis in aqueous solutions. They can easily be obtained at room temperature via interaction of sodium silicate with polyols, for example, sorbitol [26]. Formation of polyol complexes has been identified as possible mechanism in uptake and transport of silica for formation of endoskeletons in marine single-cell organisms such as diatoms. 

In the last 50 years, scientists have developed novel polymerization approaches, leading to new polymeric materials and applications, with the pace of new discoveries growing. This chapter provides an overview of this body of research, focusing on reactions involving covalent modification of double bonds to prepare monomers (particularly on the formation of polyols for employment as monomers for polyurethane synthesis), direct polymerization reactions between polyunsaturated acyl groups (eg, Diels-Alder, free radical, metathesis. 

As outhned in Fig. 3.1, the double bond is a useful moiety for modification of fatty acyl groups (as components of TAG, EEAs, or FAME) for their conversion into monomeric units useful for polymerization. Several of the reactions that involve formation of polyols (ie, the formation of II, III, Vn, VIII, and XV) will be discussed in a separate section below. Other, less common, modifications of fatty acids at double bond positions are reviewed elsewhere (Behr and Gomes, 2010). 

Protection/Deprotection. The acetylation of carbohydrates and other alcohols has been realized using Acetic Anhydride/ZnCh (eq 49). It is found that ZnCIa imparts selectivity to both acetylation and acetonide formation of polyols, which is useful in the synthetic manipulation of carbohydrates. Synthetically useful selective deprotection of acetates (eq 50) ... 

The main transformations of sorbitol include dehydrogenation of the substrate on the metal sites followed by a decarbonylation step (Path 1) and dehydration on acidic sites (Path 2), followed by hydrogenation. Path 1 leads to formation of polyol species containing one carbon atom fewer than the initial substrate, whereas Path 2 results in formation of hydrocarbons. The first initial step of dehydration can be considered as the rate determining step, while the subsequent fast steps of... 

Conversion to acetates, trifluoroacetates (178), butyl boronates (179) trimethylsilyl derivatives, or cycHc acetals offers a means both for identifying individual compounds and for separating mixtures of polyols, chiefly by gas—Hquid chromatography (glc). Thus, sorbitol in bakery products is converted to the hexaacetate, separated, and determined by glc using a flame ionisation detector (180) aqueous solutions of sorbitol and mannitol are similarly separated and determined (181). Sorbitol may be identified by formation of its monobensylidene derivative (182) and mannitol by conversion to its hexaacetate (183). 

The steric effects in isocyanates are best demonstrated by the formation of flexible foams from TDI. In the 2,4-isomer (4), the initial reaction occurs at the nonhindered isocyanate group in the 4-position. The unsymmetrically substituted ureas formed in the subsequent reaction with water are more soluble in the developing polymer matrix. Low density flexible foams are not readily produced from MDI or PMDI enrichment of PMDI with the 2,4 -isomer of MDI (5) affords a steric environment similar to the one in TDI, which allows the production of low density flexible foams that have good physical properties. The use of high performance polyols based on a copolymer polyol allows production of high resiHency (HR) slabstock foam from either TDI or MDI (2). 

The formation of isocyanurates in the presence of polyols occurs via intermediate aHophanate formation, ie, the urethane group acts as a cocatalyst in the trimerization reaction. By combining cyclotrimerization with polyurethane formation, processibiUty is improved, and the friabiUty of the derived... 

The synthesis of the polyol glycoside subunit 7 commences with an asymmetric aldol condensation between the boron enolate derived from imide 21 and a-(benzyloxy)acetaldehyde (24) to give syn adduct 39 in 87 % yield and in greater than 99 % diastereomeric purity (see Scheme 8a). Treatment of the Weinreb amide,20 derived in one step through transamination of 39, with 2-lithiopropene furnishes enone 23 in an overall yield of 92 %. To accomplish the formation of the syn 1,3-diol, enone 23 is reduced in a chemo- and... 

When hydrogenolysis of vinylepoxides is used sequentially, it allows for the controlled formation of 1,3-polyols. In the synthesis of the C11-C23 fragment 92 of preswinholide A, hydrogenolysis of ( ) olefin 93 gave the syn isomer 94 (Scheme 9.37) [159]. Methylation, reduction, epoxidation, oxidation, and olefmation of this material then gave vinylepoxide 95, which was subjected to hydrogenolysis to afford 96 in excellent yield. Repetition of this sequence ultimately afforded the desired derivative 94. 

The ATO Chemie process involves the formation of an adipic acid-capped hard segment block of poly(ll-aminoundecanoic) of molecular weight 800-1500, joined with a soft segment of polyol in a polyesterification process. 

Polyethercyclicpolyols possess enhanced molecular properties and characteristics and permit the preparation of enhanced drilling fluids that inhibit the formation of gas hydrates prevent shale dispersion and reduce the swelling of the formation to enhance wellbore stability, reduce fluid loss, and reduce filter-cake thickness. Drilling muds incorporating the polyethercyclicpolyols are substitutes for oil-based muds in many applications [195-197,1906,1907]. Polyethercyclicpolyols are prepared by thermally condensing a polyol, for example, glycerol to oligomers and cyclic ethers. 

Entry 10 was used in conjunction with dihydroxylation in the enantiospecific synthesis of polyols. Entry 11 illustrates the use of SnCl2 with a protected polypropionate. Entries 12 and 13 result in the formation of lactones, after MgBr2-catalyzed additions to heterocyclic aldehyde having ester substituents. The stereochemistry of both of these reactions is consistent with approach to a chelate involving the aldehyde oxygen and oxazoline oxygen. 

It is known that boronic acids can bind with hydroxyl compounds, including polyols such as PVA, through the complex formation of a reversible covalent bonding [56, 57]. 

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