Polyhydric alcohols, synthesis

Polyhydric Alcohols. The principal types of polyol used in alkyd synthesis are shown in Table 3. 

SYNTHESIS OF HEXITOLS AND PENTITOLS FROM UNSATURATED POLYHYDRIC ALCOHOLS... 

The system is not limited to the use of synthesis gas as feed. Mixtures of carbon dioxide and hydrogen also give rise to the formation of polyhydric alcohols, and it is also claimed that the reaction mixture can consist of steam and carbon monoxide (62). This latter claim is consistent with the presence of C02 in the reaction mixture when CO/H2 is used as feed [infrared data (62)], and suggests that these ionic rhodium systems are also active catalysts for the water gas-shift reaction (vide infra). 

In the absence of a catalyst, the reaction between a polyhydric alcohol and a carbonyl compound may proceed only as far as the formation of a semi-acetal 14 however, if water is removed as it is produced in the reaction mixture, the true acetal is obtained. For example, azeotropic distillation with a water-immiscible liquid, such as benzene, toluene or xylene, has been employed in the synthesis of butylidene, methylene and furfurylidene acetals.15 In the latter case, this technique is particularly useful because of the marked instability of furfuraldehyde under acidic conditions.15... 

From these findings with triols, it follows that, apart from the expectation that formation of five- and six-membered rings would be favored (see, however, the exceptional compound 19), no general conclusions can be drawn regarding the structures of boronates derived from more-complex polyhydric alcohols. In Table V, alditol boronates are listed with structures when these can be concluded either from the method of synthesis, from physical studies, or by deduction (as with the 1,2 5,6-diesters formed from 3,4-di-O-substi-tuted mannitols). 

Consider the simple alkyd recipe shown in Table 5-1, part (i). Alkyds are polyesters produced from polyhydric alcohols and polybasic and monobasic acids. They are used primarily in surface coatings. The ingredients of these polymers contain polyfunctional monomers and it is possible that such polymerizations could produce a thermoset material during the actual alkyd synthesis. This is of course an unwanted outcome, and calculations based on the Carothers equation can be used to adjust the polymerization recipe to produce a finite molecular weight polymer in good yield. The recipe can also be adjusted to provide other desirable characteristics of the product, such as an absence of free acid groups which may react adversely with some pigments. 

Many simple alcohols are important raw materials in the industrial synthesis of polymers, fibers, explosives, plastics, and pharmaceutical products. Phenols are widely used in the preparation of plastics and dyes. Solutions of phenols are used as antiseptics and disinfectants. Some uses of polyhydric alcohols depend on their relatively high boiling points. For instance, glycerine is used as a wetting agent in cosmetic preparations. Ethylene glycol (bp 197°C), which is miscible with water, is used in commercial permanent antifreeze. 

Approximately 65% of the PO produced is used for the synthesis of polyether polyols (in a reaction with polyhydric alcohols), one of the main components used in the manufacture of polyurethanes, propene glycol (20%), glycol ethers (5%) and butanediol, amongst others. Figure 6.1 shows an overview of the PO industry. 

Cyclic acetals, from carbonyl compounds and polyhydric alcohols, are formed with particular ease 913 their synthesis follows in general that of acetals of monohydric alcohols. 

The different reactivity of the aliphatic and cycloaliphatic epoxy groups in ACECs can be used for the synthesis of functionalized compounds with the cycloaliphatic epoxy groups preserved. As an example, an epoxy group containing polyhydric alcohol XLVII is presented (Scheme 62). The epoxy polyol XLVII was applied for the modification of isocyanates on purpose to obtain flexible coatings with good protective properties. 

Wright, L.W. and Brandner, J.D. (1964) Catalytic isomerization of polyhydric alcohols. II. The isomerization of isosorbide to isomannide and isoidide. Journal of Organic Chemistry, 29 (10), 2979-2982. Wu, J. (2012) Carbohydrate-Based Building Blocks and Step-growth Polymers Synthesis, Characterization and Structure-Property Relations. PhD thesis, Eindhoven Technical University. 

Glycerol is the polyhydric alcohol most widely used for the preparation of alkyd resins and is obtained both synthetically and as a by-product in the manufacture of soap. The principal methods for the synthesis of glycerol are based on either the chlorination or oxidation of propylene. In the former methods, the first step is the hot chlorination of propylene to give allyl chloride ... 

Alkyd resins completely based on renewable resources have been the subject of a few studies. EP 0741 175 A2 to Hoechst describes waterborne alkyd emulsions based on renewable resources. The patent describes the use of sorbitol (easily derived from starch) as the polyhydric alcohol part and succinic acid anhydride as the polycarboxylic acid part. Hajek described the use of sorbitol and xylitol in alkyd resin synthesis, whereas Bagchi et al. described the partial replacement of conventional polyols, i.e., glycerol and pentaerythritol, by sorbitol. 

---