Hydrogenation 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). 

Hydrogen iodide not only esterifies polyhydric alcohols but also reduces them. Thus glycerol passes by way of 1 2 3-triiodopropane into isopropyl iodide ... 

Mannitol hexanitrate is obtained by nitration of mannitol with mixed nitric and sulfuric acids. Similarly, nitration of sorbitol using mixed acid produces the hexanitrate when the reaction is conducted at 0—3°C and at —10 to —75°C, the main product is sorbitol pentanitrate (117). Xylitol, ribitol, and L-arabinitol are converted to the pentanitrates by fuming nitric acid and acetic anhydride (118). Phosphate esters of sugar alcohols are obtained by the action of phosphorus oxychloride (119) and by alcoholysis of organic phosphates (120). The 1,6-dibenzene sulfonate of D-mannitol is obtained by the action of benzene sulfonyl chloride in pyridine at 0°C (121). To obtain 1,6-dimethanesulfonyl-D-mannitol free from anhydrides and other by-products, after similar sulfonation with methane sulfonyl chloride and pyridine the remaining hydroxyl groups are acetylated with acetic anhydride and the insoluble acetyl derivative is separated, followed by deacetylation with hydrogen chloride in methanol (122). Alkyl sulfate esters of polyhydric alcohols result from the action of sulfur trioxide—trialkyl phosphates as in the reaction of sorbitol at 34—40°C with sulfur trioxide—triethyl phosphate to form sorbitol hexa(ethylsulfate) (123). 

If the neutral substance containing carbon, hydrogen and possibly oxygen is insoluble in ether but freely soluble in water, a polyhydric alcohol or a simple mono- or di-saccharide (or related compound) is indicated. Treatment with concentrated sulphuric acid usually produces excessive charring. 

Polyhydric alcohols are colourless viscous liquids, or crystalline solids. Upon heating with a little potassium hydrogen sulphate, they may yield aldehydes (e.g. ethylene glycol yields acetaldehyde glycerol gives the irritating odour of acrolein which can additionally be detected with Schiffs reagent). Two confirmatory tests for polyhydric alcohols are as follows. 

In this section, consideration will be given to the actual processes of acetal- or ketal-formation and not to the more indirect methods by which acetals and ketals of the polyhydric alcohols may be synthesized from compounds (e.g. derivatives of the monosaccharides) containing preformed alkylidene or arylidene groupings. The condensation of a carbonyl compound with a glycol is facilitated by acidic catalysts, and, since the reaction is reversible, by dehydration. The catalysts most frequently employed are concentrated sulfuric, hydrochloric and hydro-bromic acids, gaseous hydrogen chloride, zinc chloride and cupric sulfate others are phosphorus pentoxide, sulfosalicylic acid, and anhydrous sodium sulfate. The formation of benzylidene compounds is promoted less efficiently by phosphorus pentoxide than by either concentrated sulfuric acid or concentrated hydrochloric acid 1" the reaction is assisted by chloro- and nitro-substituents on the aromatic nucleus, but hindered by methyl- and methoxy-groups.18... 

They designated these forms ayn, amphi and anti. The writers are aware of only one occasion on which an acetal of a polyhydric alcohol has actually been isolated in isomeric forms of the type under discussion, namely that on which Ness, Hann and Hudson71 obtained two of the four theoretically possible diastereomers of 1,3 5,7-dibenzylidene-D-perseitol. One isomer, having m. p. 153-155° and [a]J° — 58.2° (in pyridine), resulted from the treatment of D-perseitol with benzaldehyde in ethanol at 25°, 50% sulfuric acid being employed as the catalyst. The other, having m. p. 280 2° and [a] ° — 58.1° (in pyridine), was produced when the condensation was carried out at 0° in aqueous ethanol saturated with hydrogen chloride. The former was converted into the latter by recrystallization from a pyridine-alcohol mixture. The corresponding labile and stable forms of l,3 5,7-dibenzylidene-L-perseitol also have been prepared.71 The facility with which the labile form could be converted into its stable isomer in the presence of basic substances may well explain why other workers have failed to isolate isomers of this type. 

Hydrogenation of aldoses to alditols (polyhydric alcohols) is usually performed in an aqueous solution with nickel or ruthenium as catalyst, as seen in the examples shown in eqs. 5.9-5.11.17-19... 

The use of ruthenium or ruthenium-based catalysts in the production of polyhydric alcohols by hydrogenation of aldoses or by simultaneous hydrolysis and hydrogenation of polysaccharides has been the subject of a considerable body of investigations.20,27 Ru-C was used in the hydrogenation of dextrose to sorbitol in both continuous and batch processing at elevated temperatures (100-180°C) and hydrogen... 

Polyhydric alcohols like glycerol have high viscosities because of the formation of a network of hydrogen bonds between the molecules. The network which extends throughout the liquid makes the flow difficult. 

G. Nemethy and H. A. Scheraga, J. Phys. Chem., 80, 928 (1977). lntermolecular Potentials from Crystal Data. 5. Determination of Empirical Potentials for O—H - O Hydrogen Bonds from Packing Configurations and Lattice Energies of Polyhydric Alcohols. 

Nemethy C, Scheraga HA (1977) Interatomic potentials from crystal data. V. Determination of empirical parameters of OH—O hydrogen bonds from packing considerations and lattice energies of polyhydric alcohols. J Phys Chem 81 928-931... 

The crossed aldol condensation of formaldehyde with aldehydes that have a-hydrogen atoms results in the replacement of these hydrogen atoms by hydroxymethyl groups. The /S-hydroxyaldehydes are then reduced to polyhydric alcohols by excess formaldehyde. 

A novel alternative to the use of hydrogenated or saturated fats for structural stability in oil-continuous emulsions is the addition of oil-soluble polymers as thickening or texturizing agents (160). These polymers are condensation products of hydroxyacids or polyhydric alcohols and polybasic acids. Currently they are not approved for food use. Another option to hydrogenated oUs is to base the product on an oil-in-water emulsion. Such a product, which contains 80% liquid canola oil, has been introduced in the United States (140). 

Both aldoses and ketoses are reduced to polyhydric alcohols (polyols) when treated with enzymes, sodium amalgam, and hydrogen under high pressure... 

Hydrogenation of oxystarch with Eaney nickel catalyst, followed by hydrolysis, gave erythritol. Simultaneous reduction and hydrolysis gave erythritol in yields of up to 71 %. Oxyamylopectin has been reduced with sodium borohydride to the corresponding polyhydric alcohol, which has been methylated both derivatives have been hydrolyzed, to give fragments enabling the structure of amylopectin to be deduced. 

Polyol or hindered esters prevent 3-hydrogen abstraction by eliminating the P-hydrogen. These are manufactured by reacting polyhydric alcohols such as neopentyl glycol, trimethylolpropane and pentaerythritol with mono-acids ranging from pentanoic, nCs, to decanoic, Cio [10] ... 

---