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Polyols cyclic

Reaction Mechanisms in the Direct Carboxylation of Alcohols, Polyols, Cyclic Ethers, and Cyclic Amines to Afford Monomeric Compounds and Polymeric Materials... [Pg.183]

Cyclic Orthoformates. When the above strategy is applied to polyols, cyclic orthoformates can be isolated. Most common are the cyclization of 1,3-diols (eq 2) and 1,2-diols, as well as the formation of caged structures from the use of polyols (eq 3). Those orthoformates obtained from 1,2-diols (eq 4) can undergo cycloelimination upon pyrolysis to afford alkenes in high yield. There are a variety of methods for carrying out this overall... [Pg.406]

Polyether Polyols. Polyether polyols are addition products derived from cyclic ethers (Table 4). The alkylene oxide polymerisation is usually initiated by alkah hydroxides, especially potassium hydroxide. In the base-catalysed polymerisation of propylene oxide, some rearrangement occurs to give aHyl alcohol. Further reaction of aHyl alcohol with propylene oxide produces a monofunctional alcohol. Therefore, polyether polyols derived from propylene oxide are not truly diftmctional. By using sine hexacyano cobaltate as catalyst, a more diftmctional polyol is obtained (20). Olin has introduced the diftmctional polyether polyols under the trade name POLY-L. Trichlorobutylene oxide-derived polyether polyols are useful as reactive fire retardants. Poly(tetramethylene glycol) (PTMG) is produced in the acid-catalysed homopolymerisation of tetrahydrofuran. Copolymers derived from tetrahydrofuran and ethylene oxide are also produced. [Pg.347]

Andersson also showed that, in addition to meso-desymmetrization, kinetic resolution of some cyclic epoxides by use of the first-generation catalyst was also possible, giving both epoxides and allylic alcohols in good yields (Scheme 7.51) [108], Kozmin reported the effective use of the same catalyst in the desymmetrization of diphenylsilacyclopentene oxide. The resulting products could be used in the ster-eocontrolled syntheses of various acyclic polyols (Scheme 7.52) [109]. [Pg.265]

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. [Pg.6]

The chelate ring size principle can have structural effects as well as effects on thermodynamic stability in aqueous solution. An example is coordination of metal ions by sugars (44). The cyclic polyol cts-inositol can coordinate metal ions in two distinct ways (Fig. 14) (45). In ax-ax-ax bonding (Fig. 14), the metal ion is part of three fused six-membered chelate rings. Alternatively, in ax-eq-ax coordination, the metal ion is part of two fused five-membered and one six-membered chelate rings. Angyal has noted that metal ions of radius more than 0.8 A adopt the ax-eq-ax structure (44), whereas with an ionic radius... [Pg.117]

Smaller aldehydes form cyclic acetal-type oligomers readily in aqueous conditions.60 Diols and polyols also form cyclic acetals with various aldehydes readily in water, which has been applied in the extraction of polyhydroxy compounds from dilute aqueous solutions.61 E in water was found to be an efficient catalyst for chemoselective protection of aliphatic and aromatic aldehydes with HSCH2CH2OH to give 1,3-oxathiolane acetals under mild conditions (Eq. 5.7).62... [Pg.157]

Fig. 3.3 Preparation of polyols (left-hand side cyclic ethers right-hand side dehydroxyhexitols) from starch hydrolysates via a two-step process. Fig. 3.3 Preparation of polyols (left-hand side cyclic ethers right-hand side dehydroxyhexitols) from starch hydrolysates via a two-step process.
Cyclic sulfates can be obtained from diols or polyols in the reaction of the latter with SOCI2 followed by mthenium catalyzed oxidation. These sulfates readily react with LiPPh2 yielding mono- and di-tertiary diphenylphosphines having alkylene sulfate substituents (54-57). This is a highly versatile procedure, since the starting diols are readily available and the products are well soluble and fairly stable in neutral or slightly alkaline aqueous solutions [57,105]. [Pg.27]

A recent example of diasteromeric amplification with achiral guests and a racemic library can be seen in the work of Iwasawa and coworkers. The library members consisted of a racemic polyol and l,4-benzenedi(boronic acid) [2], When these components were mixed in an equimolar ratio in methanol, a precipitate formed, which was insoluble in other organic solvents and thought to be a polymeric boronate. However, when the library members were mixed in the presence of toluene or benzene, a precipitate again formed, but it was soluble in several (nonprotic) organic solvents where boronic ester exchange is slow. With toluene a [2 2] complex of the polyol and diboronic acid formed, as evidenced by NMR and FAB-MS data. X-ray crystallography confirmed that a cyclic structure formed with... [Pg.157]

Di-caffeoylquinic acid (70) Cyclic polyolic derivative 1,5-DCQA(70) Antiviral (Anti-HIV HIV/AIDS and hepatitis B) Inhibits HIV-1 integrase Phase l/Il Chinese Academy of Military Medical Sciences 583-585... [Pg.62]

Magnanini had already made it plausible that readily dissociable compounds were formed in aqueous solution, and Van t Hoff had pointed out that polyols with adjacent hydroxyl groups could form cyclic esters, with either five or six atom rings, which would then be stronger acids and, as in the case of mannitol, would have a different rotatory power. [Pg.190]

Finally, it should be pointed out that in some cases epoxides are opened by a remote hydroxy group within the molecule to give the five-membered ethers [41]. We are currently investigating how the conformation of an open chain epoxy polyol might be responsible for cyclic ether formation [43]. [Pg.128]

The groups of Burczyk, Takeda, and others have made thorough studies of cyclic acetals, such as 1,3-dioxolane (five-membered ring) and 1,3-dioxane (six-membered ring) compounds, illustrated in Fig. 13. They are typically synthesized from a long-chain aldehyde by reaction with a diol or a higher polyol. Reaction with a vicinal diol gives the dioxolane [40-42] and 1,3-diols yield dioxanes [43,44]. [Pg.75]

Molecules with Two or More Functional Nonchromophoric Groups 4.4.2.4.I. Derivatives of Cyclic Diols and Polyols... [Pg.522]

Only a submicrogram amount of sample is required for this CD method of characterization of pyranose configuration169 and determination of the branching points in oligosaccharides170. A similar additivity relationship holds for 4-phenylbenzyl ethers of cyclic polyols which are more resistant to solvolysis171 172. [Pg.525]

The pairwise additivity principle when applied to bichromophoric exciton-coupled systems, such as those composed of 4-bromobenzoate (BB) and 4-methoxycinnamate (MC) derivatives of cyclic polyols, yields more information from the CD spectra of complex molecules173. In such systems both degenerate ( homo") interactions, i.e., BB/BB and MC/MC, and nondegenerate ("hetero") interactions, i.e., BB/MC, contribute to the exciton CD spectra. As the homo exciton Cotton effects arc well separated (BB 236/253 nm, MC 287/322 nm) a unique pattern of CD curves is obtained for each derivative of cyclic tri- or tetraol. This method is particularly useful in identification of glycopyranosides174, a procedure essential for microscale structure determination of oligosaccharides by the exciton chirality method175. [Pg.525]

It so happens that the great majority of compounds separated as acetates are alditols or other polyhydric compounds, and this Section is therefore concerned with the problems of reduction and acetylation. There is no a priori reason why alditols and other polyols should not be separated as their trimethylsilyl ethers, and such methods are known (see Section VII,l,p. 57 Section XIII, p. 90 Table Va, p. 119 and Table Xlla, p. 151), but experience shows that the resolution of acyclic O-trimethylsilyl derivatives is less satisfactory than that of cyclic compounds. [Pg.34]

Cyclic carbonates result from polyols by transesterification using organic carbonates (115). Thus sorbitol and diphenylcarbonate in the presence of dibutyl tin oxide at 140—150°C form sorbitol tricarbonate in quantitative yield (116). [Pg.51]

Conversion to acetates, trifluoroacetates (178), butyl boronates (179) trimethylsilyl derivatives, or cyclic acetals offers a means both for identifying individual compounds and for separating mixtures of polyols, chiefly by gas—liquid chromatography (glc). Thus, sorbitol in bakery products is converted to the hexaacetate, separated, and determined by glc using a flame ionization detector (180) aqueous solutions of sorbitol and mannitol are similady separated and determined (181). Sorbitol may be identified by formation of its monobenzyhdene derivative (182) and mannitol by conversion to its hexaacetate (183). [Pg.52]

Of all the selective, deprotection procedures that are available to carbohydrate chemists, the partial hydrolysis of polyacetals is probably the most familiar. Articles by de Beider4,5 and Brady6 contained examples of this type of reaction for aldose and ketose derivatives, respectively, and an article by Barker and Bourne7 gave useful information from the early literature on the graded, acid hydrolysis of acetal derivatives of polyols. A discussion of the stereochemistry of cyclic acetals of carbohydrates was included in an article by Mills 70 and in one by Ferrier and Overend,76 and a survey of the formation and migration of carbohydrate cyclic acetals was made by Clode.7c... [Pg.14]

With due consideration of the explanations just presented for the observed, relative stabilities of cyclic acetals derived from polyols, in terms of their constitution and conformation, nearly all of the following observations on the selective hydrolysis of cyclic acetals of alditols and dialkyl dithioacetals may be readily understood. [Pg.21]

Diols and polyols can participate in equilibria with boric acid in aqueous solution. The stability of polyolborates is determined by the number of OH groups in cis positions. Complexes with polyols are more stable than with diols, and 1,2-diol complexes are more stable than their 1,3-diol counterparts (Table 10) since the resulting five-membered chelate ring is unstrained.75120 In the case of 1,3,5-triols stable cage-like structures (5) and (6) are favored. Open-chain or five-membered cyclic polyols form more stable chelate complexes than their six-membered counterparts.120 Thus, chelates from alditols and ketohexoses are more stable than the corresponding aldose chelates (Table 10). Many polyols allow quantitative titrimetric determination of boric acid. Of these, mannitol remains the most widely used reagent on the basis of availability, cost and ease of handling.75... [Pg.95]

O-protected cyclic or acyclic carbon frameworks. The choice of acetals or ethers as derivatives allows a systematic manipulation of diols and polyols. Kinetic control and a lesser affinity for protonation on sulfur compared with oxygen allows the transformation of cyclic hemiacetals into acyclic dialkyl dithioacetals. Acetal, ether, and dithioacetal derivatives are some of the pivotal intermediates needed to explore various applications of carbohydrates in synthesis. [Pg.3]

The major mechanistic and structural aspect of the acetalation process is its orientation toward derivatives obtained either under thermodynamically controlled conditions or under kinetically controlled conditions. We will not discuss here all structural factors concerning the relative stabilities of acyclic and cyclic acetals of polyols and monosaccharides, because such a discussion has been extensively reviewed and adequately commented on [8,10,12 -14]. However, it is important to focus here on the main consequences of these relative stabilities in relation to the various experimental conditions to orientate the choice of specific conditions, particularly for the most important monosaccharides (D-glucose, D-mannose, and D-galactose). [Pg.13]

Polyether Polyols. Polyether polyols are addition products derived from cyclic ethers (Table 1). The alky lens oxide polymerization is usually initiated by alkali hydroxides, especially potassium hydroxide. In the base-catalyzed polymerization of propylene oxide, some rearrangement occurs to give allyl alcohol. [Pg.1654]


See other pages where Polyols cyclic is mentioned: [Pg.295]    [Pg.913]    [Pg.543]    [Pg.82]    [Pg.68]    [Pg.716]    [Pg.574]    [Pg.43]    [Pg.568]    [Pg.162]    [Pg.303]    [Pg.51]    [Pg.27]    [Pg.86]    [Pg.5]    [Pg.366]    [Pg.195]    [Pg.118]    [Pg.641]    [Pg.220]    [Pg.220]    [Pg.312]   


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