1.2- Diol, from hydroxylation

TPU is usually made from hydroxyl-terminated polyether or polyester diols, diisocyanates, and bifunctional chain extenders. Since the composition, the synthetic method, molecular weight, and its distribution are all changeable, there are numerous types of TPUs available, and their prices and properties vary significantly. 

The diol part of (19) could come from hydroxylation of the double bond in (20). This looks like an alkylation product of acetone, but the required halide (21) is not easy to make. An alternative is to make (20) from Grif nard attack on nitrile (22),... 

Allylcarbazole (and 3-chloro- and 3-chloro-6-nitroanalogs) hydroxylate, normally with permanganate the diol from 9-allylcarbazole cleaved normally with periodate." ... 

Exercise 13-21 Devise a synthesis of 3-hexyn-1,6-diol from two-carbon compounds using the unsaturated cyclic ether, >, as a protecting reagent for hydroxyl... 

The Woodward Reaction (or Woodward c/s-Hydroxylation) allows the synthesis of syn-diols from alkenes by the addition of iodine followed by nucleophilic displacement with acetate in the presence of water. Hydrolysis of the intermediate ester gives the desired diol. The Prevost Reaction gives crn/z -diols. 

Cross-linked PUs with shape memory properties were prepared by Galia, Meier et al. using linear polyols synthesized by ADMET [140]. In this work, ADMET of a 10-undecenoic acid-derived a,co-diene containing a hydroxyl group was performed in the presence of 0.1 mol% of C4. 10-Undecenol was used as chain stopper, and the mixture of oligomers and diols (from 10-undecenol SM) obtained was cross-linked with MDI. The PUs obtained displayed outstanding values of strain fixity and recovery. 

Thallium(in) sulfate in water brings about the anti hydroxylation of 3-r-butyl- and 4-r-butyl-cyck>-hexene. The reagent has been recommended for the one-step preparation of rranj-diols from ctmfor-mationally rigid cycloalkenes. 

To constmct the anhydro skeleton in the sugar molecule standard synthetic methods, used for the formation of normal heterocyclic derivatives, are applicable [4,5]. Generally, one of the hydroxyl groups of the diol (from which the anhydro ring is formed) is activated (by... 

Early in vitro studies showed that mitochondria from livers of hyperthyroid rats did not oxidize cholesterol-26- C to C02 at a faster rate than similar preparations from normal animals (12). A more recent study (13) led to the conclusion that the effects of thyroid hormones on bile acid metabolism must take place at a biosynthetic step preceding side-chain oxidation, perhaps involving hydroxylation of the steroid nucleus. However, it must be realized that the normal substrate for side-chain oxidation leading to the formation of cholic acid from cholesterol is not cholesterol itself but presumably 3a,7afl2a-trihydroxy-5/5-cholestane (14,15), and the substrate for the side-chain oxidation leading to chenodeoxycholate is, presumably, 3a,7a-dihydroxy-5/5-cholestane (16). Thus results of in vitro experiments in which cholesterol is employed as the substrate must be interpreted with caution, since mitochondria do not have the enzyme system required for formation of the triol and diol from cholesterol. 

Hydroxylation synthesis of 1,2-diols from alkenes (Sections 8-13 and 8-14)... 

Alkaline hydrolysis of fresh hog bile provides access to 3a-hydroxy-6-oxo-5a-cholanoic acid (about 3 g/1.5 liter of bile) (92, 93, 13). Figure 11 summarizes the routes to the four epimeric 3,6-diols from this acid. Kawa-nami (94) has studied the susceptibility of the hydroxyl groups of this series to NBS and concludes the following 6 3 (a)>3/S(e)>6a(e). Corbellini et al. (95, 96) and Ziegler (97) have investigated interconversions of isomers at Cg through the mesylates and tosylates. 

Support for the concept of an unsaturated intermediate in the formation of allo-acids is provided by recent experiments of Yamasaki et at. (98, 89). After administration of 3-ketochol-4-enoic-24- - C acid to rats and examination of the biliary metabolites, all four isomers of 3-hydroxycholanoic acid were identified other di- and trihydroxy acids were not investigated. Of the four possible 3-hydroxy-isomers about twice as much lithocholate was present as each of the other isomers. Similar results were obtained following administration of 3/3-acetoxychol-5-enoic-24-i- C acid in addition, 3f,6 -dihydroxy-5a-cholanoic acids were obtained. Yamasaki et al. (89) propose that a 3/3-dehydrogenase converts the 3/3-hydroxy-J -cholenoic acid to the a,/3-unsaturated ketone from which both 5 and 5 acids are derived, whereas hydroxylation of the above acid provides the diol from which only 5 acids are produced, somewhat analogous to the scheme of metabolism proposed by Mitropoulos and Myant (132) for the formation of chenodeoxycholic acid and the muricholic acids. 

The combination of A -bromoacetamidc, silver acetate, and dry acetic acid has been shown to be superior to Woodward s procedure for the rfy-hydroxylation of olefins. Work up of the reaction mixture is simply effected by hydrolysis of the dioxolenium ion, followed by cleavage of the hydroxyacetate intermediate with lithium aluminium hydride. The use of a co-oxidant, such as sodium chlorate or hydrogen peroxide, allows the addition of catalytic quantities of osmium tetroxide to prepare c/y-diols from olefins. However the reaction is often complicated by further oxidation of the glycol to the a-ketol. The use of tertiary amine A -oxides, particularly A -methylmorpholine A -oxide, prevents this oxidation and gives higher yields of the desired product (Table 6). Another variation on this theme employs... 

We 11 Start by discussing m more detail a class of compounds already familiar to us alcohols Alcohols were introduced m Chapter 4 and have appeared regularly since then With this chapter we extend our knowledge of alcohols particularly with respect to their relationship to carbonyl containing compounds In the course of studying alco hols we shall also look at some relatives Diols are alcohols m which two hydroxyl groups (—OH) are present thiols are compounds that contain an —SH group Phenols, compounds of the type ArOH share many properties m common with alcohols but are sufficiently different from them to warrant separate discussion m Chapter 24... 

Much of the chemistry of diols—compounds that bear two hydroxyl groups—is analo gous to that of alcohols Diols may be prepared for example from compounds that con tain two carbonyl groups using the same reducing agents employed m the preparation of alcohols The following example shows the conversion of a dialdehyde to a diol by... 

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