Triols condensation

Silane coupling agents have the structure R—Si—X3, where R represents an organofunctional group and X is generally alkoxy. They are generally applied from water solutions or from organic solvent-water mixtures. In the presence of water, hydrolysis occurs step-wise to form alkoxysilanols, and eventually silane triols. Condensation of the silanols to siloxanes also occurs. Reactions shown schematically below ... 

Because the condensation between a diketene acetal and a diol proceeds without the evolution of volatile byproducts, this method allows the preparation of dense, crossUnked materials by using reagents having a functionality greater than 2 (15). Even though either or both the ketene acetal and alcohol could have functionalities greater than 2, only triols were investigated because the synthesis of trifunctional ketene acetals is extremely difficult. 

A magnesium enolate of 99 is susceptible to aldol condensation with 4-pentenal, and the crude product can be directly protected to give its ethyl carbonate 100. a-Hydroxylation of the carbonyl group yields the hydroxyl carbonate 101. Reduction of the carbonyl group generates a triol, and this compound can be simultaneously converted to carbonate 102. Swern oxidation of 102 gives ketone 103, which can be rearranged25 to produce lactone product 104 (Scheme 7-32). 

Pentitol synthesis An asymmetric synthesis of L-arabinitol involves condensation of the (E)-a,fJ-unsaturated ester (2) with the anion of methyl (R)-p-tolyl sulfoxide (1). The resulting p-keto sulfoxide (3) is reduced stereoselectively by ZnCl2/DIBAH (13, 115-116) to 4. Osmylation of 4 with (CH,)3NO and a catalytic amount of 0s04 (13, 224-225) yields essentially a single triol (5). Finally, a Pum-merer rearrangement of the sulfoxide followed by reduction of an intermediate... 

Benzanthrone (6.73) is the source of various commercially important violet, blue and green vat dyes. This tetracyclic system can be prepared from a mixture of anthraquinone and propane-1,2,3-triol (glycerol) by heating with iron powder in concentrated sulphuric acid. The reaction involves reduction of anthraquinone to anthrone (6.74) followed by condensation (Scheme 6.14) with propenal (acrolein), the latter compound being generated... 

Preparation of a Low-Molecular-Weight Branched Polyester from a Diol, a Triol and a Dicarboxylic Acid by Melt Condensation... 

Guelcher et al. (1) prepared a hydrolyzable polyurethane foam under physiological conditions by condensing a polyester triol with e-caprolactone/glycolide and then postreacting the intermediate ester with the biocompatible diocyanate, lysine methyl ester diisocyanate. 

The principal polymeric plasticizers are the polymer hydrocarbons and the polyesters. The condensation products of diols and dicarboxylic acids, belonging to the polyester group, are most important. Higher functional compounds, like triols and tricarboxylic acids, are less important as are polyethers, polyacetals, and polymeric acids. 

Condensation reactions of aqueous solutions of methylsilanetriol with silica have been studied by NMR [13] at pH values 3.2-3.9, at various concentrations of triol and in the presence of a large excess of water. It was shown that the rates at which the methylsilanetriol polymerized with itself, and with the silica surface, were dependent on the pH of the solution and the concentration of methylsilanetriol. Concurrent with the reactions of the methylsilanols, the surface hydroxyl groups of the silica disappeared, suggesting that the methylsilanetriol adsorbs onto the silica surface. 

However, with smaller substituents the diols and triols frequently condense, under the hydrolysis conditions, to siloxanes that have Si—O—Si bonds.78 The exact nature... 

When BuSi(0SiMe20H)3 is heated, poly-condensation is immediately started, forming many different products. In order to synthesize low-molecular condensates, we have reacted BuSi(OSlMe2Cl)3 with one equivalent of the triol BuSi(0H)3 using triethylamine as HCl captor (compare also Eq. 2) the cage like BuSi(0SiMe20)3Si Bu is formed in 60% yield. In Fig. 3 the result of an X-ray structure analysis is depicted. Bicyclic molecules with the same skeleton of atoms but with different substituents are known [20,21]. 

The silicone reactive functions of alkoxy functional silanes form silanols in the presence of water (Eq. 1). The silane triols formed are very reactive and will react very quickly if other hydroxyl groups are present. For example, they will condense or crosslink with other silanols or with the surface of minerals. The hydrophilic character of the silanols will be lost after the reaction has taken place. 

The cyclic anhydride was converted into the amide acid which on Hofmann rearrangement followed by lithium borohydride reduction on the ester gave a derivative of ip-amino-2a, 3a-dihydroxy-43-hydroxy-methylcyclopentane. Condensation of the amino-triol with 5-amino-4,6-dichloropyrimidine followed by ring closure with triethyl orthoformate gave the 6-chloropurine derivative which on treatment with ammonia gave 11. ... 

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