Diols glycols, cyclic

Acetylene reacts with polyhydric alcohols, and -hydroxy acids and their derivatives.197 In these reactions 1,2-, 1,3-, and 1,4-diols give cyclic glycols preferentially.197,201,202... 

Chemical resistant Highly reactive resin, e. g., based on isophthalic acid + neopentyl glycol, cyclical diols ... 

Diols that bear two hydroxyl groups m a 1 2 or 1 3 relationship to each other yield cyclic acetals on reaction with either aldehydes or ketones The five membered cyclic acetals derived from ethylene glycol (12 ethanediol) are the most commonly encoun tered examples Often the position of equilibrium is made more favorable by removing the water formed m the reaction by azeotropic distillation with benzene or toluene... 

In practice, it s convenient to use 1 equivalent of a diol such as ethylene glycol as the alcohol and to form a cyclic acetal. The mechanism of cyclic acetal formation using ethylene glycol is exactly the same as that using 2 equivalents of methanol or other monoalcohol. The only difference is that both —OH groups are in the same molecule. 

It is clear then that more than one mechanism is operative for glycol fission. In the case of c -cyclopentanediols and camphanediols a cyclic ester is a necessary intermediate. For tra/js-decalin-9,10-diol a non-cyclic mechanism must operate which cannot function for cholestane-3/ ,6j8,7a-triol and is inefficient for /rans-camphanediols. It is pertinent that while the fission of glycols capable of forming cyclic esters proceeds several hundred times faster in benzene than in acetic acid, the reactions of trans-decalin-9,10-diol and tra/ij-hydrindane-l,6-diol are 4-5-fold slower in benzene . ... 

A novel chemoenzymatic route to polyester polyurethanes was developed without employing highly toxic isocyanate intermediates. First, diurethane diols were prepared from cyclic carbonates and primary diamines, which were subsequently polymerized with dicarboxylic acids and glycols by using lipase CA as catalyst, yielding the polyurethanes under mild reaction conditions. 

The preparative electrochemical oxidation of silyl-substituted sulfides results in the cleavage of the C Si bond [36-38]. For example, the anodic oxidation of 1-phenylthio-l-trimethylsilylalkanes takes place smoothly in methanol in an undivided cell equipped with a carbon rod anode and a carbon rod cathode. Although 1-methoxy-l-phenylthioalkanes are formed as the initial products, they are converted into 1,1-dimethoxyalkanes during the course of the reaction (Scheme 8). The electrochemical reaction in the presence of diols such as ethylene glycol affords the corresponding cyclic acetals. 

Instead of two molecules of alcohols, a diol is often used. This produces cyclic acetals. 1,2-ethanediol (ethylene glycol) is usually the diol of choice, and the products are called ethylene acetals. 

Synthesis of the cyclic acetal 25 in 63% yield by reaction of the unsaturated bromo-nitrilo sugar 24 (E configuration) with ethylene glycol in the presence of sodium hydroxide has been reported.40 An extension of this work was given for sugars having a vicinal diol... 

Cyclic carbonates are made by treating 1,2-diols with dialkyl carbonates using an alkyl ammonium and tertiary amine catalyst. The combination of propylene glycol and dimethyl carbonate has been reported to result in a 98% yield of propylene carbonate (21). 

Acetals andKetals. Acetals of 1,3-diols are prepared by refluxing the diol with the aldehyde in the presence of an acid catalyst, even in an aqueous medium. The corresponding ketals are more difficult to prepare in aqueous solution, but cyclic ketals of neopentyl glycol, eg,... 

The transesterification of 1,2-diols by reaction with carbonates, both cyclic and linear, produces five-membered alkylene carbonates almost exclusively. A well-known example of this is the reaction of DMC with propene glycol to yield PC [295],... 

Epoxides (also called oxiranes) are three-membered cyclic ethers. They are more reactive titan typical ethers due to the strain created by the small ring. Epoxides react with water in the presence of an acid catalyst to form diols, commonly called glycols. This is an anti-addition. 

The reaction of alkenes with osmium tetroxide (0s04) is an example of an oxidation reaction (Following fig.). In this case the alkene is not split, but, a 1,2-diol is obtained which is also called a glycol. The reaction involves the formation of a cyclic intermediate where the osmium reagent is attached to one face of the alkene. On treatment with sodium bisulphite, the intermediate is cleaved such that the two oxygen atoms linking the osmium remain... 

Where the glycol contains one or two secondary or tertiary hydroxyls, the products are more soluble and some are even monomeric cyclic chelates (65,66). Three compounds are obtained from 2-methylpentane-2,4-diol, depending on the mole ratio (67—70). Structure (3) represents an isolable but labile aLcoholate of (2)... 

Reactions of sulfur tetrafluoride with glycols usually proceed slightly differently. Yagupolskii and coworkers investigated reactions with 1,2-, 1,3- and 1,4-diols and found that in most cases only one of the hydroxyls was substituted, since a cyclic intermediate was formed and it reacted with a fluoride anion to give fluoroalcohols. The regioselectivity is usually governed by electronic factors (equation 63)117. 

Cyclic Acetals Formation of an acetal using a diol as the alcohol gives a cyclic acetal. Cyclic acetals often have more favorable equilibrium constants, since there is a smaller entropy loss when two molecules (a ketone and a diol) condense than when three molecules (a ketone and two molecules of an alcohol) condense. Ethylene glycol is often used to make cyclic acetals its acetals are called ethylene acetals (or ethylene ketals). 

The acetals you have met so far were formed by reaction of two molecules of alcohol with one of carbonyl compound. Cyclic acetals, formed by reaction of a single molecule of a diol, a compound containing two hydroxyl groups, are also important. When the diol is ethylene glycol (as in this example) the five-membered cyclic acetal is known as a dioxolane. 

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