Dehydration of glycols

Polyester synthesis was carried out hy insertion-dehydration of glycols into polyanhydrides using lipase CA as catalyst (Scheme 6). The insertion of 1,8-octanediol into poly(azelaic anhydride) took place at 30-60°C to give the corresponding polyester with molecular weight of several thousands. Effects of the reaction parameters on the polymer yield and molecular weight were systematically investigated. The dehydration reachon also proceeded in water. The reaction behaviors depended on the monomer structure and reaction media. 

Erlenmeyer was first to consider ends as hypothetical primary intermediates in a paper published in 1880 on the dehydration of glycols.1 Ketones are inert towards electrophilic reagents, in contrast to their highly reactive end tautomers. However, the equilibrium concentrations of simple ends are generally quite low. That of 2-propenol, for example, amounts to only a few parts per billion in aqueous solutions of acetone. Nevertheless, many important reactions of ketones proceed via the more reactive ends, and enolization is then generally rate-determining. Such a mechanism was put forth in 1905 by Lapworth,2 who showed that the bromination rate of acetone in aqueous acid was independent of bromine concentration and concluded that the reaction is initiated by acid-catalyzed enolization, followed by fast trapping of the end by bromine (Scheme 1). This was the first time that a mechanistic hypothesis was put forth on the basis of an observed rate law. More recent work... 

Dehydration of glycols is effected in the presence of phosphoric, silicic, phosphotungstic, or boric acid. The dehydrations leading to butadiene have been reviewed by Egloff and Hulla.103... 

More recently, calcium sulfate was applied to the dehydration of glycols into unsaturated carbonyls 31), cupric sulfate mounted on alumina was used for the conversion of aUyl ether to allyl alcohol 32), and some metal sulfates were used for the open-chain polymerization of ethylene oxide 33). 

The most common contaminants in produced gas are carbon dioxide (COj) and hydrogen sulphide (HjS). Both can combine with free water to cause corrosion and H2S is extremely toxic even in very small amounts (less than 0.01% volume can be fatal if inhaled). Because of the equipment required, extraction is performed onshore whenever possible, and providing gas is dehydrated, most pipeline corrosion problems can be avoided. However, if third party pipelines are used it may be necessary to perform some extraction on site prior to evacuation to meet pipeline owner specifications. Extraction of CO2 and H2S is normally performed by absorption in contact towers like those used for dehydration, though other solvents are used instead of glycol. 

Although most of the installed solvent dehydration systems have been for ethanol dehydration, dehydration of other solvents including 2-propanol, ethylene glycol, acetone, and methylene chloride, has been considered. 

A selection of industrial appHcations of extractive distillation includes (/) the separation of the / -butane—butadiene azeotrope in mixed C -hydrocarbon streams using furfural [98-01-17, as the solvent (36) (2) the dehydration of ethanol using ethylene glycol [107-21-1] (37—39) (J)... 

Here is another discussion of glycol plant troubleshooting from the article How to Improve Glycol Dehydration by Don Ballard. 

Cyclohexadiene has been prepared by dehydration of cyclohexen-3-ol,3 by pyrolysis at 540° of the diacetate of cyclohexane-1,2-diol,4 by dehydrobromination with quinoline of 3-hromocyclohexene,6 by treating the ethyl ether of cyclohexen-3-ol with potassium bisulfatc,6 7 by heating cyclohexene oxide with phthalic anhydride,8 by treating cyclohexane-1,2-diol with concentrated sulfuric acid,9 by treatment of 1,2-dibromocyclo-hexane with tributylamine,10 with sodium hydroxide in ethylene glycol,10 and with quinoline,6 and by treatment of 3,6-dibromo-cyclohexene with sodium.6... 

The formation of 5-hydroxy-2 -deoxycytidine (22) and 5-hydroxy-2 -de-oxyuridine (23) that arise from dehydration of dCyd glycols 20 and related dUrd derivatives 21, respectively, was assessed by HPLC-electrochemical detection within calf thymus DNA upon exposure to photoexcited menadione and subsequent enzymatic hydrolysis [57]. The latter two oxidized nucleo-... 

Epoxides figure in yet other routes,58,59 while even the simple dehydration of ketonic glycols is still valuable.60 Epoxides and glycols also figure in routes based upon acetylene chemistry, to which we now proceed. 

Cyclopentanecarboxaldehyde has been prepared by the procedure described above 2 3 by the reaction of aqueous nitric acid and mercuric nitrate with cyclohexene 6 by the action of magnesium bromide etherate 6 or thoria 7 on cyclohexene oxide by the dehydration of frarei-l, 2-cyclohexanediol over alumina mixed with glass helices 8 by the dehydration of divinyl glycol over alumina followed by reduction 9 by the reaction of cyclopentene with a solution of [HFe(CO)4] under a carbon monoxide atmosphere 10 and by the reaction of cyclopentadiene with dicobalt octacarbonyl under a hydrogen and carbon monoxide atmosphere.11... 

It has been shown by H naff (1963) that the rate of reaction of several carbonyl reagents (bisulphite, hydrazine, phenylhydrazine, semi-carbazide and hydroxylamine) with aqueous formaldehyde solutions is independent of the nature and concentration of the reagent, and is therefore determined by the rate of dehydration of methylene glycol. He obtained catalytic constants for hydrogen and hydroxide ions, and a detailed study of acid-base catalysis has been made by the same method by Bell and Evans (1966). 

This cobalamin-dependent enzyme [EC 4.2.1.28] catalyzes the conversion of propane-1,2-diol to propanal and water. The enzyme also dehydrates ethylene glycol to acetaldehyde. 

Various combinations of reactant(s) and process conditions are potentially available to synthesize polyesters [Fakirov, 2002 Goodman, 1988], Polyesters can be produced by direct esterification of a diacid with a diol (Eq. 2-120) or self-condensation of a hydroxy carboxylic acid (Eq. 2-119). Since polyesterification, like many step polymerizations, is an equilibrium reaction, water must be continuously removed to achieve high conversions and high molecular weights. Control of the reaction temperature is important to minimize side reactions such as dehydration of the diol to form diethylene glycol... 

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