1,3-Dioxolane, hydration

The use and reactions of glyoxal as a fixative have been reviewed extensively.3334 Glyoxal is the second smallest aldehyde, being like two formaldehyde molecules arranged back-to-back (Fig. 12.8, left). It too forms hydrates with water, the most common of which is 1,3-dioxolane (Fig. 12.8, right). 

The introduction of chloro-substituents into the methylene group of 2-methylene-1,3-dioxolan causes a decrease in the rate of the hydronium-catalysed hydration and also in the rate of the hydronium ion-catalysed breakdown of the resulting hemiorthoester. Since both rate decreases are similar, 2-hydroxy-2-chloromethyl- 1,3-dioxolan [96] and 2-hydroxy-2-dichloromethyl- 1,3-dioxolan [98] can be detected in hydration of 2-chloro-methylene-1,3-dioxolan [95] (Scheme 10) and 2-dichloromethyl-1,3-dioxolan [97] (Scheme 11) (Capon and Dosunmu, 1984). 

When the hydration of 2-chloromethylene-1,3-dioxolan was studied in CD3CN—D20 (85 5 v/v) the signal of the —CHDC1 group of the intermediate was a broadened singlet which corresponded to 1 proton at 8 = 3.66 pp. When H20 was used instead of DzO this signal was sharper and corresponded in intensity to two protons. When a similar set of experiments was... 

The reaction chemistry of simple organic molecules in supercritical (SC) water can be described by heterolytic (ionic) mechanisms when the ion product 1 of the SC water exceeds 10" and by homolytic (free radical) mechanisms when <<10 1 . For example, in SC water with Kw>10-11 ethanol undergoes rapid dehydration to ethylene in the presence of dilute Arrhenius acids, such as 0.01M sulfuric acid and 1.0M acetic acid. Similarly, 1,3 dioxolane undergoes very rapid and selective hydration in SC water, producing ethylene glycol and formaldehyde without catalysts. In SC methanol the decomposition of 1,3 dioxolane yields 2 methoxyethanol, il lustrating the role of the solvent medium in the heterolytic reaction mechanism. Under conditions where K klO"11 the dehydration of ethanol to ethylene is not catalyzed by Arrhenius acids. Instead, the decomposition products include a variety of hydrocarbons and carbon oxides. 

As discussed in Section 4.30.3.1.3,1,3-dioxolanes are normally generated from carbonyl compounds and glycols under acidic conditions. Carbonyl derivatives which tend to hydrate... 

A number of compounds substituted in this way were prepared. Thus Meister360 obtained 74 by the hydrolysis of dioxolan (73). Bulla-tenone (71), which is obtained from Myrtus buUata,361,362 is very similar, in spite of the additional conjugation with the phenyl ring, as is the compound 72, which is prepared by the hydration of a diynediol.363 The structure of a similar compound, prepared also from an acetyleneglycol,364 is not exactly known. 

A new efficient procedure has been proposed for the synthesis of 3-aryl-5-amino-l//-pyrazoles by reaction of a-chloro-/ -arylacrylonitriles with hydrazine hydrate <2004RJ01518>. Reaction of 2-(3,3-dicyano-2-propenylidene)-4,4,5,5-tetra-methyl-l,3-dioxolane 641 with hydrazine afforded 3-(2-hydroxy-l,l,2-trimethylpropoxy)pyrazole 642 (Equation 134) <2003RJ01016>. Treatment of ethyl 3,3-dicyano-2-methoxyacrylate with alkyl, aryl, heterocyclic, and sulfonyl hydrazines led to the synthesis of N-l-substituted 3-acyM-cyano-5-aminopyrazoles, which are versatile intermediates for the synthesis of many biologically active scaffolds <2006TL5797>. 2-Hydrazinothiazol-4(5//)-one reacted with a variety of cinnamonitrile derivatives and activated acrylonitriles to yield annelated pyrazolopyrano[2,3-rf thiazole <1998JCM730>. 

Heptaplatin (cis-malonate[(4i ,5i )-4,5-bis(aminomethyl)-2-isopropyl-l,3-dioxolane]platinum(II), SKT2053R, Sunpla) has high antitumor activity against various cancer cell lines, including cisplatin-resistant tumor cells. PreUminary results suggested that it is less nephrotoxic than cisplatin. However, a comparative trial showed that intravenous heptaplatin 400 mg/m was more nephrotoxic than intravenous cisplatin 60 mg/m in terms of uremia and proteinuria, which occurred despite the use of hyperosmolar mannitol and appropriate concomitant hydration (fluid intake at least 3500 ml/day) (34,35). 

As with polystyrene sulfonic resins, Nafion-based acid catalysts are highly efficient for hydration and dehydration processes and, in general, for condensation reactions that occur with the formation of water or similar secondary products. Formation of ethers has been studied for various alcohols [109-111]. Dehydration of 1,4- and 1,5-diols at 135 °C affords the corresponding cyclic ethers such as 20 in excellent yields (Scheme 10.7), while 1,3-diols experience different transformations depending on their structure [112]. The dehydration of 1,2-diols mainly proceeds via the pinacol rearrangement. Further condensation of the initially formed carbonyl compound and unreacted diol affords 1,3-dioxolanes [113]. The catalyst could be efficiently reused following a reactivation protocol. Formation of aryl ethers is also possible, and the synthesis of dibenzofurans 21 (X = O) from 2,2 -dihydroxybiphenyls has been reported (Scheme 10.7) [114]. The related reaction... 

R = Me2C=CH-CH2-CH2) with hydrazine hydrate leads to carbamate intermediates, which undergo cyclization to give 5-hydroxy-5.6-dihydro-4/f-l,3,4-oxadiazin-2(3//)-ones 311. The thermal dehydration of 311 gives 1,3,4-oxadiazin-2(3//)-ones 312 <2003CHE1057>. In contrast to the case with hydrazine hydrate, the reaction of aromatic hydrazines with l,3-dioxolan-2-ones 310 provides 3-arylamino-4-hydroxyoxazolidin-2(3//)-ones 313. 

Far-IR transmission spectra were recorded of Structure I [ethylene oxide (EtO) hydrate] and Structure 11 [cyclopropane, trimethylene oxide (TMO), 1,3-dioxolane, tetrahydrofuran (THE), and cyclobutanone hydrates] hydrates. The slight water lattice stretching due to the large size of cyclobutanone was indicated by the most... 

C2oH2 N203 0.5 H2O, 7-Methyl-5,6-dibenzo-1,7-diazatricyclo-[9.3.1.0 ]pentadeca-4(8),5-diene-2-one-spiro-9,2 -dioxolane hemi-hydrate, 446, 347... 

Glyoxal monohydrate seems to have the dimeric structure (183), but in 40% aqueous solution the presence of the hydrated monomer (184) and two isomeric dioxolans, (185) and (186), is claimed. ... 

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