Dehydration rearrangements

Davis studied the dehydration of urea nitrates as a route to iV-nitroureas. The nitrate salt of iV-methylurea undergoes dehydration-rearrangement on treatment with concentrated sulfuric acid to give Af-nitro-A -methylurea in 42 % yield. In this compound the nitro and methyl groups are attached to the same nitrogen and so its hydrolysis can provide a route to methylnitramine. In contrast, the nitrate salts of ethyl, n-propyl, n-butyl and n-amyl ureas, give iV-nitro-A -ethylurea (49 %), A -nitro-A -propylurea (60 %), iV-nitro-iV -butylurea (67 %) and iV-nitro-A -amylurea (67 %), respectively, on treatment with concentrated sulfuric acid. 

Hematite forms by a combination of aggregation-dehydration-rearrangement process for which the presence of water appears essential. Structural details about this process at 92 °C were obtained from EXAFS (Combes et al. 1989 1990) face-sharing between Fe octahedra developed before XRD showed any evidence for hematite. It is followed by internal redistribution of vacancies in the anion framework and by further dehydration. The dehydration process involves removal of a proton from an OH group and this in turn leads to elimination of a water molecule and formation of an 0X0 linkage. The local charge inbalance caused by proton loss is compensated for by migration and redistribution of Fe " within the cation sublattice. 

These species were prepared from the appropriate ethers in FSCFH-SbFs-SO2 solution at — 60°C. Like the protonated diols, these oxonium dications (i.e., 235) were observed to undergo cleavage reactions leading to mono-cationic fragments or dehydration-rearrangement to give the oxonium ion 236 (eq 80). 

Completely different properties are shown by the monosaccharides of Type II, having an unsubstituted imino group in the hemiacetal ring. These compounds contain the 2-hydroxypiperidine system, and, accordingly, exhibit the reactions of this system. They are relatively stable in alkaline solution only. In neutral or acidic solution, dehydration, rearrangement, or condensation reactions occur that are characteristic of cyclic Mannich bases. 

These data, in conjunction with previous studies (12) showed that stable char contains mainly condensed aromatic structure with intermittent paraffinic groups. This structure is formed by successive dehydration, rearrangement, loss of carboxyl, carbonyl, and paraffinic groups, formation of free radicals, and condensation of the carbon skeleton to polycyclic aromatic structures. 

Trost and Jungheim3 have developed an alternative route to 2-vinylcyclobutanones from the reagent 4, which involves a dehydrative rearrangement (8, 138— 139). 

Dlhydropyrane. Mol. wt. 84.11, b.p. 85°. Preparation by dehydration-rearrangement of tetrahydrofurfuryl alcohol over alumina. " Suppliers du Pont Electrochemicals Dept., Matheson, A, B, E, F, MCB. 

In the presence of strong acids such as aqueous H2SO4, carbonyl compounds may react with olefins to form unsaturated alcohols and other products, depending on the reaction conditions. Using H-mordenite as catalyst in a continuous-flow system, 10% conversion of formaldehyde to isoprene was observed at 300° using an isobutylene-to-HCHO (molar) ratio of 3.7. A carbonium ion-type reaction scheme, involving a Prins reaction (1,2) and a subsequent dehydration-rearrangement step... 

Reactions of the alcohols(526)—(528) with acidified methanol have been studied products include those of dehydration, rearrangement, methyl ethers, and ring-cleavage olefins and ethers. ... 

Certain alkane- and arenesulfonic acids are well known and widely used catalysts in organic transformations (27). Metanesulfonic acid, alone or in conjunction with P2O5, is applied in cyclocondensations to form carbocyclic or heterocyclic compounds (28a). p-Toluenesulfonic acid is a toxic compound applied usually as monohydrate (28b). It is most useful in the protection of ketones to form acetals and to transform ketones to enol ethers and acetates. Further uses include esterification, dehydration, rearrangement, and isomerization. 

It is tempting to speculate that some of the dibenzazonines of the Meni-spermaceae could be formed by dehydrative rearrangement of neoproaporphine-dienol precursors. In the laboratory, however, such an attempt led exclusively to aporphinoids (see Sec. 18.3.3) and no data derived from the feeding of labeled precursors is available to support such a thesis. 

Dehydration-rearrangement with preceding formation of sec. alcohols from ketones... 

Potassium hydrogen sulfate/acetic anhydride Dehydration-rearrangement... 

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