Cyclopropanes hydrate

Monfort. J.P. Nzihou. A. Light scattering kinetics study of cyclopropane hydrate growth. J. Cryst. Growth 1993. 128, 1182-1186. 

Temperature-dependent change in stability of this kind is admirably illustrated by the results of Hafemann and Miller [5] for the cyclopropane-water system. The more stable form of cyclopropane hydrate changes from type I to type II at -16 and back from type II to type I at 1.5 corresponding changes occur at -23 and 5.5 for the cyclopropane deuteriohydrates. The general conclusion that among... 

Thujane-type monoterpenes, unusual monoterpenes with a cyclopropane ring in a bicyclo[3.1.0] skeleton, are formed from the terpinen-4-yl cation directly or via the sabinyl cation. Important members include a-thujene 52, sa-binene 53, the cis isomer 54 of sabinene hydrate, sabinol 55, sabinylacetate 56, a-thujone 57, -thujone 58 and isothujanol 59 (Structure 4.13). 

Useful for opening cyclopropane rings and hydrating alkynes. 

Both main group and transition metal elements interact with the acetylenic triple bond in a variety of reactions, including hydrogenation, hydrometallation, hydration and cycloadditions. Notably, in most reactions the cyclopropane ring remains intact. 

The best-known gas hydrates are those of ethane, ethylene, propane, and isobulaue. Others include methane and I butene, most of the fluorocarbon refrigerant gases, nitrous oxide, acetylene, vinyl chloride, carbon dioxide, methyl and ethyl chloride, methyl and ethyl bromide, cyclopropane, hydrogen sulfide, methyl mercaptan, and sulfur dioxide. 

Trimethylene oxide (Hawkins and Davidson, 1966), cyclopropane (Hafemann and Miller, 1969 Majid et al., 1969), and ethylene sulfide (Ripmeester, Personal Communication, May 2,1988) are three molecules that can form in either the 51262 of structure I or the 51264 of structure II as simple hydrates. Raman spectroscopy measurements suggest that a low fraction of 512 cages may also be occupied by cyclopropane at high pressures (Suzuki et al., 2001). Such compounds change structures depending on the temperature and pressure of formation, and guest composition in the aqueous phase as discussed in Section 2.1.3. 

Table 2.4 presents the diameter ratios of natural gas components (and a few other compounds) relative to the diameter of each cavity in both structures. Also presented are two unusual molecules, cyclopropane and trimethylene oxide, which can form simple hydrates of either structure si or sll hydrates of these molecules are discussed in Section 2.1.3.3, in the subsection on structural changes in simple hydrates. 

Tables 2.5a,b provide a comprehensive list of guest molecules forming simple si and sll clathrate hydrates. The type of structure formed and the measured lattice parameter, a, obtained from x-ray or neutron diffraction are listed. Unless indicated by a reference number, the cell dimension is the 0°C value given by von Stackelberg and Jahns (1954). Where no x-ray data exists, assignment of structure I or II is based on composition studies and/or the size of the guest molecule. Tables 2.5a,b also indicate the year the hydrate former was first reported, the temperature (°C) for the stable hydrate structure at 1 atm, and the temperatures (°C) and pressures (atm) of the invariant points (Qi and Q2). Both cyclopropane and trimethylene oxide can form si or sll hydrates. Much of the contents of these tables have been extracted from the excellent review article by Davidson (1973), with updated information from more recent sources (as indicated in the tables).

Structural Changes in Simple Hydrates. Of particular interest to the question of structure are the simple hydrates of cyclopropane and trimethylene oxide because they can form hydrates of either structure I or structure II as a function of formation conditions. These hydrates are unique examples of structural change of single guest species at different conditions of pressure and temperature. 

Cyclopropanones—threc-membered ring ketones—are also hydrated to a significant extent, but for a different reason. You saw earlier how acyclic ketones suffer increased steric hindrance when the bond angle changes from 120° to 109° on moving from sp2 to sp3 hybridization. Cyclopropan ones... 

As demonstrated below, a Lewis acid-mediated reaction was utilized in the synthesis of dihydro[b furan-based chromen-2-one derivatives from l-cyclopropyl-2-arylethanones and allenic esters <070L4017>. The TiCh-catalyzed anti-Markovnikov hydration of alkynes, followed by a copper-catalyzed O-arylation was applied to the synthesis of 2-substituted benzo[6]furan <07JOC6149>. In addition, benzo[6]furan-based heterocycles could be made from chloromethylcoumarins <07SL1951>, substituted cyclopropanes <07AGE1726>, as well as benzyne and styrene oxide <07SL1308>. On the other hand, DBU-mediated dehydroiodination of 2-iodomethyl-2,3-dihydrobenzo[6]furans was also useful in the synthesis of 2-methylbenzo[Z>]furans <07TL6628>. 

The models described above assume that the reaction occurs only in the liquid phase. In some cases, such as isomerization of cyclopropane to propylene on a silica-alumina catalyst,43 reduction of crotonaldehyde over a palladium catalyst,45 and hydration of olefins to alcohols over tungsten oxide,58 the reactions could occur in the gas as well as in the liquid phases. 

Miyazaki and coworkers studied the ESR spectrum of y-irradiated pure cyclopropane at 77 K and observed the spectrum of c-CaHj radicals . When cyclopropane containing a small amount of ethane was irradiated at 77 K, a typical spectrum of ethyl radical was observed with higher intensity than that of C-C3H5, due to hydrogen abstraction from ethane by the excited cyclopropyl radical. Trofimov and coworkers studied the ESR spectrum of irradiated hydrate of cyclopropane at 77 K. A spectrum of five well resolved doublets, belonging to 1 was observed, in addition to the spectrum of H atom. 

No other radicals were formed in this system nor do they appear when the samples were heated. This ESR spectrum is different from that obtained by Miyazaki and coworkers for pure cyclopropane but since both groups claim that their spectrum is of the cyclopropyl radical, at least one of them has a wrong assignment. Trofimov and coworkers also studied the ESR spectrum of irradiated pure cyclopropane at 77 and their spectrum resembles very much that of Miyazaki and coworkers. This spectrum is more complex than that found for the radiolysis of the hydrate of cyclopropane. 

For the irradiated hydrate of cyclopropane at 77 K the intensity ratio of the lines in the spectrum differs slightly from the binomial however at 153 K it is already close to binomial. When the temperature is further increased there are no changes in the spectrum up to complete recombination of the radicals at 262 K. When pure cyclopropane was heated to 113 K the lines of the cyclopropyl radical (1) disappeared and the intensity of the lines of another radical (2) increased. At 77 K both radicals 1 and 2 are present but around 113 K all radicals 1 are converted to radicals 2. The most probable structure of 2 is given in equation 26 the end groups are bound to other molecules of cyclopropane. 

M can be a cyclopropane but not water molecules, since formation of radical 2 was not observed in the irradiated hydrate of cyclopropane. 

Changing the medium drastically from water to pentane, does not significantly affect the reaction course, and the cyclopropane derivatives still account for ca. 94 % of the products in this reaction . On the other l nd, cyclobutyl derivatives are the sole products in the acid-catalyzed hydration of 3-methylbicyclobutanecarbonitrile (equation 54) and in the methanolysis of methyl 3-methylbicyclobutanecarboxylate (equation 55) . ... 

The lack of trichloromethyl anion adducts to acrylates in these processes is possibly due to relatively tight, poorly lipophilic ion pairs Me4N CCI3 which cannot penetrate the organic phase thus, they reside in the interfacial region where the hydrated trichloromethyl anions have low activity. Consequently, dichlorocarbene reacts with acrylates to form 1,1-dichlorocy-clopropanes 2. ( )-A -tert-Butyl but-2-enamide forms the cyclopropane 3 on reaction with dichlorocarbene, generated from chloroform/base/phase-transfer catalyst, with tetramethylam-monium chloride as the catalyst. ... 

When the cyclopropane ring was incorporated between two highly activating carbonyl groups as in the hydrate of dispiro[5.0.5.1]trideca-l,5,8,12-tetraone (23), the methylene group proved to be the electrophilic center at which the nucleophilic attack of alcohols occurred. ... 

The cyclopropane ring in dispiro[5.0.5.1]trideca-l,5,8,12-tetraone (21) and its hydrate, respectively, is highly activated and has been shown to react with a variety of weak nucleophiles. Thiourea added to this dispiro compound via the nucleophilic attack of the sulfur atom at the methylene group. 

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