Phase without solvent

In the vapor phase, there are two additional considerations that are very important in understanding of carbene chemistry. The first point reflects the fact that carbene reactions are normally highly exothermic (about 90kcal mol for insertions or additions). Thus, a product molecule is frequently produced with a large amount of excess internal energy. In the vapor phase without solvent molecules to help dissipate the excess vibrational energy, the molecule may be subject to further reactions. Such reactions are often called hot molecule reactions. Cyclopropanes from cycloaddition reactions are particularly susceptible to hot molecule decomposition to the thermodynamically more stable olefin, since for cyclopropane isomerization is only 64kcal mol . ... 

Besides being at the origin of lyotropic phases, cellulose derivatives can also originate thermotropic liquid crystalline phases without solvent. This behavior is an indication that lateral chains act as solvent, or plasticizer, increasing the mobility of the polymer backbone. 

Zone refining is one of a class of techniques known as fractional solidification in which a separation is brought about by crystallization of a melt without solvent being added (see also Crystallization) (1 8). SoHd—Hquid phase equiUbria are utilized, but the phenomena are much more complex than in separation processes utilizing vapor—Hquid equiHbria. In most of the fractional-solidification techniques described in the article on crystallization, small separate crystals are formed rapidly in a relatively isothermal melt. In zone refining, on the other hand, a massive soHd is formed slowly and a sizable temperature gradient is imposed at the soHd—Hquid interface. 

There is an evolution with time the older calculations correspond to isolated molecules in the gas phase without any corrections, the more recent ones include solvent effects, with different approximations, and also some corrections, like ZPE (zero-point energy correction). The contributions of some authors to the understanding of tautomerism have been significant. Some of their contributions are collected in Table II. 

The Alphabutol process (Figure 7-8) operates at low temperatures (50-55°C) and relatively low pressures (22-27 atm). The reaction occurs in the liquid phase without a solvent. The process scheme includes four sections the reactor, the co-catalyst injection, catalyst removal, and distillation. The continuous co-catalyst injection of an organo-hasic compound deactivates the catalyst downstream of the reactor withdrawal valve to limit isomerization of 1-hutene to 2-hutene. Table 7-2 shows the feed and product quality from the dimerization process. 

Polymerization reactions can occur in bulk (without solvent), in solution, in emulsion, in suspension, or in a gas-phase process. Interfacial polymerization is also used with reactive monomers, such as acid chlorides. 

The first step is a slow ionization of the substrate and is the rate-determining step. The second is a rapid reaction between the intermediate carbocation and the nucleophile. The ionization is always assisted by the solvent, since the energy necessary to break the bond is largely recovered by solvation of R" " and of X. For example, the ionization of f-BuCl to f-Bu" and Cl" in the gas phase without a solvent requires ISOkcalmol" (630kJmol" ). In the absence of a solvent such a process simply would not take place, except at very high temperatures. In water, this... 

The ozonolysis of ethylene in the liquid phase (without a solvent) was shown to take place by the Criegee mechanism.This reaction has been used to study the structure of the intermediate 16 or 17. The compound dioxirane (21) was identified in the reaetion mixture at low temperatures and is probably in equilibrium with the biradical 17 (R = H). Dioxirane has been produced in solution but it oxidatively cleaves dialky] ethers (such as Et—O—Et) via a chain radical process, so the choice of solvent is important. 

Oxidation of these model sulfur compounds was studied without solvent to investigate the chemical structure of the products using S K-edge XANES. A solvent free tri-phase (organic/ H202aq./catalyst) was used under the described conditions. Figure 1 shows the XANES spectra from the organic and aqueous phases as well as reference materials. The thiophene oxidized to thiophene-sesquioxide [3a,4,7,7a-tetrahydro-4,7-epithiobenzo[b]-thiophene 1,1.8-trioxide ] first.. The sesquioxide solid precipitated from the solvent free reaction mixture and was identified by NMR, IR and C,H,S elemental analytical. The sesquioxide oxidized to sulfate. 2-MT and 2,5 DMT also oxidized to... 

Two important developments in the past couple of decades now allow us to better study coordination chemistry (of ions) in the gas phase, without the intrusion of the normally ever present solvent molecule or a counterion. 

Before concluding this section, it has to be reminded that all the above calculations represent gas-phase processes without solvent and/or counterion effects, and without unfavorable entropic contributions. Recent studies have shown that they modify substantially the olefin-coordination energetics. 

The most widely encountered biphasic method commences with two immiscible phases, one containing the catalyst, the other the substrate or substrates, and was first recognized by Manassen in 1973 [1], Liquid phases may be immiscible if their polarities are sufficiently different, as explained in Chapter 1. The two phases are vigorously mixed allowing reaction between the catalyst and substrates to take place. When the reaction is complete, the mixing is stopped and the two phases separate. A schematic representation of such a process is illustrated in Figure 2.1. In the ideal system, the catalyst is retained in one phase ready for reuse and the product is contained in the other phase and can be removed without being contaminated by the catalyst. In certain cases, neat substrates may be used as one phase, without additional solvents. 

A method that can decrease the viscosity of the mobile phase without impacting the mobile phase solvent strength (i.e., maintaining k) would therefore decrease the analysis time linearly. The next section illustrates the diffusion coefficients and viscosities, the unique relationship between them for EEL mixtures, their solvent-strength and other important properties. 

Two limiting mechanisms for solute retention can be imagined to occur in RPC binding to the stationary phase surface or partitioning into a liquid layer at the surface. In the previous treatment we assumed that retention is caused by eluite interaction with the hydrocarbonaceous surface, i.e., the first type of mechanism prevails. When the eluent is a mixed solvent, however, the less polar solvent component could accumulate near the apolar surface of the stationary phase. In the extreme case, an essentially stagnant layer of the mobile phase rich in the less polar solvent could exist at the surface. As a result eluites could partition between this layer and the bulk mobile phase without interacting directly with the stationary phase proper. 

Elimination of CO2 from 21 requires higher temperatures. Reported protocols include the thermolysis without solvent at 130 °C (44), heating in solution at 150-230 °C (45), as well as in the gas phase at 600 °C (FVP) (46). For synthetic purposes, this method has been used for the preparation of sterically hindered olefins and represents an extension of the twofold extrusion methodology [cf. (47,48)]. 

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