Phase condensation

Reactions with Aldehydes and Ketones. The base-catalyzed self-addition of acetaldehyde leads to formation of the dimer, acetaldol [107-89-1/, which can be hydrogenated to form 1,3-butanediol [107-88-0] or dehydrated to form crotonaldehyde [4170-30-3]. Crotonaldehyde can also be made directiy by the vapor-phase condensation of acetaldehyde over a catalyst (53). 

The Reaction. Acrolein has been produced commercially since 1938. The first commercial processes were based on the vapor-phase condensation of acetaldehyde and formaldehyde (1). In the 1940s a series of catalyst developments based on cuprous oxide and cupric selenites led to a vapor-phase propylene oxidation route to acrolein (7,8). In 1959 Shell was the first to commercialize this propylene oxidation to acrolein process. These early propylene oxidation catalysts were capable of only low per pass propylene conversions (ca 15%) and therefore required significant recycle of unreacted propylene (9—11). 

Vapor-Phase Condensations of Acetic Acid or Esters with Formaldehyde. Addition of a methylol group to the a-carbon of acetic acid or esters, foUowed by dehydration, gives the acrylates. 

Liquid-phase condensation of formaldehyde with propylene, catalyzed by BF or H2SO4, gives butadiene (52,53). 

The prepolymer is separated from the water by spray drying and then formed into cylindrical pellets of uniform size (159). At this point additives can be added to the porous pellets from solution or suspension. These pellets are then placed in a soHd-phase condensation reactor where they are heated to 260°C for up to 4 h under nitrogen, with a small amount of water added. The pressure is maintained close to atmospheric pressure. At the end, x > n. 

Other Derivatives and Reactions. The vapor-phase condensation of ethanol to give acetone has been well documented in the Hterature (376—385) however, acetone is usually obtained as a by-product from the cumene (qv) process, by the direct oxidation of propylene, or from 2-propanol. 

Gas that remains gaseous in the reservoir rock, whatever the pressure, but from which a liquid phase condenses at standard conditions. 

In the condensation reaction between chloro- and bromo-methyl aryl sulfones and carbonyl compounds, a-sulfonyloxiranes were obtained. In this condensation reaction, bases such as potassium t-butoxides372, NaH373 and aqueous concentrated hydroxide with benzyltriethylammonium chloride under two-phase condensation were used374. In the reaction with aldehydes only the trans-epoxide isomers resulted, whereas lith-iofluoromethyl phenyl sulfone 289375 and 291376 were found to add to aldehydes affording /J-hydroxysulfones 290 and 292, respectively. 

Important prebiotic sequences, for example, the linking up of amino acids to form proteins, involve acylation reactions (see Sects. 5.1 and 5.2). Condensation agents are often not very efficient in aqueous phases condensation reactions may involve drastic conditions, such as high temperatures or an acidic environment. Activated amino acids, for example, thioester derivatives, can be considered as starting... 

Then it resides on the chiral circle with modulus p and phase , , any point on which is equivalent with each other in the chiral limit, mc = 0, and moved to another point by a chiral transformation. We conventionally choose a definite point, (vac p vac) = /,T (Jn the pion decay constant) and (vac Oi vac) = 0, for the vacuum, which is flavor singlet and parity eigenstate. In the following we shall see that the phase degree of freedom is related to spin polarization that is, the phase condensation with a non-vanishing value of Oi leads to FM [20]. 

Although the effect of quaternary ammonium salts on the stereochemistry of the two-phase condensation reaction of a-chloroacetonitrile with acrylonitriles to form cyclopropanes [4, 7] is not as pronounced as with the Darzens reaction, it can be rationalized in an analogous manner (Scheme 12.2). In the absence of the catalyst, the more highly stabilized anion (4a) is favoured leading to the preferential production of the cis isomer (5). As with the Darzens reaction, addition of the catalyst causes diffusion of the anions (4a) and (4b), as ion-pairs, into the bulk of the organic phase where their relative stabilities are similar and a more equal ratio of the two isomeric cyclopropanes (5) and (6) results (Table 12.2). 

The decomposition of this intermediate on both the Ni(llO) and Ni(lOO) surfaces occurred by an autocatalytic mechanism (99) for adsorbate coverages above about one-tenth of a monolayer. In fact, the decomposition rate was observed to accelerate isothermally as the reaction proceeded on both the Ni(l 10) and Ni(lOO) surfaces (98, 99) the rate of acceleration was more pronounced on the (110) surfaces. Furthermore, the intermediates were observed to form islands, as if a two-dimensional phase condensation occurred at about one-tenth monolayer coverage. The formation of this 2D condensed phase was clear indication of attractive interactions among the adsorbed species. 

O. Friedrichs, L. Kolodziejczyk, J.C. S4nchez-L6pez, C. Lopez-Cartes, A. Fernandez, Synthesis of nanocrystaUine MgH powder by gas-phase condensation and in situ hydrida-tion TEM, XPS and XRD study, J. Alloys Compd. 434-435 (2007) 721-724. 

Carbonaceous compounds can also form in the absence of a catalyst by free-radical, gas-phase condensation reactions. The formation of this pyrolytic carbon is known in steam-reforming reactors where it can be controlled to some extent by minimizing the free volume within the reactor chamber. This type of carbon does not form readily with methane but can be severe with larger hydrocarbons. The compounds formed by free-radical reactions tend to be quite different from the graphitic carbon formed by metal catalysts. For example, Lee et al. showed that the compounds formed by passing pure, undi-... 

Equations 11.171.1 to 11.171.3 are, however, of limited practical application because they demand precise knowledge of the state of speciation of carbonates in aqueous solution during solid phase condensation (or late exchanges). The fact that different carbonate solute species distinctly fractionate is masterfully outlined by the experiments of Romanek et al. (1992), which indicate a marked control by solution pH of the fractionation between total dissolved inorganic carbon (DIC) and gaseous CO2 (figure 11.38). 

Besides oxidative coupling of methane and double bond isomerization reactions (242), a limited number of organic transformations have been carried out with alkali-doped alkaline earth metal oxides, including the gas-phase condensation of acetone on MgO promoted with alkali (Li, Na, K, or Cs) or alkaline earth (Ca, Sr, or Ba) (14,120). The basic properties of the samples were characterized by chemisorption of CO2 (Table VI). 

In contrast to laboratory scale operations, four-bond formation processes are of considerable importance as industrial routes to pyridine derivatives and have been investigated in Considerable detail. Vapour phase condensation of aldehydes and ketones with ammonia and amines in the presence of a variety of silica/alumina catalysts containing different promoters (e.g. cobalt(II) chloride) can give excellent yields of substituted pyridines (e.g. equation 151), and the nature of the products formed can be largely controlled by change in the stoichiometry of the reactants and variation of experimental conditions (equation 152). 

Supercritical (sc) fluids are materials that are heated above their critical temperatures and pressurized above their critical pressures to produce single-phase condensed fluids having densities similar to liquids and viscosities similar to gases. The solubilities of substrates in supercritical fluids vary with small changes to the temperature and pressure of the system, especially near the critical point. 

Fig. 12. Dependence of apparent rate coefficient, k (sec-1), on sodium content, mNa (mol Na per 100 g cat), in silica gel catalysts for the vapour phase condensation of formaldehyde with (1) acetaldehyde, (2) acetone, (3) acetonitrile, at 275°C [372].

Langmuir—Hinshelwood-type equations were applied in some cases. The kinetics of the vapour phase condensation of acetaldehyde with formaldehyde to acrolein at 275—300°C over sodium-containing silica gel... 

Single phases, condensation or boiling can be accommodated in either the tubes or the shell, in vertical or horizontal positions. 

Scheme 3 Synthesis of Coiled-Coil Analogues of Various Polypeptide Chain Lengths (Ac-ABnC-OH) by Stepwise Solid-Phase Condensation of Protected Heptad Fragments 21111...

The model of a deposition reactor describes the following phases gas phase, surface phase, condensed phase, reactor walls, and external ambient (see Figure 9.4). 

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