Displacement by moisture

Certain adhesive systems are more resistant to interfacial degradation by moist environments than are other adhesives. Table 15.16 illustrates that a nitrile-phenolic adhesive does not succumb to failure through the mechanism of preferential displacement at the interface. Failures occurred cohesively within the adhesive even when tested after 24 months of immersion in water. A nylon-epoxy adhesive bond, however, degraded rapidly under the same conditioning owing to its permeability and preferential displacement by moisture. 

The Stille reaction has developed as a popular protocol for the formation of C-C bonds due to the air- and moisture-stability as well as functional group compatibility of organotin compounds. Together with the Suzuki-Miyaura coupling it is one of the most powerful methods for the synthesis of molecules containing unsymmetrical biaryl moieties. However, despite its efficiency, this versatile reaction has slowly been displaced by other procedures that avoid the use of highly toxic organostannanes. 

Antimony triiodide reacts rapidly with moisture to give an oxyiodide. The same compound is formed by long exposure to dry air, part of the iodine being displaced by oxygen. 

The reaction must be performed in a dry, oxygen-free environment although the product is not sensitive to air or moisture, the intermediate C5HJ is. Cyclopentadiene is added dropwise to a stirred slurry of KOH powder and 1,2-dimethoxyethane. A solution of FeCl2.4H20 in dimethyl sulphoxide (CH3)2SO is then added. The choice of solvents is determined by obvious considerations of solubility and miscibility, and chemical inertness towards the products and intermediates. Dimethyl sulphoxide is a fairly weakly-coordinating aprotic solvent, easily displaced by C5H from Fe(II). A mixture of aqueous HC1 and crushed ice is then added this neutralises the KOH (the ice absorbs the heat evolved) and causes the precipitation of ferrocene, which is (predictably) insoluble in water. The crude product is purified by sublimation. 

After dispensing a run of prepolymer from a container, the prepolymer must be resealed in a state that will prevent attack by moisture in the air. A blanket of dry nitrogen gas must be used to displace any air present in the container. Any bungs or taps must be properly cleaned using a dry solvent such as MEK or MIBK to prevent traces of polyurethane from reacting with the moisture in the air and sealing the container. 

Hydroxyl materials (diols and triols) are very hygroscopic, and the absorption of moisture must be prevented. Positive nitrogen blanketing is often required. All air must be displaced by dry nitrogen gas and the material stored under a slight positive nitrogen pressure. The use of dried 5A molecular sieve in BDO is also advantageous. 

Effect of Water. Wood is usually treated with ammonia in the presence of some amount of water. The effect of water depends not only on the amount of water but also somewhat on the history of the wood sample and the method of treatment. Thus, when oven-dried veneer strips were treated with cold liquid ammonia-water mixtures at ambient pressure, the flexibility of the treated wood was substantially decreased when the moisture content of the ammonia was much above 10% (26). Other protonic solvents act similarly (26). In apparent contrast, the rate of sorption of ammonia from the gas phase by wood is markedly enhanced by moisture in the wood (19). Bone dry wood absorbs ammonia quite slowly at ambient temperatures but if the wood has ten to twenty percent moisture content, sorption and plasticization occur much more rapidly. Presumably the moisture opens the pore structure of the wood and also dissolves ammonia much more readily than bone-dry wood. On continued treatment, the water is presumably displaced from the wood by the ammonia... 

The water displaced by H2 was proposed to be involved in the proton transfer, e.g., H30+ may be formed from H2 heterolysis and protonate the ot-C-F bond. A similar proton-promoted CF activation in dicationic ds-[Ir(CF3)(CO)(dppe)(DIB)]2+ (DIB = o-diiodobenzene) has also been thought to occur via heterolytic activation of H2, but hydrolysis to a CO ligand by adventitious moisture to eventually form [IrH2(CO)2 (dppe)]+ is the outcome (94). An unobserved intermediate with CF3... 

The p-fluorophenylhydrazine complex is stable to air and moisture, but the hydrazine ligand is easily displaced by nucleophiles such as chloride ion. The N-bonded protons readily exchange with D20 and with D2 but are much less acidic than that of the p-fluorophenyldiimide complex.4 Prolonged hydrogenation cleaves the N—Pt bond to give the arylhydrazine and [PtHCl P (CsHs) 2]. 

Molecular sieves such as zeolite have also been used as carriers for low-molecular-weight amines. An amine, such as DETA, can be absorbed into the sieve prior to mixing with an epoxy resin. The sieve protects the amine from reacting with the epoxy resin, and a relatively long shelf life is possible. Release of the DETA is then initiated by heat or through displacement by atmospheric moisture. 

The formation of a minor side product 172 was observed which, if moisture was not rigorously excluded, could become a major product in this reaction (Scheme 36). The formation of compound 172 can be rationalized by protonation of the sulfur ylide 166, followed by deprotonation of one of the readily accessible methyl hydrogens to give the ylide 169, which then reacts at the carbonyl center to give the seven-membered ring intermediate 170. The methyl sulfide is then displaced by the alkoxide to give the oxirane 171, which upon addition of sodium azide, opens up to the azido alcohol 172 <1999T10659>. 

The compounds of formula (1) are exceedingly sensitive to air and moisture and are somewhat thermally unstable. Thus, attempted sublimation under reduced pressure results in loss of THF and formation of [ LnCp"2( i-Cl) 2] (2) (see Section B). The thf molecules are readily displaced by treatment with Me2NCH2CH2NMe2 (tmeda), yielding [LnCp"2(/i-Cl)2Li (tmeda)]. 

The emission of naphthalene, phenanthrene, and pyrene from contaminated sediments has been examined and its extent depended on a number of factors including the moisture content and the relative humidity of the air (Valsaraj et al. 1999). Reworking of the sediment and displacement by water in high moisture air increased the emission. 

The heat developed by the adsorption of the vapor will cause a rise in temperature in a dry carbon bed. Difficulties resulting from this are avoided by having the carbon in a moist condition when the adsorption cycle starts. Then, as the vapors of solvent are adsorbed, they displace some moisture, which on being evaporated absorbs the heat of adsorption. This prevents a rise in temperature. 

Displacement of the suspending liquid Dewatering of various sludges by flocculation followed by mechanical drainage on belt filters, in rotary drums, etc. Displacement of moisture from fine coal by wetting with oil. 

The presence of water vapor in the combustion air can also affect heater excess O2 levels. As the moisture in the air increases, the excess O2 drops because part of the combustion air is displaced by the water vapor. The amount of water vapor that air can hold depends on the temperature and pressure. When the air can t hold all the water, then the moisture condenses as dew. Relative humidity is the term commonly used to describe the amount of water vapor in the air and is defined as the amount of moisture in the air compared to the maximum amount the air could hold at that temperature. Figure 7.26 shows the effects of temperature and relative humidity on the amount of water vapor in air. For example, at 100°F (38°C) and 100% relative humidity, air holds about 6.5% water vapor by volume, or about 275 grains of H2O per pound of dry air (7000 grains = 1 lb , = 0.454 kg). 

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