Boiling point, of solvent

Use vacuum distillation to obtain lower boiling point of solvent to allow lower distillation temperature... 

In extraction, analyte is dissolved in a solvent that does not necessarily dissolve the entire sample and does not decompose the analyte. In a typical microwave-assisted extraction of pesticides from soil, a mixture of soil plus acetone and hexane is placed in a Teflon-lined bomb (Figures 28-8 and 28-13) and heated by microwaves to 150°C. This temperature is 50° to 100° higher than the boiling points of solvents at atmospheric pressure. Pesticides dissolve, but the soil remains behind. The liquid is then analyzed by chromatography. 

Figure 6-6 Temperature versus Concentration State Diagram Illustrating the Sol-Gel Boundao for BSA in which Threshold Times for Gelation are shown circles, 100 s A triangles up, 1,000 s triangles down, 10,000 s. Horizontal broken line is boiling point of solvent. Curves shown are based on Equation 6.26 (Tobitani and Ross-Murphy, 1997).

The boiling points of solvents are reached rapidly, often posing safety problems (e.g. explosions). To solve these problems, the operation has to be carried out in closed vessels (generally made of Teflon, a material transparent to MW and resistant up to 250°C and 80 psi) and using only small amounts of products (roughly 1/10 of the total volume). This of course constitutes a serious limitation (e. g. reduction in MW efficiency as the penetration depth is far below A, scaling up, etc.). 

Elevation of boiling point — AT/, — (boiling point of solution) - (boiling point of solvent) = AT w... 

An open-vessel approach to scale up has seen limited application, as this eliminates one of the greatest attributes of microwave heating, namely, the ability to heat reactions to well above the normal boiling points of solvents in a safe and effective manner. That said, when removal of a by-product such as water is key to the success of a synthetic transformation, or if a gas is evolved during the course of the reaction, a large-scale open-vessel batch miCTowave reactor may be an effective tool to carry out the procedure. 

How this may effect the performance of sonication to break down the target conqraunds is questionable and probably insignificant. Higher tenperatures could slightly decrease the effect of sonication on the conq>ounds in the range of 20 to 30 C. Also, if the temperature was near the boiling point of solvent (water in this case) the extreme condition of cavitation would disappear and the... 

The boiling point of liquid is frequently used to estimate the purity of the liquid. A similar approach is taken for solvents. Impurities cause the boiling point of solvents to increase but this increase is very small (in the order of O.OTC per 0.01% impurity). Considering that the error of boiling point can be large, contaminated solvents may be undetected by boiling point measurement. If purity is important it should be evaluated by some other, more sensitive methods. The difference between boiling point and vapor condensation temperature is usually more sensitive to admixtures. If this difference is more than 0.1°C, the presence of admixtures can be suspected. 

An approximate flash point can be estimated from the boiling point of solvent using the following equation ... 

The boiling point of solvent, its specific heat capacity, and its enthalpy of vaporization determine the energy required for solvent separation in a distillation column. They also determine numerous other properties of solvents (see Chapter 2). 

It was found that a selection of solvent has effect on film thickness which is related to the boiling point of solvent. Fast evaporating solvents such as n-butyl acetate and o-xylene gave thicker coatings. Thinner films were obtained when mesitylene or diglyme were used. 

Easy and high separation of solvent from the extract phase (large difference of boiling points of solvent and key component, no formation of an azeotropic mixture). 

Process Solvent Boiling point of solvent (wf) in °C (normal pressure) Extraction conditions Ratio of solvent to raw material... 

Solvents Boiling Point of Solvent (°K) Azeotropic Temp (°K) Azeotropic Composition (%w/w)... 

Electrolytes have a greater effect on the freezing and boiling points of solvents than nonelectrolytes do. 

TABLE 3.2 The Freezing/Melting Points, Normal Boiling Points, of Solvents, and their Molar Masses... 

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