Solvents, purpose

Minor Uses. Small amounts of benzene find use in production of benzene-sulfonic acid. ///- B enz ene dis ulfonic acid is used to produce resorcinol [108-46-3], C6H602, (1,3-dihydroxybenzene). Benzene is thermally dimerized to yield biphenyl [92-52-4], C12H10. Benzene can also be converted into />-diisopropylbenzene [100-18-5], C12H18, which is oxidized to hydroquinone (1,4-dihydroxybenzene), a useful antioxidant. Because of its well-recognized toxicity, litde benzene is employed for solvent purposes, and then only when no suitable substitutes are available. 

For solvent purposes various grades of xylenes (the mixture of isomers and ethylbenzene) are available purification and drying procedures are similar to those used for benzene and toluene. For chemical purposes the commercially available pure isomeric xylenes are usually available in at least 99 per cent purity. 

Xylenes for solvent purposes consist of a mixture of three dimethylbenzene isomers, ortho-, meta- and para-xylene, and ethylbenzene. The physical properties quoted are for a typical mixture and the only property that is significantly altered by the ratio of the isomers is the flash point of the mixture. This can be significant in the UK and other countries where legislation primarily aimed at the safe storage of petrol regulates the storage and handling of hydrocarbons with flash points of less than 73 °F (22.8 °C) by the Abel method. 

The propionic esters ore very similar to the acetic esters in physical and chemical praperties vrith the difference that the former have a higher boiling point, lower evaporation rate and a lesser power of solubility. They are miscible with many of the lacquer solvents and diluents and possess a distinctive but not a disagreeable odar. The consumption of these esters far solvent purposes is relatively small compared to the highly developed acetate esters. 

Abrasion. Sand with 280A-grit For general-emory doth followed by solvent purpose bonding... 

Formaldehyde, acetic acid, and MTBE represent almost two-thirds of methanol demand worldwide. The balance of methanol demand is for various other chemicals, such as DMT, methyl methacrylates, chloromethane, and methyl amines, and also for antifreeze, dehydration, and solvent purposes. Each one of these outlets is relatively individually small therefore we do not review them here. In general, methanol demand for these various chemicals and solvents uses will e q)and with regional economic developments, and this is indicated in our methanol demand tables. 

The mixed solvent used in this determination is liable to contain nitrogen in a form that is not evaluated by a simple blank determination. For example, if nitrate is present it will not be reduced in the process of applying a simple blank determination but will be substantially reduced to anmonia in the determination of nitrogen in the sample, so that high results are obtained. In such cases the mixed solvent of sulphuric acid and potassium pyro-sulphate is first evaporated to fumes of sulphuric acid, cooled, diluted with about 5 ml water to decompose stable nitro-sulphuric acid compounds, and again evaporated to fumes of sulphuric acid. The cooled reagent is then ready for solvent purposes and blank evaluation. Blank determinations should be made side-by-side with the determination of nitrogen in the sample, as subsequently outlined. 

Predicting the solvent or density dependence of rate constants by equation (A3.6.29) or equation (A3.6.31) requires the same ingredients as the calculation of TST rate constants plus an estimate of and a suitable model for the friction coefficient y and its density dependence. While in the framework of molecular dynamics simulations it may be worthwhile to numerically calculate friction coefficients from the average of the relevant time correlation fiinctions, for practical purposes in the analysis of kinetic data it is much more convenient and instructive to use experimentally detemiined macroscopic solvent parameters. 

The explicit definition of water molecules seems to be the best way to represent the bulk properties of the solvent correctly. If only a thin layer of explicitly defined solvent molecules is used (due to hmited computational resources), difficulties may rise to reproduce the bulk behavior of water, especially near the border with the vacuum. Even with the definition of a full solvent environment the results depend on the model used for this purpose. In the relative simple case of TIP3P and SPC, which are widely and successfully used, the atoms of the water molecule have fixed charges and fixed relative orientation. Even without internal motions and the charge polarization ability, TIP3P reproduces the bulk properties of water quite well. For a further discussion of other available solvent models, readers are referred to Chapter VII, Section 1.3.2 of the Handbook. Unfortunately, the more sophisticated the water models are (to reproduce the physical properties and thermodynamics of this outstanding solvent correctly), the more impractical they are for being used within molecular dynamics simulations. 

For extraction purposes, a Soxhlet apparatus (Fig. 23(H)) can be inserted between a flask of boiling solvent and the reflux condenser A above. This apparatus is similar in design to that shown in Fig. 19, p. 3b in the type shown in Fig. 23(H) the hot extract continuously overflows through the side- tube into the boiling solvent below, but the syphon type shown in Fig. 19 is also available. 

Drying of crystals. Whenever possible crystals should be dried in a smdl vacuum desiccator containing a suitable desiccant. The latter depends upon the nature of the solvent used c/. p. 19). However for most purposes anhydrous calcium chloride is satisfactory. If a hydrocarbon has been used in the recrystallisation, a few thin fresh shavings of paraffin wax are efficacious. 

The oxime is freely soluble in water and in most organic liquids. Recrystallise the crude dry product from a minimum of 60-80 petrol or (less suitably) cyclohexane for this purpose first determine approximately, by means of a small-scale test-tube experiment, the minimum proportion of the hot solvent required to dissolve the oxime from about 0-5 g. of the crude material. Then place the bulk of the crude product in a small (100 ml.) round-bottomed or conical flask fitted with a reflux water-condenser, add the required amount of the solvent and boil the mixture on a water-bath. Then turn out the gas, and quickly filter the hot mixture through a fluted filter-paper into a conical flask the sodium chloride remains on the filter, whilst the filtrate on cooling in ice-water deposits the acetoxime as colourless crystals. These, when filtered anddried (either by pressing between drying-paper or by placing in an atmospheric desiccator) have m.p. 60 . Acetoxime sublimes rather readily when exposed to the air, and rapidly when warmed or when placed in a vacuum. Hence the necessity for an atmospheric desiccator for drying purposes. 

Recrystallise from methylated spirit, using animal charcoal for this purpose, use about twice the minimum quantity of methylated spirit required to obtain a clear solution, and filter through a funnel preheated by the filtration of some boiling solvent, as the tribromobenzene separates very rapidly as the solution cools. The 1,3,5-tribromobenzene is thus obtained as colourless crystals, m.p. 122° yield, 3 g. 

If the thermometer is to be used to determine the elevation of the boiling-point of a liquid on the addition of a solute, it must be remembered that at the boiling-point of the pure solvent the mercury must now be about 1-2 above the bottom of the scale S, and hence for adjustment purposes the temperature of the beaker of water should be 6—7 above the boiling-point of the liquid itself, instead of 1-2 as before. 

IVatfr. When water is used as a solvent, an ice-salt mixture should be employed for cooling purposes. 

All glassware should be scrupulously clean and, for most purposes, dry before being employed in preparative work in the laboratory. It is well to develop the habit of cleaning all glass apparatus immediately after use the nature of the dirt will, in general, be known at the time, and, furthermore, the cleaning process becomes more difficult if the dirty apparatus is allowed to stand for any considerable period, particularly if volatile solvents have evaporated in the meantime. 

The best method for removing water (and also solvents of relatively low boiling point) adhering to solids is drying under reduced pressure. A vacuum desiccator is used for this purpose several forms are shown in Fig. II, 38, 1. These are fitted with the exception of ( ) either with... 

CAUTION. Sodium must be handled with great care and under no circumstances may the metal be allowed to come into contact with water as a dangerous explosion may result. Sodium is stored under solvent naphtha or xylene it should not be handled with the fingers but with tongs or pincers. Waste or scrap pieces of sodium should be placed in a bottle provided for the purpose and containing solvent naphtha or xylene they should never be thrown into the sink or into the waste box. If it is desired to destroy the scrap sodium, it should be added in small portions to rather a large quantity of methylated spirit. 

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