Solvent laboratory

Ader M, Coleman ML, Doyle SP, Stroud M, Wakelin D (2001) Methods for the stable isotopic analysis of chlorine in chlorate and perchlorate compounds. Anal Chem 73(20) 4946-4950 Ben Othman D, White WM, Patchett J (1989) The geochemistry of marine sediments, island arc magma genesis, and crust-mantle recycling. Earth Planet Sci Lett 94 1-21 Beneteau KM, Aravena R, Frape SK (1999) Isotopic characterization of chlorinated solvents-laboratory and field results. Organic Geochemistry 30(8A) 739-753... 

Bioaccumulatlon of some pesticides (fenitrothion, aminocarb, permethrin) with real or potential application in forestry in Canada has been examined in laboratory experiments using larval rainbow trout and common duckweed. Bioaccumulation of an aromatic hydrocarbon, fluorene, has also been examined since some commercial formulations employ hydrocarbon solvents. Laboratory exposures of fish or plants were carried out by placing the organisms in dilute aqueous solutions of C labelled pesticide or hydrocarbon, and by measuring transfer of radioactivity from water to fish or plants. After transfer of fish or plants to untreated water, loss of radioactivity was measured similarly. These measures allowed calculation of uptake and depuration rate constants which were used to predict residue accumulations under various exposure conditions. Predicted residue accumulations agreed substantially with other predictive equations in the literature and with reported field observations. 

Larger scale epoxidations are frequently performed in aromatic solvents such as toluene [104] even though it is known that the Jt-donor aromatic system of toluene competes with the olefin for coordination to the positively charged carbonyl carbon [105]. The epoxidation reaction is generally faster in more polar solvents. Laboratory scale epoxidations of PBD with peracids can be performed in chlorinated solvents such as dichloromethane or chloroform. Ethers such as dioxane are known to decrease the reactivity of peroxides in the epoxidation of PBD because their oxygen atoms can interact with the percarboxylic acid, thereby decreasing the reactivity (Fig. 2) [106]. Epoxidations in cyclohexane show lower conversion than epoxidations in toluene [107]. 

Dimeihylamine, C2H7N, (CH3)2NH. Colourless, inflammable liquid with an ammoniacal odour, mp -96" C, b.p. 7°C. Occurs naturally in herring brine. Prepared in the laboratory by treating nitrosodimetbyl-aniline with a hot solution of sodium hydroxide. Dimethylamine is largely used in the manufacture of other chemicals. These include the solvents dimethylacetamide and dimethyl-formamide, the rocket propellant unsym-metrical dimethylhydrazine, surface-active agents, herbicides, fungicides and rubber accelerators. 

The effect known either as electroosmosis or electroendosmosis is a complement to that of electrophoresis. In the latter case, when a field F is applied, the surface or particle is mobile and moves relative to the solvent, which is fixed (in laboratory coordinates). If, however, the surface is fixed, it is the mobile diffuse layer that moves under an applied field, carrying solution with it. If one has a tube of radius r whose walls possess a certain potential and charge density, then Eqs. V-35 and V-36 again apply, with v now being the velocity of the diffuse layer. For water at 25°C, a field of about 1500 V/cm is needed to produce a velocity of 1 cm/sec if f is 100 mV (see Problem V-14). 

On a laboratory scale, hydrotliennal syntliesis is usually carried out in Teflon-coated, stainless-steel autoclaves under autogenous pressure. A typical syntliesis mixture consists of up to four major constituents, a T-atoni source (silicon and aluminium, otlier elements may also be incoriiorated as indicated above), a solvent (almost exclusively... 

However, it is common practice to sample an isothermal isobaric ensemble NPT, constant pressure and constant temperature), which normally reflects standard laboratory conditions well. Similarly to temperature control, the system is coupled to an external bath with the desired target pressure Pq. By rescaling the dimensions of the periodic box and the atomic coordinates by the factor // at each integration step At according to Eq. (46), the volume of the box and the forces of the solvent molecules acting on the box walls are adjusted. 

The biologiccJ function of a protein or peptide is often intimately dependent upon the conformation(s) that the molecule can adopt. In contrast to most synthetic polymers where the individual molecules can adopt very different conformations, a protein usually exists in a single native state. These native states are found rmder conditions typically found in Uving cells (aqueous solvents near neutred pH at 20-40°C). Proteins can be unfolded (or denatured) using high-temperature, acidic or basic pH or certain non-aqueous solvents. However, this unfolding is often reversible cind so proteins can be folded back to their native structure in the laboratory. 

Although benzenesulphonyl chloride has for simplicity been used in the above discussion, tolucne-/>- sulphonyl chloride, CHaCeH SO Cl, is more frequently used in the laboratory, owing to its much lower cost, the latter being due in turn to the fact that toluene-p-sulphonyl chloride is a by-product in the commercial preparation of saccharin. Toluene-p sulphonyl chloride is a crystalline substance, of m.p. 68° the finely powdered chloride will, however, usually react readily with amines in the Schotten-Baumann reaction it does not react so readily with alcohols, but the reaction may be promoted considerably by first dissolving the chloride in some inert water-soluble solvent such as acetone. 

The most dangerous solvent in the laboratory is carbon disulphide, the flash-point of which is so low that its vapour is ignited, e.g., by a gas-ring 3 4 minutes after the gas has been turned out. CarlK>n disulphide should therefore never be used in the laboratory unless an adequate substitute as a solvent cannot be found. Probably the next most dangerous liquid for general manipulation is ether, which, however, has frequently to be employed. If the precautions described on pp. 79, 163, are always followed, the manipulation of ether should however quite safe. 

The theory of the process can best be illustrated by considering the operation, frequently carried out in the laboratory, of extracting an orgaiuc compound from its aqueous solution with an immiscible solvent. We are concerned here with the distribution law or partition law which, states that if to a system of two liquid layers, made up of two immiscible or slightly miscible components, is added a quantity of a third substance soluble in both layers, then the substance distributes itself between the two layers so that the ratio of the concentration in one solvent to the concentration in the second solvent remains constant at constant temperature. It is assumed that the molecular state of the substance is the same in both solvents. If and Cg are the concentrations in the layers A and B, then, at constant temperature ... 

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. 

Rubber stoppers are frequently employed in the laboratory in vacuum distiUation assemblies (compare Section 11,19) for distillations under atmospheric pressure bark corks are generally used. Many organic liquids and vapours dissolve new rubber stoppers slightly and cause them to swell. In practice, it is found that rubber stoppers which have been previously used on one or two occasions are not appreciably attacked by most organic solvents, owing presumably... 

The inflammable solvents most frequently used for reaction media, extraction or recrystallisation are diethyl ether, petroleum ether (b.p. 40-60° and higher ranges), carbon disulphide, acetone, methyl and ethyl alcohols, di-Mo-propyl ether, benzene, and toluene. Special precautions must be taken in handling these (and other equivalent) solvents if the danger of Are is to be more or less completely eliminated. It is advisable to have, if possible, a special bench in the laboratory devoted entirely to the recovery or distillation of these solvents no flames are permitted on this bench. 

The theory underlying the removal of impurities by crystaUisation may be understood from the following considerations. It is assumed that the impurities are present in comparatively small proportion—usually less than 5 per cent, of the whole. Let the pure substance be denoted by A and the impurities by B, and let the proportion of the latter be assumed to be 5 per cent. In most instances the solubilities of A (SJ and of B (/Sb) are different in a particular solvent the influence of each compound upon the solubility of the other will be neglected. Two cases will arise for an3 particular solvent (i) the impurity is more soluble than the compound which is being purified (/Sg > SA and (ii) the impurity is less soluble than the compound Sg < S ). It is evident that in case (i) several recrystallisations will give a pure sample of A, and B will remain in the mother liquors. Case (ii) can be more clearly illustrated by a specific example. Let us assume that the solubility of A and 5 in a given solvent at the temperature of the laboratory (15°) are 10 g. and 3 g. per 100 ml. of solvent respectively. If 50 g. of the crude material (containing 47 5 g. of A and 2-5 g. of B) are dissolved in 100 ml. of the hot solvent and the solution allowed to cool to 15°, the mother liquor will contain 10 g. of A and 2-5 g. (i.e., the whole) of B 37-5 g. of pure crystals of A will be obtained. 

The most desirable characteristics of a solvent for recrystalhsation are (a) a high solvent power for the substance to be purified at elevated temperatures and a comparatively low solvent power at the laboratory temperature or below (6) it should dissolve the impurities readily or to only a very small extent (c) it should yield well-formed crystals of the purified compound and (d) it must be capable of easy removal from the crystals of the purified compound, i.e., possess a relatively low boiling point. It is assumed, of course, that the solvent does not react chemically with the substance to be purified. If two or more solvents appear to be equally suitable for the recrystallisation, the final selection will depend upon such factors as ease of manipulation, inflammability and cost. 

Frequently the water or other solvent is so firmly held that it cannot be completely removed in a vacuum desiccator at the ordinary temperature. These substances are dried in a vacuum oven at a higher temperature. A convenient laboratory form of vacuum oven is the so-called... 

Attention is directed to the fact that ether is highly inflammable and also extremely volatile (b.p. 35°), and great care should be taken that there is no naked flame in the vicinity of the liquid (see Section 11,14). Under no circumstances should ether be distilled over a bare flame, but always from a steam bath or an electrically-heated water bath (Fig.//, 5,1), and with a highly efficient double surface condenser. In the author s laboratory a special lead-covered bench is set aside for distillations with ether and other inflammable solvents. The author s ether still consists of an electrically-heated water bath (Fig. 11, 5, 1), fitted with the usual concentric copper rings two 10-inch double surface condensers (Davies type) are suitably supported on stands with heavy iron bases, and a bent adaptor is fitted to the second condenser furthermost from the water bath. The flask containing the ethereal solution is supported on the water bath, a short fractionating column or a simple bent still head is fitted into the neck of the flask, and the stUl head is connected to the condensers by a cork the recovered ether is collected in a vessel of appropriate size. 

Redistil laboratory grade ethylene glycol under reduced pressure and collect the fraction of b.p. 85-90°/7 mm. for use as a solvent for the potassium fluoride. 

All solubility determinations for Group tests are carried out at the laboratory temperature in small test-tubes (e.g., 100 X 12 mm.) but of suflScient size to permit of vigorous shaking of the solvent and the solute. 

Zemplen helped his students in many ways. I remember an occasion in the difficult postwar period. The production of the famous Hungarian salami, interrupted by the war, was just in the process of being restarted for export. The manufacturer wanted a supportive analysis from the well-known professor. Zemplen asked for a suitable sample of some hundreds of kilograms, on which the whole institute lived for weeks. When it was gone he rightly could offer an opinion that the product was quite satisfactory. After the war, grain alcohol was for a long time the only available and widely used laboratory solvent, and, not unexpectedly, it also found other uses. Later, when it was denatured to prevent human consumption, we devised clever ways for its purification. The lab also manufactured saccharine, which was... 

Most of the modeling methods discussed in this text model gas-phase molecular behavior, in which it is reasonable to assume that there is no interaction with other molecules. However, most laboratory chemistry is done in solution where the interaction between the species of interest and the solvent is not negligible. 

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