Small-scale

Fixing the rate of heat transfer in a batch reactor is often not the best way to control the reaction. The heating or cooling characteristics can be varied with time to suit the characteristics of the reaction. Because of the complexity of hatch operation and the fact that operation is usually small scale, it is rare for any attempt to be made... 

A valuable reference to anyone involved with friction at small scales. 

The relations pertain to the fine, small-scale time variations in the phase and the log modulus, not to their large-scale changes. 

Ozone has long been used on a small scale for water purification since it destroys viruses, and recent developments suggest that this use will increase in importance. 

How come then, that although the laws of chemistry arc too complicated to be solved, chemists still can do their jobs and make compounds with beautiful properties that society needs, and chemists run reactions from small-scale laboratoiy ex-pci imcnts to large-scale rcactoi s in chemical industi y ... 

The material to be steam-distilled (mixed with some water if a solid compound, but not otherwise) is placed in C, and a vigorous current of steam blown in from D. The mixture in C is thus rapidly heated, and the vapour of the organic compound mixed with steam passes over and is condensed in E. For distillations on a small scale it is not necessary to heat C if, however, the flask C contains a large volume of material or material which requires prolonged distillation, it should be heated by a Bunsen burner, otherwise the steady condensation of steam in C will produce too great a volume of liquid. 

Although apparatus employing ground-glass joints is excellent for work on a macro scale, it is not always suitable for very small-scale work as the joints are often disproportionately large compared with the rest of the assembly. The semi-micro apparatus described on pp. 59-72 can therefore be considered as being of general utility for this scale of work, especially as the use of corks has been reduced to a minimum. 

Introduction. When only very small quantities of organic materials are available their manipulation must necessarily be carried out on a correspondingly small scale. This occurs frequently in research problems, but small-scale preparative work is often of value to the student because considerable economy of materials and of time can be achieved. It is emphasised, however, that the proper training for the organic chemist must rest upon the correct understanding and thorough practice of the manipulations on the macro-scale already described, and that he should consider small-scale work as a sequel to and not as a replacement of the above standard techniques. 

Determination of Melting-points. The determination of the melting-point, as described on pp. 2-4, is of course in itself a micro-method. Even so, when working on a very small scale it is advantageous to use either ... 

Reflux Distillation Unit. The apparatus shown in Fig. 38 is a specially designed distillation-unit that can be used for boiling liquids under reflux, followed by distillation. The unit consists of a vertical water-condenser A, the top of which is fused to the side-arm condenser B. The flask C is attached by a cork to A. This apparatus is particularly suitable for the hydrolysis of esters (p. 99) and anilides (p. 109), on a small scale. For example an ester is heated under reflux with sodium hydroxide solution while water is passed through the vertical condenser water is then run out of the vertical condenser and passed through the inclined condenser. The rate of heating is increased and any volatile product will then distil over. 

Steam generator. For small scale work the steam generator D, Fig. 15, p. 33) is too cumbersome for the production of a small amount of steam. It is preferable to use a 250 ml. conical flask fitted with cork containing a vertical safety tube and an outlet-tube (Fig. 44). Care should be taken that the length of rubber tubing connecting the steam oudet tube to the flask containing the materi to be distilled should be as short as possible and should not contain kinks. 

Sublimation. This is a most useful process for small-scale work as the losses are comparatively small. This can be performed (a) In a long narrow tube sealed at one end. The material is shaken to the closed end of the tube, which is then inserted horizontally in a metal-heating block (Fig. 50) (b) In the cold-finger device (Fig. 35, p. 62)-... 

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. 

The nitrosamines are insoluble in water, and the lower members are liquid at ordinary temperatures. The separation of an oily liquid when an aqueous solution of an amine salt is treated with sodium nitrite is therefore strong evidence that the amine is secondary. Diphenylnitrosoamine is selected as a preparation because it is a crystalline substance and is thus easier to manipulate on a small scale than one of the lower liquid members. For this preparation, a fairly pure (and therefore almost colourless) sample of diphenyl-amine should be used. Technical diphenylamine, which is almost black in colour, should not be employed. 

Osazone formation. The preparation of glucosazone has already been given (p. 137). It may be carried out on a small scale by either of the following methods, according as (a) the phenyl hydrazine base, or (Z>) one of its salts, is used. 

First carry out a small-scale test, placing about 0 5 g. of the mixture in a test-tube, adding about 5 ml. of 10% aqueous NaOH solution, and shaking the mixture well. It will be readily seen whether the neutral substance (which remains undissolved) is solid or liquid. Then repeat the extraction on a largo scale as follows ... 

Principle. This is essentially a small-scale modification of the macro piethod described on p. 416, the substance being completely oxidised in a sealed tube with fuming nitric acid in the presence of silver nitrate, the halogen being thus converted into silver halide. The collection and weighing of the silver halide require special techniques on the semi-micro scale. 

First, considerably greater emphasis has been placed on semimicro techniques and their application to preparations, separations, analysis and physical determinations such as those of molecular weight. We have therefore greatly expanded the section on Manipulation on a semi-micro scale which was in the Third Edition, and we have described many more preparations on this scale, some independent and others as alternatives to the larger-scale preparations which immediately precede them. Some 40 separate preparations on the semi-micro scale are described in detail, in addition to specific directions for the preparation of many classes of crystalline derivatives required for identification purposes. The equipment required for these small-scale reactions has been selected on a realistic basis, and care has been taken not to include the very curious pieces of apparatus sometimes suggested as necessary for working on the semi-micro scale. 

In Part III, dealing with the Reactions and Identification of Organic Compounds, greater emphasis has now been placed on the preparation of suitable crystalline derivatives. Quite apart from the importance of these derivatives for purposes of identification, encouragement is thereby given to the student to gain experience in small-scale preparative work. 

In the original planning of this book we were at pains to ensure that the preparations in particular were designed to afford a minimum expenditure of time, materials and heating. We hope that the economy thus introduced will be especially appreciated in view of the recent heavily increased cost of chemicals, fuel and laboratory service. This increased cost, incidentally, must necessarily increase the attraction of the small-scale preparations referred to above. 

The experimental details for recrystallisation from mixed solvents (or solvent pairs) will be evident from the account already given the best proportions of the two solvents are determined by preliminary small-scale experiments. 

Nitro derivatives. No general experimental details for the preparation of nitro derivatives can be given, as the ease of nitration and the product formed frequently depend upon the exact experimental conditions. Moreover, some organic compounds react violently so that nitrations should always be conducted on a small scale. The derivatives already described are usually more satisfactory for this reason the nitro derivatives have been omitted from Table IV,9. 

Mechanical stirring, although not essential for small scale preparations, is advantageous and increases the yield slightly. 

Sublimation.—This is a valuable means for the purification of many organic substances and is admirably adapted for small scale work since losses are generally small. Sublimation may be carried out either at atmospheric pressure or under reduced pressure. The apparatus shown in Fig. XII, 2, 20 is simple and effective the sublimate is collected on the cold finger condenser. 

Small scale apparatus with interchangeable ground glass joints (compare Section 11,56) are available commercially. One set of apparatus ( A) is based largely upon BlO and B14 joints, although occasionally a larger size joint is used as in the steam distillation apparatus shown in Fig. XII, 3, 1. 

This subject is dealt with ab initio in the author s book entitled Elementary Practical Organic Chemiairy. Parti. SmaU Scale Preparations. (Longmans, Green and Co. Ltd., 1957.) The treatment is comprehensive and includes a detailed account of small scale apparatus of novel design. 

If a small-scale special apparatus is not available, proceed as follows Place 1-5 g. (1-9 ml.) of re-butyl alcohol and 0 28 g. of purified red phosphorus in a 25 ml. round-bottomed flask, and add 2-5 g. of io ne in 2 portions. Allow to stand for 2-3 minutes, heat on a boiling water bath under reflux for 30 minutes, add 5 ml. of water and distil. Separate the lower layer of the distillate. Work up the product as described in 111,40. 

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