Small-scale preparations

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. 

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. 

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

Chapter XII is concerned with Semimicro Technique. There can be little doubt that preparations on a smaller scale than has hitherto been customary have many advantages particular reference may be made to cost, time and bench space, all of which are important factors in teaching laboratories and also in training for research. Once the student has mastered the special technique, no difficulty should be experienced in adapting most of the preparations described in the book to the semimicro scale. A few examples of small-scale preparations are included together with a suggested list of experiments for an elementary course. 

For small-scale preparation of samples for scientific studies, the precursor polymer may be dissolved in xylene at 80°C, followed by addition of the cation source. A gelled fluid is normally obtained immediately, and the ionomer is recovered as a powder by chopping the gel in a large excess of acetone using a laboratory blender. 

Originally, p-tolylsulfonyldiazomethane was prepared by passing an ethereal solution of its precursor, ethyl i 7-nitroso-iV -(j3-toly]8ulfonyI-methyl)carbamate, slowly through a column of alumina, This procedure, which results in yields about 10% higher, is convenient only for small-scale preparations, up to a maximum of 5 g. of p-tolylsulfonyl-diazomethane. The present modification is due to Middelbos, ... 

Following the completion of the polymerization process, the beaded polymer is recovered from the suspension mixture and freed from the stabilizer, diluents, and traces of monomers and initiators. For laboratory and small-scale preparation, repeated washings with water, methanol, or acetone are appropriate. Complete removal of the monomer diluent, solvents, and initiator, especially from macroporous resin, may require a long equilibration time with warm methanol or acetone. In industry, this is usually accomplished by stream stripping. 

Hydrogen can be prepared by the reaction of water or dilute acids on electropositive metals such as the alkali metals, alkaline earth metals, the metals of Groups 3, 4 and the lanthanoids. The reaction can be explosively violent. Convenient laboratory methods employ sodium amalgam or calcium with water, or zinc with hydrochloric acid. The reaction of aluminium or ferrosilicon with aqueous sodium hydroxide has also been used. For small-scale preparations the hydrolysis of metal hydrides is convenient, and this generates twice the amount of hydrogen as contained in the hydride, e.g. ... 

The rapid reaction of 1,2,3,4-tetrahydronaphtha-lene (tetralin) with Br2 at 20° affords an alternative small-scale preparation though only half the Br2 is converted, the other half being lost in brominating the tetralin ... 

Small-scale preparations can conveniently be effected as follows ... 

The a>-amino acids are available at high purity but are generally more expensive titan their lactams and only suitable for the small-scale preparation of polymers. As they are bulk polymerizations, the polymerization temperature is preferably above die melting temperature of the polymer. 

Approximately 95% of the iron pentacarbonyl is added within 2 hours, and the remaining 5% is then added dropwise over the next 30 minutes. The blue color should never be completely discharged prior to the end point, particularly toward the end of the reaction, since the remaining solution may be deactivated. Avoiding premature discharge of the blue color is especially important in small-scale preparations. At the end point 1 ml. or less of the iron pentacarbonyl remains in the dropping funnel. 

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

Small-scale preparation is recommended [1], in view of a previous explosion through superheating of the liquid dining distillation at 109°C [2],... 

In 1978, Corey reported a general synthetic route for the conversion of alkenes to conjugated nitroalkenes via nitro-mercuration and demercuration.74 Since then, many chemists have used this method for the preparation of cyclic nitroalkenes such as 1-nitrocyclohexene. However, the use of mercury salts is not recommended even for the small-scale preparation of nitroalkenes. This reaction is not as clean as expected, and formidable efforts are required to remove the mercury in the waste. 

LiCl precipitation—for large- and small-scale preparations At the end of... 

A chapter dedicated to the laboratory (small scale) preparation methods of inter-metallics has then been included (Chapter 6). In the preparation of intermetallic phases, indeed (or, more generally, of alloys), in comparison to other chemical compounds a number of interesting and significant peculiarities are pointed out, for instance, those related to their high melting points, insolubility in many common solvents, etc. The presentation of selected examples of preparative methods, therefore,... 

Small-scale preparations and the chemical modification of fine chemicals and elaborate intermediates are usually conducted in solution. For this purpose soluble metathesis catalysts of predictable and reproducible activity are generally preferred. The catalytic systems presently known can be grouped into multi-component and single-component catalysts (Tables 3.14-3.16). 

There is limited patent literature available on manufacturing techniques for aluminophosphates. Although many patents describe AlPO synthesis, most described examples are small-scale preparations. The fact that at least two catalytic applications have been commercialized for SAPO molecular sieves indicates that they have been scaled-up to large quantities [55, 56]. A large-scale preparation of SAPO-34 is described in a recent patent [57]. 

Selected applications of small-scale preparative l.c. of carbohydrates are given in Table IV. Although the amounts of carbohydrate isolated are low (several pig to 20 mg), they are often enough for subsequent qualitative methods such as H-n.m.r. spectroscopy. By computer automa-... 

In some small-scale preparations of this type in the checkers laboratory, commercial household bleach (Chlorox , 5.25% NaOCl) has been used and the course of the reaction has been followed by thin layer chromatography. The yields appear to be somewhat lower than those obtained with sodium hypochlorite prepared as described above. The obvious attractive alternative, preparation of potassium hypochlorite as described elsewhere in this series, apparently has not been tried. 

The hydration of alkenes is one important method of synthesizing alcohols. Industrially, sulfuric acid is used as a catalyst, while small-scale preparations often utilize toxic mercury compounds. (Definitely not the kind of stuff you want to drink.)... 

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