Laboratory methods

General Directions to the Student.—Before beginning an experiment read through to the end the directions which are to be followed. Many mistakes which involve additional work can be prevented by understanding beforehand just what is to be done. The import of the experiment should be clear, and the chemical reactions involved at each step should be understood before the work is started. 

References are given in each experiment to the section in the author s textbook The Principles of Organic Chemistry in which the chemical reactions involved are discussed. These references are given in bold-face type thus, (SECTION 359). References to paragraphs in this book are indicated thus, 64, page 42. 

Keep a clear and concise record of the laboratory work. The notes should be written as soon as the experiment has been per-forned, and care should be taken to have the original record, made during the course of the experiment, of such a character that it serves as the permanent record of the work. Notes should not be taken on loose pieces of paper and afterward written out in the notebook they should be written carefully in good English, and should state briefly what was done and what was observed. It is necessary for the student to recognize what the experiment is to teach—why he was asked to do it. If the 

The student should use reasonable care in his manipulations. He should endeavor to get as large a yield as possible of the product sought, but should use judgment as to whether it is advisable to spend a large amount of time to increase by a small amount the yield of the product. The processes should not be carried out in the manner used with a quantitative analysis—a few drops may be lost here and there if they form but a very small portion of the total amount formed, and their recovery entails the expenditure of much extra time. It is not meant by this that the student be careless be should develop judgment as to the relative value of a slightly higher yield of product and the time required to obtain it. 

Integrity in Laboratory Work.—The student should record in his notebook his own observations only, and the results he has obtained himself, unless there is a definite statement to the contrary. If a student has carried out an experiment along with another student a statement to this effect should be put into the notes. 

---

C00H)2 + PCI5 -+ 0=PCl3 + COJ + COi + 2HC1I This is a convenient laboratory method. 

On the industrial scale oxygen is obtained by the fractional distillation of air. A common laboratory method for the preparation of oxygen is by the decomposition of hydrogen peroxide. H Oj, a reaction catalysed by manganese(IV) oxide ... 

Describe one laboratory method for the preparation of a dilute solution of hydrogen peroxide. 

Alternatively a mixture of almost any solid chloride and manganese-(IV) oxide will yield chlorine when warmed with concentrated sulphuric acid. These are the most common laboratory methods but there are many others. 

It should be emphasised that whereas the interaction of a sodium salt and an acid chloride is a convenient general laboratory method for preparing all classes of anhydrides, acetic anhydride is prepared on a large scale by other and cheaper methods. Industrial processes are based on reactions indicated by the equations ... 

Dehydrogenation of alkylbenzenes is not a convenient laboratory method but is used industrially to convert ethylbenzene to styrene... 

Polyethylene (Section 6 21) A polymer of ethylene Polymer (Section 6 21) Large molecule formed by the repeti tive combination of many smaller molecules (monomers) Polymerase chain reaction (Section 28 16) A laboratory method for making multiple copies of DNA Polymerization (Section 6 21) Process by which a polymer is prepared The principal processes include free radical cationic coordination and condensation polymerization Polypeptide (Section 27 1) A polymer made up of many (more than eight to ten) amino acid residues Polypropylene (Section 6 21) A polymer of propene Polysaccharide (Sections 25 1 and 25 15) A carbohydrate that yields many monosacchande units on hydrolysis Potential energy (Section 2 18) The energy a system has ex elusive of Its kinetic energy... 

Rump, H. H. Krist, H. Laboratory Methods for the Examination of Water, Wastewater and Soil. VCH Publishers New York, 1988. 

Tucker, S. A. Acree, Jr., W. E. A Student-Designed Analytical Laboratory Method, /. Chem. Educ. 1994, 71, 71-74. 

The first sample to be analyzed is the field blank. If its spike recovery is unacceptable, indicating that a systematic error is present, then a laboratory method blank. Dp, is prepared and analyzed. If the spike recovery for the method blank is also unsatisfactory, then the systematic error originated in the laboratory. An acceptable spike recovery for the method blank, however, indicates that the systematic error occurred in the field or during transport to the laboratory. Systematic errors in the laboratory can be corrected, and the analysis continued. Any systematic errors occurring in the field, however, cast uncertainty on the quality of the samples, making it necessary to collect new samples. 

Industrial production is often based on transformation of this laboratory method into a continuous process (10). Another route is acetonitrile [75-05-8] hydration ... 

Several methods have been developed to estimate the oxygen demand in waste water treatment systems. Commonly used laboratory methods are biochemical oxygen demand (BOD), chemical oxygen demand (COD), total oxygen demand (TOD), total organic carbon (TOC), and theoretical oxygen demand (ThOD). 

Formic acid [64-18-6] (methanoic acid) is the first member of the homologous series of alkyl carboxyHc acids. It occurs naturally ia the defensive secretions of a number of insects, particularly of ants. Although the acid nature of the vapors above ants nests had been known since at least 1488, the pure acid was not isolated until 1671, when the British chemist John Ray described the isolation of the pure acid by distillation of ants (1). This remained the main preparative method for more than a century until a convenient laboratory method was discovered by Gay-Lussac (2). The preparation of formates using carbon monoxide was described by Berthelot in 1856. 

Beckman Elutriation Method. The Beckman elutriation method uses a chamber designed so that the centrifugal effect of the radial inward fluid flow is constant (Fig. 3). The separation chambers are made of transparent epoxy resin which faciUtates observation of the movements of the cell boundary in strobe light illumination. This enables detection of the radius at which the cells are separating. When a mixture of cells, eg, mononuclear white cells, enters the chamber, separation can be achieved by fine tuning centrifuge speed and inward fluid flow to the specific cell group. This is a laboratory method suitable for relatively small numbers of cells. Chambers are available in sizes to handle 2-3 x 10 , 1 2 x 10 , and 1 x 10 ° cells. The Beckman chambers can be appHed to collect mononuclear cells from bone marrow aspirates. 

Properties. Results for the operation using subbituminous coal from the Wyodad mine near Gillette, Wyoming, are shown in Table 13. Char yields decreased with increasing temperature, and oil yields increased. The Fischer assay laboratory method closely approximated the yields and product assays that were obtained with the TOSCOAL process. 

Laboratory methods for isolating lignosulfonates iaclude dialysis (56,57), electro dialysis (58), ioa exclusioa (58,59), precipitatioa ia alcohol (60,61), and extraction with amines (62—64). They can also be isolated by precipitation with long-chain substituted quartemary ammonium salts (65—67). 

Fig. 15. Laboratory methods for measuring sohds suspension quahty (a) visual, and (b) light transmission.

Other simple tests include the soil burial test used to demonstrate the biodegradabiUty of polycaprolactone (25), following its disappearance as a function of time, and the clear 2one method which indicates biodegradation by the formation of a clear 2one in an agar medium of the test polymer or plastic as it is consumed (26). The burial test is still used as a confirmatory test method in the real-world environment after quantitative laboratory methods indicate bio degradation. 

The photolysis of carbonyl sulfide is a laboratory method for the production of monoatomic sulfur, a short-Hved species (29). 

A number of processes have been devised for purifying thionyl chloride. A recommended laboratory method involves distillation from quinoline and boiled linseed oil. Commercial processes involve adding various high boiling olefins such as styrene (qv) to react with the sulfur chlorides to form adducts that remain in the distillation residue when the thionyl chloride is redistilled (179). Alternatively, sulfur can be fed into the top of the distillation column to react with the sulfur dichloride (180). Commercial thionyl chloride has a purity of 98—99.6% minimum, having sulfur dioxide, sulfur chlorides, and sulfuryl chloride as possible impurities. These can be determined by gas chromatography (181). 

Processes that are essentially modifications of laboratory methods and that allow operation on a larger scale are used for commercial preparation of vinyhdene chloride polymers. The intended use dictates the polymer characteristics and, to some extent, the method of manufacture. Emulsion polymerization and suspension polymerization are the preferred industrial processes. Either process is carried out in a closed, stirred reactor, which should be glass-lined and jacketed for heating and cooling. The reactor must be purged of oxygen, and the water and monomer must be free of metallic impurities to prevent an adverse effect on the thermal stabiUty of the polymer. 

A convenient laboratory method for the preparation of BCl is by the reaction of AlCl and BF or BF (47—49). More recently a patent describing the preparation of BCl by halogenating B(OH)2 or esters of B(OH)2 using an excess of the oxychloride of S or P in the presence of a dessicant and catalytic amounts of Fe, Co, or Ni, at temperatures below 100°C was issued (50). This process eliminates formation of carbonic dichloride [75-44-5] ... 

There are many laboratory methods for testing the relative merits of one defoamer against another. It is a simple matter to measure foam height as a function of time to compare the performance of various foam surfactants and defoamers. Unfortunately, this simplicity has led to a wide variety of methods and conditions used with no standard procedure that would make the measurement of foaminess as characteristic of a solution as its surface tension or viscosity. It has been suggested that the time an average bubble remains entrapped ia the foam is such a quantity (49), but very few workers ia the defoamer iadustry have adopted this proposal. Ia practice, a wide variety of methods are used that geaerally fall iato oae of five maia categories ... 

More objective laboratory methods employ a mechanical device such as a Terg-O-Tometer (110). Food soils are appHed to microscope sHdes or glass tape rather than to actual plates. The soils are tagged with fluorescent materials or with dark pigment to faciUtate measurement of residual soil. Reflectance or transmittance may also be read directly (111). 

There are several laboratory methods useful for the preparation of suberic acid. One starting material is 1,6-hexanediol which can be converted to the dibromide with HBr. Reaction of the dibromide with NaCN gives the dinitrile which can be hydrolyzed to suberic acid. The overall yield is 76% (42). Another laboratory method is the condensation of 1,3-cyclohexanedione with ethyl bromoacetate foUowed by reductive cleavage to give suberic acid in 50% yield (43). 

The acid chlorides are generally more reactive than the corresponding acid anhydrides. In fact, the alcoholysis of acid chlorides is probably the best laboratory method for preparing esters. Frequentiy, basic materials are added during the course of the reaction to neutralize by-product hydrochloric acid. When the basic material is aqueous caustic, the procedure is referred to as the Schotten-Baumann procedure (73). Esterification of tertiary alcohols by acid chlorides is described in Reference 74. Esters of tertiary alcohols can also be formed through an intermediate /-butyl thioate group (75) ... 

Analytical Methods. Most of the analytical and testing methods used for ethyl ether are conventional laboratory methods. Ethyl ether that is to be used for anesthetic purposes or in processes that involve heating or distiHation must be peroxide-free, and should pass the USP standard test with potassium iodide. This test detects approximately 0.001% peroxide as hydrogen peroxide. 

The most convenient laboratory method for the preparation of 2,4-dimethyl-5-carbethoxypyrrole is that given above. A cheaper method of obtaining large quantities consists in the partial hydrolysis of 2,4-dimethyl-3,5-dicarbethoxypyrrole with sulfuric acid, followed by decarboxylation. The ester has been obtained also by the alcoholysis of 5-trichloroaceto-2,4-dimethyl-pyrrole in the presence of sodium ethylate. The free acid has been obtained fronii-[2,4-dimethylpyrrole-5]-2,4-dimethylpyrrole-5-carboxylic acid and from 2,4-dimethylpyrrole-5-aldehyde. ... 

The use of the Grignard reagents of the type RMgX for the production of alkyl-and aryl-chlorosilanes was pioneered by Kipping in 1904 and has been for a long time the favoured laboratory method for producing these materials. 

Cobalt and cobalt compounds in air - Laboratory method using flame atomic absoiption spectrometry... 

Methods of testing plastics. Method 140D Flammability of a test piece 550 mm x 35 mm of thin polyvinyl chloride sheeting (laboratory method). Supersedes BS 2782 Part 1 Method MOD 1980... 

Withdrawn) 1974 AMD 1 Laboratory methods of test for determination of smoke generation charactenstics of cellular plastics and cellular rubber materials. Part 1 Method for testing a 25 mm cube test specimen of low density material (up to 130 kg/metres cubed) to continuous flaming conditions (AMD 7688) dated 15 July 1993. Withdrawn, superseded by BS ISO 5659-2 1994... 

Withdrawn) 1974 AMD 1 Laboratory methods of test for determination of smoke generation charactenstics of cellular plastics and cellular rubber materials. Superseded by BS ISO 5659-2 1994... 

Fuhrhop, J.-H., Smith, K. M. laboratory Methods in Porphyrin and Metalporphyrin Research. Elsevier Publ., Amsterdam 1975, 243ff. 

Polymerase chain reaction (Section 28.16) A laboratory method for making multiple copies of DNA. 

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. ... 

A suitable laboratory method is to shift the Schlenk equilibrium in a Grignard solution (p. 132) by adding dioxan to precipitate the... 

---