Alternative Procedure

If sufficient rate data are unavailable for acidities below H0 -8.5, extrapolated rate coefficients may be obtained from the high-acidity region of the rate profiles by a different procedure. This latter may also be used for the extrapolation of data for compounds which show a mechanistic changeover [75JCS(P2)1600]. 

The data available for —130 compounds were processed in this way to derive the standard rate coefficients [75J(P2) 1600]. Note that when nitration occurs at more than one position, the slope of the rate profile refers to the overall reaction. Standard rate coefficients for nitrations at the individual positions are then obtained using the isomer distribution at the measured acidity nearest to 75 wt% H2S04. When nitration occurs at two or more equivalent positions, the calculated log k% values refer to overall reactivity, and must therefore be statistically corrected. 

The error involved in the standard procedure is estimated on the basis of standard rate coefficients obtained from different data sets for the same compound to be 0.2 log units. The error involved in the alternative procedure is expected to be much larger, although fair agreement between the two methods was found in the only two cases where both applications were possible. 

For some reactions, particularly those in which the reverse reaction is known to occur readily, it is necessary to determine if the product isomer distribution is due to thermodynamic rather than kinetic control. Products which are sterically hindered are particularly susceptible to rearrangement to less hindered isomers. It is also necessary to determine whether reaction occurs on the free base or conjugate acid, though for many of these reactions the conditions are considerably less acidic than those used in nitration or hydrogen exchange. 

In the following account, references are given to some examples of the uses of particular reagents and methods these are described in greater detail in subsequent chapters. 

Apparatus A 100-mL beaker. 10-mL graduated cylinder, Pasteur pipet, glass rod or 15-cm length of copper wire. 

Setting Up Pour 10 mL of a 5% aqueous solution of 1,6-hexanediamine into the beaker and add 10 drops of 20% aqueous sodium hydroxide solution. Stir the solution to ensure homogeneity. 

Reaction Carefully pour 10 mL of a 5% solution of decanedioyl dichloride into the beaker to produce a biphasic mixture. Touch the tip of the glass rod or end of the copper wire to the interface between the two layers and gently remove the rod or wire from the mixture, pulling the fiber of polymer along with it. Twist the rod or wire to spin the fiber around it. 

Work-Up and isolation Follow the procedure described for the Nylon Rope Trick.  

Fiber Formation Form fibers by carefully melting the dry polymer in a metal spoon or spatula with gentle heating over a very small burner flame or a hot plate, and then drawing fibers from the melt with a small glass rod. If necessary, combine your polymer wifh fhaf of several students to provide enough material to be melted 

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A modem alternative procedure involves computer matching of the entire drop profile to a best fitting theoretical curve in this way the entire profile is used, rather than just d and de, so that precision is increased. Also, drops whose ds is not measurable (how does this happen ) can be used. References 61 and 71-74 provide examples of this type of approach. 

Before taking up the results of measurements of heats and entropies of adsorption, it is perhaps worthwhile to review briefly the various alternative procedures for obtaining these quantities. 

Alternative procedure TMOHAS. The procedute tisitig TMOB.AS is the same as for QMOB.AS, The TMOB.AS program is slightly different in appearance from QMOB.AS, but it functions in the same way. See the True/iasic documentation for details. 

Alternative procedure Mathcad. Follow the procedure above except that where QMOBAS is indicated, use Mathcad instead. Enter the Huckel molecular orbital matrix, modified by subtracting xl, with some letter name. For example, call the modified matrix A. Type the command eigenvals(A) = with the name of the modified HMO matrix in parentheses. Mathcad prints the eigenvalues. The command eigenvecs(A) yields the eigenvectors, which are useful in ordering the energy spectrum. 

If preferred, the following alternative procedure may be adopted. The absolute alcohol is placed in a 1 5 or 2 litre three-necked flask equipped with a double surface reflux condenser and a mercury-sealed mechanical stirrqr the third neck is closed with a dry stopper. The sodium is introduced and, when it has reacted completely, the ester is added and the mixture is gently refluxed for 2 hours. The reflux condenser is then rapidly disconnected and arranged for downward distillation with the aid of a short still head or knee tube. The other experimental details are as above except that the mixture is stirred during the distillation bumping is thus reduced to a minimum. 

For water insoluble aldehydes or ketones, the following alternative procedure may be used. Reflux a mixture of 0-6 g. of the aldehyde or ketone, 0 5 g. of hydroxylamine hydrochloride, 5 ml. of ethanol and 0 5 ml. of pyridine on a water bath for 15-60 minutes. Remove the alcohol either by distillation (water bath) or by evaporation of the hot solution in a stream of air (water pump). Add 5 ml. of water to the cooled residue, cool in an ice bath and stir until the oxime crystallises Filter off the solid, wash it with a little water and dry. Recrystallise from alcohol (95 per cent, or more dilute), benzene, or benzene - light petroleum (b.p. 60-80°). 

When the derivative is appreciably soluble in ether, the following alternative procedure may be employed. Dissolve the cold leaction mixture in about 60 ml. of ether, wash it with 20-30 ml. of 10 per cent, hydrochloric acid (to remove the excess of base), followed by 20 ml. of 10 per cent, sodium hydroxide solution, separate the ether layer, and evaporate the solvent [CAUTION/]. Recrystallise the residue from dilute alcohol. 

The following alternative procedure may sometimes be employed. Dissolve 0-5 g. of the amine in 5 ml. of rectified spirit and add 5 ml, of a cold saturated solution of picric acid in alcohol. Warm on a water bath... 

An alternative procedure for the above test is as follows. Mix 2-3 ml. of 2 per cent, aqueous paraperiodic acid solution with 1 drop of dilute sulphuric acid (ca. 2 5N) and add 20-30 mg. of the compound. Shake the mixture for 5 minutes, and then pass sulphur dioxide through the solution until it acquires a pale yellow colour (to remove the excess of periodic acid and also iodic acid formed in the reaction). Add 1-2 ml. of Schiff s reagent (Section 111,70) the production of a violet colour constitutes a positive test. 

An alternative procedure is to leave the syrupy residue in a vacuum desiccator over anhydrous calcium chloride and siUca gel, and to Alter ofl the successive Crops of crystals as they separate. These are washed with light petroleum, b.p. 40-60°, spread on a porous tile and recrystallised. 

In an alternative procedure 26 g. of anhydrous ferric chloride replace the aluniiniuni chloride, the mixture is cooled to 10°, and the 50 g. of tert.-butyl chloride is added. The mixture is slowly warmed to 25° and maintained at this temperature until no more hydrogen chloride is evolved. The reaction mixture is then washed with dilute hydrochloric acid and with water, dried and fractionally distilled. The yield of tert.-butyl benzene, b.p. 167- 170°, is 60 g. 

I) An alternative procedure is to cool the solution containing the sodium sul. phanilate and sodium nitrite in a bath of crushed ice to about 5° and then add 10-5 ml. of concentrated hydrochloric acid diluted with an equal volume of water slowly and with stirring the temperature must not be allowed to rise above 10 and an excess of nitrous acid should be present (the solution is tested after standing for 5 minutes). The subsequent stages in the preparation—addition of dimethyl-aniline solution, etc.—are as above. 

The following alternative procedure is sometimes useful. Heat the amine with the theoretical quantity of benzoyl chloride (if the molecular weight is unknown, use an equal weight of benzoyl chloride in the preliminary experiment) to 100° for 20-30 minutes. Allow to cool, add excess of 5 per cent, sodium hydroxide solution and shake, if necessary,... 

An alternative procedure, more suitable for the preparation of somewhat larger quantities of the bromo derivative, is the following. Dissolve 10 g, of the compovmd in 10-15 ml. of glacial acetic acid, cautiously add 3-4 ml. of hquid bromine, and allow the mixture to stand for 15-20 minutes. Pour into 50-100 ml. of water, filter off the bromo compound at the pump, and wash with a httle cold water. Recrystallise from dilute alcohol. 

An alternative procedure, which does not require ice cooling, is to add all the 10 ml. of benzoyl chloride rapidly to a mixture of 50 ml. of concentrated ammonia solution and 60 ml. of water contained in a 200 ml. conical flask, stopper securely and shake vigorously for about 15 minutes. Heat is evolved So that the stopper should be held down tightly. After 30 minutes the benzamide is filtered off and worked up as above. 

The following alternative procedure is recommended and it possesses the advantage that the same tube may be used for many sodium fusions. Support a Pyrex test tube (150 X 12 mm.) vertically in a clamp lined with asbestos cloth or with sheet cork. Place a cube (ca. 4 mm. side = 0 04 g.) of freshly cut sodium in the tube and heat the latter imtil the sodium vapour rises 4 5 cm. in the test-tube. Drop a small amount (about 0-05 g.) of the substance, preferably portionwise, directly into the sodium vapour CAUTION there may be a slight explosion) then heat the tube to redness for about 1 minute. Allow the test tube to cool, add 3-4 ml. of methyl alcohol to decompose any unreacted sodium, then halffill the tube with distilled water and boil gently for a few minutes. Filter and use the clear, colourless filtrate for the various tests detailed below. Keep the test-tube for sodium fusions it will usually become discoloured and should be cleaned from time to time with a little scouring powder. 

The determination of the saponification equivalent of an ester by the alcohohc potassium hydroxide method is described in Section 111,106 an alternative procedure using diethylene glycol is given below. This constant should be determined if possible in the prehminary examination, since a knowledge of its value together with the boihng point provides a basis for a fairly good approximation of the size of the ester molecule. 

An alternative procedure involves use of alkyl nitrites and traps the desired product as an acetal[16],... 

Castillo, C. A. Jaramillo, A. An Alternative Procedure for Titration Curves of a Mixture of Acids of Different Strengths, /. Chem. Educ. 1989, 66, 341. 

In an alternative procedure the acids themselves undergo cyclization cataly2ed by hydrogen fluoride. y-Phenylbutyric acid [36541-31-8] can be cychzed to a-tetralone [29059-07-2] by this method ... 

Moderate yields of acids and ketones can be obtained by paHadium-cataly2ed carbonylation of boronic acids and by carbonylation cross-coupling reactions (272,320,321). In an alternative procedure for the carbonylation reaction, potassium trialkylborohydride ia the presence of a catalytic amount of the free borane is utilized (322). FiaaHy, various tertiary alcohols including hindered and polycycHc stmctures become readily available by oxidation of the organoborane iatermediate produced after migration of three alkyl groups (312,313,323). 

In an alternative procedure (84), the electrolyte is pumped through the cells at such a rate that the outlet concentration is 50 g/L MnSO and 67 g/L H2SO4. This spent electrolyte is then mixed with equal parts of make-up solution containing 150 g/L MnSO and the mixture returned to the electrolysis step. The electrolysis is continued over a period of days and terrninated when the EMD layer deposited on the anode reaches a specific thickness, usually on the order of 1—3 or 6—8 mm. Following completion of the electrolysis cycle, the entire electrode assembly is removed from the cell for removal of the deposited EMD, either manually or by an automated system (85). The product is repeatedly washed with water to extract the occluded acid (83) and dried at about 85°C in air. 

An alternative procedure for the preparation of (R)-calcium pantothenate (3) is to condense (R)-pantolactone (9) with the preformed calcium salt (12) of p-alaniue (15). 

Chloroform may be estimated quantitatively by determining the amount of copper oxide produced when it is warmed with Fehling s solution, which is potassium cupritartrate (34). An alternative procedure consists of heating the chloroform with concentrated alcohoHc potassium hydroxide in a sealed tube at 100°C and determining the amount of potassium chloride produced (35). 

This alternative procedure is called the xyz method. The amount of change hy the first reaction is x, hy the second y, and hy the third z. For the same example,... 

Isolation procedures for many biochemicals are based on chromatography. Practically any substance can be selected from a crude mixture and eluted at relatively high purity from a chromatographic column with the right combination of adsorbent, conditions, and eluant. For bench scale or for a small pilot plant, such chromatography has rendered alternate procedures such as electrophoresis nearly obsolete. Unfortunately, as size increases, dispersion in the column ruins resolution. To produce small amounts or up to tens of kilograms per year, chromatography is an excellent choice. When the scale-up problem is solved, these procedures should displace some of the conventional steps in the chemical process industries. 

Confirmation of the formation of the radicals during combustion reactions has been made by inuoducing a sample of dre flames into a mass spectrometer. The sample is withdrawn from a turbulent flame which is formed into a thin column, by admitting a sample of the flame to the spectrometer drrough a piidrole orifice, usually of diameter a few tenths of a millimetre. An alternative procedure which has been successful in identifying the presence of radicals, such as CHO, has been the use of laser-induced fluorescence. 

For shorter penetration the use of p emitting isotopes is widely made applying much the same absorption law for p radiation as for y rays, with a minor modification. An alternative procedure used by Kingety and Paladino for the study of diffusion in AI2O3 employs two right cylinders, one only containing the radioactive Al isotopic species which emits relatively low energy ( ,nax = 0.511 MeV) p particles. 

An alternative procedure used for large apparatus is to rinse the apparatus with a 5% solution of dichloromethyl silane in chloroform, followed by several rinses with water before baking the apparatus at 180°/2h (for glass) or drying in air (for plasticware). 

An alternative procedure rescales the coordinates of each atom at each time step [24]. The atomic coordinate x and the characteristic distance for repeating boundary conditions, d, are rescaled to values uc and fid, respectively, where... 

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