Dry reactions

Qualitative analysis utilizes two kinds of tests, dry reactions and wet reactions. The former are applicable to solid substances and the latter to substances in solution. Most of the dry reactions to be described can be used with only minor modifications for semimicro analysis. Dry tests appear to have lost their popularity in certain quarters they do, however, often provide useful information in a comparatively short time and a knowledge as to how they are carried out is desirable for all students of qualitative analysis. Different techniques are employed for wet reactions in macro, semimicro, and micro analysis. 

2 DRY REACTIONS A number of useful tests can be carried out in the dry, that is without dissolving the sample. Instructions for such operations are given below. 

The tests are carried out upon a clean charcoal block in which a small cavity has been made with a penknife or with a small coin. A little of the substance is placed in the cavity and heated in the oxidizing flame. Crystalline salts break into smaller pieces burning indicates the presence of an oxidizing agent (nitrate, nitrite, chlorate, etc.). More frequently the powdered substance is mixed with twice its bulk of anhydrous sodium carbonate or, preferably, with fusion mixture (an equimolecular mixture of sodium and potassium carbon- 

Flame tests In order to understand the operations involved in the flame colour tests and the various bead tests to be described subsequently, it is necessary to have some knowledge of the structure of the non-luminous Bunsen flame (Fig. II.2). 

The non-luminous Bunsen flame consists of three parts (i) an inner blue cone ADB consisting largely of unburnt gas (ii) a luminous tip at D (this is only visible when the air holes are slightly closed) and (iii) an outer mantle ACBD in which complete combustion of the gas occurs. The principal parts of the flame, according to Bunsen, are clearly indicated in Fig. II.2 The lowest temperature is at the base of the flame (a) this is employed for testing volatile substances to determine whether they impart any colour to the flame. The 

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Endo-exo ratios of the micelle-catalysed reactions have been determined by adding 0.25 mmol of 5.1c and 0.5 mmol of 5.2 to a solution of 5 mmol of surfactant and 0.005 mmol of EDTA in 50 ml of water in carefully sealed 50 ml flasks. The solutions were stirred for 7 days at 26 C and subsequently freeze-dried. The SDS and CTAB containing reaction mixtures were stirred with 100 ml of ether. Filtration and evaporation of the ether afforded the crude product mixtures. Extraction of the Diels-Alder adducts from the freeze-dried reaction mixture containing C12E7 was performed by stirring with 50 ml of pentane. Cooling the solution to -18 C resulted in precipitation of the surfactant. Filtration and evaporation of the solvent afforded the adduct mixture. Endo-exo ratios... 

Yields of the order of 85% were secured in the dry reaction (48). (Propionic anhydride and butyric anhydride can be obtained similarly from their sodium salts.) Inasmuch as dinitrogen tetroxide can be regenerated, the economic prospects of this novel way of making anhydride are feasible. 

B. Preparation of Methoxime (MO)-TMS Derivatives (especially for hydroxyketosteroids, which may decompose under the given GC conditions unless the MO-TMS derivatives are prepared.) Add 0.25 ml of methoxime hydrochloride in pyridine to the dried extract. Let stand for 3 hours at 60° or overnight at room temperature. Evaporate to dryness with clean, dry nitrogen. Add 0.25 ml of TRI-SIL TBT and 0.25 ml of pyridine to the dried reaction mixture. Cap tightly and heat at 60° for a few hours or overnight at room temperature. 

Quartz glass (silica), pyrex (borosilicates) and other household and laboratory glasses (boroaluminosilicates) owe their high chemical resistance to the (tetrahedral) network forming properties of Si, B, P and A1 (cf., the borax and phosphate bead tests in qualitative dry reactions on the salts of numerous metals). 

Interaction with a chemical indicator Can be highly specific, if suitable indicator. Can measure total exposure over time (dosimetry), if a non-reversible reaction is used. Can allow operation at a convenient wavelength, when gas has no convenient absorption in that spectral range. Poisoning can occur, and is easily fouled. Sensitive to groups of chemicals, e.g. acid gases, rather than to a specific gas. May exhibit non-reversible behaviour, which, in many cases, may be undesirable. May need water vapour present, to act as a catalyst, if dry reaction is too slow. 

A second example of aldolization (Eq. 42) is the dry reaction of ferrocene carbal-dehyde with carbonyl compounds in the presence of potassium hydroxide, and Aliquat as catalyst [63]. Reactions which are too slow at room temperature are efficiently accelerated by use of microwaves, giving good yields within a few minutes. 

Steam heat. It is very easy to produce and can be used safely for so many things steam distillations, steam cleaning, creating a vacuum, etc. No lab should be without it. Make sure that steam does not get into anhydrous or dry reactions. 

Solutions containing several species (but mainly 84 and 85 ) are obtained upon digesting sulfur with aqueous sulfide. Solutions in methanol and ethanol may be prepared correspondingly. Salts of S (n = 2-8) can be obtained not only from such solutions but also from liquid NHj and in dry reactions. 

The PTS uses the principle of a specific colorimetric reaction, each toxic substance being detected by a reaction system specific to that gas. This principle provides the capability for extreme sensitivity down to less than one part per billion (10 ) while maintaining excellent specificity. Reactive chemicals are impregnated onto a continuous paper tape by a special process producing a dry reaction system. The tape is put into cassettes for convenient use and replacement in the Personal Tape Sampler (PTS). 

B. Dry Reactions.—When heated in the reducing flame a bead of microcosmic salt assumes a blue, violet, or brown colour with increasing quantities of niobic acid the heated bead becomes red on the addition of ferrous sulphate. With tantalic acid under these conditions the bead remains colourless. 

Niobium and Tantalum Gravimetric Methods, Volumetric Methods, Colorimetric Methods—Detection of Niobium and Tantalum Wet Reactions, Dry Reactions. 

Another assay commonly referred to as in vitro is the chemical synthesis assay of p-hematin. Developed by Egan et al. [64], a heme substrate solution, with or without inhibitors, is prepared in 0.1 M NaOH. The substrate is added to a pre-equilibrated (60 °C) acetate buffer (final concentration 4.5 M) reaction mixture and stirred for 10-30 minutes. After cooling on ice, the precipitate is filtered, washed with water and dried over silica gel or P2O5. The dried reaction mixture is analyzed by FT-IR and for solubility in 0.1 M sodium bicarbonate (pH 9.1). Several researchers have expressed concerns about extrapolating biologically... 

Uranium tetrafluoride precipitated from aqueous solutions exists as UF4 5H20, and it is difficult to remove the waters of hydration so that the dry reaction above is preferred.) UF4 is frequently used to make accelerator targets of uranium by vacuum volatilization. 

There have been reports of syntheses of cyano complexes in fused potassium cyanide, though the characterization of the products has not always been satisfactory.1 The dry reaction between potassium cyanide and potassium hexaiodoplatinate(IV), however, certainly gives the impure hexacyano-platinate(IV) and substitution of cycloocta-1,5-diene bonded to platinum(II) may be achieved by the use of solid potassium cyanide in the presence of a crown ether catalyst.16... 

The acid filtrate is treated with excess of ammonium chloride and with ammonia to precipitate the ferric oxide and any alumina, the precipitate being tested for the latter in the usual way. The filtrate is divided into three parts one is acidified with acetic acid and tested for copper with ferrocyanide in another the manganese (if present) is precipitated with ammonium sulphide, lime and magnesia being then tested for in the third sulphates are tested for with barium chloride. Manganese is best sought in a separate portion of the substance by the well-known dry reaction. 

Reaction scale < 100 g (dry reaction) < 100g up to 3000 g (depending on reactor type)... 

To a clean, dry reaction vessel add cesium fluoride on aluminium oxide (40 wt. %, 1.1 g, 2.2 mmol), ((l-phenyl-methylidene)amino)acetic acid methyl ester (0.35 g, 2.0 mmol), and 3-bromopropylbenzene (0.40 g, 2.0 mmol). 

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