Diazonium salt solution

Gattermann s reaction A variation of the Sandmeyer reaction copper powder and hydrogen halide are allowed to react with the diazonium salt solution and halogen is introduced into the aromatic nucleus in place of an amino group. 

The excess of acid (0-5-1 equivalents) maintains a proper condition of acidity required to stabilise the diazonium salt solution by reducing the secondary... 

The diazonium salt solution decomposes on standing and hence must be mixed with the Cuprous chloride solution without delay. Mechanical stirring is an advantage. 

Dissolve 46-5 g. (45-5 ml.) of aniUne in a mixture of 126 ml. of concentrated hydrochloric acid and 126 ml. of water contained in a 1-htre beaker. Cool to 0-5° in a bath of ice and salt, and add a solution of 36-5 g. of sodium nitrite in 75 ml. of water in small portions stir vigorously with a thermometer (1) and maintain the temperature below 10°, but preferably at about 5° by the addition of a httle crushed ice if necessary. The diazotisation is complete when a drop of the solution diluted with 3-4 drops of water gives an immediate blue colouration with potassium iodide - starch paper the test should be performed 3-4 minutes after the last addition of the nitrite solution. Prepare a solution of 76 g. of sodium fluoborate (2) in 150 ml. of water, cool, and add the chilled solution slowly to the diazonium salt solution the latter must be kept well stirred (1) and the temperature controlled so that it is below 10°. Allow to stand for 10 minutes with frequent stirring. Filter... 

Unsymmetrical diaryls may be prepared by treating an aryl diazonium salt solution with sodium hydroxide or sodium acetate in the presence of a liquid aromatic compound. Thus 2-chlorodiphenyl is readily formed from o-chloro phenyl diazonium chloride and sodium hydroxide solution (or sodium acetate solution) in the presence of benzene ... 

The reactivity of the 5-position of 2-aminothiophene in diazo coupling, which is present also in the acylated derivatives, complicates the formation of a diazonium salt from 2-aminothiophene. Thus Steinkopf and Miiller obtained only an azo dyestuff, although they proved, through the isolation of small amounts of 2-thienyl diazonium chloride, the diazotizability of 2-aminothiophene which had earlier been denied. However, recent Russian work claims the preparation of 2-thienyldiazonium chloride by treating the double salt in 10% hydrochloric acid with sodium nitrite. Amazingly high yields (over 90%) of azo compounds were then achieved by coupling the diazonium salt solution with y9-naphtol, w-toluidine or with the 2-aminothiophene double salt. These authors have also studied the... 

Preparation of 2-Hydroxy-4,4 -Dicyanostilbene 10 grams of 2-amino-4,4 -dicyanostilbene thus prepared were dissolved in 400 cc of boiling glacial acetic acid and 200 cc of dilute sulfuric acid added the solution was suddenly chilled and diazotized over one and a half hours at 5° to 10°C with sodium nitrate (3.0 grams/15 cc H O). The diazonium salt solution was decomposed by boiling for 15 minutes with 600 cc of 55% aqueous sulfuric acid solution the solution was diluted, cooled and filtered. The residue crystallized from ethyl alcohol as lemon yellow prismatic needles, MP 296°C. 

An increased hydrogen ion concentration, that is a considerably greater amount of acid than the theoretical two equivalents of Scheme 2-1, is necessary in the diazotization of weakly basic amines. The classic example of this is the preparation of 4-nitrobenzenediazonium ions 4-nitroaniline is dissolved in hot 5-10 m HC1 to convert it into the anilinium ion and the solution is either cooled quickly or poured onto ice. In this way the anilinium chloride is precipitated before hydrolysis to the base can occur. On immediate addition of nitrite, smooth diazotization can be obtained. The diazonium salt solution formed should be practically clear and should not become cloudy on standing in the dark. Some practice is necessary, and details can be found in the books emphasizing preparative aspects (Fierz-David and Blangey, 1952 Saunders and Allen, 1985 in Houben-Weyl, Vol. E 16a, Part II, the chapter written by Engel, 1990). These books give a series of detailed prescriptions for specific examples and a useful review of the principal variations of the methods of diazotization. Such reviews have also been written by Putter (1965) and Schank (1975). 

Ultraviolet spectra of diazonium salt solutions were recorded for the first time by Hantzsch and Lifschitz as early as 1912. However, electron spectra did not provide significant information on the structure of diazonium ions, either at that time or later. For example, Anderson and coworkers (Anderson and Steedly, 1954 Anderson and Manning, 1955), compared spectra of 4-amino-benzenediazonium salts with those of diphenylquinomethane (4.18). Their conclusion that the structures of these compounds are analogous is basically correct, but the arguments given by Anderson can easily be refuted, as shown by Sorriso (1978, p. 102). 

H5C20 —C-S K+) to the diazonium salt solution. This leads to replacement of... 

It has been suggested that the initial formation of iodine on addition of iodide to a diazonium salt solution is caused by oxidation of the iodide by excess nitrite from the preceding diazotization. Packer and Taylor (1985) demonstrated that, if urea was added as a nitrite scavenger (see Sec. 2.1) to a diazotization solution, that solution produced iodine much more rapidly than a portion of the same diazonium salt solution not containing urea, but eventually the latter reaction too appeared to follow the same course. This confirms the role of excess nitrite, and suggests that the iodo-de-diazoniation steps only occur in the presence of iodine or triiodide (I -). The same authors also found that iodo-de-diazoniation is much slower under nitrogen. All these observations are consistent with radical-chain processes, but not with a heterolytic iodo-de-diazoniation. 

In the older literature and in papers by some industrial azo chemists up to the 1960s it was claimed that (Z)-diazoates react in azo coupling processes. This belief can be traced back to the paper by Schraube and Schmidt (1894), who discovered the (Z)/(ii)-isomerism of diazoates (see Sec. 1.1). The most important tool used by Schraube and Schmidt for distinguishing between the two isomers was the (correct) observation that only one of the isomers reacted with coupling components, forming the same azo dye as when diazonium salt solutions were used. The apparent reactivity of the (Z)-diazoate is due to the fact that its equilibrium with the diazonium ion is relatively rapid, whereas the diazonium ion is produced only very slowly from the (ii)-diazoate (see Sec. 7.1). 

Heat 85.5 g 3-carbethoxy-2-piperidone and 30 g KOH in 1 L water for twelve hours at 30°. Filter, cool to 0°, add 50 ml 6N HCI. Prepare a fresh solution by diazotizing at 0-5° a mixture of 85 g 3-amino-4-Cl-acetophenone, 250 ml concentrated HCI and 750 ml water with a solution of 36 g Na nitrite in 125 ml water. Add the piperidone solution at 0° to the diazonium salt solution and stir five hours at 10°. Filter, wash precipitate with water to get 80% yield of the hydrazone (1) (recrystallize-95% ethanol). Reflux 62 g (I) in 310 ml 88% formic acid to get 40 g of the carboline (II) (recrystallize-absolute ethanol) (test for activity). Reflux 40 g (II), 100 g KOH, 480 ml ethanol and 360 ml water for eighteen hours and evaporate in vacuum. Add 480 ml water to the residue, cool and adjust pH to 6 with glacial acetic acid. Scratch glass to precipitate filter, wash precipitate with cold water to get 41 g 4-acetyl-2-COOH-7-CI-tryptamine (recrystallize-50% ethanol) which can be alkylated to the active dialkyltryptamine as described elsewhere here. 

As the range of components available for use in the azoic dyeing process expanded, research was simultaneously targeted on improvements designed to make the process more attractive to the commercial dyer. The necessity for the dyer to diazotise the Fast Base was removed with the introduction of stabilised diazonium salts [111], known as Fast Salts. Stabilisation was achieved by a judicious selection of the counter-ion to the diazonium cation various anions have found use in commercial Fast Salts and some examples are listed in Table 4-4. Particularly effective is the diazonium tetrachlorozincate, which can be readily prepared by adding an excess of zinc chloride solution to a solution of the diazonium salt. The precipitated complex diazonium salt is usually admixed with an inert diluent, which enhances its stability, and in use the dyer only needs to dissolve the powder in water to prepare the necessary diazonium salt solution. 

In addition to these active stabilised diazonium salts that give a diazonium salt solution immediately on dissolving in water, there are certain derivatives of diazonium compounds from which the diazonium salt can be readily regenerated. One group of such derivatives is the class of compounds known as tmti-diazo fates [112]. Diazotates are formed when the pH... 

The clarified acidic diazonium salt solution is first transferred to a coupling vat equipped with a mechanical agitator, and the clarified alkaline coupling component solution is then added above or under the surface of the diazonium salt solution. Constant agitation is essential. 

The kinetics of the coupling mechanism include a number of sometimes very fast and competitive side reactions. The following steps, for instance, proceed simultaneously as a separately prepared diazonium salt solution is combined with an initially dissolved coupling component ... 

Another variety of the continuous-coupling technique operates by transporting the coupling component suspension as a laminar flow upwards inside a vertical reaction tube. Portions of the diazonium compound, dissolved in an acidic aqueous medium, are added through appropriately located inlets in the walls of the reaction tube. The concentration of the added solution decreases as the reaction mixture flows upward and is designed to synchronize the uppermost inlet for the diazonium salt solution with the stoichiometric end point of the coupling reaction. 

The pigments are obtained by treating the appropriate amine with water/hy-drochloric acid to form the amine hydrochloride. In most cases, subsequent dia-zotization is carried out in the cold (0 to 5°C) with an aqueous sodium nitrite solution (a). The resulting diazonium salt solution is then transferred onto sodium... 

The rapid addition of the diazonium salt solution to the sodium sulfite seems to be advantageous. 

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