Diazonium compounds, preparation

Commercial sodium nitrite contains 1—3% sodium nitrate, the harmful effect of which on diazonium compounds may be obviated by adding to the amine solution or the nitrite solution an amount (1-5—4 5% of the weight of nitrite used) of sodium metabisulphite slightly in excess of that necessary to reduce the nitrate. Diazonium compounds prepared in this way or with pure sodium nitrite are much more stable (J. Soc. Dyers, 41, 275.)... 

Thiophois Fused with other Nitrogm-cMitainiiig Heterocycles.— Thionaph-thenophenazines (486) have been prepared by the condensation of thionaphthaquinones with o-phenylenediamines/ Thieno[2,3-d]-1.2,3-tri-azines (487) were obtained by intramolecular cyclizations of diazonium compounds prepared from derivatives of 2-aminothiophen-3-carbox-amides/ In a similar way (488) gave (489). ... 

In preparing an aqueous sol ution of a diazonium salt, such as benzene-diazonium chloride, it is usual to dissolve the amine in a slight excess (about 2 2 molecular equivalents) of dilute hydrochloric acid (or alternatively to dissolve the crystalline amine hydrochloride in i 2 equivalents of the acid) and then add an aqueous solution of a metallic nitrite. Nitrous acid is thus generated in situ, and reacts with the amine salt to give the diazonium compound. For a successful preparation of an aqueous solution of the diazonium salt, however, two conditions must always be observed ... 

The student is recommended to carry out the preparation of iodo-benzene in order to gain experience in the preparation of aqueous solutions of diazonium compounds, and then to prepare a solution of benzenediazonium hydrogen sulphate with which to carry out the chief reactions that diazonium compounds undergo. 

Solid diazonium salts are very sensitive to shock when perfectly dry and detonate violently upon gentle heating they are, therefore, of little value for preparative work. Happily, most of the useful reactions of diazonium compounds can be carried out with the readily-acoeasible aqueous solutions, so that the solid (explosive) diazonium salts are rarely requir. ... 

The solution must be strongly acid in order to avoid the coupbng reaction between the undecomposed diazonium salt and the phenol (see under Azo Dyes). For the preparation of phenol and the cresols, the aqueous solution of the diazonium compound is warmed to about 50° at higher temperatures the reaction may become unduly vigorous and lead to appreciable quantities of tarry compounds... 

The conversion of an aromatic diazonium compound into the corresponding arsonic acid by treatment with sodium arsenite in the presence of a catalyst, such as copper or a copper salt, is called the Bart reaction. A modification of the reaction employs the more stable diazonium fluoborate in place of the diazonium chlorid.i. This is illustrated by the preparation of />-nitrophenylarsonic acid ... 

CAUTION. Diazonium compounds have been used for the preparation of —... 

Aryl diazonium ions prepared by nitrous acid diazotization of primary arylamines are substantially more stable than alkyl diazonium ions and are of enormous synthetic value Their use m the synthesis of substituted aromatic compounds is described m the following two sections... 

Whilst azo compounds prepared from diazonium salts and phenolic or keto-enol coupling components are often depicted in the hydroxyazo form (4.11), an alternative tautomeric structure can be drawn for such compounds (Scheme 4.19). This ketohydrazone tautomer (4.21) can, in cases where the azo and hydroxy groups are located on adjacent carbon atoms, exhibit hydrogen bonding between the two groups as shown. Similar pairs of structures, but without hydrogen bonding, can be drawn for p-hydroxyazo compounds. 

In order to manufacture a diarylide yellow pigment, the diamine, dissolved in hydrochloric acid or sulfuric acid, is bisdiazotized with an aqueous sodium nitrite solution. The resulting diazonium compound is subsequently coupled onto two equivalents of acetoacetarylide. Since a material with a very fine particle size is needed for a fast and complete coupling reaction, the coupling component is prepared by dissolution in an alkaline medium and reprecipitation with an acid, such as acetic acid or hydrochloric acid. Dichlorobenzidine cannot be diazotized stepwise. A lack of sodium nitrite does not produce the monodiazonium compound, but an excess of 3,3 -dichlorodiaminodiphenyl remains. 

Several of these internal diazonium salts, prepared by diazotisation of anthranilic acids, are explosive in the solid state, or react violently with various materials. Individually indexed compounds (including analogous sulfonates) are Benzenediazonium-2-carboxylate, 2659 Benzenediazonium-3 or 4-carboxylate, 2661... 

Both 2- and 3-azidodibenzothiophene have been prepared by the action of sodium azide on the appropriate diazonium compound (>90%). Heating 2-azidodibenzothiophene in polyphosphoric acid yields 2,2 -azodibenzothiophene (54%). ... 

Aromatic diazonium compounds which are prepared readily by diazotization of primary amines can be converted either to their parent compounds by replacement of the diazonium group with hydrogen, or to hydrazines by reduction of the diazonium group. Both reactions are carried out at room temperature or below using reagents soluble in aqueous solutions, and usually give high yields. 

Pschorr cyclization of diazotized A-mesyl-o-aminodiphenylamine yields A-mesyl-5,7-dihydro-6H-dibenz[c,e]azepine (73AJC1307). Diazonium compounds also feature in the preparation of 1 lH-dibenz[6,e]azepines via nitrilium ions (Scheme 21) (72CB1634), and in the only synthesis reported so far of a tribenz[6,rf,/]azepine (10 R=Ph) (72CB880). 

Diazotise 223 g. of 2-naphtliylamine-l-sulphonic acid as detailed under fi-Bromonaphthalene in Section IV,62. Prepare cuprous cyanide from 125 g. of cupric sulphate pentahydrate (Section IV,66) and dissolve it in a solution of 65 g. of potassium cyanide in 500 ml. of water contained in a 1-litre three-necked flask. Cool the potassium cuprocyanide solution in ice, stir mechanically, and add the damp cake of the diazonium compound in small portions whilst maintaining the temperature at 5-8°. Nitrogen is soon evolved and a red precipitate forms gradually. Continue the stirring for about 10 hours in the cold, heat slowly to the boiling point, add 250 g. of potassium chloride, stir, and allow to stand. Collect the orange crystals which separate by suction filtration recrystallise first from water and then from alcohol dry at 100°. The product is almost pure potassium 2-cyanonaphthalene-l-sulphonate. Transfer the product to a 2-litre round-bottomed flask, add a solution prepared from 400 ml. of concentrated sulphuric acid and 400 g. of crushed ice, and heat the mixture under reflux for 12 hours. Collect the -naphthoic acid formed (some of which sublimes from the reaction mixture) by suction filtration... 

Arsonium ylides have also been prepared from the decomposition of diazonium compounds in the presence of a tertiary arsine. Thus tet-raphenylcyclopentadiene triphenylarsorane (13) was obtained by heating diazotetraphenylcyclopentadiene at its melting point in the presence of triphenylarsine (66). 

Reaction VIH. Action of certain finely divided Metals on Diazonium Compounds in Alcohol or Acetic Anhydride Solution.—This reaction is limited to the preparation of s-diaryl compounds. Copper, zinc, or iron powder may be used, but the former is, on the whole, the most satisfactory, especially when it has been freshly prepared according to Gattermann s... 

As usual in Sandmeyer reactions, the product, if volatile, is separated by distillation in steam if non-volatile, extraction or filtration is used. The manner in which the cuprous salt reacts is not exactly known it certainly unites at first with the diazonium compound to form a double salt (c/. Reaction CLXVI.). The method is widely applicable, and as the yields are usually good, it is a standard method for the preparation of aromatic nitriles. 

This reaction can be employed to remove a primary amino group from an aromatic compound, especially. when the ordinary method of direct reduction of the diazonium compound by sodium stannite or alcohol is not applicable. Although in the application of this method the hydrazine can be prepared as the hydrochloride, and reduced in the same solution, yet it is better to isolate the free base and oxidise it separately, since in the oxidation of the hydrochloride there is a tendency for the hydrazine radical to be replaced by chlorine. 

Diazonium compounds are usually prepared in mineral acid solution, and the nitrous acid generated from sodium nitrite. Sufficient acid must be used to generate nitrous acid and to form the salt of the base, and still leave the solution acid. In practice 2J—2f mols. of hydrochloric acid are generally employed. In most cases it is essential that the reaction be carried out at about 0°, as many diazonium solutions decompose above this temperature. The reaction goes very readily in some cases but in others, and especially where an acid group is present, e.g., naphthylamine sul-phonic acids, the reaction is only carried out with difficulty. It is possible to diazotise a solid in suspension, but the reaction is usually very slow. If the solid is dissolved and reprecipitated in a fine state of division the action goes much more quickly. 

Diazodinitrophenol (DDNP, Dinol) 4,6-Dinitrobenzene-2-diazo-l-oxide, or diazodinitrophenol as it is more commonly called, occupies a place of some importance in the history of chemistry, for its discovery by Griess56 led him to undertake his classic researches on the diazonium compounds and the diazo reaction. He prepared it by passing nitrous gas into an alcoholic solution of picramic acid, but it is more conveniently prepared by carrying out the diazotization in aqueous solution with sodium nitrite and hydrochloric acid. 

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