Diazonium formation

Rearrangement of fused cyclie systems has been studied and migratory aptitudes compared. For example, in the fused system 32, diazonium formation and rearrangement provided a mixture of 33a, 33b, and 34 arising from phenyl migration and cyclohexyl migration in a 50 3 33 ratio. ... 

General Procedure for the Diazonium Formation. To a round-bottom flask fitted with an addition funnel and N2 inlet was added boron trifluoride etherate (4 equiv) that was then chilled in a dry ice-acetone bath (-20 °C). To the reaction flask was added dropwise over 5 min a solution of the aniline derivative (1 equiv) in dry THF, followed by a solution of tert-butylnitrite (3.5 equiv) in dry THF over 30 min. The chilled mixture was stirred an additional 10 min, and the cold bath was allowed to warm to 5 °C over 20 min. To the mixture was added diethyl ether, and the mixture was chilled in an ice-bath for 15 min. The solid was collected by filtration, washed... 

Diazonium compounds are usually very soluble in water, and cannot be readily isolated, since on warming their aqueous solutions, decomposition occurs with the formation of a phenol ... 

When an aqueous solution of a diazonium salt is added to an alkaline solution of a phenol, coupling occurs with formation of an azo-compound (p. 188). If ho vc cr the ntiueous solution of the diazonium salt, t. . ., />-bromohenzene diazonium chloride, is mixed with an excess of an aromatic hydrocarbon, and aqueous sodium hydroxide then added to the vigorously stirred mixture, the diazotate which is formed, e.g., BrC,H N OH, dissolves in the hydrocarbon and there undergoes decomposition with the formation of nitrogen and two free radicals. The aryl free radical then reacts with the hydrocarbon to give a... 

A similar reaction occurs when an aqueous solution of a diazonium compound is made strongly alkaline and then warmed with an alkaline solution of stannous chloride. This reaction, however, involves the intermediate formation of the... 

C,H5N,NHC,Hs+HC1 = C,H 5N C1+H,NC,H5- C H5N NC H NH +HC1 gen atom of the aniline molecule, giving aminoazobenzene. Since this reaction is irreversible, whilst the former is freely reversible, the final result is the complete conversion of the diazoaminobenzene into the aminoazobenzene. (The intermediate formation of the benzenediazonium chloride can be demonstrated by adding dimethylaniline, with which the diazonium chloride couples preferentially, giving dimethylaminoazobenzene, C6HsN NC6HiN(CH3)i.)... 

The most noteworthy reaction of azo-compounds is their behaviour on reduction. Prolonged reduction first saturates the azo group, giving the hydrazo derivative (C NH-NH C), and then breaks the NH NH linkage, with the formation of two primary amine molecules. If method (1) has been employed to prepare the azo-compound, these two primary amines will therefore be respectively (a) the original amine from which the diazonium salt was prepared, and (6) the amino derivative of the amine or phenol with which the diazonium salt was coupled. For example, amino-azobenzene on complete reduction gives one equivalent of aniline, and one of p-phenylene diamine, NHaCeH NH benzene-azo-2-naphthoI similarly gives one equivalent of aniline and one of... 

Azo-dye formation. Dissolve 2-3 drops of aniline in 1 ml. of cone. HCl and add 3 ml. of water. Shaike to dissolve any hydrochloride which may have separated and cool in ice. Add a few drops of 20% sodium nitrite solution. Add this cold diazonium solution to a cold solution of the phenol in an excess of aqueous NaOH solution. Solutions or precipitates of azo-dyes ranging in colour from orange through scarlet to dark red, according to the phenol used, are obtained. Note in particular that i-naphthol gives a brownish-red, 2-naphthol a scarlet precipitate. Catechol decomposes. 

Note on the laboratory preparation of monoethylaniline. Although the laboratory preparation of monomethyl- or monoethyl-aniline is hardly worth whUe, the following experimental details may be useful to those who wish to prepare pure monoethylaniline directly from amline. In a flask, fitted with a double surface reflux condenser, place 50 g. (49 ml.) of aniline and 65 g. of ethyl bromide, and boU gently for 2 hours or until the mixture has almost entirely sohdified. Dissolve it in water and boil off the small quantity of unreacted ethyl bromide. Render the mixture alkaUne with concentrated sodium hydroxide solution, extract the precipitated bases with three 50 ml. portions of ether, and distil off the ether. The residual oil contains anihne, mono- and di-ethylaniline. Dissolve it in excess of dilute hydrochloric acid (say, 100 ml. of concentrated acid and 400 ml. of water), cool in ice, and add with stirring a solution of 37 g. of sodium nitrite in 100 ml. of water do not allow the temperature to rise above 10°. Tnis leads to the formation of a solution of phenyl diazonium chloride, of N-nitrosoethylaniline and of p-nitrosodiethylaniline. The nitrosoethylaniline separates as a dark coloured oil. Extract the oil with ether, distil off the ether, and reduce the nitrosoamine with tin and hydrochloric acid (see above). The yield of ethylaniline is 20 g. 

Primary aromatic amines differ from primary aliphatic amines in their reaction with nitrous acid. Whereas the latter yield the corresponding alcohols (RNHj — ROH) without formation of intermediate products see Section 111,123, test (i), primary aromatic amines 3neld diazonium salts. Thus aniline gives phcnyldiazonium chloride (sometimes termed benzene-diazonium chloride) CjHbNj- +C1 the exact mode of formation is not known, but a possible route is through the phenjdnitrosoammonium ion tlius ... 

The controlled thermal decomposition of dry aromatic diazonium fluoborates to yield an aromatic fluoride, boron trifluoride and nitrogen is known as the Schiemann reaction. Most diazonium fluoborates have definite decomposition temperatures and the rates of decomposition, with few exceptions, are easily controlled. Another procedure for preparing the diazonium fluoborate is to diazotise in the presence of the fluoborate ion. Fluoboric acid may be the only acid present, thus acting as acid and source of fluoborate ion. The insoluble fluoborate separates as it is formed side reactions, such as phenol formation and coupling, are held at a minimum temperature control is not usually critical and the temperature may rise to about 20° without ill effect efficient stirring is, however, necessary since a continuously thickening precipitate is formed as the reaction proceeds. The modified procedure is illustrated by the preparation of -fluoroanisole ... 

The mechanism of the reaction probably involves the intermediate formation ofthe covalent dlazo-hydroxide from the diazonium salt the former decomposes... 

The product of this series of steps is an alkyl diazonium ion, and the amine is said to have been diazotized Alkyl diazonium ions are not very stable decomposing rapidly under the conditions of their formation Molecular nitrogen is a leaving group par excel lence and the reaction products arise by solvolysis of the diazonium ion Usually a car bocation intermediate is involved... 

Figure 22 5 shows what happens when a typical primary alkylamine reacts with nitrous acid Because nitrogen free products result from the formation and decomposition of diazonium ions these reactions are often referred to as deamination reactions Alkyl... 

Primary arylamines like primary alkylammes form diazonium ion salts on nitro sation Aryl diazonium 10ns are considerably more stable than their alkyl counterparts Whereas alkyl diazonium 10ns decompose under the conditions of their formation aryl diazonium salts are stable enough to be stored m aqueous solution at 0-5°C for a rea sonable time Loss of nitrogen from an aryl diazonium ion generates an unstable aryl cation and is much slower than loss of nitrogen from an alkyl diazonium ion... 

Reaction of aryl diazonium salts with iodide ion (Section 22 17) Adding po tassium iodide to a solution of an aryl diazonium ion leads to the formation of an aryl iodide... 

Reaction with arenediazonium salts Adding a phe nol to a solution of a diazonium salt formed from a primary aromatic amine leads to formation of an azo compound The reaction is carried out at a pH such that a significant portion of the phenol is pres ent as its phenoxide ion The diazonium ion acts as an electrophile toward the strongly activated ring of the phenoxide ion... 

Azo coupling (Section 22 18) Formation of a compound of the type ArN=NAr by reaction of an aryl diazonium salt with an arene The arene must be strongly activated toward... 

Aromatic Ring Fluorination. The formation of an aryl diazonium fluoride salt, followed by decomposition, is a classical reaction (the Schiemaim reaction) for aryl fluoride preparation (21). This method has been adapted to the production-scale manufacture of fluorobenzene [462-06-6]... 

When a diazonium salt is allowed to react with antimony pentachloride or an aryltetrachloroantimony compound, the onium salts [ArN2] [SbClg] or [ArN2] [Ar SbCl ], respectively, are formed. These can be decomposed ia an organic solvent by the addition of a powdered metal such as iron or ziac, with the formation of a diaryltrichloroantimony compound ... 

Unsaturated hydrazones, unsaturated diazonium salts or hydrazones of 2,3,5-triketones can be used as suitable precursors for the formation of pyridazines in this type of cyclization reaction. As shown in Scheme 61, pyridazines are obtainable in a single step by thermal cyclization of the tricyanohydrazone (139), prepared from cyanoacetone phenylhydrazone and tetracyanoethylene (76CB1787). Similarly, in an attempted Fischer indole synthesis the hydrazone of the cyano compound (140) was transformed into a pyridazine (Scheme 61)... 

DUTT - WORMALL Azide formation Synthesis of aromatic azides from anilines via diazonium salts. 

GOMBERG - BACHMANN - GRAEBE - ULLMANN Arylatwn Atykaryl bond formation via diazonium salts Carbazole synthesis by intramolecular aryl-aryl bond formation. 

LEUCKART Thiophenot Synthesis Formation of Ihiophenols from diazonium salts and xanthates... 

Among the reagents that are classified as weak electrophiles, the best studied are the aromatic diazonium ions, which reagents react only with aromatic substrates having strong electron-donor substituents. The products are azo compounds. The aryl diazonium ions are usually generated by diazotization of aromatic amines. The mechanism of diazonium ion formation is discussed more completely in Section 11.2.1 of Part B. 

Some of the cuprous chloride compounds of the diazonium salts have been isolated and analysed, and coirespond to the formula CoH.-.NjCl.CuoCIo (Hantzsch). The formation of a crystalline copper compound is rendeied very evident in the present preparation.. A modification of Sandmeyer s reaction IS the introduction of precipitated metallic copper in place of the cuprous salt (Gattermann). 

Methyl Orange.--The first point to notice in this reaction is that the diazonium salt forms no diazoamino-compotind with the dimethylanilinc, but at once pioduces an azo-compound. This is always the case with tertiary amines, some secondary amines like diphenyl.amine and the phenols. The reaction may be regarded as typical of the formation of all azo-colounng m.atters. At least two substances are requisite in this process on the one hand. an aromatic compound containing an amino-groujD in the nucleus, and, on the other, a base or phenol... 

The coupling of enamines with aromatic diazonium salts has been used for the syntheses of monoarylhydrazones of a-diketones (370,488-492) and a-ketoaldehydes (488,493). Cleavage of the initial enamine double bond and formation of the phenylhydrazone of acetone and acetophenone has been reported with the enamines of isobutyraldehyde and 2-phenylpropionalde-hyde. Rearrangement of the initial coupling product to the hydrazone tautomer is not possible in these examples. 

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... 

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