Diazonium bromide

Gattermann s Method.— Accoiding to this method the diazonium bromide is first picparcd and then decomposed by finely divided metallic copper. The 50 grams /-toluidine is dissohed in 200 c.c. liydrobromic acid previously diluted with too c.c. water and diazoliscd in the usual way. To this solution... 

Gnnamaldehyde, by reduction of, cinnamonitrile with Raney nickel alloy in formic acid, 51, 23 ester-mesylate, 51,16 Gnnamic acid, 50,18 CINNAMONITRILE, 50,18 Condensation, of p-acetylbenzene-diazonium bromide with acrylic acid, 51,1... 

Prepare copper(i) bromide from 75 g (0.33 mol) of crystallised copper(n) sulphate as detailed in Section 4.2.27, p. 428, and dissolve it in 40 ml of 48 per cent hydrobromic acid heat the solution to boiling and add o-chlorobenzene-diazonium bromide solution as detailed above. When all the latter has been introduced, continue to pass steam through the mixture until no more organic material distils. Follow the procedure, including purification, given for p-bromotoluene. Collect the o-bromochlorobenzene (a colourless liquid) at 200-202 °C. The yield is 85 g (89%). 

Amino-8-bromophenanthridone can be deaminated smoothly by the action of cold hypophosphorus acid on the diazonium chloride.122 1-Bromophenanthridone is formed in moderate overall yield from the amino compound when the diazonium bromide-mercuric bromide complex is heated at 120° and a number of bromo- and chloro-phen-anthridones have been obtained recently by Sandmeyer procedures.26, 101... 

An unexpected displacement of a diazonium group in diazotized aminonaphthalenes by hydrogen was discovered when diazonium mercury(II) bromides, prepared by treatment of diazonium bromides with mercury(II) bromide, were stirred at room temperature for 10-20 min in hexamethylphosphoramide (HMPA) (equation 99). ... 

T. Sohda and co-workers prepared a series of novei thiazoiidinedione derivatives of the potent antidiabetic piogiitazone (AD-4833, U-72, 107). The para-substituted aniiine was diazotized with NaN02/HBr, and the diazonium bromide was used to aryiate methyi acryiate in the presence of copper(ii) oxide. The bromopropionate product was first treated with thiourea, and the resuiting iminothiazoiidinone hydroiyzed with aqueous hydrochioric acid to afford the desired thiazoiidinedione derivative. 

Diazonium bromides and bromine in hydrobromic acid give diazonium perbromides that are sparingly soluble in water. In the presence of water or when... 

Copper 1) chloride, bromide and cyanide were used by Sandmeyer to introduce a chlorine, a bromine atom and a cyanide group respectively into a benzene ring by addition to the phenyl diazonium salt. 

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. 

Prepare a solution of p-tolyldiazonium chloride from 53 -5 g. of p-tolui-dine using the proportions and experimental conditions given under p-Chlorotoluene (Section IV,61). Add the diazonium chloride solution to the boiling cuprous bromide solution, and proceed as in Method 1. The yield of pure, colourless p-bromotoluene, b.p, 182-184° (mainly 183°), is 40 g. m.p. 26°,... 

The diazonium salts 145 are another source of arylpalladium com-plexes[114]. They are the most reactive source of arylpalladium species and the reaction can be carried out at room temperature. In addition, they can be used for alkene insertion in the absence of a phosphine ligand using Pd2(dba)3 as a catalyst. This reaction consists of the indirect substitution reaction of an aromatic nitro group with an alkene. The use of diazonium salts is more convenient and synthetically useful than the use of aryl halides, because many aryl halides are prepared from diazonium salts. Diazotization of the aniline derivative 146 in aqueous solution and subsequent insertion of acrylate catalyzed by Pd(OAc)2 by the addition of MeOH are carried out as a one-pot reaction, affording the cinnamate 147 in good yield[115]. The A-nitroso-jV-arylacetamide 148 is prepared from acetanilides and used as another precursor of arylpalladium intermediate. It is more reactive than aryl iodides and bromides and reacts with alkenes at 40 °C without addition of a phosphine ligandfl 16]. 

Diazotization of a primary arylamine followed by treatment of the diazonium salt with copper(l) bromide or copper(l) chloride yields the corresponding aryl bromide or aryl chloride. 

Arylamines are converted by diazotization with nitrous acid into arenediazonium salts, ArN2+ X-. The diazonio group can then be replaced by many other substituents in the Sandmeyer reaction to give a wide variety of substituted aromatic compounds. Aryl chlorides, bromides, iodides, and nitriles can be prepared from arenediazonium salts, as can arenes and phenols. In addition to their reactivity toward substitution reactions, diazonium salts undergo coupling with phenols and arylamines to give brightly colored azo dyes. 

MNN is obtained in 3—5% yield by the nitration of naphthalene and is present at this level in coml MNN. It is best prepd by indirect methods for example, by the removal of an amino group from an appropriately substituted nitro-naphthylamine. The amine is treated with Na nitrite and acid to form the diazonium salt which is replaced with a H atom by redn with EtOH (Ref 7). It may also be prepd by treatment of 6-nitro-l, 2,3,4-tetrahydronaphthalene with Br to form a dibromo compn (probably the 1,4-isomer), followed by removal of two moles of H bromide by distn in the presence of base (Ref 10). 2-Naphthalenediazonium fluoroborate... 

When aqueous solutions of aromatic and heteroaromatic diazonium salts are treated with cuprous chloride, -bromide, or -cyanide, the corresponding aromatic chlorides, bromides, or cyanides are formed, respectively. In many cases the anions mentioned must be present in excess. This reaction, the Sandmeyer reaction, was discovered by Sandmeyer in 1884. A variant carried out with copper powder and HBr or HC1 was for many years called the Gattermann reaction (Gattermann, 1890). As it is often confused with the Gattermann-Koch reaction (ArH + CO + HC1 ArCHO), and as it is mechanistically not significantly different from Sandmeyer s procedure, the name Gattermann reaction should be avoided. 

A number of approaches have been tried for modified halo-de-diazoniations using l-aryl-3,3-dialkyltriazenes, which form diazonium ions in an acid-catalyzed hydrolysis (see Sec. 13.4). Treatment of such triazenes with trimethylsilyl halides in acetonitrile at 60 °C resulted in the rapid evolution of nitrogen and in the formation of aryl halides (Ku and Barrio, 1981) without an electron transfer reagent or another catalyst. Yields with silyl bromide and with silyl iodide were 60-95%. The authors explain the reaction as shown in (Scheme 10-30). The formation of the intermediate is indicated by higher yields if electron-withdrawing substituents (X = CN, COCH3) are present. In the opinion of the present author, it is likely that the dissociation of this intermediate is not a concerted reaction, but that the dissociation of the A-aryl bond to form an aryl cation is followed by the addition of the halide. The reaction is therefore mechanistically not related to the homolytic halo-de-diazoniations. 

The arylation of alkenes by treatment with a diazonium chloride (or bromide) solution and cupric chloride (or bromide) is called the Meerwein arylation reaction, after its discoverer (Meerwein et al., 1939). Originally, it was discovered using a,P-unsaturated carbonyl compounds, namely coumarin (Scheme 10-43) and cinnamic derivatives (Schemes 10-44 and 10-45). As Scheme 10-45 shows, the Meerwein reac-... 

With regard to the mechanism of these Pd°-catalyzed reactions, little is known in addition to what is shown in Scheme 10-62. In our opinion, the much higher yields with diazonium tetrafluoroborates compared with the chlorides and bromides, and the low yields and diazo tar formation in the one-pot method using arylamines and tert-butyl nitrites (Kikukawa et al., 1981 a) indicate a heterolytic mechanism for reactions under optimal conditions. The arylpalladium compound is probably a tetra-fluoroborate salt of the cation Ar-Pd+, which dissociates into Ar+ +Pd° before or after addition to the alkene. An aryldiazenido complex of Pd(PPh3)3 (10.25) was obtained together with its dediazoniation product, the corresponding arylpalladium complex 10.26, in the reaction of Scheme 10-64 by Yamashita et al. (1980). Aryldiazenido complexes with compounds of transition metals other than Pd are discussed in the context of metal complexes with diazo compounds (Zollinger, 1995, Sec. 10.1). 

One of the best methods for the introduction of iodine into aromatic rings is the reaction of diazonium salts with iodide ions. Analogous reactions with chloride, bromide, and fluoride ions give poorer results, and 14-25 and 13-20 are preferred for the preparation of aryl chlorides, bromides, and fluorides. However, when other diazonium reactions are carried out in the presence of these ions, halides are usually side products. Aniline has also been converted to fluorobenzene by treatment with t-BuONO and Sip4 followed by heating. A related reaction between PhN=N—N C4Hg and iodine gave iodobenzene. ... 

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