Reactions of Diazonium Salts

Reactions of Diazonium Salts. Many of the reactions of diazonium salts appear to proceed by free radical mechanisms. Thus, depending upon the environment of the diazonium salt, it is possible that cleavage might occur by free radical scission (A) or by ionization (B)  

Carbon-carbon bonds can be formed in very varied ways in reactions of diazonium compounds. For example, l-chloro-4-(/ -nitrophenyl)-2-butene (88% yield) is formed from diazotized / -nitroaniline and butadiene in aqueous acetone containing copper chloride and sodium acetate,787 whereas in the same conditions 5-phenyl-2,4-pentadienoic acid gives l-(/ -nitrophenyl)-4-phenyl-1,3-butadiene.788 The latter reaction is a special case of Meerwein arylation, by which stilbenes are formed in good yields from diazonium salts and cinnamic acids 789 

A solution of /7-chloroaniline in water (100 ml) and hydrochloric acid (80 ml) is diazotized at 0° by a solution of sodium nitrite (15 g) in water (30 ml). The clear (filtered, if necessary) diazonium solution is added to a cold solution of cinnamic acid (30 g) in acetone (250 ml). Then sodium acetate (44 g), followed by a solution of copper(n) chloride (8.5 g) in water (20 ml), are added. The temperature may rise slowly to 16° when gas evolution has begun. The mixture is stirred at 14-16° for 3 h. By the end of the coupling reaction two layers will have been formed — an upper layer of dark green oil and a lower layer of pale green aqueous acetone. The whole is distilled in steam. The residue is extracted in benzene and washed several times with 3N-ammonia solution and then with water. Distilling off the benzene leaves a crystalline residue of 4-chloro-stilbene which recrystallizes from 2-propanol in shiny leaflets, m.p. 129° (40%). 

Diazonium salts and acrylonitrile react by addition and loss of nitrogen, yielding l-chloro-2-arylpropionitriles in ca. 80% yield 790 but use of formaldox-ime leads to an aldehyde synthesis 792 

Nitriles can be obtained from diazonium salts by the Sandmeyer method, which involves treatment with copper(i)in the hot.793 An example of this valuable reaction is the preparation of 0-nitrobenzonitrile from 0-nitroaniline 794 

Clarke and Read795 have given further directions for carrying out the Sand-meyer reaction. 

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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. ... 

Reaction of diazonium salts with oximes, followed by hydrolysis... 

Introduction of Other Nucleophiles Using Diazonium Ion Intermediates. Cyano and azido groups are also readily introduced via diazonium intermediates. The former involves a copper-catalyzed reaction analogous to the Sandmeyer reaction. Reaction of diazonium salts with azide ion gives adducts that smoothly decompose to nitrogen and the aryl azide.56... 

One very common example is the displacement of N2 in the reactions of diazonium salts, ArN2 , a very useful preparative series ... 

A number of the reactions of diazonium salts, particularly in less polar solvents, may proceed via the initial generation of an aryl radical, however cf. p. 334). 

Superior passive stabilised diazo compounds are afforded by the diazoamino compounds (triazenes) that arise by reaction of diazonium salts with a variety of secondary amines [114]. Typically, sarcosine (CH3NHCH2COOH), which gives products based on structure 4.114, as well as N-methyltaurine (CH3NHCH2CH2SO3H) and N methylaniline-4 Sulphonic acid,... 

The azo produets obtained have an extended conjugate system having both the aromatie rings joined through the -N=N- bond. These compormds are often coloured and are used as dyes. Benzene diazonium chloride reacts with phenol in which the phenol molecule at its para position is coupled with the diazonium salt to formp-hydroxyazobenzene. This type of reaction is known as coupling reaction. Similarly the reaction of diazonium salt with anUtne yields p-aminoazobenzene. This is an example of electrophilic substitution reaction. 

The resulting l-(p-chlorophenylazo)-5-isopropylbiguarude is cleaved by hydrochloric acid to p-chlorophenol and 1-isopropylbiguanide. Similar observations concerning the reaction of diazonium salts with biguanides have appeared in the patent literature 403). 

REACTION OF DIAZONIUM SALTS WITH NITRITE ANION... 

Diazonium salts can also be used to form ethers and phenols. Reaction of diazonium salt with an alcohol generates an ether, while thermal hydrolysis of the diazonium salt yields a phenol. Figure 13-30 illustrates both formations. As seen in Figure 13-31, this process also works on substituted aromatic systems. 

Chloro- and bromo-l,3,4-thiadiazoles are usually prepared by nucleophilic processes, e.g., Sandmeyer reactions of diazonium salts [56CB1534 68AHC(9)165 86CHE1148], and reactions of thiadiazolinones with phosphorus halides [68AHC(9)165]. The halogeno derivatives are important... 

The reaction of diazonium salts with methin- and phosphamethin cyanines gives interesting results which are now investigated in detail. 

G. Reaction of Diazonium Salts with Grignard and Related Reagents. 307... 

For a review of reactions of diazonium salts, see Wulfman, in Patai, Ref. 526, pt. 1, pp. 247-339. Korzcniowski Leopold Beadle Ahern Sheppard Khanna GokelZ. Org. Chem. 1981,46,2153, and references cited therein. For reviews, see Bartsch, in Patai Rappoport The Chemistry of Functional Groups, Supplement C, pt.l Wiley New York, 1983, pp. 889-915 Bartsch Prog. Macrocyclic Chem. 1981, 2, 1-39. 

The cyclization of a-hydrazono oximes (635) with orthocarboxylates is an excellent way of preparing 1,2,4-triazine 4-oxides (636) (73TL1429,7lLA(750)12,77LA1713). Using aldehydes or ketones instead of orthoesters provides 2,3-dihydro derivatives (637 Scheme 22) (75S794). Cyclization of a-hydrazonocarboxamides (638) with carbonic acid derivatives such as ethyl chloroformate affords l,2,4-triazine-3,5-diones (639) (68M1808). The a-hydrazonocarboxamides (638) can be prepared by the reaction of diazonium salts with a-activated acetamides such as cyanoacetamide as shown. 

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