Benzenediazonium chloride, decomposition

Place the distillate in a separating-funnel and extract the benzonitrile twice, using about 30 ml. of ether for each extraction. Return the united ethereal extracts to the funnel and shake with 10% sodium hydroxide solution to eliminate traces of phenol formed by decomposition of the benzenediazonium chloride. Then run off the lower aqueous layer, and shake the ethereal solution with about an equal volume of dilute sulphuric acid to remove traces of foul-smelling phenyl isocyanide (CaHjNC) which are always present. Finally separate the sulphuric acid as completely as possible, and shake the ether with water to ensure absence of acid. Run off the water and dry the benzonitrile solution over granular calcium chloride for about 20 minutes. 

Modifications of this method, such as the use of the more stable diazonium trifluoroacetates and the decomposition of benzenedia-zonium zincichloride with zinc dust, have been used as sources of aryl radicals, although not in the arylation of heterocyclic compounds. Pyridine, quinoline, and thiophene can be phenylated by treatment with benzenediazonium chloride and aluminum trichloride. ... 

The CgHs-N Cl- (benzenediazonium chloride) enthalpy of decomposition was calculated. Comparing its value (AH j = -1.5 kJ/g) with the CHETAH criterion C, makes it moderately stable. Accidents have been observed during reactions that are schematised below and these illustrate what has been stated. They are all due to the explosive character of the diazonium sulphides formed. Here is one example ... 

Dining preparation of thiophenol by addition of a cold solution of potassium O-methyldithiocarbonate to a cold solution of benzenediazonium chloride, a violent explosion accompanied by an orange flash occurred [1], This was attributed to the formation and decomposition of bis(benzenediazo) disulfide. A preparation in which the diazonium solution was added to the xanthate solution proceeded smoothly [2],... 

Careful studies of the action of absolute ethyl alcohol on various diazonium salts obtained from aniline have proved that phenetole is the main product, along with a very small quantity of benzene.10 The decomposition of benzenediazonium chloride, for example, results in a 61% yield of phenetole and a 5% yield of benzene.11 The remainder of... 

The reactions in the decomposition of 13,6-trimethyl-2-oxo-l, 2-dihydropyrazine methiodide with alkali metal hydroxide to give 1,4,6-trimethyl-3-methylene-2-oxo-1,2,3,4-tetrahydropyrazine (1105) and its reaction with benzenediazonium chloride or phenylhydrazine to give l,4,6-trimethyl-2-oxo-3-phenylazomethylene-l,2,3,4-tetrahydropyrazine (1105,1132) have been described. 

Using the decomposition of benzenediazonium chloride, Reed et al. (120) compared the kinetic results obtained by several different methods these comparisons are shown in Table 5.12. They concluded that the Borchardt and Daniels method can be used for the quantitative determination of kinetic parameters if the experimental conditions closely approximate the assumptions of the theory, namely, reaction order, n. with respect to only one component, and the absence of temperature gradients and overlapping peaks. 

Table 5.12. Kinetic Constants for the Decomposition of Benzenediazonium Chloride...

The most widely used illustration for the 5 1 mechanism is the uncatalyzed decomposition of diazonium salts. Such substrates carrying amino substituents have scarcely been investigated, except for the magnetochemical study on the photodecomposition of p- N,N-dimethylamino)benzenediazonium chloride . Tlie result of this and other work indicated a free-radical mechanism. 

Table 16.10 Results for the decomposition of benzenediazonium chloride with time... 

The decomposition of benzenediazonium chloride in water is given by the reaction equation... 

Another approach to the foregoing is to study the effect of anions on the product composition. This has been done by Lewis (17) who determined chlorobenzene in the decomposition of benzenediazonium chloride in varying concentrations of added chloride ion. With the assumption that % phenol formed = 100% — % chlorobenzene formed, Lewis calculated competition factors kci /k ) and found that, with added chloride ion varied from 0.25-3.0Af, the derived competition factors varied randomly from 2.0-3.5. However, as the author points out, the same competition factors can be derived assuming a bimolecular mechanism. The two mechanisms lead to different rate laws, but a clear-cut distinction between them is difficult when fcci- is small. 

The procedure described for the preparation of l-(m-nitro-phenyl)-3,3-dimethyltriazene is the method of Elks and Hey,2 and the preparation of m-nitrobiphenyl is also a modification of their procedure. The other principal methods for the preparation of m-nitrobiphenyl are the decomposition of N-nitroso-w-nitroacetanilide in benzene 3 and the decomposition of alkaline m-nitrobenzenediazohydroxide in benzene.4 Other methods that have been reported include the decomposition of potassium ire-nitrobenzenediazotate in benzene with acetyl chloride,6 the decomposition of m-nitrobenzoyl peroxide in boiling benzene,6 the decomposition of benzenediazonium borofluoride in nitrobenzene 7 at 70°, and the reduction of 4-(3 -nitrophenyl)-benzenediazonium acid sulfate in boiling ethanol.8... 

During interaction of the diazonium chloride, and the o-ethyl dithiocarbonate ( xan-thate ) solutions, care must be taken to ensure that the intermediate diazonium dithiocarbonate decomposes to 2-thiocresol as fast as it is formed [1]. This can be assured by presence of a trace of nickel in the solution to effect immediate catalytic decomposition. When the 2 solutions were mixed cold and then heated to effect decomposition, a violent explosion occurred [2]. Caution The experiments claimed to show catalysis by nickel appear to have been performed on diazotised anthranilic acid which is the only benzenediazonium system never known to give explosive intermediates with sulfur nucleophiles [3]. 

If benzyne was generated instead from o-carboxybenzenediazonium chloride in the presence of 108, the remarkable siloxepine 111 was formed (>70%) its structure was confirmed by X-ray diffraction.79 It was shown that the intermediate 1 1 adduct 110 reacts with benzenediazonium-2-car-boxylate (4) at a lower temperature than is required for the decomposition 4 -+ 5 -+ 1 (Scheme 1) this step includes the formation of the strong Si—O bond, and subsequent loss of nitrogen and cyclization lead to 111. The germanium analog of 111 was similarly obtained from 109. 

Kinetics have been measured for the dediazoniation reactions of 2- and 3-methyl-benzenediazonium cations in water and in aqueous methanol. The results are consistent with a heterolytic mechanism involving rate-determining formation of reactive aryl cations which show little discrimination for nucleophiles present. Results for the dediazoniation of 4-nitrobenzenediazonium ions in aqueous acid catalysed by Cu(II) chloride are also consistent with a heterolytic pathway at low acidity and with conditions designed to avoid the formation of Cu(I) the reaction may yield chloroarenes in high yield. Activation parameters have been reported for the decomposition of some arenediazonium tetrafluoroborates in polar solvents. The results are generally consistent with heterolysis, although in ethanol there is competition from a radical mechanism, with characteristically different activation parameters, which leads to hydrodediazoniation f... 

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