The invention further relates to a process for the preparation of the compounds of formula 1, and to the use of said compounds in the organic synthesis.

Most diazonium salts in the dry state are known to have a marked instability (to heat, shocks and, in some cases, light) which can cause even explosive decompositions. Such a dangerous behaviour has of course negatively affected the development of synthetic processes on the laboratory scale, and even more so, of industrial processes based on the use thereof. However, most arenediazonium tetrafluoborates, some diazonium salts in which complex anions are present, such as tetrachlorozincates or hexafluorophosphates, and some

arenediazonium sulfonates, have not, as a rule, such behaviour. The first examples of arenediazonium tetrafluoborates which can be kept at the dry state (p- chloro, p-methoxy, p-nitro and p-ethoxybenzenediazonium tetrafluoborates) were disclosed in 1913 by Bart [H.

Bart, Ger. pat. 281,0 55 (1913); Chem. Abstr., 1915, 9, 1830], who claimed their use as intermediates for the preparation of pharmaceuticals and dyes. Researches on the preparation and properties thereof were given a substantial boost by the study of the Schiemann's reaction (G. Balz and G. Schiemann, Chem. Ber., 1927, 60B, 1186) which is known to permit a fluorine atom to be introduced into an aromatic nucleus starting from the corresponding arenediazonium tetrafluoborate at the dry state (A. Roe, in Organic Reactions, John Wiley and Sons, Inc., New York, Vol. V, 1949, pages 193-228).

Other synthetic applications of tetrafluoborates concern the preparation of acetates (I.E. Smith and H. L.

Haller, J. Am. Chem. Soc. 1939, 61, 143), nitriles (P.

Ruggli and E. Caspar, Helv. Chim. Acta, 1935, 18, 1414), nitroderivatives (E.B. Starkey, Org. Synth., Coil. Vol 2, 1943, 225), hydrocarbons (M.S. Lesslie and E.E.

Turner, J. Chem. Soc., 1933, 1588; F.C. Schmelkes and M.

Rubin, J. Am. Chem. Soc., 1944, 66, 1631) and azoderivatives (M. E. Garst and D. Lukton, Synthetic Commun. 1980, 10, 155).

It should also be stressed that a certain number of diazonium salts at the dry state, mostly in the form of tetrafluoborates and tetrachlorozincates, have been suggested as photosensitizers for use specifically in lithographic processes [as recent examples: (a) M.

Oguni, K. Goto, M. Suezawa, S. Yanagida and N. Ikeda, WO 9512146 (1995); Chem. Abstr. 1495, 123, 156497. (b) H.

J. Schlosser, Hoechst A.-G., EP 307776 (1989); Chem.

Abstr. 1989, 111, 164277] or as control agents for polymerization reactions [for example: S. S. Jacobs, American Can Co., Ger. Offen. 2615373 (1976); Chem.

Abstr. 1976, 85, 193674] or still for dyeing and printing of textiles [for example: E. Feess, Hoechst A.- G., Ger. Offen. 2360791 (1975); Chem. Abstr. 1975, 83, 165692]; whereas the use of the other arenediazonium salts, at the dry state, with anions different from tetrafluoborate appears to be very limited in the organic synthesis.

In principle, the preparation of arenediazonium tetrafluoborates involves no specific problems and, in suitable conditions, they can be obtained in very good yields (R. Putter, Methoden der Organischen Chemie, Houben-Weyl-Muller eds., Georg Thieme Verlag, Stuttgart, Vol. X, Part. 3, 4th ed., 1965, p. 16; K. Schank, in The chemistry of diazonium and diazo groups, S. Patai ed., Part 2, Chap. 14, p. 645). Arenediazonium tetrafluoborates are, however, highly affected by humidity, which quickly decomposes them and, as a rule, they are used immediately after being prepared; some of them irregularly decompose by heating, even explosively (W. W. Hartman and J. R. Byers, Org. Synth., Coll. Vol.

2, 1943, 295; A. Roe, in Organic Reactions, John Wiley and Sons, Inc., New York, Vol. V, 1949, pages 199, 200, 211; D. H. Hey, C. W. Charles and A. R. Todd, J. Chem.

Soc. (C), 1967, 1518).

Now it has surprisingly been found that

arenediazonium salts of formula 1 have a series of very advantageous characteristics, which can thus be summarized: A) they are easy to prepare B) they are easy to purify C) they have generally a very high stability D) they can react in aqueous solution as well as in organic solvents E) are very good candidates for industrial applications.

A further advantage is that o-benzenedisulfonimide is easy to recover, nearly completely, after use of said salts, contrary to what occurs for the fluoborate anion, which is environmentally difficult to be disposed of.

According to the process of the invention, an aro- matic amine is diazotized, for example with an alkyl ni- trite (for example i-pentyl nitrite) and o-benzenedisul- fonimide in glacial acetic acid (Scheme I). The reaction is carried out at 0-5"C. Most salt precipitates during the reaction; the precipitation of the salt can be com- pleted by addition of an acetic acid-miscible solvent, which decreases the polarity of the medium, for example a dry ether (diethyl, diisopropyl and the like).

Scheme I Alternative processes to the above mentioned scheme which lie within the scope of the invention involve the use of both alkyl and alkali metals nitrites; of acids

different from the acetic one, for example chloroacetic or trichloroacetic, optionally in combination with acetic acid itself. The following example shows the process according to the invention.

Example 1. Benzenediazonium o-benzenedisulfonimide (lea) A solution of aniline (0.93 g, 10 mmol) in glacial acetic acid (20 ml), cooled at 0-5"C with an ice bath and kept under stirring, is slowly added (in about 10 minutes) with a solution of o-benzenedisulfonimide (2.63 g, 12 mmol) in the same solvent (40 ml). After that, isoamyl nitrite (1.28 g, 11 mmol) is dropped therein at such a rate as to keep the temperature of the reaction mixture at 0-5"C (about 10 minutes). During the addition, the title salt starts separating as a fine white precipitate. When the addition is completed, the cooling bath is removed and the reaction mixture is stirred for a further 5 minutes. Then the precipitation of the salt is completed by addition of dry ethyl ether (about 20 ml). The precipitate is collected by suction and washed with successive portions of dry ethyl ether (totally 40-60 ml) to completely remove acetic acid then dried under vacuum. Benzenediazonium o- benzenedisulfonimide is obtained in a 98% yield (3.18 g); crystallized by warm dissolution in dry acetonitrile and subsequent cold precipitation with dry ethyl ether, has m.p. 110"C (with decomposition).

1H NMR (CF3COOD): S = 7.40-8.05 and 8.05-8.35 ppm (2 m, 7:2, 9 H arom).

Elementary analysis: C12HgN304S2 calc. C% 44.58 H% 2.81 N% 13.01 S% 19.80 (323.34) found 44.45 2.76 12.99 19.91

With the same procedures, the salts of formula 1 wherein Ar has the meanings reported hereinbelow were prepared, inter alia also the diazonium salts of aromatic amines which, in aqueous solution, are diazotized in more drastic conditions (for example, 4- nitroaniline). For the preparation of 1- naphthalenediazonium o-benzenedisulfonimide (1t), glacial acetic acid has been replaced by the same amount of trichloroacetic acid. la: Ar = C6H5; ib: Ar = 2-CH3-C6H4; lc: Ar = 3-CH3- C6H4; id: Ar = 4-CH3-C6H4; le: Ar = 2-CH3O-C6H4; 1f: Ar = 3- CH3O-C6H4; Ig: Ar = 4-CH3O-C6H4; ih: Ar = 2-Cl-C6H4; li: Ar = 3- Cl-C6H4; lj: Ar = 4-Cl-C6H4; 1k: Ar = 3-Br-C6H4; 11: Ar = 4-Br- C6H4; 1m: Ar = 2-NO2-C6H4; in: Ar = 3-NO2-C6H4; lo: Ar = 4- NO2-C6H4; ip: Ar = 4-(CH3)2N-C6H4; 1q: Ar = 2,6-(CH3)2C6H3 1r: Ar = 2-CH3O-5-Cl-C6H3; is: Ar = 2,6-Cl2C6H3 ; 1t: Ar = 1-C10H7. o-Benzenedisulfonimide can be prepared following the sequence (A) of scheme II, starting from anthranylic acid (M. Barbero, I. Degani, R. Fochi and P. Perracino, J. Org. Chem. 1996, 61, 8762). Alternatively, the sequence (B) can be followed, starting from 2- aminobenzenesulfonic acid (A. Blaschette et al. . . , Z.

Anorg. Allg. Chem. 1993, 619, 912). Scheme II The prepared diazonium salts, the corresponding yields, m.p., 1H NMR spectra and elementary analysis data are reported in Tables 1 and 2.

TABLE 1 Salt Ar Yield(%) M.P.(°C)* 1H NMR (CF3COOD), # (ppm), J (Hz) 1a C6H5 98 110 7.40-8.05 e 8.05-8.35 (2 m, 7:2, 9 Har.) 1b 2-CH3C6H4 93 105 2.57 (s, 3 H, CH3), 7.30-8.25 (m, 8 Har.) 1c 3-CH3C6H4 92 96 2.32 (s, 3 H, CH3), 7.30-7.90 (m, 8 Har.) 1d 4-CH3C6H4 91 121 2.37 (s, 3 H, CH3), 7.40 e 8.06 (2 d, 1:1, J 8.5, 4 Har.), 8.65 (m, 4 Har.) 1e 2-CH3OC6H4 98 146 3.82 (s, 3 H, OCH3), 6.80-7.20, 7.58 e 7.60-8.00 (3 m, 1:2:1, 8 Har.) 1f 3-CH3OC6H4 94 90 3.58 (s, 3 H, OCH3), 6.40-7.20 e 7.30-7.80 (2 m, 1:3, 8 Har.) 1g 4-CH30C6H4 89 151 3.78 (s, 3 H, OCH3), 6.98 e 8.08 (2 d, 1:1, J 8.5,4 Har.), 7.62 (m, 4 Har.) 1h 2-ClC6H4 96 142 7.25-8.02 e 8.10-8.40 (2 m, 7:1, 8Mar.) 1i 3-ClC6H4 96 117 7.30-8.00 e 8.00-8.30 (2 m, 3:1, 8 Har.) 1j 4-ClC6H4 94 153 7.55 e 8.15 (2 d, 1:1, J 8.5, 4 Har.), 7.65 (m, 4 Har.) 1k 3-BrC6H4 98 130 7.30-7.90 e 7.90-8.50 (2 m, 5:3, 8 Har.) 1l 4-BrC6H4 95 140 7.58 (m, 4 Har.), 7.68 e 8.02 (2 d, 1:1, J 8.5, 4 Har.) 1m 2-NO2C6H4 98 173 7.58 e 7.82-8.80 (2 m, 1:1, 4 Har.) In 3-NO2C6H4 97 157 7.40-8.10, 8.50-8.90 e 9.00-9.35 (3 m, 5:2:1, 8Mar.) 1o 4-NO2C6H4 88 143 7.62 (m, 4 Har.), 8.32 e 8.58 (2 d, 1:1, J 8.5, 4 Har.) 1p 4-(CH3)2NC6H4 99 154 2.92 (s, 6 H, 2 CH3), 6.53 (6, J 8.5, 2 Har.), 7.40-7.80 (m, 6 Har.) 1q 2,6-(CH3)2C6H3 85 108 2.82 (s, 6 H, 2 CH3), 6.52 e 7.62 (2 m, 3:4, 7 Har.) 1r 2-CH3O-5-ClC6H3 99 151 4.00 (s, 3 H, OCH3), 7.15 (6, J 8.5, 1 Har.), 7.50-7.85 (m, 5 Har.), 7.92 (s, 1 Har.) 1s 2,6-Cl2C6H3 95 183 7.40-8.10 (m, Har.) 1t 1-C10H7 95 122 7.30-8.10 e 8.30-8.72 (2 m, 9:2, 11 Har.) All the salts melt with decomposition

TABLE 2 Salt Formula Analitycal data Calculated (%) Found (%) M.W.C Er N S Alg C Er N S Mg 1 a C12H9N3O4S2 323.34 44.58 2.81 13.00 19.83 44.45 2.76 12.99 19.91 1 b C13H11N3O4S2 337.37 46.2S 3.29 12.46 19.01 46.22 3.39 12.56 18.83 1 c C13H11N3O4S2 337.37 46.28 3.29 12.46 19.01 46.17 3.29 12.48 18.94 1 d C13H11N3O4S2 337.37 46.2S 3.29 12.46 19.01 46.15 3.22 12.48 19.07 1 e C13H11N3O5S2 353.37 44.19 3.14 11.89 18.15 44.26 3.16 11.93 18.11 1 f C13H11N3O5S2 353.37 44.19 3.14 11.89 18.15 44.22 3.11 11.90 17.99 lg C13H11N3O5S2 353.37 44.19 3.14 11.89 18.15 44.24 3.22 12.05 18.26 1 h C12H8ClN3O4S2 357.79 40.28 2.25 11.74 17.92 9.91 40.32 2.24 11.80 17.78 9.89 1 i C12H8ClN3O4S2 357.79 40.28 2.25 11.74 17.92 9.91 40.41 2.22 11.77 17.76 9.95 1 j C12H8ClN3O4S2 357.79 40.28 2.25 11.74 17.92 9.91 40.39 2.19 11.80 18.01 10.07 1 k C12H8BrN3O4S2 402.24 35.83 2.00 10.45 15.94 19.86 35.87 2.10 10.43 15.96 19.73 11 C12H8BrN3O4S2 402.24 35.83 2.00 10.45 15.94 19.86 35.93 1.82 10.49 15.79 19.83 1 m C12H8N4O6S2 368.34 39.13 2.19 15.21 17.41 38.99 2.15 15.13 17.28 1 n C12H8N4O6S2 363.34 39.13 2.19 15.21 17.41 39.06 2.15 15.09 17.29 1 o C12H8N4O6S2 368.34 39.13 2.19 15.21 17.41 39.05 2.19 15.22 17.43 1 p C14H14N4O4S2 366.41 45.89 3.85 15.29 17.50 46 02 3.78 15.18 17.67 1 q C14H13N3O4S2 351.39 47.35 3.73 11.96 18.25 48.01 3.71 11.89 18.42 1 r C13H10ClN3O5S2 387.81 40.26 2.60 10.84 16.53 9.14 40.18 2.53 10.79 16.44 9.12 1 s C12H7Cl2N3O4S2 392.23 36.75 1.80 10.71 16.35 18.08 36.65 1.79 10.65 16.21 18.14 1 t C16H11N3O4S2 373.40 51.47 2.97 11.25 17.17 51.35 2.91 11.21 17.04

The salts prepared following the process described in A, as evidenced by the spectroscopical (NMR) and elementary analysis data of the crudes, are in a highly pure state and can be used for synthetical purposes without further purifications. If required, they can be further purified to obtain samples of analytical degree, hot-dissolving them in acetonitrile and reprecipitating them by addition of cold dry ethyl ether.

STABILITY - Cold stability: samples of the salts reported in Table 1, stored in a glass container with a polyethylene plug, kept at 0°C for 6 weeks, remained unchanged (m.p., NMR).

- Room temperature (r.t.) stability: samples of the salts reported in Table 1 were stored in glass containers with a polyethylene plug, and left at r.t. (about 25"C) for six weeks; aniline and aniline methyl derivatives diazonium salts underwent more or less marked degradations; all the other salts remaining unchanged (m.p. and NMR unvaried).

- The salts reported in Table 1 have defined and reproducible decomposition points.

- The salts reported in Table 1, when placed near heat sources, decompose without exploding.

- In the preparation, purification and handling steps, no explosive decompositions ever occurred.

- Air stability: the salts of Table 1 can be handled in the air, without alterations.

- An indirect prove of their stability is provided by the results of the elementary analysis, carried out

even days after their preparation.

- The salts stable a r.t. proved to be stable also to sun light.

As stated initially, an object of the invention is the use of the stable arenediazonium salts of formula 1 for the preparation of those compounds usually prepared from diazonium salts, through reactions carried out in aqueous solution or in organic medium.

Non limiting examples of the great number of reactions wherein the salts of the invention can be made use of are reported hereinbelow.

A - Diazo coupling reactions. All the salts reported in Table 1 were reacted in aqueous solution, at basic pH, with -naphthol, according to the procedure described in Example 2 (Scheme III).

Scheme III ExamPle 2. Preparation of l-phenylazo-2-naphthol A solution of -naphthol (0.72 g, 5 mmol) in a 10% NaOH aqueous solution (0.44 g, 11 mmol, in 4.4 ml of water) is prepared. Said solution is added slowly to a suspension of benzenediazonium o-benzenedisulfonimide (la; 1.61 g, 5 mmol) in water (20 ml), kept under strong stirring. A red color develops and the formed azoic

compound immediately separates as a red precipitate.

Stirring is continued for 15-20 min to complete the reaction. The reaction mixture is extracted with chloroform (3 x 60 ml), the combined organic extracts are washed with water (2 x 50 ml) and dried over sodium sulphate. Solvent is evaporated off under reduced pressure, to obtain 1.15 g of the crude product, which is substantially pure; the yield is 93%. The product has been further purified by chromatography on a silica gel column, using chloroform as eluent. The yield in pure 1- phenylazo-2-naphthol is 92t (1.14 g); crystallized from chloroform - petroleum ether, m.p. 133"C (lit.: m.p.

133"C). The aqueous solution is concentrated to small volume (about 4-5 ml) under vacuum and then chromatographed through a column containing 15 g of a ion exchange resin, namely Dowex 50 x 8 (Fluka), and eluting with water (about 15 ml). Water is evaporated off to obtain substantially pure (NMR control) o-benzenedisulfonimide in a 94% (1.03 g) yield.

Following the same procedure, the following compounds were also prepared: 4-nitrophenylazo-2-naphthol, 94% yield; crystallized from chloroform - petroleum ether, m.p. 251"C (lit., m.p. 251"C).

2,6-dimetilphenylazo-2-naphthol, 94% yield; crystallized from ethanol - petroleum ether, m.p. 147"C (lit., m.p.

147"C).

2-methoxy-5-chlorophenylazo-2-naphthol, 91% yield; crystallized from chloroform - petroleum ether, m.p.

204"C (lit., m.p. 203"C).

2,6-dichlorophenylazo-2-naphthol, 92% yield; crystallized from chloroform - petroleum ether, m.p.

141"C (lit., m.p. 140-141°C), As it can be noted, yields are always high, although the reaction conditions for the single cases have not been optimized. Using the diazonium salts 1, aqueous solutions with a specific concentration can be prepared. All the known reactions of the diazonium salts in aqueous medium can be virtually effected. The poor or null nucleophilia of the o-benzenedisulfonimide anion prevents any competitive reactions of the anion itself. o-Benzenedisulfonimide amounts ranging from 90 to 100% on the theoretical can always be recovered.

The diazo coupling with the salts 1 according to the invention can be also carried out in non aqueous solvents, at low temperature, in conditions analogous to those described in Example 3.

ExamPle 3. Preparation of (3-bromophenyl)(4- tolyl )diazene A suspension of 3-bromobenzenediazonium o- benzenedisulfonimide (ilk; 2.01 g, 5 mmol) in dry tetrahydrofuran (15 ml) is cooled at - 78"C, under nitrogen atmosphere. After that, a solution of 4- tolylmagnesium bromide in tetrahydrofuran (1.0 M; 5 ml) is slowly dropped therein (in about 10 minutes), and under stirring. A red colour develops. Stirring is maintained for about 1 hour to complete the reaction (negative i3-naphthol test). The reaction mixture is poured into water (30 ml), the organic phase is separated and the aqueous phase is extracted again with ethyl ether (2 x 30 ml). The combined organic extracts

are washed with water (30 ml) and dried. The reaction crude from the evaporation of the solvent under reduced pressure is purified by chromatography on a silica gel column, using petroleum ether - ethyl ether (9.8:0.2) as eluent. The title product is obtained in an 89% yield (1.22 g); crystallized from ethanol, m.p. 119-120°C (Y.

Nomura, Bull. Chem. Soc. Jpn. 1961, 34, 1648: m.p.

119.5"C). The aqueous solution is treated as described in the preceding preparations, to recover o- benzenedisulfonimide in a 93% yield (1.02 g).

B - Preparation of thioethers. They can be obtained reacting the diazonium salts 1 with thiol alkali salts in alcohol medium (Scheme IV).

Scheme IV Example 4. Preparation of phenyl 4-methoxyphenyl sulfide A solution of thiophenol (0.55 g, 5 mmol) and lithium methoxide (0.21 g, 5.5 mmol) in dry methanol (8 ml) is cooled at 0-5"C, on an ice bath. A solution of 4- methoxybenzenediazonium o-benzenedisulfonimide (lug; 1.79 g, 5 mmol) in the same solvent (8 ml) is then slowly dropped therein, under stirring. The reaction has to be carried out in a strictly dry environment. An exothermic reaction takes place, accompanied by gas evolution.

Stirring is continued for about 1 hour, raising temperature from 0-5"C to room temperature. The reaction mixture is poured into an ethyl ether - water mixture (1:1, 80 ml), the ether phase is separated and the aqueous solution is extracted again with ethyl ether (2

x 40 ml). The ether extracts are combined, washed with water (40 ml) and dried. After evaporation of the solvent under vacuum, the crude residue is chromatographed on a column, using petroleum ether as eluent. The first product eluted is diphenyl disulfide (0.20 g, 42%); the second product eluted is phenyl 4- methoxyphenyl sulfide (0.62 g, 57%). The basic aqueous solution is acidified with hydrochloric acid and worked up as described in the illustrative preparation of 1- phenylazo-2-naphthol. Substantially pure o- benzenedisulfonimide is recovered (control NMR).

Following the same procedure, diphenyl sulfide and bis(4-chlorophenyl) sulfide, were also prepared, in comparable yields.

Whereas the reactions of the up-to-now known diazonium salts with various thio reagents, carried out in aqueous medium, often undergo violent decompositions, the reactions described above in which salts 1 were used gave no problems, even when repeated many times. Also in this case, o-benzenedisulfonimide amounts ranging from 90 to 100% on the theoretical can always be recovered from the aqueous phase.

C - Preparation of phenols (Scheme V). It is possible to operate in trifluoroacetic acid, according to the procedure reported in Example 4 Scheme V Example 5. Preparation of 4-nitrophenol A solution of 4-nitrobenzenediazonium o-

benzenedisulfonimide (lo; 1.84 g, 5 mmol) in trifluoroacetic acid (20 ml) and water (0.18 ml) is heated to 80-85"C in an open reactor and the progressive disappearance of the salt in time is controlled by means of tests with {3-naphthol. The reaction is completed after about 2 hours, when the -naphthol test is negative. The reaction mixture is cooled and treated with an ethyl ether - water mixture (1:1, 25 ml). The ether phase is separated and the reaction mixture is further extracted with two successive portions of ethyl ether (2 x 25 ml). The aqueous solution is treated as described in the preparation of 1-phenylazo-2-naphthol, to recover o-benzenedisulfonimide in an 88% yield (0.96 g). Phenol is then extracted from the combined ether phases by treatment with a 5% sodium hydroxide aqueous solution (2 x 15 ml). The combined basic solutions are acidified with hydrochloric acid and extracted with ethyl ether (3 x 40 ml). After drying and removing the organic solvent under reduced pressure, 0.49 g of 4- nitrophenol are obtained which, by TLC, GC and NMR analysis, proves to be substantially pure. The yield is 70%.

Following the same procedure, starting from 4- chlorobenzenediazonium o-benzenedisulfonimide (lj; 1. 78 g, 5 mmol) in trifluoroacetic acid (20 ml) and water (0.18 ml) at 80-85"C for 2 hours, 4-chlorophenol was obtained in a 72% yield (0.39 g) and o- benzenedisulfonimide (0.94 g, 86%) was recovered. On the other hand, the hydrolysis of 3-methylbenzenediazonium o-benzenedisulfonimide (inc; 1.68 g, 5 mmol) in trifluoroacetic acid (20 ml) was carried out at room

temperature for 15 hours. 3-Cresol was obtained in an 81% yield (0.44 g) and the recovery of o- benzenedisulfonimide was 95% (1.04 g).

As in the above cases, o-benzenedisulfonimide is recovered in high yields (88 - 95% on the theoretical amount).

D - Preparation of aryl halides (Schemes VI-VII-VIII).

Scheme VI Scheme VII Scheme VIII Example 6. Preparation of chlorobenzene A suspension of benzenediazonium o- benzenedisulfonimide (la; 0.32 g, 1 mmol) in dry benzene (3 ml) is added, under strong stirring at room temperature, with tetrabutylammonium chloride (0.30 g, 1 mmol) and with a catalytic amount (0.1 g) of powder copper. An immediate reaction takes place, with strong evolution of nitrogen. After 5 min, the reaction is milder. Stirring is continued for 90 min, until disappearance of the diazonium salt (negative 3-naphthol test). The gas chromatographic analysis of the reaction mixture (internal standard o-dichlorobenzene) shows

formation of chlorobenzene in an 88% yield.

Example 7. Preparation of bromobenzene The reaction is carried out at room temperature and under strong stirring, as described for the preparation of chlorobenzene, starting from benzenediazonium o- benzenedisulfonimide (la; 0.32 g, 1 mmol) in dry benzene (3 ml), tetrabutylammonium bromide (0.32 g, 1 mmol) and catalytic amounts (0.1 g) of powder copper. The reaction is completed in 75 min (negative l3-naphthol test). The gas chromatographic analysis of the reaction mixture (internal standard o-dichlorobenzene) shows a 79% yield in bromobenzene; 2.9% of diphenyl is also present.

ExamPle 8. Preparation of iodobenzene A suspension of benzenediazonium o- benzenedisulfonimide (la; 0.32 g, 1 mmol) in dry benzene (3 ml) is added, under strong stirring at room temperature, with tetrabutylammonium iodide (0.37 g, 1 mmol). Even with no copper as catalyst, an immediate reaction takes place, with a strong evolution of nitrogen. The reaction is completed (negative f3-naphthol test) after 3 hours. The gas chromatographic analysis of the reaction mixture (internal standard bromobenzene) shows a iodobenzene quantitative yield.

Operating with the salts 1, the aryl halides are always obtained in high yields, whereas the amount of formed diaryl (diphenyl) is minimum. From the aqueous phase, o-benzenedisulfonimide amounts ranging from 90 to 100% on theoretical can always be recovered.

E - Preparation of aryl methanesulfonates (Scheme IX).

Scheme IX Example 9. Preparation of 4-chlorophenyl methanesulfonate A solution of 4-chlorobenzenediazonium o- benzenedisulfonimide (2j; 1.79 g, 5 mmol) in methanesulfonic acid (12 ml) is heated to 80-85"C and the progressive disappearance of the salt in time is controlled by means of -naphthol tests. The reaction ends after about 6 hours, when the -naphthol test is negative. The reaction mixture is cooled and treated with an ethyl ether - water mixture (1:1.30 ml). The ether phase is separated and the reaction mixture is further extracted with two successive portions of ethyl ether (2 x 30 ml). The imide and the main part of methanesulfonic acid remain in the aqueous phase. The combined ether extracts are washed with a 5% sodium hydroxide aqueous solution (30 ml), then with water (30 ml). After drying and evaporation of the organic solvent under reduced pressure, 0.92 g of substantially pure 4- chlorophenyl methanesulfonate are obtained (NMR; GC; GC- MS; TLC, eluent chloroform). The yield is 89%. The product, crystallized from ethanol, has m.p. 71"C (Chem.

Abstr. 1964, 61, 600e: m.p. 69-71.5"C).

Following the same procedure, the following compounds were also prepared: 3-Nitrophenyl methanesulfonate: reaction time 8 hours. The product was purified by chromatography on a silica gel column, using chloroform as eluent; 61* yield; crystallized from ethanol, m.p. 69"C (J. Chem.

Soc. Perkin Trans. 1, 1991, 307: m.p. 64-65"C).

4-Nitrophenyl methanesulfonate: reaction time 8 hours. The product was purified by chromatography on a silica gel column, using chloroform as eluent; 79% yield; crystallized from ethanol, m.p. 90-91"C (J. Chem.

Soc. Perkin Trans. 1, 1991, 307: m.p. 87-88"C).

The above applicative examples show that the salts 1 are suitable for all the organic synthesis usually carried out with diazonium salts, both in aqueous solution and in many different organic solvents.

The salts 1 can be suitably used for various applications, in view of the easiness of their preparation, their very high stability, their general chemical properties and the easiness of recovery and reutilization o-benzenedisulfonimide. In particular, many of them can be prepared and directly used or, which is an even more interesting aspect, they can be marketed as intermediates or as ready-to-use analytical reagents.

In consideration of their properties, the use of salts 1 for industrial applications could also be envisaged, for example those applications described in the introduction (photosensitizers, control agents for polymerization reactions, or still for dyeing and printing of textiles).