Phosphorus pentachloride with sulfonic acids

Pyrazolesulfonic acids, like (493), have high melting points (Table 24) and probably exist as the zwitterions (497). They are very stable to hydrolysis and only afford pyrazolones at high temperatures. The replacement of the SO3H group by bromine has also been reported (B-76MI40402). Pyrazole-3-, -4- and -5-sulfonic acids react with phosphorus pentachloride to form sulfonyl chlorides. 

Sulfonyl chlorides are usually prepared by treating sulfonic acids with phosphorus pentachloride. 

General Reaction Chemistry of Sulfonic Acids. Sulfonic acids may be used to produce sulfonic acid esters, which are derived from epoxides, olefins, alkynes, allenes, and ketenes, as shown in Figure 1 (10). Sulfonic acids may be converted to sulfonamides via reaction with an amine in the presence of phosphorus oxychloride [10025-87-3], POCl3 (11). Because sulfonic acids are generally not converted direcdy to sulfonamides, the reaction most likely involves a sulfonyl chloride intermediate. Phosphorus pentachloride [10026-13-8] and phosphorus pentabromide [7789-69-7] can be used to convert sulfonic acids to the corresponding sulfonyl halides (12,13). The conversion may also be accomplished by continuous electrolysis of thiols or disulfides in the presence of aqueous HQ [7647-01-0] (14) or by direct sulfonation with chlorosulfuric acid. Sulfonyl fluorides are typically prepared by direct sulfonation with fluorosulfuric acid [7789-21-1], or by reaction of the sulfonic acid or sulfonate with fluorosulfuric acid. Halogenation of sulfonic acids, which avoids production of a sulfonyl halide, can be achieved under oxidative halogenation conditions (15). 

Conversion of 2-hydroxypyridines to 2-chloropyridines has been effected using triphenylphosphine and NCS <1999TL7477, 2001HCA1112>. Interestingly, 5-nitropyridine-2-sulfonic acid is converted to 2-chloro-5-nitropyr-idine in 87% yield when treated with phosphorus pentachloride (Equation 41). This reaction provides a new pathway to chloronitropyridines <20030BC2710>. 

Since sulfonation of pyridine iV-oxide is about as difficult as is that of pyridine itself and takes place at the 3-position,17 it has been assumed18 that, in fuming sulfuric acid, pyridine iV-oxide reacts only in the salt form (3), when the prediction is that substitution at C-3 would take place. It is, however, difficult to account for the fact that bromination, even at 110° in the presence of iron powder, does not occur.17 Bromination in chloroform solution in the presence of acetic anhydride and sodium acetate (when the O-acetate is the the probable substrate) take place readily, however, to give 3,5-dibromopyridine JV-oxide.19 The predicted order of nucleophilic reactivity, on the basis of both atom localization energies and ground-state v-electron density calculations, is 4 > 2 > 3. The same order is predicted for the nucleophilic substitution reactions of the salts of pyridine JV-oxide. In actual practice, iV-alkoxypyridinium derivatives undergo nucleophilic attack preferentially at C-2.20-23 The reaction of some pyridine iV-oxides with phosphorus pentachloride may involve the formation... 

Sulfinic esters, aromatic, by oxidation of disulfides in alcohols, 46, 64 Sulfonation of D,L-camphor to d,l-10-camphorsulfonic acid, 46,12 Sulfoxides, table of examples of preparation from sulfides with sodium metaperiodate, 46,79 Sulfur dioxide, reaction with styrene phosphorus pentachloride to give styrylphosphonic dichloride, 46,... 

In contrast to the ease of N-functionalization, shown in Scheme 1, the triazolopyridine nucleus is resistant to direct nuclear oxidation or electrophilic additions. Electrophilic additions will occur on aryl substituents for example, nitration of l-phenyltriazolo[4,5-c]pyridine (26) and sulfonation of 2-phenyl-2i/-triazolo[4,5-6]pyridine (28) occur exclusively in the para position of the phenyl ring <34LA(514)279, 38MI 710-01). Nuclear functionalization was observed when l-( -butyl)-5-methyl-tri-azolo[4,5-c]pyridinium iodide (30) was treated with potassium ferricyanide to afford triazolopyridin-4-one (31), as shown in Scheme 2. Similarly, the iodide (30) is converted by either phosphorus oxychloride-phosphorus pentachloride, or bromine or nitric acid to 7-substituted triazolopyridin-4-ones (32) <37LA(529)288>. 

Sulfonic acids and carboxylic acids can be converted into their acid chlorides by treatment with phosphorus pentachloride or phosphorus oxychloride. Thionyl chloride, SOCl is effective for the synthesis of acyl chlorides, and sulfonyl chlorides can be prepared directly from the aromatic compound by reaction with an excess of chlorosulfonic acid. The acid chlorides are efficient Friedel-Crafts acylating agents, yielding sul-... 

Sulfonic acids are converted to the corresponding acid halides in much the same way as carboxylic acids. Thionyl chloride is the best reagent for the preparation of methanesulfonyl chloride (83%). By heating with a large excess of thionyl chloride, however, p-toluenesulfonic acid is converted into its anhydride (87%). Benzenesulfonyl chloride is made in 80% yield by the action of either phosphorus pentachloride or phosphorus oxychloride at 180° on sodium benzenesulfonate. Chlorosulfonic and fluorosulfonic acids are used in the conversion of sodium p-chloro-benzenesulfonate to the corresponding sulfonyl halides (85 8S>%). ... 

In considering the synthesis of this compound several alternatives are possible. Two will be considered. Aniline may be sulfo-nated to sulfanilic acid, and after acetylation the chloride may be prepared by the action of phosphorus pentachloride. The acyl chloride, on ammonolysis, will give the acetylated sulfonamide. The other possibility is to use chlorosulfonic acid and introduce the sulfo and chloro groups simultaneously. Aniline is acetylated, and the acetanilide is sulfonated with excess of chlorosulfonic acid. The sulfonic acid group is introduced first, and by further reaction the acid chloride is formed ... 

Sulfonyl chlorides (51) may also be obtained by heating the sulfonic acid or its sodium salt with thionyl chloride or phosphorus pentachloride (Scheme 31). The reaction with thionyl chloride is catalysed by the addition of a few drops of DMF. The chlorosulfonation of organic compounds may also be achieved by reaction with sulfur dioxide and chlorine this is an important industrial process (the Reed reaction) (Scheme 32). 

Prepared by treatment of methyl formate with phosphorus pentachloride, the reagent reacts with a carboxylic acid or anhydride to give the corresponding acid chloride in high yield. Sulfonic acids or their sodium salts afford sulfonyl chlorides ... 

Preparation of acid chlorides. The thionyl chloride method of preparing acid chlorides fails with some carboxylic acids (e.g., p-NOjCsHaCOzH) and with all sulfonic acids. Bosshard and co-workers" found that dimethylformamide catalyzes both reactions, either when used as solvent or when employed in catalytic amount in an inert solvent. The reactive, hygroscopic intermediate dimethylformirainium chloride was isolated from one equivalent each of dimethylformamide and thionyl chloride, and also obtained by reaction of dimethylformamide with phosgene, oxalyl chloride, or phosphorus pentachloride. It reacts with an acid with regeneration of dimethylformamide, the catalyst. In one example, 0.3 mole of p-nitrobenzoic acid was heated briefly at 90-95° with 0.315 mole of thionyl chloride and 0.03 mole... 

Loev and Kormendy147 first synthesized a 2,1-benzothiazine 2,2-dioxide by converting 2-(o-nitrophenyl)ethanesulfonyl chloride to the sulfonate salt 221 which was catalytically reduced to the amine 222. Treatment of 222 with phosphorus pentachloride/acetyl chloride afforded 3,4-dihydro-1//-2,1-benzothiazine 2,2-dioxide (223). They also prepared 4-phenyl-3,4-dihydro-IH-2,1-benzothiazine 2,2-dioxide (225) by treating styrene sulfonanilide (224 R = Ph) with polyphosphoric acid. However, they were unable to cyclize the ethylene sulfonamide (224 R = H) to 223 using this route.147... 

Reducing agents such as hydroiodic acid, hydrobromic acid, hypophosphorus acid, and hydrazine can be utilized in this reaction. Sulfonyl chloride group (S02C1), the most common starting chemical moiety, can be prepared from the sulfonic acid group by reaction with phosphorus pentachloride or phosphorus trichloride and chlorine (18, 20, 21, 36, 37,... 

Cleavage of the S-0 bond of sulfonic acids and its salts by the action of halogenating agents is one of the most important methods of preparing sulfonyl halides it is effected by treating the free acid with thionyl chloride722,723 or phosphorus trichloride,589 or a salt with phosphorus pentachloride.690,724... 

The most familiar of the sulfonic adds derived from camphor is 10-camphorsulfonic add (44, Reychler s acid45). Both enantiomers are commercially available and convenient procedures exist for their preparation by sulfonation of camphor (ref 46 exemplifies the racemate, but the procedure works equally well for optically active camphor). The free acid is often applied to the resolution of basic compounds such as amines. A detailed review on the use of derivatives of this acid as auxiliaries has been given3. Esters of this add are normally obtained by the reaction of the alcohols with the sulfonyl chloride which is also commerdally available (or readily obtained by the reaction of the free acid with phosphorus pentachloride or thionyl chloride46,48). Such esters with unsaturated alcohols have been used for diastereoselective [1,2] sigma tropic rearrangements (Section D.1.6.3.3.). Allyl esters have been used for enantioselective alkylation reactions, in which camphorsulfonic acid reacts as the chiral leaving group (Section D.1.1.2.2.). 

From the sulfonic acid or its sodium or potassium salt with phosphorus pentachloride without solvent For directions and examples see Cheronis, p 638, Linstead, p 89, Shrmer, pp 268, 270, Vogel, p 553, Wild, p 161... 

From the sulfonic acid or its sodium or potassium salt with phosphorus pentachloride without solvent... 

In related work, solid-phase-mediated synthesis of isonitriles from formamides was achieved by using polystyrene-bound sulfonyl chloride as a suitable supported reagent [115]. The sulfonyl chloride resin could be quantitatively regenerated by treatment of the sulfonic acid resin formed with phosphorus pentachloride (PCI5) in N,N-dimethy]formamide at room temperature. 

Sulfonyl chlorides are highly reactive derivatives of sulfonic acid and possess similar properties and reactivity to acid chlorides of carbo Q lates. The reaction with nucleophiles such as amines requires alkaline conditions (pH 9-10) and proceeds through the formation of an unstable pentavalent transition state (Scheme 1.10). Hydrolysis is a major competing reaction in water therefore the reaction with amines proceeds with better yield when done in organic solvents. Sulfonyl chlorides have played an important role in bioconjugation chemistry, since sulfonic acids can be easily converted into sulfonyl chlorides using thionyl chloride or phosphorus pentachloride in non-aqueous conditions. ... 

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