Thionyl chloride reaction with aromatic compounds

Aromatic sulfonyl chlorides can be prepared directly, by treatment of aromatic rings with chlorosulfuric acid. Since sulfonic acids can also be prepared by the same reagent (11-7), it is likely that they are intermediates, being converted to the halides by excess chlorosulfuric acid. The reaction has also been effected with bromo- and fluorosulfuric acids. Sulfinyl chlorides (ArSOCl) have been prepared by the reaction of thionyl chloride and an aromatic compound on Montmorillonite KIO clay. ii... 

Diaryl sulfoxides can be prepared by the reaction of aromatic compounds with thionyl chloride and triflic acid. Diaryl sulfones have also been prepared using... 

A totally different picture is presented by 3-phenylazo-2-naphthol. This unusual isomer cannot be prepared by a normal coupling procedure but has been obtained by reaction of 3-amino-2-naphthol with thionyl chloride to give the N-sulphinylamine (4-24), condensation of which with N-phenylhydroxylamine yields the desired product [59]. Here, assumption of a ketohydrazone form would entail loss of aromatic character in both rings of the naphthalene nucleus and the energetic unfavourability of this situation ensures that the compound exists solely in the hydroxyazo form. 

Diaryl sulfides can be prepared by treating aromatic compounds with SC12 and a Friedel-Crafts catalyst. Other reagents that can bring about the same result are S2C12, thionyl chloride, and even sulfur itself. A catalyst is not always necessary. The reaction has been used for ring closure ... 

Several reactive chloro compounds have been used to attempt to effect the controlled monochlorination of aromatic amines. One such reagent is N-chlorosuccinimide, with which the chlorination of aniline, for example, can be largely restricted to monosubstitution, although a mixture of isomers (orthopara, 1.9 1) is obtained.24 One approach to the achievement of specific ortho chlorination is illustrated by the synthesis of o-chlorobenzanilide (Expt 6.61), readily hydrolysable to o-chloroaniline. The anilide is formed, by a type of Swi mechanism indicated below, when AT-phenylhydroxylamine is benzoylated and the product is treated with thionyl chloride.25 The reaction has been successfully applied to several substituted JV-phenylhydroxylamines, prepared by the controlled reduction of the corresponding substituted nitro compounds (cf. Expt 6.87). 

Most compounds of this type are cyclic sulfite and sulfate esters of aromatic 1,2-diols as well as anhydrides of aromatic 1,2-disulfonic acids. The simplest representatives with unsubstituted benzene rings are 1,3,2-benzodioxathiole 2-oxide (48) (catechol sulfite), the corresponding 2,2-dioxide (156) (catechol sulfate) and 2,1,3-benzoxadithiole 1,1,3,3-tetroxide (158) (1,2-benzenedisulfonic anhydride). Compound (48) was synthesized by refluxing catechol with thionyl chloride in the presence of pyridine. In a similar fashion, from 2-mercaptophenol 1,2,3-benzoxadithiole 2-oxide was prepared (81AG603). The dioxide (156) was obtained in two steps by reaction of catechol monosodium salt with sulfuryl chloride in benzene at 0-10 °C and subsequent reflux of the intermediate (155) in the presence of pyridine. 

Bids is very easily hydrated and commercial samples may need to be dried or sublimed if anhydrous material for use in sensitive reactions (e.g. with Grignard reactions) is required. Refluxing a thionyl chloride suspension of Bids is an effective method for dehydrating the solid. Anhydrous Bids is soluble in aromatic hydrocarbons and donor solvents such as ethers where complexes are formed. Bismuth(III) halides are useful starting compounds for the production of many other bismuth(lll) compounds. (see also Bismuth Organometallic Chemistry). 

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-... 

Sulphonation of aromatic compounds with sulphuric acid can take place under a wide variety of conditions depending upon the aromatic compound being used. The reaction is a reversible one, as shown in equation 4, and so either a large excess of mineral acid is required or the water must be removed, either by azeotropic distillation or by another process. One such procedure involves the addition of thionyl chloride to the sulphonating mixture. In this case, any water that is produced reacts with the thionyl chloride to form HC1 and sulphur dioxide6. 

Therefore, reaction of iminium chlorides, or their complexes with phosphorus oxychloride, thionyl chloride, carbonyl chloride, etc., with suitable substrates, such as aromatic hydrocarbons, activated methylene compounds and nucleophilic olefins, occurs quite readily. The overall reaction generally results in the formylation of the corresponding substrate. 

Reactions with Aldehydes and Ketones. Aromatic or a, -unsaturated aldehydes or their bisulfite addition compounds are converted to gem-dichlorides by treatment with SOCI2, either neat or in an inert solvent such as nitromethane (eq 1This process is readily catalyzed by RMPA." Thionyl chloride may be preferred over the more commonly used PCI5 if removal of byproducts is problematic with the latter reagent. 

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