Chlorosulfite

The reactions of thionyl chloride with organic compounds having hydroxyl groups are important. Alkyl chlorides, alkyl sulfites, or alkyl chlorosulfites form from its reaction with aUphatic alcohols, depending on reaction conditions, stoichiometry, and the alcohol stmcture ... 

However, when sulfur monochloride is used as the catalyst, chlorosulfites form. 

When the reaction is performed in dioxane solution, an o onium ion is formed from the solvent and the chlorosulfite ester. The oxonium ion then undergoes substitution by chloride. l vo inversioRs are involved so that tiie result is overall retention. ... 

The reaction occurs by a nucleophilic acyl substitution pathway in which the carboxylic acid is first converted into a chlorosulfite intermediate, thereby replacing the -OH of the acid with a much better leaving group. The chloro-sulfitc then reacts with a nucleophilic chloride ion. You might recall from Section 17.6 Hint an analogous chlorosulfite is involved in reaction of an alcohol with SOCb to yield an alkyl chloride. 

The example shown is the most important case of this mechanism yet discovered, since the reaction of alcohols with thionyl chloride to give alkyl halides usually proceeds in this way, with the first step in this case being ROH -I- SOCI2 ROSOCl (these alkyl chlorosulfites can be isolated). 

Another general method for converting alcohols to halides involves reactions with halides of certain nonmetallic elements. Thionyl chloride, phosphorus trichloride, and phosphorus tribromide are the most common examples of this group of reagents. These reagents are suitable for alcohols that are neither acid sensitive nor prone to structural rearrangement. The reaction of alcohols with thionyl chloride initially results in the formation of a chlorosulfite ester. There are two mechanisms by which the chlorosulfite can be converted to a chloride. In aprotic nucleophilic solvents, such as dioxane, solvent participation can lead to overall retention of configuration.7... 

In the absence of solvent participation, chloride attack on the chlorosulfite ester leads to product with inversion of configuration. 

It is extremely shock-sensitive, a 4.0 kg cm shock causing detonation in 50% of test runs (cf. 3.5 kg cm for propargyl bromide 2.0 kg cm for glyceryl nitrate). The intermediate bis-chlorosulfite involved in the preparation needs low temperatures to avoid vigorous decomposition. The corresponding diiodo derivative was expected to be similarly hazardous [1], and this has been confirmed [2]. Improvements in preparative techniques (use of dichloromethane solvent at —30°C) to avoid violent reaction have also been described [3], An attempt to distill the compound (b.p. 55-58°C/0.6 mbar, equivalent to about 230°C/l bar) at atmospheric pressure from a heating mantle led to a violent explosion [4], The compound involved was erroneously given as l,6-dichloro-2,4-hexadiene [5],... 

There are also some rare domino sequences where two anionic and two radical reactions are combined (Scheme 2.152) [347]. According to a report of the Wang group, thionyl chloride is able to promote a succession of reactions by an initial formation of a chlorosulfite 2-673 of the tertiary alcohol 2-672, followed by an SN-type reaction to produce the chloroallene 2-674. A Schmittel cyclization reaction [348] then generates... 

The reaction mechanism involves the initial formation of the alkyl chlorosulfite ... 

Treatment of the propargylic alcohol 144, readily prepared from condensation between benzophenone (143) and the lithium acetylide 101, with thionyl chloride promoted a sequence of reactions with an initial formation of the chlorosulfite 145 followed by an SNi reaction to produce in situ the chlorinated and the benzannulated enyne-allene 146 (Scheme 20.30) [62], A spontaneous Schmittel cyclization then generated the biradical 147, which in turn underwent a radical-radical coupling to form the formal [4+ 2]-cycloaddition product 148 and subsequently, after a prototropic rearrangement, 149. The chloride 149 is prone to hydrolysis to give the corresponding 11 H-bcnzo h fluoren-ll-ol 150 in 85% overall yield from 144. Several other llff-benzo[fc]fluoren-ll-ols were likewise synthesized from benzophenone derivatives. 

Pritchard and co-workers (147) reported the preparation of an acyclic chiral sulfite, 98, which is formed as a mixture of diastereo-mers in the reaction between racemic methyl chlorosulfite and (+)-diphenacyl malate. The pure diastereomers of 98 were isolated by fractional crystallization. 

Halogen abstraction from hypervalent sulfur halides has also been reported for the imidazol-2-ylidenes (IV) (Scheme 8.22). This reaction gives a nice example of the synthetic utihty of V-heterocyclic carbenes. Indeed, this adduct is the first structurally characterized derivative featuring the chlorosulfite ion (SO2CI ). ... 

Problom 7.62 Depending on the solvent, ROH reacts with SOCl to give RCl by two pathways, each of which involves formation of a chlorosulfite ester. 

On heating, the chlorosulfinate is catalytically decomposed by pyridine hydrochloride to the corresponding alkyl chloride and sulfur dioxide (see Eq. 6). Secondary chlorosulfites give olefins even under the mildest conditions [11], The use of excess pyridine reduces the yield of sulfite by the method described in Eq. (4). 

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