Alkyl chlorosulfites

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 ... 

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). 

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

The thionyl chloride reaction apparently can proceed from the alkyl chlorosulfite stage by more than one mechanism an ionic SN2 chain reaction with chloride ion,... 

Action of Alkyl Chlorosulfites or Alkyl Sulfates on Salts of Carboxylic Acids... 

Chlorosulfites, see Alkyl chlorosulfites ChugacT reaction, 42 Claisen condensation, of aromatic aldehydes, 53 of esters, 345... 

As models for the investigation of the S i and S i mechanisms the thermal decompositions of alkyl chlorosulfites and allyl chlorosulfites have received considerably more attention than that of other desulfonylation reactions. The usual method of converting alcohols into alkyl chlorides is by treatment with thionyl chloride. This reaction has been shown to proceed through an alkyl chlorosulfite which can often be isolated and shown to decompose by a homogeneous first-order process yielding alkyl chloride and 802 " , although frequently substantial amounts of alkene are formed in the reaction , viz. 

Other leaving groups can also be replaced by OCOR. Alkyl chlorosulfites (ROSOCl) and other derivatives of suffuric, sulfonic, and other inorganic acids can be treated with carboxylate ions to give the corresponding esters. Treatment with oxalyl chloride allows displacement by carboxylate salts.The use of dimethyl... 

Alkyl chlorides can be prepared by the reaction of alcohols with thionyl chloride (SOCl2) in the presence of a nitrogen base (e.g. triethylamine or pyridine). An intermediate alkyl chlorosulfite (ROSOC1) is formed by nucleophilic attack of ROH on the sulfur atom of thionyl chloride. The OH group is converted to an OSOCl-leaving group, which is displaced on reaction with the chloride anion (e.g. in an SN2 mechanism when R is a primary alkyl group). 

The intermediate alkyl chlorosulfite could be formed via an intermediate dichloride... 

In the absence of a nitrogen base, HC1 is formed, and this cannot act as a nucleophile and attack the alkyl chlorosulfite in an SN2 reaction. Therefore, an SNi mechanism operates. 

Mechanism 4.3 shows the conversion of a primary alcohol to the alkyl chloride using thionyl chloride. The reaction involves the formation of an alkyl chlorosulfite that is attacked by the nucleophilic chloride ion. 

Hence, the displacement of the chlorosulfate groups in (II) and 1, 2,3,3, 4,4 -hexa-O-benzoylsucrose 6,6 -bis (cElorosulfate) by chloride ion, probably involved am intramolecular process, similar to the Sjjl reaction of alkyl chlorosulfites or alkyl chloroformates. (See Figure 12). 

As we have just seen, alcohols react with thionyl chloride to form alkyl chlorosulfites. Alcohols also react with compounds called sulfonyl chlorides to form alkylsulfonates. Sulfonyl chlorides are derived from sulfonic acids, which are comparable in strength to sulfuric acid. 

Reaction with SOCij and SOBtj (Section 10.5C) Alcohols react with SOClj to initially give an alkyl chlorosulfite intermediate, which is displaced from the backside by Cl to give the chloroalkane. This is often the method of choice for converting a primary or secondary alcohol to an alkyl chloride or alkyl bromide. 

The formation of a tight (or intimate) ion pair can also lead to retention of configuration. This is observed when alcohols (ROH) with chiral centres react with thionyl chloride (SOCI2) in the absence of a nitrogen base. The intermediate alkyl chlorosulfite (ROSOCl) breaks down to form a tight ion pair (R+ OSOCl) within a solvent shell. The OSOCl anion then collapses to form SO2 and Cl the Cl then attacks the carbocation from the same side that OSOCl departs. 

Chloride ion Alkyl chlorosulfite Alkyl chloride Sulfur dioxide Chloride ion... 

---