P-Toluenesulfonyl chloride, reaction with alcohols

If the temperature is not kept below 25°C dunng the reaction of primary alcohols with p toluenesulfonyl chloride in pyndine it is sometimes observed that the isolated product is not the desired alkyl p toluenesulfonate but is instead the corresponding alkyl chlonde Suggest a mech anistic explanation for this observation... 

Conversion to p toluenesulfonate es ters (Section 8 14) Alcohols react with p toluenesulfonyl chloride to give p toluenesulfonate esters Sulfo nate esters are reactive substrates for nucleophilic substitution and elimma tion reactions The p toluenesulfo nate group is often abbreviated —OTs... 

The reaction of alcohols with acyl chlorides is analogous to their reaction with p toluenesulfonyl chloride described earlier (Section 8 14 and Table 15 2) In those reactions a p toluene sulfonate ester was formed by displacement of chloride from the sulfonyl group by the oxygen of the alcohol Carboxylic esters arise by displacement of chlonde from a carbonyl group by the alcohol oxygen... 

When a primary alcohol is treated with p-toluenesulfonyl chloride at room temperature in the presence of an organic base such as pyridine, a tosvlate is formed. When the same reaction is carried out at higher temperature, an alkyl chloride is often formed. Explain. 

Alcohols react with p-toluenesulfonyl chloride (tosyJ chloride, p-TosCl) in pyridine solution to yield alkyl tosylates, ROTos (Section 11.1). Only the 0-H bond of the alcohol is broken in this reaction the C—O bond remains intact, so no change of configuration occurs if the oxygen is attached to a chirality center. The resultant alkyl tosylates behave much like alkyl halides, undergoing both SN1 and Sjsj2 substitution reactions. 

Axenrod and co-workers reported a synthesis of TNAZ (18) starting from 3-amino-l,2-propanediol (28). Treatment of (28) with two equivalents of p-toluenesulfonyl chloride in the presence of pyridine yields the ditosylate (29), which on further protection as a TBS derivative, followed by treatment with lithium hydride in THF, induces ring closure to the azetidine (31) in excellent yield. Removal of the TBS protecting group from (31) with acetic acid at elevated temperature is followed by oxidation of the alcohol (32) to the ketone (33). Treatment of the ketone (33) with hydroxylamine hydrochloride in aqueous sodium acetate yields the oxime (34). The synthesis of TNAZ (18) is completed on treatment of the oxime (34) with pure nitric acid in methylene chloride, a reaction leading to oxidation-nitration of the oxime group to em-dinitro functionality and nitrolysis of the A-tosyl bond. This synthesis provides TNAZ in yields of 17-21 % over the seven steps. 

Compound A is the p-toluenesulfonate ester (tosylate) of /ran.v-4-/cr/-butylcyciohexanol. The oxygen atom of the alcohol attacks the sulfur of p-toluenesulfonyl chloride, and so the reaction proceeds with retention of configuration. 

Symmetrical aliphatic ethers (C -Ci,) are prepared by the removal of water from alcohols under acidic conditions. Thus, in the preparation of diisoamyl ether, the alcohol is heated with concentrated sulfuric acid or p-toluenesulfonyl chloride in a flask equipp>ed with a condenser and a water sep>arator. The top layer of alcohol and ether is returned to the reaction flask until water no longer separates. Any alcohol remaining in the ether is converted to the higher-boiling triisoamyl borate, and the ether is purified by fractional distillation. Several suitable water separators have been described. High reaction temperatures must be avoided to prevent the formation of unsaturated hydrocarbons (cf. method 19). 

RC = CCH,X — RCX = C==CH,. /S.y- and 7,S-Acetylenic alcohols can be transformed to the halides in better yields by an alternative procedure, which consists in their esterification with p-toluenesulfonyl chloride and subsequent cleavage of the ester by the action of sodium iodide, lithium chloride, or calcium bromide in an appropriate solvent (60-90%). Halo ethers are prepared by the action of phosphorus tribromide on hydroxy ethers, as in the preparation of /3-ethoxyethyl bromide (66%). In a similar manner, /3-halo esters have been prepared without appreciable dehydration of the /3-hydroxy ester (40-60%). The reaction of cyanohydrins leads to a-halo nitriles. Treatment of 2-nitro-l-propanol with phosphorus pentachloride gives l-chloro-2-nitropropane (47%). ... 

Alkyl chlorides, bromides and iodides can be formed by the reaction of alcohols with p-toluenesulfonyl chloride (or tosyl chloride, abbreviated as TsCl) in the presence of a nitrogen base (e.g. triethylamine or pyridine). The OH group is converted into a tosylate (abbreviated as ROTs), which can be displaced on reaction with CF, BF or I-. The stable tosylate anion is an excellent leaving group (SN1 or SN2 mechanism depending on the nature of the alkyl group, R). 

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