Sulfolane, reagents

A mixture of methanesulfonic acid and P Oj used either neat or diluted with sulfolane or CH2CI2 is a strongly acidic system. It has been used to control the rcgiosclcctivity in cydization of unsymmetrical ketones. Use of the neal reagent favours reaction into the less substituted branch whereas diluted solutions favour the more substituted branch[3]. 

Whereas sulfolane is relatively stable to about 220°C, above that temperature it starts to break down, presumably to sulfur dioxide and a polymeric material. Sulfolane, also stable in the presence of various chemical substances as shown in Table 2 (2), is relatively inert except toward sulfur and aluminum chloride. Despite this relative chemical inertness, sulfolane does undergo certain reactions, for example, halogenations, ting cleavage by alkah metals, ring additions catalyzed by alkah metals, reaction with Grignard reagents, and formation of weak chemical complexes. 

Mild acid converts it to the product and ethanol. With the higher temperatures required of the cyano compound [1003-52-7] (15), the intermediate cycloadduct is converted direcdy to the product by elimination of waste hydrogen cyanide. Often the reactions are mn with neat Hquid reagents having an excess of alkene as solvent. Polar solvents such as sulfolane and /V-m ethyl -pyrrol i don e are claimed to be superior for reactions of the ethoxy compound with butenediol (53). Organic acids, phenols, maleic acid derivatives, and inorganic bases are suggested as catalysts (51,52,54,59,61,62) (Fig. 6). 

Nitration with concentrated nitric acid degrades chlorins which are sensitive to oxidation. Here nitronium tetrafluoroborate in sulfolane is the reagent of choice. Both mononitrooc-... 

Alkyl esters are efficiently dealkylated to trimethylsilyl esters with high concentrations of iodotrimethylsilane either in chloroform or sulfolane solutions at 25-80° or without solvent at 100-110°.Hydrolysis of the trimethylsilyl esters serves to release the carboxylic acid. Amines may be recovered from O-methyl, O-ethyl, and O-benzyl carbamates after reaction with iodotrimethylsilane in chloroform or sulfolane at 50—60° and subsequent methanolysis. The conversion of dimethyl, diethyl, and ethylene acetals and ketals to the parent aldehydes and ketones under aprotic conditions has been accomplished with this reagent. The reactions of alcohols (or the corresponding trimethylsilyl ethers) and aldehydes with iodotrimethylsilane give alkyl iodides and a-iodosilyl ethers,respectively. lodomethyl methyl ether is obtained from cleavage of dimethoxymethane with iodotrimethylsilane. 

Fig. 1.34. Chlorination of adamantane to furnish tert-adamantyl chloride (A) and sec-adamantyl chloride (B), using differents reagents. In the reaction with the A B selectivity amounts to 68 32 in carbon disulphide and 39 61 in carbon tetrachloride (each at 25°C). In the reaction with S02CI, in sulfolan the A B selectivity is > 97.5 2.5 (at 60°C). The formation of sec-adamantyl chloride (B) proceeds via the secondary radical C, tert-adamantyl chloride (A) is formed via the tertiary radical D.

With triphenylphosphine in sulfolane, this reagent converts allylic alcohols to chlorides without rearrangement699. 

Materials. Sulfolane (99%purity) (Aldrich) was treated with calcium hydride and distilled under reduced pressure. The freshly prepared solvent had a specific conductivity of 1.0 X 10 7 O"1 cm"1 and a residual water content of 8 X 10"3M as determined by Karl Fisher titration. Conductivity water and reagent grade ether (Baker) were used. Glacial acetic acid (CIL), trifluoroacetic acid (Baker), and trifluoro-methanesulfonic acid (3M) were used as received. All these acids had a minimum purity of 99.5% as determined by titration with standard sodium hydroxide. Methanesulfonic acid (Eastman), distilled under reduced pressure, had a purity of 99.6%. Sulfolane solutions of these acids were prepared by weight, and the acid concentrations were checked by acidimetry after the samples were flooded with water. The solutions... 

Sodium borohydride, a representative borohydride reagent, behaves as an effective source of nucleophilic hydride in an aprotic polar solvent, such as DMSO, sulfolane, HMPA, DMF or diglyme, and is used for the reduction of alkyl halides. As shown in Table 3, primary and secondary iodides, bromides and chlorides are converted to hydrocarbons at temperatures between 25 and 100 C using sodium borohydride. Vicinal dihalides, such as 1,2-dibromooctane, are smoothly converted to the corresponding saturated hydrocarbons, in contrast to the reductions using LiAlH4 or low-valent metal salts, which predominantly afford alkenes. 

Oxidative cleavage of l -deols. The reagent catalyzes the cleavage of 1,2-glycols by oxygen in an aprotic, polar solvent (benzonitrile, DMF, sulfolane). Yields of aldehydes tre 60-81 %. Further oxidation to carboxylic acids is possible.1... 

Reagent. Tetrahydrothiophene 1,1-dioxide (commonly called sulfolane) was obtained from Shell Chemical containing 3% water. Anhydrous sulfolane was obtain by distillation under reduced pressure. Re-... 

Alkyl groups are not the only substituents that can be attached to boron in order to generate new borohydride derivatives. Reaction of NaBH4 with HCN gives sodium cyanoborohydride (NaBH3CN), for example, a remarkably stable reagent that does not decompose in acid solution (the pH should be less acidic than pH 3). It is soluble in THF, MeOH, H2O, HMPA, DMF and sulfolane and is unreactive, making it very... 

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