Thiourea, reaction with alkyl halides

Indirect formation of thioglycosides can also be performed from glycosyl halides. Reaction with thiourea yields a pseudothiouronium salt, which (as the thioacetate above) can be hydrolyzed under mild, selective conditions to give the anomeric thiol, which then can be alkylated in an efficient, non-smelling procedure to produce... 

Thiols, the sulfur analogs of alcohols, are usually prepared by Sjv 2 reaction of an alkyl halide with thiourea. Mild oxidation of a thiol yields a disulfide, and mild reduction of a disulfide gives back the thiol. Sulfides, the sulfur analogs of ethers, are prepared by an Sk2 reaction between a thiolate anion and a primary or secondary alkyl halide. Sulfides are much more nucleophilic than ethers and can be oxidized to sulfoxides and to sulfones. Sulfides can also be alkylated by reaction with a primary alkyl halide to yield sulfonium ions. 

Thiols may be prepared from the corresponding alkyl halide by reaction with thiourea followed by treatment of the isothiouronium salt with base. 

Sec. 18.8) from primary alkyl halides by Sn2 reaction with thiourea, followed by... 

The formation of an alkanethiol by reaction of an alkyl halide or alkyl p-toluenesulfonate with thiourea occurs with inversion of configuration in the step in which the carbon-sulfur bond is formed. Thus, the formation of (f )-2-butanethiol requires (5)-5ec-butyl p-toluenesulfonate, which then reacts with thiourea by an Sj 2 pathway. The p-toluenesulfonate is formed from the corresponding alcohol by a reaction that does not involve any of the bonds to the stereogenic center. Therefore, begin with (iS )-2-butanol. 

The reaction often works poorly unless an excess of the nucleophile is used because the product thiol can undergo a second S 2 reaction with alkyl halide to give a sulfide as a by-product. To circumvent this problem, thiourea, (NH2J2C=S, is often used as the nucleophile in the preparation of a thiol from an alkyl halide. The reaction occurs by displacement of the halide ion to yield an intermediate alkyl isothiourea salt, which is hydrolyzed by subsequent reaction with aqueous base. 

Thiophene, aromaticity of, 530 Thiourea, reaction with alkyl halides, 667... 

Disulfides can be prepared by treatment of alkyl halides with disulfide ions and also indirectly by the reaction of Bunte salts (see 10-41) with acid solutions of iodide, thiocyanate ion, or thiourea, or by pyrolysis or treatment with hydrogen peroxide. Alkyl halides also give disulfides when refluxed with sulfur and NaOH, and with piperidinium tetrathiotungstate or piperidinium tetrathiomolybdate. ... 

Silicon tetraisothiocyanate, reaction with 2,6-dimethylaniline to yield 2,6-diraethylphenyl thiourea, 46, 70 Silver cyanide, reaction with alkyl halides in synthesis of isocyanides, 46, 77... 

The use of sodium dithionite (Na2S204) and thiourea dioxide (TUDO HN=C(NH2)S(0)0H) has been introduced later as a reducing agent for the preparation of sodium telluride in an aqueous medium, followed by reaction with n-alkyl halides to give dialkyl teUiirides. - ... 

Oxetanes are much less susceptible to cleavage by nucleophiles than oxiranes, except in the presence of acids. Several types of acid-catalyzed nucleophilic reactions are described in the previous section, such as reaction of hydrogen halides to give 3-halogeno-1-propanols and various acid-catalyzed solvolysis reactions. Another example of this type is the reaction of thiourea with 2-alkyloxetanes in the presence of hydrochloric or perchloric acid to give excellent yields of 3-alkyl-3-hydroxybutylisothiouronium salts (equation 39) <67CR(C)(264)1309>. 

Before the synthesis of the pseudoureas was published, Bernthsen and Klinger [6] reported a pseudothiourea synthesis involving the reaction of thioureas with alkyl halides. This reaction was briefly reviewed by Dains [16] and Stieglitz [49, 50], and it found many commercial applications [51-53]. The preparation of isothiouronium salts by the direct action of thiourea and halogen acids on alcohols (primary, secondary, and tertiary) was reported by Stevens [8] and further developed by Johnson and Sprague [54, 55] (Eq. 25). 

Elemental chlorine, bromine, and iodine, sulfuryl chloride and thionyl chloride convert diorgano ditellurium compounds to organo tellurium trihalides (p. 314). The reactions are carried out in inert organic solvents with stoichiometrically required amounts of reagents. Dialkyl ditellurium compounds may lose alkyl halides if the halogenolysis is not performed under mild conditions at low temperatures. When equimolar amounts of halogens and diaryl ditellurium derivatives are combined in appropriate solvents, aryl tellurium halides are formed (p. 239). The formation of aryl tellurium halides is facilitated by stabilizing substituents in the orf/to-position to the tellurium atom or by the presence of thioureas or selenoureas in the reaction mixture. 

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