A Facile Conversion of Thiols to Alkyl Halides by Triphenylphosphine/N-Halosuccinimides

Abstract

Thiols are efficiently converted to alkyl halides in high to excellent yields when treated with triphenylphosphin/N-halosuccinimide (halogen: Br,Cl, and I) in dichloromethane at room temperature.Although the conversion of alcohols to alkyl halides with tertiary phosphines and electrophilic halogens has widely been studied 1-9 the reports on the formation of alkyl halides from thiols are scarce. Some of these reports are considered as follow; organic halides and tertiary phosphinsulfides are coproduced by heading a thiol with a tertiary phosphine/X 2 10a (X = Cl, Br) in solvent. This reaction with iodine has been reported to occur in the presence of pyridine or tertiary butyl amine as a base. 10b The reaction of thiols with triphenyl-and trialkyl-phosphines and poly halogenomethanes especially carbon tetrachloride, to give alkyl chlorides has also been reported. 4 In addition, thiols were converted to alkyl chlorides by reaction with carbon tetrachloride and cross-linked polystyrenes containing phosphine residues, 5a Ph 3 P/chlorocarbonylsulfenyl chloride, 5b or Ph 3 P/sulfuryl chloride. 5c In spite of oxidation of thiols to disulfides by N-bromosuccinimide, 11 and in relation with our pervious works on the use of triphenylphosphine/(SCN) 2 , 12,13 we introduce a very simple, mild and efficient method for the conversion of thiols to alky halies (X = Cl, Br, and I) using a combination of triphenylphosphine and N-halosuccinimide (PPh 3 / NXS, X:Cl, Br, and I) in dichloromethane at room temperature (Scheme 1). Scheme 1In order to optimize the reaction conditions, we first examined the effect of different ratios of triphenylphosphine /N-bromosuccin-imide (PPh 3 /NBS) as brominating agent on the conversion of 1-buthanethiol to 1-bromobutane. As shown in Table 1, entry 5, when the stoichiometry of PPh 3 is slightly more than NBS, the oxidation of thiol to disulfide is minimized and alkyl halide is obtained in its highest yield. Table 1 a) GC analysis using n-octane as internal standard.

Dynamic Response of Thin‐Film Semiconductors to AC Voltage Perturbations

“…Simple chromatography on silica gel or prolonged heating over 70 °C can cause intramolecular rearrangement to the thermodynamically favored isothiocyanate isomer (this rearrangement occurs preferentially with primary thiocyanates, and so heating or use of dissociative solvents such as HMPA or DMF should be avoided for such fragile compounds) 15. Thiocyanates can also be obtained from alcohols,12 silyl ethers,16 or amines17 by use of the electrophilic phosphorane Ph 3 P(SCN) 2 , produced in situ. However, the results are unreliable and not reproducible because of the low thermal stability of the required intermediate (SCN) 2 , and—once again—various quantities of rearranged isothiocyanate by‐products.…”

Desulfurization–bromination: direct chain-end modification of RAFT polymers

“…Inspired by the non-quantitative bromination of cysteine residues 40 and other small molecule thiols 41 using a combination of triphenylphosphine (PPh 3 ) and N -bromosuccinimide (NBS), we envisioned an improved protocol for the conversion of thiols to bromides. The conversion of alcohols, thiols and selenols to halides has also been reported using a complex of triphenylphosphine and 2,3-dichloro-5,6-dicyanobenzoquinone, where the halides were introduced as ammonium or quaternary ammonium salts.…”

Thiosulfonates as Emerging Reactants: Synthesis and Applications

“…Thed eoxygenation of S-phenyl benzenethiosulfonate (10)c ould be achieved by Silphos [PCl 3Àn (SiO 2 ) n ], ah eterogeneous phosphine reagent, in the presenceo facatalytic amount of iodine. [207] Phosphorus-based deoxygenation was already discovered by Horner andN ickel in 1955 (route 2). [208] On the other hand, Oae andT ogo reduced S-alkyl alkanethiosulfonates (7)b yt reatment with triphenylphosphine and iodine to affordt he corresponding alkyl iodides( 301)q uantitatively (Scheme 101).…”