Organic sulfides

Organic sulfides (thioesters) are compounds of the general formula R'-SR, where R 'and R are organic radicals ^[1] . Sulfur analogues of ethers .

Content

Nomenclature

When naming sulfides in the IUPAC nomenclature, additive nomenclature is most often used, in which sulfides are treated as derivatives of hydrogen sulfide and the names are formed by adding the suffix α-sulfide to the names of the substituent radicals, for example, CH ₃ SC ₂ H ₅ - methyl ethyl sulfide.

To a lesser extent, a substitute nomenclature is used in which sulfides are considered as heterosubstituted alkanes and the names are formed by adding the thia prefix to the name of the parent compound, for example, CH ₃ SC ₂ H ₅ - 2-thiabutane.

Sometimes sulfides are referred to as thio analogs of ethers , in this case the name is formed by adding the thio prefix to the name of the oxygen-containing analogue, for example, C ₆ H ₅ SCH ₃ - thio anisole .

Properties

Lower sulfides are colorless liquids or fusible solids that are insoluble in water and highly soluble in organic solvents. Unrefined thioesters have a characteristic unpleasant "organosulfur" odor, pure ones do not smell. The boiling points of sulfides are higher than their oxygen counterparts - ethers.

The SC bond length in aliphatic sulfides is ~ 0.18 nm; in diaryl sulfides, the bond length is reduced to ~ 0.175 nm due to partial conjugation of the free electron pair of the sulfur atom with π-electrons of the aromatic nucleus. The value of the С – S – С valence angle for spatially uncomplicated sulfides is ~ 100 ° (98.9 ° for dimethyl sulfide) and increases with the growth of the volume of substituents (105.6 ° for bis (trifluoromethyl) sulfide, 109 ° for diphenyl sulfide).

In the IR spectra, the characteristic band of stretching vibrations of the SC bond is in the range of 570–705 cm ^{– 1} , the intensity of the alkyl sulfide band is low, and in the case of aryl and vinyl sulfides, the intensity is medium. The methyl sulfides are characterized by a band at 1325 cm ^{– 4 of} bending vibrations of the CH bonds of the CH ₃ S fragment.

In the UV spectra of alkyl sulfides, absorption bands are observed at 200, 220, and 240 nm; in the case of vinyl and aryl sulfides, they undergo a bathochromic shift in the range 205–230, 235–270, 275–300 nm due to conjugation with double bonds or an aromatic system.

Reactivity

The greater polarizability and lower electronegativity of sulfur compared with oxygen leads to less basicity and greater nucleophilicity of sulfur sulfides compared to ethers. So, the sulfide substituent RS, in the aromatic nucleus, as in the case of RO, activates it in electrophilic substitution reactions and orientates the incoming substituents in the ortho and para positions . Sulfides are much easier to alkylate than ethers, forming sulfonium salts under the action of alkyl iodides, alkyl sulfates, oxonium salts and other alkylating agents:

{\mathsf {R_{2}S+R'X\rightarrow R_{2}R'S^{+}X^{-}}}

{\ displaystyle {\ mathsf {R_ {2} S + R'X \ rightarrow R_ {2} R'S ^ {+} X ^ {-}}}}

Under the influence of mild oxidizing agents ( hydrogen peroxide in acetone or glacial acetic acid, peroxyacids) sulfides are oxidized to sulfoxides :

{\mathsf {(CH_{3})_{2}S+H_{2}O_{2}\rightarrow (CH_{3})_{2}SO+H_{2}O}}

{\ displaystyle {\ mathsf {(CH_ {3}) _ {2} S + H_ {2} O_ {2} \ rightarrow (CH_ {3}) _ {2} SO + H_ {2} O}}}

under the action of energetic oxidizing agents ( potassium permanganate , nitric acid ), oxidation goes to sulfones :

{\mathsf {(CH_{3})_{2}S{\xrightarrow[{}]{[O]}}(CH_{3})_{2}SO_{2}}}

{\ displaystyle {\ mathsf {(CH_ {3}) _ {2} S {\ xrightarrow [{}] {[O]}} (CH_ {3}) _ {2} SO_ {2}}}}

These reactions are used as a preparative method for the synthesis of sulfoxides and sulfones.

The С-S bond is much more labile than the С-O bond; therefore, sulfides, in contrast to ethers, are characterized by reactions with a С-S bond breaking.

So, arylalkyl sulfides under the action of chlorine or bromine in the presence of water form arylsulfonyl halides:

{\mathsf {ArSAlk{\xrightarrow[{}]{H_{2}O,Hal_{2}}}ArSO_{2}Hal}}

{\ displaystyle {\ mathsf {ArSAlk {\ xrightarrow [{}] {H_ {2} O, Hal_ {2}}} ArSO_ {2} Hal}}}

Under the action of reducing agents ( lithium aluminum hydride , sodium borohydride , sodium in liquid ammonia), the CS bond is cleaved with the formation of thiol and hydrocarbon:

{\mathsf {RSR'{\xrightarrow[{}]{[H]}}RSH+R'H}}

{\ displaystyle {\ mathsf {RSR '{\ xrightarrow [{}] {[H]}} RSH + R'H}}}

The direction and ease of cleavage are determined by the nature of the substituents.

Under the action of chlorine, sulfides form unstable sulfonium salts, which are split into sulfenyl chloride and halide:

{\mathsf {RSR'+Cl_{2}{\xrightarrow[{}]{}}[RR'S^{+}Cl]Cl^{-}}}

{\ displaystyle {\ mathsf {RSR '+ Cl_ {2} {\ xrightarrow [{}] {}} [RR'S ^ {+} Cl] Cl ^ {-}}}}

{\mathsf {[RR'S^{+}]Cl^{-}\rightarrow RSCl+R'Cl}}

{\ displaystyle {\ mathsf {[RR'S ^ {+}] Cl ^ {-} \ rightarrow RSCl + R'Cl}}}

In this case, the cleavage and formation of chloride occurs with the participation of a radical forming the most stable carbocation .

Synthesis

Most preparative methods for the synthesis of sulfides are based on the functionalization of readily available highly nucleophilic thiols in nucleophilic substitution or addition reactions, and two main approaches are distinguished - the alkylation or arylation of alkali metal thiolates and the addition of thiols to multiple bonds of alkenes and alkynes.

Sulfides can also be synthesized from electrophilic sulfur halides or sulfenic acid derivatives by addition to alkenes or sulfenylation of aromatic compounds.

Thiol Sulphides

In the reactions with thiolates, alkyl halides, dialkyl sulfates and sulfonates (usually tosylates) are used as alkylating agents, aryl halides activated by electron-withdrawing substituents also enter the reaction:

{\mathsf {RS^{-}+RX\rightarrow RSR'+X^{-}}}

{\ displaystyle {\ mathsf {RS ^ {-} + RX \ rightarrow RSR '+ X ^ {-}}}}

β: X = Hal, AlkOSO ₃ , ArSO ₃ , Ar A particular case of this approach is the alkylation of alkali metal sulfides, which goes through the formation of thiolates, this method is used in the synthesis of symmetric sulfides:

{\mathsf {Na_{2}S+2RX\rightarrow R_{2}S+2NaX}}

{\ displaystyle {\ mathsf {Na_ {2} S + 2RX \ rightarrow R_ {2} S + 2NaX}}}

For the synthesis of diaryl sulfides, arylthiolates are arylated with the corresponding diazonium salts:

{\mathsf {ArS^{-}+Ar'N\equiv N^{+}\rightarrow ArSAr'+N_{2}}}

{\ displaystyle {\ mathsf {ArS ^ {-} + Ar'N \ equiv N ^ {+} \ rightarrow ArSAr '+ N_ {2}}}}

The addition of thiols to multiple bonds of alkenes under conditions of acid catalysis proceeds by the ionic mechanism similar to the addition of alcohols and obeys the Markovnikov rule , in the case of the synthesis of symmetric sulfides, hydrogen sulfide can be used instead of thiols:

{\mathsf {2(CH_{3})_{2}C{\text{=}}CH_{2}+H_{2}S\rightarrow [(CH_{3})_{3}C]_{2}S}}

{\ displaystyle {\ mathsf {2 (CH_ {3}) _ {2} C {\ text {=}} CH_ {2} + H_ {2} S \ rightarrow [(CH_ {3}) _ {3} C ] _ {2} S}}}

In the presence of peroxides or when irradiated with ultraviolet light, the addition proceeds according to a radical mechanism and gives a mixture of products with a predominance of the sterically least difficult:

{\mathsf {RSH+CH_{2}{\text{=}}CHR'\rightarrow RSCH_{2}CH_{2}R'}}

{\ displaystyle {\ mathsf {RSH + CH_ {2} {\ text {=}} CHR '\ rightarrow RSCH_ {2} CH_ {2} R'}}}

In the case of alkenes activated by electron acceptors ( acrylonitrile , vinyl ketones, etc.), the addition of thiols occurs under alkaline conditions and leads to the product of attachment to the β-position to the acceptor substituent according to the Michael reaction type:

{\mathsf {RSH+CH_{2}{\text{=}}CH{\text{-}}CN\rightarrow R{\text{-}}CH_{2}CH_{2}{\text{-}}CN}}

{\ displaystyle {\ mathsf {RSH + CH_ {2} {\ text {=}} CH {\ text {-}} CN \ rightarrow R {\ text {-}} CH_ {2} CH_ {2} {\ text {-}} CN}}}

Sulfides from sulfur halides and derivatives of sulfenic acids

Sulfur dichloride is attached to alkenes with the formation of bis (β-chloroalkyl) sulfides, for example, mustard was first synthesized by the addition of sulfur dichloride to ethylene ^[2] :

{\mathsf {SCl_{2}+2C_{2}H_{4}\rightarrow (ClCH_{2}CH_{2})_{2}S}}

{\ displaystyle {\ mathsf {SCl_ {2} + 2C_ {2} H_ {4} \ rightarrow (ClCH_ {2} CH_ {2}) _ {2} S}}}

Sulphenyl chlorides also attach to alkenes to form β-chloroalkyl sulphides:

{\mathsf {PhSCl+C_{2}H_{4}\rightarrow PhSCH_{2}CH_{2}Cl}}

{\ displaystyle {\ mathsf {PhSCl + C_ {2} H_ {4} \ rightarrow PhSCH_ {2} CH_ {2} Cl}}}

Aromatic compounds catalyzed by Lewis acids and CH-acids in the presence of bases are sulfenylated with sulfenyl chlorides to form sulfides:

{\mathsf {RH+R'SCl\rightarrow RSR'+HCl}}

{\ displaystyle {\ mathsf {RH + R'SCl \ rightarrow RSR '+ HCl}}}

Dithiodichloride is attached to alkenes and alkynes, and symmetrical α-chloroalkyl disulfides are formed with good yields ^[3] :

{\mathsf {2CH_{3}CH{\text{=}}CHCH_{3}+S_{2}Cl_{2}\rightarrow CH_{3}CH(Cl)CH(CH_{3})SSCH(CH_{3})CH(Cl)CH_{3}}}

{\ displaystyle {\ mathsf {2CH_ {3} CH {\ text {=}} CHCH_ {3} + S_ {2} Cl_ {2} \ rightarrow CH_ {3} CH (Cl) CH (CH_ {3}) SSCH (CH_ {3}) CH (Cl) CH_ {3}}}}

With activated aromatic and heteroaromatic compounds, a substitution reaction takes place, as a result of which disulfides are also formed ^[3] :

{\mathsf {2ArH+S_{2}Cl_{2}\rightarrow ArSSAr+2HCl}}

{\ displaystyle {\ mathsf {2ArH ​​+ S_ {2} Cl_ {2} \ rightarrow ArSSAr + 2HCl}}}

In turn, disulfides can be desulfurized under the influence of bases, Lewis acids (BF ₃ , SbF ₅ ), trivalent phosphorus compounds (PR ₃ , P (OR) ₃ ) or, in some cases, when heated:

{\mathsf {RSSR'\rightarrow RSR'+S}}

{\ displaystyle {\ mathsf {RSSR '\ rightarrow RSR' + S}}}

{\mathsf {RSSR'+R_{3}P\rightarrow RSR'+R_{3}P{\text{=}}S}}

{\ displaystyle {\ mathsf {RSSR '+ R_ {3} P \ rightarrow RSR' + R_ {3} P {\ text {=}} S}}}

An example of such in situ desulfurization is the reaction of unactivated aromatic hydrocarbons with dithiodichloride in the presence of aluminum chloride. So, for example, the reaction with benzene is accompanied by the elimination of sulfur and leads to the formation of diphenyl sulfide ^[4] :

{\mathsf {S_{2}Cl_{2}+2C_{6}H_{6}\rightarrow (C_{6}H_{5})_{2}S+2HCl+S}}

{\ displaystyle {\ mathsf {S_ {2} Cl_ {2} + 2C_ {6} H_ {6} \ rightarrow (C_ {6} H_ {5}) _ {2} S + 2HCl + S}}}

Biological role

The thioether group is part of important biological compounds - vitamin B ₇ and the essential amino acid methionine .

Thioethers are contained in garlic , causing its specific taste.

Links

An article on thioethers in the encyclopedia on XuMuK.ru

Notes

↑ sulfides // IUPAC Gold Book
↑ Frederick Guthrie. XIII. — On some derivatives from the olefines (Eng.) // Quarterly Journal of the Chemical Society of London. - 1860. - Vol. 12, no. 1 . - P. 109-126. - DOI : 10.1039 / QJ8601200109 .
↑ ¹ ² Katritzky, Alan R. Comprehensive Organic Functional Group Transformations: Synthesis: carbon with one heteroatom attached by a single bond. - Elsevier, 1995 .-- P. 226. - ISBN 9780080423234 .
↑ Hartman, WW; Smith, LA; Dickey, JB Diphenyl sulfide. Organic Syntheses, Coll. Vol. 2, p. 242 (1943); Vol. 14, p. 36 (1934).

[1] sulfides // IUPAC Gold Book

[2] Frederick Guthrie. XIII. — On some derivatives from the olefines (Eng.) // Quarterly Journal of the Chemical Society of London. - 1860. - Vol. 12, no. 1 . - P. 109-126. - DOI : 10.1039 / QJ8601200109 .

[Katritzky_1995_226-3] ¹ ² Katritzky, Alan R. Comprehensive Organic Functional Group Transformations: Synthesis: carbon with one heteroatom attached by a single bond. - Elsevier, 1995 .-- P. 226. - ISBN 9780080423234 .

[4] Hartman, WW; Smith, LA; Dickey, JB Diphenyl sulfide. Organic Syntheses, Coll. Vol. 2, p. 242 (1943); Vol. 14, p. 36 (1934).