Xanthate

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dithiocarbonate
)
Structure of a xanthate ester
Cellulose xanthate (orange)

A xanthate is a

organosulfur compounds are important in two areas: the production of cellophane and related polymers from cellulose and (in mining) for extraction of certain sulphide bearing ores.[2] They are also versatile intermediates in organic synthesis
.

Formation and structure

Xanthate salts of

electrophilic carbon atom in CS2.[3] Often the alkoxide is generated in situ by treating the alcohol with sodium hydroxide or potassium hydroxide
:

ROH + CS2 + KOH → ROCS2K + H2O

For example,

carbonates as well as residual raw material such as alcohol and alkali hydroxide
. These salts are available commercially as powder, granules, flakes, sticks, and solutions are available.

Some commercially or otherwise useful xanthate salts include:

The OCS2 core of xanthate salts, like that of the carbonates and the esters has trigonal planar molecular geometry. The central carbon atom is sp2-hybridized.

Reactions

Acid-base properties

Xanthatic acids, with the formula ROC(S)SH, can be prepared by treating alkali metal xanthates, e.g.

pKas near 2.[5] These compounds thermally decompose in the presence of base to the alcohol and carbon disulfide.[6]

Xanthic acids characteristically decompose:

ROCS2K + HCl → ROH + CS2 + KCl

This reaction is the reverse of the method for the preparation of the xanthate salts. The intermediate in the decomposition is the xanthic acid, ROC(S)SH, which can be isolated in certain cases.

Other reactions

Xanthate anions also undergo alkylation to give xanthate esters, which are generally stable:[7]

ROCS2K + R′X → ROC(S)SR′ + KX

The C-O bond in these compounds are susceptible to cleavage by the Barton–McCombie deoxygenation, which provides a means for deoxygenation of alcohols.

They can be oxidized to dixanthogen disulfides:

2 ROCS2Na + I2 → ROC(S)S2C(S)OR + 2 NaI

Acylation of xanthates gives alkyl xanthogen esters (ROC(S)SC(O)R') and related anhydrides.[2]

Xanthates bind to transition metal cations as bidentate ligands. The charge-neutral complexes are soluble in organic solvents.[8]

Structure of typical metal tris(ethylxanthate) complex.[9]

Xanthates are intermediates in the

RAFT
process, also termed MADIX (macromolecular design via interchange of xanthates).

Industrial applications

Simplified image of xanthation of cellulose.[10]

Cellulose reacts with

viscose rayon or cellophane paper (Sellotape or Scotch Tape
).

Xanthate salts (e.g. sodium alkyl xanthates,

flotation
agents in mineral processing.

Related compounds

Rarely encountered, thioxanthates arise by the reaction of CS2 with thiolate salts. For example, sodium ethylthioxanthate has the formula C2H5SCS2Na. Dithiocarbamates are also related compounds. They arise from the reaction of a secondary amine with CS2. For example, sodium diethyldithiocarbamate has the formula (C2H5)2NCS2Na.

Environmental impacts

While biodegradable, this class of chemicals may be toxic to life in water at concentrations of less than 1 mg/L.[11] Water downstream of mining operations is often contaminated with xanthates.[12]

References

  1. doi:10.1351/goldbook.X06696
  2. ^
    ISBN 978-3527306732
    .
  3. doi:10.15227/orgsyn.028.0082
    .
  4. doi:10.15227/orgsyn.086.0333
    .
  5. doi:10.1021/jo01324a018
    .
  6. ISBN 3135262014
    .
  7. ^ Gagosz, Fabien; Zard, Samir Z. (2007). "A Xanthate-Transfer Approach to α-Trifluoromethylamines". Organic Syntheses. 84: 32; Collected Volumes, vol. 11, p. 212.
  8. ^ Haiduc, I. (2004). "1,1-Dithiolato ligands". In McClevert, J. A.; Meyer, T. J. (eds.). Comprehensive Coordination Chemistry II. Vol. 1. pp. 349–376.
  9. ISBN 9780470132418
    .
  10. ISBN 3-342-00280-8
    .
  11. PMID 18603298
    .
  12. S2CID 2696850
    .
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