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A xanthate is a salt or ester of a xanthic acid. The formula of the salt of xanthic acid is (where R is organyl group and M is usually Sodium or Potassium).IUPAC does not recommend the use of the term xanthate, although it is in current use in the scientific literature: Xanthate also refers to the anion . The formula of a xanthic acid is , such as ethyl xanthic acid, while the formula of a xanthate ester is , where R and R' are organyl groups. The salts of xanthates are sometimes called O-organyl dithioates. The esters of xanthic acid are sometimes called O, S-diorganyl esters of Dithiocarbonate. The name xanthate is derived from Ancient Greek ξανθός ( xanthos) meaning 'yellowish' or 'golden', and indeed most xanthate salts are yellow. They were discovered and named in 1823 by Danish chemist William Christopher Zeise. These 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. They are also versatile intermediates in organic synthesis.
Some commercially or otherwise useful xanthate salts include:
The OCS2 core of xanthate salts and esters, like that of the and the has trigonal planar molecular geometry. The central carbon atom is sp2-hybridized. The potassium salt of the amyl xanthate () has been characterized by X-ray crystallography. The COCS2 portion of the anion is planar. The C-S bond lengths are both 1.65 Å, and the C-O distance is 1.38 Å.
Xanthic acids characteristically decompose:
Xanthates are intermediates in the Chugaev elimination process. They can be used to control radical polymerisation under the RAFT process, also termed MADIX (macromolecular design via interchange of xanthates).
They can be oxidized to dixanthogen disulfides:
Acylation of xanthates gives alkyl xanthogen esters (ROC(S)SC(O)R') and related anhydrides.
Xanthates bind to transition metal cations as bidentate . The charge-neutral complexes are soluble in organic solvents.
Xanthate salts (e.g. sodium alkyl xanthates, dixanthogen) are widely used as flotation agents in mineral processing.
Industrial applications
Cellulose reacts with carbon disulfide (CS2) in presence of sodium hydroxide (NaOH) to produces sodium cellulose xanthate, which upon neutralization with sulfuric acid (H2SO4) gives viscose rayon or cellophane paper (Sellotape or Scotch Tape).
Related compounds
Rarely encountered, arise by the reaction of CS2 with thiolate salts. For example, sodium ethylthioxanthate has the formula C2H5SCS2Na. 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. Water downstream of mining operations is often contaminated with xanthates.
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