When an alcohol is treated with carbon disulphide and aqueous sodium hydroxide, a compound called a xanthate is obtained. Treatment of the xanthate with aqueous acid regenerates the starting materials.
Cellulose undergoes an analogous reaction to form cellulose xanthate, which dissolves in the alkali to form a viscous colliodal dispersion called viscose.
When viscose is forced through a spinnerette into an acid bath cellulose is regenerated in the form of fine filaments which yield threads of the material known as rayon. There are other processes for making rayon. but the viscose process is still the principal one. If viscose is forced through a narrow slit, cellulose is regenerated as thin sheets which, when softened by glycerol are used for protective films (cellophane).
Thus, rayon is made by treating cellulose (from cotton or wood pulp) with `CS_(2)` in a basic solution. This reaction converts cellulose to a soluble xanthate:
`"Cellulose"-OH+CS_(2)overset(NaOH)rarr"cellulose"-underset("Cellulose Xanthate")(O-overset(S)overset(||)(C)-bar(S)overset(+)(N)a)`
The solution of cellulose xanthate is then passed througha small orifice of slit into an acidic solution. This operation regenrates `-OH` groups of cellulose, causing it to precipitate as a fibre or a sheet.
`"Cellulose"-O-overset(S)overset(||)(C)-bar(S)Na^(+) overset(H_(2)O^(+))rarr underset("Rayon or cellophane")("Cellulose"-OH)`
The fibres are rayon, the sheet, after softening with glycerol, are cellophane.
Alginic acids occur in marine alge, and polymannuronic acids.
