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This heading covers esters of other inorganic acids of non-metals, that is, acids in which the anion contains only non-metal elements. This heading does not cover :
(a) "Esters" of the hydrogen halides (generally heading 29.03), and (b) Esters included in later headings of this Chapter (e.g., "esters" of isocyanic acid (isocyanates) (heading 29.29) and "esters" of hydrogen sulphide (generally heading 29.30). The esters of this heading include : (A) Thiophosphoric esters (phosphorothioates) and their salts, including sodium O,O‑dibutyl- and O,O-ditolyldithiophosphates. (B) Sulphuric esters and their salts.
Sulphuric esters may be either neutral or acid. (1) Methyl hydrogen sulphate (CH3OSO2OH). An oily liquid. (2) Dimethyl sulphate ((CH3O)2SO2). Colourless or slightly yellow liquid with a slight odour of mint; toxic, corrosive, lachrymatory and irritating to the respiratory tracts. Used in organic synthesis. (3) Ethyl hydrogen sulphate (C2H5OSO2OH). Syrupy liquid. (4) Diethyl sulphate ((C2H5O)2SO2). Liquid with an odour of mint. (C) Nitrous and nitric esters.
Nitrous esters are liquids with an aromatic odour, e.g., methyl, ethyl, propyl, butyl and pentyl nitrites.
Nitric esters are mobile liquids with an agreeable odour; they decompose when suddenly heated. They include methyl, ethyl, propyl, butyl and pentyl nitrates.
Nitroglycerol, tetranitropentaerythritol (penthrite) and nitroglycol are classified here if unmixed; when presented in the form of prepared explosives they are excluded (heading 36.02). (D) Carbonic or peroxocarbonic esters and their salts.
Esters of carbonic acid may be acid or neutral. (1) Diguaiacyl carbonate. Crystalline light white powder, with a slight odour of guaiacol. Used in medicine and as an intermediate in synthesis of perfumes. (2) Tetraethyl orthocarbonate (C(OC2H5)4). (3) Diethyl carbonate (C(OC2H5)2). (4) Bis(4-tert-butylcyclohexyl) peroxodicarbonate.
Ethyl chlorocarbonate (or ethyl chloroformate) is excluded (heading 29.15). (E) Silicic acid esters and their salts (tetraethyl silicate, etc.).
This heading does not cover alcoholates or esters of acid-function metal hydroxides, e.g., titanium tetra-n-butoxide (also known as tetrabutyl titanate) (heading 29.05).
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