WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
29.01 - Acyclic hydrocarbons. 2901.10 - Saturated - Unsaturated : - - Ethylene 290 1.22 - - Propene (propylene) 2901.23 - - Butene (butylene) and isomers thereof 290 1.24 - - Buta-1,3-diene and isoprene 2901 -29 - - Other 290 1.21 Acyclic hydrocarbons are compounds containing only carbon and hydrogen which have no rings in their structure. They can be classified in two categories : (A) Saturated acyclic hydrocarbons. (B) Unsaturated acyclic hydrocarbons. (A) SATURATED ACYCLIC HYDROCARBONS These form a homologous series which may be represented by the general formula (CnH2n+2). They occur abundantly in nature and are the main components of petroleum oils. The basic hydrocarbon is methane (CH.4) with one atom of carbon. Methane and also propane (C3Hs) with three atoms of carbon are, however, classified in heading 27.11 even if they are pure. The saturated acyclic hydrocarbons of this heading include : (1) Ethane (Czl&) with two atoms of carbon. To be classified in this heading, ethane must have a purity of 95 % or more by volume. Ethane of lower purity is excluded (heading 27.11). (2) Butanes (C4HI0)with four atom of carbon. (3) Pentanes, with five atoms of carbon. (4) Hexanes, with six atoms of carbon. (5) Heptanes, with seven atoms of carbon. (6) Octanes, with eight atoms of carbon. (7) Nonanes, with nine atoms of carbon. (8) Decanes, with ten atoms of carbon. (9) Pentadecanes, with fifteen atoms of cxrbon. (10) Triacontanes, with thirty atoms of carbon. (1 1) Hexacontanes, with sixty atoms of carbon. These saturated hydrocarbons are all insoluble in water. At normal temperature apd pressure, such hydrocarbons containin up to four atoms of carbon are gaseous; those containing five to fifteen atoms of carbon are iquid; hydrocarbons with a greater number of carbon atoms are generally solid. f One or more of the hydrogen atoms in these hydrocarbon molecules may be replaced by alkyl radicals (e.g., methyl, eth 1, propyl); thus isobu~tane(2-methylpropane, trimethylmethane) has the same molecular fomu a as the normal butane. r In industry and commerce, the most important 'hydrocarbons of this heading are ethane and butane gases which are derived £tompetroleum oil and natural gas. To fall in this heading, these saturated acyclic hydrocarbons must be in the form of separate chemically defined compounds, whether obtained by refining etroleum oils and natural gas or by synthesis (as regards the urity criterion for ethane, see Item ( ) above). But the heading excludes crude butane, crude petro e m gases and similar crude gaseous hydrocarbons of heading 27.11. f P (B) UNSATURATED ACYCLIC HYDROCARBONS These unsaturated hydrocarbons contain two, four, six, etc., less atoms of hydrogen than saturated acyclic hydrocarbons having the same number of atoms of carbon. This involves the presence of double or triple bonds. (1) Monoethylenic hydrocarbons. These constitute a homologous series repres,entedby the general formula (CnH2,).They are found in the products obtained by thermal decomposition of numerous organic substances (coal gas, products of the cracking of petroleum oils, etc.); they may also be produced by synthesis. (a) The first members of the series are gaseous, these are : (i) Ethylene (ethene) (Cz&). Colourless gas with a faint odour of ether and strong anaesthetic roperties, Used in the reparation of a wide range of organic compounds &.g, ethylene oxide, ethyl enzene, synthetic ethanol, polyethylene). g To fall in this heading, ethylene must have a purity of 95 % or more by volume. Ethylene of lower pmty is excluded (heading 27.11). (ii) Propene (propylene) (C3H6). Colourless, highly inflammable gas which is an asphyxiant. To fall in this heading, ropene bropylene) must have a puri of 90 % or more by volume. Propylene o lower purity is excluded (heading 2 11). ! 3: (iii) Butenes (butylenes) (C4H8). To fall in this heading, these unsaturated acyclic hydrocarbons must be in the form of separate chemically defined compounds. But the heading excludes crude gaseous hydrocarbons of heading 27.11. In normal trade, all these products are in liquid form, under pressure. (b) Monoethylenic hydrocarbons containing five to fifteen atoms of carbon are liquid. The most important include : (i) Pentenes (arnylenes). (ii) Hexenes. (iii) Heptenes. (iv) Octenes. (c) Those containing more than fifteen atoms of carbon are solids. (2) Polyethylenic hydrocarbons. These constitute a series with two or more double bonds. They include : (a) Propadiene (allene) (C3&) (b) Buta-1,Zdiene (1,Zbutadiene, methylallene) (C4H6) (c) Buta-13-dime (1,3-butadiene) (C4H6)a colourless, highly inflammable gas and (d) 2-Methylbuta-1,3-diene (isoprene) (C5Hs),a colourless, highly inflammable liquid. (3) Acetylene series. Acetylenic hydrocarbons contain either one triple bond (mono-acetylenes, general (CnHZn4 or more than one triple bond (polyacetylenes). The most important product is acetylene (C2H2), a colourless gas with a characteristic odour. From acetylene a wide range of products can be synthesised (e.g., acetic acid, acetone, isoprene, chloroacetic acid, ethanol). It is presented dissolved in acetone under ressure in special steel cylinders packed with diatomite, and remains classified under the eading (see Chapter Note 1 (e)). R Other members of the series are (a) Propyne (allylene, methylacetylene). @) Butyne (ethylacetylene). (4) Ethylene-acetylene hydrocarbons. These contain both ethylenic and acetylenic bonds in their molecules. The most important of these are vinylacetylene (acetylene in which one h drogen atom has been replaced by a vin 1 group), and methylvinylacetylene, in whic both hydrogen atoms have been rep aced - one by a vinyl group and the other y a methyl group). P K -
1.- Except where the context otherwise requires, the headings of this Chapter apply only to : (a) Separate chemically defined organic compounds, whether or not containing impurities; (b) Mixtures of two or more isomers of the same organic compound (whether or not containing impurities), except mixtures of acyclic hydrocarbon isomers (other than stereoisomers), whether or not saturated (Chapter 27); (c) The products of headings 29.36 to 29.39 or the sugar ethers, sugar acetals and sugar esters, and their salts, of heading 29.40, or the products of heading 29.41, whether or not chemically defined; (d) The products mentioned in (a), (b) or (c) above dissolved in water; (e) The products mentioned in (a), (b) or (c) above dissolved in other solvents provided that the solution constitutes a normal and necessary method of putting up these products adopted solely for reasons of safety or for transport and that the solvent does not render the product particularly suitable for specific use rather than for general use; (f) The products mentioned in (a), (b), (c), (d) or (e) above with an added stabiliser (including an anti- caking agent) necessary for their preservation or transport; (g) The products mentioned in (a), (b), (c), (d), (e) or (f) above with an added anti-dusting agent or a colouring or odoriferous substance or an emetic added to facilitate their identification or for safety reasons, provided that the additions do not render the product particularly suitable for specific use rather than for general use; (h) The following products, diluted to standard strengths, for the production of azo dyes : diazonium salts, couplers used for these salts and diazotisable amines and their salts. 2.- This Chapter does not cover : (a) Goods of heading 15.04 or crude glycerol of heading 15.20; (b) Ethyl alcohol (heading 22.07 or 22.08); (c) Methane or propane (heading 27.11); (d) The compounds of carbon mentioned in Note 2 to Chapter 28; (e) Immunological products of heading 30.02; (f) Urea (heading 31.02 or 31.05); (g) Colouring matter of vegetable or animal origin (heading 32.03), synthetic organic colouring matter, synthetic organic products of a kind used as fluorescent brightening agents or as luminophores (heading 32.04) or dyes or other colouring matter put up in forms or packings for retail sale (heading 32.12); (h) Enzymes (heading 35.07); (ij) Metaldehyde, hexamethylenetetramine or similar substances, put up in forms (for example, tablets, sticks or similar forms) for use as fuels, or liquid or liquefied-gas fuels in containers of a kind used for filling or refilling cigarette or similar lighters and of a capacity not exceeding 300 cm3 (heading 36.06); (k) Products put up as charges for fire-extinguishers or put up in fire-extinguishing grenades, of heading 38.13; ink removers put up in packings for retail sale, of heading 38.24; or (l) Optical elements, for example, of ethylenediamine tartrate (heading 90.01). 3.- Goods which could be included in two or more of the headings of this Chapter are to be classified in that one of those headings which occurs last in numerical order. 4.- In headings 29.04 to 29.06, 29.08 to 29.11 and 29.13 to 29.20, any reference to halogenated, sulphonated, nitrated or nitrosated derivatives includes a reference to compound derivatives, such as sulphohalogenated, nitrohalogenated, nitrosulphonated or nitrosulphohalogenated derivatives. Nitro or nitroso groups are not to be taken as “nitrogen-functions” for the purposes of heading 29.29. For the purposes of headings 29.11, 29.12, 29.14, 29.18 and 29.22, “oxygen function”, the characteristic organic oxygen-containing group of those respective headings, is restricted to the oxygen-functions referred to in headings 29.05 to 29.20.