Download the zipped version of the first installments of this series, originally published in the Sci-Tech Translation Journal, of the American Translators Association. The file is approximately 87 KB.
Parts I to VII of this series, which began with the assumption that the reader has no knowledge of chemistry, appeared in the seven consecutive issues of the Sci-Tech Translation Journal of the ATA from October 1994 to July 1996. Some knowledge of organic chemistry is recommended for those starting with this Part VIII.
We will now pick up the thread where we left it a year ago, when we discussed organic oxygen compounds, specifically alcohols and ethers.
V. Organic Oxygen Compounds
Glycols, Glycol Ethers, and Polyhydric Alcohols
We have seen that alcohols and ethers can be considered to be derivatives of water, in the sense that ROH and ROR' can be obtained by replacing the hydrogen atoms of water (HOH) with alkyl groups R or R'. They can also be viewed in the other direction, as hydrocarbons whose hydrogen atoms have been replaced by hydroxyl or alkoxyl radicals HO
. With this approach, ethyl alcohol would be formed by the (hypothetical) reaction:
OH --> CH3CH2OH
Continuing this hypothetical procedure one step further, we obtain:
OH --> HOCH2CH2OH
The product is a diol, a dihydroxy compound, otherwise called a glycol. It can be called 1,2-ethanediol, 1,2-dihydroxyethane, or most commonly ethylene glycol. Recall that CH2=CH2 is ethylene and ClCH2CH2Cl is ethylene chloride;
is the ethylene radical or the ethylene group. The term glycol is preferably reserved for only two compounds, ethylene glycol and propylene glycol (1,2-dihydroxypropane or 1,2-propanediol), but other usages will occasionally be encountered, such as butylene glycol (1,2-, 1,3-, or 2,3-butanediol).
While the subject of glycol ethers may seem too narrow to be addressed in a broad treatment of organic nomenclature, their ubiquitousness in the industrial sector, their commonly used trade names, and their odd treatment in German nomenclature, prompt a careful look. German-to-English translation errors abound in this tiny niche.
Ethylene glycol can form ethers with alkyl groups in the same way as ethyl alcohol:
CH3 --> HOCH2CH2OCH3
Ethylene glycol monomethyl ether
Although an article on this subject was published in the Sci-Tech Newsletter in 1990, the table from that paper bears repeating to show the possible pitfalls when translating the German names of some members of this family of compounds:
Table 10. Representative Glycols, Polyglycols, and Their Ethers
| Chemical Formula ||English Name(s)||German Name(s)|
|HOCH2CH2OH||Ethylene glycol||Äthylenglykol; Glykol|
|H(OCH2CH2)nOH||Polyethylene glycol; poly(ethylene glycol)||Polyglykol; Polyäthylenglykol|
|CH3OCH2CH2OH||Ethylene glycol monomethyl ether; 2-methoxyethanol; Methyl Cellosolve®||Methylglykol|
|C2H5OCH2CH2OH||Ethylene glycol monoethyl ether; 2-ethoxyethanol; Cellosolve®||Äthylglykol|
|CH3OCH2CH2OCH3||Ethylene glycol dimethyl ether; 1,2-dimethoxyethane; monoglyme||Dimethylglykol|
|C2H5OCH2CH2OC2H5||Ethylene glycol diethyl ether; 1,2-diethoxyethane||Diäthylglykol|
|HOCH2CH2OCH2CH2OH||Diethylene glycol||Diglykol; Diäthylenglykol|
|CH3OCH2CH2OCH2CH2OH||Diethylene glycol monomethyl ether; Methyl Carbitol®||Methyldiglykol|
|C2H5OCH2CH2OCH2CH2OH||Diethylene glycol monoethyl ether; Carbitol®||Äthyldiglykol|
|CH3(OCH2CH2)2OCH3||Diethylene glycol dimethyl ether; diglyme||Dimethyldiglykol|
The most common triol is glycerol (1,2,3-propanetriol or 1,2,3-trihydroxypropane). You will also encounter the name glycerine or glycerin, which is not as acceptable but has become familiar from its derivative nitroglycerin(e) (more properly called glycerol trinitrate). The common name for 1,2,3,4-tetrahydroxybutane is erythritol. The 5-carbon tetrol tetra(hydroxymethyl)methane is called pentaerythritol; pentaerythritol tetranitrate (PETN) is a powerful explosive. Specific optical isomers (to be defined later) of the straight-chained 5-carbon and 6-carbon polyols analogous to glycerol are arabitol and mannitol. Polyhydric alcohols (polyols) can also form ethers and polyethers, in the same way as diols (glycols).
Two molecules of an alcohol in reality form an ether by losing a molecule of water between them; one molecule loses a hydrogen atom H
and the other loses a hydroxy group
RO-H + HO-R --> ROR + HOH
Since this is the case, it is possible for a molecule with two hydroxyls on different carbon atoms to form internal ethers:
|| + H2O|
The product in this case is called ethylene oxide, and is an important monomer and reactive intermediate. A catalyst RXM (not specified here) can open the ethylene oxide ring, which then adds to itself to form polyethylene glycol (PEG):
| RXM + x ·
If RXM is an alcohol ROH, the product is an ethoxylated derivative of the alcohol, RO(CH2CH2O)xH. A simple example of this type of derivative, when RXM is CH3OH and x = 2, is CH3OCH2CH2OCH2CH2OH, Methyl Carbitol® (see Table 10).
Ethylene oxide is an epoxy compound, and can also be named 1,2-epoxyethane. Diepoxy compounds are commercially important as components of epoxy adhesives. The simplest diepoxy compound is erythritol anhydride, or 1,2,3,4-diepoxybutane:
Terminological purists will name compounds with 3-membered epoxy rings as derivatives of oxirane, the internationally recognized (IUPAC) name for ethylene oxide.Part IX will continue the discussion of organic compounds of oxygen.