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.
Previous installments of this series appeared in the July 1997, October 1997, January 1998, and April 1998 issues of the Translation Journal.
The enormous effort required to name and catalog chemical compounds can be judged from the Facts and Figures 1997 section of the American Chemical Society's Annual Report:
Total substances in the Chemical Abstracts Service registry:|| 17,243,000|
|Substance records added in 1997 (more than 2 per minute!):|| 1,380,000|
Clearly this field of information management (including translation) is challenging and growing.
V. Organic Oxygen Compounds (continued)
The traditional method of synthesizing esters is to react a carboxylic acid with an alcohol with the loss of water:
RC(=O)OH + R'OH RC(=O)OR' + H2O
When a dicarboxylic acid such as succinic acid is esterified with a diol such as ethylene glycol, reaction occurs stepwise in both directions to form a linear polyester, in this case polyethylene succinate:
n HOC(=O)CH2CH2C(=O)OH + n HOCH2CH2OH
HO[-CH2CH2OC(=O)CH2CH2C(=O)O-]nH + n H2O
Polymerization of this nature in which a small molecule (water in this case) is eliminated is called condensation polymerization, in contrast to addition polymerization such as vinyl or acrylic polymerization, discussed in Chapter IV, in which no substance is split off from the monomer(s) during polymerization.
Other linear aliphatic polyesters would be named similarly, for example polypropylene adipate, polybutylene maleate, etc. Such linear polyesters are thermoplastic, i.e., they can be melted, extruded, or molded. They may be liquid, waxy, or solid at room temperature, depending on the starting materials and the degree of polymerization (DP).
If the reaction mixture contains even a small amount of a tricarboxylic acid or a triol (glycerol, for example) in addition to the difunctional starting materials, the polyester will contain pendant carboxyl or hydroxy groups that will also react to form branched polymers. The polymeric chains can become interconnected or crosslinked through these branches and the product then becomes insoluble and infusible. The polymer may resemble an artgum eraser or it may be hard and brittle, depending on the starting materials and the proportion of crosslinking agent.
Since a carboxylic acid can be condensed with an alcohol to form an ester, hydroxy acids with the proper configurations can form cyclic internal esters called lactones. An example would be the formation of g-butyrolactone from g-hydroxybutyric acid:
Other examples of lactones are:
Two molecules of a carboxylic acid can eliminate a molecule of water to form an anhydride; acetic acid can be converted to acetic anhydride as follows:
Dicarboxylic acids can form cyclic anhydrides if the two carboxyl groups are properly positioned. Succinic acid and maleic acid form anhydrides very readily, but fumaric acid will not do so because its carboxyl groups are on opposite sides of the molecule:
||Fumaric anhydride does not exist!
Anhydrides are very reactive compounds. When mixed with alcohols they form esters spontaneously; acetic anhydride with an alkanol gives an alkyl acetate and acetic acid:
(CH3CO)2O + ROH CH3CO2R + CH3CO2H
A cyclic anhydride reacts with an alkanol to give a monoalkyl ester:
Derivatives of carboxylic acids in which the -OH group has been replaced by a halide are called acyl halides. The nomenclature is as follows:
CH3CH2C(=O)Br||=||Propionyl bromide (or propanoyl bromide)|
CH3CH2CH2C(=O)Cl||=||Butyryl chloride (or butanoyl chloride)|
Acyl halides, like anhydrides, are very reactive toward alcohols and produce esters while eliminating a hydrogen halide:
RC(=O)Cl + R'OH RC(=O)OR' + HCl
VI. Organic Sulfur Compounds
Mercaptans and Sulfides (or Thiols and Thioethers)
In many respects the chemistry of sulfur resembles that of oxygen, but it also differs in many respects as we will see later.
The sulfur analog of an alcohol is a mercaptan, also called a thiol:
CH3OH = Methanol or methyl alcohol
CH3SH = Methanethiol or methyl mercaptan
C4H9SH = Butanethiol or butyl mercaptan
The odors of the lower alkyl mercaptans (and of many other organic sulfur compounds) are horrendous. Butyl mercaptan is best known as the defensive liquid of the skunk.
The sulfur analog of an ether is a sulfide:
CH3OCH3 = Dimethyl ether
CH3SCH3 = Dimethyl sulfide
ClCH2CH2SCH2CH2Cl = 2,2'-Dichlorodiethyl sulfide (mustard gas)
The sulfur analogs of peroxides are called disulfides:
C2H5SSC2H5 = Diethyl disulfide
A few other representative thiols and thioethers are:
2,2'-Thiodiethanol (or thiodiglycol)
|=||Thioglycolic acid (or mercaptoacetic acid)|
In Part XIII we will continue to discuss sulfur compounds with sulfenic, sulfinic, and sulfonic acids and some of their derivatives.
Readers are urged to e-mail questions, comments, or suggestions for further topics in the field of organic nomenclature to the author at: