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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.

Statistical Yardsticks:

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)

Polyesters

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.

Lactones

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:

b-Valerolactone
d-Caprolactone
e-Caprolactone

 

Anhydrides

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:

	Succinic anhydride
	Maleic anhydride
	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:

	Monoalkyl maleate

Acyl Halides

Derivatives of carboxylic acids in which the -OH group has been replaced by a halide are called acyl halides. The nomenclature is as follows:

CH3C(=O)Cl	=	Acetyl chloride
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:

	=	Thiophene
HSCH2CH2CH2CH2SH	=	1,4-Butanedithiol
HOCH2CH2SCH2CH2OH	=	2,2'-Thiodiethanol (or thiodiglycol)
HSCH2CO2H	=	Thioglycolic acid (or mercaptoacetic acid)
HO2CCH2SCH2CO2H	=	Thiodiglycolic 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: 74654.1335@compuserve.com.