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, and January, 1998 issue of the Translation Journal.
For sale as advertised in Chemical & Engineering News, Feb. 10, 1998:
Can you name these compounds? (Answer at the end of this article).
V. Organic Oxygen Compounds (continued)
Salts of Carboxylic Acids
We learned in the chapter on covalent bonds that such bonds consist of one or more electron pairs, and that when such an electron pair splits symmetrically, free radicals are formed, each free radical having an unpaired electron. This is the case in the (theoretical) loss of a hydrogen atom from a methane molecule, CH4 ® CH3 + H, to yield an electrically neutral methyl radical and a hydrogen atom. It is also possible for one member of the team to escape with both of the electrons of a covalent bond, becoming electrically charged and leaving its partner positively charged, as in RO:H ® RO: + H+. In such an event, two ions are formed, a negative alkoxide ion and a positive hydrogen ion. Even without being broken, some covalent bonds between dissimilar atoms are polar, which means that one partner in the bond holds more tightly to the electrons than the other, or is more electronegative than the other. If and when such a polar bond splits, the electronegative partner is most likely to depart with both of the electrons and become an ion. Many inorganic salts, such as common table salt, sodium chloride, exist mainly in ionic form, so that true molecules of NaCl are not present in the strict sense of the word, but rather a conglomerate of equal numbers of Na+ and Cl ions, with the charges balancing one another in an ionic lattice even on the submicro scale.
Water is strongly polar and has great affinity for ions. It tends to form shells around ions and is held to them by coordinate bonds or hydrogen bonds. These are loose bonds of a polar nature, but are not covalent bonds in the usual sense of the word. When ionic substances dissolve in water, their ions become hydrated in this way. Nonionic and nonpolar substances tend to be insoluble or only slightly soluble in water because there is no energy of hydration to drive them into solution. Some molecules have a polar or ionic (hydrophilic) region and also a nonpolar (lipophilic) region. In water they tend to form micelles, small aggregates of molecules with their hydrophilic ends hydrated, but with the lipophilic ends extending inward toward the center of the aggregate (Chem. Eng. News, Jan. 2, 1984, pp. 25-38). If nonpolar substances are present also, they are attracted to the lipophilic portions of the micelles, and are suspended in the aqueous phase by this attraction. This, in brief, is how soaps and detergents (surfactants, surface-active agents) work.
The O-H bond in carboxylic acids RC(=O)OH is very polar. When dissolved in water, a carboxylic acid ionizes to an extent depending on the R group, and therefore exists partly as carboxylate anions RCO2 and hydrogen cations H+. Both of the ions are hydrated, as discussed above, and the ionic forms are stabilized in this way. The pH of the aqueous solution is defined by a formula depending on the concentration of hydrogen ions formed spontaneously when the acid is dissoved in water. The higher the concentration of hydrogen ions, the lower the pH. Water itself has a pH of 7.0, so that solutions of acids show a pH ranging from 0 to 7. As examples, a standard solution of formic acid in water has a pH of about 2.3, and a solution of acetic acid is about pH 2.4 to 2.9, depending on concentration. Any substance with a pH below 7 in aqueous solution can be described as acidic.
All acids can form salts with metal cations. When acetic acid CH3CO2H reacts with sodium hydroxide Na+OH, the products are sodium acetate CH3CO2Na+ and water H2O. Many other metals and acids can form salts, such as magnesium citrate, calcium oxalate, lithium palmitate, zinc stearate, and potassium cis-9-octadecenoate. Their names consist of the name of the metal followed by the name of the acid (either the trivial name or the systematic name), with the -ic ending changed to -ate (with the exception of tartaric acid, which becomes tartrate). Either one or two of the carboxyl groups of dicarboxylic acids may be neutralized by metal ions, in which case the salt can be named in several different ways: monosodium malonate, sodium acid malonate, and sodium hydrogen malonate are all the same, with one of the two carboxyl groups being neutralized.
Sodium stearate is a soap, with the sodium carboxylate end of the molecule being hydrophilic, attached to a long lipophilic C17H35 alkyl group.
If the acidic hydrogen atom of a carboxylic acid is replaced by an alkyl group, the product is an ester. Examples are:
ethyl acetate CH3C(=O)OC2H5,
dibutyl glutarate C4H9O2C(CH2)3CO2C4H9,
ethyl acetoacetate (also called acetoacetic ester) CH3COCH2CO2C2H5.
Acétate d'éthyle (French), acetato de etilo or etanoato de etilo (Spanish), and Essigäther, Essigester, Essigsäureäther, Essigsäureäthyläther, and Essigsäureäthylester (German) are all ethyl acetate; no other translation will do! These are not ethers. In English, the names of esters are always in two parts - first the group that has replaced the acidic hydrogen, and then the group constituting the original carboxylic acid, ending in -ate. When translating the names of esters, do not hesitate to grab the first part of the name from the end of the foreign name, and to continue with the name of the acid, no matter how different such a construction may seem to be from the source document's nomenclature. Occasionally you may find in English the ethyl ester of such-and-such an acid. This is acceptable and sometimes convenient, but the construction described above will subtly denote erudition!
The next topics of discussion will be polyesters, lactones, and anhydrides.
The names of the compounds at the beginning of this article are:
3-Butyn-1-ol or 1-hydroxy-3-butyne, 2-Butynoic acid, 1-Chloro-4-pentyne.
Readers are urged to e-mail questions, comments, or suggestions for further topics in the field of organic nomenclature to the author at: