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Part IX of this series appeared in the October,
1997.issue of the Translation Journal.
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V. Organic Oxygen Compounds (continued)
Carboxylic Acids
In Part IX of this series we saw that compounds with two hydroxyl groups bonded to a
terminal carbon atom split off a molecule of water spontaneously to form aldehydes. A similar
process occurs when a terminal carbon atom carries three hydroxyl groups, giving rise to
carboxylic acids as follows:
The carboxylic acids are usually written as RCO2H, RC(O)OH, or
RC(=O)OH, where R can stand for any organic group. When R is an aliphatic group, the acids are
called fatty acids. Depending on whether or not the group R contains one or more
double bonds, the fatty acids can be saturated or unsaturated (referred to popularly as
monounsaturated or polyunsaturated fatty acids).
Some of the more common fatty acids are described below in Table 11.
Table 11. Representative Fatty Acids
R |
Trivial
(Common)
Name |
Systematic Name |
H |
Formic acid |
Methanoic acid |
CH3- |
Acetic acid |
Ethanoic acid |
CH3CH2- |
Propionic acid |
Propanoic acid |
CH3CH2CH2- |
Butyric acid |
Butanoic acid |
n-C4H9- |
Valeric acid |
Pentanoic acid |
n-C5H11- |
Caproic acid |
Hexanoic acid |
n-C6H13- |
Enanthic acid |
Heptanoic acid |
n-C7H15- |
Caprylic acid |
Octanoic acid |
n-C8H17- |
Pelargonic acid |
Nonanoic acid |
n-C9H19- |
Capric acid |
Decanoic acid |
n-C11H23- |
Lauric acid |
Dodecanoic acid |
n-C13H27- |
Myristic acid |
Tetradecanoic acid |
n-C15H31- |
Palmitic acid |
Hexadecanoic acid |
n-C17H35- |
Stearic acid |
Octadecanoic acid |
n-C8H17CH=CH(CH2)7
SUB>- |
Oleic acid |
cis-9-Octadecenoic acid |
n-C5H11CH=CHCH2CH=CH(CH
2)7- |
Linoleic acid |
cis,cis-9,12-Octadecadienoic acid |
Some possible sources of confusion exist between caproic acid and capric acid, and between
linoleic acid and linolenic acid (9,12,15-octadecatrienoic acid, which has three double
bonds).
Halogenated fatty acids are also common. Some examples are: chloroacetic acid
ClCH2CO2H, trichloroacetic acid
Cl3CCO2H, a-chloropropionic acid (2-chloropropanoic
acid)
CH3CHClCO2H, b-bromopropionic acid
(3-bromopropanoic acid)
BrCH2CH2CO2H, and g-iodobutyric acid
(4-iodobutanoic acid)
ICH2CH2CH2CO2H. Note that
locants can be of either type. The a-position, on the carbon adjacent to the carboxyl
group, is the same as the 2-position.
In German, Carbonsäure nearly always means carboxylic acid, not
carbonic acid which
is properly Kohlensäure. In compounds, -carbonsäure always means carboxylic acid
and -säure means acid. Thus Essigsäure is acetic acid and Propionsäure is
propionic acid. In the case of acetic acid, there are two German terms that require some
explanation. Pure acetic acid freezes (and conversely melts) at just below room temperature
(62°F,
16.7°C), and may
thus be solid or liquid depending on laboratory conditions. Since it freezes so readily, pure acetic
acid is called glacial acetic acid in English and Eisessig in German. Small amounts of water liquefy
the substance, in which case it is called simply acetic acid or Essigsäure. Vinegar, of course,
is dilute acetic acid.
Locants for cyclic ethers are also designated as a, b, or g,
or 2, 3, or 4 with respect to the oxygen atom. Thus
furan can give rise to a-furoic acid (2-furancarboxylic acid) or
b-furoic
acid (3-furancarboxylic acid). Names such as 2-tetrahydrofurancarboxylic acid
(2-carboxytetrahydrofuran) or analogous names for its 3-isomer are also acceptable.
Dicarboxylic Acids
Dicarboxylic acids are common in nature and in the laboratory, and have been given their own
trivial names. They are used with diols to produce polyesters and are also used to produce
polyamides (Nylon). Some of the common ones are listed below in Table 12.
Table 12. Representative Dicarboxylic Acids
Chemical Structure |
Trivial (Common) Name |
HO2CCO2H |
Oxalic acid |
HO2CCH2CO2H |
Malonic acid |
HO2CCH2CH2CO2H |
Succinic acid |
cis-HO2CCH=CHCO2H |
Maleic acid |
trans-HO2CCH=CHCO2H |
Fumaric acid |
HO2C(CH2)3CO2
H |
Glutaric acid |
HO2C(CH2)4CO2
H |
Adipic acid |
HO2C(CH2)5CO2
H |
Pimelic acid |
HO2C(CH2)6CO2
H |
Suberic acid |
HO2C(CH2)7CO2
H |
Azelaic acid |
HO2C(CH2)8CO2
H |
Sebacic acid |
A simple mnemonic for remembering the names of the saturated
aliphatic a,w-dicarboxylic acids is Oh
My, Such Good Apple Pie, Sweet As Sugar! (This does not include the unsaturated maleic
and
fumaric acids).
Hydroxy Acids
Some of the simple hydroxy acids have also been given trivial names:
Table 13. Representative Hydroxy Acids
HOCO2H |
Carbonic acid |
HOCH2CO2H |
Glycolic acid |
CH3CH(OH)CO2H |
Lactic acid |
HO2CCH(OH)CH2CO2H |
Malic acid |
HO2CCH(OH)CH(OH)CO2H |
Tartaric acid |
HO2CCH2C(OH)(CO2H)CH
2CO2H |
Citric acid |
Keto Acids
Some examples with trivial names are:
CH3C(=O)CO2H | Pyruvic acid |
CH3C(=O)CH2CH2CO2H |
Levulinic acid |
HO2CCH2C(=O)CH2CO2H
| Acetonedicarboxylic acid |
CH3C(=O)CH2CO2H |
Acetoacetic acid |
Unsaturated Acids
In addition to maleic and fumaric acids (Table 12), some important unsaturated acids
are: |
CH2=CHCO2H | Acrylic acid |
CH2=C(CH3)CO2H |
Methacrylic acid |
CH3CH=CHCO2H
| Crotonic acid |
HO2CCH2C(=CH2)CO2H
| Itaconic acid |
HO2CC(CH3)=CHCO2H |
Citraconic acid |
HO2CCH=C(CO2H)CH2CO2
H | Aconitic acid |
HCºCCO2H | Propiolic acid |
|
Acrylic and methacrylic acids are widely used in polymerization to prepare polyacrylic
resins.
IN THE NEWS - Review your comprehension of Parts I to X:
The November 24, 1997, issue of Chemical & Engineering News reports:
BP Chemicals to build butanediol plant...
BP Chemicals ... will build a $100 million, 140-million-lb-per-year 1,4-butanediol plant ...
Geminox uses a direct dual-reactor route to produce 1,4-butanediol and its derivatives using
butane instead of acetylene, butadiene, or propylene oxide, as do other technologies ...
1,4-Butanediol is used to make tetrahydrofuran, which is used to make fibers and
solvents...
We have discussed all of the organic chemicals mentioned in the extract above. Can you draw
their structures and roughly understand how the processes might work? If so, you are on the way
to being chemistry-literate! The terminology you have learned not only is of
theoretical interest,
but will help you to understand and appreciate practical industrial matters of current
significance.
Part XI will describe derivatives of carboxylic acids including esters, anhydrides,
lactones, and
salts.
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.
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