Page 391 - Biosystems Engineering

368 Cha pte r T h i r tee n

Above caprylic acid, fatty acids are solid at room temperature at
25°C. The lower fatty acids up to capric acid are steam volatile. Butyric
acid is soluble in water and others are insoluble.

Unsaturated Fatty Acids Unsaturated fatty acids present in fats make
them industrially important. Actually, the drying power of the oils
depends on the presence of unsaturated fatty acids in oil. The use of
oil in the foundry industry depends on the presence of unsaturated
fatty acids (e.g., oleic acid and linoleic acid). These acids contain one,
two, or three double bonds that may be conjugated or nonconjugated.
The various types of unsaturated acids present in fats are as follows:
Acids containing one double bond: The general formula is C H COOH.
n 2n-1
These fatty acids are 9,10-decanoic acid (C H O ), present in
10 18 2
milk fat; dodecanoic acid (C H O ), and 9,10-hexadecanoic acid
12 22 2
(C H O), present in marine animals. By far, the most important
16 30
monoethylenic unsaturated fatty acid is octadecanoic acid, or oleic
acid, (C H COOH) or (CH – (CH ) CH = CH (CH ) COOH. This
17 33 3 2 7 2 7
acid is important and very common in most fats and oils.
Acids containing more than one double bond: Linoleic acid and linole-
nic acids are widely present in drying and semidrying vegetable
oils. Linolelic acid is dienoic acid and the double bonds are present
at the 9,10 and 12,13 carbon positions. For linolenic acid the double
bonds are present at the 9-10, 12-13, and 15-16 positions.

18 13 12 11 10 9 1

C H (CH ) – C H = CH – CH CH = CH (CH ) COOH
3 2 4 2 2 2 7
Linoleic or 9,12-octadecadienoic acid (C H O )
18 32 2
CH CH CH = CHCH CH = CHCH CH
3 2 2 2
= CH (CH ) COOH (C H O )
2 7 18 30 2
Linolenic or 9,12,15-octadecatrienoic acid: An acid isomeric with
linolenic acid is the conjugated acid eleostearic acid. It is 9,11,13-
octadecatrienoic acid. It is present in Chinese wood oil (tung oil)
and has the following structure:

18 17 16 15 14 13 12 11 10
C H – C H – C H – C H – C H = C H – C H = C H – C H
3 2 2 2
9 1
= CH – (CH ) C OOH
2 7
Tung oil: Due to the presence of conjugated double-bond fatty acids
in its glyceride form, polymerize very rapidly to a gelatinous form.