Environmental Engineering Reference
In-Depth Information
Functional groups having C=O bond
Functional groups having N
Nitrile group
O
O
C
R
C
N
Carbonyl
group
Carboxyl
group
C
OH
C N
Benzonitrile
O
O
Carboxylic
acid
Aldehyde
R
1
C
H
R
C
OH
Amine group
O
COOH
Primary
Ketone
R
1
R
2
C
Benzoic
acid
R NH
2
O
Secondary
R
1
C
N
Amide
R
1
O
NH
Ester
group
R
2
C
O
O
Acid
chloride
R
1
C
Tertiary
Cl
R
1
R
2
O
N
R
3
Ester
compound
R
1
C
O
R
2
R
n
= organic compound
FIGURE 9.11
Some common functional groups for organic chemical contaminants.
manufacture of industrial products and pharmaceutical agents. Both alcohols and phenols
can function as weak acids and weak bases.
Functional groups exert considerable inluence on the characteristics of organic com-
pounds, and contribute signiicantly to the processes that control accumulation, persis-
tence, and fate of the organic chemical compounds in soil. Organic chemicals with C=O
bond functional groups and nitrogen-bonding functional groups (see Figure 9.11) are ixed
or variable-charged organic chemical compounds. They can acquire a positive or nega-
tive charge through dissociation of H
+
from or onto the functional groups depending on
the dissociation constant of each functional group and the pH of the soil-water system.
An increase in the pH of the soil-water system will cause these functional groups (i.e.,
groups having a C=O bond) to dissociate. The outcome of the release of H
+
is a develop-
ment of negative charges for the organic chemical compounds. Charge reversal (i.e., from
positive to negative charges) could lead to the release of organic chemical contaminants
held originally by cation bonding to the negatively charged reactive surfaces of the soil
particles. The phenomenon is a particular case of environmental mobility of previously
sorbed contaminants.
9.4.4 Reactions in Porewater
Since contaminants consist of both inorganic and organic chemicals, it is more convenient
to use the Brønsted-Lowry concept of acids and bases to describe the various reactions,
and interactions occurring in a soil-water-contaminant system. In the Brønsted-Lowry
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