Biomedical Engineering Reference
In-Depth Information
O
C
H
2
C
O
H
2
C═CH─CH
2
─CH
3
+ CO
2
(3.112)
H
2
C
CH
CH
3
To illustrate the reaction in a more easily readable fashion, we write
O
CO
2
3H
2
O
H
2
O
H
2
C
2H
2
O
HCOOH
H
2
C
H
2
C
O
O
H
2
C═CH─CH
2
─CH
3
──
C
5
H
8
O
3
C
6
H
12
O
6
C
6
H
6
O
3
H
2
C
H
2
C
2
1
3
4
CH
CH
CH
3
CH
3
(3.113)
In this case, one can follow easily from glucose to butene. Sometimes, we even omit the side
branches (species) shown above the horizontal arrowmaking it more simplified. In so doing,
we only showed part of a reaction in each step. This is different from the approximate reac-
tions as the side species may or may not be in excess in the reaction mixture that we can
understand. As it stands, one can read carefully to discover that the stoichiometry is
preserved in each step. However, our focus may not be on the complete reaction. For
example, in step 2, our focus is on the (incomplete) reaction:
C
H
O
3
ð
hydroxymethylfufural
Þ /
C
H
O
3
ð
levulinic acid
Þ
(3.114)
6
6
5
8
This reaction as shown is incomplete, neither carbon nor hydrogen are balanced. In order for
this (incomplete) reaction to occur, one C needs to be removed and two H need to be added.
One can consider that this reaction is coupled with another reaction that can provide two H
and remove one C. This coupled reaction is shown above the horizontal arrow in step 2, that is
2
H
O
/
HCOOH
ð
formic acid
Þ
(3.115)
2
which by itself is not a complete reaction either. However, when we add these two reactions:
⎯→
C
6
H
6
O
3
C
5
H
8
O
3
2H
2
O
⎯→
HCOOH (+
⎯→
C
6
H
6
O
3
+ 2 H
2
O
C
5
H
8
O
3
+ HCOOH
The resulting reaction is stoichiometrically correct. Therefore, for simplicity and brevity in
describing complex reaction networks, we may write incomplete reactions to illustrate steps
following a key substrate. However, each step will need to be coupled with another incom-
plete reaction in order to occur. We call the pair of (incomplete) reactions “coupled reactions,”
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