Page 183 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

5B.3 PHOSPHORUS IN BIOLOGY: WHY NATURE CHOSE PHOSPHATE 163
Accounting for the full stoichiometry of the reaction (5B.15) is rather tedious, but do work
through a few additional steps to make sure that you can handle them. It’s worth noting
that this reaction is a ligand exchange: oxide and chloride ligands are traded between two
pentavalent phosphorus centers. As emphasized in Section 1.19, reactions of this type gene-
rally involve bridged intermediates; observe that the migrating oxygen acts as a bridging
group in a number of the intermediates above.

REVIEW PROBLEM 5B.6
Suggest a mechanism and an HSAB rationale for the following ligand exchange
(metathesis) reaction:
PCl + AsF → PF + AsCl 3
3
3
3

REVIEW PROBLEM 5B.7
Suggest a mechanism for the following reaction:

SO + PCl → SOCl + POCl 3
2
5
2
5B.3 PHOSPHORUS IN BIOLOGY: WHY NATURE CHOSE PHOSPHATE

A chapter on group 15 elements cannot be complete without some discussion of phosphorus
in biology. Phosphates in particular are everywhere in biology! In this section, we will
be able to present only a few key structures and reactions of biological phosphates, with
a little flavor of some of the classic mechanistic work that has taken place in the field.
Glycolysis, the 10-step metabolic pathway that breaks down glucose to pyruvic acid, begins
with phosphorylation of glucose with adenosine triphosphate (ATP):
Phosphoric anhydride
OH
H
OH OH OH
OH N
O γ + β + α + H 2
HO + − P P P C O N NH 2
H OH O O − O O − O O − O
H OH
N
OH H Triphosphate N
HO OH
OH
Ribose Adenine
+
− P
O
− O H H O
OH OH
N
OH O + P + H 2 O NH
C
HO + − O P O O N 2
H OH O − O −
H OH
N N
OH H
HO OH
(5B.16)