Abstract
Ph.D.
The main objective of the research described in this dissertation was the preparation and
characterisation of hindered organophosphorus compounds. For this purpose, ionic and free
radical mechanisms were applied in the synthesis of selected hindered organophosphorus
compounds, some with interesting spectral properties.
A brief background of the element phosphorus and the early development of organophosphorus
chemistry is provided. The early development of the chemical nerve agents derived from
phosphorus, their toxicity and illicit manufacture by terrorist groups is discussed. The vital role
played by the organisation for the prohibition of chemical weapons in enforcing the prohibition of
the development, production, acquisition, stockpiling and the use of chemical nerve agents and
their destruction by the state party is highlighted. The methodologies such as Michaelis Arbuzov,
Michaelis Becker,
Perkow Pudovik, Abramov and radical protocol reactions used to
synthesise phosphorus containing compounds, are reviewed.
In the present research project, diphenylphosphonous chloride and phenylphosphonous
dichloride reagents were used in nucleophilic substitution reactions with bulky alcohols. This
resulted in the synthesis and characterisation by 1H, 13C, 31P NMR and GCMS
spectroscopy of
the compounds shown in Scheme 0.1, where R’ was derived from 2,2dimethylpropanol,
3methylbutanol,
1,2dimethylpropanol,
3,3dimethyl2butanol,
1,1dimethylethanol
and 2methyl2butanol.
(R)xPCl(3x)
R'OH
Et3N
(R)xP(OR')(3x)
H2O2
or
S8
(R)xP(OR)(3x)
Y
R=Aryl, and Y=O, S
The importance of using activated alcohols in the form of metal alkoxides in the cases of 1,1dimethylethanol
and 2methyl2butanol
for successful reactions was demonstrated.
The influence of steric hindrance on the reactivity of these ionic reactions was studied by
substituting diphenylphosphonous chloride, or phenylphosphosphonous dichloride, with tertbutylphosphonous
dichloride or ditertbutylphosphonous
chloride. This resulted in no nucleophilic
substitution reaction taking place between tertbutylphosphonous
dichloride and hindered
alcohols in the presence of triethylamine. For successful reactions, the use of excess activated
hindered alcohols in the form of either the lithium or potassium alkoxide was required. It was
found that replacing both of the chlorine atoms in tertbutylphosphonous
dichloride with hindered
alcohols like 1,1dimethylethanol
and 2methyl2butanol
was sluggish, and in the present study
this could not be realised. It was demonstrated that ditert
butylphosphonous chloride is resistant
to react with activated hindered alcohols due to enhanced steric hindrance in the
organophosphorus reagent.
The use of freeradical
mechanisms in the phosphoruscarbon
(PC)
bond forming reaction is
briefly reviewed. The importance of finding a nontoxic
replacement of organotin reagents in
radical protocols is also highlighted.
The scope of the present work was limited to the reaction of phosphonylcentered
radicals
generated by the triethylboraneoxygen
system with various alkenes ranging from less electron
rich to more electron rich alkenes, including those containing a free hydroxy moiety.
The reaction of diphenyl thiophosphite or diphenyl phosphite (Scheme 0.2) in the presence of
triethylborane under aerobic conditions with enol ether alkenes afforded the expected antiMarkovnikov
products.