Analysis and reactions of cyclopropenoids with rhodium complexes.
cyclopropene fatty acids (CPEFA) and cyclopropane fatty: acids
(CPAFA) occur as glycerides in many plant families and the former
are of particular interest because of their adverse physiological
effects. The cyclopropenoid seed oil Gossypium hirsutum
(cottonseed) and Ceiba pentandra (kapok) are widely used to
provide food for man and animals.
Methods currently described in the literature for the
determination of CPEFA particularly at low levels, are either
inaccurate or are criticised due to the complicated nature of the
The aim of this work was to develop a method so as to allow the
quantitative determination of CPEFA and also CPAFA where both are
present in important natural seed oil. This method involves a
series of reactions using a homogeneous transition metal complex,
bromotris(triphenylphosphine)rhodium(l). This developed method
involves the following reactions.
a) Analysis one; Direct analysis of methyl esters.
b) Analysis two; Hydrogenation of methyl esters. During this
reaction, the unstable CPEFA are hydrogenated to their
stable CPAFA analogues, thus allowing subsequent GLC
analysis. The difference between the quantitative results
(for the CPAFA content with other components of similar
retention volume) obtained from the direct GLC analysis of
methyl esters (analysis one) and the hydrogenated sample
allows the determination of CPEFA content of the sample.
N.B. The CPEFA content obtained by direct GLC analysis of
methyl esters (analysis one) is unreliable owing to the
instability of CPEFA on the GLC column.
c) Analysis three; CPEFA destroyed using the catalyst.
d) Analysis four; CPEFA destroyed using excess catalyst
followed by hydrogenation .
Similarly, the differences between the quantitative results
obtained from the above two reactions, allows the determination
of CPAFA. Reactions (c) and (d) are necessary because
unsaturated components of similar retention volume to CPAFA are
present in the sample ego kapok.
The latter part of the study was concerned with identification of
reaction products formed during analysis three. Complete
degradation of CPEFA by the catalyst was achieved within five
minutes using ethanol/toluene solvent system. Numerous compounds
were isolated using preparative TLC and structure elucidation was
carried out using NMR and MS.