How to reduce alkenes
المؤلف:
Jonathan Clayden , Nick Greeves , Stuart Warren
المصدر:
ORGANIC CHEMISTRY
الجزء والصفحة:
ص535-536
2025-06-21
540
To alkanes Hydrogenation with a palladium or a platinum catalyst is the most common way of reducing alkenes. You may find our mechanism rather unsatisfactory, but it is hard to draw curly arrows for the reactions involved here. There is, however, plenty of evidence that the hydrogenation occurs like this, for example the alkene below reacts in such a way that the major product receives both hydrogen atoms on the same face of the molecule—just what we would expect from a reaction at a surface.
Hydrogenated vegetable oil
Plants such as soya, rapeseed, cottonseed, and sunflower are useful sources of edible vegetable oils, but these oils are unsuitable as butter substitutes because of their low melting points. Their low melting points relative to animal fats are largely due to cis double bonds that disrupt the packing of the alkyl chains in the solid state. Treating the crude vegetable oil with hydrogen over a metal catalyst removes some of these double bonds, increases the proportion of saturated fat in the oil, and raises its melting point, making it suitable for making margarine.
The reaction is usually stopped before all the double bonds are hydrogenated, of course: margarine manufacturers are desperate to tell us that their products are still ‘high in unsaturated fatty acids’. Many also advertise that they are ‘low in trans unsaturated fatty acids’ because of a suggested link between incidence of coronary heart disease and trans unsaturated fatty acid intake.
Where have these trans double bonds come from? Well, partial hydrogenation can lead to significant double-bond isomerization, not just to regioisomers but to geometrical isomers too.
الاكثر قراءة في مواضيع عامة في الكيمياء العضوية
اخر الاخبار
اخبار العتبة العباسية المقدسة
