Holly,
Our nutrition teacher says that if you shake a mixture of oil and vinegar, as in salad dressing, the oil gets hydrogenated. This sounds unlikely based on what we learned in class. Don't you need hydrogen gas and a metal catalyst?
A questioning student
Dear questioning,
Oh dearie, dear me. You can NOT hydrogenate oil by shaking it with water or with vinegar or any acid.
Perhaps your professor mis-spoke, or perhaps things came out of their mouth backwards and it was misunderstood. Let's try to give your professor the benefit of the doubt.
If you could hydrogenate oil by shaking it with water or with acid, the ancients would have discovered margarine. It would not be a modern invention of the 20th century. The oil would start to become a solid, and permanently so.
An acid such as vinegar donates H+, but hydrogen ion is not enough to hydrogenate. Hydrogen ion has NO electrons. None. Zip. Zero.
You need a source of donate-able electrons to make a bond, and there just isn't any in the mixtures that you described. Bonds are made out of electrons.
Hydrogen gas is very different from hydrogen ion. Hydrogen gas has two electrons, shared by two hydrogen nuclei, and those electrons are needed to become part of the hydrogenated oil. But salad dressings do not contain hydrogen gas. That would be...interesting.
It's always a good idea to pay attention to where your electrons are, and to make sure you have the right number for whatever task you want to accomplish.
Hydrogenation is an important issue these days, because we have good evidence that when the reaction goes half-way, trans fats can be created, and those are a cardiovascular risk factor in the diet. The double bond normally starts in the cis orientation in an oil, the pi bond breaks, one half of the molecule rotates around the remaining sigma bond, and re-forms the pi bond in the opposite orientation (trans). But this of course can't happen if you just shake oil and water or oil and vinegar, for the above reason. You need the industrial process known as "partial hydrogenation" in order to create trans fats from cis fats.
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