Waxes, Oils, and Fats 7/2/19

By Richard Bleil

Editorial note: my friend pointed out that I had confused the term “gross” with “score”. I’ve corrected this error.

Definitions have been weakening of late. These days, for example, a “wax” is generally considered to be anything that happens to have a waxy consistency. I thought it might be fun to discuss the chemical definition of these four things.

Some years ago, an insect climbed into my ear. I did the usual dance and ear torture, and thought it had gotten out, but no. It was caught by my body’s natural defense mechanisms (not unlike, say, a Venus Flytrap). The sticky wax in my ear trapped it to prevent it from going deeper, and before long my ear plugged up. On cleaning it out (I use the old-fashioned method that probably hurts the eardrum and fragile bone structures), I found a large plug of ear wax that had encased the insect.

Your body produces wax. The technical term for a wax is “long-chain ester”. Unless you’re a chemist, that doesn’t mean much, but it’s a combination product between a long chain alcohol, and a long chain acetic acid.

An alcohol is an organic compound that has an -OH (oxygen/hydrogen) functional group. Ethanol (drinking alcohol) is probably the best known alcohol. It has two carbons (with associated hydrogens) and the -OH functional group, so its formula is CH3CH2OH. This formula means there is one carbon with three hydrogens, one with two hydrogens and the -OH. When I shave, I like to use cologne, so to avoid the perfumes of aftershave I use isopropanol (which you know is an alcohol because the name ends in -ol), with a formula of CH3CH2CH2OH.

Notice that isopropanol has more carbons than ethanol. This is what we mean by “chain”. You can really have as many carbons as you want; one, two, three, four, a dozen, a score (20), a gross (a dozen dozen, or 144), anything that you want. If you have a lot of carbons (say five or more) then we say it’s a “long chain” alcohol.

An organic acid has a “carboxylic acid” group, -CO2H, rather than just -OH. The hydrogen on -CO2H is on one of the oxygens, but because of the presence of the second oxygen, it’s only loosely held and easily dissociates (comes off) in water. This is why these are acidic. There are several well-known acids common in our society, such as acetic acid, CH3CO2H, which is the common ingredient in vinegar.

When you react an acid with an alcohol, you get a combination product called an ester. For example, if you react isopropanol with acetic acid, you would get CH3CO2CH2CH2CH3, where the three carbon side is from the alcohol and the other from the acetate. Esters tend to have very pleasing aromatic smells, as this one smells vaguely fruity like raspberries or pears. These compounds do occur naturally in fruits and flowers and is the cause of their smell.

Now, if you have very long chain esters, you have a wax. So, CH3CH2CH2CH2CH2CO2CH2CH2CH2CCH2CH2CH2CH3 is a real compound and would be a wax. The long carbon chains makes it heavy and hard to vaporize, and is the reason waxes do not dissolve in water. The structure makes it hard for these substances to crystallize, but they kind of hold onto and slide around each other giving the waxy texture.

Fats and oils are triglycerides. To discuss these, we need to talk about fatty acids. Fatty acids are just long-chain organic acids. When discussing fatty acids, we often use the terms “saturated” (having all of the hydrogen) or “unsaturated” (missing some hydrogens). Without going too far into the chemical explanation, something like CH3CH2CH2CH2CH2CH2CO2H would be saturated and CH3CH2CHCHCH2CH2CO2H would be unsaturated. Unsaturated is healthier, by the way.

Now, just as an ester is formed by combining an acid with an alcohol, a triglyceride is formed by the reaction of three fatty acids with a very special type of alcohol called “glycerin”. Glycerin has three carbons with a hydroxide attached to each carbon; CH2OHCHOHCH2OH. Glycerin is a clear viscous (thick) fluid, highly water-soluble (dissolves in water) and is often found in cosmetics, for example as a base for lip gloss. For wine drinkers, it is glycerin that gives wine its “legs”, the clear liquid that coats the wine glass when you swirl it which can be seen running back down into the wine on standing.

Okay, triglycerides are tri-esters formed from three fatty acids with glycerin. Both fats and oils are actually triglycerides, very similar structurally, but by definition, a fat is solid at room temperature (because the fatty acids are saturated) and an oil is liquid (because the fatty acids are unsaturated).

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