Synthetic Detergent ("SynDet") Bars

Next time you are in the grocery store, pick up a product that avoids the word "soap", but rather advertises itself as a "beauty bar" or "deodorant bar" or "body wash", and look at the ingredient list. It will say something like "sodium cocoyl isethionate" or something similar. What you will have in your hand is a bar of synthetic detergent, not soap. So, just how does this new substance compare to soap? Before we get too far into this, let's have a look at history once again.

Along about the time of The Great War (now called World War I), things got a little tense in Europe. The normal raw materials used for soap became scarce because there were blockades to shipping and imports, so they set out to create an alternative to soap. Coal was abundant, and coal can yield a type of oil that has benzene in it, similar to petroleum, and the chemists came up with a new substance. It was called linear alkyl benzene sulfonate, or LAS for short, and that was the first detergent.

LAS acts like soap because it can form an emulsion, meaning that it can mix with both oil and water. But there is a twist. Detergents don't form a bathtub ring! True soap will interact with the calcium and magnesium in hard water to form a substance called "soap curd" which is insoluble in water. It sticks to the sides of the bathtub and is hard to wash off. Detergents don't form any such substance.

Another common detergent used in body care is sodium lauryl sulfate, or SLS. SLS is used in many shampoos and body washes and bath gels. There are many other detergents that have been developed. Some are used for textiles, some for pots and pans and dishes, and some for personal care.