Why do we use alcoholic base baths for cleaning glassware?

1 Answer
Dec 4, 2016

Because alcoholic hydroxide is a much more powerful nucleophile than aqueous hydroxide.


The normal means of cleaning greasy glassware in a laboratory is to stand the glass for 12-24 hours in an alcoholic base bath. After this time the glass is retrieved from the base bath (the retriever wears LONG gloves, and a lab coat), is rinsed with water, and then soaked in an acid base briefly.

A base is a more powerful nucleophile in an alcoholic medium because the ethanolic solvent does not solvate the hydroxide ion as effectively as an aqueous solvent. The hydroxide ion is a less powerful nucleophile in aqueous media.

The aqueous medium is clearly capable of effectively stabilizing ions, which are part of the mechanism of an #S_N1# reaction. In this scenario, bond-making, not bond-breaking, is the mechanism of reaction, and this lends itself to ionic reactivity.

Note that the use of acid-baths and base baths illustrate the danger of concentrated base as opposed to conc. acid. Sometimes the long gloves that you use develop a hole ... it is an easy thing to occur. When you fish things out of the base bath with the holey glove it you don't much notice...the base still does damage, but the slimy, soapy nature of bases means that it does not hurt so much. After you rinse your gloves, and retrieve items from the acid bath, it is HERE than you notice the hole in the glove. The acid stings like buggery. And this is when you change the gloves, and give your hands a wash and a close inspection.