Dehydration of Alcohols to form Ethers Simple, symmetrical ethers can be formed from the intermolecular acid-catalyzed dehydration of 1° (or methyl) alcohols (a “substitution reaction”) 2° and 3° alcohols can’t be used because they eliminate (intramolecular dehydration) to form alkenes Unsymmetrical ethers can’t be made this way because a mixture of products results:

Mechanism of Formation of Ethers from Alcohols First, an alcohol is protonated by H3O+ Next, H2O is displaced by another alcohol (substitution) Finally, a proton is removed by H2O to form the product

Oxidation of Alcohols Recall that oxidation is a loss of electrons and reduction is a gain of electrons However, red-ox does not always involve ions Oxidation can also be defined as a gain in bonds to oxygen This is because O is more electronegative than all other elements (besides F), so it removes electron density from any element with which it forms a covalent bond Primary alcohols can be oxidized to aldehydes and carboxylic acids and secondary alcohols can be oxidized to ketones

Oxidation of Primary and Secondary Alcohols Primary alcohols are initially oxidized to aldehydes, but aldehydes are easily oxidized to carboxylic acids In order to stop the reaction at the aldehyde a very mild reducing agent must be used The most common reagent is PCC (pyridinium chlorochromate) Other oxidizing agents (like CrO3/H3O+) will oxidize primary alcohols all the way to carboxylic acids Secondary alcohols can be oxidized with either reagent

Oxidation of Thiols Oxidation can also be defined as a loss of bonds to hydrogen This is because H is less electronegative than all other nonmetals (besides P which is the same), so adds electron density to any element with which it forms a covalent bond Thiols can be oxidized to disulfides using I2 (or Br2) In proteins, disulfide bonds between sulfur-containing amino acids (cysteines) are a major factor in preserving their shape