Oxidation of Alcohols using DMSO

With alcohols, the oxidation of primary and secondary alcohols to make aldehydes and ketones will change the oxidation state of the carbon atom but not the oxygen molecule. The oxidation of sulfur compounds will change the oxidation state of the sulfur atom but not the carbon atom. Mild oxidation will turn a thiol into a disulfide. This does not happen with oxygen molecules because the O-O bond is not as strong as the S-S bond, while the OH bond is stronger than the SH bond. This means that peroxides (having an O-O bond) aren’t as stable as a disulfide bond. Figure 92 shows the oxidation of thiols with mild oxidizing agents:

Figure 92.

There can be a carbon-sulfur double bond, indicated by the word “thione”. Anytime there is a sulfur in a carbon ring rather than an oxygen molecule, the molecule has the prefix “thia”.

OXIDATION OF ALCOHOLS USING DMSO

Making an aldehyde or ketone by oxidizing a primary or secondary alcohol is important in organic chemistry. Basically, it is a dehydrogenation reaction, losing H2 in the process. Oxygen must be present in the reaction to stabilize the H2 to make water. One good source of this oxygen is the sulfoxide solvent known as DMSO or dimethyl sulfoxide or CH3SOCH3. The alcohol becomes oxidized and DMSO gets reduced to Dimethyl sulfide with water taken up by the electrophilic substance. It is so exothermic it has to be done at extremely low temperatures with cosolvents because the freezing temperature of DMSO is 18 degrees. An example of this is the oxidation reaction shown in figure 93: