Oxidation of alcohols

The carbon atoms connected to the hydroxyl groups of primary and secondary alcohols contain hydrogen, which can be oxidized into aldehydes, ketones, or acids; The carbon atoms connected to the hydroxyl groups of tertiary alcohols do not have hydrogen and are not easily oxidized. For example, under acidic conditions, they are easily dehydrated to form olefins, and then the carbon carbon bonds oxidize and break, forming small molecule compounds.
1. Oxidize with potassium permanganate or manganese dioxide
Alcohols are not oxidized by cold, dilute, or neutral aqueous solutions of potassium permanganate. Primary and secondary alcohols can be oxidized under relatively strong conditions (such as heating). The primary alcohol generates potassium carboxylate, which is soluble in water and precipitates manganese dioxide. After neutralization, carboxylic acid can be obtained.
Secondary alcohols can be oxidized to ketones. However, due to the oxidation of secondary alcohols to ketones using potassium permanganate, it is prone to further oxidation, leading to the breaking of carbon carbon bonds, so it is rarely used for the synthesis of ketones.
Tertiary alcohols are not easily oxidized by potassium permanganate under neutral and alkaline conditions. However, under acidic conditions, they can dehydrate to form alkenes, which then undergo carbon carbon bond cleavage and generate small molecule compounds.
Potassium permanganate and manganese sulfate can be used to produce manganese dioxide under alkaline conditions, and the newly produced manganese dioxide can β Primary and secondary alcohols with unsaturated bonds on carbon are oxidized to corresponding aldehydes and ketones, and the unsaturated bonds are not affected. 
2. Oxidize with chromic acid
Chromic acid can be used as an oxidant in the form of a mixture of sodium dichromate and 40% to 50% sulfuric acid, a glacial acetic acid solution of chromic anhydride, and a complex of chromic anhydride and pyridine.
The first order alcohol is commonly oxidized by a mixture of sodium dichromate and 40% to 50% sulfuric acid to obtain aldehydes, which are further oxidized to acids. If appropriate oxidation conditions are controlled and the aldehyde is immediately evaporated from the reaction system after oxidation, it can avoid further oxidation of the aldehyde to acid. The reaction needs to be carried out at a temperature lower than the boiling point of the alcohol but higher than the boiling point of the aldehyde. Propanol is added dropwise to a solution of sodium dichromate, sulfuric acid, and water at a temperature of~75 ℃. Once propanal is generated, it is distilled out. The yield of this reaction is not high because there is always a portion of aldehydes oxidized to acids. The boiling point of aldehydes is below 100 ℃ in order to use this method, so its use is very limited.
Secondary alcohols are commonly oxidized with the aforementioned chromic acid oxidants, and ketones are relatively stable under these conditions. Therefore, it is a relatively useful method.
The chromic anhydride bipyridine complex formed by the reaction of chromic anhydride with pyridine is a hygroscopic red crystal, called Sarrett reagent, which can oxidize primary alcohols to aldehydes and secondary alcohols to ketones with high yield. Because pyridine is alkaline, it is a good oxidant for alcohols that are unstable in acids. The reaction is generally carried out in dichloromethane at around 25 ℃. If there are double or triple bonds in the molecule, they are not affected during oxidation.
Secondary alcohols can also be oxidized to corresponding ketones by Jones reagent. If the reactant is an unsaturated secondary alcohol, the corresponding ketone is generated during oxidation with Jones reagent without affecting the double bond. This reagent dissolves chromic anhydride in dilute sulfuric acid and then drips it into a propanone solution of the alcohol to be oxidized. The reaction is carried out at 15-20 ℃ to obtain higher yields of ketones.