reactivity of carboxylic acid derivatives

Reaction mechanisms for these transformations are displayed on clicking the ' Show Mechanism' button. Oxidation with the PCC reagent converts 1º-alcohols to aldehydes whereas Jones reagent continues the oxidation to the carboxylic acid product, as shown in the second reaction. Both reagents effect the oxidation of 2º-alcohols to ketones, but the outcome of 1º-alcohol oxidations is different. The following equations illustrate some oxidations of alcohols, using the two reagents defined here. Indeed, this is the chemical transformation on which the Breathalyzer test is based. Since chromate reagents are a dark orange-red color ( VI oxidation state) and chromium III compounds are normally green, the progress of these oxidations is easily observed. The oxidation state of carbon increases by 2, while the chromium decreases by 3 (it is reduced). In each case a chromate ester of the alcohol substrate is believed to be an intermediate, which undergoes an E2-like elimination to the carbonyl product. Two such oxidants are Jones reagent (a solution of sodium dichromate in aqueous sulfuric acid) and pyridinium chlorochromate, C 5H 5NH (+)CrO 3Cl (–), commonly named by the acronym PCC and used in methylene chloride solution. The most generally useful reagents for oxidizing 1º and 2º-alcohols are chromic acid derivatives. The decomposition of 1º and 2º-alkyl hypochlorites, referred to earlier, is an example of such a reaction. Instead, alcohol oxidations are carried out in solution, using reactions in which the hydroxyl hydrogen is replaced by an atom or group that is readily eliminated together with the alpha-hydrogen. Gas phase dehydrogenations of this kind are important in chemical manufacturing, but see little use in the research laboratory. This catalytic dehydrogenation reaction produces aldehydes (as shown below) and ketones, and since the carbon atom bonded to the oxygen is oxidized, such alcohol to carbonyl conversions are generally referred to as oxidation reactions. Simple 1º and 2º-alcohols in the gaseous state lose hydrogen when exposed to a hot copper surface.

Reactivity of carboxylic acid derivatives