الكيمياء العضوية العملي

IDENTIFICATION OF ALDEHDES AND KETONES
Aldehydes are compounds of the general formula RCHO; ketones are compounds of the general formula RR,CO. The groups R and R, may be aliphatic or aromatic, and in one aldehyde, formaldehyde , R is a hydrogen atom .
Both contain the carbonyl group (C=O), which lends to their chief chemical and physical properties. Examples of them include formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde ,salicylaldehyde, acetophenone, benzyl methyl ketone, and benzophenone .
Physical Properties :
- 1 All aldehydes and ketones are liquids except formaldehyde which is a gas (boiling point = -21°C) and benzophene, which is a solid (milting point=48°C). Formaldehyde is handled either as an aqueous solution (formalin)or as one of its solid polymers: Para formaldehydes,(CH2O)n, or trioxune, (CH2O)3 .
-2 The lower aldehydes and ketones are appreciably soluble in water (containing five or less carbon atoms), aromatic one are insoluble in water, and all of them are soluble in organic solvents .
-3 They are colorless except benzaldehyde, which has a pale yellow color(due to oxidation) with characteristic odors .
-4 The boiling points of aldehydes and ketones are lower than those of the alcohols from which they are derived. For example, isopropyl alcohol boils at 82.5°C while its oxidation product, acetones, boils at 56°C;ethanol boils at 78 °C while its oxidation product, acetaldehyde, and boils at 21°C .
-5 Igonition: Aliphatic aldehydes and ketones burn with a blue flame (without smoke) while aromatic ones burn with a smoky yellow flame .