Aldehydes and Ketones Lab 2024 PDF

CHY 32.1: Organic Chemistry (Lab) Aldehydes and Ketones Prepared by: John Michael A. Santillan RCh, RChT Central Mindanao University Chemistry Department [email protected] Structure and Bonding  The carbonyl is sp2 hybridized and trigonal planar,...

CHY 32.1: Organic Chemistry (Lab) Aldehydes and Ketones Prepared by: John Michael A. Santillan RCh, RChT Central Mindanao University Chemistry Department [email protected] Structure and Bonding  The carbonyl is sp2 hybridized and trigonal planar, making it relatively uncrowded. The electronegative oxygen atoms polarizes the carbonyl group, making the carbonyl compound polar and electrophilic.  Physical Properties 1. Boiling and Melting Point The stronger the IMFA present in an organic compounds, the higher the mp and bp. 2. Solubility Aldehydes and ketones are soluble in organic compounds. Aldehydes and ketones having 5 (and below) numbers of carbons are soluble because they can hydrogen bond with water.  Reactivity As steric hindrance (crowded) increases, reactivity decreases. This is the reason why aldehydes is much more reactive than ketones. Increasing Reactivity  Oxidation of Aldehyde The presence of that hydrogen atom makes aldehydes very easy to oxidize. Under acidic conditions, the aldehyde is oxidized to a carboxylic acid. Under basic conditions, this could not form because it would react with the alkali. A salt is formed instead.  Jones’s Test: Tests for Aldehyde The Jones reagent is chromium trioxide (CrO3) in sulfuric acid (H2SO4). It is a potent oxidizing agent which rapidly oxidizes primary alcohols and aldehydes to carboxylic acids, and secondary alcohols to ketones. The orange Cr6+ reagent converts to a blue-green Cr3+ species, which often precipitates in acetone. Expected Results  Benedict’s Test The difference between an aldehyde and a ketone is the presence of a hydrogen atom attached to the carbon-oxygen double bond in the aldehyde. Ketones don't have that hydrogen. The presence of that hydrogen atom makes aldehydes very easy to oxidize or, put another way, they are strong reducing agents. Because ketones don't have that particular hydrogen atom, they are resistant to oxidation.  Benedict’s Test Benedict's solution contains copper(II) ions complexed with citrate ions in sodium carbonate solution. Complexing the copper(II) ions with citrate ions prevents precipitation of copper(II) carbonate. An insoluble Cu2O is the inorganic product of this reaction, which usually has a red-brown color The reaction may only work for compounds that are water soluble as the reaction seems to initiate at the surface and aldehydes that formed an insoluble layer on the surface to be unreactive. Time-lapse reaction progress of the Benedict’s reagent reacting with glucose  Fehling’s Test Fehling’s solution is a complex compound of Cu2+.When the aldehyde compound is treated with Fehling’s solution Cu2+ is reduced to Cu+ and the aldehyde is reduced to acids. During the reaction, a red precipitate is formed.  Expected Results O O H C H 2Cu+2 2OH- H C OH Cu2O H2O  Sodium Nitroprusside Test: Test for Ketones Ketone reacts with alkali and forms an anion which further reacts with sodium nitroprusside and forms a colored complex ion. Aldehydes do not respond to sodium nitroprusside test  Expected Results [Fe(CN)5NO]2- + → [Fe(CN)5NO.CH3COCH2]3-  Iodoform Tests Iodoform Test reveals the presence of an ketone in which a methyl group is connected to the carbonyl group (methyl ketone) Ketones having at least one methyl group linked to the carbonyl carbon atom (i.e., methyl ketones) are oxidized by sodium hypophalite to sodium salts of carboxylic acid with one carbon atom less that that of the ketones. The methyl group is converted to haloform, which appears as a yellow precipitate This oxidation does not affect a carbon- carbon double bond, if present in the molecules Expected Results Brady’s Test: Phenylhydrazone Formation 2,4 – dinitrophenylhydrazine can be used to qualitatively detect carbonyl group functionality of an aldehyde or ketone functional group. A positive test is designated by a yellow to red precipitate, known as dinitrophenylhydrazones. Yellow derivatives are formed from isolated carbonyl groups and orange-red to red derivatives from aldehydes or ketones conjugated with double bonds or aromatic rings.  Expected Results Sample Observations Chemical Formula After 2 min After 10 min of main product RED-ORANGE (DARK RED) Acetone YELLOW PRECIPITATE PRECIPITATE C9H10O4N4 RED-ORANGE (DARK RED) Formaldehyde YELLOW PRECIPITATE PRECIPITATE C7H6O4N4 O2 N O 2N O CH3 H 3C C CH3 H2 N NH NO2 CH3 C N NH NO2 2,4-dinitrophenylhydrazine ethanal 2,4-dinitrophenylhydrazone O2 N O2 N O H C H H2N NH NO2 CH2 N NH NO2 2,4-dinitrophenylhydrazine methanal 2,4-dinitrophenylhydrazone